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Very tricky Solar-Module Disconnecting Problem

  1. May 4, 2015 #1
    My non-ee boss gave me a design assignment I'm not sure is physically possible. I work at a solar panel manufacturing company.

    He wants me to essentially add a device to the mc4 connectors between modules which would allow disconnecting each module in a string from one another. He wants this added to our modules for safety reasons for fire fighters and installers. He wants it to be possible to achieve this from a switch down by the inverter, without the use of wifi/bluetooth and without using any more wires or any use of complex power electronics!

    Seems as though relays wouldn't be possible, could there be some sort of AC fuse I could use? send the signal on the DC wires and pop the fuse? The problem is is that they are connected in series, so there would need to be some form of delay so the furthest from the AC signal generator would pop first and so on down the string... My boss doesn't want to hear "this is not possible" but I'm not sure it is with the constraints provided... any advice would be greatly appreciated!

    Edit: Here is a one line diagram http://imgur.com/a4WYyXh
     
  2. jcsd
  3. May 4, 2015 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    You could use latching relays (so they don't draw power except when they are swtiched). It would take 2 extra wires to each relay, though. You could just use Cat-5 twisted pairs to run to the relays, and gather each pair down at the control panel to switch them On/Off...
     
  4. May 4, 2015 #3

    rbelli1

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    Gold Member

    What kind of cost constraints do you have for this project?

    You could add a modem to each module. This would likely require a large inductor to isolate each panel from the bus as well as the modem device.
    http://www.ti.com/lit/an/sboa130a/sboa130a.pdf
    This TI device with some modification could work. The line coupling and filter networks would need to be redesigned. Various current and voltage sensors would also be available to monitor the string.

    Another idea would be to use some 555 timers to make pulse detectors. If the correct frequency pulses are seen then the panel is switched on. If the pulses are not detected then they would go offline. Any break in the line would indicate to the modules down the line that they should shut off. Disabling the signal generator would break the string completely. This idea would also probably need the inductors.

    BoB
     
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