Second MPPT Controller

54d1854d18 Solar Expert Posts: 78 ✭✭✭

I've been thinking of expanding my solar, my present controller is maxed

out, so I've been thinking of adding a second controller and solar panel.

What would the best configuration for settings between the 2 controllers?

I kinda think that one should be set a bit lower than the other for purpose of

switching between charge modes.

Has anyone else attempted this?




  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin

    The big issue is to have separate cables from the charge controller (through a circuit breaker) to the battery bus for each controller (star wiring--Central point to each controller).

    If you share (daisy chain) from the battery to controller 1 to controller 2, the two can get a bit confused from the increased voltage drop and "electrical noise" between the two controllers.

    Generally, people just set both controllers to the same settings (voltage setpoints, absorb times, etc.). They will not be "in sync" (they will transition from bulk to absorb to float at different times)--But that is really not an issue. Each controller will make its own decision on charging--but are close enough that it is not an issue.

    The one thing you might program different (depending on batteries and actual size of your arrays), is program one to never equalize, and the other to equalize once per month. If your controller is at least 2.5% to 5.0% rate of charge minimum, then a single controller can do the equalization (you do not need 10%+ rate of charge to equalize).

    Many folks like manual EQ anyways--They want to be there and monitor the bank voltage/gassing/temperature etc. when the batteries are equalized.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 54d1854d18 Solar Expert Posts: 78 ✭✭✭

    Thanks for the heads up BB, I will be going from the new controller independent of

    the existing setup, and as for equalizing, I also prefer to be there to monitor.

    I just wasn't sure about the settings.



  • mcgivormcgivor Solar Expert Posts: 3,549 ✭✭✭✭✭✭
    edited March 2019 #4

    Totally in agreement with being present during an EQ, the only time auto EQ should be implemented is in a remote application, even then it's taking chances, my opinion naturally.

    The settings for the second controller could be set at slightly lower voltage than the main controller, this would gaurentee it would cease charging before the main one has completed its cycle, avoiding any conflicts, at this stage demand is usually at very low current values anyway, so no loss in the big picture.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭

    Network the controllers! Much easier. Yet another reason to stay with the same brand.....

    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • 54d1854d18 Solar Expert Posts: 78 ✭✭✭

    Mcgivor, that is pretty much what I was thinking, this is not a very large system,

    just planning to put an electric fridge on it, so I'm adding to allow for that.

    Dave Angelini, my present controller does not allow for networking, and is discontinued,

    but works flawlessly, simply adding another controller is the least cost for sure.



  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭

    I posted that with the intent of helping others and maybe you also. Good Luck!

    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

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