Source for power relays

Joe_B
Joe_B Solar Expert Posts: 318 ✭✭✭✭✭✭
in Advanced Solar Electric Technical Forum #1
I run a 45 amp dump load off of my 24 volt battery bank. Up until yesterday I was using a Power-IO Solid state relay to do the switching. Well, it thermally ran away and self destructed. The sad part was it that it was a 75 amp / 60 volt device mounted on a heatsink that the manufacturer specified for my application. Well inn any case when it failed, it failed shorted. Not good and if I did not notice it fast, my battery bank would have been toast. So I have decided to switch to a mechanical contactor. Unfortunately, the XW system can only supply 12 volts at 250 ma max for the coil drive. Magnecraft as well as Potter & Brumfield make relays that will do it for me but they are very hard to find. I have checked all the usual outlets, Digikey, Allied and Newark but they dont stock the ones I can use.

Does anyone know of a source for this type of relay?

Thanks,

Joe
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Comments

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Re: Source for power relays

    OK, Joe,

    Well, guessing at the spec for the relay/contactor that you are looking for:

    30 VDC contacts 50 Amps Max? with 12 VDC Coil at 250 Ma Max coil current?

    DC is wicked stuff on mechanical relay contacts. Think a contactor style "Double Break" contacts would be best of the mechanical jobs.

    Did you use conductive grease on the SS relay? Perhaps using another SS relay with a larger heatsink, grease and a fan for turbo cooling?

    AND, are you certain that the current spec of the SS relay was not exceeded?

    More later ... Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Joe_B
    Joe_B Solar Expert Posts: 318 ✭✭✭✭✭✭
    #3
    Re: Source for power relays
    Vic wrote: »
    OK, Joe,

    Well, guessing at the spec for the relay/contactor that you are looking for:

    30 VDC contacts 50 Amps Max? with 12 VDC Coil at 250 Ma Max coil current?

    DC is wicked stuff on mechanical relay contacts. Think a contactor style "Double Break" contacts would be best of the mechanical jobs.

    Did you use conductive grease on the SS relay? Perhaps using another SS relay with a larger heatsink, grease and a fan for turbo cooling?

    AND, are you certain that the current spec of the SS relay was not exceeded?

    More later ... Vic

    Hi Vic,

    You got the specs correct. Yes DC is a problem but most of these big boy contactors have something called a blowout magnet that pulls the arc off the contacts (whooda thunk it).

    The SSR was connected to a non inductive heating element with the manufacturers recommended clamp diodes, etc. The assembly was put together by the manufacturer who quoted a 19 degree F rise in the HS temp at my situation. They sized the heatsink, put the silpad on and mounted the relay.

    After spending an hour on the phone, we concluded that the heatsink design was inadequate resulting in destruction of the MOSFETs due to thermal runaway. Since they designed it, they should replace it but they dont think so, Hmmmm....

    In any event I was fortunate enough to be home when the failure occured as it failed SHORTED which would have totally croaked my battery bank if I did not find it and disconnect it. I cant risk another failure when I am not around so I am going with a form 1X (SPST DM) which should be less prone to failure than the FET. (that is if I can find someone to sell me one)
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