sbms soc percentage reading not accurate.

[jedics]

My shunt is wired to the positive side and read its why yesterday after charging to full by the next day the sbms said I was only at 20% charge yet voltage was 26.6v.

Is my shunt being wired to positive why its not accurate?

[Dacian Todea (electrodacus)]

What model of SBMS do you have ?

Shunt's for all models will be on the positive side.

You need to set the shunt resistance correctly so that current will be measured accurately. Also battery capacity will need to be set correctly.

The SOC is calculated by integrating the current over time.

Say you have a 300Ah battery and overnight means about 12h and battery showed 20% after being full at 100% that means 80% of 300Ah = 240Ah used over 12 so an average of 20A discharge current showed by the shunt.

If your shunt shows 20A but you know that is not the real current it means you either set the current shunt resistance incorrectly in the SBMS menu or zero offset calibration was done incorrectly at last SBMS0 power up (current flowed trough the shunt at power up if the SBMS is not able to turn OFF all your charges and loads).

[jedics]

sbms120 

have a 200A 75mV Shunt

I also noticed that the smbs was saying I was using more power than I was, so I turned off all loads and it still said I was using 9amps, turned sbms on/off and appears to be normal now. Here are the settings for it, is this right?

[Dacian Todea (electrodacus)]

Current shunts values are correct.

Last time when you powered ON there was a 9A charge current trough the shunt thus zero offset calibration was incorrect.

[jedics]

Even if the sbms was reporting no charging? 

The sbms is all over the shop, showing me with 30% soc when one battery is dropping below 2.4v then another time showing about 30% when the battery is at 26.6v . Is it because thiese batteries are damaged or Could it be oxidization of my connections because I used aluminium?

[Dacian Todea (electrodacus)]

Of course the SBMS was reporting no charging if the zero offset calibration was incorrect.

If you have bad connections than it could show as full charge when it will in fact not be anywhere close to full charge because of the high charge current the voltage drop on the connection will show up as high cell voltage and thus SBMS will think cell is fully charged.

The SBMS can only correctly calculate the SOC if current is measured correctly (so correct zero offset calibration) and when there is no large voltage drop due to bad cell connections.