Amps differ from measured panel output

backoftheblackstump

I can take an amp reading from 2 parallel mounted panels  at rooftop say 12A but at the controller input might read only 3A. The owner believes the controller is pulling what it needs as the batteries are near end stage usability and they are, in any case,  near full capacity. But I cant figure why amps are measuring such a big difference. 

BB.

Welcome to the forum.

Do you have a DC capable current clamp meter to measure current?

https://www.amazon.com/UNI-T-Multimeter-Voltmeter-Continuity-Capacitor/dp/B0BBMKLL5H (inexpensive, good enough for most of our needs)
https://www.amazon.com/Auto-Ranging-Resistance-Klein-Tools-CL800/dp/B019CY4FB4 (mid-priced AC+DC current clamp meter)

Current, in general, should add... If you measure 5 amps on one panel, and 7 amps on another, they should add to 12 amps. Using a current clamp meter is quicker, easier, safer, and does not require you to "break connections" to do current measurements.

Remember that solar charge controllers will vary the current they draw from the array... You may have 2x 6 amp panels in full sun, but if the battery is near full charge, then the controller will draw less than max available current.

-Bill

backoftheblackstump

Yes I am using a clamp meter. It may be the controller is misreporting the amps going into it from the panel. The owner is reporting back to me the controller amps coming into the meter as I measure the amps at the panel(s). I cannot see how it is possible for two different amp readings to occur in a 10 ft length of standard 30amp solar cable. There is no resistance in the cable as we have not yet fitted a fuse. I will investigate further. Thanks Bill.

BB.

What brand and model of solar charge controller?

Most "don't care" about negative connections (between solar array negative and battery negative).

Some are true 4 port devices where array +/- wires must connect to array inputs and battery back must connect to controller battery output (Schneider was one that "care".

Have you connected the clamp meter (DC mode and zeroed) to one of the controller array cable input?

About the only way I can see the per panel (each parallel panel output) and the combined output would not add up correctly would (possibly) be caused by a panel with the +/- connecting reverse...

Or confusion between reading controller meter at full current into discharge battery bank vs another day/time into a full battery bank or different time (noon vs 4pm for example).

-Bill

backoftheblackstump

Thank you. I will double check the panel connections.