Watts needed
I have read where folks suggest any where from 1 to 2 watts of solar per ah of battery. My question, is this based on battery rating (ie 215 AH) or is it based on useable amp hours(105)? All reply...
Forum Discussion
Your panel specs for amps are for the input to the controller. The amps "size" of the controller is for its output. That is what you are missing. Read this again.
A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.
Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.
MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)
2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:
483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps
A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.
Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.
MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)
2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:
483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps
