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battery pack fault

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confounded

New Member
Hi, i dont understand whats going on with my battery pack :confused:

When i measure voltage across the battery pack i get 6v.

When i attach the wires to the battery pack and measure voltage i get AC millivolts, which when looked at with my oscilloscope is 50hz rough looking sinewaves.

I measured the resistance between the wires when my batterys unplugged and it is infinite.

Why does voltage go to practically zero when i attach the wires to the battery, it cant be a short as the resistance between them is infinite?

pic attached
 

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colin55

Well-Known Member
You are picking up AC "hum" from the mains. It is because the leads of the CRO are effectively open-circuit or maybe because the wires to the battery snap are faulty and not making contact.
 

Sceadwian

Banned
He wouldn't be getting 6 volts if one was open.
 

zeppblimp

New Member
open cell

what would you expect to see on an open cell? a short or partial would read less voltage, correct?
 

Sceadwian

Banned
An open cell, nothing, there would be no path for the other batteries to produce a voltage. Cells generally don't fail open I don't think, they usually fail short circuit.
 

audioguru

Well-Known Member
Most Helpful Member
6V without the connecting wires and zero volts with the connecting wires.
Duh! It is obvious that the connecting wires are broken.
 

RODALCO

Well-Known Member
A DMM has y high impedance 1MΩ or more per volt.
As hardly any load is put on the pack it will read your full voltage.

As soon you apply a small load on the battery pack (eg 10 or 20 mA) it drops to zero, indicates a poor connection in between cells.

I have found that in drill battery packs occasionally poor spotwelds between cells do fail.
 
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