12v relay suggestion

wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
I have a zephyr 24v battery box fan and I would like to trigger it using the 12v aux on my outback mx60 charge controller. Any suggestions for a relay to use? Can I find one at a hardware store, or will I need to get one specific to the application?


  • VicVic Solar Expert Posts: 3,029 ✭✭✭✭
    Re: 12v relay suggestion

    Here is one that will handle most load currents:


    Depending upon the current requirements of the fan this is prob OK.

    A Radio Shack may have something that will suffice. It is possible that an auto type high current relay would work, just pay attention to the coil resistance of the relay. You do not want to exceed the max current capabililty of the Aux output, which is about 500-ish Ma (0.5 A) on the MX-60, at least. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: 12v relay suggestion

    Consider a voltage controlled switch for the Zepher fan,, one that turns on and of with preset voltages. You don't want the fan to turn on until batteries get to gassing voltage and you want them to turn off when gassing voltage drops. I th ink NAWS sells such a controller.


  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: 12v relay suggestion

    Vic -- Thanks, I was able to find a relay at radio shack that I think will work. The coil resistance is 66 Ohms, so it draw only 0.18A at 12V. The mx60 ux is rated at 0.2A, so I should be good to go.

    Tony -- Outback's charge controllers have a setting that will activate the auxiliary relay at user defined setpoints. It essentially does the same thing as the controller you referenced, but doesn't cost me an extra $120. Thanks for the suggestion though.

  • BB.BB. Super Moderators, Administrators Posts: 30,955 admin
    Re: 12v relay suggestion

    I don't know the details of the Charge Controller's output control... But it is usually a good idea to place a "Clamp Diode" to prevent the coil inductance from creating a damaging voltage spike backup to the Outback AUX output.

    Autoshop 101 Relays

    You just need to pick a diode with reverse voltage at least a few volts higher than the control voltage (17+ volts for a 12 volt signal voltage). And current needs to be rated > than the coil's operating current (small diode for this application).

    The diode will be placed across the coil (or from signal to ground) with the "Cathode" (bar end of diode) on the positive terminal (typically signal out). Installing the diode "backwards" will not conduct current when the signal is "ON". When the signal turns off, the inductive current of the coil will be shorted by the diode (~0.7 volts below ground). This will keep the (sometimes) several hundred volt kick back from the inductor/coil damaging the AUX driver.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: 12v relay suggestion

    Here's probably a better relay from Radio Shack. 2750249. 5 amp contacts. 200 ohm, 43ma,12 volt coil. I've used these for a lot of similar jobs for years. And don't forget the diode that BB mentioned. Add the diode as suggested and save the tears.
  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: 12v relay suggestion

    Thanks Bill and Wayne. I will pick up the higher resistance relay and a diode before finish the install. I'm not sure what I would do without this forum.

    Regards, Bill
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