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Battery build issue

ian123

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Feb 20, 2021
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So I bought 8 cells to make 2 x 272amp 12v batteries. Bought 2 x overkill bms.
Before connecting all up, each cell was showing 2.99v.
Hooked all up.

Problems:-

1. the Bluetooth is not detecting for the overkill? Have app, says searching but never finds.

2. on each bank, 1 cell is nearly at 2.99v, but other 3 have dropped to less than 1 volt each??

Im a newbie, be gentle!
 
If you have 2 sets of cells and 2 BMS doing the same thing .... It is very likely you have something connected wrong.

Hopefully the BMS are not damaged
 
That’s first thought. So I took all wires and bussbars off. And started from scratch following overkill diagram. Still no Bluetooth signal.
 
Did it fix the problem with some cells dropping to 1V?

Android or IOS?
 
On my Android phone, I turn on bluetooth and location services. Works every time. The location services tripped me up the first time. You do not need to pair the phone to the BMS. Just go straight to the BMS app.
 
iOS.

well, I don’t know how the cells have lost so much voltage when all they have been doing is sat on a bench for 2 weeks. Gone from 2.99 down to under 1 for some cells. Only the +ve terminal cell has stayed up at 2.89 on both banks.

move deleted the Xiang whatever app and downloaded again. Reconnected all wires and no Bluetooth signal.

totally lost ?
 
I think you need to disconnect the BMS as soon as possible and see what the cell voltages are individually.

If they really are that low of voltage you need to get some charge on there right away .... If the voltage drop is only when connected to the BMS something is wrong with connections, BMS, or both.

Maybe the overall voltage is too low for the Bluetooth to work?
 
Can you post a picture of the cells with your BMS connected?
 
6C13F2ED-BE29-486A-9C5E-4916275F4DC3.jpeg
 

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Have now disconnected Bluetooth cable and tested each end to end wire to ensure no break etc - ok.

done same with bms to cell wires - all ok.

I was thinking the low volta in pack was the cause, but that’s the whole point of the bms monitor, so I can see which cell is at what charge. Would t be a good system if didn’t work when down to under 50% of full capacity!
 
On some of these cells, the black is positive and the light color is negative .... Have you verified polarity with your meter?
 
When using your multimeter, check the voltage on the cell terminal, not on the bus bar or the stud. Slip the probe under the bus bar.
 
On some of these cells, the black is positive and the light color is negative .... Have you verified polarity with your meter?
If the black is positive .... you have things connected wrong.
 
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On some of these cells, the black is positive and the light color is negative .... Have you verified polarity with your meter?
Yes. Shows -be on meter when I put the red probe on black terminal and black probe on white terminal.
 
Whew .... Are you sure the meter leads are connected to the correct place on the meter? ;)
What voltage do you have on each cell with the BMS disconnected from the plug?

If you put your meter negative on the black lead .... at the plug and work your way down with the positive lead and see if the voltages increment as they should.
 
Yes. Shows -be on meter when I put the red probe on black terminal and black probe on white terminal.
I believe you have the BMS's red positive wire connected to the cells negative. I would disconnect everything and start over. It's possible having the BMS connected wrong drained the cells.
 
Also the black wire coming from the BMS and the Blue cable coming from the BMS both should be connected to the cells negative terminal. I am attaching the wiring diagram for 8 cells but it also applies to 4 cells. Again I suggest you disconnect everything, verify the cells polarity, and start over.
 

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