Solid state relay size and type

gactrx
gactrx Solar Expert Posts: 72 ✭✭
in Solar Beginners Corner #1
Hi, just waiting for a quote for my Midnite controller at the moment but an looking at solid state relays to use with aux 1 to divert the pv panels to an element. PV array rated current ie 26 amps, battery charging current at 24 volts is 66.7 amps. My element is rated at 12 amps. Panel VMP is 73 volts element 6 ohm.
I expect I need a SSR to handle 66.7 amps dc and a control voltage of 24 volts plus a bit. I see there is also PWM graphs on the dc_ip20_200.pdf (Crydom) I am looking at. Not sure if this relates to the Auxillary relay on the Midnite 150. I am also getting the Wiz Bang Jr which I understand uses aux 2. Will having this cause me any problems with power diversion?
Thanks,
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #2
    Re: Solid state relay size and type

    WbJr ties up aux2, which is the only PWM capable aux port. (there was some talk about fixing this, but dont hold your breath).

    Your doing DC side diversion it sounds like. Most people ive talked to use a aux1 hold time of 20secs or so. Its enough to prevetn any major discharges.

    At those sort of currents make sure you get a decent SSR, and a decent heatsink for it.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    #3
    Re: Solid state relay size and type

    Hi, thanks for your answer. Yes I'll probably get a 40 amp Crydom SSR to handle the 12 amps my element will draw. If I use Aux 1 then I won't need to worry about the PWM characteristics. I also plan to get a voltage controlled DC switch in case the SSR blows and I can't get another. For a heat sink I was thinking of using the fins from my Trace C60 which died a while ago.
    Cheers,
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,654 admin
    #4
    Re: Solid state relay size and type

    Watch for counterfeit SSRs:

    http://www.homebrewtalk.com/f170/reputable-source-ssrs-432418/index2.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • gactrx
    gactrx Solar Expert Posts: 72 ✭✭
    #5
    Re: Solid state relay size and type

    Thanks for that link. I had a read and it mentions a good option which I happen to be doing:
    "My vote goes to Crydom SSRS (I have them). Buy them on Digikey." Although Digikey is in the US, purchases over $145 I think it was are freight free so works out cheaper than in NZ.
    Cheers,
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