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24 Volt solar panels on small cabiin

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  • 24 Volt solar panels on small cabiin

    I just purchased 2-210watt 24 volt solar panels they are Solaria. I have a small remote cabin. We have been using 2 Harbor Freight 45 watt set up for 3 years and 2 12 volt deep cycle batteries from Interstate Battery. We use a small 6 volt radio and 2 cfl lights provided by Harbor Freight, a 700 Watt inverter to run 3 floor lamps with 60 watt LED lights that use about 9 watts each. For anything else ie: vacuum or large floor fan we run a generator. We only use the cabin about 1 weekend a month and the initial system was fine however we are going to use it more and plan to install a small 12 volt water pump.. We need to keep cost down and purchased the 2 solar panels used, we tested them at full power rating and they look new. We have bought 2 Duracell Ultra Batteries and plan to buy 2 more in the next week from the same vendor. The specs are 20AH cap, 230 with 120 minutes at 75 amps. Our charge controller is a pwm charge controller from Ebay. one of the $20.00 types. I still have questions as this system is 24 volts from solar panels to charge controller. So I believe I want 4-6 volt batteries to equal the 24 voltage coming down from panels to charge controller. Do I need 24 volt to 12 volt airplane style converter to power my small amount of 12 volt items still and a 24 vdc to 120 vac inverter for the lamps. We don't use a lot of power and expect this is going to be a big upgrade for us. So The question is does this sound right and any suggestions on which 24vdc to 24 12 vdc an 24vdc to 120vac should I buy.

  • #2
    Originally posted by Pmedic8 View Post
    The specs are 20AH cap, 230 with 120 minutes at 75 amps.
    Non sense. 20 AH = 20 AH. I think what you wanted to say is you have 2 x 6-volt 230 AH golf cart batteries. I know this because you said 75 amps x 2 hours = 150 AH which is a standard golf cart Peukert rating at the 2 hour discharge rate. 230 AH is the 20 hour discharge rate. So at C/2 the batteries are 150 AH and C/20 is 230 AH




    Originally posted by Pmedic8 View Post
    Our charge controller is a pwm charge controller from Ebay.
    Get rid of it that piece of Chi-Com junk, and get a real MPPT charge controller. At 410 watts you would need a 15 amp MPPT CC at 24 volt battery, or 30 amp @ 12 volt battery.

    Sounds like you have 12 volt gizmos which means you want to operate at 12 volt battery. You cannot use the PWM controller on a 12 volt system with 24 volt panels. You must use MPPT. If you tried you turn your 410 watt panels into 90 watts. If that is your intent, just use the Harbor Fright POS you had before and throw everything away you just bought.
    Last edited by Sunking; 05-21-2018, 02:35 PM.
    MSEE, PE

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    • #3
      When you call the panels "24V panels" if you look at the sticker on the back, what is the voltage @ Vmp ____ ?
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #4
        The panel has a rating plate Pmax 210, Vmp 33.81, Imp 6.21, Voc 41.59, Isc 7.13, Max fuse 15 amps. I am trying to get rid of the Harbor Freight stuff completely and switch to a real system although low power. What would you recommend for an MPPT controller for this system that is reasonably priced. I will have 4 6 volt C-20 golf cart batteries. To use this power I am assuming I should get a 24 volt to 120 volt inverter and a 24 volt to 12 volt inverter for my 12 volt lighting. We have a 4000 watt generator to power the big stuff. I do not see any increase in the system size for the future.

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        • #5
          If your stuff is already 12 volts stick with 12 volts. Wire the panels in series, no fuses required into a 30 Amp MPPT Controller out to your batteries wired 2S2P. You cannot have both 12 and 24 volts. If you insist on 24 volts, then you are going to have to buy a 24 to 12 volt converter which makes no fricking sense.
          MSEE, PE

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