Its a diode to make current to flow in the one direction sometimes called a snubber or flyback diode to eliminate the back emf or inductive spike of a coil, lenz's law
@@MechanicMindset yeah inductive spike like you see on an injector tho also good case study as the protection is primarily there to stop the contacts burning out on the relay
Great video. A good ECU designer would place components to prevent this problem from happening, but sometimes OEMs sacrifice protection for cost savings
The solution to voltage spikes is a reverse diode across the coil. Actually, the preferred positioning of the diode is directly across the switching transistor (FET these days), in other words within the ECU itself. I don't quite understand how a "resistor" would do much, but sometimes they're included in the circuit to help drop the relay quicker, as the back EMF keeps the relay energized for a few extra milliseconds..
Ah ok, interesting. My thought around the resistor providing some protection was that it would be a lower resistance value than the path through the ECU, directing the majority of current back around the resistor circuit. I’ve got a load of automotive relays, not one of them had the diode. Which is odd as it always comes up in training materials. There is a clear difference in spike with and without the resistor, what do you think? I’m no electronics engineer 😁
@@MechanicMindset The diode is more effective at clamping the inductive kick back to the ECU low side driver. However, the low side drive in the ECU is usually an N-Channel MOSFET which has a parasitic diode (intrinsic diode which is an unavoidable part of the MOSFET transistor design) and if you combine this with a diode across the relay coil, if the power is connected reverse battery the two diodes are now forward biased and in series directly from power to ground. If there is no polarity protection device or polarity protection relay to prevent reverse polarity, you will definitely blow a fuse, but you could also take out the ECU MOSFET or the relay diode or both. If a resistor is used instead of a diode in reverse polarity there is enough resistance to protect against reverse polarity high current damage, but still provide some inductive current path to minimize the spike voltage EMI (EMC radiated noise, radio frequency noise, pop sound on old AM radio). If the wrong relay is installed, one without a resistor and higher coil inductance (usually a higher rated or much lower contact resistance relay switch), the energy rating of the smart low side driver MOSFET will be exceeded, but usually only when the module PCB, and subsequently the smart IC, is very hot if the module is under hood. So, when the device is hot and the energy too high, then device go KABOOM.
Very impressed with this vid! Something that most techs never think about I'm sure. It will definitely change the way that I look at a relay from this point on. Your videos are very informative and definitely helpful. Thank you!
This is a really good point that I hadn't considered when replacing relays. Quite often I'll just pull one out of my toolbox drawer and shove in the hole. I've been blessed that I've not done serious damage to a vehicle
Ranjeet Singh Thanks, still early days and getting lots of positive feedback and growth. Started posting in April so going well I think. Thanks again for the kind comment and glad you are enjoying the channel!
Not that it makes a huge difference in this scenario, the outcome would likely be the same, but many circuits or relays may use a clamping/flyback diode as well for midigation voltage spikes on inductive loads. Sometimes internal to the diode, sometimes in the circuit.
Crikey! just when you think you have got you head round vehicle electrics, this guy comes along and show how much more there is to learn. THANKS [ & keep em comin].
Nice video, had a similar instance once on a Skoda where the starter solenoid when de-energised, would back feed and blow the main terminal 30 fuse. Traced it to a faulty protection diode within the main vehicle harness near to ignition switch. The solenoid "bounces" and generates a voltage. Keep up the great work.
I just subscribed to the channel, and why I did?, because every minute in all your videos I got useful informations and polite presentation, no jokes or waist of time, in a budget shop equipment, I'm a half way to my technician carrier, automotive electronics inspired me, thank you for your time and efforts
Thanks for your humbling feedback Hussam! Great to have you on the channel. Which you all the best in your career and hope my videos help you on your way!👍
This is what is known as a TRANSIENT. They can occur in both AC or DC circuits. Fly-back is a term the old-timers used to use with tube type color CRT TV's back in the 60's in the fly-back transformer circuit. Older CRT TV's would actually have the fly-back transformer (a coil of sorts) discharge in such a way that the picture tube (CRT) when turning the set would cause a burst of color in the picture tube like a bright flash as the fly-back coil magnetic field collapsed. This was done in a manner as to prevent damage to the CRT (picture tube) but also to collapse the magnetic field of the fly-back in a safe and controlled manner. Fly-back transformers worked with the picture tube (CRT) circuitry to create a magnetic field to stabilize the picture along with the very high voltage (25KV) required to make a CRT color television of that day work. Turning off the TV created the very same condition at a much more significant transient level of course than the relays being discussed here. But in same context if not controlled, transients are very destructive to electronic systems and components even when all that is involved is a small relay coil. REMEMBER IF IT CAN CREATE MAGNETISM OR WORKS BY MAGNETISM, TURNING IT OFF WILL CREATE A TRANSIENT. Sadly the auto manufacturers are not transient proofing their ECM units, so they are vulnerable to peripherals that do not have transient resistant components installed such as coil surge/transient snubber (the resistor in the correct relay's coil circuit) which is the function of the resistor in the proper relay. Remember the CRT in the TV was operating at a much higher voltage than the relay here. But even though that is the case magnetic fields of whatever intensity will tend to create a "fly-back" or transient when power is cycled on then off during the turn off part of the operating cycle. Of course the voltage and transient involved due to the tolerance of the CRT in the TV example and the circuit is the same phenomenon and is much more intense yet controlled.. However any time we exceed the reverse voltage due to wrong polarity or exceeding the transient threshold of any delicate electronic component (often a 5 volt or 12 volt signal, pass block or forward/reverse bias in a diode, Core operating voltage {V core max punch through or destructive voltage level} in a transistor or IC) as a transient will do we will destroy components or systems not properly protected against this condition. This is deadly for electronics and will kill transistor logic or IC logic so this advice is very relevant! The ECM died due to an internal surge related failure!
Thanks for the insights! I have also seen that even reducing the current (not switching off) can also create this transient. Lots to consider for electrical engineers! 👍
Very Informative Video ...normally I would only replace a relay with exactly the same manufacturer Number .......Circuits are so very sensitive ....Enjoyed The Video ....👍
I'm so glad you did this video, I've known about the resistor in a relay for along time, but many don't. It's the same as any coil of wire collapsing the magnetic field inducing a voltage spike, just like a fuel injector. Great video, great teacher.
i know this is a older video, but with the resistor there are still over 40V spikes compared to the normal maximum voltage of 14,7V on a car. In electronics is a resistor not used for eliminating the socalled Back EMF voltage of a relay, but is the resistor replaced by a Diode connected in reversed direction, and in parallel over the relay coil. The Back EMF voltage is then reduced to 1V. (the typical breakdown voltage of a very common diode like the 1N4007).
Don't know for car's but in electronic if we use relay we always use diode connected in parallel with a relay but inverted. And that saves our circuits from relay coil discharge when the relay is powered off. Yes, the resistor can help but it is not fast enough as a diode can be.
As soon as I clicked this video I had a feeling it would be about flyback suppression. I recognized the German car style relay in your hand from years of classic BMW ownership
I will call it very informative & professionally made video, very happy with the way you put things straight to us... Keep it up sir..may God bless you
Back EMF is well known phenomenon that is the bane of all branches of electronics and is countered by placing a free wheeling diode / snubber circuit across the coil to prevent back EMF / voltage spikes destroying the driver electronics EG MOSFETs, transistors etc ⚡⚡⚡ Nice video dude
The relay driver in the ECU is called a smart power device, meaning it is an N-Channel MOSFET low side drive with many beneficial added features. One of these is what is called an active clamp. When the device experiences an output over voltage (inductive load kick) the active clamp will turn on the device to protect it. So, the device protection is now more related to how much energy it can actively clamp and at what device temperature (the energy capacity is greatly reduced at higher temperatures, like if the ECU is under hood). Other features are overcurrent shut down and full OBD II diagnostic coverage; load open, load short, MOSFET switch open (which is usually the end failure mode even if the device shorts). The diagnostics is usually communicated by a single pin output (very generic) or more specifically, through SPI or I2C. The resistor across the automotive relay is really to minimize EMI and not to protect the smart driver IC. However, if you install a relay that has no resistor and higher inductance then it can take out the driver. In the past the device dies were so large (DPAK sized device) that it did not really matter what automotive relay was installed. But, as you take more and more cost out of the ICs (reduce the die size) they are prone to overstress.
I guess just a resistor is considerded good enough spike protection, but you could do even better with a diode and a 15v zener and that way extra power won’t be burned away in the resistor. I would think you would want to set up your oscilloscope in singe shot mode and the acquire to peak detect mode.
Very awesome. Have never thought about it. Always wondered why some oe relays were so much higher. But when a ECM is at risk I’d rather pay more for the correct resistance (circuit protection) keep up the good work.
Hi! I really appreciate your time what you spend to sharing such a good and informative video. What I really missing are peoples out there who are all the time screaming to all of as who are using scopes every day, does we are just cheating with our "fancy" tools the customers. Cos using such of tools we can earn more money for the job and we just make unnecessary repairs and job with the scope. But, actually, in today's modern cars, there is nothing to do without proper knowledge and measurement tools. And of course, it is not enough to go to YT and watch what we are doing. Must be read books, be informed and ask if we are not sure in something before it is to late. Thanks mate for this nice vid. Keep it rolling. !
For sure, never stop learning or you go backwards! Especially with all the new technology. The scope is a great tool and will give us a definite diagnosis, rather than checking the DTC and replacing parts. The people who say this probably just don't understand, send them to my channel! Haha. Thanks!
More likely a flyback / fee wheeling diode than a resistor mate but the point is the same if the relay has built in inductive back spike clamping then its important to replace it with another comparable part..
@@MechanicMindset oh okay, they are obviously just using a resistor to keep a load on it when its opened, that's strange though, I'm an EE and have never seen it although I know it's a option, normally a diode on DC and C or RC snubber on AC thanks mate I learned something new😎
@@T2D.SteveArcs I suppose it would serve also in a voltage divider circuit for open circuit diagnostics. A diode wouldn’t do that right? I’ve not checked to see if it does log a fault code when open circuit but I suppose it would depend on the diag circuit being present in the ECU
Yeah they are there for good reason as your Video graphically demonstrates...A/C clutches and even blower motors are often equipped with diodes for the same reason. Good Vid. Thx & Cheers 👍
What is negative voltage? Is negative voltage considered when analyzing how much of a spike the circuit was subjected to when the magnetic field of the coil collapses?
I am curious. Why did the BMW ECU not have the protection resistor on the ECU? Seems that any engineer would put protection on any circuit that has this vulnerability.
Agreed. My experience tells me it has something to do with money! Also it seems that suppressing the spike at the relay is a norm for more than just the motor industry. Thanks for watching 👍
The spike amplitude is impressive - I have many times "measured" it touching wire ends when checking relay coil (if relay is clicking 🙂) - you get a good shock, and they say this is good for arthritis 😁, Thanks for flyback visualization!
Hi, very interesting, thanks for sharing but how do we avoid these problems, can we check something beforehand or do we have to check all the relays ???
I think most relays have the resistor to present the spike. Some also have a diode that does the same job, just recirculates the current around the coil circuit, diverting it from the ECU. Thanks for watching!
Excellent video. Basic stuff but none the less very important. Must admit i assumed all automotive relays were created equal with a back emf diode. now I know other wise
Literally came down here to say the same thing. Spikes can come from numerous outside sources too, not only coil flyback. ECU shall handle it, no excuse, no exception... Good on you Bryan!
Good question! It’s actually the oscilloscope that’s taking the beating. I have the attenuator on there which is protecting it (reducing input voltage). It also quite resilient. The scope connects to the laptop via USB so only data travels to the laptop 👍
Hello. Awesome video. I’m retired now, but if I’d lost my flying medical, this is definitely the retraining I would have willingly paid for in order to make a fresh start. My Ulysse 2.0 Hdi went through an enormous puddle on the periferique in Paris, outside Lane, in the rush hour , in the dark, and it stopped dead. I was so stuck I had time to plug in my tester, which confirmed what I suspected as my mil light was not on, a dead écu. A very expensive tow to the southern outskirts….yes my breakdown policy had just run out…..and totally uneconomic to put into a French dealer, I messed around for a few months checking this and that , trying to translate a handbook in French, until I bought a plug and play écu on eBay. I finally fitted it, the mil light came on, and it started first time. Not long after I came home in it for an mot, having got by on an old ZX I bought in Dover. It was drizzling on the way home and next morning as it was reversed out of the mot garage , it stopped unexpectedly . It restarted but next morning it didn’t. No mil light again !! I bought another écu from the same eBay source, but he said the écu’s were bomb proof, and to check for bad earths etc…. I did that , and it started first time with this now 3rd ecu. I sent the original off to a specialist repairer, not for repair as such, but to find out which circuit was dead. When he got back with his findings….I didn’t fully understand them….but essentially I had a voltage spike which shouldn’t occur and the ecu was designed to protect against them !? Anyway , again more and more checking before I fitted the plug and play écu, and this time I drove it extensively every time I came back from Paris. 3 months later, I finally set off for Paris, and thoroughly enjoyed the drive, passing Stansted in light drizzle, and in heavy traffic reached the top of the Dartford Bridge…..where it stopped dead !! I coasted to the toll booths, just managing to steer and brake into the lay-by there, before I was towed away. Out came the AA and despite my protestations that the ecu was dead , he did try and fix it. If you saw someone changing into pilots uniform by the Dartford Bridge, it was me, and the AA man towed the Ulysse to my home in the NE, dropping me at Luton where I flew back to Paris, free as the orange airline I worked for didn’t have anyone to replace me for my duty next day. So about 8 years later, it’s still on my drive, a project, with a replacement wiring harness to be fitted, before I try again, because every man and his dog has told me I have a corroded harness, and no one, repeat no one, has suggested a relay is causing the problem. Did someone mention some had diodes, so in heavy rain, or light rain, it’s conceivable the relay “breaks down”, and a spike kills my ecu. This is a true story !!……and my trusty £400 ZX went on forever until a builder sideswiped it in B&Q !!
Amazing journey you have been on with this car! So will you check the relays? It might be easier to just replace them all. Will love to hear how you get on 👍
@@MechanicMindset I certainly will. The last time I did any serious reading , about 4 years ago, I was alarmed to find that the piezoelectric injectors could cause voltage spikes too, and I found that pretty demoralising. It’s really put me off modern cars and I’m making my 306 diesel estate….not the hdi engine, last as long as possible. The Ulysse , when it ran , was very economical , and comfortable, and a great load carrier. One of my F/Os was Swedish , and had been into electronics, and I showed him the ECU fault report. It mentioned mosfets I think. It was in fact a bit of a nightmare, struggling to get even a wiring diagram, and so much “talk” about bad earths, cheap French wiring looms, and water entering the loom through a crack and then tracking by capillary action causing all sorts of problems…..and yet , particularly in France these cars are very very popular , so my problem is extreme. I just don’t want a car to get the better of me !! Thanks for not dismissing my post.
I actually knew about this issue,heard about it on some random video i watched a year or so ago,just lucky i stumbled upon it and it really sticks in your head from then on! :-)
this goes as far back as the "80's. small devices(mostly gm and ford ignition modules) were getting fried. inductive spikes from relays and other coils(ignition and a/c clutch to name a few) were suspected as was heat. everyone knew about the heat fix with potting compounds or relocations but what wasnt really known was the change in relays. some had resisters put in some had diodes added. i seen a few with a capacitor and resister installed as a shock asorber bleed configuration. i came across this by accident noting part number changes at oem level. it sparked my curiosity as the oems only saying to use the correct parts, never explaing why. if the relay you use has a diode in it is absolutely critical that the coil terminals have the correct wire configuration.
@@MechanicMindset Seems to me like the roadside assistance guys are giving you people a lot of extra work. By now it should be commonknowledge among these towing people that they just cant plug any old relay that looks like it fits into a customers car to get it going. So what really is going on here? It was the ignorance of the roadside assistance people in the first place that caused a huge, expensive and perplexing problem, by not really checking the relays to see if they were both exactly the same. By now, any organization that offfers these roadside plans should be aware of the potential damage they are causing by giving thier tow drivers a few spare relays so they can plug into these cars without first checking for compatibility issues.
wow. very interesting video. Do you think (or know),if it's ok to replace every time a relay which doesn't have a resistor , with a relay which having a resistor?it going to work ok,or depending the system, you have to use the relay with a resistor?
Good question! I don’t think it would have an effect on the circuit if you add a relay with the resistor. The resistor value is very high and connected in parallel so only has a minute effect on the total circuit current when switched on 👍
As a tech for 37 years you would not believe how many random control unit's that I have seen ruined by jump starting cars with dead batteries particularly those that were completely dead. When the jumper cable or booster is removed the alternator senses voltage going down and with no voltage reference shoots voltage really high and with the battery being dead and not being able to absorb the spike something is going to die!
Do you use any protection on the Pico when testing in these situations. I thought the 2040 wasn't actually built for automotive use, and even with the attenuator you are measuring above it's specs?
BryanByTheSea Hi, the 2204A is fine for automotive. Not the best but does the job. There are some areas in which it struggles. I did put an attenuator on the scope when we saw it exceeded the maximum range. Thanks for watching 👍
As an electrical engineer, I would have just assumed that the ECU had transient protection. (especially since the Germans are renowned for their engineering skills!) I would have also assumed the relays have a DIODE not a resistor. After 30 years in the profession, a guy can still learn something...like never assume! You know what that does!
It's surprising that ecus and relays are not equipped with a proper snubber circuit. A resistor mitigate the field collapse effect nonetheless is not an ideal solution. Thanks. Good to know.
From an electronics design perspective, I think it is very negligent of any automaker to not include input protection in their ECMs to begin with. Cars are a very abused and long-lasting commodity and the electronics in them need to be very rugged to make it through all of the abuse they get for decades. Input protection for the ICs is very inexpensive to implement and will prevent these things from happening - or at least decrease its likelyhood.
Yes, I agree. I might imagine that most modern ECUs do have protection; however I still see this fitted in most relays. I must share that the story I mention was from a late 90's vehicle
Hi, the voltage spike is sometimes called an inductive kick. Basically, the magnetic field around the coil collapses when it’s turned off and generates the voltage spike (like an ignition coil)
Wow. I knew they put out a kick, but I didn't know it was that bad. I build game room props using Arduino with an n channel mosfet to drive an automotive relay coil in some props. usually put a diode across the coil terminals for this very reason though. I'm curious what the measured value of your take out resistor was. Most things I build these days use small relay boards designed for 5V, very low current triggering using a surface mount mosfet. Now I understand better why the schematic is so complex for those boards.
tonyfremont How interesting! I bet it’s great getting to build all that custom gear! It’s a 560 ohm (green blue black black). As you might see in my comments, the diode method is common, although one I’ve not come across this with the Euro cars I mainly work on. I suppose the diode will stop it all together, whereas the resistor just reduces the spike. Thanks for watching!
@@MechanicMindset it's kinda like traveling for business, it sounds good, but the reality isn't as much fun. ;) I need to do some testing to see just how well a diode really helps. You were getting positive and negative spikes, but maybe that's because the lack of a diode resulted in an oscillation of sorts. I've never seen a resistor symbol on a typical automotive relay, but that doesn't prove anything. I usually switch the ground connection with a mosfet, and they generally have a "built in" diode of sorts. So far I haven't killed any yet and they're only rated between 40 and 60 volts breakdown, so maybe it works, or I've been lucky. ;)
@@MechanicMindset as close to the coil as possible! All de-energized coils behave the same way - why not raise the price 0.01 cents and build in proper protection?
I've got a customer with Mercedes e350 cdi 2009 , he's had ecu checked as fault was crank no start I didn't remove the ecu but , I've been asked to refit ecu , I cleared fault codes and re-read them and current codes appeared one which I think related to a terminal 87 fault as I got a code ' 143400 a short circuit was detected at pin (0) of circuit (1) ' Any info would be greatly appreciated if possible to help me out Thanks Rob mobile man
It’s a diode not a resistor This take the spike from earth and returns it to the power side of the circuit These can be upward of 600 volts Most relays are sold as a diode protected relay and used for the reason of spike voltage protection for your ECM ITS A COMMON method as is your zener diode inside your ECM So your relay must be bleeding the excess voltage off with a high resistance I will test some here I wouldn’t think it as good as our diode protection
Hi, 100% a resistor in these relays. Actually, all the relays I have are resistors. I took it out and measured it. You’re right on the spike, you probably saw it in the video 😁
I suppose it could if the resistor was open circuit. Thinking about it, if the resistor shorted, would the relay not works at all? Hopefully they have watched this video 🤣
@@alanw5879 Depends how it is shorted; if we dead short directly across the resistor, no current would flow through the coil, and if fitted the fuse would blow (or FET wouldn’t switch)
@@MechanicMindset would the fuse pop tho, I checked 2 relays, one with the resistor removed and the other wasn't and they both measured the same resistance across the control side. So I'm not sure.
@@alanw5879 Ah ok, so that’s an open circuit (same as what I do in this video), which you are right. Short circuit is different, like replacing the resistor with a piece of wire, essentially short circuiting the coil. If it was open, yeah it could be difficult to find 👍
I doubt that most viewers understand what is going on. The circuit is not protected. A resistor alone does not protect. What's needed is a Diode and a capacitor.
this also goes to show how crappy the engineering is in these modules. any engineer worth a grain of salt would add flyback protections to the circuits- at very least the ones controlling inductive or high capacitance loads. but no they want to send that protection downstream to the inductor itself. this has become the norm as it reduces the rfi flowing back through the wires where it can be inductively or capacitvely coupled to other circuits. and we all know how the bean counters would want to save $1.50 on a $800.00 module.
I think because we are just discharging a coil with nothing in the circuit to dictate which way the current flows, it could go either way. It’s quite unpredictable
![HOW TO DIAGNOSE CAN BUS FAULTS [PicoScope 2204A Low Speed CAN] Mechanic Mindset](http://i.ytimg.com/vi/ncQfdhzUFCk/mqdefault.jpg)
Its a diode to make current to flow in the one direction sometimes called a snubber or flyback diode to eliminate the back emf or inductive spike of a coil, lenz's law
Yeah some have diodes too; these are definitely resistors, I tested them once removed. Crazy spike right?! 👍
@@MechanicMindset yeah inductive spike like you see on an injector tho also good case study as the protection is primarily there to stop the contacts burning out on the relay
Great video. A good ECU designer would place components to prevent this problem from happening, but sometimes OEMs sacrifice protection for cost savings
Great video. Shows how important it is to use the correct parts whenever replacement is needed.
For sure! Such an unsuspecting culprit too! Thanks
Hi Joe, Hope things are getting better for you. Best wishes.
@@garybrown5500 thank you...no change unfortunately..but I'm still breathing
The solution to voltage spikes is a reverse diode across the coil. Actually, the preferred positioning of the diode is directly across the switching transistor (FET these days), in other words within the ECU itself. I don't quite understand how a "resistor" would do much, but sometimes they're included in the circuit to help drop the relay quicker, as the back EMF keeps the relay energized for a few extra milliseconds..
Ah ok, interesting. My thought around the resistor providing some protection was that it would be a lower resistance value than the path through the ECU, directing the majority of current back around the resistor circuit. I’ve got a load of automotive relays, not one of them had the diode. Which is odd as it always comes up in training materials. There is a clear difference in spike with and without the resistor, what do you think? I’m no electronics engineer 😁
@@MechanicMindset Diode is the correct solution. While the resistor provides some relief... a diode is faster and provides better clamping.
@@MechanicMindset The diode is more effective at clamping the inductive kick back to the ECU low side driver. However, the low side drive in the ECU is usually an N-Channel MOSFET which has a parasitic diode (intrinsic diode which is an unavoidable part of the MOSFET transistor design) and if you combine this with a diode across the relay coil, if the power is connected reverse battery the two diodes are now forward biased and in series directly from power to ground. If there is no polarity protection device or polarity protection relay to prevent reverse polarity, you will definitely blow a fuse, but you could also take out the ECU MOSFET or the relay diode or both. If a resistor is used instead of a diode in reverse polarity there is enough resistance to protect against reverse polarity high current damage, but still provide some inductive current path to minimize the spike voltage EMI (EMC radiated noise, radio frequency noise, pop sound on old AM radio).
If the wrong relay is installed, one without a resistor and higher coil inductance (usually a higher rated or much lower contact resistance relay switch), the energy rating of the smart low side driver MOSFET will be exceeded, but usually only when the module PCB, and subsequently the smart IC, is very hot if the module is under hood. So, when the device is hot and the energy too high, then device go KABOOM.
Very impressed with this vid! Something that most techs never think about I'm sure. It will definitely change the way that I look at a relay from this point on. Your videos are very informative and definitely helpful. Thank you!
Glad you enjoyed the video! The spike is crazy right?!
This is a really good point that I hadn't considered when replacing relays. Quite often I'll just pull one out of my toolbox drawer and shove in the hole. I've been blessed that I've not done serious damage to a vehicle
Close call! Haha
This channel deserves more appreciation, great video and as always, very informative. Keep it going mate, love and support from Melbourne.
Ranjeet Singh Thanks, still early days and getting lots of positive feedback and growth. Started posting in April so going well I think. Thanks again for the kind comment and glad you are enjoying the channel!
Also this guy so professional. I work with GSE and this mistake which someone replaced with normal relay cost the business almost 100k
Reza KHorshidi Thanks! Wow, that’s an amazing case study to support this example. Thanks for sharing 👍
Not that it makes a huge difference in this scenario, the outcome would likely be the same, but many circuits or relays may use a clamping/flyback diode as well for midigation voltage spikes on inductive loads. Sometimes internal to the diode, sometimes in the circuit.
Crikey! just when you think you have got you head round vehicle electrics, this guy comes along and show how much more there is to learn. THANKS [ & keep em comin].
Haha! Glad you enjoyed the video. Never stop learning! 👍 More to come, cheers
Nice video, had a similar instance once on a Skoda where the starter solenoid when de-energised, would back feed and blow the main terminal 30 fuse. Traced it to a faulty protection diode within the main vehicle harness near to ignition switch. The solenoid "bounces" and generates a voltage. Keep up the great work.
Cheers! That sounds like a crazy one, bet it was fun to find!!
@@MechanicMindset yeah I had to ask some people with knowledge higher than my pay grade.... And it wasn't tech support at skoda 😂
SY Diagnostics Haha, brilliant! We all got to learn somehow 👍
@SY Diagnostics
Fancy seeing you here! 😀
Was shown this on a training course, the trainer had us hold the wiring to the relay, it gave out a right zap, won`t forget this in a hurry :)
Haha! I bet it did. Never thought to try 😂
I just subscribed to the channel, and why I did?, because every minute in all your videos I got useful informations and polite presentation, no jokes or waist of time, in a budget shop equipment, I'm a half way to my technician carrier, automotive electronics inspired me, thank you for your time and efforts
Thanks for your humbling feedback Hussam! Great to have you on the channel. Which you all the best in your career and hope my videos help you on your way!👍
@@MechanicMindset ❤
Nothing wrong with showing a bit of personality, otherwise many people will find it too dry and simply turn off. Then no one hears the information.
Great video. That's the rattling noise you get when pull a non working Honda a/c relay out. The resistor has come loose inside.
Ah right cool, not heard of that issue before 👍
Thank you for another informative video. It is amazing what a 2204A (dirt cheap) DSO can do in the hands of a real diagnostician!
George Beuselinck Cheers! It really is a great tool, I’m learning more about it all the time, so many features! Glad you enjoyed the video 👍
This is what is known as a TRANSIENT. They can occur in both AC or DC circuits. Fly-back is a term the old-timers used to use with tube type color CRT TV's back in the 60's in the fly-back transformer circuit.
Older CRT TV's would actually have the fly-back transformer (a coil of sorts) discharge in such a way that the picture tube (CRT) when turning the set would cause a burst of color in the picture tube like a bright flash as the fly-back coil magnetic field collapsed.
This was done in a manner as to prevent damage to the CRT (picture tube) but also to collapse the magnetic field of the fly-back in a safe and controlled manner. Fly-back transformers worked with the picture tube (CRT) circuitry to create a magnetic field to stabilize the picture along with the very high voltage (25KV) required to make a CRT color television of that day work.
Turning off the TV created the very same condition at a much more significant transient level of course than the relays being discussed here.
But in same context if not controlled, transients are very destructive to electronic systems and components even when all that is involved is a small relay coil. REMEMBER IF IT CAN CREATE MAGNETISM OR WORKS BY MAGNETISM, TURNING IT OFF WILL CREATE A TRANSIENT.
Sadly the auto manufacturers are not transient proofing their ECM units, so they are vulnerable to peripherals that do not have transient resistant components installed such as coil surge/transient snubber (the resistor in the correct relay's coil circuit) which is the function of the resistor in the proper relay.
Remember the CRT in the TV was operating at a much higher voltage than the relay here. But even though that is the case magnetic fields of whatever intensity will tend to create a "fly-back" or transient when power is cycled on then off during the turn off part of the operating cycle.
Of course the voltage and transient involved due to the tolerance of the CRT in the TV example and the circuit is the same phenomenon and is much more intense yet controlled..
However any time we exceed the reverse voltage due to wrong polarity or exceeding the transient threshold of any delicate electronic component (often a 5 volt or 12 volt signal, pass block or forward/reverse bias in a diode, Core operating voltage {V core max punch through or destructive voltage level} in a transistor or IC) as a transient will do we will destroy components or systems not properly protected against this condition.
This is deadly for electronics and will kill transistor logic or IC logic so this advice is very relevant!
The ECM died due to an internal surge related failure!
Thanks for the insights! I have also seen that even reducing the current (not switching off) can also create this transient. Lots to consider for electrical engineers! 👍
Very Informative Video ...normally I would only replace a relay with exactly the same manufacturer Number .......Circuits are so very sensitive ....Enjoyed The Video ....👍
Same, got to be careful for sure! Glad you’re enjoying the channel 👍
I'm so glad you did this video, I've known about the resistor in a relay for along time, but many don't. It's the same as any coil of wire collapsing the magnetic field inducing a voltage spike, just like a fuel injector. Great video, great teacher.
Exactly that 👍 Cheers Alan, glad you enjoyed the video!
i know this is a older video, but with the resistor there are still over 40V spikes compared to the normal maximum voltage of 14,7V on a car. In electronics is a resistor not used for eliminating the socalled Back EMF voltage of a relay, but is the resistor replaced by a Diode connected in reversed direction, and in parallel over the relay coil. The Back EMF voltage is then reduced to 1V. (the typical breakdown voltage of a very common diode like the 1N4007).
Don't know for car's but in electronic if we use relay we always use diode connected in parallel with a relay but inverted. And that saves our circuits from relay coil discharge when the relay is powered off. Yes, the resistor can help but it is not fast enough as a diode can be.
For sure, I think some relays do feature diodes instead - most of the automotive relays I have seen feature resistors (maybe they're cheaper?)
@@MechanicMindset that's main reason, i am quite sure. Resistors are far cheaper.
As soon as I clicked this video I had a feeling it would be about flyback suppression. I recognized the German car style relay in your hand from years of classic BMW ownership
I will call it very informative & professionally made video, very happy with the way you put things straight to us... Keep it up sir..may God bless you
Thanks for the positive words! Glad you are enjoying the channel 👍
Back EMF is well known phenomenon that is the bane of all branches of electronics and is countered by placing a free wheeling diode / snubber circuit across the coil to prevent back EMF / voltage spikes destroying the driver electronics EG MOSFETs, transistors etc ⚡⚡⚡
Nice video dude
Cheers! 👍
The relay driver in the ECU is called a smart power device, meaning it is an N-Channel MOSFET low side drive with many beneficial added features. One of these is what is called an active clamp. When the device experiences an output over voltage (inductive load kick) the active clamp will turn on the device to protect it. So, the device protection is now more related to how much energy it can actively clamp and at what device temperature (the energy capacity is greatly reduced at higher temperatures, like if the ECU is under hood). Other features are overcurrent shut down and full OBD II diagnostic coverage; load open, load short, MOSFET switch open (which is usually the end failure mode even if the device shorts). The diagnostics is usually communicated by a single pin output (very generic) or more specifically, through SPI or I2C.
The resistor across the automotive relay is really to minimize EMI and not to protect the smart driver IC. However, if you install a relay that has no resistor and higher inductance then it can take out the driver. In the past the device dies were so large (DPAK sized device) that it did not really matter what automotive relay was installed. But, as you take more and more cost out of the ICs (reduce the die size) they are prone to overstress.
I guess just a resistor is considerded good enough spike protection, but you could do even better with a diode and a 15v zener and that way extra power won’t be burned away in the resistor.
I would think you would want to set up your oscilloscope in singe shot mode and the acquire to peak detect mode.
Yes agree, single shot would probably have been better. Cheers
Very awesome. Have never thought about it. Always wondered why some oe relays were so much higher. But when a ECM is at risk I’d rather pay more for the correct resistance (circuit protection) keep up the good work.
Gera Grabovich Yes, best to stick with original. Thanks for watching 👍
Hi!
I really appreciate your time what you spend to sharing such a good and informative video.
What I really missing are peoples out there who are all the time screaming to all of as who are using scopes every day, does we are just cheating with our "fancy" tools the customers. Cos using such of tools we can earn more money for the job and we just make unnecessary repairs and job with the scope.
But, actually, in today's modern cars, there is nothing to do without proper knowledge and measurement tools.
And of course, it is not enough to go to YT and watch what we are doing.
Must be read books, be informed and ask if we are not sure in something before it is to late.
Thanks mate for this nice vid.
Keep it rolling. !
For sure, never stop learning or you go backwards! Especially with all the new technology. The scope is a great tool and will give us a definite diagnosis, rather than checking the DTC and replacing parts. The people who say this probably just don't understand, send them to my channel! Haha. Thanks!
EXCELLENT video, once again , Darren, Thanks for all that you do, All i can say about picking the wrong relay is 'SHOCKING' 🙂
For sure! 😖
These types of videos are the most educational ones, thank you
Thanks Darren excellent video and explanation, keep up with your great work 👌
Love to see you test and show minimum injector pulse width with the skope.
Never pay atention on this so far.Thanks.....amazing.
VA Tuning It’s easily over looked. But I think most relays have the resistor; beware of the cheap aftermarket ones! Thanks for watching
More likely a flyback / fee wheeling diode than a resistor mate but the point is the same if the relay has built in inductive back spike clamping then its important to replace it with another comparable part..
For sure. 100% a resistor. I took it out and checked it. None of the relays I have feature a diode, all resistors 👍
@@MechanicMindset oh okay, they are obviously just using a resistor to keep a load on it when its opened, that's strange though, I'm an EE and have never seen it although I know it's a option, normally a diode on DC and C or RC snubber on AC thanks mate I learned something new😎
@@T2D.SteveArcs I suppose it would serve also in a voltage divider circuit for open circuit diagnostics. A diode wouldn’t do that right? I’ve not checked to see if it does log a fault code when open circuit but I suppose it would depend on the diag circuit being present in the ECU
Yeah they are there for good reason as your Video graphically demonstrates...A/C clutches and even blower motors are often equipped with diodes for the same reason. Good Vid. Thx & Cheers 👍
Good info to know! Cheers for watching 👍
What is negative voltage? Is negative voltage considered when analyzing how much of a spike the circuit was subjected to when the magnetic field of the coil collapses?
I suppose I was just looking at the total difference. Negative is just opposite flow of the circuit is complete
I am curious. Why did the BMW ECU not have the protection resistor on the ECU? Seems that any engineer would put protection on any circuit that has this vulnerability.
Agreed. My experience tells me it has something to do with money! Also it seems that suppressing the spike at the relay is a norm for more than just the motor industry. Thanks for watching 👍
The spike amplitude is impressive - I have many times "measured" it touching wire ends when checking relay coil (if relay is clicking 🙂) - you get a good shock, and they say this is good for arthritis 😁, Thanks for flyback visualization!
Haha, be careful! Thanks
Ohh that was just great
Thanx for sharing
Love from India 🇮🇳
Glad you enjoyed the video!
Hi, very interesting, thanks for sharing but how do we avoid these problems, can we check something beforehand or do we have to check all the relays ???
I just try to replace relays with the same one that came out - go for genuine parts 👍 Cheers!
I have never heard about resistor relays. Thanks.
I think most relays have the resistor to present the spike. Some also have a diode that does the same job, just recirculates the current around the coil circuit, diverting it from the ECU. Thanks for watching!
Recently found your channel. Clear concise information 👌 forgot I learned this year's ago! Lol! Great knowledge, great refresher!
Thanks Brent! Glad you’re enjoying the channel
Wow that’s a sad story , sure cost a pretty penny to get that fixed ...thanks for the informative video.👍
Easy mistake to make. Good diagnostic process (i.e. taking your time) will help avoid this
some good info . it almost looks like same as the felids in an ignition coil collapsing
Yes, very similar! 👍
Excellent video. Basic stuff but none the less very important. Must admit i assumed all automotive relays were created equal with a back emf diode. now I know other wise
Glad you found it useful, might save some headaches in the future! Thanks for watching
Poor designs on the ECU's they really should have some internal protection built in to protect the inputs and outputs.
BryanByTheSea Many probably do, although the example in this story was from some years ago 👍
Literally came down here to say the same thing. Spikes can come from numerous outside sources too, not only coil flyback. ECU shall handle it, no excuse, no exception... Good on you Bryan!
Great video, you learn something new everyday with mechanic mindset.. I never knew that a relay without a resistor could kill the ecu.
Thanks! The story I heard was from the 90s but it’s still something to be careful of 👍
the resistor or diode which is better for voltage spike in relay
Not sure really, I suppose a diode would stop the spike altogether where the resistor just reduces it
@@MechanicMindset ok but the diode sometime dead short out maybe that the reason they start using resistor over diode
Hi! One question just to learn, sorry for the ignorance. Home come you're not frying your laptop with this tests as if it was an ECU? Thanks.
Good question! It’s actually the oscilloscope that’s taking the beating. I have the attenuator on there which is protecting it (reducing input voltage). It also quite resilient. The scope connects to the laptop via USB so only data travels to the laptop 👍
Very good ! Thanks for the warning ! Super helpful !!
Great video and information shown with the scope!
Thank you!! Subbed!
Thanks, great to have you on the channel! Do you have a scope yourself?
That’s very interesting in deed! Defo a useful bit of info, thanks again for the very useful vids/info.
Glad you enjoyed it. Thanks for watching 👍
A brilliant video.
Keep up the good work and would love to see the channel go to great heights 👍👍
Amit Ahuja
Neeta Ahuja Thanks! Me too 😁. Great to have you on the channel!
Mechanic Mindset Diagnostic Coach program is here! Click link: www.mechanicmindset.com/diagnostic-coach
Hello. Awesome video. I’m retired now, but if I’d lost my flying medical, this is definitely the retraining I would have willingly paid for in order to make a fresh start.
My Ulysse 2.0 Hdi went through an enormous puddle on the periferique in Paris, outside Lane, in the rush hour , in the dark, and it stopped dead. I was so stuck I had time to plug in my tester, which confirmed what I suspected as my mil light was not on, a dead écu. A very expensive tow to the southern outskirts….yes my breakdown policy had just run out…..and totally uneconomic to put into a French dealer, I messed around for a few months checking this and that , trying to translate a handbook in French, until I bought a plug and play écu on eBay. I finally fitted it, the mil light came on, and it started first time. Not long after I came home in it for an mot, having got by on an old ZX I bought in Dover. It was drizzling on the way home and next morning as it was reversed out of the mot garage , it stopped unexpectedly . It restarted but next morning it didn’t. No mil light again !! I bought another écu from the same eBay source, but he said the écu’s were bomb proof, and to check for bad earths etc…. I did that , and it started first time with this now 3rd ecu. I sent the original off to a specialist repairer, not for repair as such, but to find out which circuit was dead. When he got back with his findings….I didn’t fully understand them….but essentially I had a voltage spike which shouldn’t occur and the ecu was designed to protect against them !? Anyway , again more and more checking before I fitted the plug and play écu, and this time I drove it extensively every time I came back from Paris.
3 months later, I finally set off for Paris, and thoroughly enjoyed the drive, passing Stansted in light drizzle, and in heavy traffic reached the top of the Dartford Bridge…..where it stopped dead !! I coasted to the toll booths, just managing to steer and brake into the lay-by there, before I was towed away. Out came the AA and despite my protestations that the ecu was dead , he did try and fix it. If you saw someone changing into pilots uniform by the Dartford Bridge, it was me, and the AA man towed the Ulysse to my home in the NE, dropping me at Luton where I flew back to Paris, free as the orange airline I worked for didn’t have anyone to replace me for my duty next day.
So about 8 years later, it’s still on my drive, a project, with a replacement wiring harness to be fitted, before I try again, because every man and his dog has told me I have a corroded harness, and no one, repeat no one, has suggested a relay is causing the problem. Did someone mention some had diodes, so in heavy rain, or light rain, it’s conceivable the relay “breaks down”, and a spike kills my ecu.
This is a true story !!……and my trusty £400 ZX went on forever until a builder sideswiped it in B&Q !!
Amazing journey you have been on with this car! So will you check the relays? It might be easier to just replace them all. Will love to hear how you get on 👍
@@MechanicMindset I certainly will. The last time I did any serious reading , about 4 years ago, I was alarmed to find that the piezoelectric injectors could cause voltage spikes too, and I found that pretty demoralising. It’s really put me off modern cars and I’m making my 306 diesel estate….not the hdi engine, last as long as possible. The Ulysse , when it ran , was very economical , and comfortable, and a great load carrier. One of my F/Os was Swedish , and had been into electronics, and I showed him the ECU fault report. It mentioned mosfets I think.
It was in fact a bit of a nightmare, struggling to get even a wiring diagram, and so much “talk” about bad earths, cheap French wiring looms, and water entering the loom through a crack and then tracking by capillary action causing all sorts of problems…..and yet , particularly in France these cars are very very popular , so my problem is extreme. I just don’t want a car to get the better of me !! Thanks for not dismissing my post.
I actually knew about this issue,heard about it on some random video i watched a year or so ago,just lucky i stumbled upon it and it really sticks in your head from then on! :-)
Ah cool, a few people have also had similar experiences!
this goes as far back as the "80's. small devices(mostly gm and ford ignition modules) were getting fried. inductive spikes from relays and other coils(ignition and a/c clutch to name a few) were suspected as was heat. everyone knew about the heat fix with potting compounds or relocations but what wasnt really known was the change in relays. some had resisters put in some had diodes added. i seen a few with a capacitor and resister installed as a shock asorber bleed configuration. i came across this by accident noting part number changes at oem level. it sparked my curiosity as the oems only saying to use the correct parts, never explaing why. if the relay you use has a diode in it is absolutely critical that the coil terminals have the correct wire configuration.
Interesting to know, thanks for sharing!
Who’d a Thunk! Turned a relay into an ignition coil firing right into the PCM... GOOD FUN 🤩
😂 Many wouldn’t know about this, including myself (10 years in the game before finding out!)
@@MechanicMindset Seems to me like the roadside assistance guys are giving you people a lot of extra work. By now it should be commonknowledge among these towing people that they just cant plug any old relay that looks like it fits into a customers car to get it going. So what really is going on here? It was the ignorance of the roadside assistance people in the first place that caused a huge, expensive and perplexing problem, by not really checking the relays to see if they were both exactly the same. By now, any organization that offfers these roadside plans should be aware of the potential damage they are causing by giving thier tow drivers a few spare relays so they can plug into these cars without first checking for compatibility issues.
Excellent excellent video Darren. This is gold for the community. I
JC Mobile Diagnostics Thanks! Glad you enjoyed the video. True story!
wow. very interesting video.
Do you think (or know),if it's ok to replace every time a relay which doesn't have a resistor , with a relay which having a resistor?it going to work ok,or depending the system, you have to use the relay with a resistor?
Good question! I don’t think it would have an effect on the circuit if you add a relay with the resistor. The resistor value is very high and connected in parallel so only has a minute effect on the total circuit current when switched on 👍
@@MechanicMindset Thank you very much for the answer. it sounds very logical.
You are doing very good job with your UA-cam channel.
@@Lambros_Stefaneas Great to hear your enjoying the channel, more to come!
As a tech for 37 years you would not believe how many random control unit's that I have seen ruined by jump starting cars with dead batteries particularly those that were completely dead. When the jumper cable or booster is removed the alternator senses voltage going down and with no voltage reference shoots voltage really high and with the battery being dead and not being able to absorb the spike something is going to die!
For sure! This is a biggie. We used to advise turning in some large electrical loads before disconnecting the jump leads
Great bid👍, never thought of a relay blowing up ECU, YEA pretty expensive.
Do you use any protection on the Pico when testing in these situations. I thought the 2040 wasn't actually built for automotive use, and even with the attenuator you are measuring above it's specs?
BryanByTheSea Hi, the 2204A is fine for automotive. Not the best but does the job. There are some areas in which it struggles. I did put an attenuator on the scope when we saw it exceeded the maximum range. Thanks for watching 👍
@@MechanicMindset Good on the Pico, sounds like it can take a bit of abuse.
BryanByTheSea It sure can! I have exceeded input a few times and it’s been fine. Nothing sustained, just spikes like this 👍
Like that Peco scope machine,,i need one 👌
It’s a great tool!
As an electrical engineer, I would have just assumed that the ECU had transient protection. (especially since the Germans are renowned for their engineering skills!) I would have also assumed the relays have a DIODE not a resistor. After 30 years in the profession, a guy can still learn something...like never assume! You know what that does!
Haha! For sure 👍. Yeah I rarely come across relays with diodes in. I can’t find one in any of our cars 🤷🏻♂️ But it’s always in training material.
Not sure why the mfr isn't using a diode instead of a resistor. Cost maybe?
Possibly, most relays I have seen use resistors
KNOWLEDGEABLE Mechanic Mindset
Thanks 👍
Mechanic Mindset
From Nick Ayivor from London England UK 🇬🇧
Hiii sir I'm trying to buying New oscilloscope which one is better low price starting beginners (autel is best)
Hi, personally I think the 2204A is a great oscilloscope to start 👍
@@MechanicMindset tq sir
It's surprising that ecus and relays are not equipped with a proper snubber circuit. A resistor mitigate the field collapse effect nonetheless is not an ideal solution. Thanks. Good to know.
From an electronics design perspective, I think it is very negligent of any automaker to not include input protection in their ECMs to begin with. Cars are a very abused and long-lasting commodity and the electronics in them need to be very rugged to make it through all of the abuse they get for decades. Input protection for the ICs is very inexpensive to implement and will prevent these things from happening - or at least decrease its likelyhood.
Yes, I agree. I might imagine that most modern ECUs do have protection; however I still see this fitted in most relays. I must share that the story I mention was from a late 90's vehicle
Dear bro,I'm confused because how to created 350volt in this relay.
Hi, the voltage spike is sometimes called an inductive kick. Basically, the magnetic field around the coil collapses when it’s turned off and generates the voltage spike (like an ignition coil)
Wow. I knew they put out a kick, but I didn't know it was that bad. I build game room props using Arduino with an n channel mosfet to drive an automotive relay coil in some props. usually put a diode across the coil terminals for this very reason though. I'm curious what the measured value of your take out resistor was. Most things I build these days use small relay boards designed for 5V, very low current triggering using a surface mount mosfet. Now I understand better why the schematic is so complex for those boards.
tonyfremont How interesting! I bet it’s great getting to build all that custom gear! It’s a 560 ohm (green blue black black). As you might see in my comments, the diode method is common, although one I’ve not come across this with the Euro cars I mainly work on. I suppose the diode will stop it all together, whereas the resistor just reduces the spike. Thanks for watching!
@@MechanicMindset it's kinda like traveling for business, it sounds good, but the reality isn't as much fun. ;) I need to do some testing to see just how well a diode really helps. You were getting positive and negative spikes, but maybe that's because the lack of a diode resulted in an oscillation of sorts. I've never seen a resistor symbol on a typical automotive relay, but that doesn't prove anything. I usually switch the ground connection with a mosfet, and they generally have a "built in" diode of sorts. So far I haven't killed any yet and they're only rated between 40 and 60 volts breakdown, so maybe it works, or I've been lucky. ;)
Great information and demonstration. Thanks!
Thanks for watching 👍
Odd there is not a snubber diode too for added protection .
In the relay or the control module?
@@MechanicMindset as close to the coil as possible! All de-energized coils behave the same way - why not raise the price 0.01 cents and build in proper protection?
Very interesting, thank you for sharing! 👌
Very good! Thank you! From Brazil.
Thanks for watching 👍
I've got a customer with Mercedes e350 cdi 2009 , he's had ecu checked as fault was crank no start I didn't remove the ecu but , I've been asked to refit ecu , I cleared fault codes and re-read them and current codes appeared one which I think related to a terminal 87 fault as I got a code ' 143400 a short circuit was detected at pin (0) of circuit (1) '
Any info would be greatly appreciated if possible to help me out
Thanks
Rob mobile man
Ah ok, I would probably try to confirm that this fault code it related to your symptom. Then maybe check that circuit for a short or open circuit
well illustrated!
we do similar things, you and I...
Denis
Cheers! Yes I saw a few of your vids. I like the parasitic draw tester. I played with a similar idea using something different. Thanks for watching 👍
interesting ... thank you very much it's really useful
Hope it helps you in the future! Thanks for watching 👍
Nice one Matt, good vid ,
Robert mobileman Cheers!
Excellent as always.
Thanks Kelly 👍
Great vid buddy.
Thanks for watching!
Hi possibly to do m ore basic scope testing on sensor and other components wave forms etc.Thanks for a great channel
Will do, time permitting! 👍 Glad you enjoy the videos
Thank you sir. Good job. Have a blessed and safe week to you and your family.
Thanks Billy, you too 👍
Resistor or capacitor?
Resistor. Sometimes diode 👍
Great content darren thanks for sharing
Ian Kelly Cheers Ian
Nice work and video 👍
Abbott Automotive Thanks, glad you enjoyed it!
It’s a diode not a resistor
This take the spike from earth and returns it to the power side of the circuit
These can be upward of 600 volts
Most relays are sold as a diode protected relay and used for the reason of spike voltage protection for your ECM
ITS A COMMON method as is your zener diode inside your ECM
So your relay must be bleeding the excess voltage off with a high resistance I will test some here I wouldn’t think it as good as our diode protection
Hi, 100% a resistor in these relays. Actually, all the relays I have are resistors. I took it out and measured it. You’re right on the spike, you probably saw it in the video 😁
Thank you
thats why you allways need an attenuator on your scope when a coil is envolved.
Best to attach an attenuator first if you are not sure - especially on this 2204A with on 20V max input
What happens if the resistor shorts out for whatever reason, a technician could be chasing that problem forever. Driver after driver burning out.
I suppose it could if the resistor was open circuit. Thinking about it, if the resistor shorted, would the relay not works at all? Hopefully they have watched this video 🤣
@@MechanicMindset I think the relay would still work, but the driver would burn quick
@@alanw5879 Depends how it is shorted; if we dead short directly across the resistor, no current would flow through the coil, and if fitted the fuse would blow (or FET wouldn’t switch)
@@MechanicMindset would the fuse pop tho, I checked 2 relays, one with the resistor removed and the other wasn't and they both measured the same resistance across the control side. So I'm not sure.
@@alanw5879 Ah ok, so that’s an open circuit (same as what I do in this video), which you are right. Short circuit is different, like replacing the resistor with a piece of wire, essentially short circuiting the coil.
If it was open, yeah it could be difficult to find 👍
thank for video
Thanks for watching 👍
Is that an internal resistor? You would expect a diode for that job and not a resistor.
All the different automotive relays I have feature a resistor. But yes, I can be a diode too.
Interesting, thanks alot.
AN AN Thanks for watching. Are you a technician or DIY?
@@MechanicMindset Only an enthusiastic DIY :-)
AN AN Awesome, great that you are getting in to this! 👍
I doubt that most viewers understand what is going on. The circuit is not protected. A resistor alone does not protect. What's needed is a Diode and a capacitor.
very good video ! excellent - well done. GARAGE PIGRAM FRANCE - Subscribed
Glad you enjoyed the video, great to have you on the channel 👍
this also goes to show how crappy the engineering is in these modules. any engineer worth a grain of salt would add flyback protections to the circuits- at very least the ones controlling inductive or high capacitance loads. but no they want to send that protection downstream to the inductor itself. this has become the norm as it reduces the rfi flowing back through the wires where it can be inductively or capacitvely coupled to other circuits. and we all know how the bean counters would want to save $1.50 on a $800.00 module.
I think you hit the nail on the head there with the bean counters!
Sorry but why minus voltage? You lost me there lol
I think because we are just discharging a coil with nothing in the circuit to dictate which way the current flows, it could go either way. It’s quite unpredictable