paralelling charge controllers

so riddle me this. If I have a mx60 and a morningstar mppt and the battery outputs are in paralelle how does one unit know not to think that the battery voltage it sees is the charge from the other one instead of the battery bank voltage??? I might not have put that right but I think you get my does this work??? thanks mark


  • BB.BB. Posts: 28,083Super Moderators, Administrators admin
    Re: paralelling charge controllers

    The voltage error generally comes from large currents going through small wires... So, that is why it is recommended that you create a "battery bus" which is a very low resistance path directly to the battery / battery bank.

    Instead of, for example, running a separate light weight cable from the battery to one charge then some more distance to a second charger. In this case, the second charger would be seeing the voltage "increase" caused by the current supplied by both chargers--and possibly under charge the battery.

    For larger charge controllers (and computer power supplies), you will find that they have a separate battery voltage lead (like a remote volt meter). You can tie these directly to the battery bus--and no matter how much current/voltage drop you get in the cable from the charge controller to the battery, you will be measuring the "true battery voltage" rather than battery voltage + wiring drop. But, unfortunately, I don't see these remote sense leads on the more popular solar charge controllers--so your best bet is to use large diameter cable and short runs between the charge controller and the battery bus connections.

    And, since we are talking about accurately charging a battery--you will want to get a charge controller than has a remote battery temperature sensor (sometimes called a BTS). That too ensures that the battery / bank is being properly charged.

    The battery voltage itself also changes with charge and discharging currents--but the charge controllers are programmed to take into account (the best they can) the charge voltage and current to ensure that the batteries are quickly and safely charged.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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