36v Battery repair - Head scratcher ?

[KirstinS]

Hi all,

I’ve got an old style bottle battery 9ah 36v that is misbehaving, not taking a charge properly. I’m getting 32v out so lost 10v from full

I opened her up and measured the voltages across series via the 9 pin balance lead that goes from the cells into the BMS. I got some very odd results that I can’t understand

Between pin 1 and 2 = 4.17v
2 and 3 = 0v
3 and 4 = 3.9v
4 and 5 = 3.95v
5 and 6 = 4.1v
6 and 7 = 3.8v
7 and 8 = 4.15v
8 and 9 = MINUS 10.8v


What on earth is going on here ? I tested and retrested using back, front and top of the balance plug as test points for each pin. Same everytime

It looks pretty clear there is a dead series between 2 and 3 but what on earth is going on between 8 and 9 to get minus 10.8v ??

Any help appreciated

Thanks
Kirstin

 

[trex]

blown FETs at the output?

 

[KirstinS]

But the balance lead comes directly from the cells. Each series should be 3.6v nominal

So why one reads minus 10.8v rather than plus 3.6v is the question as it is pre BMS

 

[trex]

are there two groups of balance leads on your BMS?

 

[mfj197]

Yes, surely a balance lead from a 36V battery (10S) should have 11 contacts, not 9? Unless the balance board takes the end points from the main +ve and -ve from the battery. Is there any way of knowing where the balance wires actually are in the batter pack (i.e. tracing back between cells 1 and 2, 2 and 3 etc.)?

 

[KirstinS]

no trex , just the one 9 pin
I can take a photo when I get home later

It is a Panasonic celled one from 8fun

 

[KirstinS]

Yes, surely a balance lead from a 36V battery (10S) should have 11 contacts, not 9? Unless the balance board takes the end points from the main +ve and -ve from the battery. Is there any way of knowing where the balance wires actually are in the batter pack (i.e. tracing back between cells 1 and 2, 2 and 3 etc.)?

Yes, I think this is how it works on this bms

 

[KirstinS]

I'm beginning to think some balance wires must be shorting or connecting in the cell pack itself