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Energy storage for off-grid

Discussion in 'Off-Roading & Trails' started by DaMaDo, Aug 29, 2018.

  1. Aug 29, 2018 at 10:16 AM
    #1
    DaMaDo

    DaMaDo [OP] Well-Known Member

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    So I have been contemplating three options for a solar-chargeable system on my rig.

    I want to be able to go off-grid with a 50 ARB fridge, cpap, and other (very) small electronics for one to two weeks at a time.

    These are my current options:
    solar.jpg

    Option 1 requires a lot of time and work, but I learn all the components well and I can easily upgrade.

    Option 2 is all in one, simple, but not upgradeable in the future.

    Option 3 is a bit of a mix since I can chain batteries to the older Yeti 400 if I find I need more juice. I can also swap the battery to the car battery in case of emergency.

    Any thoughts? Anything I'm missing?
     
  2. Aug 29, 2018 at 12:55 PM
    #2
    jbrandt

    jbrandt Well-Known Member

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    I assume you've gone through all the amp-hour calcs for the cpap and fridge so you're pretty confident a 200w panel is enough...

    What type of cpap machine do you plan to use? There are some models out there that are specific for camping, small, lightweight, battery powered. You loose a LOT of power when you convert from 12v (your solar/battery) to 110v for the cpap machine.

    https://www.soundsleephealth.com/blog/the-best-portable-cpap-machines-for-camping-z1-vs-transcend

    For perspective, I don't even plan to have a 200w panel on my 17' RV trailer. 100w is plenty for me, but I also have a LP fridge and no cpap, but I do have water pumps, lights, 2.5amp fans, etc...

    I would say that you could do it for a LOT less than the costs you've laid out here. You can get 2 100w RENOGY panels for like $250 off Amazon. The charge controller I use has a 30amp capacity (more than enough for 200watts) and cost $15. ~110amp-hr lead-acid RV batteries cost ~$100. Another $50 in some bulk wire and $200 for a 400watt sine wave inverter, and you're all set.

    https://www.amazon.com/Renogy-RNG-1...d=1535571833&sr=1-5&keywords=200w+solar+panel
    https://www.amazon.com/Controller-B...-spons&keywords=solar+charge+controller&psc=1
     
    tacoma16 likes this.
  3. Aug 29, 2018 at 12:59 PM
    #3
    tacoma16

    tacoma16 Well-Known Member

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    Similiar to how I did mine. Have a 100w solar panel mentioned above tied into a second battery. Then a cheap inverter, solar controller and battery. I do have the blue ml acr which charges both batteries as I am driving.

    In good sun I can keep the auxiliary battery charged to 14.6 volts.

    Run a Whytner fridge, lights, water pump



    Think I am into my setup for a lot less than your costs in cnd mulla as well.
     
  4. Aug 31, 2018 at 6:15 PM
    #4
    DaMaDo

    DaMaDo [OP] Well-Known Member

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    Thanks guys, I decided to build my own and will go with renogy panels as you pointed out. That makes a lot more sense than the Goal Zero briefcase.

    I also found a 100AH AGM battery for just $169 on Amazon. I'll go with that rather than the $276 55AH Optima.

    I'll look into the blue seas switch you mention to charge the battery while the car is on.

    The Phillips Dreamstation cpap, without the humidifier or heated hose, only uses .12A at 12V. I have the cigarette lighter cable for it and used my multimeter to get the amperage using a 12V battery.

    Supposedly the ARB fridge uses an average of 2amps, but that greatly depends on set temp and ambient, so I'm not sure what it will actually draw. I'll test it when I get it and since I'm making my own, I can expand as I need. I can use any extra juice for LED lights, etc.
     
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  5. Sep 6, 2018 at 3:26 PM
    #5
    jbrandt

    jbrandt Well-Known Member

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    Oh man, that cpap is far better than the 120v ones I was basing my calcs off of.

    According to the link below, ARB says their 50qt only draws an "intermittent" 1.35 amps, and maxes out at 2.3 amps. Assume a max amp draw all the time for your calcs (will very likely be less)

    http://store.arbusa.com/ARB-Fridge-Freezer-50-Qt-10800472-P3626.aspx

    ARB Fridge: 2.3A x 12v x 24 hrs = 660 W-hrs
    Your CPAP: .12A x 12v x 8 hrs = 11.5 W-hrs
    Assume maybe 2 amps for everything else(?): 2A x 12v x 8 hrs = 192 W-hrs

    Total: = <900 W-hrs

    Now for power storage (12v), you only need 75 A-hrs to fullfill your 24 hr needs.

    A single 100W panel will probably produce 800-1000 W-hrs depending on how many hours of sunlight.

    So you could *probably* do it with a 100W panel, but with power loss, inefficiency, and not-so-sunny days, the 200w should be more than enough. And the 100A-hr battery should be plenty as well.

    As for charging, I think all you'd really need is a setup not unlike a trailer 12v power wire. I have a fused hot wire direct form my battery to my trailer harness (per the harness instructions) and a ground wire. While it's not a pure isolated battery setup, it's pretty simple and cheap.

    I would think you could get a simple switch like this to ensure it is isolated when you're not driving so you don't accidentally drain the primary battery. Then flip the switch when driving to allow the truck to charge the other battery. You just have to remember to flip the switch.
    https://www.amazon.com/dp/B07DDGLRBD/ref=sspa_dk_hqp_detail_aax_0?psc=1
     

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