Solar Help
I have an older Class B motorhome and have been thinking about solar. I can boondock now for 2 days before I have to recharge my 125ah battery. The only thing that draws power is the 12V fridge whic...
Forum Discussion
We should note that a "17v" panel is so named for its Vmp (?) and that its Voc will be 21 or 22v, but that is also called a "12v" panel since it is for "12v" batteries.
So the same panel can be called a 12v, a 17v, or a 22v panel.
Not to be confused with higher voltage panels like 36v ones that are called "24v" panels except if they are higher voltage to go with 36v or 48v battery systems.
controller sizing depends on not going over their rated input voltage spec from the panel(s), so you need to pay attention what voltage you are talking about. also note that voltage will rise when it gets cold, so allow for that extra amount too when sizing the controller for voltage input.
controllers also have an amps rating, so you do need to have some idea of your expected max amps and allow another 20% margin on top of that.
Nobody tells you your expected max amps for any given wattage of panels--except me! :) here it is:-
use the same for either PWM or MPPT, they are nearly the same for this purpose:
expected amps = chosen wattage/130w x 8.2
EG, 230w/130w x 8.2 = 14.5a (jimindenver gets 15a from his with MPPT)
EG 80w/130w x 8.2= 5a (the Isc of an 80w panel and what I got with my 80w.) It works and its free! You are welcome.
So the same panel can be called a 12v, a 17v, or a 22v panel.
Not to be confused with higher voltage panels like 36v ones that are called "24v" panels except if they are higher voltage to go with 36v or 48v battery systems.
controller sizing depends on not going over their rated input voltage spec from the panel(s), so you need to pay attention what voltage you are talking about. also note that voltage will rise when it gets cold, so allow for that extra amount too when sizing the controller for voltage input.
controllers also have an amps rating, so you do need to have some idea of your expected max amps and allow another 20% margin on top of that.
Nobody tells you your expected max amps for any given wattage of panels--except me! :) here it is:-
use the same for either PWM or MPPT, they are nearly the same for this purpose:
expected amps = chosen wattage/130w x 8.2
EG, 230w/130w x 8.2 = 14.5a (jimindenver gets 15a from his with MPPT)
EG 80w/130w x 8.2= 5a (the Isc of an 80w panel and what I got with my 80w.) It works and its free! You are welcome.
