diy solar

diy solar

cell and total voltage difference

workbox

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Apr 12, 2021
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Hi

Between jbd bms and victron shunt 0.04 voltage differences, who to believe?

If bms shown 3.34 per cell x 4 = 13.36, victron smartshunt connected after bms displays 13.32 v

Calibration issue ?
 
It could either be a difference in the calibration, or the wires that are reading the voltage have different resistances.

Check your connections and make sure they are all tight, and don't use a bunch of excess length for the voltage sense wires.
 
My question would be what is the advertised accuracy and repeatability of either unit.
IMO your in no mans land and normal DIY guys do not own any test equipment that can detect that small of a range accurately.
 
Chinese shunts are often based on 75 mV drop at max current. Vitron are usually 50 mV drop at max current.

I would not put much expectation on accuracy of a BMS current readout with multiple chip resistor current shunts on BMS PCB. Even if individually calibrated they have terrible temp coefficients and baked by series MOSFET heating.

Some really cheap BMS's just measure voltage drop across series MOSFET's for their current measurement and throw in a fudge factor for MOSFET Rds_ON shift with temperature.
 
Last edited:
My question would be what is the advertised accuracy and repeatability of either unit.
IMO your in no mans land and normal DIY guys do not own any test equipment that can detect that small of a range accurately.
My ~$50.00CAD meter may or may not be accurate but it is demonstrably consistent.
 
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