MMPT 80-600 charger fault codes over and under charging

I have a pair xantrex mmpt 80-600 with a hybrid inverter first four months it worked flawlessly now I nave one MMPT that has constant fault code of over voltage and under voltage it wont reset itself and stays off. The solar company takes months to come out and they each time just change out the cat five cables and restart. It will fail in just a couple days again same codes. any ideas what would cause this its a 48 volt flooded system. I seem to know more that the tech they send out. I have two arrays one goes to the grid and the other goes to dc circuit breakers that split that array in half and split the load to each solar charger so not only am in not charging with one charger it appears half of my array is not selling as well. The installers seem as afraid of this monster as I am.


  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: MMPT 80-600 charger fault codes over and under charging

    You cannot parallel two MPPT inputs off the same array, even if you separate them by circuit breakers. The two MPPT processes will eventually compete with each other in trying to scan the PV output and one will pull the DC voltage below what the other is expecting at the time, producing an error signal that will turn that one off.

    As a test, open one of the two CC breakers and see if the other CC works properly. Switch the breaker positions and try the other one, resetting if necessary.
    My guess is that the underlying problem is the competition between the two CCs.
    The one array that "goes to the grid" is connected to what, since I do not think that the Xantrex has a GTI function independent of the battery input?

    You need to show us a detailed diagram of the connections between your two arrays and the two Xantrex boxes.

    Ideally, one array should go to one box and the other array to the other with no cross connections. Or if pointed in different directions, half of each array (not wired to other half) should go in parallel to one Xantrex box.
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MMPT 80-600 charger fault codes over and under charging

    What Inetdog said is spot on.

    Your do seem a bit unclear on the configuration. When charge controllers are used arrays connect to them, they connect to batteries, batteries connect to inverter, inverter connects to loads and/or grid.

    A single 80 Amp controller can take about 5kW of PV on a 48 Volt system.
    This is more than enough to charge the minimum 600 Amp hours of 48 Volt batteries required for an XW 6048 inverter (for example).

    I have no idea why you got landed with two $1,200 charge controllers. Can you provide us with more equipment details? It sounds as though this system was not well-thought-out.