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Thread: Solar, ARB Fridge, Sears Platinum PM-1 - Group Size 31M QUESTIONS

  1. #1
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    Default Solar, ARB Fridge, Sears Platinum PM-1 - Group Size 31M QUESTIONS

    I looked, but am unable to really find an answer. So here goes:

    I am running a single Sears group 31 Platinum battery and ARB 50qt fridge. I pretty much move everyday but there are times when i may sit for 1-2 days and enjoy the scenery. My question is will a 27 or 30 watt solar panel compensate for the draw of the fridge? Or, will it compensate enough for me to not worry about the truck starting in 2 days? I carry a jump pack, but would rather not draw down the battery that much. I set my fridge to turn off when the battery gets low, but again, don't want to risk things and i like my food and beverages to remain nice and cold. The battery has 1150 CCA and 205 minutes of reserve capacity and i believe the fridge draws (on average) .87 ah. So, will a 27/30 watt solar panel help or will it be a waste?


    I did the "math" and please let me know if this is correct:

    27w panel/12vdc = 2.25 x .7 (70% effecency) =1.575 x 6 hours of sunlight per day = 9.45amp hours placed back in the battery.


    Cheers,
    Sean
    Last edited by SoCal_80; 02-22-2011 at 05:04 PM.
    '93 Toyota Land Cruiser FZj80
    SoCal Teardrops 459 Krawler
    Tread Lightly! Tread Trainer

  2. #2
    Join Date
    Mar 2009
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    I went through the same thought process when I installed a fridge and solar combination. Some things to think about:

    A friend just did a test on his ARB fridge to figure out the actual average power draw. With a 50F temperature differential, the fridge draws about 1.4A on average. The group 31 Diehard Platinum has a 100AH capacity, but if you are using it as your starting battery you probably never want to go below 50% charge, so budget about 50Ah. So if you are using your fridge with average temps in the mid 80s where the fridge is, you can easily run the fridge for 36 hours and still have plenty of reserve to start the car. Longer if it is cooler out. A 30W solar panel will realistically give you about 10 - 15 Ah per day depending on where you are, how you have mounted, time of year etc. You will extend your ability to sty put by about 12 hours with the solar panel. If you went up to say a 60W solar panel (20 - 30 Ah per day) you are getting close to the point where you can stay put indefinitely.

    I have an 80W solar panel and my fridge draws slightly more power (1.7A at 50F differential) , and I am almost at the point where I can sit indefinitely.





    Quote Originally Posted by SoCal_80 View Post
    I looked, but am unable to really find an answer. So here goes:

    I am running a single Sears group 31 Platinum battery and ARB 50qt fridge. I pretty much move everyday but there are times when i may sit for 1-2 days and enjoy the scenery. My question is will a 27 or 30 watt solar panel compensate for the draw of the fridge? Or, will it compensate enough for me to not worry about the truck starting in 2 days? I carry a jump pack, but would rather not draw down the battery that much. I set my fridge to turn off when the battery gets low, but again, don't want to risk things and i like my food and beverages to remain nice and cold. The battery has 1150 CCA and 205 minutes of reserve capacity and i believe the fridge draws (on average) .87 ah. So, will a 27/30 watt solar panel help or will it be a waste?

    Cheers,
    Sean

  3. #3
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    Thank you Rando. So it appears a 27-30watt panel will not really do much for me. So it looks like it need to look at the very least a 60watt panel if not 80 to get me where i need to be. I was hoping to get away cheap. oh well. now to the rigid vs. foldable debate....

    Thanks again!
    '93 Toyota Land Cruiser FZj80
    SoCal Teardrops 459 Krawler
    Tread Lightly! Tread Trainer

  4. #4
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    In sunny Southern California you should get about 6.5 kwh/square meter/day, or approximately the equivalent of 6.5 hours per day of full sun. Given a 1.5A average load (to include lights in the evening and some inefficiency etc), you will need 36Ah per day to have no net loss of power. That would translate into a 80W panel and an MPPT charge controller or a 100W panel with a traditional charge controller.

    As for flexible vs rigid - unless you really don't have a place to mount a rigid panel, go with rigid. Rigid beats flexible on W/$ and W/m2, usually by a factor of 2 or more. This is just my opinion - but I prefer to have a system that is semi-permanently mounted to a roof rack or the like. That way it is always charging your battery whenever you park in the sun, it is not something else you have to remember to set up. If I want to I can unmount mine from the rack and position for maximum sun, but most to the time it just sits on my rack, charging my battery. It is also a lot less likely to be stolen if it is mounted to your vehicle.

  5. #5
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    I recommend a 60 watt panel, that is what Martyn suggested I get when I bought mine from him to keep my batteries topped off running the ARB fridge when base camping with the rig.
    My rig will often sit for five days or more without running.

  6. #6
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    Quote Originally Posted by SoCal_80 View Post
    I did the "math" and please let me know if this is correct:

    27w panel/12vdc = 2.25 x .7 (70% effecency) =1.575 x 6 hours of sunlight per day = 9.45amp hours placed back in the battery.
    Yes, the math is correct.

    In reality though, the voltage would be more like 13v (or more) and for a flat mount panel you might only get 5 hours of good sun. Try it with those numbers plugged into the formula.
    ...
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  7. #7
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    Thank you everyone! So, it looks like i need at least a 60w panel and should probably stick with a rigid panel. I am thinking i can place the panel in my RTT while in travel and set it out when i arrive. The folding/roll up panel concept sounds great to me, but given the additional cost and lower efficiency, i guess i need to stick with the rigid.
    '93 Toyota Land Cruiser FZj80
    SoCal Teardrops 459 Krawler
    Tread Lightly! Tread Trainer

  8. #8
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    Arizona Territories
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    Hmmm, lots of cyphering, lots of assumptions.

    Why not park it in the driveway, run the fridge, check batt volts every six hours, see when it dies?

    I can go 24 hrs without a problem, 36 hrs and its dead. Engel 40 which AFAIK is a little more miserly than the ARB.

  9. #9
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    Quote Originally Posted by SoCal_80 View Post
    I was hoping to get away cheap. oh well.
    How much was the 27 watt panel going to cost you and how cheap you trying to go?

    Looks like you're less that 1hr from this place and could avoid shipping costs if you wanted:
    75 watt panel for $162

    80 watt panel for $175

  10. #10
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    Jan 2008
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    Phoenix, AZ
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    So I'm new to this whole idea, but my question is if you go with one of the rigid panels either permanently mounted or set out when you need it what do you need to get the juice from the panel to the battery?
    Heidi - KF7CKI
    1985 Vanagon GL Diesel Convert

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