Battery build troubleshoot

Batteries, Chargers, and Battery Management Systems.
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Monte   1 µW

1 µW
Posts: 2
Joined: Jan 16 2020 9:11am

Battery build troubleshoot

Post by Monte » Jan 16 2020 9:47am

Edit: Think I figured it out. The electric tape I had shielded connections with (can be seen in picture) had had a piece of nickel strip poke throught it and was creating a connection. I think I'll wire the rest of the connections with 12AWG silicone wire that I'll solder on.

Hi guys,

First post on the forums and I hope it's in the relevant area!

Doing my first ever E-bike build making a carbon frame cyclocross bike int a "modular" e-bike where all electrical components can be removed in around 5 minutes (rear hub motor, cables through frame and waterproof connectors).

I ordered 98 Samsung 25R cells to make a high-capacity battery (14s7p) for the bike, but decided on splitting the battery into two smaller ones instead.

First battery I made was 14s3p, and that worked fine with a DIY spot welder I made.


Now, making the second battery (14s4p) I made a slight mistake with my cell groups. I placed one cell group the wrong way around resulting in 8 groups of 4 cells in one orientation and 6 in the other. Somehow I managed to weld the whole thing together before noticing my error...

Well I got a surprise after finishing the welds and measurinng 14V through the battery and noticed my error. I disconnected the errorous series connection that was between plus terminals of two parallel groups. I thought I would just fix my mistake by closing the loop with thick copper wire from one side of the battery to the other.

However, after disconnecting the part of the battery where I made a mistake, the battery is still showing a voltage from one end to the other when measured with a multimeter (14V). I don't understand this, as I have clearly disconnected a series connection in the battery and to my reasoning it should now be two seperate batteries. I've looked through the connections a dozen times and can't figure out the problem.

Here's a picture of the pack from both sides and lines drawn for connections:
Image

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