Solar fuseing, confuseing
Were installing a Renogy 400 watt solar system on our fith wheel. We stay on our property about two months in the summer up near Canada in Washington.Anyway this is the kit I bought. Mind you I'm comp...
Forum Discussion
You get points for not starting out swearing! :)
Ok, so here is how an MPPT works, like it or not. It has a buck converter so it is all about input watts vs output watts. You then divide the output watts by battery voltage to get the amps to the battery.
A panel out in the sun will be hot by about 25c over ambient temp so if ambient is 25C (77F) the panel will be 50c, which means its watts is 10% less than as rated (look it up)
So a 255w panel will be at 229.5w output at 50C.
Line loss to the controller 1-3% so let's use 2% = 4.6w so 229.5-4.6 = 224.9 input. Controller efficiency call it 98% (could be 96 or whatever) = 220.4 output watts
220.4 /12= 18.37 amps
220.4/13= 16.9 amps
220/4/14 = 15.74 amps
Meanwhile no matter the panel temp, with the panels aimed at a high sun, you get the rated Isc. 255w worth of 12v panels would have total Isc of 255/130 x 8.2 = 16 amps
So your MPPT advantage is tiny, teeny weeny, at 13v being 16.9 vs 16.0 amps
Which is what everyone is trying to explain here! :(
Ok, so here is how an MPPT works, like it or not. It has a buck converter so it is all about input watts vs output watts. You then divide the output watts by battery voltage to get the amps to the battery.
A panel out in the sun will be hot by about 25c over ambient temp so if ambient is 25C (77F) the panel will be 50c, which means its watts is 10% less than as rated (look it up)
So a 255w panel will be at 229.5w output at 50C.
Line loss to the controller 1-3% so let's use 2% = 4.6w so 229.5-4.6 = 224.9 input. Controller efficiency call it 98% (could be 96 or whatever) = 220.4 output watts
220.4 /12= 18.37 amps
220.4/13= 16.9 amps
220/4/14 = 15.74 amps
Meanwhile no matter the panel temp, with the panels aimed at a high sun, you get the rated Isc. 255w worth of 12v panels would have total Isc of 255/130 x 8.2 = 16 amps
So your MPPT advantage is tiny, teeny weeny, at 13v being 16.9 vs 16.0 amps
Which is what everyone is trying to explain here! :(
