Please help me troubleshoot my battery

[Tomy]

Hi all!

I have a 42V/17Ah (LG 18650 cells) battery and am now having issues with the battery.

When in use, the battery voltage will not be stable but will constantly vary between 42V and 20V something. This occurred less when the problems started and now, a few months later, the battery will not function at all most of the time. When connected to the bike, the battery voltage will be unstable and the display will show that the battery is empty. If removed and voltage checked with a multimeter, it will show that the battery is in fact charged and the voltage is stable. I have another battery and the bike runs fine with that, so that should isolate the issue to the battery. The battery is 2 years old.

The battery does charge ok and will display a normal voltage of 41.8V after a charge. Just like it did when new.

I opened up the battery case and tried to look for any bad connections or poor soldering. All looks good. I also ran a multimeter through the cells and they all have a 4.18 or 4.19 voltage.

I am wondering, though, if it is possible to measure the voltage of each cell individually when they are stick welded together. I believe I am in fact measuring the voltage of 10 cells connected in parallel. If this is so, and the reading is 4.18-4.19. shouldn´t that be an indications that the group of cells are ok?

I know very little about electronics and would very much appreciate if anyone could advise me what to do to troubleshoot the battery as far as it is possible with a mutlimeter and visual inspection.

Thanks!

Tomi

 

[docw009]

Looks like it came out of a Dolphin case. Are you sure the rear connector is firmly making contact in the battery cradle. When I first built it, I had to ride my e-bike 30 miles w/o power on my first long ride with it because that connector slipped into the case.

If the connector is OK, then the battery may not be able to deliver under load. You might carefully place the insides onto your battery cradle and measure the voltage output at the connector when it's connected up.

 

[Tomy]

Thank you for your advice.

And yes, I am a little suspicious about the rear connector (the one in the bottom right corner in the second image, just to make sure we are talking about the same connector).

The connector casing itself was in place, but the + pin inside looks like it has been pushed deeper into the connector.

I have been asking to buy this connector locally. But here in my small town in Central Finland the guy at the electronics parts shop has never seen this connector.

Does anyone know where to source them online?

Thanks!

Tomi

 

[markz]

2 obvious places to look, the main connector and that BMS. Do the simplest task first, main connector. Rule that out then move onto the BMS. If its not proprietory, then take the BMS out of the equation and see what happens with a battery pack without a BMS.

 

[Tomy]

Thanks, markz!

I managed to find a place to buy the main connector online:
https://www.greenbikekit.com/accessories/ebike-connectors-cables.html

I hope this is a reliable place to buy. So once, and if, the connector arrives, I will know more.

I have no idea how to disconnect the BMS and run the battery without it, but I hope to find advise on that later, if need be.

Tomi

 

[Tomy]

The connector from greenbikekit.com arrived within a week from my order. I replaced the connector a few days ago and the battery is running fine now!