Homemade Panel Question

System

I am new here I accidentally posted this thread in the wrong place earlier,

I built 2 panels that put out about 25 v max and 3.5 amps. I was going to hook them up in parallel to get ~7 amps. I have a 12/24 v 10 amp charge controller and I was wondering if it would be too much juice to charge a single 12 v deep cycle battery with about 90 amp hours for my camper.

BB.

Re: Homemade Panel Question

Don't worry about the first thread--easy to clean up.

It sounds like your panels are around ~18 volts Vmp or so on a 12 volt battery bank (and a PWM charge controller--not the more expensive MPPT type).

7 amps into a 90 AH battery bank:

• 7amps charging/90 AH battery bank = 0.078 = 7.8% charge rate

We recommend as a general rule of thumb of between 5 to 13% rate of charge--so you are right there in the middle.

Depending on the seasons, tilt of panel, etc... You will in summer months average around 4-5+ hours of "noon time sun" per day. A off-grid system using an AC inverter for much of the loads works out to around 52% efficiency--so the maximum "average" usable power per day would be around:

• 7 amps * 14.5 volts charging * 5 hours of sun * 0.52 eff = 264 Watt*Hours per summer day

If you have a few AC loads (30 watt computer, 13 watt CFL) adding up to 43 Watts--Then you should expect around:

• 264 Watt*Hours / 43 Watts = 6.1 hours of power per day

The above numbers are just a wild guess--Depends on lots of things (how much power you really use, angle of panels, where you park the RV, type of charge controller, actual rating of panels, etc.).

Also, keep a close eye on the output current of the panels... Thermal cycling (expansion/contraction), vibration from driving, water/humidity, etc. are all really tough on home made panels.

If you see your expected current drop by 1/2 or more--you will have to hunt down the open circuit.

-Bill