Sizing a battery bank. Ah VS wh?
Hi again! So, I'm trying to size out the battery bank I will need for my husband and I to live off grid in a camper. We don't have tons of time or money, so that's a bit of a factor. We plan on usi...
Forum Discussion
Lwiddis wrote:
“That seems like such a little amount. I thought it would be more about the solar's charging rates. Like "25amps per hour" or 25ah x 4.5hrs of sunlight = 100 amps charged in 'one day.' I havnt quite gotten to that research yet...”
if you looking at it as 25AH then no, they will never put out full power. a 12V panel on a PWM controler will put out 17ish v all day long which is 17v to the controler at 17.6 amps. since a PWM doesnt convert it only used a percentage of that and is faily inefficent so lets say 14.4 at about 15 amps.
this should be fairly close as 480 watts of 12V panels on a PWM in my 5th wheel will only give me about 23 amps.
this changes when you go to something like MPPT controler and say what I have on my camper which is a 72 cell 24V panel. this puts out aproximatly 32 to 36v depending on the panel so with a MPPT controler it is actualy a built in dc to dc charger so it takes that input and converts it directly to the output voltage and you only lose the effeciency of the controler. mine is 98.6% so lets pick 34V at 300 watts that is 8.8 amps but since the battery needs 14.4 it converts it to that output - the effeciency loss so you end up with 295.8 watts of 14.4v and 20.54 amps.
so the same output panel in different configurations with different controlers in ideal conditions can varry widely with out having to get into increased preformance in low light of a split cell 24V panel.
I realy started looking into this when I found I got more charging out of a 325 watt system than my 480 watt system and wondered why.
Steve
