BMS Wiring HELP!

The-J-Man

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Greetings,

I have a BMS here for a 36v battery and I dont know where to attach the battery + - and output / input. There are 4 spots.
Balance leads is a 15 lead connector. 11 for for the cells plus 4 for 2thermal sensors.

Can someone help? :)

cheers

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Korishan

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P+ (3 & 4) is common Positive leads.
A- and P- are your negative lines
I would guess that P is for Pack.

If you look at the traces, 3 & 4 are the same terminal as the green trace runs around the right side of the board. All the FET's are connected to the common Pos side.
It looks like there is a current shunt between 1 & 2 and that is how it monitors the amps coming in and going out of the pack.

Again, that's a guess
 

The-J-Man

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Korishan said:
P+ (3 & 4) is common Positive leads.
A- and P- are your negative lines
I would guess that P is for Pack.

If you look at the traces, 3 & 4 are the same terminal as the green trace runs around the right side of the board. All the FET's are connected to the common Pos side.
It looks like there is a current shunt between 1 & 2 and that is how it monitors the amps coming in and going out of the pack.

Again, that's a guess

Ahh yes.
A- could mean Ausgang - (German for output).

So most likely:
1: output -
2: input - (from battery)
3:
4:

does it matter which + is connected at what P+ (3 &4)?


Well I carefully wired it up and its reading a correct voltage out of the socket. So thats seems to have been correct. No sparks or smoke or anything :D

However its not charging so, There was this other cable with the BMS that goes into a slot next to the A-. The wires are the exact same arrangement as the ones coming out of the other socket I have. So im guessing there is a communication that needs to take place between the charger and BMS. Thats how the other BMS does it that I have from the same company.

I got this 36v pack, it was discharged to 14V ::( So I carefully had it plugged in to a charger and I turned it up to 22V and 0.6A. Then i turned it up to 38V and it automatticaly increased amperage, dont know how much but it was a lot and all of a sudden the pack was at 30v...
So my plan of carefully psuhing it up failed.
Plugged in that other BMS i had and started charging. Two banks of 4 cells shot up in voltage and the otherswere somewhat similar. So there was an issue somewhere. Not sure if maybe these cells are just crapped out now ::( trying this BMS instead, this one was the original one for this pack.

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Korishan

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Yeah, if it's a two part setup, then it needs the other 1/2 to do the brains work.
 

The-J-Man

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Korishan said:
Yeah, if it's a two part setup, then it needs the other 1/2 to do the brains work.

hmmm, need to find out what the other half is then...
 

The-J-Man

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Allright so I hooked up one of those hoverboard BMS's I have lying around and started to charge this 36v pack and the same to banks of cells are overcharging.
What could be the cause? this is a different BMS doing the same thing as the one I had plugged in earlier (which I thought was defective)

broken cells?

cheers
 

Korishan

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you may have some cells that are different in resistance, causing them to not fill up as fast as the others.

However, it's possible, the bms that comes with the boards are not charge balancers in the full sense. They might not be active balancers, but passive. They may bleed off heat.

Does the bms get hot in spots when the cells are overcharged?
 

The-J-Man

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Korishan said:
you may have some cells that are different in resistance, causing them to not fill up as fast as the others.

However, it's possible, the bms that comes with the boards are not charge balancers in the full sense. They might not be active balancers, but passive. They may bleed off heat.

Does the bms get hot in spots when the cells are overcharged?

They are cheapo boards for sure.
Looked for that but hadnt had it plugged in long enough, didnt get warm in those 10-15mins. by that time the 2 banks of cells had reached 4.23v and the others are at 3.8.
The first bms I tried was one out of an ebike battery, looked like quite a serious BMS and it had same results.

Left the BMS plugged in overnight and not sure its done anything tbh, cells have dropped to 4.04 and mostothers are at around3.75. (it wasnt charging). Once I had unplugged from charging they dropped to 4.1 so im thinking this could still be from resting. Seems they just recieved heaps more voltage then the others and peaked.

If there were to be 2 bad cells in each of those 2 banks (4p) could this cause double thecurrent to flow into them, and there fore make them charge double as fast?
maybe its wired up wrong ::D who knows :p
 

daromer

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Many of those cheap ones only balance with like 50mA and even lower. So if you got them so uneven as you do you need to charge the pack for X hours at just 50mA... Because if you try to charge with 100 or more the ones in top will just keep raising. This is the big issue with the cheap bms systems that doesnt have active feedback.
 

Wattsup

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Were the cells balanced before you tried the bms?
 

The-J-Man

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daromer said:
Many of those cheap ones only balance with like 50mA and even lower. So if you got them so uneven as you do you need to charge the pack for X hours at just 50mA... Because if you try to charge with 100 or more the ones in top will just keep raising. This is the big issue with the cheap bms systems that doesnt have active feedback.
Ha thats close to nothing. Crazy
Wattsup said:
Were the cells balanced before you tried the bms?

They were somewhat yes. I charged and discharged them with my imax to get some somewhat similar, all around 3.6V.But as soon as i charge the pack those two rows just shoot up. Seems like thy are just getting heaps more current.
 

The-J-Man

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Oh no not looking very good, 1200mAh and all ready down to 3.6V.... and thats from 4 cells :mad:
 

daromer

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Just because they are even at 3.6 doesnt say they are even at top and the BMS will balance at top. So balance them up with the iMax first. neither less yes balance current is low on those.
You get what you pay for kind of :)

Thing is also that when already balance they should not need much more than 50mA current to keep in balance.
 

The-J-Man

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daromer said:
Just because they are even at 3.6 doesnt say they are even at top and the BMS will balance at top. So balance them up with the iMax first. neither less yes balance current is low on those.
You get what you pay for kind of :)

Thing is also that when already balance they should not need much more than 50mA current to keep in balance.

Sadly the cells shoot past 4,2V and up to 4,28 if Itry to charge the whole pack.
It only managed to discharge 2100mAh from those 4 cells in parallel..... Seems like I killed them whole reviving. Really annoyed that that charger automatically ramped up to 8A when I set it to 36V. Definitely killed some cells it seems :mad:Super frustrating.

Im testing the single banks of cells now one by one before I play around with BMS's again :D
 

The-J-Man

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Yep so around 4000-4500mAh from all the banks but those two I have been talkingabout which are coming in at about 2000mAh. 4000 is only 1/2 of what its supposed to have so pretty useless any way.

Solved that mystery then ::D
I just wrecked the pack when reviving it thats all. Real shame that, its a very well put together pack.
 
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