Help diagnose JBD 200A BMS issue-smoked SMD resistors

[Thingol]

I recently purchased this JBD BMS here at the IC GOGOGO Aliex store and I am currently locked in a refund tussle with the seller. Seller is unsurprisingly unwilling to replace or refund. I would like some assistance diagnosing and fixing the problem to see whether repair would be the best solution. Here is what's going on:

BMS got delivered fully functional, no signs of damage or wear, we hooked it up to our 48V bank (after testing correct balance lead connection) and everything worked without issues. Two weeks later, the BMS voltage sensing was completely wrong e.g., reading 2.5V for a cell whose actual voltage (measured on the connector and at cell) was 3.3V. The BMS has never run more than 80 amps, and is rated 200 amp. We took it out and:

1) The 3 resistors on BC0 side were charred and one was even split midwise. All 6 resistors on BC0 side and on BC21 side are labelled 620, meaning each one is 62 ohms-we could read this from older photoes from before the ones on BC0 burned out.

Current BMS photos showing burned out BC0 resistors:


Photos from earlier showing resistor ratings for both ends:


2) Now, on the BC21 side (positive end), the resistors are not burned out, but they all measure 20 ohm-against the expected 62 ohm:


My best guess here as an electonics noob is that the unit was built with low quality components and the BMS is not up to scratch (expecially having tested the leads voltages to ensure correct arrangement before plugging in). Other than that, I cannot tell why the BC0 resistors (-ve end) smoked, or why the BC21 resistors (+ve end) are reading 20 ohms instead of 62 ohms. Any help / insights as to what went wrong and whether we should simply replace all the resistors would be greatly appreciated!! @upnorthandpersonal

 

[upnorthandpersonal]

IC GOGOGO

Avoid them in the future, they're notoriously bad...

You can't however measure the resistor in circuit. They might be part of a voltage divider etc. so you're not really measuring a single resistor. You'd have to take them out and measure.

I'm trying to remember what those resistors were for but it's been so long since I had a JBD opened up and I don't have one here to check. It does feel strange that those resistors would pop though, even if they were lower quality ones... I would replace them and then hook it up to a power supply with current limiting to see if something shorts out somewhere.

If you're stuck and they don't refund you, let me know. I'll buy it from you to have some fun with.

 

[Thingol]

Avoid them in the future, they're notoriously bad...

You can't however measure the resistor in circuit. They might be part of a voltage divider etc. so you're not really measuring a single resistor. You'd have to take them out and measure.

I'm trying to remember what those resistors were for but it's been so long since I had a JBD opened up and I don't have one here to check. It does feel strange that those resistors would pop though, even if they were lower quality ones... I would replace them and then hook it up to a power supply with current limiting to see if something shorts out somewhere.

If you're stuck and they don't refund you, let me know. I'll buy it from you to have some fun with.

Thanks a lot for the info-I'll have someone take them all out and measure the resistance correctly! The problem is that the thing is at my project site in Kenya so sending it out your way is prohibitively expensive. I will bring it back to Europe with me next time I go though-and check with you if you still want it.

I will have them all replaced tomorrow. But more diagnosis with a power supply will likely not be possible (very hard to find those down there-i'll get one at some point in future for home use).

I have asked the seller for a circuit diagram for this BMS-if they accept to share it, it could help a lot.