winter charging

[Jerry Pierson]

Has anyone ever used a vertical small (50w) PV panel on the side of a bunky to keep the batteries charged during the winter? How would one wire such a panel and is a small charge controller required? It would act as a trickle charger. Fully charged batteries are not supposed to freeze so I'm told.
It's vertical to keep the snow off it.

[Andy Rhody]

What's a "bunky"? This "Yank" doesn't know.

Are we talking about a 12 volt system?

I don't think a 12 volt car battery with a trickle charge panel (1.5 watts or so) needs a controller but with a 50 watt panel, I'd think you would.

[Jerry Pierson]

What's a "bunky"? This "Yank" doesn't know.

Are we talking about a 12 volt system?

I don't think a 12 volt car battery with a trickle charge panel (1.5 watts or so) needs a controller but with a 50 watt panel, I'd think you would.

A bunky is a 12'x16' shed used to contain my solar equipment
I have 4-6v S-550 Surrette batteries - 12v system with inverter.

[Andy Rhody]

So it sounds like you have the four 6 volt batteries in series and parallel for 12 volts. It still sounds like you'd need a controller to be safe from overcharging.

I have panels on my cabin that are almost vertical to avoid snow and they charge just fine.

http://i41.photobucket.com/albums/e295/andy47bottles/Science/002-3_zpsbf75087f.jpg (http://s41.photobucket.com/user/andy47bottles/media/Science/002-3_zpsbf75087f.jpg.html)

[Rob Beckers]

Jerry, yup, fully charged batteries have to drop below -65C (about the same in F) before they'll freeze. Fully empty batteries are pure water, so they'll freeze at 0C.

As Andy says, a small panel and a little charge controller should do the trick. Morningstar SunSaver 6A (SS-6-12V) for example (very reliable controller!).

-RoB-