Solar charger ?

[Bukiman]

I am looking to buy a portable solar battery charger for my 21 ft class c for boondocking, I need it to keep batteries charged for furnace fan at night and use it for charging phones exc. what watt panel would I need, I only have one aux battery.
Thx

[bfisher003]

We have two batteries and currently use a Renogy 100 watt suitcase charger. It outputs a bit over 6 amps in good sun and has a built in multi-stage charge controller. While I plan to add more solar this one has worked very well for us.

[okmunky]

Depending on nighttime temperatures, one battery might not be enough to get you thru the night if you run the furnace. I added a propane fueled catalytic heater this winter that is wonderful. Your refrigerator also needs 12 volt power, even on propane mode.

The rule of thumb is 1 watt of solar for each amp hour of battery capacity. I have 2 golf cart batteries. They are 6 volt connected parallel to put out 12 volts. They have 207 amp hours each, but make a total of 207 at 12 volts. I have 372 watts of solar panels because I run a humidifier all day. If I could find more space for batteries I'd add 2 more.

[bfisher003]

I think you meant you installed the two 6 volt batteries in series, didn’t you?

[okmunky]

Originally Posted by bfisher003

I think you meant you installed the two 6 volt batteries in series, didn’t you?

Yep, I know how to do it better than how to explain it. thanks for the correction.

[ktn1966]

If your need is to charge batteries 100w will be just fine. You will have to make sure you change the panel with the suns position throughout the day to optimize your charge. I watched a guy pit or his panel one morning, left for the day and was surprised that or didn't charge very well. My last trailer had 200w and was more than enough for limited use. If you decide to start running an inverter for television, kitchen appliances and other energy hogs then you might want to upgrade to 200w.

[Dan McMartin]

Originally Posted by okmunky

Depending on nighttime temperatures, one battery might not be enough to get you thru the night if you run the furnace. I added a propane fueled catalytic heater this winter that is wonderful. Your refrigerator also needs 12 volt power, even on propane mode.

The rule of thumb is 1 watt of solar for each amp hour of battery capacity. I have 2 golf cart batteries. They are 6 volt connected parallel to put out 12 volts. They have 207 amp hours each, but make a total of 207 at 12 volts. I have 372 watts of solar panels because I run a humidifier all day. If I could find more space for batteries I'd add 2 more.

That's about right (save the parallel part ). You'd be right in the neighborhood with 100 watts but the furnace might use more power than your battery can provide. More batteries would be my first purchase. You'll nearly triple you battery capacity with two 6 volt golf cart batteries giving you a buffer and they'll last longer too.

Then look into solar. Since you're running such a small system, adding more watts than you need isn't going to break the bank. Going with 300 -400 watts will give you plenty of charging capacity and will help charge the batteries on cloudy days, winter days and when you use more power than usual. Plus when the sun is out, you can use the excess to charge devices, use the laptop, etc.

[okmunky]

Originally Posted by ktn1966

If you decide to start running an inverter for television, kitchen appliances and other energy hogs then you might want to upgrade to 200w.

But first increase your battery capacity. It's not wise to mix battery types and ages. The old battery will draw down the new one. I'd suggest two 6 volt golf cart batteries.

[Soppy]

A 100 watt solar panel will give you between 30 -40 amp hrs of charge per sunny day. If your furnace draws 10 amps , you should be able to run it for 3 hrs. With the other electrical requirements , you would be taking more power out of your battery than you can replace in a day. I would consider at least 200 - 300 watts of solar. That way you will have enough charging power even if you get some clouds during the day.

[Bukiman]

Do all units come with something to keep them from over charging or do u add that later ?

[tmw188]

Originally Posted by Bukiman

Do all units come with something to keep them from over charging or do u add that later ?

If you by it as a kit it should come with a controller.

[ktn1966]

Make sure when you do buy it comes with the controller. I did meet a person who bought a solar panel, it was off some ones house, he thought he got a deal but could not figure out how it was supposed to work.

If you have question there is a website, http://www.marxrv.com/12volt/12volt.htm that I found very helpful when setting up my system. Best of luck.

[talk2cpu]

I have 2 12 volt (different size and different age) and 160 watts of portable. We can go 2 nights with the furnace, CPAP (no heat), and all other required drain. One full day of sunshine will fully charge the batteries, often by mid afternoon. Then we can watch a movie or use the sewing machine until no more sunshine. Our holding tanks fill up in the desert forcing us to move, not the lack of battery power. Any less sunshine will have a significant effect on the charge. So planning size to work with less than full sun could be a good idea.

[ByeTheWay]

Here are some links that may come in handy: Solar:
RV Electrical
https://handybobsolar.wordpress.com/