Charge Controller Sizing / Panel / Array wiring

Hi All - 

I am new to the 12V side of solar for my RV, cant stand the generator. So what I have so far is four (4) 275w panels ( 38.6 Voc, 31.50 Vmp, 8.74 Ipm), a 2000w Inverter charger, and three (3) 150ah / 12V AGM telecom batteries ( I have the ability to get more should I want)  and of course all of the necessary wiring etc ... My last piece of the puzzle is a charge controller and how to wire up the panels. 

I have been looking towards the Midnite Solar charge controllers as I think @ 12v I'm pushing into high wattage territory. I have outback controllers in the house and like them but am thinking the Midnite Solar may fit this use case better.  

Are there any charge controllers I am overlooking ? 

Does anyone have any thoughts ? Insight would be greatly appreciated. 


  • EstragonEstragon Registered Users Posts: 1,810 ✭✭✭✭
    I have my 12v system (4x250w panels) wired as 2 series strings of 2 into a classic 150 which works well.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • PhotowhitPhotowhit Solar Expert Posts: 4,335 ✭✭✭✭
    At 4 x 275watt panels, you seam to be close to maxing out any charge controller at 12 volts, the math may seem odd. 

    1100 watts of panels will only put out about 75% of their panel rating in normal every day conditions. If you look for a spec sheet .pdf for your panels look for the Normal Operating Cell Temperature Values, NOCT values. These will be roughly 75% of the name plate value. Also even if you allow your battery to go down to 50% state of charge, or about 12 volts,  you need a voltage about 10% higher than that to effectively charge the battery bank.

    So the math looks more like 1100 watts x 75% to arrive at NOCT value = 825 watts / 13 volts = @63.5 amps

    While I like the Midnite classic and use them at home, they do have internal fans to cool the electronics. For a Camper, I'd suggest a Morning Star TS 60 MPPT. It has no internal fan and used large cooling fins instead.  You might be slightly over paneled for it, but that is not bad at all.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • SupraLanceSupraLance Registered Users Posts: 13 ✭✭
    Don't forget that you can use two charge controllers, with two panels on each, into the same battery bank.  In addition to saving you money in some cases, this also allows you to tilt the panels differently or better account for partial shading.
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