Community Forums

donie · 09-26-2013, 09:32 AM

I'm thinking about getting a small solar panel to maintain the charge on the coach battery for maintaining the battery when the rig isn't being used.
What size would be recommended to do this?
Thanks.

BFlinn181 · 09-26-2013, 10:00 AM

15 watt panel can maintain a battery, but won't 'charge' it very quickly. 30-45 watts will charge a bit faster. Some of the above depends on geographic location, Arizona and Texas get more sun in winter than Montana or Michigan.

Gary RVRoamer · 09-26-2013, 10:17 AM

Also, are you talking about the engine (chassis) battery or the house system? And how many batteries in each? A 15 watt panel will "maintain" one previously-charged battery in reasonable sunlight, or maybe even two in some climates.

donie · 09-27-2013, 08:41 AM

Gary, I was looking to maintain the coach battery but now that you mention it, I'd like to do them all.
By "all" there is one 12 V to start the engine and a pair of 6 V for the house.
Right now the coach is stored at a storage unit in Utah but is normally parked beside the garage in Cali.

BFlinn181 · 09-27-2013, 08:46 AM

I'd think 30 - 45 w would be more than adequate to do as you want in Utah or CA. Not enough to 'boondock' but plenty to maintain charge while in storage.

vsheetz · 09-27-2013, 12:55 PM

I would suggest a 100w panel and appropriate Morningstar controller.

RV Solar System Sizing by "Rules of Thumb"

camaraderie · 09-27-2013, 04:10 PM

I think the 15-20amp panel will be sufficient to keep the 6Vpair topped up and then you could just use a fall-over device like the trickle charge to keep the chassis batt topped. A 15amp panel in a reasonably sunny location will on average deliver 4-5 amp hours per day...this exceeds what the batteries themselves will use in loss of charge BUT it does not count parasitic loads. If you're gonna leave everything connected and have loads...you need to understand exactly what those loads are...(a clamp meter is handy for measuring them). Take the basic 15watt panel and add 4timess more watts than your parasitic loads to cover them.
Example: Lets say you have a 1/2 amp load on the batts when everything is turned off in the coach. That is 12 amp hours a day...so you would need a 48 watt panel (roughly) to keep up with that load in addition to the 15 amp...so roughly 60 watts. Make sure you account for loads on the chassis battery as well as the house batteries (with any trickLstart devices disabled!)
Chances are the 40watt panel is all you will need if leaving things connected...but a clamp meter is a lot less expensive than a new set of batts!

Note...the 4x multiplier I use is for situations of low power needs with minimal equipment. If you someone is doing a larger scale solar power project, then the use of an MPPT charger can reduce that multiplier to 3.