Voltage weirdness

[Ken R]

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]

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]

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]

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).

[Marinepower]

I have something similar happen a number of times before after disconnecting and reconnecting the 12 pin ribbon cable.  

In my case however, all the cell voltages read low. They read about 600MV low ( around 2.24v when in fact they were 3.1v when read with a meter.)  

Unplugging and reconnecting the 12pin ribbon cable seems clear the fault.  This has happened several times. 

If there is a known wring or other fault issue that causes this, I would love to know.  I have admittedly extended the sense wires to 9 feet with a breakout board using 20 awg wire. 

Marinepower

[Dacian Todea]

Marinepower,

Your description is not at all similar and suggest maybe a damaged ISL94203 if all cells read low. If all cells except one reads low then is related to your cabling and cell balancing current drop but 9ft with 20AWG can not have this sort of drop so best guess the ISL94203 is somehow damaged.

You can ship the SBMS to me so I can replace the ISL94203.  I guess both load and charging is turned OFF when this happens so it is not usable.

[Marinepower]

Dacian,

thxs for reply and for the offer of assistance.

The funny thing is that the problem seems to clear by power cycling the unit (with the 12pin ribbon cable).

I have combined wires 11 & 12, which I understand is OK to do.   I assume this would not be the issue.

Let me double check every connection and see if I can get a photo of the fault on the monitor screen and share with the group.

MP

[Dacian Todea]

There will not be any condition where you will get this sort of behaviour unless the ISL94203 is damaged and the fact that it is temporarily fixed by a reset means nothing as it is likely a subtle defect maybe something heating internally over time or an intermittent short or open inside the IC.