Hey

Do we have local guys that can repair these?

One of my bmses decided to no longer read the voltages of pin 7 and 8, I have tested the wires and they are all good and reading correctly. However, when I tested the resistance on the board itself, pin 7 & 8 read at 0.00.

So wondering if there are local repairers?

Already ordered a replacement in the meantime, if anyone is up to try

Edited December 12, 2025Dec 12 by Pho3niX90

So I managed to track down the issue.

A small resistor has went caput, but not on pin 7 or 8, but 6.

Getting this small resistor replaced is the main issue. Suggestions?

4 hours ago, Pho3niX90 said:

Getting this small resistor replaced is the main issue. Suggestions?

If you cannot solder the surface mount resistor, you can try and get a leaded 1% tolerance 1/8W and solder that in, but with a fine soldering tip on a Weller or similar temperature controlled soldering Iron, you should be able to do this yourself, assuming you're not like me, needing serious magnification to see that the fly dirt is actually a SMD device...

Edited December 13, 2025Dec 13 by Kalahari Meerkat

3 hours ago, Kalahari Meerkat said:

If you cannot solder the surface mount resistor, you can try and get a leaded 1% tolerance 1/8W and solder that in, but with a fine soldering tip on a Weller or similar temperature controlled soldering Iron, you should be able to do this yourself, assuming you're not like me, needing serious magnification to see that the fly dirt is actually a SMD device...

I initially took the device here to a local shop, they replaced the resistor with another. Here comes the problem

Device turned on, but complained about high resistance on 6 and 7, although voltages were now there.

So I opened it up again

They used a 1.0Ohm resistor, vs , what barely had resistance at all (0.01 Ohm). So l, got the soldering iron out, took the new one of, and just used the correct resistor from my stash of electrical goodies.

It's now perfect, just not sure what caused this in the first place.

15 hours ago, Pho3niX90 said:

It's now perfect, just not sure what caused this in the first place.

I assume the balancing current is run though the resistor as well, not just the cell Voltage measurement... lets see how screwed up I can get the math on this, if the cell is, let's say at 3.5V and the BMS is running 1A (assuming a 1A balancing current) into the cell, that would be 3.5W, the 1A X 0.01Ohm is 10mV across the resistor, (I hope) and thus 10mW dissipation needed by the resistor, not sure what those fly-manure speck sized resistors are rated at... I think the particular one that waved the magic smoke of defeat might have been under spec./less than 100% ok from the get go... maybe...

Was working fine untill last night, now it's worse.

This time, cells 1,2,3 | 10,11,12 | 13,14,15
are all without voltage, most probably the same reason.

Going back into the logs, there was no balancing happening at the time. 200 watts were discharged into the home at the time, no weird temprature rises, no strange spikes.

This is clearly a lemon

Although I ordered a replacement locally, I decided to try the chinese supplier and report the issue.

They requsted a screenshot from the app, and stated the are sending a new one. So this one will just turn into a donor unit.

Edited December 15, 2025Dec 15 by Pho3niX90

4 hours ago, Pho3niX90 said:

This time, cells 1,2,3 | 10,11,12 | 13,14,15
are all without voltage, most probably the same reason.

Have you had lightning in your area shortly before the BMS started giving trouble? Only thing I can think of, else a dud, but how likely is that? Either way, glad that the overseas supplier is willing to replace...

Not in the last week.

The same battery rack, has 3 of the same bmses from the same supplier, all 3 connect to the same busbar.

I initial thought there might have been a surge, but I would expect the other 2, to also then display the same symptoms?

The other option, is a critter decided to take a stroll on the PCB, causing the issues at hand, which isn't unlikely, since they aren't enclosed.