XR bms wrong cell group reading
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@weno66 Could you share a pic of the BMS? Ideally around IC1.
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.
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@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.
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@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.
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@lia nope. All looks fine..
Up..
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@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.![IMG_8631[1].JPG](/assets/uploads/files/1721579126244-img_8631-1-resized.jpg)
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@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?
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@weno66 Here you go.
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@lemur amazing!! Thank you!!
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Resurfacing this topic as my Pint BMS appears to have at least 1 - 2 bad Mosfets.
When I charge my board cell 6 slowly drains over subsequent days. If I don't pull the battery it will drain to 0v (ask me how I know). If I charge the pack again (in my pint), all cell voltages come up as they should but cell 5 tends to hit max volts first. When I remove from the charger cell 5 remains high, whilst 6 starts to drop.
So basically I think cell 6 is locked open and is constantly bleeding whilst cell 5 is closed and not bleeding when it should be.
I've found someone local that seems confident to resolder fresh mosfets if I supply them. Could someone confirm if these are suitable?
My soldering guru was also wondering if there is a preferred method for removing the clear coating before beginning soldering?
Many thanks in advance :-)
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@ikaruspint Yes, the 2n7002ps-115 are the correct mosfets.
