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Keeping battery charged via external solar plug

Grandby Shell Solar

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#1 RicoPolo

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Posted 31 August 2019 - 08:34 PM

Hi all,

 

I have a 2018 Grandby Shell, with factory solar set up but no shore power plug.  When I store the camper in the garage, the solar panel obviously can't keep the battery charged and I'm too absent minded to remember to disconnect the battery cables every time I put it away.  I've forgot twice now, and both times the battery was drained.  :(

 

I can look for a shore power kit, drill holes in the side of the camper, figure out how to tie it into the existing solar system, etc.  But why not use the existing solar plug that's meant to plug in a portable additional solar panel?  Maybe some kind of DC power supply that I can plug into an outlet in the garage?  I have a pigtail for the external solar plug, I'm just not sure exactly what needs to be done.

 

I don't think the power supply needs to be 100 watts, since it's basically just keeping the battery charged with no load on the system.

 

Has this been done already, with a good how-to posted somewhere?  I didn't find anything like this using the search function here.

 

Is this a really bad idea somehow?  Looking forward to some feedback.  :)

 

Rich

 


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#2 Wandering Sagebrush

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Posted 31 August 2019 - 10:22 PM

Does the shell not have a battery on/off switch? I don’t recall any parasitic load when we had our Grandby and the switch was off.

If not, that would be a good addition.

A quality battery maintainer is another option.
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#3 Frank_in_AZ

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Posted 01 September 2019 - 12:14 AM

I mounted a solar panel on the back of my garage and ran the wire inside.

I plug it in when I park the camper inside.

It's been working fine for 2 years.


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#4 JHanson

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Posted 01 September 2019 - 01:01 AM

If your battery is draining within a couple months with nothing on in the camper you have another issue. An AGM battery should hold voltage for many months with no drain on it. Even a standard deep-cycle lead-acid battery should hold voltage for several months.

 

With that said, you should be able to hook up a 12-volt source to the inlet, with a couple of caveats. You'd need a charge controller to prevent overcharging, unless you're prepared to monitor the state of charge very carefully. If the input runs through the controller already there for the roof-mounted panels, you'd be fine.

 

You could also install a rotary switch to disconnect the battery(s)—but see my first point.


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#5 larryqp

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Posted 01 September 2019 - 02:24 AM

Couldn't you mount a small 120v battery maintainer/trickle charger in the camper connected to your batteries and run an extension cord  from your garage into the camper and plug it in. I thought the battery maintainers were designed to not overcharge batteries. Your batteries would be charged fully, I suspect after driving and the charger would just maintain them


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#6 rando

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Posted 01 September 2019 - 02:35 AM

Which solar charge controller do you have?  If you have an MPPT charge controller, then I don't see a problem using a DC power supply into the solar panel connector, in fact Victron even states that their charge controllers can work that way.  Something like this would allow you to use the full power of your charge controller when necessary:

https://www.amazon.c...e/dp/B07RMTNT9B


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#7 RicoPolo

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Posted 01 September 2019 - 01:47 PM

Thanks for the replies everyone.

 

I do have the cutoff switch that FWC includes in the solar package, but that's what I occasionally forget to check to make sure it's closed.  :) 

 

I'd really like to get a portable solar panel to supplement the one on the camper's roof, but using that in the garage isn't practical in my case.  I have a large quonset and I keep the camper on a dolly I built, so I can roll it around to different parts of the garage depending on what I'm working on in there.

 

I'm pretty sure the outside connection for the solar system in the camper is already connected to the solar controller, so Rando's suggestion looks perfect.  I was hoping someone had done this and had wiring diagrams or something similar posted where I could follow along.  I've heard that the solar wiring is "backwards" from standard wiring, or something like that?


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#8 rando

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Posted 01 September 2019 - 02:21 PM

The outside plug is in parallel with the panel on the roof, so park in the sun and measure the voltage on the outside plug - it will tell you which is plus and minus.   

 

Which charge controller do you have?  This should work with an MPPT controller, but I am not sure I would try it with a PWM controller.


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