Positve Voltage b/w Battery Negative and Frame

[nomad123]

Hi all,
I built a 30P12S battery pack using 18650 cells (3.7V Nominal). To house the pack I made a frame out of square tube Mild Steel.
The problem I am facing is that, when I install the pack in the frame I get a positive reading on the voltmeter between the negative of the battery pack and the frame. The voltage reads 7 to 8 Volts. If I hold one lead of the voltmeter in my hand and place the other on the negative terminal of the battery, again I get a reading but of 3 to 4 Volts. Doing the same with the positive terminal results in a low voltage of about 0.5 Volts.
There is no short circuit. The reading between battery positive and negative is 48 Volts. So there is no voltage drop in the battery itself.
What is causing this voltage? Is it harmful?
Google hasn't been able to provide me with the answers and I am not sure what to search for. After a lot of head scratching I am hoping I can find some answers here.

 

[HK12K]

"If I hold one lead of the voltmeter in my hand and place the other on the negative terminal of the battery, again I get a reading but of 3 to 4 Volts."

Changed the batteries in your volt meter lately?

 

[nomad123]

"If I hold one lead of the voltmeter in my hand and place the other on the negative terminal of the battery, again I get a reading but of 3 to 4 Volts."

Changed the batteries in your volt meter lately?

No. Do you mean to say that I should?

 

[obcd]

Connect a small 12V lamp between a terminal of your battery and the case. See if there is any current flow.
The rest voltage you measured should dissappear when that lamp is connected. Digital meters are very sensitive and hardly need any current to get a readout. It's for instance possible that a 100K resistor between your battery minus and it's case is enough to make the voltage go away. If the voltage doesn't go away, you have a resistance somewhere between your cell connections and the battery case.

 

[HK12K]

"If I hold one lead of the voltmeter in my hand and place the other on the negative terminal of the battery, again I get a reading but of 3 to 4 Volts."

Changed the batteries in your volt meter lately?

No. Do you mean to say that I should?

I'd give it a shot.

If you're holding one probe with your fingers, touching the other probe to the battery and you're seeing voltage on the meter, there is something very much amiss. As described that shouldn't be a complete circuit.

Low batteries in meters are known to give wacky results so I would swap it out and retest.

 

[nomad123]

Connect a small 12V lamp between a terminal of your battery and the case. See if there is any current flow.
The rest voltage you measured should dissappear when that lamp is connected. Digital meters are very sensitive and hardly need any current to get a readout. It's for instance possible that a 100K resistor between your battery minus and it's case is enough to make the voltage go away. If the voltage doesn't go away, you have a resistance somewhere between your cell connections and the battery case.

I can confirm that there is no resistance between the frame and the terminals. I used a DMM in continuity mode to check.
I did connect a resistor between the frame and battery negative. The voltage reduced but did not go away entirely. I am not sure what to make of it. At this point I think it is probably the meter being funky, or some sort of stray voltage?
I am 100% sure there are no stray wires etc connecting the cells to the frame.

 

[nomad123]

"If I hold one lead of the voltmeter in my hand and place the other on the negative terminal of the battery, again I get a reading but of 3 to 4 Volts."

Changed the batteries in your volt meter lately?

No. Do you mean to say that I should?

I'd give it a shot.

If you're holding one probe with your fingers, touching the other probe to the battery and you're seeing voltage on the meter, there is something very much amiss. As described that shouldn't be a complete circuit.

Low batteries in meters are known to give wacky results so I would swap it out and retest.

Now that you mention it, I have seen some wacky results on the meter. Turning it on and off again fixed those. I will replace the battery in the DMM and check again.