My BMS voltage readings and my multi meter readings are different

[Aussie]

When I look at my cell voltages on my phone app they are different then my multi meter readings. My multi meter showed most cells within 0.005 of each other but the app shows different voltages for the cells. As much as 0.031. checked my connections , all good. Any ideas why and is this going to be a problem. It is a new build, it has just got top balanced. My concern is that if the BMS readings are wrong it won't function properly. So is the BMS "broken"? Any ideas?

 

[Aussie]

It is a JBD, BMS

 

[sunshine_eggo]

With the overkill solar app, you can calibrate the voltages by entering an actual voltage for each cell.

 

[Brett V]

How are your sensing leads from the BMS connected to the cells?

 

[time2roll]

With the multimeter are you checking the voltage as it enters the BMS or at the cell?

 

[Aussie]

With the overkill solar app, you can calibrate the voltages by entering an actual voltage for each cell.

How do I go about that?

 

[Aussie]

How are your sensing leads from the BMS connected to the cells?

The leads have crimped connectors

 

[Aussie]

I

With the multimeter are you checking the voltage as it enters the BMS or at the cell?

I am checking at the cell terminal.
The Total voltage reading i.e. 53.0v is the same with the multimeter at the terminal as the BMS reading

 

[Aussie]

With the overkill solar app, you can calibrate the voltages by entering an actual voltage for each cell.

I attempted to do this. I got on the calibrate screen, entered the correct voltage, pushed "write" and nothing happens. Do the cells have to be at rest when this is done? Mine were discharging at the time I attempted to rewrite the voltages. I tried several cells.

 

[featherlite]

Do you have the Overkill manual?
Appendix B tells how to calibrate.
Elsewhere, the manual says:

If you plan to calibrate your BMS, the voltmeter needs to be accurate to at least 1 millivolt. If you use a cheap or badly-calibrated voltmeter, you will only make your calibration worse.

 

[time2roll]

I
I am checking at the cell terminal.
The Total voltage reading i.e. 53.0v is the same with the multimeter at the terminal as the BMS reading

I would try my best to ignore the differences unless a significant capacity issue shows up.

53.0 does not say much at the calibration accuracy level. Is it 53.000 and 53.000? almost need a fourth decimal to have good faith in the third.

 

[Aussie]

Do you have the Overkill manual?
Appendix B tells how to calibrate.
Elsewhere, the manual says:

If you plan to calibrate your BMS, the voltmeter needs to be accurate to at least 1 millivolt. If you use a cheap or badly-calibrated voltmeter, you will only make your calibration worse.

Thank you. I have downloaded the manual. I shall see what it says and have a go.

 

[Aussie]

I would try my best to ignore the differences unless a significant capacity issue shows up.

53.0 does not say much at the calibration accuracy level. Is it 53.000 and 53.000? almost need a fourth decimal to have good faith in the third.

I think I have got a significant variation. 0.080 v Or is that nothing to worry about?

 

[time2roll]

I just can't imagine if the total voltage is correct that there are 80 mV of calibration errors between cells.

 

[Aussie]

I just can't imagine if the total voltage is correct that there are 80 mV of calibration errors between cells.

I haven't noticed the difference in the total voltage total as I was only checking cells.

 

[Aussie]

I am using the overkill app and when I go to calibrate no warning comes up . I can input figures, but when I push "Write" it does not change the existing figure. Any thoughts?

 

[featherlite]

It appears that the Overkill manual was written for the Xiaoxiang app.
On the the Xiaoxiang app, a warning appears saying "Note: only use if you know what you are doing".

Maybe try using the Xiaoxiang app.

If that does not work, I would ask Overkill for support.

 

[Aussie]

It appears that the Overkill manual was written for the Xiaoxiang app.
On the the Xiaoxiang app, a warning appears saying "Note: only use if you know what you are doing".

Maybe try using the Xiaoxiang app.

If that does not work, I would ask Overkill for support.

How do you access the calibration screen on the Xiaoxiang app ?

 

[featherlite]

Below is the "home screen" to click Config




Below is the next screen to click Voltage Cal

 

[Aussie]

Below is the "home screen" to click Config


View attachment 208477

Below is the next screen to click Voltage Cal


View attachment 208478

Thanks featherlite. My app looks different. Is your app one you pay for? The one I have was free.