In this
article on building a BMS, one comment I received cautioned about "phantom" voltage reasons if one of the battery cell voltage sense wires broke, or a fuse blew. His experience was that the phantom voltage was essentially the average of the two adjacent cells, and could appear to be a healthy battery when it's not. That would be a problem, so I wanted to test it out.
Thankfully, my BMS doesn't exhibit that problem. The three pictures below show the cell voltage readings, first with the sensor wires for cell #4 connected correctly, and then with each of the sense wires disconnected.
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| All sensor wires connected, voltage read correctly |
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| Positive sense wire disconnected from cell #4. Cell alarms and shows "phantom voltage of 17mv. |
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| Negative Sense wire disconnected from cell #4. Cell alarms and shows phantom voltage of 17mv |
There is a small phantom voltage, but no where near enough to not realize there is a problem.
I think this all comes down to the internal circuitry of the sensing device, and in particular how much impedance there is between channels.
