battery pack fault

[confounded]

Hi, i dont understand whats going on with my battery pack

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

 

[colin55]

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.

 

[confounded]

thanks for replying,

Yes i think your right its a wire connection, should of seen it myself really

 

[zeppblimp]

do you have an open cell?

 

[Sceadwian]

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

 

[zeppblimp]

open cell

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

 

[Sceadwian]

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]

6V without the connecting wires and zero volts with the connecting wires.
Duh! It is obvious that the connecting wires are broken.

 

[confounded]

yes

The wires look perfectly connected though but obviously theres no other explanation.

 

[RODALCO]

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.