Saturday, Mar 13, 2010 at 14:42
Steve,
similar thing happended to me in the past.
The solar regulator's PWM circuitry controls the output voltage to the battery within a fairly narrow band. You could assume this voltage is a constant while comparing the currents.
The current now becomes a function of the battery voltage (SOC) and circuit resistance.
I.e. delta V=0.2V, R tot=0.05Ohms, I=4A.
R tot contains the ammeter's shunt resistance and resistances of the
test leads.
If you omit the resistance of your
test leads (like in case of your panel meter), then the total series resistance would have dropped by say 25 milliOhms, which effectively doubles your measured current (8 amps in this example).
Therefore it's advisable to ensure the lowest contact resistance of your
test lead plugs.
Spray them with contact spray and wiggle them in their receptacles.
Or, use a DC current clamp which won't have this problem (these tend to be a bit inaccurate at lower current values though).
Hope this has you un-puzzled?
@ Allan,
the integration times of a standard multimeter are in the order of hundreds of milliSeconds.
The PWM period of a typical solar controller is at least by an order of magnitude lower than this.
Thus, both panel- and multimeters will show a time integrated (time averaged) value of the pulsed charging current.
If the regulator was DC/DC like in MPPT, then the output will be smooth DC, so there won't be any issues at all.
The only way there could be interference is when the regulator is set to 'on/off' control mode with a time period of 250 milliseconds f.e.
But this would result in wild
swings on any digital (AND coiled) meter display and would make an accurate reading very hard if not impossible.
Best regards, Peter
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