# simple solar battery charger



## trapperJim (Jan 24, 2008)

I see a zillion solar battery chargers on the market, available in many different wattages. I have a cabin in NH and one in NY and will be bouncing back and forth between the two quite a bit this year. These cabins are remote so I'll be running a few things on battery power, mostly task lighting, a laptop occasionally and possibly a portable DC fridge like the Engle. 

If you were doing this, what would be your choice for a mobile setup to keep my battery up? I see 5 watt, 10 watt, 15 watt solar chargers and so on. Would I be better off to just by a 50 watt panel and build a portable suitcase type carrier for it? What are your thoughts on the subject? What would you do?

Thanks


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## 12vman (Feb 17, 2004)

Some of those frridges pull ~4 amps. Your laptop .. About the same..

How long do ya figure these things will run? With lighting, you'll need more than 50 watts..


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## trapperJim (Jan 24, 2008)

The cabins have gas lights and kerosene lanterns, but for task such as cooking and doing dishes there are CFL's over the sink and stove. These are run only when doing these task. The laptop is run to watch a movie at night for entertainment, but kept in hibernation mode the rest of the time. I don't have the portable fridge yet but am considering one. The reason for this post is to get an idea of what is a feasible method of keeping a battery (or batteries) charged for my needs without running a generator all the time.


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## wy_white_wolf (Oct 14, 2004)

trapperJim said:


> The cabins have gas lights and kerosene lanterns, but for task such as cooking and doing dishes there are CFL's over the sink and stove. These are run only when doing these task. The laptop is run to watch a movie at night for entertainment, but kept in hibernation mode the rest of the time. I don't have the portable fridge yet but am considering one. The reason for this post is to get an idea of what is a feasible method of keeping a battery (or batteries) charged for my needs without running a generator all the time.


Without clearly defining and calculating your usage no one will be able to give you a solid answer.

That said for a 3 season system you could go with the basic calculation of 1 watt of panel for every amphour of battery capacity at 12VDC with the understanding that you plan on discharging no more than 25% on any givin day.

So if you have a 100AH battery you will want about a 100watt panel and have your daily usage of no more than 25AH. The reason I say this is a 3 season system is winter solar insolation is too variable to guess a system. Even early spring and late fall that may be short. Much of Upper NY has less than 1 hour average in the winter and you would need at least 500watts of panels than to supply the same power. Problem then becomes that may be too high of a charge rate for said battery.

WWW


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## MichaelK! (Oct 22, 2010)

Jim, are you thinking of carrying in batteries or will they be dedicated batteries that stay at your cabins?

If the former, you're limited by the size of what you can carry back and forth, and also limited by what number of amps your panel can put out during a day. I sometimes use a portable jump-starting battery pack that has an inverter for 120V power. Just powering a single 7 watt CFL, the battery will be drained in 3-4 hours of use.

The latter stratege might work better for you. If you had dedicated batteries that you leave at the cabin, they can sit there charging all week long with a relatively small panel. When you show up on the weekend, you start depleting the batteries faster than they can charge in a day. However, since you won't be back for a week, they'll have that much time to reach full charge again.

This system will be significantly more expensive because you'll need bigger batteries, a controller, and a panel installation you leave in place. But, in the long run, I think you'll be more satisfied with it.


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## trapperJim (Jan 24, 2008)

Well what I was hopig for was to carry a battery or pair of batteries back and forth. Presently I have one deep cycle battery that I haul back and forth. I run the CFL's for the task of cooking and such and generally watch a movie on the laptop after dark. I have been using the trolling motor battery from my boat and throwing it on the charger when I return home. So far this has worked slick and I been doing this since last fall. Sometimes the battery goes through several days of usage without a charge. The cabins are wired with just a few outlets running on one single feed in a loop with no breaker panel. I have a 2' cord with a male plug on each end and one end goes in my inverter and the other in a wall outlet and the cabins are powered up and so far no issues. What I was hoping for was to have a simple method of charging the batteries on site without the use of a generator but it's sounding that it's not a simple fix. 

Since I am already getting several days of lights and laptop out of one battery charge, couldn't I have one battery charging by the sun while one is in use and switch them as needed? How big of a panel does it take to charge a battery if the battery is not being used? Are all these 5, 10 and 15 watt solar charges you see on the market inadequate for charging batteries? If so why do they offer them?

The lights and laptop are already being powered nicely and I'm plenty satisfied with the performance of my boat battery. The fridge idea? who knows if that'll come into play. I'd just like a simple solution for charging a battery on site in a remote location. I don't mind spending money to get what I need, just don't want to waste any by going in the wrong direction.


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## Jim-mi (May 15, 2002)

Not sure what you have in mind for a "fridge" but if it is one of those thermal jobs that uses a constant 4 amps . .then do the math . . . your battery is going to be depleted in a big hurry.

Those who go with the "15 watt" kits will find out in a big hurry that they have very little energy put in to a battery . . so the battery is constantly run down . . very short bat life.........


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## wy_white_wolf (Oct 14, 2004)

trapperJim said:


> ..... How big of a panel does it take to charge a battery if the battery is not being used? Are all these 5, 10 and 15 watt solar charges you see on the market inadequate for charging batteries? If so why do they offer them?.....


Depends on how far it's been discharged and how fast you want it charged up. How big is that battery charger your using now? 10amp? 

10 amp times 12vdc = 120watts How long does it take to charge it when you get back?

The 5 to 15 watt panels are just to maintain a battery at it's current level to prevent one from self discharging while it sits not being used.


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## trapperJim (Jan 24, 2008)

wy_white_wolf said:


> Depends on how far it's been discharged and how fast you want it charged up.
> 
> 10 amp times 12vdc = 120watts How long does it take to charge it when you get back?
> 
> The 5 to 15 watt panels are just to maintain a battery at it's current level to prevent one from self discharging while it sits not being used.


Now THAT right there helps clarifying things. Those of us that are babystepping into this solar world can easily get lost in the jargon of amps, watts, kilowatts, KWH







when we are not used to dealing with all that. This is like a whole new language to learn. 

Thanks for your help. From the looks of things, at this present time anyway, I'm thinking my easiest fix for the refridgeration issue is a small gas fridge at both cabins and continue on with my electrical system as is, but maybe work in a decent size panel into the game for charging purposes. 

One more question regarding battery drain, If I'm out trolling in my boat and I have a digital monitor displaying my battery condition, At what point (in the voltage displayed) would you consider a safe "stopping point" to stop draining and start charging without damaging the life of the battery?

Thanks again.


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## fantasymaker (Aug 28, 2005)

Wouldn't it be better to have the solar charging tied to the batteries ALL the time so they run down less and have a shallower discharge cycle?


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