Topic-icon BMS errors in reported charge and load currents

2 weeks 3 days ago #29534688 by ed_solomon
When charging a battery pack with a known charging current of, for example, 3.0A and with no load connected, the Run screen of the RoboBMS Configuration Utility (Rev 1.3 10/15/18) shows the correct 3.0A charging current on the RHS of the screen. However the LHS of the screen reports a charge current of 2.7A and a load current of 0.3A. Although the sum of these currents is correct, the split is incorrect.

The Setup screen of the RoboBMS Configuration Utility has a Calibrate Zero button. What is its function?

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1 week 5 days ago #29534693 by ed_solomon
Here is more data on the errors in reported Charge, Load, and Total currents noted in my original post. I tested nine different BMS1060 modules with nine different 15-cell LiFePO4 packs while charging at 3.0A +-1% with no load attached.

Charge Load Total
(A) (A) (A)
2.8 0.3 3.1
2.2 0.9 3.1
2.3 0.8 3.1
2.7 0.4 3.1
2.9 0.2 3.1
2.4 0.7 3.1
3.0 0.1 3.1
2.9 0.2 3.1
2.9 0.2 3.1

The Total current, presumably measured in the Pack- to Load- path, is reasonably accurate, within a few percent.

The accuracy of the Charge current measurement in the Charge+ line is poor, with errors of up to 30%.

The system block diagram does not show a current measurement capability in the Load+ line so presumably Load current is calculated as Total current - Charge current.

A few questions:
1. Is my understanding correct?
2. Are the error magnitudes expected?
3. Can the errors be calibrated out?

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