Question: What size Solar Controller for the Solar Panel?

[matthewp]

WOW! You guys are great! I haven't specifically figured out my consumption yet, but I will be running a fridge, a few LED lights here and there and a 12v water pump; all powered by 2 X 100ah AGM Marine batteries. The trailer will be set up with direct charge capability from the tow-vehicle and shore-line if that's available. Therefore I'm not dependent on my solar as the only source of charging. I can figure out what my average consumption will be if that will affect your recommendations drastically.

Thanks again very much for the great info you guys are providing!

 

[4x4junkie]

I haven't specifically figured out my consumption yet, but I will be running a fridge, a few LED lights here and there and a 12v water pump; all powered by 2 X 100ah AGM Marine batteries.

Doesn't sound too different from what I got going myself, other than my batteries are in the vehicle itself (2×105Ah).

Since you plan to also have the batteries charge from your vehicle's alternator, I suspect you could get away with 110W of solar capacity (the 140W panel w/PWM controller) as long as you don't plan to be parked idle for more than a few days... You've got a pretty decent amount of battery capacity available. This should restore approximately the power your fridge consumes, though not much more than that (figure 110W × 5 hours of decent available sun per day = 550Wh, or maybe 7-8 hours of sun if you're able to follow the sun directly with your panel). It's imperative however that you run very heavy gauge wiring from your car's charging system (or from your isolator) out to the trailer though, as that's a rather long run of cable. Any resistance here very quickly degrades your alternator's ability to fully charge the batteries (#1/0 AWG and using an Anderson power connector like what you usually see on a removable winch mount carrier is the minimum I'd recommend, like their SB-series connectors).
http://www.andersonpower.com/products/multipole-sb.html


Hopefully that helps... Sounds like a nice setup you're working on.

 

[matthewp]

Hopefully that helps... Sounds like a nice setup you're working on.

That helps a lot! And, yes, I'm using a heavy gauge power wire with Anderson connectors like you recommend.

 

[dwh]

Any resistance here very quickly degrades your alternator's ability to fully charge the batteries

Not exactly. It degrades the ability to charge quickly, but has nothing to do with reaching full charge.

Since voltage drop is a function of load, as the battery voltage rises, the amperage flow rate goes down - and the voltage drop becomes less and less. By the time the battery is at 14v or higher, the voltage drop is negligible and pretty much irrelevant.

So, even with small wire, the battery can still reach a full charge voltage - it'll just take longer.

 

[4x4junkie]

Well... Given the limited amount of time an engine (alternator) typically is running, quickness is the key here.