Post #10
10)Since I also have another trailer with PWM controller and use the same portable panels with this trailer, I was curious what effect a long (90ft) run between the panels and PWM controller has when used with a PWM controller. Can I predict the results?
I've updated this post with some "before and after" data I forgot to include initially. MPPT parallel output current before the swap and after the swap. Just to check that conditions were similar to the day before and that solar conditions didn't likely change much during the test. Also to verify that I was operating the panels near Imp. Since I thought the biggest influence of changing resistance would occur with the PWM controler operating between Imp and Isc. No point in swapping controllers if I wasn't near Imp for panel current.
Thanks to BFL for bringing this to my attention.
OK, I’ll start with the last part first. Can I predict how cable run length (or more accurately additional resistance) will affect the current when used with a PWM controller? Qualitatively yes, quantitatively NO. Assuming the panel is operating near or above Imp, additional wire resistance will cause the panel voltage to rise up on the VI curve, and in the area of interest, increasing voltage will cause a slight decrease in current. How much? That’s the hard part. It’s highly non linear. My guess is not near as much as with an MPPT controller.
Test method. As quick as I could, I swapped out the MPPT controller for the PWM controller. Time to swap was about 10 minutes. In this case series connected panels make absolutely no sense, your throwing away current; all I’d get would be 4.5A or so. No reason to even do that test with a PWM controller.
Since a PWM controller is not a power converter more like a voltage controlled current source, I didn’t bother measuring voltages, just battery current.
Test:
parallel connected panels with MPPT controller and very short interconnect as a baseline comparison to previous days test.
Battery current: 10.4A (trimetric)
Parallel connected panel with PWM controller and very short interconnect.
Battery current: 9.5A (Trimetric)
Parallel connected panel with 90ft of cable BETWEEN the panel and PWM controller.
Battery current 9.0A (Trimetric)
parallel connnected panels with MPPT controller and very short interconnect
Battery current 10.3A (Trimetric)
solar conditions likely stable "enough" during the tests.
Conclusion:
First, test conditions are "close enough" to the day before that I was operating under similar conditions and the panel output is near Imp, something I wanted to see for the PWM data.
With panels in parallel, 90ft cables and the MPPT controller I saw a drop of almost 1.1A from optimal configuration of very short cable.
Under similar test conditions with PWM the drop was about half, 0.5A.
The % drop was 5.3% for the PWM case, 10% for the MPPT case with parallel cables. The effect of additional cable resistance between the solar panel and PWM controller clearly is not as significant with a PWM controller as it is with a MPPT controller, at least when the PWM controller is operating between Imp and Isc. I suspect if the PWM controller is operating at or below Imp, the drop would be even less noticeable.
This is for the case of resistance between the panel and controller. The effects of a long run with PWM controller between the controller and battery bank is not part of this investigation. That experiment is “left as an exercise to the reader”. Any volunteers???
