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Old 12-13-2019, 07:08 PM   #1
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How many watts to keep batteries up?

Our rig gets stored away in a covered building that has no electrical, so my rooftop solar panels canít contribute to keeping my batteries charged. The View has two 12 volt coach batteries and thereís a Tik-L-Start to keep the chassis battery up.

I can set up a portable solar panel to maintain the batteries while in storage. It would get direct sunlight until about noon, then daylight for the rest of the day. No appliances or such need to be running.

Any estimate on what size solar panel I should consider? Thanks.

Warren and Debbie, Deep in The Heart of Texas
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Old 12-13-2019, 07:36 PM   #2
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You might be better off taking the batteries home and hook them to a trickle charger.
If you choose solar start with a 100 watt. As a trickle charger that should do. Remember battery abilities go down as temps go down.

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Old 12-14-2019, 08:59 AM   #3
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There's the amount of power the batteries need to make up for self discharge but another variable that you'd have to know is what other loads may be present drawing them down. You'd have to measure that, since there's no way anyone else could predict it.

Since you only have half a day of sun and unknown panel tilt you need "more" than if it were a panel in full sun.

All of that being said what I'd do is get more panel than you think you need, and incorporate a charge controller. Then you're covered for some less than optimum charging days and whatever phantom loads are present, rather than to try and critically size a directly connected panel for the insolation and loads you have.

Simpler would be to give them a full charge and disconnect but not sure if that's an option for what you're trying to do.

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Old 12-14-2019, 09:27 AM   #4
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I have 4 6v t105's and my 150 watt panel has no trouble keeping the batteries up when parked between trips if it is sunny everyday. More than a couple days of clouds and things start changing. It seems like my monitoring panel says I have a 3 or 4 amp (about 50 watts) parasitic draw when everything is off. Of course that includes the monitor itself.
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Old 12-14-2019, 09:40 AM   #5
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My coach came with a 85 watt solar panel from the factory and PO installed 2 more 125 watt panels so I have 335 watt total.

Even with this it will not keep up with the parasitic draw if I leave the salesman switch on but I can leave the battery disconnect switchs connected.

If you have battery disconnect switch a 100 watt panel should work, maybe less.
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Old 12-14-2019, 09:53 PM   #6
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When this question comes up, I suggest about a 100-130 watt solar panel, these are available in kit form with a solar controller, mounting brackets and 30-40 feet of cable for around $130 online on sites like Amazon. This may be overkill for part of the country that tends to get ample sunlight, like much of Texas, but given it only cost about 1/3 more than a panel half its size, it is cheap insurance in case of extended cloudy weather, poor mounting angle, etc.

See https://smile.amazon.com/ECO-WORTHY-.../dp/B07VJFXBTT or https://smile.amazon.com/HQST-Monocr...dp/B01I0HAKJA/
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Old 12-14-2019, 11:33 PM   #7
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Originally Posted by SeeTheUSA View Post
Any estimate on what size solar panel I should consider? Thanks.
I use one of these for each of my 12 v batteries on my sailboat in the PNW.


My MH has a 40 watt panel to maintain batteries. Since I am full time I have not tested it.
Kit & Rita
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Old 12-14-2019, 11:54 PM   #8
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Recognize there are some loads that are not disconnected. My rig draws about 300 ma so some math, .3x24hrs=7.2ah per day. So I need to replace that used power. Guess what a 100 watt solar panel will provide in 1 hour 7.2 amps but that is in a perfect world without any losses. Say you get 4 hours of really good sun and there is a 30% loss, so you get 20 ah of charge in one day. Basically this shows you a 100 watt panel is plenty of power.
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Old 12-15-2019, 12:13 AM   #9
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My rig is in storage with only a couple of rodent devices running.
A 5 watt panel seems to be keeping my 300AH battery bank in good condition.
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Old 12-17-2019, 03:16 PM   #10
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My TT has a battery disconnect circuit breaker. So no parasitic loads in storage. Just battery self discharge issues. My 10W panel is more than enough to bring the 2 size 31 AGMs up to full charge eventually. After that I tuck the panel out of direct sunlight.
This 10W solar maintainer panel does not have a controller. It has a blocking diode.

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