Step Down DC Voltage?

I have 14 Kyodera panels wired in series, with Vmpp of 372.4 volts and Impp of 7.9 amps, feeding a grid-tied Solectria PVI3000. I also have a Magnum MS4448PAE inverter/charger. I  have  this set to work as AC-coupled with the Solectria (through a sub-panel) if the grid  goes down, but with  mixed results. The Solectria will trip offline with any reduction  in load (I don't have a diversion load set up).

I would like to step the voltage from the panels down to an amount directly useable by the Magnum and run the system off-grid when commercial power is out, if this is possible. The  Magnum can take up to 68 volts, so it would  have  to be by a factor of six, giving Vmpp of about 62 and Impp of less than 48.

Is  there equipment  available that would do  such a thing? Thanks for help.

Buck
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Comments

  • EstragonEstragon Registered Users Posts: 1,620 ✭✭✭✭
    I have read that dc/dc converters can fail in a way that exposes the low voltage gear on the stepped down side to be exposed to the high voltage supply. As such, it would be safer to just wire panels in a series/parallel configuration for voltage and current appropriate to the gear.

    The inverter/charger is designed to hook up to a 48v battery bank though, not to solar panels directly.

    Others may know more about your charge controller and be able to help with the tripping problem.
    Off-grid.  
    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
  • BB.BB. Super Moderators Posts: 26,872 admin
    edited August 10 #3
    Not cheap, but there are high voltage DC MPPT controller out there now:

    Morningstar TriStar 600 Volt 60 Amp MPPT Solar Charge Controller
    Schneider Electric Conext XW MPPT 80 Amp 600VDC Solar Charge Controller

    There might be others--But these are the two I am aware of.

    I would suggest that any sort of DC to DC buck converter (solar panel to GT inverter) is going to be a difficult item to configure into your array/system. It would be more fool proof to install a DC transfer switch and pick GT Inverter or Solar MPPT charge controller.

    The other choice would be to pick a new DC to AC Inverter that supports GT inverters on its AC output (usually will take excess AC power to charge battery bank, then shift AC 60 Hz +/- more than 1.0 Hz to knock the GT off line for 5 minutes).

    Which brings up the question--I am not sure if the Magnum supports GT inverters on the output--But if it does (by frequency dithering), then that is how it would work--Batteries are full, shift frequency and knock GT inverter off line for 5 minutes, repeat until battery bank is discharged and/or AC loads exceed GT inverter output.

    -Bill

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