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I have a SparkFun USB LiPoly charger that by (default) is set at 500mA. If I try and measure the charge current with my DIY multimeters, the charging LED goes out and the meter reports zero current?

I guess this is because of the multimeter's internal series Vsense resistor confusing the onboard MCP73831 controller chip?

If this assumption is correct, can anyone suggest a DIY method method of measuring small Lithium battery charge currents?

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  • \$\begingroup\$ What current range are you using on the multimeter? I'd assume the sense resistor value should be tiny on the 10A range. \$\endgroup\$ – tangrs Nov 30 '18 at 9:01
  • \$\begingroup\$ please add a schematic showing how you connect the multimeter. I suspect that you are doing it incorrectly. \$\endgroup\$ – Jasen Nov 30 '18 at 9:39
  • \$\begingroup\$ Thank you. Yes the 10A range does have the lowest sense resistor (0.1ohm) but on that range the resolution is only +or- 0.01A. The 200mA range (on many meters that I have checked) averages 2ohm but even at that value it seems to be sufficient to cause the charger to miscalculate the battery voltage and turn off? \$\endgroup\$ – mprowe Nov 30 '18 at 11:43
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Add a low value resistor and measure the voltage drop across that.

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