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Small off-grid system for 24v: freezer & laptop & lights - no inverter

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  • Small off-grid system for 24v: freezer & laptop & lights - no inverter

    Hello, this forum has been a great resource and help in the past and I hope it can be again.
    I'm planning to setup a off-grid solar panel system in next couple weeks, in my inventory:

    12 x Canada Solar CS6P-235 235 Watt 24 Volt, Vmp 29.8. Imp 7.9A, Voc 36.9 Isc 8.46A
    Outback MX60 CC
    SunDanzer DCF390 (Energy use : 800 Watt-hrs/day @ 32C, -12C Freezer (67 Amp-Hr @12V)

    Also I have ability to purchase these batteries locally: 6 volt(T-105)225Ah / 8 volt(T-875)170Ah / 12 volt(T-1275)150Ah.

    The end goal is to have a system using the minimum amount of panels (I have other plans for them) that is balanced and will reliably supply the freezer & small laptop with 24volt plug as well as some led lights.

    Currently I'm thinking along these lines:
    4 x T105 for 225AH configured for 24v
    2 x 235w panels in one string
    Outback MX60

    Could someone help with the wiring diagram design?



  • #2
    The panels that you mention are not "24 volt" panels, but they will work just fine wired in series, I beleive that these are 60 cell "grid tie type" panels, not 72 cell "24 volt" panels, no worries there, as better controllers such as the MX60 will be able to transform the voltage to the 24 volt battery.
    Batteries, I would choose the T-105 6 volt batteries in series. This will provide quite enough power for the freezer.
    Freezer.....well you picked the "Rolls Royce" of the freezers, that is the best that there is. But do note the maximum running voltage might be a bit too low for a 24 volt battery on equalization mode. Do Check the maximum running voltage, it might be 30.00 volts and some batteries equalize ar 32.00 volts, just turn off the freezer if you equalize at that high of voltage. I'm not sure of the max voltage on the Sundanzer, I have a less expensive referigerator similar to the Sundanzer and mine does not like voltage over 30.00.

    I do not have a decent drawing editor but wiring is simple, wire two panels in series and install a DC circuit breaker in the positive wire to the p.v. This is needed as the controller needs to initialize before applying solar input. Size of breaker 15 amps DC. Some controllers will be damaged by having solar input with no battery connection. Run 6 g.a. wire from the output of the MX-60 directly to the battery, through a DC rated breaker, it is very important that the controller is wired directly to the battery as it needs to "see" the battery, not the system voltage, use a breaker larger than the maximum charge current expected, for a 2 panel array 30 amp DC rated breaker would be good.

    DC systems are affected more by voltage drop so oversized wire is not a waste of money, I would use 10 g.a. THHN building wire for all except the charge controller output to the battery where 6 g.a. THHN building wire is needed for low voltage drop. Do not be tempted to use a common feed wires to the breakers for the freezer and the charge controller as the freezer turning on and off will upset the voltage that the charge controller will "see"
    Breaker suggestion, A MidNite Big Baby breaker box, A MidNite Solar MNPV-30 breaker for the charge controller, a MidNite Solar MNPV-15 breaker for the p.v. input to the c.c. And a MidNite Solar MNPV-10 amp breaker for the Sundanzer. The MidNite Baby Box will work as well but the Big Baby has a bit more room inside which makes it a bit easier to wire up.

    AC breakers are less expensive but do not work well on DC and may arc and cause a fire , use DC rated breakers....

    System startup, turn on battery breaker to Charge controller first, let controller initialize then turn on solar breaker
    System shutdown, turn off solar, wain a minute for charge to be transferred to battery, then turn off breaker to battery

    This is important as some charge controllers will be damaged by having power input with no where for it to go.

    You are choosing great components for your system it should be completely trouble free.

    If you have any questions, please do feel free to post and someone will be willing to help out....
    david

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    • #3
      Thank you David for informative reply.

      I checked the specs, the Sundanzer will operate 24V 21--31.5V

      Follow up question:
      - If placing the panels 100ft away from battery bank (maximum solar exposed location is 80ft away from the house). Would I need to add a 3rd panel to the string to account for voltage drop?

      Comment


      • #4
        Even if you have a total voltage drop of 2 volts on the p.v. voltage drop that will be only 16 watts lost, I do not think that you will need another panel to cover that, by comparison my Grape Solar GS-5 referigerators. , two of them draw only about 500 watt hours a day and will run just fine on my standby system with only 200 watts of panel, PWM controller and 100 a.h. AGM battery that I use when equalizing my FLA main banks. So I do not see that you will have any issues with your proposed setup.

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        • #5
          Is there a way I can keep this system running with once a year maintenance?

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          • #6
            Originally posted by tverdok View Post
            Is there a way I can keep this system running with once a year maintenance?
            I would say NO. You need to look in on it at least weekly, to see if any issues are developing, If you cant spend the time to manage the system, that's why you pay the power company - to manage it on their end. AGM has little actual maintenance but it still needs to be visually seen and some energy logs compared to make sure all is good.
            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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            • #7
              Update:
              I've come into possession of UB-8D AGM battery, it's 12volt @ 250AH.
              If I make the system 12 volt could I use this battery for the freezer or would it be too small?
              I realize I'll have to spend more on breakers & wiring if I go 12 volt.

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