Solar Powered Battery Charger

[Rich S]

Hello;

After much perusing of the archives I thought about purchasing a solar battery charger for our trip to Yellow Pine next week. Needless to say there is a myriad of them out there. I have read about folks using the 2 watt versions that stick on to the windows and found several at reasonable pricing. However,.. after some discussions with some of the suppliers it appears that they are all recommending 5 watts or more to replace lost voltage. It seems that the 2 watt versions are for maintaining a battery in storage or parked for a long time to prevent drain. They won't replace the volts reduced due to use as in a RV or trailer. In order to replace voltage that you've used by your lights, fans, etc. 5 or more watts are required.

So,..... my question then is: Is this consistent with what those of you who are using them are finding? If you have drained your battery significantly are you in need of a 5 watt or stronger charger to get it back up to snuff while on a trip?

I like the convenience afforded by the ability to plug it into the 12v receptacle and to be able to place it in a window, but my idea was to have one that I could plug in during the day to RE-CHARGE the battery while I was out and about or while not in use.

Thanks,
Rich

[Victor Benz]

Rich;

It's actually a simple calculation anyone can do, but it is unique for each trailer. One needs to think of the battery as a bank, the usage as withdrawls, and the solar panel charging as deposits.

This worksheet appeared in the April 1998 Highways, the Good Sam journal.



Here is a hypothetical workup with relatively low daily power usage, giving a required array size of 165 watts.



Note that the penalty for a lie-flat array on top of the trailer is a whooping 44 watts of array size! I have assumed 7 hours of daily average sunshine, which is relatively typical for my area, Stony Plain, Alberta.

Note that if all the power one used was for 2 incandescent fixtures two hours a night, the array would still have to be 15 watts to keep the battery fully charged.

[Alistair Camelford]

Rich, I've completed a 10000 mile coast to coast trip using a 15 watt panel that I clip to the gravel guard when I boondock. Its main function is to power a CPAP machine (I have sleep apnea) and I had planned several boondocking sites. I converted the interior to five LED pods which draw little juice. We used a fluorescent camp lantern for Scrabble and Cribbage.Put the frig on propane, and made out OK. By the third night I had to hook up the tug and run the Toyota for half an hour to top up, but other than that we were fine. Like Victor said...it is matching power needs to power generation. I didn't want a roof array (and the resultant mounting holes) so this is fine. I might add a second 15 watter next year, but this is good for now. Good luck...Alistair

[Gina D.]

2 watt or 5, it's not enough to do anything but keep it topped off. You will need at least 15 to charge, and even then, you will need to be conservative in use.

The best way to make solar the most efficient is NOT to add more and more power, but to set yourself up to USE less. And I don't mean you have to go without, or work more than needed to perform simple tasks, or resort to using the old car camping stuff. I am in my trailer right now with a tv going, the computer and almost ALL my lights on. The heater is on low as well. My Soda is cold, my water flows freely and I am looking forward to LOTS of coffee in the am.. without worry of draining the battery.

I am charging with 45 watts for the house battery. It was overcast all day. When the sun went down, I was sitting at 13.2 volts. All this stuff went on, now I am at 12.8 after 2 1/2 hours.

I am working on a web page that has all my systems on it, when it is done, I will post a link. It's really astounding what you can do with solar if you just look at usage a little differently.

A 15 watter should do OK to get an evenings charge. If you want to get more, the beauty of solar is it is "add onable".

[jack maloney]

UHauls were all made with 15W roof panels, for the specific purpose of keeping the battery topped up. They knew what they were doing! In 20,000 miles use, we've done zero battery maintenance.

[Terry G.]

UHauls were all made with 15W roof panels, for the specific purpose of keeping the battery topped up. They knew what they were doing! In 20,000 miles use, we've done zero battery maintenance.

and where does one go to mesure it to see if it is in fact charging

[Per Walthinsen]

Terry:

Xantrex Link 10 or an equivalent battery monitor.