Solar battery charger

Starter battery is not the best choice for trailer. After this one will have died, get a "deep cycle battery" rated 80 Ah - 100 Ah. Or a pair of 6V deep cycle batts. Or whatever your needs are. For now, 3W-5W should keep it charged, with no loads.

Battery is an Energizer Marine Starting
Group 24
CCA @0°F 500
MCA @32°F 625
RC minutes is 95

michelb wrote:
(5W panel) only able to maintain them if the disconnect switch is on (i.e. there is 0 load on the battery).

Yes. Forgot to mention this solution. Get some battery cut-off switch, they start from $3. Then 5W, or even 3W, will maintain the existing charge between trips. Again - it will not add any charge, it will maintain the existing level, so that it won't drop due to self-discharge.

FWIW, we have a 5W panel on our A/C and it was able to keep 2 12V and 2 6V batteries in usable shape from Nov-May in Ottawa, Ontario, Canada and this is with snow (so panel was certainly completely covered some days and short winter days. But as others have mentioned, it's only able to maintain them if the disconnect switch is on (i.e. there is 0 load on the battery).

afinepoint wrote:

HiTech wrote:

afinepoint wrote:
Looking for one to keep the battery charged between trips.

One battery with no loads on it, or parasitic loads from the RV too?

Jim

With. Because I'm bound to forget to disconnect the loads.

you have to be more specific. The term "parasitic loads" may include a lot of things. Most often it's a clock radio - can be anywhere from 1 to 7 Ah in 24 hours, plus detectors - those draw very little. Some people have huge TV set that draws some on standby. Some have 2000W inverter idling 24/7 even when there is nobody home. Who knows...

If you are really unsure, start with 20W solar AND controller, and see where it gets you. 3W-5W is only enough to compensate for self-discharge of "wet" battery in absence of any loads, not even a clock radio.

HiTech wrote:
I was looking at that one. Sears sells it for $58. Does it have a blocking diode?

Jim

No blocking diode but as others have said, just add one.
It's the smallest panel in this photo.

BTW, if you want 20W, the SolarBlvd 20W for $29 is a great deal.
Not real big either (it's the middle one in this photo).



1n400x diodes are cheap cheap cheap. I think I paid $0.03 each for 100 qty. They're everywhere too so take apart things and scrounge.
Forward drop is kind of big though it doesn't matter much. Schottky is better.

Why pay a premium for one with clips and a blocking diode when you can add your own from junk in your tool box for cheap. On our Ranger, I have a blocking diode, a fuse tap, and a connector to the panel that sits on the dashboard.

Thank you for all of the great feedback. I'm getting the trailer tomorrow evening.

I will get a charger that can handle parasitic loads with some reserve to spare.

Almot wrote:
Not enough info.
"To keep charged" - with what loads? Do you physically disconnect the battery, or just turn the lights off and call it a day? Is it a single battery, and if so, what size?

Assuming the easiest scenario, - a single battery under 100 Ah (this is what dealers normally push to sell), AND if you physically disconnect the loads, then to compensate for self-discharge that goes inside the battery and never stops no matter what, you need 3W-10W solar charger. Get one from Amazon, where it says "charger" - not "panel", and that comes with cable and clips - those usually have a blocking diode built-in. Costs around $20.

If any loads are present, then you need a charger/panel with more watts. How much more - depends on how much loads.

If there is more than 100 Ah of batteries, then again you need more watts.

If you need more than just "keep it charged", i.e. you want to add some or all of the charge that you drew out of the battery during the last trip, then again you need more watts.

Good questions. Like I told pianotuna I'll look tomorrow.

HiTech wrote:

afinepoint wrote:
Looking for one to keep the battery charged between trips.

One battery with no loads on it, or parasitic loads from the RV too?

Jim

With. Because I'm bound to forget to disconnect the loads.

pianotuna wrote:
Hi,

How big is the battery in amp-hours?

I'll look tomorrow.