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gotsmart's avatar
gotsmart
Explorer
Aug 21, 2015

Removable Solar battery maintainer for chassis battery

I'm currently working at an RV park and the parasitic draw in my E450 has already drained the chassis battery once. I put a battery charger on the chassis battery, charged it up and it came back to life. So I bought a 5W solar charger for the purpose of maintaining the charge in the battery. I wanted to hang it in a window to keep it out of the weather and from those discount shop at other people's RV sites. Here is my solution. The pictures are clickable so you can view a larger image and zoom in on it.

Go Power! GP-SF-5 SUNfilm 5 Watt Solar Panel

The windows in my Cruise America 28R have top and bottom wooden rails on which the curtains slide. This mod is specific to RVs with similar window shade setups. With this setup I can easily remove the solar panel before driving away. I can also move the panel to a window on the drivers side when that side is facing south.

What makes this work is the fact the the cigarette lighter on my dashboard is live at all times. This lets the solar panel backfeed power into the chassis battery. One should unplug the solar panel before starting the MH's engine. I don't know if it will damage the solar panel, but I'm not going to find out.

The solar panel's cord easily reaches the cigarette lighter port on my E450's dashboard. The robe hooks are hanging on the top rail. There are 4 holes in the frame of the solar panel for mounting purposes. The mirror clips are screwed to the back of the panel - with the hook facing the window. I used 2 pieces of 12 inch chain to distribute the weight better across the robe hooks.

Material list for mounting (all from Home Depot):
Over-the-Door Single Robe Hook in White (2 Per Pack)
6 in. L x 4 in. W Fixed-Mount Mirror Mounting Clips (4-Pack)
(clips are actually 1 5/8 in. L x 1/2 in. W)
#8-32 x 1 in. Phillips-Slotted Pan-Head Machine Screws (4-Pack)
#8-32 Coarse Stainless Steel Nylon Lock Nut (4 per Pack)
#8 Stainless Steel Flat Washer (12-Pack)
#100 x 1 ft. Black Decorator Chain (QTY 2 @ 12 inches each)




7 Replies

  • Almot's avatar
    Almot
    Explorer III
    Jan 10, 2016
    4-6 months is called a "storage". In storage you do need a maintainer, hardly any news.

    2.5W is enough for maintenance without any loads (like in my old truck where I disconnect the battery).

    5W "might" be enough with some loads like computer and radio standby, or it might not. They come a bit cheaper though: 5W.

    Without any loads (like when you disconnect the battery) with 5W I would be worried about overcharging, but not much. These are very simple chargers, with night diode but without charge control.

    I keep it on the roof or on the hood, tied with a shoelace to something. There is enough flex in the door rubber trim to put the cable through and close the door (if plugged into cig socket). Or - clip it to battery and run cable under the hood. Or put it on the dash, but there will be more shading there. If plugged into cig socket, make sure that it's On, because in some cars it's Off when you turn the ignition Off.

    Vertical placement on the window is about same good in winter as flat on the hood, as the optimal angle in winter is close to 45 deg. In summer it should better be horizontal.
  • gotsmart's avatar
    gotsmart
    Explorer
    Jan 09, 2016
    **UPDATE**

    This afternoon at 3:00 PM (Pacific Time) I unplugged the solar panel from the cigarette lighter socket (very important step) and started the engine. This is the first time the engine has been started since I plugged in the solar panel. I stood on the ground outside the cab and turn the key in the ignition. It started in less than 5 seconds, with no hesitation at all. I will run the engine for about an hour - to get it hot enough to cook any water/condensation out of it.

    Recap: before I plugged on the solar panel on Aug 20, 2015 I charged the chassis battery with a really good (read "old") Sears charger. Only after the chassis battery was fully charged did I plug in the solar panel. The intent was that the panel would generate enough power to negate the parasitic draw from any active systems in the chassis (clock in the radio, onboard computer, etc). I've opened a cab door to access items - probably 2 dozen times since plugging in the panel.

    Conclusion: It appears to me that the solar panel is doing everything I want from it. All that I can say is that it seems to be working for me. YMMV
  • Vulcan_Rider's avatar
    Vulcan_Rider
    Explorer
    Aug 21, 2015
    gotsmart wrote:
    Try letting it set 4, 5, 6 months at a time without starting the engine.

    2)I really don't think that 5 watts is enough to do any actual good.
    It's enough.


    Letting it sit for 6 months unattended is not good for ANY kind of vehicle.....so that is no surprise.

    5 watts at 12 volts comes out to 4 tenths of an amp and that is maximum. Most of the time it probably will be much less.

    And the battery itself looses some charge just sitting there; it's called "self discharge" and that gets worse as it gets older.

    I hope it works out for you but my 50 years in the electronic industry leads me to believe otherwise. I personally would feel much more comfortable with an actual battery tender......or a 20 watt panel with an actual controller.

    Please let us know how this works out for you.
  • gotsmart's avatar
    gotsmart
    Explorer
    Aug 21, 2015
    Vulcan Rider wrote:
    gotsmart wrote:
    I'm currently working at an RV park and the parasitic draw in my E450 has already drained the chassis battery once.


    Two comments:
    1) Why does this occur ? My E450 will sit for weeks and weeks and still be good. AFAIK the only parasitic drain is the memory for the radio and some engine computers.
    Try letting it set 4, 5, 6 months at a time without starting the engine. I'm a bit lazy in this regard during the dry season. You know the battery is dying when the cab's dome light won't come on or the power door lock switch doesn't lock the doors.

    2)I really don't think that 5 watts is enough to do any actual good.
    It's enough. Read the product reviews in the Amazon link. I wanted a unit that is capable of negating the parasitic draw. The customer reviews indicate the 5W panel works fine for this purpose. If I had wanted more I would have bought a Battery Tender. The other reason for going with this solar panel is that it is not taking any amps away from the pedestal.

    I start mine every 30 days or so and let it run for 15-30 minutes.
    This charges both sets of batteries.....if I remember to throw the battery disconnect switch for the coach.
    My MH has no battery disconnect switches. It's plugged into a pedestal, so charging the coach battery is not a problem. I don't bother starting the engines (includes the generator) during the summer dry season here. I do exercise the engines in the winter rainy season about every month and a half - to cook the moisture out of them from the super-high humidity.
  • Vulcan_Rider's avatar
    Vulcan_Rider
    Explorer
    Aug 21, 2015
    gotsmart wrote:
    I'm currently working at an RV park and the parasitic draw in my E450 has already drained the chassis battery once.


    Two comments:
    1) Why does this occur ? My E450 will sit for weeks and weeks and still be good. AFAIK the only parasitic drain is the memory for the radio and some engine computers.

    2)I really don't think that 5 watts is enough to do any actual good.

    I start mine every 30 days or so and let it run for 15-30 minutes.
    This charges both sets of batteries.....if I remember to throw the battery disconnect switch for the coach.
  • gotsmart's avatar
    gotsmart
    Explorer
    Aug 21, 2015
    VTR wrote:
    How well is it working for you? What wattage solar panel? Is this to keep your coach battery topped? I have a TT but still interested in the post.

    It is a 5 watt panel. For details click on the very 1st link in the post. Yes, its purpose is to keep the chassis battery topped off.

    My coach battery is maintained by the converter, but it does not maintain the chassis (truck) battery.
  • VTR's avatar
    VTR
    Explorer
    Aug 21, 2015
    How well is it working for you? What wattage solar panel? Is this to keep your coach battery topped? I have a TT but still interested in the post.

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