# Shorted battery pack



## F16bmathis (Jun 6, 2008)

Always seems I'm asking more than I'm helping..

With a Fluke meter across my Battery Pack to the trucks ground, I'm reading some voltage. I have 46 Thundersky 160 AH. Measuring from ground to the 40th battery, I get very little voltage, but measuring at battery 41-46, the voltage increases, and measuring to the negative side, I'm getting about 150 volts.

But here's the weird part... disconnecting the BMS wires and battery voltage display wires, I'm still getting this voltage centered at battery 40!

My BMS system took a hit and burnt a board because of the short, so the pack needs to be fixed, but this makes no sense. Cables have been checked and possible shorts to ground have been taken care of, but I still get this weird voltage differential at battery 40.

Any ideas?


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## Woodsmith (Jun 5, 2008)

I would start by pulling some of the links out of the pack to split the pack up into smaller parts while checking to see where the short is.

I would start with spliting in to two halves to see which half the short is in and then split the faulty side again and so on until the fault is found.

It could be something as simple as a battery strap touching somewhere or a conductive film on the top of a cell.

You have voltage, do you have current flow as well? Check with a test bulb to see if there is current to light the bulb as well as measurable voltage.


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## F16bmathis (Jun 6, 2008)

I was told to use a resistor between the meter and the battery, but I like the light bulb idea better. I'll also disconnect links tonight and test each battery in that area to ground. Crossing my fingers hoping its nothing serious...


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## F16bmathis (Jun 6, 2008)

The short keeps moving. Every time I go to the battery that displays nearly 0 volts to ground, I disconnect it and the "0" moves over a few batteries. I think I need to clean the tops of the batteries, even though they are in a box, I'm guessing there is room for water/salt spray to get in through the bottom between the batteries.


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## GerhardRP (Nov 17, 2009)

F16bmathis said:


> The short keeps moving. Every time I go to the battery that displays nearly 0 volts to ground, I disconnect it and the "0" moves over a few batteries. I think I need to clean the tops of the batteries, even though they are in a box, I'm guessing there is room for water/salt spray to get in through the bottom between the batteries.


I guess that you are using a modern DMM with 10 MegOhm impedance. A ground fault interrupter trips with about 25 kOhms to ground.
I guess the question is what resistance do you have to ground? You need to put a resistor (25k) in PARALLEL with your meter to find out.
Maybe our community can tell what should be the allowed resistance between motor-controller-battery and ground.
Gerhard


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