Dead cell balancing on JK BMS

[jontm]

Thanks for the generous offer. Let me have a talk to the alibaba seller, she is discussing with JK what could be wrong.
I am a electrical power engineer and have done the most basic troubleshooting steps by measuring body diodes of mosfets, fuses etc.. But then again my expertise is on high voltage and high power inverter design. Electronics are not my primary area of expertise.
If you are interested i can probably ship it to you. I live in Norway so should not be too far to ship, if I take you up on the offer I will cover shipping.
Sounds like a cool project. I will have to read up it some time. Personally I much rather put my budget into more batteries or solar panels than spending like 1000 USD on a REC BMS and 3000-4000 USD on a new Victron Quattro. Therefore i am trying to make due with a JK BMS and a old used Quattro that i got cheap (1700 USD)

 

[upnorthandpersonal]

I have run my JK BMSes for two years now, without issues. They sit there, do their job, and don't have to mess with them.

You can see the link in my sig to my system, which I built precisely to be cost effective - so I know where you're coming from. I'm expanding my battery pack soon; the rest is running just fine anyway.

Norway isn't far - keep me posted on the progress with your Alibaba seller.

 

[jontm]

I will, right now the BMS is dead and not able to start. So I guess I have a new issue to troubleshoot When I got the BMS it started right up without the charge detection connected and without any charger connected. The last couple of days it has only started when I connect the charge detection circuit to battery pluss.
Now connecting charge detection to battery + does nothing. Connecting a battery between battery + and charge detection does not start it either. Tried 3-9 V above battery voltage
Had hoped to transport it up to the mountain cabin where it was going to be used this weekend, before the snow is gone and I cannot transport by snowmobile any more, but I guess I might have to transport it by helicopter now...

Edit:
Think i have traced it down to the buck converter for 5 V. It is a SL3036H. Has battery voltage in and is supposed to output 5 V. Actual output is closer to 0.8 V right now. There was a capacitor between pin 2 and 6 that looks a bit suspect, but it is hard to tell with SMD caps and measuring capacitors in circuit is a bit hard since it is difficult to tell what's inside the chip between these two pins. There was no obvious things that showed up on the thermal camera. I guess i could solder out the capacitor to measure just in case, but i fear it might be the SL3036H that is bad, seems like i cannot find any pin compatible alternatives on western webshops, so i hope it just a case of a bad cap

 

[jontm]

I was able to resurect it again by removing the DC-DC converter and apply external voltage to where the output of the converter was previously. Looking a bit more at it, it looks like a 8.5-9 V circuit going into a couple of other converters supplying 5 V and 3.3 V.
Will probably put in a linear regulator for now taking power from the big 12 V supply that this BMS has to be able to supply power to relays.

This did not however solve my balancing issues unfortunately. I was however able to record some video of the issue as captured by the app, so that if anyone is interested they can see what the issue seems to be.

Right now, it seems like the balance circuit is only able to push something like 0.2-0.4 A. If I set the balance current any higher than this, I get instant errors for too high resistance in the balance wires. If I set the balance current lower than 0.4 then the initialization is able to push enough current to record the balance lead resistance and show that the resistance in the balance leads are fairly low.
I know that if I enable discharge and the inverter, so the voltages get unbalanced, then it will only be able to balance for a limited amount of time (even at these low currents) before the balancing stops and it is just small spikes of some mA left going into and out from the cells. It almost seem like something is discharged to the point of no more balance current to give. If I get in this condition, it is not possible for me to initialize the balancing any more, even if I set it to 0.3 A.
Just out of curiosity, have anyone measured the voltage on their super capacitors? Mine measures in at 2.493 V each today. The last time I was not able to turn on the balancing any more, it was at 2.533 V. Don't yet know if it matters yet though.
Will try to understand how the mosfets switch during the balancing action to try to find out what is happening. It seems like it is controlled by a combination of the microcontroller and some analog comparators. At least I assume that the microcontroller does control some of this, as of not I have only found control signals from comparators for the bit of the circuit handling switching the super capacitors.

 

[nunak]

Did you find any solution ? I have same issue on JK BMS and ID3/ID4 battery pack. So I am also not balancing.

 

[jontm]

I did not solve the issue and got a discounted JK 200A BMS.
I did not have any extra cells to test and try to repair the BMS.
Got some extra cells this week and got some ICs to replace the bad ones.
I will try to fix and test it and will report if I am able to find and fix the issue.