What size solar panel to charge batteries while in storage?

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rkwfxd

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Aug 13, 2006
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What size solar panel do I need to charge 2 12-volt batteries while in storage? 

I am not looking to run off solar, just keep my batteries in good condition for 4-6 weeks while it is in storage between trips.  I live in So Cal with usually nice sunny weather.

I have a 2001 Coachman that has only one house battery with an Onam 4.0.  Most of our camping is dry camping (3-4 days) and the house battery just does not hold up.  I have replaced it at least three if not four times.  I have put the biggest (deep cycle) one in I can find but it still does not last.      I put the battery on a charger for a couple of days before we go out and I have verified that it is getting charged by the alternator while driving and the generator when it is running.  The last few trips I have just plugged into a Honda EU2000 generator and let it run all day and the battery just makes it through the night.  I do not have a TV or other electrical appliances.  All the drain comes from refer, water pump, lights, sensors.

I have measured and shopped and I just barely have enough room to mount two 12v Optima batteries side by side under my step.  I am hoping the extra battery, with a solar trickle charge, will keep things strong enough so that my charge indicator shows something other than "low" the entire time I am in the desert and the batteries maintain enough juice to start my generator without having to push the "emergency start" button to get juice form the motor battery.  My only other option seems to be to pull out the wleder and die grinder and build a bigger battery box for some 6-volts. 
 

Gary RV_Wizard

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One battery, probably only a group 24 size, isn't much for several days of bondocking. Definitely increase the number of batteries if you can and of course use the largest size you can. You may be able to find a case size that is taller rather than longer or wider, if you have height to spare.

I wouldn't other with the expensive Optimas - they have no more amp-hours than any other battery of the same case size.

If you are detroying batteries, you may need a better quality converter/charger.  I suspect your 2001 Coachman has the usual Magetek piece of crap that has  a poor rate of charge and boils the liquid out besides.  A Progressive Dynamics or Iota converter/charger with Smart Charger opton will do a better/faster job of charging and save your batteries as  well.

Are you having a problem with the battery discharging in storage?  Have you investigated to see what is consuming power when you think that everything is turned off? Do you have a battery disconnect switch?  How about adding a switch right at the battery terminal - you can get a simple knife switch disconnect for around $10-12.

As for solar panels,  if you don't go with the disconnect idea, I would suggest a basic 20-40 watt panel to keep the battery(s) topped up while sitting in storage. 20 watts yields about 1.5 amps of charging, equivalent to a plug-in trickle charger. 40 watts is double that. Make sure the charge circuit includes a regulator so you don't overcharge.
 

rkwfxd

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Aug 13, 2006
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*****I wouldn't other with the expensive Optimas - they have no more amp-hours than any other battery of the same case size.

The only real reason I was going with the optimas was their size, I need a battery no more than 10" long.

*****If you are detroying batteries, you may need a better quality converter/charger.? I suspect your 2001 Coachman has the usual Magetek piece of crap that has? a poor rate of charge and boils the liquid out besides.? A Progressive Dynamics or Iota converter/charger with Smart Charger opton will do a better/faster job of charging and save your batteries as? well.

I have no idea what kind of converter/charger I have, in fact, I can't even locate it within the coach.  I have a fuse panel below the frig, would it be behind that?

*****Are you having a problem with the battery discharging in storage?? Have you investigated to see what is consuming power when you think that everything is turned off? Do you have a battery disconnect switch?? How about adding a switch right at the battery terminal - you can get a simple knife switch disconnect for around $10-12.

The coach has a battery disconnect switch but playing with it yeasterday I discovered even with the switch in the "storage" mode the radio is still drawing current.  The radio will not turn on and gives no indication that it is drawing current UNLESS you take the faceplate off.  Then you can see a small LED blinking.  Once I physically disconnected the battery, the light stopped blinking.  I believe this has been part of my problem.

*As for solar panels,? if you don't go with the disconnect idea, I would suggest a basic 20-40 watt panel to keep the battery(s) topped up while sitting in storage. 20 watts yields about 1.5 amps of charging, equivalent to a plug-in trickle charger. 40 watts is double that. Make sure the charge circuit includes a regulator so you don't overcharge.

hanks
 

Bob Zambenini

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Mar 4, 2005
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Orange County California
rkwfxd said:
What size solar panel do I need to charge 2 12-volt batteries while in storage? 

I am not looking to run off solar, just keep my batteries in good condition for 4-6 weeks while it is in storage between trips.  I live in So Cal with usually nice sunny weather.

I have a 2001 Coachman that has only one house battery with an Onam 4.0.  Most of our camping is dry camping (3-4 days) and the house battery just does not hold up.  I have replaced it at least three if not four times.  I have put the biggest (deep cycle) one in I can find but it still does not last.      I put the battery on a charger for a couple of days before we go out and I have verified that it is getting charged by the alternator while driving and the generator when it is running.  The last few trips I have just plugged into a Honda EU2000 generator and let it run all day and the battery just makes it through the night.  I do not have a TV or other electrical appliances.  All the drain comes from refer, water pump, lights, sensors.

I also live and store in Southern California. I have a 99 Dutch Star Diesel and have coped with this problem. I have a small, believe 15w solar panel about 15 inches square. It charges my chassis batteries but if we get a lot of cloudy days, it does not keep up the batteries. I have checked and the only thing on chassis batteries is the engine computer but it draws  down the chassis batteries.

My house batteries have a cutoff switch and I just isolate them and have never had a problem as they hold 12.2 or more for weeks.

With all that said, sounds like you have a different setup than most I know about. My generator starts off the chassis batteries and will not run unless they are charged, even after it starts.

The best solution is to have cutoff switches. I can't get one on my chassis batteries due to space so I just disconnect the grounds on both batteries and let them sit. That is better than having them drain and having this small solar panel that does not do the trick. In our climate they will hold charge for a long time sitting disconnected.

Sounds like your  one house battery is not enough. When dry camping if I run my generator for an hour in morning and hour in evening I have plenty of power for TV, Furnace and some microwave use. I have never changed my house batteries and have never equalized them in 6 years and they are fine for my needs.

So I would look at getting more house battery capability and cutoff switches for storage. Also, solar panel addition just to maintain batteries in storage is expensive compared to cutoff switches or a wrench to disconnect the grounds.

Bob
 

rkwfxd

Member
Joined
Aug 13, 2006
Posts
5
Bob Zambenini said:
I also live and store in Southern California. I have a 99 Dutch Star Diesel and have coped with this problem.

My house batteries have a cutoff switch and I just isolate them and have never had a problem as they hold 12.2 or more for weeks.

The best solution is to have cutoff switches. I can't get one on my chassis batteries due to space so I just disconnect the grounds on both batteries and let them sit.

So I would look at getting more house battery capability and cutoff switches for storage. Also, solar panel addition just to maintain batteries in storage is expensive compared to cutoff switches or a wrench to disconnect the grounds.

Bob

Sounds like my first step is to add a battery by purchasing two new ones at the same time.

How many house batteries do you have?

My house battery is currently connected to the cables with wingnuts so it is a very simple thing for me to lift the step and remove one or both cables.

I think the answer to this next question is yes, but....When I install dual batteries (in parallel) is it OK to leave them connected to each  other while in storage?
 

Gary RV_Wizard

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At our Silver Springs FL home
I have no idea what kind of converter/charger I have, in fact, I can't even locate it within the coach.  I have a fuse panel below the frig, would it be behind that?

The converter/charger will hum most of the time when power is on. Some rigs have it combined with the AC power panel (where the breakers are) and others have a separate unit, usually located somewhere near the batteries.  It might be near the 12V fuses too. I'm not familiar with Coachman motorhomes, so don't know whatheir usual practice is.
 

Carl L

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west Los Angeles
I think the answer to this next question is yes, but....When I install dual batteries (in parallel) is it OK to leave them connected to each  other while in storage?

The answer is yes.  In fact, the two batteries should be idenitical in all respects including age.  They will age as unit when connected either series for the 6 V units and parallel for the 12 V units.

If you wish to disconnect the batteries from potential loads, install a switch between the positive pole of the battery and the distribution board in the trailer.  I use a marine switch myself, a 2 pole Perko.
 

rkwfxd

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Joined
Aug 13, 2006
Posts
5
Thank you gentlemen, this has been very helpful.? I have done some additional research and found that two group 34-96 batteries at Kragen will fit side by side in the space I have for about the same cost as one Optima.

Hmm.? From an auto parts store!

Be absolutely sure that they are deep cycle units and neither starting batteries nor marine 'dual purpose'.? ?If the units advertize any starting capability at all land or water, look for something else.
 

Ron

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Jan 29, 2005
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Home is where we park it
I would also suggest when you go to buy the deep cycle battery that you inquire who the manufacturer of the battery is.  If it is made by Excide I would look elsewhere.  Interstate is a good battery.
 

King

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Jan 30, 2006
Posts
354
Location
MA
I have owned boats for about 45 years.  In my experience, you just be sure the battery(s) are fully charged (with a hygrometer) and disconnect the leads.  A battery in good condition will maintain a good charge for up to six months.  Make a sketch to verify where the wires go.
Art
 

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