First Look: LTC3780 Buck/Boost DC/DC Converter 10A 130W
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- Опубліковано 11 січ 2015
- A first look at this high efficiency (up to 98%) high current (10A) DC/DC converter employing 4-switch synchronous rectification. Based on the LTC3780 controller IC.
LTC3780 Automatic lifting pressure Constant voltage step up step down 10A 130W www.ebay.co.uk/itm/-/221595657364 - Наука та технологія
Rather surprisingly your channel is quickly becoming my most anticipated channel to watch when I load up youtube. Doing a project of my own and a number of videos cover things directly related to things I'm using. Keep up the good work.
elminz Hey thanks, keep at it.
Great vid/ demo as usual Julian, you really do provide good explanations of your circuits and toys, thanks for your shares an keep em comin!
That 3rd pot that you talked about @9:55 into your video is called the "input under voltage fadeout" this is used for two things.
1)MPPT, If you connect a solar panel to this. you can adjust this to load your panel to it maximum power point. This will allow you to load your panel to it's most efficient I.V. curve as possible.
2)Over discharge protection. You can set this to start fading the load as the voltage of the battery get lower. Note that this does not do a hard cutoff and there is no hysteresis in this ether. for example. if you use this as an LED driver. Once the voltage of the battery reached the setting of the pot. the LED will begin to fade and not just shut off.
Thanks a lot for this info.
joyange1 u
MPPT? More like MPP, if it doesn't track MPP and we have to manually adjust it then it would be MPP and not MPPT.
@@luongmaihunggia and what about using arduino an digital pot to control the buck boost converter?
Hello, friend! You've been very misleading with your comment. There is no mpp or mppt function in this device at all. Instead, the 3rd potentiometer turns off the device completely when the input voltage drops below the set value. This is very easy to trace - if you apply a voltage to the device below the one set by the third potentiometer, then the output will be zero. Solely thanks to your comment, I bought this garbage that doesn't even know about mpp.
Thank you Julian for this presentation. This Unit looks practical enough,will order one.
I just found this on ebay. Thank you for reviewing it!
Thanks Julian for a very helpful review. +1 for oscilloscope based ripple voltage performance of the output like others suggested.
would it be possible to use the chip to power more FETs and a larger inductor to build a very high current boost buck converter?
The third pot is almost surely either for turning on an LED when a desired Vout is reached (i.e. if you want to charge a 3s LiPo up to 12,6V it could light up above 12,5V), or for input low voltage alert. LiFePO4 cells have a very rapidly increasing voltage at the end of their charge: I played with A123 18650 and charging them at 0.5A the voltage went form 3.5V to 3.9V in like 30 seconds, so there is really no need to cut off the current when you approach 3.65V/cell, they will just very quickly stop drawing current on their own. I also used this "property" of the chemistry to make a really cheap "balancing" circuit by employing 3.9V zener diodes plus a small series resistor. It is not ideal, but the battery pack that I made has been powering a cordless drill for more than two years now and it is stil rocking: the torque increase from the original crappy NiCd battery was immense.
Hi Julian,
I think the left hand pot is used to set the low limit for input voltage. e.g. it could be set to switch off if input is less than 11.5V, to save your lead acid battery from over discharge.
I could set this Vin limit anywhere from approx 5V upwards.
I had it taking 5V at 4.6A converting to 10V at 2A and it ran perfectly.
The potentiometer closest to the input is an input voltage (low-voltage) cutoff.
I bought this off of Amazon a few weeks ago to float charge my 4S LiFePO4 packs and a bank of supercapacitors. I'm super impressed! Even at a constant 6A output, this thing only gets warm.
+Shawn L Hi Shawn, I am trying to make a portable power bank with 4 18650 batteries and this board. I'd really appreciate it if you could share how are you are measuring the current output, thanks. Or even better, if you could give me some tips.
Are your 18650 batteries in parallel or series? 1) if you're running them in parallel, I haven't seen my board accept an input voltage lower than 4v~, so this may be a show stopper for you (assuming yours acts the same way). There is another, cheaper boost board that I bought on eBay which went down close to 3V DC.
2) to measure current, I use a cheap multimeter with a 10A DC ammeter function inline with my circuits.
very informing video thanks, if you max out the current setting of the board, will a dc motor spin faster or keep spinning as the same?
You can trim the voltage control range by adding a resistor in series to the pot
I have a question..
if my input is 24v - 5A, which voltage and current to the output I get?
I have done some more testing.
The buck-boost module with 2 heat-sinks uses a standard SB diode rectifier, which explains the lower efficiency and mre heat. It also has a habit of locking up and shorting the supply when the output voltage is set close to the input voltge and a load connected that draws a high peak current; a 12W lamp in my test. This is a major failing.
I also tested a smd based buck-boost module with a small finned heat-sink on the back. It is more efficient; 0.5W loss for 27W output, 24V in and 12V out.
Also interesting; there are a few missing components on the board and the overlay text "MPPT". If this was available as a MPPT regulator, it would be quite useful.
Very similar if not the same as: Dealextreme, Jtron DC 5~32V to 1.25~20V Boost Buck Module w/ Quiescent Current 4mA - Blue
Hi, can you set the constant current to a particular value before applying any load to it?
does anyone know how to wire up a switch to this board ? There seem to be 3 pins available next to the input terminal but i have no idea which one to short in order to make the board disable itself
I am looking for a variable low voltage cut off to protect my battery packs. I would like to be able to set it so if voltage drops to 14 it automatically disconnects battery. any suggestions would be appreciated.
Since this is a boost converter does it still properly current limit with the output shorted or does it overshoot?
Hi, Nice video!
Do you know what is the minimum amp that this thing can do?
I have been using this buck boost converter for awhile with a 9v battery being the input and the output 12v.
Do you think I could use a LiPo battery instead of a 9volt battery or is the input voltage going to be too low?
Hi Julian, great in depth video as always. So i have brought both types the LTC3780 and the other boost/buck converter with both the lm2577s lm2596s and with the three pods on. As far as i can tell the LTC3780 has better efficiency as the other converter is only around 80% and the LTC3780 also can handle more watts at around a recommended 80w rather than the 15w from the other one. Here's the ebay search for the other one'DC-DC Step Up Down Boost Buck Voltage Converter Module CC/CV LM2577S LM2596S' but apart from what i have just mentioned any reason to use one over the other? Regards
I would like to use this in a led strip lighting setup with the max voltage at 12v and the minimum voltage at 6v or so. I would mount this in an enclosure and need to use an external potentiometer. What would be the best approach? Do I need to desolder the voltage pot from the circuit board and replace it with the external potentiometer or is their a better way? Thanks.
Hi Julian, Does it have reverse polarity protection in it?
So mine didn't come with the heat sink on the back but with a couple of plastic ones one the surface of the board. My question is can you pott this module in a non acidic silicone?
Hello
if I want to set the current value with the potentiometer, is it allowed to short-circuit the poles?
When I want to reduce the output current to 1.5A for chargeing a Battery, what is the right way to do this?
Thank you
Some performance testing would be good.
I have used a variety of these low cost buck, boost and combined regulators. Generally the work pretty well at 30% or less of rated current. At higher currents, they need much larger heatsinks or fans. Some of the smaller ones claim higher output current than the components are rated for; may work, but not long term reliable.
I have just tested the efficiency of three different 10-12A modules; 2 buck and 1 buck-boost. All 3 have two finned heatsinks on opposite edges. I'm looking for the most efficient module for a low power system.
Setup was 24V in, 12V at 2.25A out. For about 27 watts out, losses were 2W each for the buck and 3.6W for the buck-boost. 2W made the modules quite warm but not too hot. 3.6W made the buck-boost quite hot, at only 1/4 of its rated output.
The ground (0V) is common, but there is a low value current sense resistor in there. Connecting the ground input to output, bypassing the module, would likely disable or upset the current sensing.
I haven't looked at noise levels, but have sometimes added an extra LC filter on the output.
This device can connect to solar panel dual axis, to improve there efficiency?
so this type of dc-dc converter will keep the same output voltage even if the input voltage gose up or down
can you ajust the current and will it stay at that current?
I'm really interessed to see if this thing would be good for a small bench power supply with some nice displays showing max current and volts. would be interessting to see how clean the power output is
Julilan: Did you ever do test in terms of output voltage regulation. When watching your voltmeters, there seems to have been some voltage drift when running the lamp test ......
Does it have reverse voltage protection on the output to safely connect and charge lithium batteries? Obviously when the output voltage and current is set, there is no danger to damage the board but what if I connect the battery when the board is not powered?
BEST Buck/Boost DC/DC Converter topolgy explanation ;-]
Nice video, is the output 100% DC or it contains harmonics ? and does it affected by the load type ? thanks
Julian have you ever had a problem with kits with missing parts.,if so what do you usually do about it.anyone
Hi Julian, what is the potential of the heatsink? In short I would like to bolt it to some 0V metal work
are these worth buying i want to use one for a 24 watt fold up solar power set up to charge my equipment. off grid
Hi Julian where did you get your RYOBi multimeter please??
Hi Julian, I really want one of these things to make a cheap-o bench power supply - and it's good that you can also set a current limit on the output. I understand you can provide a visual feedback of the output voltage by simply measuring the output. However, do you know if there are any points to measure the current limit? It would be great to use a little oled display and a small box to make an awesomely portable cc/cv power supply, using an arduino, ofcourse.
Hi Julian- I'm looking for a DC to DC boost converter to power my laptop while in my caravan from the 12V battery. The specs for the AC wall charger that comes with my laptop state it requires 20V DC at 6.75A. Do you think the 3780 boost converter is capable of powering a laptop for these conditions?
Hi Julian. Where can one get one of those very handy trimpot screwdrivers?
Why not charge the LiFePO4 battery sets in parallel so you dont have to use 30V?
Excellent video! Would be nice if you could have shown effect of changing input voltage on output voltage. I am thinking in terms of a variable source from solar panels being presented at ideal voltage to storage batteries. Would thgis do the biz?
The last pot seems to be for undervoltage protection if you run the unit on batteries.
Hi sir, As you have mentioned that there is no need for shottky diodes in this module. Can I wire in parallel 2 or more of this units without having an isolating diode in each units?
Hello Julian, would you be able to check out high power ir LEDS? an make a video for it?
WOW!!! LTC3780 is an expensive part and the p/s is also expensive. thanks for sharing.
Hi, Julian,
I've just received mine and was puzzled by the markings on the five electrolytics viz e4 330V CD. I note that yours are marked 9C 330 VZA, presumably these are 330 microfarads, but what of voltage marking?
Love your videos they've prompted me to buy quite a few of the items that you have reviewed, mostly in the PSU category like this little gem.
I just bought this to make a benchtop supply. What are the pot values?
EDIT: was able to catch the markings in the video. 500k and 200k.
Hello. I'm thinking on building a digital power supply with this. Actually I think (I'm not an expert please correct me if I'm wrong. :) ) the potentiometer that adjusts the voltage, is basically a voltage divider that supplies a variable voltage (usually 0-5V). So is it possible to feed Arduino digital output to a rc low pass filter to get analog values out of PWM and then feed that voltage to the pin that adjusts the voltage. Repeating the same idea for the Current limit. Are there any problems with this idea ? Thanks!
sir please help i am putting together a 3s 18650 battery pack for a small solar system i would like to use a buck converter to charge the battery in place of the regular charge controller which of these buck converters would you recommend for this
Great videos, keep them coming! I have got to ask though, what is it with that torch you have always got on your desk lol?
seems like an interesting converter. unfortunately, this seller does not ship to Belgium and I can't even contact the seller to ask if this is in error, he seems to ship to the rest of europe.
only alternatives I have found with the ltc3780 are single pot devices, so only voltage regulation.
just wondering - can someone check how low the input voltage can go, and what output current is possible with different input voltages? can't seem to find this information in the data sheet.
Last I heard, graphite was conductive?
Great video!! I think I might pick one up for charging some 18650s with solar power!!
Hi Julian I have a question. What kind of PSU can you use with that DC/DC converter? Any current or voltage limit? I have very less idea about that devices but I like seeing this videos, and I´d like to try one just for fun.
Bye.
Hm, why do I see two SS54 (5A 40V schottky) diodes on there? I know they only "provide a lower drop during the dead-time", but are they being used within spec?
I'm interested in seeing some tests done on this. Efficiency tests of wide input-output voltage differences. Also, how does the ripple look on the output? I'd say that thing would need to be very efficient to run at full load with that heatsink. Some quick estimates and calculations lead me to think that the resistance (I^2R) losses would be around 1 to 2 (maybe 3) watts at 10A. Even at 95% efficiency, it will probably loose a few more watts from the inductor core and other losses (switching losses, etc...). Can that wimpy heatsink really do that?!
What fets do they use ?
So I found an issue with this little device (running from a 12v 10A SMPSU), if the output voltage is set anywhere above 15v and the current limit is reduced until it cuts out, this board seems to actually short out the PSU.
could you run a (homemade) wind turbine into te inputs of your module to charge Valve Regulated Lead Acid(VRLA) batteries (LTC3780 Buck/Boost DC/DC Converter 10A 130W)???
Some information I have found suggests the following for the 3 Potentiometers: 1, voltage adjust. 2, current adjust. 3, low-voltage protection adjust. I'm guessing that 3 maybe cuts the converter if the supply voltage falls below a set point (i.e. to protect the battery). Regards. Daryl.
do you know how to adjust the 3° pot?
man that was a wholesome explanation!! LOVED IT!. SUBBBED :D
Hello Sir, How can the LTC 3780 be used to charge Battery and be connected to Load at the same time The LTC3780 board does not show have a separate connection to load. Kindly explain how I can charge a 12volt batery and also connect to Load at the same time such that load is being supplied with a 12 volt while the battery is also being charged. Any assistance will be appreciated.
Can't believe you paid top dollar, this must be extravagant!
Question that I've been itching to ask on a few of these videos about power converters... are you able to drive PWM loads with them?
For example a channel on a 10W RGB LED (potentially resistive current limited if necessary) through a power mosfet.
Lee Cook It would probably work, but better to use a purpose-designed LED driver with an enable input - they're designed to be pulse width modulated (and often have a spec for frequency range etc.)
thank for the review julian !
can we change the multi turn pots to regular pots? (i want to make a bench power supply with a non linear circuit)
Pots appear to be 500k, 200k, 500kohm respectively. I've considered doing this too, but the provided trim pots are nice for precision, and I like the compactness of this board by itself.
Great video! Thanks for sharing.
i assembled a workbench power supply using this converter and would like to add a LED to indicates when the converter goes to constant current mode. Any idea on how to implement it?
Look for the current-limiting signal at pin 1 of the LM358 opamp. It may need boosting to drive an LED, though. Someone has posted partial schematics here: wiki.beyondlogic.org/index.php?title=WD2002SJ_LTC3780_Synchronous_Buck_Boost_Converter_Ebay_Automatic_lifting_pressure
I do enjoy your videos!
i want to use this in combo with an atx psu with a gnd,5v,12v and an adjustable voltage source.
Should i use a separate ground for the adjustable source using the board in this video or can i just use the same ground for everything ?
If you want the current-limiting feature (center pot) to work, the output ground/negative must be kept separate, so that all current flows through a 7-milliohm sense resistor in the negative output line where it can be measured. Aside from this, common ground works fine.
As you suggested, a very economic bench supply with perhaps the addition of a bigger heatsink for higher
currents.There must be many more applications than these ?
Hello please i need an advise i have variable input 8-22volt but i need fixed output 13 volt can i use LTC3780 Buck/Boost?
+Joseph Hashem Yes, if I remember rightly. Make sure you don't exceed the maximum current.
The under voltage to charge LiFePO4 is good, 3,55V per cell is good those cells stay at constant voltage from 15 to 85% of their capacity. in a car you can charge ok a 4 cells liFe by just having 13,7V and it works not only now but on the (very) long run (7 years and counting) and this is 3,425 V per cell !
Hi i have just bought one of these units, the type without the large heatsink on, when i tried the unit out like your video it works fine, 12v 16 amp sauce, unit set to 12.5 volts i connect a 12 v car stop/tail lamp with the two filliments togeather this result is 12v 26w (at 12 v = 2.2 amps) this works on the unir great. but with the current limmit fully on and the volt out set the same as with the 26 watt bulb, i connected a 12v 55 watt buld spot, the voltage dropped of to 7.9 volts and ajusting the current and the volt pot the volt will turn lower but no high than the 7.9 volts, my point is will this unit deliver the 7 to 10 amps ? the spec says yes the unit says no i have a video on youtube showing this "teasting the LTC3780 unit" by david Teale check it out.
Hey, anyone could help me? I got this thing 3 times and no one work properly. I just opened the package and give it an input from switching power supply 12v 5A. But what i got is no output voltage but only red led fault light up
Is there any advantage using 24v as a power supply instead of 12v if my most used output range is 13v and below?, my point is to keep the converter always in step down mode.
Highest efficiency should be achieved when Vin is just slightly above Vout. Check the efficiency curves in the LTC3780 datasheet, also shown in this video.
Hi i bought one of those and it die after 30 s of using. Can someone help me?
what will happen if you make a short circuit at the output of this module? does he have any security ... I am asking because no one is talking about it
It will enter constant current mode to whatever the value you put with the CC potentiometer.
Love these quick reviews!
I tried to charge a 3S 12,6V LiPo battery, used a 20V 8A power supply of my laptop. At once after connecting the power supply the converter died, it has a short at the input even without battery. It worked without load before. Is there a sequence what to connect first, power supply or battery, I remember reading something in a description, but can't find it any more. And I read an article that others had the same problem.
How can I find the defect parts to replace ?
did you put a diod in series with the battery ?, theat can be the problem
now if the voltege at the exit of the converter is inferior to the voltage of the battery , whit no diode in series , it will hapend a backflow of current , and distroy your board, A.K.A. what happend too you
I do not know haw too fix it, normaly this boards ar not economicly viable to bee fix´t
if you only need too charge lipo battery´s you have better options, this option is overkill :)
So, what is behind the third door? The third pot is the cut off (shut down charge mode) adjustment. When charging Li-ion batteries, in the constant voltage mode, current goes down to 10% of the constant current mode current setting and the charger shuts down. On the tp4056 boards, the LEDs shift from charge to charge complete. The third pot adjusts this percentage. To adjust it, get a battery into the CV charge mode. Monitor the current and adjust the pot to cut off at the current level you want. You have to wait until the current drops to the level you want. The LTC 3780 is a fantastic Li-ion charger. I think that this feature raises it's ugly head when the user is not even charging batteries. When in constant voltage mode and below the max constant current setting (10%) , the unit thinks that the battery being charged (it doesn't know better) is ready for cut off. Voompah, game over. Aside. 200k and 500k ten turn pots (today) seem to be made out of unobtainium. Regular 1 turn pots are too course to get 3 digit accuracy (like the trim pots on the board). I use a pot 10% the size of the course pot as a fine tuner. Just put it in series with the course adjustment pot. I use the mini OLED 33v 10a electrical parameter meter (from your mail bag) to complete my bench top power supply. The primary power comes from a computer power supply 12v dc output, but anything from batteries to wall warts seem to work fine. Just do the math, power in less losses is power out.Oh ya, Thanks for all the great stuff. Keep up the good work.
hey, great video. Can you please tell me where i can buy those connectors you have going into and out of the module?
+Joshua B www.ebay.at/itm/2-1mm-Male-Female-PAIR-DC-Jack-Connector-with-Screw-Terminals-/252244576584?hash=item3abaf2c948:g:ZhMAAOSwoydWkbld from
or more www.ebay.at/itm/5-Pair-DC-Power-Socket-Plug-Screw-Terminal-12V-Volt-CCTV-Adaptor-2-1mm-x-5-5mm-/281285306454?hash=item417de92856:g:tPYAAMXQPatTIecU
Can't see if someone already mentioned this but maybe the third pot is for frequency control? Might be worth checking where the trace for it is going and see if it makes sense to what is described in the data sheet for frequency adjustments.
Hampus Sandberg These converters are normally fixed frequency, or the frequency is varied to maintain maximum efficiency. It seems the third pot controls a disconnect mechanism for low input voltage.
Have you seen any super high efficiency boost-buck converters like this but that can do much higher voltage? like 110-120VDC ? I would love to be able to power certain AC devices that also work well with DC current and have a solar panel be the source. If I can do higher efficiency with these than I can with a normal inverter, I would love to use these for that purpose (for devices that can run off 110-120VDC in place of 110-120VAC).
Can anyone in the comments recommend a circuit board that starts out 12V and then switches that same output to 5 V and holds steady till i turn it off?? I Just need 12 v for a second or two Then hold 5v indefinately.
Works fine as an LED driver...you don't need to push the LED over 30v because then it becomes incredibly inefficient. Amps climb up for slight increase in brightness and more heat. For a battery set-up that would not be ideal. For increase in brightness rather get a 50w or 100w LED and run it at 29volts. Less heat, more efficient, running with a more efficient LTC3780 modal.
does anyone know where the middle connection for the volt pot goes i scratch mine
Assuming you mean output voltage selection rather than undervolt-cutout, its center pin and one side are tied together and to Vout, and the remaining side goes to VOSENSE (pin 4) of the LTC3780.
Very nice little found Quite pricy I'd say but I guess when you need high efficiency you have it :) I have a few of those little cheap solar buck boost converter they do a decent job for cheap mini power supply :) and also handle couple of amps. Thanks for sharing!
Looking for something just like that just half the size.
HI Julian,
I HAVE A PROBLEM WITH LTC3780. WHEN I TURN THE VOLTAGE POTENTIOMETER THE FAULT LED LIGHTS UP. IT LIGHTS UP AFTER 6V AND VOLTAGE DOESN'T INCREASE FURTHER. WHAT COULD BE THE PROBLEM. COULD YOU PLEASE THROW SOME LIGHT..
The fault LED may be connected to the PGOOD pin of the LTC3780. Check the data sheet for details about the PGOOD output pin.
The reason I was asking is you seem to have a great understanding of it.
It's just a hobby. Silly really, the UK is a very bad place to be interested in solar power :(
Yes when I was in the milatary,we stop by there ,lots of clouds,I use to no a English band when I was I Germany ,they say that it's like that all the time,me I n.am in California nothing but sunny dessert this would be the place for solar,I had offer every five mins trying to get me to install it.what about wind power
Surely wind power would be viable! Why didn't ou set up and use that turbine we had seen a while back, was it broken?
That 3rd pot is a under-voltage protection potentiometer and you only use it if your power supply is a battery like a 12v and you don't want to completely kill it so you set this to 10 volts and it terminates the connection.
There is a similar looking LTC3780 buck-boost converter on Banggood.com for about 15 dollars. It has two black heatsinks on the front.
I have that first buck boost inverter. At 120w controll chip burned. After 5 sec. Stable use 70w
You mean this one @6:39
I wish I had ordered the damn IC in qfn, I think the sample was only avalible in ssop...either way the thing was design in imperial... try finding a break out/dip board for .625mm pitch for a decent price, the other obvious use for that board it car laptop adapter. Some people have laptops that could max the thing. now days its becoming less common but 65-90w is still pretty common
I saw this video a few years ago and it convinced me to get the ltc3780 it has proven to be a primary staple and a true workhorse it is amazing.
Im seeking advice from you on how I can parallel two of them together for a dual supply. I've tried a few different configurations but the boards go into protect mode and could use some advice please.
gatsctt has an instrctabls where he used one of these and the people that made them did do a parallel configuration
I have the other version of this. I did not manage to test it but I will probably also order the version with current limiting.
The third potentiometer is usually to control an LED to a set voltage point so when you get there you have a visual indication to say that a battery is charged since it reached the set charge voltage.
28V is good for charging 8x LiFePO4 cells is 3.5V/cell if they are properly balanced and that is more than good enough there will not be more than 1% capacity gain if you go to 3.6V/cell. You can make a test to check that.
Also just cc is good enough for LiFePO4 with just CC (constant current charge) at 3.6V you get over 95% of the battery capacity depending on the charge current value and the internal resistance of the cell.
So you can use this power supply with my SBMS or other BMS (take care the BMS I sent you is not good for LiFePO4 even if is advertised as such) The cut off is at 3.9V and that is a proper limit for LiCoO2 cells (the most popular rechargeable cells present in most mobile phones and Laptops).
LiCoO2 is usually charged at 4.2V in this mobile applications to provide the maximum energy density in the detriment of battery life. But different other upper limits are used of this cells. Each 100mV decrease in max charge voltage will double the cell life cycle. And 3.9V or 3.95V is about the smallest practical use. 3.9V will offer up to 8x the cycle life but with only about 60% of the battery capacity used when compared to 4.2V. Still there are applications where life is more important than energy density and this 3.9V voltage level is used primarily by military or space applications.
Those 5 pin IC one for each cell have this protection limits fixed in hardware 3.9V upper limit and only 2V lower limits both are quite detrimental to LiFePO4. With normal 3.6V max 3.65V on the high end and 2.8V min 2.5V on the low end.
***** Interestingly, eclipsebikes sent me an email after I bought the LiFePo4s telling me not to let them go over 3.9V or under 2.0V - not really surprising as they also sell those fixed voltage BMS units too. I'l probably just show and talk about the BMS boards, probably not connect them up as there would be little to see. I may need to ask you a few questions about the SBMS, for example, does it cut the input at the end of the CC phase? I can't see how it could do any current limiting.
Julian Ilett
Yes the SBMS dose CC charge only so it cuts the output when the highest cell gets to the set limit.
CV is necessary for Lead Acid and they use PWM to limit the average current or constant current limiting on MPPT where they use a DC-DC converter and can do that.
Lithium especially LiFePO4 is almost like a capacitor after CC is fully charged or very close. And since Lithium prefers not to be fully charged using CV will reduce battery life with almost no gain SOC usually 1 to max 5% depending on the charge rate.
With solar the PV panel will reduce the current anyway at the end of day so you actually get 100% SOC with not need for CV.
Best indication of how a LiFePO4 is charged is to look at a charge discharge curve.
The charge on the SBMS will start again when the voltage on the highest cell drops under the set limit (you can set any limit) but 3.4V is probably a good value.
So the SBMS will do ON and OFF for charging in between this two limits say 3.4 and 3.6V. You can almost call this a slow PWM.
The capacity between this 3.4 -3 .6V limit is really small maybe 0.2% to 0.5% of the battery capacity.
Tests on LiFePO4 where done with shallow discharge top 5 to 10% charge discharge cycles with almost no degradation in battery capacity after many thens of thousand cycles getting close to 100k cycles in some test.
I thought, that LTC3780 is step-down only, but no. It can do boost mode too! That's great!
Another great video Jullian and a useful device.
I think one could go to town on this using a microcontroller, LCD, a handful of switches and rotary encoders to make a digitally controlled variable PS.
I'd be interested to see just how clean the output is at various voltages and loads on an oscilliscope
Rob B Yeah, what we need is for Ming-He to bring out a digitally controlled version of this with their standard 4-digit 7-segment LED and 4-switch interface board.
Julian Ilett That’s exactly what I was thinking. Maybe this Buck / Boost converter could be converted to digital and then hooked up to a micro controller for some waveform generation. If you had a micro controller
generate the waveforms on the input side and then read interference on the output side, I wonder if you could feed negative interference in on the input side to cancel out the interference created by the buck / boost converter, might be a way of getting a very smooth output? Someone’s no doubt already made one of those and I just don’t know what it’s called yet! Great videos as always Julian, very much appreciated, keep ‘em coming!
I too would be very interested in seeing what the scope says about the output of these buck boost converters. I would also be interested in learning the efficiency of them at varying voltages.
I think it should be easy enough to do with a couple of volt/amp meters on the input and output; calculate volt/amps into watts for both, then work out the percentage of efficiency from the differing values. I have done this myself with a couple of cheap buck converters and shockingly found that if the output is way off the input the efficiency can be in the order of 70% or so, but gets more efficient as the output nears that of the input.
Anyway just some food for thought. Love your videos Julian, I really appreciate the time and effort you put into them and the way in which you do. Your'e a good man for sharing your research/experience and especially in the medium you choose to! I'm an old school EE that has forgotten most of what I learned when I was younger, but trying to grab hold of it now days as I have been bitten again as I once did years back and trying to get a grip on EE these days.... So different now, but exciting times!
For digital control, we could use, say, a 4096 (or more) step digital pots, or multiplexed digital pots, controlled by an MCU. I've done it with a Ti 4050c (boost only), and it works quite well.
therd trim pod is for sollar charging cut off volts if its down to a serten point
Does anyone know why there are 3 pots on buck-boosts? So output voltage, output current limit and what does the other control?
Tera Volt With the third potentiometer you can shut off the module when the input voltage is under the adjusted voltage. Then the red led lights up. For battery safety for example.
Oh right, I've ordered a few and played with them, there was nothing to tell me even which were V and I adjusts. I managed to figure out those two but never found what the third did, I turned it and nothing happened but I never changed the input voltage from my SMPS. I'll give it a try, thanks.
What's the name of that pen to adjust the blue pots?
I need one to avoid frying my boards when the screwdriver falls out and shorts something...
Anyone knows?
+Nuno Oliveira Philmore 63-8608 $2 at Frys, or online
+tedmich Thanks!