Programmable voltage controlled switches

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tallgirl
tallgirl Solar Expert Posts: 413 ✭✭
in Advanced Solar Electric Technical Forum #1
Greets,

I'm starting on a design for a 2kW AC coupled array. I'm looking for a voltage controlled switch to control the AC feed in from a 2kW ACPV array to a twin stack of GVFX 3648. The plan is to aggregate the output of the OutBacks and the 2kW ACPV array before it goes to the load center. The ACPV array will be disconnected at both high voltage (over voltage for batteries) and low voltage (suspected battery voltage sense wire loss).

The ideal switch will have programmable limits and be either Modbus (RS-485) accessible or Ethernet.

Am I asking for too much?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: Programmable voltage controlled switches

    The "easy" way (from what little I know) would be a to use a DC Breaker with a remote trip coil or even use a ganged breaker (main breaker rated for array current, second ganged breaker rated at 1/2 amp connected with a control line to the 12-48 volt battery bank to trip the main breaker). Basically just the DC GFI breaker assembly.

    A DC rated breaker with remote trip may be difficult to find.

    You might also look at the Midnite "Bird House" compatible remote off combiner boxes (PDF manual)... I am not sure how they work, but it is very possible that they would do all the UL/NEC side of the high voltage/high power controls you need--And you just have to figure out the "bird house" (emergency remote disconnect) side of the equation for your battery bank protection requirements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #3
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    Re: Programmable voltage controlled switches

    Outbacks should have a programmable AUX that can act on low/high voltage. Why no to use these?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Re: Programmable voltage controlled switches

    I think Julie is looking for a "fail safe" design (that integrates into her hardware/software control package)... At least something to protect the expensive battery bank if the charge controller stops working correctly and just dumps unregulated current into the battery bank.

    Another way would be to throw a CXX (Xantrex/Schneider) shunt/diversion/by-pass controller on the battery bank and set it to turn on a dump load with a never to exceed voltage (i.e., 15.5 volts @ 12 volt bank). Cheap, testable, and you could hook an alarm to the dump load to indicate when it activated.

    Of course, if you are looking at large arrays--You are going to need a large load bank and diversion controller to manage the operation (here, it would not hurt to just use a voltage sensor board driving a standard DC High Current Relay to the heater/load bank (with some hysteresis
    so the relay does not end up chattering/cycling excessively).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #5
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    Re: Programmable voltage controlled switches

    If I'm reading the op correctly she's looking to switch on/off AC current not DC. I suppose a SSR controlled by Aux outputs of Inverters and/or CCs - but that would not be independent of their voltage sense wires. With it's own voltage sensor input a MCU could be programmed to control the SSR of course but that's not an off the shelf solution (though an Arduino or similar would be close). I'd think throwing that kind of functionality into one of those fancy GreenMonitor boxes would be easy peasy, no?
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
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    Re: Programmable voltage controlled switches
    BB. wrote: »
    I think Julie is looking for a "fail safe" design (that integrates into her hardware/software control package)... At least something to protect the expensive battery bank if the charge controller stops working correctly and just dumps unregulated current into the battery bank. -Bill

    Yes, good thought. Couple of years ago my MX-60 had a brain seizure which resulted in it locking up in EQ mode. When I discovered it near the end of the sun day, the batteries were actually hot. :(
    Did a complete shutdown and restart of the MX-60 and it has never recurred. At least not so far.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #7
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    Re: Programmable voltage controlled switches
    waynefromnscanada wrote: »
    Yes, good thought. Couple of years ago my MX-60 had a brain seizure which resulted in it locking up in EQ mode. When I discovered it near the end of the sun day, the batteries were actually hot. :(
    Did a complete shutdown and restart of the MX-60 and it has never recurred. At least not so far.

    Wouldn't hurt my batteries. I do that to them everyday, but they don't get hot.
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #8
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    Re: Programmable voltage controlled switches

    I'm looking for the third tier solution. Yes, there will be a software control solution for the first, and a charge controller operated DC dump load for the second. However, there needs to be a third to prevent thermal runaway.

    And it isn't for the DC charge controller -- it's for the inverters. When FX chassis are operating in "AC Coupling" mode they DO NOT regulate the DC voltage. If they have 5 amps AC they need to down-regulate to keep the voltage on target, they will convert those 5 amps AC into some numbers of amps DC, regardless of battery voltage.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #9
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    Re: Programmable voltage controlled switches
    tallgirl wrote: »
    When FX chassis are operating in "AC Coupling" mode they DO NOT regulate the DC voltage. If they have 5 amps AC they need to down-regulate to keep the voltage on target, they will convert those 5 amps AC into some numbers of amps DC, regardless of battery voltage.

    There must be something that regulates DC voltage. If these are not Outbacks, this must be something yours. Which means that you already have the DC voltage measured and its only a matter of operating a relay. Are you developing a circuit? Or do you want something third-party that provides safety net independently of your hardware?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Programmable voltage controlled switches
    NorthGuy wrote: »
    There must be something that regulates DC voltage. If these are not Outbacks, this must be something yours. Which means that you already have the DC voltage measured and its only a matter of operating a relay. Are you developing a circuit? Or do you want something third-party that provides safety net independently of your hardware?

    If you AC couple an FX there is no regulation to charging the batteries; push more current from the GTI's and the batteries go sky high - and fry. Why? Because the inverters were not designed to be used this way. Evidently Julie is looking to design an add-on that would facilitate the use of FX's in this manner (other than just a dump-load controller on the batteries).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #11
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    Re: Programmable voltage controlled switches

    The AC Switch itself can just be a digital AC relay rated for voltage/current. They have low voltage input available.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #12
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    Re: Programmable voltage controlled switches
    BB. wrote: »
    The AC Switch itself can just be a digital AC relay rated for voltage/current. They have low voltage input available.

    -Bill

    Basic voltage controlled relays / switches are readily available. I just want one I can monitor. Because I like to monitor things :D
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #13
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    Re: Programmable voltage controlled switches
    tallgirl wrote: »
    I'm looking for the third tier solution. Yes, there will be a software control solution for the first, and a charge controller operated DC dump load for the second. However, there needs to be a third to prevent thermal runaway.

    The only complication seems to be monitoring the third tier relay. If it's there as a safety net to prevent overcharging, how about monitoring for high battery voltage and then infer that the relay isn't working?
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #14
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    Re: Programmable voltage controlled switches
    stephendv wrote: »
    The only complication seems to be monitoring the third tier relay. If it's there as a safety net to prevent overcharging, how about monitoring for high battery voltage and then infer that the relay isn't working?

    I'd like to be able to control it remotely as well as verify its state.

    At some point enough is truly enough. If the ACPV modules don't get turned off, and the dump load doesn't dump, I'd be pretty boned if the voltage controlled relay also craps out.
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  • jwrgorman
    jwrgorman Registered Users Posts: 22 ✭✭
    #15
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    Re: Programmable voltage controlled switches

    Hi Tallgirl,

    We really like these CANbus switches from a company here in NZ called JF2:

    http://www.jf2.co.nz/

    we use them from a USB interface on our solar switching implementations, and they are great - you can check state and attach relays to them to switch larger currents. I believe CANbus is what they use in automobiles for brakes etc. so it's pretty robust stuff, and you can run a connection a long way (1000m?) or daisy chain them.

    Anyway just an idea - John
    John Gorman / SolarNetwork Foundation
    e:john@solarnetwork.net
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