# Looking for simple 12v solar battery charger



## dablack (Jul 21, 2011)

Ok, we have a 1990 ford RV that we keep next to the house while we are building. It gives us somewhere to cool off in the summer and somewhere to eat meals. Well, everyone couple of weeks I have to move it so I can work on that side of the house. Also, once the house is done, I'm going to build a barn to keep the RV in. 

My problem is the engine battery in the RV keeps running down. If I remember to start the thing every week, it does fine, but it is sits there for a month, it runs down. I would REALLY like to have a simple solar charger. I've seen the battery tender ones with a 15 watt panel but it seems a little high for such a small panel. I was hoping for a little more power. 

Can I pick up a 100 watt panel and then pick up a cheap 12v charger that won't over charge the battery? I'm hoping maybe later if we get rid of the RV, I can use the charger for an electric gate or something like that. Maybe use it to solar power my kids power wheel jeep. 

thanks
Austin


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## jwal10 (Jun 5, 2010)

You must have a small drain in the system. May take more to overcome that. Install a battery cutoff switch to save the battery. Turn it on and start, off when done....James


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## dablack (Jul 21, 2011)

I wouldn't be surprised but everything does work as it is supposed to. Yes, a battery switch is a good idea but what about the charger? Surely, there is a simple 12v overcharge protection device I could put between a 100w panel and the battery. 

thanks
Austin


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## TnAndy (Sep 15, 2005)

You want a charge controller. For a single 100w 12v panel, you'll want something like a 8-10amp version.

Though I normally don't recommend cheap stuff, I did pick up one at Northern Tool.....I think it was about 20 bucks and is a 5 amp controller. VERY basic unit, has only a single "charge" light to tell you power is flowing. Also got a 30w panel there. Both of them I use on a 12v battery on my sawmill to keep it topped off, as I often go months between using it, and this way the battery is held at 100%. Been on it several months now, and so far, so good.

I have another small panel ( 8w ) that I use no controller, mounted to the roof of my garden shed that keeps my tiller battery topped off between uses.

IF you want to step up a bit in quality, features, and price, look here: http://www.solar-electric.com/stpwmchco.html


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## Nimrod (Jun 8, 2010)

To get a really cheap setup get a 50 watt panel and a Morningstar charge controller. http://www.wholesalesolar.com/products.folder/controller-folder/sunguard4.html This should be enough to keep your starting battery topped off. It will probably work for an electric gate that's only used a few times a day. 

For the kids battery operated vehicle you should use a 110 volt charger, overnight. I don't think anything short of an expensive solar set up can keep up with the demands of a kid.


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## SolarGary (Sep 8, 2005)

Hi,
If all you want to do is offset the batteries self discharge it does not take much. Something like this 
http://www.ebay.com/itm/4-5W-Multi-...758?pt=LH_DefaultDomain_0&hash=item3cd157666e

might do the job. The PV panel is small enough that no charge controller is needed. 

I use something similar on my tractor in the winter (when its hard to start), and it helps a lot by keeping the battery up to full charge. Its not going to charge a depleted battery in any reasonable time, but its enough to keep a charged battery from slowly losing charge as it sits.

Gary


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## Jim-mi (May 15, 2002)

It could be that the battery in question is well into it's "declining years" . . . .
Get--- at least--- what Solar Gary links to and give it a whirl . . . .


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## wy_white_wolf (Oct 14, 2004)

The main problem with using a 100w panel and a charge controller designed for deep cycle batteries is the voltage is wrong. The alternater in your RV holds the voltage at 13.6 to 13.8 volts. That is where starting batteries are designed to be charge to. A solar charge controller will take it between @14.1 and 14.5 volts depending on it's settings.

I don't know of any charge controller that could handle the 100w and are designed for starting batteries.

You are better off using a disconnect switch and a smaller panel designed only to maintain the battery. You may also want to check the battery as it may have been damage already with being discharged down so low so many times.

WWW


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## dablack (Jul 21, 2011)

Thanks guys. I could be wrong but I swear that the starter battery is a deap cycle marine type battery. I will take a look and get back.

Austin


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## plarkinjr (Oct 24, 2012)

Would something like this not work?

https://www.tractorsupply.com/webap...ory_rn=&top_category=&urlLangId=&cm_vc=-10005


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## Jim-mi (May 15, 2002)

Yes that would work well if:
there is still some reasonable life left in the battery.
and there is not a hidden / undiscovered load some where.

Those little panels work just fine for that tiny little trickle charge.....
But it would take forever and a day for that miliamp charge to bring a depleted battery back up.


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## jwal10 (Jun 5, 2010)

Me, just make sure the battery is good, use the disconnect and start the vehicle every month. Run for 20 minutes to lube the engine and get it to operating temps. May need a piece of cardboard in front of radiator....James


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## Jim-mi (May 15, 2002)

Who amongst us earthly peons has not been guilty, at one time or another, of pushing the lowly *car* battery beyond the point of no return. The cursing, cajoling, teeth gnashing, foot stomping, is as always to no avail....................

And then the sudden warm glow when a new battery. makes all our earthly problems mellow out. . . . .


Myself.....I had the trickle charger on the tractor battery for a very long time. Wouldn't do more than *click*--- oh--oh --new starter may be?????? ($375)
clean all terminals.........

Finally I put my DVM on the battery . . and hit the preheat (diesel) . . . oh s*** . . .
watched the voltage drop to 9.5 or so.......
. . . . .after a trip to NAPA........Every thing is working just fine with that new bat.

bottom line ---unloaded / at rest the bat voltage read ok......
But as soon as a load was put on it . .that bad cell caved under........


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## LincTex (Oct 11, 2010)

wy_white_wolf said:


> The alternater in your RV holds the voltage at 13.6 to 13.8 volts. That is where starting batteries are designed to be charge to. A solar charge controller will take it between @14.1 and 14.5 volts depending on it's settings.


I disagree; take a digital V-O-M and touch the leads to a car battery while the engine is running... all modern vehicles charge over the 14 volt range. 

13.6 volts would be from an alternator that is weak.


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