Repairing a named make battery with a faulty BMS, battery cells all good, full pack nearly 40v off charge but under load 11v! still 40v into the bms, so i ordered a BMS from Andy at Woosh, and it looked like a dead easy swap out, until I got to the balance wires. The plug was wired the wrong way round! Not the new one which was correct, but the one on the board and the cable. So if I'd just plugged in it would have been fun! The custom BMS didn't follow any standard wiring of the balance lead apart from using the same plug.

 

So check and check again! Then check again.

 

Both plugs the same way round, note the "-" on the manufacturers plug in the same place as the "+" on the new, correct lead!

 

Replacement BMS

can you push the crimps out of the old connector and reload them back in the right order?

I'm more inclined to desolder the lot and wire it properly with a new lead. I'd probably end up breaking some of the old pins.

it's a lot of work soldering directly on to the tabs in comparison to extending the old connector with the new cable. I tried desoldering some balance wires with a Maplin 30W iron, it could not melt the solder they put on at the factory.

d8veh, what do you think?

Edited March 10, 201412 yr by trex

The individual plugs pop out quite easily.

looking at your connector block in the picture, from the opposite side you'll see an opening on to each plug, this lets you press down onto the metal tab that holds the plug into the block, allowing you to pull the plug from the main block.

I've recently swapped the wires from 2 smaller connectors into 1larger block.

Hey I might give it a go, and If I screw it up do the soldering route. Like how you have the tape to hold it. At least yours wires are multi coloured, mine are all white! Or could just fix the BMS, yeah right.

you could write down the voltage of each white wire against the battery minus terminal on sticky labels and attach the labels back to the white wires before marrying them to the black wires!

As the new black wired cables are 10s extensions I could reverse one end and use it as a kind of "crossover cable"?

I'd pull the pins and reverse the sequence, you'd have to insulate each one when they're out because they're all live. They'll vapourise if they touch.

I may go down the extender cable route, I can swap the pins without any chance of any shorts then just plug in. They're only a quid and i can do it at my desk rather than brave the cold of the garage!

Crossover lead made! Safer than messing with live balance leads. Test it tomorrow, listen out for the bang!

 

Worked fine. next problem. I've one cell that's a lot higher than the rest, by at least 2V and as such when charging, the bms sees this cell first, tops it up then stops charging the rest as it thinks its done. Any idea how I can safely discharge a 3.7v 10ah pouch cell. My imax isn't up to doing the discharge as it flashes "over voltage".

Try a 4.5v or 6v torch bulb out of a an old-fashioned flash-light.

Cheers I'll try that. Do you think that's why the bms isn't charging?

Yes, but why has it gone so high?

 

It happened on my Ping battery,so I opened it to see why. one of the cells on the 12S4P configuration had swelled up,so only 15aH in that group instead of 20aH.

It's a brand new cell, measured 4.43v out of the box, If I can discharge it to the same as the others (all sat at 3.9 at the moment and not getting any more) the pack should start to charge ok i believe.