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Son_of_Norway's avatar
Son_of_Norway
Explorer
Jun 16, 2019

Use a solar controller as a DC to DC charger?

I have been thinking about installing a DC to DC charger to properly charge my coach batteries from my alternator while driving. I have a dual-output alternator that delivers a constant voltage of about 14.4 V to the coach batteries. The DC to DC chargers I see are pretty expensive. I had the idea, why not just install a properly-sized solar controller, maybe about 30 amps, for the job. Is there something that I don't understand about this or will a solar controller work? Thanks for your advice.
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 16, 2019
    wopachop wrote:
    Fun topic i like learning here
    Let's hope the OP does too.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jun 16, 2019
    wopachop,

    The alternator and "brains" see the starter battery. When it is full (which happens quickly) very little charging happens.
  • wopachop's avatar
    wopachop
    Explorer
    Jun 16, 2019
    Fun topic i like learning here. Isnt the limitations wire size and amp output? How many amps would you guys expect he could get to the house batteries assuming he had proper wire gauge?

    I think with a tow behind setup isnt it only around 2 amps back to the trailer plug? That is due to wire size correct, not the alternator output?
  • twodownzero's avatar
    twodownzero
    Explorer
    Jun 16, 2019
    If you're going to spend money on a solar controller, why not put on a few panels? My moderate battery bank is full within a few hours of the sun coming up. Why make it complicated?
  • MrWizard's avatar
    MrWizard
    Moderator
    Jun 16, 2019
    all solar controllers 'buck' the voltage that is reduce the input from somewhere above 15+ even 12v panels have an open circuit voltage 21+

    no solar controller i have read the specs on will increase voltage on the output side
    MPPT will take higher voltage and make more amps at battery charging voltage
    but that is still less voltage than what is on the input side

    you need DC to DC voltage BOOST, output volts higher than input volts

    that doesnt come cheap
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 16, 2019
    An MPPT controller is a buck converter so output is lower in voltage than input.

    We had some threads about using controllers with other than solar panels as input such as a DC power supply, and it does work in some cases (not all) I forget the details. Idea was to take advantage of the controller's adjustable settings ISTR.
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 16, 2019
    Not sure if the 14.4 is enough to properly operate a controller, never seen a minimum voltage spec.

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