Watts needed

The cooler it is the longer between needing charges. I, too, recommend a small solar panel system.

cliffy49 wrote:

As far as batteries, I have 2 Deka GC2's wired for 12 volts. At this time I am just lookinig to keep the batteries charged when the trailer is in storage.

I had a feeling the question was about storage again. Every few weeks somebody is asking this, without telling that this is for storage.

Deka GC2 exist in both flooded and AGM version if I'm not mistaken.

Fully charged flooded batteries are fine in storage at 77F without charging for a month or two. If longer, you need 30-50W solar to keep 200 AH bank topped up when they are disconnected from all the loads - no radio on standby, no propane detector, nothing. Panel of this size is small enough to attach on top of A/C box. There will be a faster self-discharge when it's hot.

Fully charged AGM are fine for 3-5 months without charging - again, shorter time when it's hot.

cliffy49 wrote:
I am still here. Been busy trying to get the trailer ready.

Cool, thanks. Batteries can stay charged for quite a while if they're disconnected.

2oldman wrote:

Almot wrote:
The OP never told what battery he has. Or how he is going to use his solar -

Appears to be MIA

I am still here. Been busy trying to get the trailer ready.

As far as batteries, I have 2 Deka GC2's wired for 12 volts. At this time I am just lookinig to keep the batteries charged when the trailer is in storage. Last year I just took the 1 12 volt out when ever I came back from a trip but have since purchased the 2 Dekas and they are jsut a little heavy to be taking out of the battery box after every trip.

At some point we may try boondocking but have not yet.

Almot wrote:
The OP never told what battery he has. Or how he is going to use his solar -

Appears to be MIA

2oldman wrote:

StirCrazy wrote:
for a 6V GC battery the recomended charge amprage is 10% of your total amp hour capacity at the 20h rate of your entire battery bank.

With Li's you can go way over that.

Acceptance rate for a 100 amp-hour flooded lead acid at 85% state of charge is 12.5. That translates to 12.5%, not 10%. Further lead acid are self regulating--that's why it takes nearly the same time to get from 50% to 85% as it does from 90% to 100%

Battleborn recommends 0.5 c for longest life, but 1c is safe.

2oldman wrote:

StirCrazy wrote:
for a 6V GC battery the recomended charge amprage is 10% of your total amp hour capacity at the 20h rate of your entire battery bank.

With Li's you can go way over that.

With flooded you can go below 0.1C, it will just take longer to get to Absorption. AGM recommend 0.2C optimum current, and again, you can go way below 0.2C.

The OP never told what battery he has. Or how he is going to use his solar - daily energy needs, days of camping etc - IMO, this is what solar planning should start with.

cliffy49 wrote:
I have read where folks suggest any where from 1 to 2 watts of solar per ah of battery. My question, is this based on battery rating (ie 215 AH) or is it based on useable amp hours(105)?

All replys are greatly appreciated.

Do 1.5 watts of solar per AH of battery and you should be fine.
(300 watts of solar for 215 AH of battery)

Generally, RVers tend to do the same things, use the same appliances, the same amount of power needs etc, in general in a wide-range statement...
200 watts minimum I suggest. 300 is much better. If you do use a lot of DC power, or if you use an inverter to run a TV or other things then you will be on the high side of power users as opposed to the one LED light users who uses one gallon of water a day and charges a phone or two...

How many panels can you fit on the roof?
Put more than you need as panels are cheap at 75 cents per watt or so, and adding one later might be difficult depending how you run the panels - if you run two in series then later want to (and only have room for) one, then this requires more than just extra wire.

Panels will put out 18 volts. It is the amperage that varies. Max amps at noon pointed directly into the sun; minimal later in the day when panel is flat on the roof and getting the sun at an angle...

Your calculation seems to rely on ideal, maximum solar. You will have sub-maximum sun most of the time.

I think "too much solar" and "too much battery" are in the same category as "too much truck". The only time anyone complains about it is when they're paying the bill to buy it... ;)