XR bms wrong cell group reading

[weno66]

My bms had water damage and has been fixed. A few M2t mosfets, a few rb capacitors and one of the two big 80v mosfets were changed for new ones.

The board lit up and was able to ride it. Alas it died on me at 50% and never was able to recharge or balance it. Charger goes red, charges up to 50% then stays green.

Upon installing a owie I saw what I thought initially that the cells are out of balance (group 8 showed low reading).

I manually checked the cells inside the pack and their reading was perfectly balanced. I also tested another battery, same wrong reading on group 8: https://ibb.co/zGqBvJn

Im sure it's something on the bms still.. But cannot figure out what.

Any ideas please?

[Lia]

@weno66 Could you share a pic of the BMS? Ideally around IC1.

Spoiler

This one

I've noticed bad cell readings that are not the battery tend to be a broken solder joint on caps C1-C15 or they're just dead. Easy to do removing a port like the XT60 and slamming them accidentally on removal.

[weno66]

@lia I've been there before 😅 pulled out a capacitor when removing the xt and it did show above normal readings. Figured it out quickly as c11 was missing and I fixed it by replacing. But that was another bms from another board.

This one looks like this : https://imgur.com/a/EGamaYX

I made sure to even check them one by one with a multimeter and they all give me readings.

[Lia]

@weno66 I'm not seeing anything that stands out as wrong. Could you compare resistances between components and traces to see if any are abnormal on the faulty group compared to one that seems fine.

[weno66]

@lia nope. All looks fine..

Up..

[Lemur]

@weno66 When you say m2t mosfets, did you mean m8t mosfets?
When you get high and low cell voltages on adjacent cell groups usually it's a m8t mosfet.
There are 8 mosfets controlling 15 cell groups, but #1 m8t mosfet controls only one cell group.
Best bet is to get the bms repaired at Atlowshop or source a good working bms.

[weno66]

@lemur yes m8t mosfets. That was a typo. A professional fixed it recently and changed a few of those.

Apparently there was water damage and corrosion that went deep into the connectors which connect the circuits inside the board layers.

He said he will have another look and try to pinpoint which one is the mosfet and capacitor that deals with group 8 cells and redo the circuit.

To help him out, have you or anybody got a diagram of the groups on the board please?

[Lemur]

@weno66 Here you go.

[weno66]

@lemur amazing!! Thank you!!