Hi All

My solar panels when connected to my BM system have a single pair Red / Black.
When I measure the current using my Tongs I get a difference of 1.5 A between reading the
red or the black.This is in the 16 A range.

Even when I measure a load in the mA range the same way, there is always a difference.
Granted my Tongs are no-brand, but am I missing something.

I am careful about having a nice loop of cable and away from others when I measure.

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Regards
Hervey Bay Qld.

If you have the panels connected to a switch-mode MMPT or charge controller the high frequency may be affecting the accuracy of the meter.

An old analogue Hot Wire ammeter will give true RMS from DC-to-Daylight.
It uses a thermocouple connected to a short piece of resistance wire.
Slow response and +/- 3% of full scale are its limitations.

Hi All

  Quote  

If you have the panels connected to a switch-mode MMPT or charge controller the high frequency may be affecting the accuracy of the meter.

My BMS is a Rpi switching SSR's, so the only time the SSR switches is when target Voltage is achieved.
I would think the error would be the same on both leads.


The tongs actually show the Red lead as Negative current and the Black lead as positive current. Either way whatever comes out of one, MUST go back through the other.

So perhaps the accuracy of measurement differs from one direction to the other.

Turning the meter around at the same place on the same lead should produce the same results if that is the case.
You probably need to check it against a known good meter in both directions.

Hi All

Good suggestion, will try that tomorrow.

If by "Tongs" you mean current clamp tester then yes, I find that most DC clamp meters can give a slightly different result in one direction (-/+) and a slight difference between clamping the positive and negative leads.

Hi All

Definitely the Tongs.
Just rotating the meter, but keeping the cable nicely in the center,
gave me 1.8 Amp difference at 16 A this morning.

The only other Clamp meters I have access to, one is the same brand as mine
and the other is an old analogue only for AC.