I did a bad thing and now need advise to fix it.

[zedconnor]

I did it several months ago when I accidentally shorted it with a wrench.

It's all laser welded. It is a 51.2V 200Ah pack.
The style is 8 batteries facing each other.
Very difficult to work in that narrow area.

But that damage on the busbar is making me worried to just keep using it.

Any advise on how to fix it?
Are spot-welders any good on welding the busbars back to the cells?

Current Condition of Battery Pack
_________________________________
All cells except cell no.9 are balanced.
No.9 will jump up high if charged with anything higher than 10A and trigger Cell OVC bms.

 

[Samsonite801]

Could you just grind or file off the slag and then soldier the gap? The gap doesn't look like it goes super far into the bar / lug... If you wanted, could cover the gap with some copper strands like a wire section or something (and flow the soldier in to fill the gap with copper embedded in).

 

[zedconnor]

Additional pictures of pack.

 

[Samsonite801]

All cells except cell no.9 are balanced.
No.9 will jump up high if charged with anything higher than 10A and trigger Cell OVC bms.

I didn't see this part the first time. Do you think shorting it damaged a FET on the board maybe? Perhaps the shorting on it did more unseen damage than just burn the connector...

Is that connector on the BMS itself or where is it exactly?

 

[zedconnor]

I didn't see this part the first time. Do you think shorting it damaged a FET on the board maybe? Perhaps the shorting on it did more unseen damage than just burn the connector...

Is that connector on the BMS itself or where is it exactly?

No it is on the connector.

I stripped everything down now.
And I tested it again with bms all connected and cell no 9 is no longer causing any troubles.

Maybe loose connection was the culprit.

 

[Zapper77]

Clean the connections. Repair that balance lead.

BTW That cell(s) maybe damaged.

Go ahead and manually top balance your pack. If you don't have an adjustable power supply, you can use a known DC load to bleed power from the high voltage cells. (DC Light buld, resistor, DC fan.)

 

[zedconnor]

Clean the connections. Repair that balance lead.

BTW That cell(s) maybe damaged.

Go ahead and manually top balance your pack. If you don't have an adjustable power supply, you can use a known DC load to bleed power from the high voltage cells. (DC Light buld, resistor, DC fan.)

All cell voltages are perfectly balanced.
(It is only when charging or discharging does cell no.9 was draining/charging up very rapidly and causing bms to shutdown.
But the problem seems have disappeared after i disassembled the pack and temporarily reassembled it outside the box and tested with a 2000W load.<induction stove>)

 

[Zapper77]

All cell voltages are perfectly balanced.
(It is only when charging or discharging does cell no.9 was draining/charging up very rapidly and causing bms to shutdown.
But the problem seems have disappeared after i disassembled the pack and temporarily reassembled it outside the box and tested with a 2000W load.<induction stove>)

Balanced...at what voltage did you check the balance?

 

[Zapper77]

But the problem seems have disappeared after i disassembled the pack and temporarily reassembled it outside the box and tested with a 2000W load.<induction stove>)

Maybe one of the connections was bad.

 

[zedconnor]

Voltages were around 3.33V

Maybe one of the connections was bad.

 

[Zapper77]

Voltages were around 3.33V

Its best to check (compare) balance when cells are 3.45 or higher.

 

[Partimewages]

With all your cells at 3.33 you can not determine the actual SOC. The Lifepo4 voltage curve is so flat they each could be anywhere from 30 to 80%. You need to fully charge and start the balance at 3.4.

 

[Zapper77]

With all your cells at 3.33 you can not determine the actual SOC. The Lifepo4 voltage curve is so flat they each could be anywhere from 30 to 80%. You need to fully charge and start the balance at 3.4.

You explained that well. I need caffeine, too early.

 

[Partimewages]

I might add you probably don't need to charge above 3.55v if you start to balance at 3.4.

 

[Zapper77]

I might add you probably don't need to charge above 3.55v if you start to balance at 3.4.

Yea, after I though about it. 3.5 might be high for some cells/situations.

 

[Zapper77]

A faulty balance lead connection would confuse the BMS and trigger shutdown.