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Old 05-09-2021, 02:40 PM   #1
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Solar Battery Maintainers

I've used a 1.5 watt solar battery maintainer on a couple of vehicles and it has worked well. I'm now faced with a situation where my coach is parked and there is no power available. I'm looking at getting a 7.5 watt solar maintainer to keep the chassis and house batteries charged. I have a couple of questions:
1. Is 7.5 watts sufficient to keep two chassis batteries and two house batteries charged? I think it is since 1.5 watts worked on one battery.


2. How do I keep all four batteries connected all of the time. Will the emergency start switch do this or are they connected all the time unless the voltage drops too low on the chassis batteries?

Any help is appreciated.
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Old 05-09-2021, 03:46 PM   #2
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7.5 watts of power is really going to be a struggle to keep 4 batteries up to charge. It may work if there is no load of any type and the batteries are fully charged to begin with but I would not trust it. I do not know how you can keep the chassis and the house all connected either. Perhaps get a charger for each set. You can always charge up the batteries and completely disconnect them and they will hold a charge for a long time.
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Old 05-09-2021, 05:59 PM   #3
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I don't think it would work considering all the phantom loads you'd have to cover. You'd have to look around at how many items you have that are always on and go from there. Then consider solar is only making rated power for a short time on good days.
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Old 05-09-2021, 07:51 PM   #4
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Will this be stored a long time? For less than six months you could disconnect and the batteries will ride through. If they're left connected you'd need a panel big enough to keep up with any parasitic drain present which is likely a lot more than 7.5W.

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Old 05-09-2021, 08:01 PM   #5
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Quote:
Originally Posted by Mark_K5LXP View Post
Will this be stored a long time? For less than six months you could disconnect and the batteries will ride through. If they're left connected you'd need a panel big enough to keep up with any parasitic drain present which is likely a lot more than 7.5W.

Mark B.
Albuquerque, NM
It will be stored for quite a while, but not exactly sure how long yet. I'll be close by so it's not like it will be ignored. Right now the plan is until mid September and then again over the winter. I guess I'm going to have to look at the phantom loads.
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Old 05-10-2021, 05:57 AM   #6
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Disconnecting has the least risk. Nothing can happen that will cause the batteries to go flat and be damaged. Solar can work, but there's still some risk there since stuff is energized in the RV and it's additional equipment to buy, set up and maintain. Small risk but an expensive discovery when it happens. And it does happen, there are plenty of "house/chassis battery died what happened?" posts here on the forums. In my experience it's a lot less effort to lift a battery cable and reconnect a couple times a year than dork around setting up a solar system.

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Old 05-10-2021, 06:45 AM   #7
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Just for comparison I have 325 watt of solar. If I do not turn my house disconnect "saleman switch" off (this only sheds some of the parasitic load in house), and we have a period of cloudy weather, my batteries will slowly be depleted. If I turn the saleman switch off the 325 watt seem to keep up, barely. The only way I can keep my batteries up is to shut off the battery disconnect.



My coach came with an 85 solar panel, which I assume was calculated to be enough to maintain the batteries with the disconnect switch off. If I were going to go through the trouble of installed a solar panel for keeping the batteries up I'd rather go big versus small.
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Old 05-10-2021, 08:13 AM   #8
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Quote:
Originally Posted by arcaguy View Post
I've used a 1.5 watt solar battery maintainer on a couple of vehicles and it has worked well. I'm now faced with a situation where my coach is parked and there is no power available. I'm looking at getting a 7.5 watt solar maintainer to keep the chassis and house batteries charged. I have a couple of questions:
1. Is 7.5 watts sufficient to keep two chassis batteries and two house batteries charged? I think it is since 1.5 watts worked on one battery.


2. How do I keep all four batteries connected all of the time. Will the emergency start switch do this or are they connected all the time unless the voltage drops too low on the chassis batteries?

Any help is appreciated.
1) In Lansing, not likely. I used a 20W panel in SoCal for about a year to keep 2 chassis batteries charged, with the chassis battery switch in the off position. You may need a 100W panel to get sufficient charging during a Michigan winter. And youíll need to keep it free of snow. A 100W panel will charge at ~6A in full sun, a 7.5W panel will charge at ~.45A.

2) Jumper cables. I donít know how your battery isolation/inter-tie/charging system is set up.

Disconnecting the batteries and/or running the generator for a couple of hours every month to charge the batteries is a good, but time consuming solution. If you choose a solar option, be sure to check the battery voltage with the solar charger disconnected, every week or two until youíve determined that the system is working.
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Old 05-10-2021, 09:03 AM   #9
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Can generators run where you'll have it? Can an auto start be added to your generator? They do need to run, it might be something to consider.
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Old 05-10-2021, 03:09 PM   #10
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I do have auto start but I'm thinking I don't want it running when I'm not around. I do know I have to run the genny once a month so I'm thinking my best bet might be to just disconnect the batteries and start the genny a couple of times a month like I'm supposed to.
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Old 05-21-2021, 11:00 PM   #11
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I have a 7 watt propped up in the windshield and it keeps the house batteries charged just fine. I have the salesman switch off/disconnect. I got two 1.5 watt in a buy one get one deal just to try them out. I used the suction cups and stuck one out on the bumper and it gets lots of sun. It's the "free" one so if it walks away no big deal. But it won't keep the chassis battery charged. I may hook the second 1.5 up (in parallel) to see if 3 watts does it.

Oh, and I advise getting a charge controller (or two). Inexpensive protection against over charging.

I'm just an amateur, scratching the surface, to keep the batteries up while in storage and I can't get there as often as I'd like.

No off-grid or boondocking for me - yet.

Good luck.
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