Solar fuseing, confuseing

CA Traveler wrote:

Ed_Gee wrote:

CA Traveler wrote:
Doubtful that a serial or serial/parallel setup is practical but it depends... So your best option is 4 parallel panels in which case there is no MPPT advantage over a PWM CC. But you already have the MPPT CC.

Each panel should have a fuse (15A) in the combiner box. Otherwise a short could cause excessive heating from the other 3 panels.

I must take a small exception to the above comment. In full sunlight, even with parallel panel wiring, maximum voltage out of the panels will be around18 volts.....about 4 volts more than needed even for bulk charging the batteries. His MPPT charge controller will be able to convert that extra voltage into extra charge current; a PWM charge controller won't.

Nope it won't be 18V panel output. Panel voltage drops with increasing panel temperature due to the sun. Combined with MPPT conversion efficiency it's basically a wash between the 2 controllers as PWM procduces full Isc amp output. His MPPT will end up operating in PWM mode. MPPT does have an advantage for cooler temperatures.

MPPT does have advantages for serial panels or 24V panels for a 12V battery bank.

The original poster is up at the Canadian border for his solar operations. I highly doubt temperature is going to be a significant issue for his solar panels. The 18VDC I cited is operating voltage....under load....not open circuit voltage which for my 36 cell panels, and probably his, would be around 21 or 22 volts. The MPPT charge controller certainly will add a small amount of charge current over the PWM controller. They are highly efficient and under optimum conditions can provide 30% more current to the battery under charge. I have measured such on my own system in central Oregon coast and seen such results. PS: there is no such thing as a MPPT controller having PWM mode.