Cheap China Solar Controller Failure

KJINTF wrote:
2 x 140 = 280 watts /13.2 (Floating voltage / Bulk with higher voltage will reduce the output current) = > 20 amps

Actually many quality panels are under rated
Many of them can & do easily exceed their rated outputs

140watt / 8amps = 17 Volt Vmp
Have to assume you have a PWM controller

An example my 550 watts / 13.2 = Give me in excess of 40amps to the loads under good conditions but NOT to the batteries they never need that much

Using the rated panel watts as the "output" doesn't work to get the actual "expected amps" at the battery.

PWM gets you the rated Isc passed through to the battery as your "expected amps" with panel pointed at high sun. With many poly panels that will be proportionate with 130w and 8.2 amps for Isc. the Isc amps is the "output" not the watts.

So 280w would be 280/130 x 8.2 = 17.66 amps

It is bogus to go back and say with battery at 13.2 and 17.66 = 233w so 280-233 = 47w "wasted" or "lost" unlessyou are trying to sell MPPT and that is your "spin" :(

MPPT does make amps out of watts so that is different. But you still can't use rated panel wattage as your "output" since you don't get that many watts with MPPT either. Heat reduces panel voltage and so its watts, making some watts "wasted" or "lost" same as with PWM.

The proper comparison with PWM is to use "expected amps" that you will get at the battery with panel aimed at a high sun.

Jim gets 17a with his 245w and 16 with his 230 ( approx. same as I get with my 230w and same as others with that size panel have reported)

So 280/245 x 17 = 19.43a

19.43 x 13.2 = 256w so 280-256 = 24w "wasted" or "lost"

550w flat here in May at high noon with PWM would get you 550/130 x 7.2 = 30.5 amps Tilted at sun would be 550/130 x 8.2 = 35 amps

If MPPT gets you 10% more, then that would be about 33.5a flat and 38.5a tilted. (49.3N in mid-May at high noon)