Did I Blow Up the Inverter?
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- Опубліковано 22 лип 2024
- This is a follow up video to: • Cheap 8000w Reliable I...
Several UA-camrs left comments suggesting I blew up the inverter in my past video "Cheap 8000w Reliable Inverter, DIY Powerwall, Chevy Volt Batteries". I'm addressing several comments in this video. I really appreciate all the comments, questions, and concerns. This helps us all get better by sharing knowledge.
My overall goal is to make a diy powerwall with solar, batteries, and inverter to backup my house if the grid goes down.
Table of contents:
#1: Overview of Surges, 1:32
#2: Midnite Solars Opinion, 3:16
#3: Inverter Design, 5:08
#4: Measuring In-Rush Amps, 8:42
#5: Circuit Breaker Specifications, 11:08
Midnite Solar website: www.midnitesolar.com/
Multi-meter: amzn.to/2qsNDjA
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I am an electrical engineer who specializes in power. The circuit breaker did exactly what it was supposed to do. The spark very likely came from the circuit breaker and this is very normal. The circuit breaker has a very large current flowing through it and they often draw an arc when opening during a fault or large surge. One sure way to tell it came from the circuit breaker is the color of the spark. It was a green blue color indicative of molten copper from an arc blast. The continuity test you performed is not necessarily indicative of a short. The bulk input storage capacitors will act like a short when they are empty and will indicate a false short. The capacitors look like a short when they are discharged. I can tell by the internals of the inverter it was designed to a very tight budget. All the mosfets appear to be lacking any type of snubber or protection circuitry although it's a little hard to tell from the video. The inductive surge from the motor will likely cause an instantaneous voltage spike somewhere in the inverter and I would be willing to bet that spike exceeded the power transistors specification for max voltage causing the transistors to fail short circuit. The saw inrush current is very fast typically few ac cycles so it can't be measured using the method you used. It could be measured using an oscilloscope and it is certainly many times its operating current.
You r awesome....
Also an EE, though not a power specialization. I completely agree, tho. It doesn't appear it was taken into account how devastating a large inductive kickback can be. Also the fact that the wires are of a pretty sizable length difference between the different sections of the supply sharing the load is a bit suspect. If you're dealing with an impulse even an inch difference can have some drastic effects.
Actually I think it´s unlikely the inductive back-EMF from the motor exceeded the mosfet´s ratings. The motor was not even moving yet, meaning there is almost no magnetic field yet, which of course is also the reason why the motor would draw a high inrush current.
My bet is on badly matched/controlled mosfets, which may also be under-specced.
In any case, the bad design is to blame, nothing else. A good quality inverter shouldn´t even be damaged by a permanent short circuit on the output.
I agree with is probably missing snubber protection, or even some TVS diodes. But I have to wonder if the transformers arced causing the failure and in Truro would also knock out some of the mosfets ? The other think I would love to see is the bottom of the PCB, maybe some arc burn I’ll show up? This would confirm thin traces, or traces to close to each other with out any high voltage slots. Or a maybe even some components that are to close. I think the bottom of this board could possible lead to a more defined reason. Either way, it’s a flaw in the unit and wasn’t the breaker.
eh my I bet it was them cheaping out and using the same gate driver in the 3000 watt inverter, all these signs point to internal bridge short across the fets, (As if they where not switch correctly) 8000 watt units using the same gate driver the 3000 unit is, switching too many FETS it can't drive properly, causing switching delay of some kind. Wrong two FETS on at the same time. Bang, short circuit across them thus also giving a short between The batteries themselves through the circuit breaker he was using. just my theory. Interesting such a failure on the input side, thats typically happens near the output side in most cases.
Great video I have the 1500w 24v inverter same make I overloaded AC with hoover .... looking to repair mine and your videos inspire me in theses inverters ....hope you do the fix so we can see ......well done that man !!!!!!!!
I've designed inverters and switching power supplies for years and is now retired. It appears there is no load balancing and over current protection: they just hooked those individuals in parallel. To make it simple, these individuals have a heroic tendency to be "I can do it by myself" and when you hit it with big motors and/or capacitive loads that's pretty much a short circuit for the first few seconds, that fries the hero's mosfets in no time. Stay away from that brand or such design. Very tricky to start loads that are virtually a short circuit for the first few seconds.
thanks for this!
Looking at the picture of inverter, It appears it has nine DC to DC boost blocks converters. To save idle current and improve efficiency at lower power levels, the nine boost blocks are brought online as needed to supply the load demand. Each of the nine DC-DC block can up supply about 1kW. They produce DC voltage output of likely 180 to 200 vdc. The nine transformers are high frequency ferrite, likely running at 25KHz to 50 KHz range. The other side of the inverter is the sinewave PWM switcher to create the 120 vac sinewave output from the HV DC boost supply.
Problem with this parallel boost circuit design is the time it takes to engage additional boost blocks, especially during surge demands. At best case, there will be a slump in output voltage. At worse case, the surge overload on a given boost block will saturate the small ferrite transformer causing the MOSFET current to shoot to extremely high level, blowing the MOSFET's out. This happens before additional block can power up and assist in the surge load demand.
This type of design needs to have additional circuitry to avoid hard saturating the ferrite cores of the transformers and current limiting on the MOSFET's. It is also possible the surge creates high voltage overshoots on the transformers exceeding the breakdown voltage of the MOSFET's. Surge snubbers are required on MOSFET/transformer to absorb this.
This is one of the best videos I have watched...A great one for instruction and to share...I'm a former HVAC/ELECTRICAL/MECHANICAL BLDG. systems maintenance foreman....Whew...Try saying that three times fast...I'm a former instructor too, soon to be doing it again...Semi retired, just couldn't stay out of it...I will use this video...The explanations and troubleshooting are detailed, clear, and the best part," understandable " with out talking over a guys or girls heads....I think, pulling one component fuse at a time, while the meter is ringing, may point to the bad circuit, but, reading through all the components, makes a circuit, and it will ring the meter too....You have to isolate the feed from the return and meter each one to ground...Maybe the base of the unit...With the fuses out, if reading the terminals of the socket, where the fuse goes in, one rings to ground, bingo....Where you go from there is determined on how deep you want to go, is it worth your time and /or the bucks, or just send the thing back...This is still a video worth watching and more than once...My thanks to the gent that made it.
Thanks for the kind words. I hope your class finds it useful. It helps me out a lot if you share the link and/or channel name "DavidPoz". Thanks.
Great analysis very logical, maybe check all of the 9 positive to negative leads one at a time to see which transformer (for lack of a better word) has the short. likely the mosfets are gone.
I agree with Jacob about the inductive starting surge from the motor and the lack of MOSFET protection.
hi David. Great vid. The initial In-rush current is a dead-short that cannot be measured accurately using a meter. You need to use a soft start circuit to protect the inverter.
For taking a video of the amp meter. The meter samples at once per second. If the saw pulls 100 amp for 0.1 second when 1st pull the trigger, would likely miss getting sampled. The 30 amp you measured was while saw was spinning up. When the inverter failed was right away when pulled trigger.
David, Your certainly learning as you go, thats ok. You have to Check the Specification of the Invertors and Big Current Loads, ie your drop saw. The Invertor should come with a Continuous Rating, probably 8000 watts but you need to Find the Surge rating, it may be as low as 10000 watts. Also some invertors have Output Current limit capabilities which can explain the difference between Invertors. Circuit breakers are old reliable technology, hence it is rare that there is a problem is there. If the Breaker is tripping 99 times out of 100 it is doing what it should do. You do have to make sure you have the Max Power supply Current and volts on the 48 V DC Input. Check the Surge Rating on Invertor Dave, if your Drop Saw is 15 amp typical Start up currents are Very Quick but 5 to 7 times full load so 75 amps for 1 second. Good luck.
I just got a look at the bottom of the 3000W board. Reliable does use a similar topology to what I described. The transformer secondaries are in series, primaries driven individually. Current sharing isn't an issue.
Just based on the shorted input on the inverter I'm positive that it was junk mosfets in the inverter that shorted thus, causing the breaker to trip. It threw sparks because it was disconnecting the inverter under a direct short condition, house circuit breakers will throw sparks the same way if you have a short in the line.
Your right on with your evaluation, great detective work.
Hi,
I have a Reliable 48v 240vac 3000w inverter which I have carried for a spare. On wiring it up I found it is sensitive to voltages.
It decided to not work so taking the top cover of I found the blade fuses.
They are only the cheap yellow auto type. Trying to pull these out to check them was nearly impossible.
Few of the holders came away from the PCB.
My first idea was to throw it in the bin.
They have gone up so much in price in Australia that I decided to have a
go at replacing the blade fuses with a resettable type blade fuse.
Hi David. You should understand what to expect from an ohm meter when you try to measure continuity at the input to the inverter. With the on-off switch in the off position on a known good inverter you would expect to see a very low resistance because of the capacitors that are acrossed the input to the electronics. The capacitors are there too try to absorb any spikes that come in on the DC line. Therefore if using an ohmmeter across the DC input do the inverter you would see the ohmmeter trying to load the capacitors. You may or may not have a direct short with the fuses put back in unless you expect to see a solid short across the DC. Leave the ohmmeter on there for a few seconds to observe whether or not if the resistance changes due to the charging of the capacitors. The point that I am trying to make here is that there are capacitors across the DC input to try to absorb any Spike that may occur on the battery side ie the inrush current.
Just as a note, my Outback Power inverters, VFXR3524A (2 of them) use a 250 amp Schneider circuit breaker each. Each inverter is a 3500 watt inverter. I run them in a split phase 240 volt system. My system will start and run a 2200 wad 240 volt air conditioning compressor. I decided not to run it through the inverter because of the start current always hammering the inverters on Startup. I do have an air compressor, and a washing machine that does flicker the lights when they start up. I have 3500 ampure hour of battery running my system.
If you want a project to spend time on, then go ahead to try and fix the 8000 Watt inverter but do it only as a hobby to prove to yourself that you can fix it on your own or send them both back to them stating that they both failed just moments out of the box! Make us all another video telling us what your decision is. I enjoyed the discussions with the group. I have more tube and transistor theory under my belt than I do with mosfet applications.
MY Reliable 3000 watt inveters has been running perfectly for two years also. i can run a Hitachi saw an air compressor and have never had a problem.
you are right on! you are not misreading this chart. the invert has no protection diodes, it has no snubber network. It is totally the designers fault of the inverter. Go to a you tube technician called (Diodes Gone Wild) and his power supply designs always have snubbers and diode protection circuits in every one containing Mos fet drivers
Focusing on the breaker is not the issue, voltage sag on input is the problem. With the circuit breaker taking the brunt, but the total resistance of the input circuit (internal resistance if you drew it systemically, a non ideal power source) was high enough to reduce the voltage on the input side, and thus raising the current in the mosfets above the safe area of operation. Like I said on the other video, this is often seen when people are wiring up huge audio amps in vehicles, and cheaping out on the wire. Currents go up, and the mosfets let out the magic smoke. In my estimation, the same thing happened here.
Hi DavidPoz;
(prequel: sorry about the length of this post, before I knew it, it was looooong! My question regarding your system is near the bottom)
I just wanted to commend yourself, for posting this video series, and the great community feedback which resulted from it; I've learned much more than I expected from all the great EE community feedback regarding your video, some of which I hope to put to good use when I retire in Hawaii to my mother's property, which has a 48V (2x24) solar/deep cycle battery powered system currently; I found your video while looking up pure sine wave inverters on UA-cam as she had requested that I look at sending her information on a good (but inexpensive) 48V DC input pure sine wave 3000W to 120V inverter;
Upon researching this system I have noticed how many people have commented almost without fail, about having problems with the cheap china inverters...
And I can't tell you how many times I've read "Spend the money on a good inverter, you'll save money in the long run!"
I wanted to mention that I did like the fact that you did not immediately start bashing the manufacturers of the devices in this system; rather you simply go thru some of the troubleshooting steps, and working with your forum to try and resolve your issue! Good Form!
So one thing I would like to ask about (hopefully one of the more knowledgeable EE's can comment;) is the fact that many of the new chop saw designs include a braking feature on the blade. Now I understand that this would take effect normally when releasing the trigger of the saw, it's when when you let off the trigger the blade doesn't "free wheel" in the newer saws, hopefully saving your knuckles as you reach in to gather your freshly cut work piece...
But if it's a mechanical friction brake used to slow the saw blade, which on startup of the saw doesn't fully release until the motor spins past a given RPM (most likely due to some kind of centrifucal clutch release system), could this not be also putting some extra load on the circuit at startup of the saw?
Of course as many have pointed out, David's inrush current measuring was a bit flawed due to the measuring equipment that he had on hand, and even with that said, the measurement would be what the measurement would be, but could this be adding to the overall load experienced by the system on startup?
Questions or comments, as long as it leads to someone learning something!
Thanks for your comment. I don't know what the electric braking system does to startup draw. As you said, hopefully someone will know the answer. Good luck helping your mother out finding an inverter to suit her.
@@DavidPozEnergy read my other post... just had a brain fart...
Now I'm going to spend my evening looking at more of these chevy volt/bolt battery systems DIY powerwalls; I gotta get her off of those big 24v deep cycle lead acids!
Just a shot in the dark but you can't just use a beeper. You have to check resistance to see if it's a complete short or just some kind of resistant load. It's common to have resistant load across leads.
The failure mode is definitely shoot through on the low-voltage MOSFETs. My educated guess is this is caused by poor driver circuitry failing during the in rush, basically turning on both sides of the MOSFET bridge shorting the battery input between two or more MOSFETs.
From wikipedia "When an electric motor, AC or DC, is first energized, the rotor is not moving, and a current equivalent to the stalled current will flow, reducing as the motor picks up speed and develops a back EMF to oppose the supply. AC induction motors behave as transformers with a shorted secondary until the rotor begins to move, while brushed motors present essentially the winding resistance. The duration of the starting transient is less if the mechanical load on the motor is relieved until it has picked up speed.
For high-power motors, the winding configuration may be changed (wye at start and then delta) during start-up to reduce the current drawn." ... on wikipedia they show a sample graph that this brief "in-rush" current can be like 50x of nominal ...
GRACIAS AMIGAZO, MUY BUEN VIDEO , NADA ASI E VISTO EN UA-cam, SALUDOS DESDE EL SUR!
Great video, keep them coming.
You referenced a part as a transformer at time index 6:30. I think you are right, because they sure do look like that. Transformers are AC devices and if you power them with DC they will act as a short, especially if you have a bunch of them wired together to share a load. If I didn't know any better, I'd guess that that inverter was designed to accept 48V AC as an input. Just a stab in the dark. Hope you figure out the problem. Good vid.
Likely you have a cascaded failure. Its the same as if you put a lot of LEDs in parallel. Not all LEDs are created equal, meaning some will have less resistance than others. For LEDs this means that some might be brighter (and hotter) than others if they are wired in parallel. For this reason LEDs are usually driven with constant current drivers to give the same power to each LED. In your case having 9 parallel transformer driver circuits, chances are that one of them took a bit more of the startup load than the rest. Potentially because of the gauge and different length of wire used inside the inverter (which in turn gives the path of least resistance). Once one of the nine circuits blows the load is shared between the rest. Then the second one blows until you blow the main external fuse triggers, which stops the cascade. Long story short, it is likely that it does not like the full load being drawn suddenly (due to the design), you might be okay gradually adding load up to 8000w.
( and all those motors have a capacitor that initially drops a huge start up amperage )Just found your videos... nice work.
Thanks.
My inverter failure was a BAD GFCI receptacle!!!!! Had to take it all apart to replace it.
I'm more careful of how much surge current I'm making.
Awesome- the time delay chart tells the entire story ... :-)
Thanks Mark. I struggled with this video because it's such a dry topic, but seemed to be an important one based on the comments.
@@DavidPozEnergy l understand that a breaker has momentary allowance for high draw of amps. I recently replaced an old tired 20 amp breaker with a new 30 amp these are 220v for a 5hp compressor I have the 20 amp 220v breaker in hand it has a rating of current interrupting of 10,000 amps ! My question during that start up phase of your miter saw is your breaker allowing your inverter to over draw/feed amps into the inverter and overload it ? Your running an 80 amp dc breaker at what voltage ?
Hi LN, This breaker is just like you described in your first sentence, it allows for a momentary high draw beyond it's rating. The amount of over-current is shown in the chart starting at 11:52 in the video. The breaker is on my battery side, at the time of the video the battery voltage was 48.9 VDC, which I stated at 10:22 in the video. When you replaced your 20 amp breaker with a 30 amp, did you re-wired that circuit to a thicker wire (probably from 12 AWG to 10 AWG.) Thanks for watching.
Question? Did you hook up all three input lines for positive and negative?
Can you help me to set-up a 6000w peak inverter, help me to find out what 🔋 battery I need and how many solar panels I do need. Please
I had the same problem with Circuit breakers on large induction loads put in a 300 amp class T fuse, problem solved. DC breakers have arcing problems causing voltage drop and super high ampere rise. Lost nice inverters before I figured it out. If your wondering why your 3000 watt inverter ran it. Look up voltage sag. It’s designed into some inverters to increase start up load for induction motors.
another vid with the verdict, can't wait
Great explanation, appreciate you time for this.
Thank You
You could be a good chap and send me the one that you don't want to fix. In all reality if they say that is a 800 It's probably safe to run at 400 half of what the rated. I love what you have created lifestyle independence
nice video and good logical approach to fault finding. I think you are right at pointing the finger at the inverter having a short circuit, which then caused the breaker to instantaneously open on to a short circuit(causing the spark). The design of that inverter is very questionable, they are relying on paralleling MOSFETS to get the power rating but do NO design effort to ensure good parallel current flow across all MOSFETS on the input side. The differing lengths of blue/red cable show that they have not even thought about that. A MOSFET can turn on in 10's of nanoseconds and at the moment of switch-on of the saw motor the first MOSFETS closest to the input see very little inductance to help with inrush and probably blow since they take ALL the current and effectively short circuiting the first few MOSFETS whilst the devices with the longer blue cables get an easy ride and don't see so much inrush due to the inductance of the longer cables. I doubt any short circuit protection on the MOSFETS such as de-saturation protection exists on their gate drives, so they rely on fuses but this is way to slow for the MOSFET which see the short circuit and die before the fuse even reacts. One solution if you want to continue using such a [bad] inverter is to put a large inrush inductor on the input of the inverter where the batterys connect, this way the MOSFETs closest to the terminals get some inductance to reduce inrush surges, or rewire the blue /red cables so they all have equal and longer lengths to gain some needed series inductance.
David, firstly thank you for the recording & insights. Additionally, I really like the way you do your reviews as they are in-depth, clean & clear, and are well weighted in the positive & negative. As an electronic engineer, there are a number of things that you may not be bringing into the discussion. The first being that what you are starting is an AC Motor. AS you have stated there are startup surges that occur, but there are also power feedbacks that occur due to induction fields collapsing with-in the motor that can cause huge power spikes back into the power grid. Normally the power grid is very capable of taking this millisecond surges, but as this is a switch mode power supply/inverter providing the power source, I suspect that the parallel design of the inverter was not designed to take these reverse in-rush power spikes. The way this inverter is designed is also not very inspiring as it relies on a number of Parallel configurations (The MOSFETs, Transformers, Transistors, Switching systems) works with close to the same speeds as each other, which off the shelf electronics without going through a strict matching process, do not do well. So I think you will eventually find 2x things that have caused the cascading fault. 1 is the way the Inverter was designed to leverage low-cost groups of parallel models that seemingly are meant to work as one. 2 the reverse in-rush current that is caused by an induction motor startup within its first 50 milliseconds of operation. Again thank you for the review, the insight and the opportunity for feedback.
Did you increase the input wire wire size or triple them from your DC buss to the circuit breaker and inverter? I think someone mentioned that in the comments. It looked like you only used one of the supplied wires which would not supply enough current from the battery to the inverter to handle the surge and if you were to run a prolong draw of over 3k watts the wire would most likely melt. Hense, the 3 wires. A sudden drop of voltage at the input to the inverter would most likely cause a sudden current current overload to the mosfets' causing them to short and blow there fuses.
Breakers have two kinds of protection. Short-circuit protection uses EM force. Very high power draw will trigger EM protection and cut power in fraction of second. Second protection is thermal. This one is quite simple, it will pop when it is heated too much. If you are under limit, then it will not heat up. If you exceed limit on breaker, it will start to heat up depending on how much you exceeded this limit. You can run 20A on 16A breaker for quite awhile before it pops. You could run 50A on 16A breaker but it will pop much sooner. For this thing you have classes which determine reaction time versus current. This protection works when it's not short circuit but is too high power draw.
I just saw Part 1 and Part 2. Did you finally find out what happen to those two Inverters that the circuit breaker from these two videos you just uploaded in these problems. Is there a Part 3. ?
Hi David,Seems there are already too many comets, so here is another. I design inverters over 40 years now, the first was square wave. Nobody seems to talk about your inverters wave form that is not pure sine wave as power company is and is called a step wave and has THD (Total Harmonic Distortion) rating. Motors or any inductive loads have a reaction to wave forms because a magnetic field is produce around the coil that during zero cross cycle will induce a back EMF (Electro Magnetic Force), This can be helpful if the transformer is tuned to the load but the loads and type vary. The only perfect DC driven inverter that simulate a perfect sine wave is the Ferro Resonance Transformer. Most inverters work fine with resistive loads and the better inverters have protection devices to handle more types of loads. Looking at your video it appears that the inrush and inductive reaction caused a voltage spike across the Drain and Source leads of a MOSFET called Vds (Voltage Drain Source) and on average can be 700 volts and that spike arced across the insulator inside the device and destroyed the MOSFET. (look for pin hole) If it used standard transistor would be the Vce rating (Voltage Collector to Emitter) and because your inverter does not have trans/surge absorbers to clamp and dissipate the spike it shorted allowing DC current not AC to travel through the motor windings and that could easily be 200+ peek amps in the 1/2 second way over taxing and destroying the CB. If you measure your saw's motor winding it will read as a short circuit because DC travels in a loop but with AC its changing direction back and forth and there is never really a short circuit @ 60 Hz so the failure was not normal for the circuit breaker as an overload it was designed to handle. Hope this give you a better in site and toss the breaker/inverter.
A junk inverter + lithium batteries = smoke. Your batteries have a very low internal resistance (I use the same batteries with a Schneider XW6848 by the way). That means they will provide an immense amount of instantaneous current. Couple that with your meter. You are on the right track but there is no way you captured the full inrush event with that meter. You need something with a LOT more processing speed. The inrush event is a huge spike that lasts for a few milliseconds and quickly tapers down. If the inverter doesn't have some internal processing to limit the current through it when loads like this happen they go boom. The engineers expected you to have slower reacting batteries so they didn't build that into their design. The mosfets shorted due to the spike in current and it was over. Instant boat anchor.
I've heard great things about the XW6848 and it is on my very short list of "Big-Boy" equipment to get. How's it been working for you?
A very nice machine. Not cheap though. I'm in the beginnings of putting everything together. The goal is to have the house on UPS. :D
I have about 40kw/hr of batteries that I'm testing and getting matched up. Unfortunately a 12s setup like you have now is not a good match for larger inverters. 14s is the sweet spot. I'm modifying the volt batteries to put together 14s groups. It takes three 12s packs and one 6 s pack to do it.
I agree about the 14s. When I called Shnieder tech they said the same, that 12s would be too low of voltage sometimes. Make the inverter work harder. If I buy another batch of Chevy Volt then I might re-wire everything to 14s. Do you have any photos of your wiring?
TrackGeeks - your reply makes a ton of sense when you talk about capturing 'inrush' with his $45 inductive meter (probably not completely accurate) However, he captured roughly 3 times running current - which is about right for most electric motors I've tested. Given that, how is it the 3000 watt Reliable inverter handled it (the same saw) OK, yet the 8000 didn't ? I'd love to get your spin on that as you are obviously well seasoned
@@DavidPozEnergy FYI. Magnum's inverters have a lower low voltage disconnect (LVD) spec. They will work better with 12s. It's something like 36v or 38v compared to Schneider's 40v. I'm using Schneider with 14s batteries, but I may use Magnum on a future project so I can use the Tesla model S modules.
My question is warranty/customer service will they replace how long would it take.
Circuit breaker like this one has two opening mechanisms. One is bi-metalic thermal based which is what the rated current is based on. It takes some time to heat up and throw its latch opening, by design, to allow surges. The other is a magnetic fast reaction trigger which responds to very high current like a momentary short and trips immediately. A DC breaker also has an arc inhibitor which throws a barrier across the gap as it opens for both bi-metalic rating trip and magnetic fast trip. Problem was not the circuit breaker, it is the inverter design. A good inverter would protect itself against an overload. A circuit breaker is to protect you if the inverter fails, which it did and the circuit breaker did its job.
if you are splitting the load across individual mofsets, without some sort of individual feedback to balance them; and they are all just individually clustered/phased and tied together at the outputs; an inrush of current could go through and short out by overloading one mofset more than the rest; then they cascade in failure due to a short.
Another possible thing; is all the mofset's gates are controlled by an ic; sometimes one for all; but typically one mofset controller per-cluster and each (cluster)phase will have a mofset for - and one for +per and most controllers can control both + and - mofsets; [this is how they do it in most buck/boost converters nowadays]; a simple small ic can take the place of many control circuits and logic... so it could be an array of transistors and capacitors/resistors.... i have only seen the top of that circuit board; not the underside.
Many converters have inrush/outrush(if added to the AC output instead) limiters to prevent there are common components that are meant to specifically limit inrush current to prevent these very types of issues.
I also personally believe that these types of motors should not be used on modified sine wave inverters (use an oscilliscope to see the fake squared sine wave they make and you'll see what i mean [you can look up YT videos as well if you dont have access to an oscilliscope, AvE has a good video], especially if you scope it under load) as they produce strange issues because of things like power factor dynamics as the motor ramps up, etc. I know I spat out a mouthful, but it should help you in your process of figuring it out.
But if you can source all mofsets test them, source to drain, drain to gate, gate to source with the diode mode on your meter (I bet all mofsets for + and - rails will be bad on the input [DC] side), as well as check in diode mode on the pins of what controls the gates for shorts (could be a circuit cluster, or an ic as I mentioned above); and it will lead you to other potential components to replace.... but in theory; just replacing the mofsets and if necessary the controllers should give you back a functioning unit. Just check out a few tutorials on YT about using diode mode on a multimemter to diagnose shorts in transistors. if the fuses blew; it probably protected the rest of the device's electronics.
Hope the info helps; but I think it all is from the surge that particular type of wound motor draws when it's first juiced....
its a high torque relatively low RPM....
A previous comment by another poster pointed out a couple of points I missed. 1. lithium batteries have low internal resistance so can produce very high input surge currents. 2 that if the inverter is only switched on and is in standby / idle mode the inverter protection circuits are not active until a minimum load has been attained. Going from standby to a high load instantly may well be outside the manufactures design parameters. Lack of a useful manual or specifications or operating instructions may be a contributing factor to this failure. When I run inverters I connect a 30watt fan to the load side and point this at the inverter, its a side benefit to keep it cool in 34C (typical Aussie air temperatures) but by using the fan the inverter is already working into a load so is "fully switched on and not in standby". To properly test this inverter a storage oscilloscope would be needed to capture the input current and voltage transitions. Difficult as amps will be in units of hundreds and voltage spikes in tens of thousands. So maybe 2 scopes on different settings would be better. Bench testing of complex electronic equipment by untrained but enthusiastic users is often not effective without a good understanding of electronics and electrical theory.
In practice the tests carried out would be typical of most purchasers, in a suck it and see approach.
I would do the bench testing as previously posted and get as much info / data on the inverter via specs and the manufacturer so that the testing was designed within the designed working and surge conditions.
Black box inverters from China (branded or unbranded) are hit and miss as so many do not have specs, just pics and tempting low prices.
I'm a telecom stand-by/backup power guy. I work with multi-battery string, high current DC power plants and stand-by generators up to 500kw. One thing i noticed that would be critical is that the internal DC distribution leads are not the same length. This does not allow for a balanced dc load across the input stages during surge. In high current discharge conditions, the cables have to be of equal length or the load will be highest on inrush on the shorter cables (and component stages). The existing wiring places more load on the first groups than equal across all the groups. Notice the MOSFETs of the first 4 parallel groups were failed. If one were to replace the DC leads with equal length leads, I'll bet the failure would not occur. I will admit that they seem to have poorly engineered the whole thing "too close to the edge" of the required spec. Now on battery string interconnect cables from lower string on shelf to upper or to the "chandelier" (busbars) overhead, this would not be such an issue, though it can be problematic and cause excess heating at cable attachment points, plates, and crimps which causes "loosening" over time. On component groups, that's a whole different story. If you were able to catch the transient surge on ammeters attached to each group input, you would find that the first and second groups took the brunt of the load and way exceeded their rating by 10+ amps. Remember, surge can be up to twice the continuous, depending on the device. This definitely due to bad engineering, but a fairly simple fix. I would also eliminate the multiple cable per crimp at the input attachment points and stack individual lugs on the bolt of the inputs.
Thank you, excellent point. And it sounds like you have an awesome job.
@@DavidPozEnergy Check the previous video for more detailed notes..forgot to update this one. Thx! Glad i could help!
Were you using that breaker on the battery side or output side of the inverter? Because none of those chart values apply about average rating if you are using it for AC output. It’s not AC rated. The same gauges of wires will have different ratings depending on AC or DC applications because DC heats wires up much more quickly than AC, thus DC wiring has to have much larger gauges for the same amperage.
Everybody keeps saying it's a junk inverter. But you forget that the 3000W version worked fine with the saw.
So I believe the company got something wrong somewhere in the 8KW version. This happens with even the best name-brand equipment. More rigorous testing is what they need.
To hard to measure now. But low voltage output from invertor could have been a factor. The focus has been on current from what I have read so far. Can the invertor handle the instant current draw and maintain a steady voltage?
Dude, it's the junk inverter. Nothing to do with your setup... the mosfets failed
Upgraded vrs of the 8000
ua-cam.com/video/riZBuepBb68/v-deo.html
Cascade failure of the mosfets. I don't know if the mosfets were faulty, the load balancing was lacking, or a bit of both, but the actual failure mode is obvious. Cascade failure of the power stage.
If they failed they usually blow up and release the magic smoke i see no damage at all
@@awesomusmaximus3766 usually, but not always.
My guess is that the failure is related to the low inductive power-factor of the load (the miter-saw motor at startup). When driving an inductive load, the current will lag the voltage. This means, the instantaneous current WILL NOT be zero when the voltage crosses zero. A significant current flow through the mosfets while they are switching off will cause them to overheat. That's why most inverters cannot drive full output power into a low power-factor load. You are stressing this inverter beyond what it was designed for.
Has the breaker been looked at in a forensic manner? An EE with specialization in DC circuits. An example of AC -DC to AC is the NB Power interconnect with Quebec Power's Grid. Now that is a grand scale. The advice I got from an installer - with 20 years experience - was to double the size of the breakers. He had been into fix a lot of somebody else's messes - and that was his advice. Also - go look for an old Metered Amp clamp - The instantaneous spikes are seen on dials. Not so much with electronic meters. They do not react quick enough. The trigger timing of the Meter - is much less than dial meters. Cheers
Yes, the breaker video is here: ua-cam.com/video/Woigo3sTp_E/v-deo.html Thanks for watching.
Just a thought... I wonder if they made all the internal DC cables supplying the MOSFETs the same length, that might allay the problem? I would expect the shorter run cables nearer the input to provide significantly greater current than the far end MOSFETs.
My guess as an engineer not knowing the circuit, is that the harmonic frequencies caused by the saw starting is triggering the FET circuit causing them to form a short. About five months ago I had to fix the power in a manufacturing plant that converted over to LED lighting that was causing motor soft starts to fail weekly. I attenuated the harmonic frequencies using low pass filters on each power run to the LED lighting. In the office area some of the printers when printing would make some of the LED light flicker when they were printing. I fixed this by adding a extension cords to attenuate the power line noise. A filter would have been better but the extension cords was a much chipper fix. With all this said the working unit must have some type of filter system or a better circuit for firing the FETs and that could be as simple as Ferrite beads.
my question is the current on it???how may amperes??? tnx
My guess is that the breaker was to big(80A) and the motor was in short at that particular start and so it was acting as shortcut to the output of the inverter and that make the mossfet+fuses blow . Now if you had a lower value breaker (60A rapid) that may save your inverter (it may cut off the output in real time). In general the motors are surging a lot of current at start. That is why for this power tools applications special inverters are needed.
What are the specs on your saw, does it have ratings on it anywhere, and like some others have mentioned about your battery bank, can it supply the amps (factoring in the burst load starting the saw) for that 8kw inverter., if not the volts will lower which then requires more amps. And saw's make horrible noise on the power lines, maybe even enough to upset the inner working of the switching inside the inverter like altering the switching time of one or more of the input stages which can put them out of sync, I wonder how it would go if you had an isolation transformer after the inverter (just curious, maybe someone can give some info how they would work.). I think by design that inverter can handle most regular house appliances up to the 8kw but no so great with power tools, but I would at least expect it to cope with a home AC system. Im surprised the makers of that inverter havn't asked you to ship that saw to them so they can test in house before too many more Blown Inverter videos get posted to youtube. Thanks for sharing, we all learn from this stuff. Look forward to more updated.
My read on this is that the inverter failed first, and it is primarily the fault of the inverter..... but one extra factor is that the Lithium cells you are using are capable of very high current, and their output is very "stiff", it will not sag under sudden high loads... and I think this is where you have defeated the testing that Reliable will have done using Lead Acid batteries!...
The two boards in the inverter are literally input, and output... the input board will step up the voltage to around 170vdc (the peak voltage of a 120v sine wave), while the output board will turn it into the 120v(RMS) sine wave.
The fact that the input board failed amazes me, since it means that the output board is built like a brick outhouse!... I imagine if Reliable do any redesign work here, it may be to beef up the mosfets on the input board, but they should probably also consider adding some mitigation for a sudden surge current... I don't think the mosfets would fail that fast due to overload, but perhaps the sudden surge caused some high voltage back EMF spike at the primary winding of the transformers... it's possible that the modfets simply need a better snubber array... or perhaps some small filter on the high voltage interconnect between the input and output would help.... It's almost impossible to say without a circuit diagram.
I'm also wondering if I've been saved a similar issue because my unit has a 340vdc input board for 240v output.... so the interconnect carries less current.
Duracell bought a company that made a UPS battery backup inverter done the same way as the knot on this. But if the transformers are using wire to thin, or the insulation between the windings are thin then the transformer wires would heat up, melt the insulation, maybe even arc to another winding if they don’t have enough insulation. The power from inductive load (saw) has to be release somewhere and will go back out of the input to the breaker. The transform fuses would blowout as power exits and because of the power coming out it probably aced on the breaker wires.
OK, if my theory is correct then the transformer after the last fuse was the fat to go. And the other could also low out and short as the power exits backwards trough the input terminals.
Also, not only could this be using sub par transformers, but some heart TVS diodes between the transformers could have stoped most of the damage cased with maybe only pop get a fuse or two.
On second thighs back to sub par transformers, maybe on would be damaged even with the diodes since that it’s one is the weak spot and the flaw in the systems under load with inrush current.
I have a 4000w reliable.
Powers my entire house. Furnace, 2 freezers, large fridge and Kuerig coffee maker, and also misc. power outlets.
Never a problem.
Everything is done with 4/0 supply wiring throughout 24 31 series 105 amp hrs 12 volt batteries, and 10 or 14ga house supply wiring. Separate from grid power.
200 amp inline fuses on neg. and positive on battery side.
System goes into 60 amp main then to separate breakers 15-20 amp. Inverter is rated at 30 amps.
Point is the inverter works very well. Over 3 months now.
It appears these inverters rely on lead-acid battery specific characteristic to sag voltage under high current surge situations. David must be using Lithium batteries which are capable of delivering much bigger surge currents with much less voltage sag which inverter is not designed to deal with.
@@andriusst It's the other way around. Lead Acid delivers far more instantaneous current than Lithium. And, it's a demand for more current than can be supplied which will result in a destructive voltage drop.
Hi your correct to a degree regarding the circuit Breaker, but circuit breakers are designed for different applications, inrush of motors require a different type of circuit breaker, compared to a circuit breaker protecting a lighting circuit,
The current limiting is off or too high, higher than what the mosfets and or igbts can handle. A simple flaw in choices of parameters in the psw current sensor modul.
So normally, when an unbearable surge rush in, the current sensing modul will easily turn off the inverter, no harm done, and after a few moment, will power back up *with the normal gradual voltage climb* , and if we keep on pressing the power button of the miter saw, it will run with that slow start very easily amd smoothly this time, without any in rush
I hope they can fix that current sensing fault for their future products
Yes! Time Delay Circuit breakers. They have a Magnetic trip and a thermal trip. Good Job!
Should find a chop saw with a speed control, so you can slowly spin up the saw and should result in a lower start up current.
An electric motor is a dead short when you pres the trigger switch and it has not started running yet. A 15 amps rated electric motor may draw in excess of 45 amps at startup. Unfortunately, semiconductors react way much faster that a fuse or a breaker. A breaker may trip after some 50 msec or more. That 35 amps breaker will trip at about 50 amps... If that current is present long enough. A fuse will blow within 10 msec, and faster if the overcurrent is high enough. A semiconductor like a MOSFET will likely blow within 100 microseconds if the absolute maximum rating of the part is exceeded. Furthermore, there is the voltage issue which a breaker or a fuse does not protect against. An electric AC motor is basically a DC motor on which the connections are switched. A coil switching can create voltage spikes over 10 time higher than the driving voltage. So, driving the motor with 120 VAC may have given spikes in excess of 1,000 V. That would certainly exceed the absolute maximum rating of the MOSFETs, blowing them up. In turn, the fuses would blow as MOSFETs often short when they blow up. Conclusion: A strong voltage limiter in the dV/dt domain would need to be used.
uk electrician here. A CB has 2 forms of protection on AC. A bi metallic strip for overload. (prolonged) and a coil pushing a projectile for short circuit. (almost instantaneous) forgive me but it's late here. but I cannot think of a way to get the latter form of protection to working a DC supply.
I wonder if the ground supplying the inverter is under gauge? I know from car stereo days that if the power can't flow back out the ground fast enough it will blow mosfets.... If the amplifier is under a big load and you were to disconnect the ground supply it will immediately fry the amp. Perhaps the ground wire supply is too thin to allow the voltage to "flow" properly.... I'm just a guy though who knows.
The system can work by using starting current limiter.
My inverter when on grid showing wrong battery voltage. When no utility power is supplying battery voltage automatically corrected.
Great video and love the way you explain everything
Thanks.
if you notice some of those heavy blue cables are shorter, therefore less resistance and not sharing equally
There may be capacitors in parallel of the battery input of the on the inverter. That can give you a false reading that it is a short.
@davidpoz you put a 80 amp breaker on a 66 amp circuit, 8000W at 120V is the output which pulls ~66.6 amps IF the resistance is ~1 ohm. You should have put a 20A at first then tested with a 40A breaker if the 20A worked. The fuses are the giveaway. Each fuse is rated at 10A which means those Mosfets are rated around 10-15A. You stated the chopsaw pulled 15A which on start-up can be 20-25A depending how long the extension cord is. On that circuit design, in that inverter, it will be possible to pull the whole 20-25A across one 10A circuit. That blows the fuse and the Mosfet. Replace all the Mosfets (you had continuity across the outputs which means the fets are shorted closed) then yank all the fuses and test voltages across across each fet one at a time. If that doesnt fix the inverter then I would need to put a meter across it. The spark coming out of the breaker is normal on an ungrounded/poorly grounded circuit that shorts! I'm no expert but that's what my ohms calculator tells me.
After reading through most of the comments I just want to throw out a few things which may help.
I bought a clamp-on meter with a very cool 'Motor Start Current" capture function. It was about the same price as all of the decent ones. Even the peak hold feature will get you close.
Snubbers and Transient Voltage Suppressors (TVS) are not used on DC circuits from a battery source. They are used on utility input circuits to handle Transient Voltage Spikes which are added on the power distribution circuit, aka power lines.
The very slight variations of length on the internal power conductors will have zero effect. It's a DC circuit so frequency is zero.The resistance difference would be insignificant but I can calculate. I have to guess at the gauge, maybe 12 ga. so about 1.6 ohms per 1000FT. The longest loop is about 2' longer than the shortest so about 3.2 mohms variance from best to worst.
This inverter is not poorly designed. It is value engineered. There is a huge market for this. It's designed to delivery exactly what it claims. It is not designed to survive incorrect installation. The protection systems in the design assume correct installation. Many folks commented that they have seen failures due to undersized conductors. We watched it happen TWICE. This is extremely common in the consumer arena.
When hobbying with electrical equipment please read all instructions and every label. Be sure to follow everything on the label exactly. The labels are required by UL to keep you safe and to prevent fires.
I have been designing industrial 48VDC power and battery systems, and inverter systems for 3 decades. I have 100s running nationwide. However, I have not designed consumer products. It's fun seeing your innovative ideas here. Please be careful.
A large part of the problem is current distribution within the inverter. There needs to be a centralized bus system where all the wire lengths from the bus to each bank of MOSFETs are the same, otherwise the ones that are closer to the source will end up doing more work under load. This is apparent in the fact that the MOSFETs closer to the terminals ended up burning out first. One failure mode in transistors/MOSFETs is a short to ground, and it looks like this is exactly what happened. This, in turn, ended up pulling enough current through the circuit breaker for it to do its job and shut the power almost immediately. I wouldn’t be surprised if the traces on the underside of that board are scorched too.
I think a centralized power and ground bus inside the inverter, coupled with MOSFETs that are a little bit beefier, will make that inverter run like a raped animal.
A few bucks more in parts, and a slight redesign of the internal component layout and power distribution should do some justice.
Question did you manage to sort out the problem with inverter because something just came to mine I don't know if it would help or not if you look at the AC input the grounds and the Neutral are still live maybe that might of course the problem please let me know
Thanks for your idea. I no longer have the broken inverter. The manufacturer does not make this model anymore, they updated the whole design.
The typical in rush current for a motor can be 20 times the full load current, the in rush only lasts a few mil seconds. It is due to the motor presenting a short circuit until the magnetic field in the coils produces enough back emf to resist the current flow. I believe you may have hit the cause of the failure in the 8kW over the 3kW as being the way the dc is distributed within the 8kW unit; the wires from the dc in terminals should all be the same length hence the same resistance therefore the current flow will be equal, its possible that one or two of the inverters are grabbing most of the current going short circuit blowing their fuses and this cascades along the string.
Its quite possible that manufacture has not designed their inverters to handle motor starts of the rating you are attempting, its worth asking them
(I an electrical engineer in the UK :) )
Dave, I think the inverter has a fundamental fault in handling surge. As well, I don't think it is the problem of the circuit breaker. You may need to ascertain first if the inverter is really 8000 watts as described. Here is my suggestion: if you are able to repair the inverter into working again, instead of taking it through such surge with the big saw, give it a lower load and keep increasing the loads to see what it can handle (up to how many watt is can handle). This would help you determine if actually it is 8000 watts as rated.
I hope to work on fixing the inverters in the future, but I'm afraid I need to learn more about the electronics first. Right now I don't know exactly what needs replacing, or how to determine that.
@@DavidPozEnergy Fixing electronics is fairly straight forward. As long as you have a DMM, a solder iron, some patience, and some time, you can do it. I've only recently within the last year really gotten into electronics and have learned a lot. But, it started with tinkering and fixing LED tvs and other gadgets.
The FETs blow first. We know they need replacing. Pop the old ones out and while out, test a few other components (I mentioned in another comment the caps and resistors); also test the transformers (yes, that's what those particular ones are) as well. Make sure they didn't go dead short as well. They should all have the same Ohm. Then replace with the new FETs. That should be your only problems to replace.
LithiumSolar has a few videos on repairing an AIMS inverter and shows how he did it: ua-cam.com/channels/h85wOuqCsD3gh_lkAXbQEQ.htmlvideos
@@korishan the first problem in this tv's are the caps... Overloading the mosfets..< This inverter needs new (paired!!) mosfets, and a rebuild in the feeding power cables, these should be all the same lenght.... (to devide the power equally over all the mosfet bridges)
@@MrBugsier5 Dude wtf? If a design requires matched discrete MOSFETs and power cables that have the same length, it's a shitty design. Look at how redundant server power supplies share the load if you wanna see the right way to do this.
Hello is there a differance between an ac and a dc breaker? You said it was a dc breaker and the power coming from the inverter is ac...?
Yes, there is a difference in AC and DC breakers, but some can be used with both. I'm using a DC breaker on the connection between the battery and inverter. This is the DC side. Thanks for watching.
heya I think your write a short cut in the inverter as I have bean calulateted it 3X most likely the mosfet(s) or the capicator('s)
I'm really dumb about all this but I think if the inverter was working properly there should have been protection in it to prevent this mess. Good vid, keep us informed.
Are the inverters true sine wave? A few years ago my brother (electrical engineer now, in school at the time) was telling me if I wanted to run motors on inverters I should use true sine wave because it could damage some types of motors if not. I am not sure it it could damage the inverters but it seems like a possible avenue of inquiry.
Thanks. "Reliable Electric" says they are true sine wave. However, I don't own an oscilloscope to say otherwise.
When I made inverters in my younger days, to change DC to AC, I remember using a high-level MOSFET and a low-level MOSFET to switch one output node to the positive and to the negative. This was used in a half or a full H bridge. The storage capacitor on the DC side had to be very close to the Mosfet as at that current high spikes are generated even in short wires. Well, the firing of the upper and lower Mosfet had to have a delay time as if they switched together that would be a dead short circuit across the storage capacitors. From what I can conclude in this video the fact that the fuses were blown and the MOSFETs were also failed and at the battery end there seems to be a short circuit...... then I am afraid the firing of those Mosfets either to get the high frequency to step up the voltage or to get the sine wave shape due to switched modulation...... well that part of the circuit needs a lot of attention before one markets an inverter.
Thanks for your input. Does anyone make an inverter that has protection built into it so that it will just shut off instead of burning up?
@@DavidPozEnergy Unfortunately in high current inductance switching, voltage spikes occur so fast that no protection system is fast enough to stop any damage. Fuses, Circuit breakers, and electronic current or voltage protection are not fast enough. Good design, good components, and testing and testing and testing is the only solution.
@@DavidPozEnergy the Schneider conext sw4024 I have is a beast, it's a large transformer inverter, 4000 watt 240v, I have two of them and we live off grid powering everything like a normal house, it's pricey but well worth it and have had 0 issues with it.
So, there's something we haven't looked at:
The voltage drop across the wires on the DC side.
Not saying it was or wasn't the setup, but I didn't see you address that.
Why could voltage drop cause the inverter mosfets to fail, you might ask?
Because, the output voltage regulation of the inverter causes more current to be drawn from the batteries on the DC side as the battery voltage, or at least the voltage at the inverter terminals, falls.
This is of course because to maintain the same power output at a lower voltage, more current is needed.
The mosfets don't actually care about the voltage drop, but what they do care about is the current increase. The mosfets can only handle certain amount of current before they fail, usually closed circuit, causing the short you are seeing on your input terminals.
For this reason, I'm curious about what would have happened if you had used a larger gauge wires, or simply more of the smaller ones.
Again, I realize that you use to the wire supplied, this is clearly reliable electric's fault if my theory is correct as they supplied wires that are just not suitable for the application.
However, it definitely seems to me like this would be possible, the voltage falling and the current increasing, triggering the overload of one or more mosfets.
One thing to consider is that smaller circuit breakers tend to have higher contact resistance than larger ones. If the resistance of that breaker caused a sag at the moment of the switch on surge the mosfets would have been overloaded for slightly longer than otherwise - possibly enough to bring about that cascade failure. So unfortunately it points back to the smallish breaker being used again.
I do agree with other commenters about the differing wire lengths inside the unit possibly contributing to the failure and that would be a design issue of course. The best thing to do when running big motorised appliances from inverters is to use a LOW FREQUENCY TOPOLOGY inverter. These are far more robust when it comes to starting "surgey" items.
Interestingly, I watched your previous video a day before I went out and purchased a 1250 watt circular saw, which I intend to run on an old high frequency MSW 3000 watt inverter. Your video made me nervous about popping the thing the first time I spin up the saw so I am putting together a soft-start unit. I have already developed it to the point where I have tested the principle of it with the inverter and the saw. It worked nicely.
Could my inverter fire up the saw on it's own? I'll never know, because I am never going to try it that way! The other advantage of the soft-start unit is the saw doesn't kick back the same when it's spun up. Which is a useful feature on a hand held tool.
People have said it in other comments and I think they're right. The mosfets may be the problem. Power switching capabilities of mosfets are generally slower than that of igbts. A quick look at the bus layout would mean each mosfets would be taking just less than 1000watt continuous. And peak draw is way higher. But I'd be interested in seeing the part number of the mosfets used. I'm more inclined to think they cheaped out on out of spec fets or regulator caps. If the drive voltage doesn't switch fast enough and gets the fet fried. Looks like bad component choices at first glance but until we know specifics, we're all just talking out of our asses. By the way it started I don't think it has much of a soft start circuit for the PA side either. Another shortcut to make the unit cheaper maybe?
Explanation sounds good
Your inverter had a cascade failure. What it does is splits the voltage into a positive and negative DC then creates a 120V 60hz output from digital pulses in the upper kilohertz range. The reason it failed is one of the FETs shorted out, then stressed the other ones till they shorted out.
check on google that 8kw inverter can take up to 16kw surge and the surge would probably last no more than 500ms so the inverter would give out 133 amps say for half a second or less but the immediate draw from the batteries @48 volts would be UP TO 770 amps. dont forget the load is inductive and not resistive. you can get special breakers for high inductive start loads. check the small print with the breakers they should tell you how many start up amps they will stand perhaps try a contactor with thermal cutouts but needs to be wired in a single phase "easy when you know how lol" I hope this helps, Paul UK
Hey David, the only way to measure irush current is with an o-scope. using a clamp meter introduces errors, becauses it has a sampling frequency, so you cant assure it measured exactly the peak, in adition to analize the breaker you need the pulse width of the inrush peak, again, you need the o scope to see it the breaker tripped or not in a given time. Asi you mention, the smaller one has less mosfet in parallel, reducing the paramters i mentioned last video.... the inverter side works as an SMPS, so I gues in a push pull technilogy, if the secondary of the high frequency transformers are not well designed and connected current directions can vary causing an overload and , blowing the mosfets. if the euipment is out of warranty desolder every mosfet , short the three legs and then measure resistance on channel ( Drain to source) look for the datashhet pinout. if you got a short circuit, they mosfet suffered an overcurrent, if its open, it suffered a reverse voltge peak, caused when current stop flowing throw transformers and circuit opens, a big current in transformers will cause a bigger voltage spikes. replace mosfets, and get softstarters, no one of garage tools starts engine with load.
Thank you Martin Ezequiel Kutter. I only half follow what you are saying because I have recently watched some videos about mosfets. I'll be referring back to your comment when I go to replace the mosfets. However, it is probably going to be a while because I'm working on the solar array at the moment. I appreciate the helpful feedback.
@@DavidPozEnergy Ni prob, glad to help. just a comment, when I said short the three legs it's only momentaneous, to assure the gate is properly discharged and no channel is formed (y) you have to measure the mosfet with all three legs open using the multimeter ( I prefer analogue ones) . As per intrinsic construction of mosfets, they have an anti-parallel diode between drain and source, this allows in some cases to create a path to close the circuit when mosfets opens, avoiding voltage to increase above mosfet channel specifications. most of the time, this diode is not fast enough so the voltage grows anyway, the way to avoid this is to put a Schottky diode in series with the load ( transformer winding) and a Ultrafast recovery diode in anti-parallel with mosfet, such as MUR line, but, as I saw in a below comment, a snubber network can also work.. switching coils at high frequency its one of the most complex things in electronics. Too much physics there. The way of choosing a protection is a bit different, you have to have the specs of the motor and according to the inrush current and duration of inrush current you have to choose the most suitable protection,( in addition to repairing the inverter now). If its too sensitive, the motor will not start and probably inrush current will exceed the absolute maximum power allowed for the switch,. if its too "hard" never will trip causing a phenomenal short circuit blowing the inverter if it can not withstands that current flow for that period Try to look for universal motors soft starters or suitable dimmers, if you go with dimmers you will have to manually increase the speed, do not load the tool until about you feel its at full speed
David , I'm liking the videos! I was going to suggest checking out some videos from (going off grid ) but after reading about 400 comments I saw he chimed in already. But one thing he had a problem with and was a concern with others who have bought these is did you check for a live ground? Direct wiring is the preferred method but the inverter will blow if the neutral is not addressed. This is explained more in some of the videos from going off grid. Also what do you plan on doing with the inverter
Thanks for your comment. I watch "Going Off Grid", he has fixed a few of these inverters. As to the live ground: I never checked the 8000w, sorry I didn't think of it before it blew. My 3000w still works and I've checked that one. It does not have a live ground. Right now I still have the inverter because I think it would make a fun video to try and fix it. However, there are several other projects I'm working on right now and making videos of. So if I get to this it's going to be a while.
@@DavidPozEnergy thanks for the reply, from what I've seen of these the live ground was only an issue on the 8000 w and not the 3000 w , if you end up not doing anything with the inverter, I might be interested in it , I'd like to have some components checked out. I've been aquiring my off grid set up and have been looking at these as a possible choice for inverter, but prefer to follow a few people who already have them to see what issues and solutions they have.
Looking forward to future updates.
Dear Bro,
Is it possible to have the diagram? Thanks.
You are correct, now check the transistors on the heatsink and you will find a bunch shorted. You should get around .6v base to collector, and base to emitter on a diode check. You may have to unsolder them for accurate reading but the shorted ones will be obvious without desoldering. Not sure why this failed other than a crappy inverter.
There is a lot of discussion about the "load sharing" between the various sections of this inverter.
I haven't worked on a "Reliable Electric" unit but I have worked on a number of large inverters from another manufacturer, and I've seen the bottom of Reliable's 3000W model (in another video on another channel) and seen that it is similar.
The sections are NOT parallelled on the output sides at all. The length of the supply conductors isn't hugely relevant, and no section ever sees more current than the other.
What you have is nine different, isolated, voltage converters. They are synchronized but otherwise independent. The secondary sides of these converters are in SERIES and produce about 360volts DC, with a center tap (ie: ground, +180VDC, -180VDC).
The second board that David here is calling the output board is just exactly that. It uses PWM to generate a somewhat-accurate 60Hz sinewave that swings between the two 180V rails.
Since the input sections are in series, they all see the same current. One may output a slightly higher or lower voltage than another, but we're talking a couple of percents here, if even that. There should be enough headroom in the design that a few volts drop on the HVDC rails is irrelevant, and, in any case, the difference will not stress one section more than another.
@TrackGeeks also makes an interesting point. MOSFETs can easily be killed by instantaneous current, faster than a fuse can blow. Those fuses are protecting the wiring from dead short current, but they're not really protecting the fets themselves.
Most traditional applications consist of a big lead battery. They have scary current capability but it's still "tame" in comparison to lithium batteries.
When you try to start up that motor, it's initially a dead short, and the current is limited only by the DC resistance of the motor windings and the impedance of your wiring...
... your wiring is pretty short. There's not a lot of resistance there. The inverter is, for all intents and purposes, seeing a dead short.
What would normally happen is that the DC input voltage would sag a bit -- the resistance of the INPUT wiring (and batteries) would limit the actual current through the MOSFETs. It would likely be higher than the fuse value but lower than the value at which the mosfets explode... but you don't have (as much) resistance in your batteries AND the supply wiring is short. Your battery bank is able to provide a much higher (and thus more destructive) instantaneous current than "Reliable Electric" expects of their usual lead-wielding customers.
that might be true if the 3KW inverter blew up too!
but it didnt
To see the inrush current you need an oscilloscope. That way you can see the current waveform in the sub-microsecond time frame. Your meter can barely do tenth of a second.
and to see it instantaniously on the scope you need a Memory scope to freeze the event on the screen. but that is not his responsibility. He is a customer with a company that has deadbeat engineers that were asleep during their electrical engineering classes
Yep.. you'd probably be surprised, and maybe a little scared, if you saw the Real instantaneous max current. But it's perfectly normal, and it only lasts a few milliseconds, dropping back to normal in usually less than half a second. What your clamp on ammeter showed was an average value over a half second or two (AC ammeters show an average because they have to, since AC is constantly oscillating) as the current peaked then dropped to normal. Something like an A/C or large refrigeration compressor is much worse on startup than a saw - they can take several seconds to get up to speed. But circuit breakers are made for that, too.
not an expert but i think that when some mosfets fail the fail in the "closed" position causing a short. inverter probably using chinisium crap parts.
might try a choke on the output side to limit the surge current
You mentioned the Manufacturer was attentive and engaged, I wonder what their feedback on your video has been? I had a similar experience with a Japanese manufacturer who sent a team to San Francisco to interview me about the flaws in their design of Pneumatic tube bank systems. ( I was trained by their competitor and was a factory certified tech.) After I listed the flaws in their design I was worried the chief engineer was going to commit Hari Kari.
I'd say your assumption is pretty good, the inverter just shorted out. Hope I don't run into the same trouble when I get mine running.
Interesting bits....
I agree with your assessment that the inverter is to blame. I don't think you were drawing 135% though. Based purely on the time it took to spark and die, it seemed closer to 600%.
The inverter is overly technical.
It's running 3 phase power in 3 parallel feeds to a single toroid inductor for smoothing purposes. The amount of capacitors alone guarantees component failure.
Go for a large transformer and immerse it in baby oil.