Voltage weirdness

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Ken R

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Apr 29, 2021, 4:55:02 PMApr 29
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SBMS120 was disconnected over the winter.  Hooking it back up this spring I have a voltage weirdness.  On connection of the ribbon cables, the cell voltage display is
3.335
3.339
3.945
4.790
3.334
3.338
3.337
3.322

My multimeter shows 3.3 across the board even when I am careful to measure across the screws holding the ribbon cable sense wires.  I see the discussions on dirty connectors causing transient measures, but 4.7 volts?

Just keep cleaning and reseting until it is correct?

Ken

Dacian Todea

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Apr 30, 2021, 12:25:47 PMApr 30
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Ken,

That 4.790 seems like that max voltage a chanel can measure and is either due to a bad connection between cells maybe cell 3 to cell 4 as cell 3 is also reading higher so check the cell sensor wires connections maybe one of the is disconnected /broken.

SolarChain

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May 1, 2021, 8:00:26 PMMay 1
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I've seen this occur more than a few times on batteries where cells were all balanced and connections between the cells was not the issue.   Of course just be double sure that you connections are secure.   I find that if you connect and disconnect at the SBMS side of the ribbon it can clear the issue, but not always.   Be careful here though because the SBMS0 will act on attempting to balancing out these cells.   

Dacian Todea

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May 1, 2021, 8:25:22 PMMay 1
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SolarChain,

He has the SBMS120 a bit different from SBMS0 but you should not see incorrect cell voltage readings on the SBMS0. Can you take a photo next time to see exactly what you are talking about as that should not happen.
If you where to see a 4.8V like he is on one of the cells then is either a bad cell sense connection or a damaged ISL94203 (main BMS IC).

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