My new 2-3S Lithium battery charger burned out!!!!!!!!! - Page 1
Forum section: electronics / projects

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 01:36:24 am
content: Its been two days now since i am testing my new 2-3S lithium battery charger project prototypes.I am charging and discharging measuring voltages, currents etc two days now.Until half an hour ago, i thought all was perfectly fine.I use MP26123 and the datasheet reference design, nothing special, nothing fancy.I disconnected the charger from the power supply couple hours ago and had an electronic load hooked to the battery to discharge it (i am testing cut-off voltages) so only need to drain the battery from 12.6 down to 11.9V so i have a voltmeter to check voltage and draw around 500mA from the battery pack (3S5P).half an hour ago the traces going from the current sense resistor to the IC burned out, i mean completely dissappeared and there was flame and the pcb was scorched..How could this happen and why did it happen while there was no power through the IC and no current passing through the resistor really?Any ideas?

author: Rerouter
author_rank: Super Contributor
timestamp: March 29, 2018, 07:19:26 am
content: First and most obvious one is, was there a supply to the Vin pin, if not, is there anything connected to it that may act like a load? could the wires VIN and GND have made contact??If you look on the block diagram, the switching mosfet has a body diode to VIN so if the battery is higher than VIN, power can flow through that diode,There is also that "mini refresh' switch in the diagram that i cannot find an explanation for, if the chip decided to switch that on, I can forsee some smoke,

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 09:14:26 am
content: Quote from: Rerouter on March 29, 2018, 07:19:26 amThere was no power supply to the charger when it got on fire.There was nothing connected to anything other than the battery and load (and a voltmeter next to it which wasn't affected. No way VIN & GND could have made contact. The traces that got on fire are the 2 current sense lines of a Kelvin topology from the sense resistor to the IC. The current there when @ full power charging a battery should not be over a few micro-amps and the voltage over the sense resistor in the range of 170-230mVQuote from: Rerouter on March 29, 2018, 07:19:26 amThis might be so, i recon this is a "rough" diagram showing the very basic internal design but, to prove this as not being the issue the IC is either 2 or 3S and in my original design and first prototype tested i had a soft switch with a push button switching from 2 to 3S which i abandoned and i am replacing with a simple toggle switch because everytime i powered the charger it was setting it to 2S and i had to push the button to switch to 3S... all while a 3S pack was connected to the charger fully charged and the input was at 9-10V so, i think it had plenty of opportunities to fail because of this but didnt!Quote from: Rerouter on March 29, 2018, 07:19:26 amAgain... the traces that got on fire and dissapeared from the pcb are the two sense lines back to the IC (CPS & BATT pins and inputs of a comparator as you can see), one of the few design points actually that in all similar designs and topologies i have seen so far are calling for thin traces... i did a "mistake" adding zero ohm resistors to each line and the part that burned was from these resistors to the IC as if these two lines shorted but i dont see how this might happen... (i used the zero ohm resistors to allow another trace cross that section but i re-routed it then forgot removing the resistors... they might have caused an error to the current reading while the IC was powered and charging but i dont see why the part from the resistors to the IC would catch fire while IC was not powered and idle and the battery was (and kept) happily discharging to the electronic load!!!

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 09:32:41 am
content: Not to mention, this IC is in the market since 2011 (based on the date on datasheet)....I am sure if it had so serious flows in its design it wouldn't still be out there !!!Unfortunately, the manufacturer (or their European office) is not responding well to my inquiries as both times i contacted them now about this problem as i am using their reference design which i hope they could "debug" easier than i ever could and about a month ago regarding some other IC i needed info about. They keep asking me "company name" which if nothing else i find irritating and utterly stupid in this time and age where "makers" and DIYers are a formidable market and there are "big" players who would not only respond but they'd be happy to do so!Frankly i am already considering looking for another charge IC for this job, i just dont want to throw away good parts if they are not to blame (i need a few 2-3S chargers anyway) but most of all, i want to find out if this is my mistake in design or other (i think of pcb error too but come on, there should only be less than 1V and a few ?? over those traces!!!! Really, i dont think they should have a problem even if they were sorted!! The IC might not be able to regulate the charge but it shouldnt catch fire !!!!

author: TheDane
author_rank: Regular Contributor
timestamp: March 29, 2018, 09:46:13 am
content: Pin 6 - Enable- it seems to be not connected.The datasheet doesn't mention anything (as I could see), but the Enable pin controls the Vref and Iref - connected to an Op.Amp - which is connected to your fried pins.Also, the soldering job doesn't seem superb in general imho - left side of C7 has a lot of excess soldering, so perhaps you had a soldering issue after all?

author: Rerouter
author_rank: Super Contributor
timestamp: March 29, 2018, 09:47:20 am
content: VIN is connected directly to the Load, can your load pull a negative voltage, or its it a simple mostfet / op amp current load,If so, is your load stable, or does it oscillate (I'm looking for a way that you could somehow bias the protection diodes negative)

author: capt bullshot
author_rank: Super Contributor
timestamp: March 29, 2018, 09:49:13 am
content: Looks like some transient overvoltage might have killed or latched the IC, creating a low impedance path from the sense inputs to GND. The battery has enough power to burn the traces in this case.Transient voltages happen with this design, since you've got ceramic capacitors only for the VCC / Vin bypassing. These have high Q and can create heavy ringing with the stray inductance of your supply wiring.See this application note:http://cds.linear.com/docs/en/application-note/an88f.pdfYou're not the only one to experience this, I remember a similar problem here in the forum some weeks ago ...

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 10:08:06 am
content: Quote from: TheDane on March 29, 2018, 09:46:13 amEN pin is low or floating for the chip to be enabled, High to disable itQuote from: TheDane on March 29, 2018, 09:46:13 amI wish it was a soldering issue... if it was, dont you think it would fry when i was shooting 2A through it and it reached high temps, not while it was cool as ice and not powered?

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 10:14:37 am
content: Quote from: Rerouter on March 29, 2018, 09:47:20 amVIN is indeed connected to the LOAD same as battery via a mosfet blocking reverse voltage.At the time it got fire there was no VINThe electronic load is a simple LM324 based one and at the time i had the "accident" it was drawing only about 400-500mA.. could it oscillate if powered with low voltage? if it could, how could that affect the battery causing the sense resistor connection to the IC to catch fire? hmmmm this is strange and interesting....

author: TheDane
author_rank: Regular Contributor
timestamp: March 29, 2018, 10:20:40 am
content: Quote from: soubitos on March 29, 2018, 10:08:06 amI just briefly skimmed the datasheet, and it did not mention anything about floating Enable pin. It showed a definite high, and a low in the typical applications.A floating pin, in my experience, can easily be influenced by external fields - causing oscillations, especially if the input impedence is high enough. The datashet specifies voltage and current, no input impedence is specified.Regarding soldering issues, a small ball of solder (can be non-visible, under the chip) could be surrounded by flux contaminents or dirt in general. A sudden high humidity in the surrounding air could cause the contaminents to conduct 'slightly more', causing a run-away situation with the solder as the arch/flash over main conductor path. This is not something easily to say afterwards, as it will melt/blow away.Have you tried with other boards, or is this your only prototype?

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 10:21:28 am
content: Quote from: capt bullshot on March 29, 2018, 09:49:13 amNow this ... is more than frustrating to say the least !!!!At least its comforting that its not my "fault" (it is but if i am not the only one doing the same mistake then learning from it is the good news of the day right?)I am now "burning in" the 3rd pcb/module trying to emulate the conditions that damaged No2 so far i cannot even make it warm.. i even drew 5,5A from the pack for a second maybe... i dont think it has to do with the electronic load or the amps i draw so the "ringing" is a very possible cause..... thank you very much!!!!

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 10:36:27 am
content: Quote from: TheDane on March 29, 2018, 10:20:40 amI am pretty sure if the input had to be either high or low and could not be left floating (as the reference design shows) it would be shown accordingly.. anyway, it worked for two days without any problems, touching and abusing the pcb, i think if the EN pin was that "sensitive' (as for example the EN pin of MT3608 boost converter i am using is) i would have noticed the charger enabling-disabling randomly. No, i dont think this has anything to do with this problem, after all, the IC was NOT under power when this happened, no matter the EN pin status high low or floating, it couldnt do anything!!!Quote from: TheDane on March 29, 2018, 10:20:40 amI cannot disagree with good soldering practices and quality.. these are indeed not "cleaned" pcbs and are for the most part hand soldered/hot air gun soldered parts with a lot of rework done testing this and that... The problem though is, under normal conditions, the traces that got wiped out and got on fire really should be at a voltage of no more than 230mV and perhapa a few ?A! this, with the IC powered on... i dont see how "a spike in humidity" (highly unlikely where my workspace is located" could cause this specific point to burst in flames!Quote from: TheDane on March 29, 2018, 10:20:40 amThis was No2... I am now running No3 & 4 and will spend all 10 pcbs testing them under various conditions before i deem this is OK and try to start selling it.. i normally use the prototypes for a while and try to abuse them as much as i can to find weak spots in the design or pcb etc but this was the first time something that serious happened so i need some enlightenment from you guys with more experience than me which i really appreciate you share with the lot of us and thank you for it!

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 10:48:21 am
content: This is the response i got from MPS when i answered their request to "identify my business" (WE need to identify your company and qualify your project before we provide any support), telling them i dont have a company (yet) as i am trying to put a and b together, create a few designs etc, who starts a company without a product really?This was their last responseI’m sorry but we don’t have the resources to support such requests.Really MPS... one of your products got on fire you dont have the resources to see if it was YOUR fault or my stupidity or both or what? Excellent "business" mentality! If you are not a "company" perhaps even if you are one but not buy x reels a month, you get no support...Good to know now, before i had my "company" invest in your products or bring a project to the market and have someones house on fire...

author: mikerj
author_rank: Super Contributor
timestamp: March 29, 2018, 10:58:11 am
content: Quote from: soubitos on March 29, 2018, 10:48:21 amYou must be dreaming if you think a company would provide all the resources required to investigate a single failure in a hobbyists design. This won't impact their business in the slightest, compared to say a customer buying 100k devices per year suffering an endemic fault.

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 11:03:28 am
content: Quote from: mikerj on March 29, 2018, 10:58:11 amIndeed.. I would suspect this could be the case from huge companies.. but.. are they perhaps huge because they care for their customer a liiiitle bit more?Or, if i identified myself as a "company" (which i could) it would make any difference?Or, if i had plans to build 100k chargers this year and use 3-4 of their chips after i got my plans financed and approved and prototyped and ready for the "company" stage?This is to say the least, stupid

author: TheDane
author_rank: Regular Contributor
timestamp: March 29, 2018, 11:03:59 am
content: Searching the datasheet for 'floating' yields 1 result:"Bootstrap. Requires a charged capacitor to drive the power switch’s gate above the supply voltage. Connect a capacitor between SW and BST pins to form a floating supply across the power switch driver. "I would agree that a soldering issue seems unlikely if more than 1 board fails.ESD damaged chips?Fraudlent chips?If it was me, I would connect the EN pin to ground, and see if that board survives your 'BURN'in test- sorry, couldn't resist- know why.I think and thought and found out I was wrong before, and know I will most likely be wrong again. Experience, trap for young players, chancing it, etc.- reverse voltage is not an uncommon thing, as clamping diodes can be added internally - providing Vcc to the circuit, even if Vcc isn't directly powered.Oh, on the environment thing - you said ice cold, so no freeze spraying to condensate water during testing?. Louis Rossman did a video not long ago on how clean water damages a powersupply:

author: TomS_
author_rank: Frequent Contributor
timestamp: March 29, 2018, 12:11:08 pm
content: Quote from: TheDane on March 29, 2018, 10:20:40 amIf you were to ask me for my interpretation of this, I would say that this quite clearly indicates that you need to either pull the EN pin low to enable or pull it high to disable. It doesnt seem to suggest to me that it can be left floating.OP should build another board, tie this pin low, and perform his tests again and see what happens IMO.

author: soubitos
author_rank: Frequent Contributor
timestamp: March 29, 2018, 12:25:57 pm
content: Quote from: TomS_ on March 29, 2018, 12:11:08 pmIn most cases i have experience with it has no problem left floating..In ALL cases where it needs to be tied to either high or low it is clearly stated on the datasheet.This being said I am now testing pcb 3 & 4 without any problems... i soldered a tiny wire from pin 6 (EN) to the gnd pin of C1 just bellow it and i didnt see ANY change in behavior of the IC charging, discharging the pack, certainly not while idle and without power (LOL).In any case, i have made my decision to order 5 more pcbs with corrections and improvements to the design and keep them for personal use. I would not like to "help" MPS any longer choosing their products for my projects when i would get absolutely no support from them when i need it (i am confident if i turn out a multi-million dollars company i wouldnt even care to deal with such a company, they would like to "talk" with me though and i really hate this sort of "business")All i need is to verify that i did nothing wrong with the pcb layout etc as that would certainly repeat itself with other designs and i like to improve my skills and designs.

author: soubitos
author_rank: Frequent Contributor
timestamp: March 30, 2018, 10:42:25 am
content: I am confident the culprit was the electronic load.I didnt understand why i couldn't draw more than 500mA at some point and certainly while the charger cought fire.As i found out, the battery on the TP4056FlexAdv module i used to power the electronic load was discharged and the under-voltage protection has kicked in. The protection IC i use recovers after a while when the battery voltage raises naturally but the MT3608 boost converted "shut down" trying to boost from 2.90-3.00V up to 12V.The electronic load was only powered with maybe 4V at the time and its very possible as mentioned already that the LM324 oscillated. If that was the case, it does indeed explain the failure.BTW, if any of you who took time out of your life to try and offer a helping hand are interested, i can send 1-2 "samples" for you to mess with! Feel free to contact me, first requests served first!