Need 3 or 4 Circuit 12V Relay @180-200W max

Discussion in 'General Electronics Chat' started by Justpassinthru, Aug 13, 2009.

  1. Justpassinthru

    Thread Starter New Member

    Aug 13, 2009
    I have a vehicle lighting device that needs a 12V relay with 3 or 4 switchable circuits that can handle 180W-200W total max.


    Circuit #1= 35W
    Circuit #2=70W
    Circuit #3=180W
    Circuit #4 Off(Open)

    The circuits need to be triggered by a 12V momentary switch.

    Relay needs to fit in a 4" X 4" space.

    Any ideas on where to get such a relay?

    If a relay's not available and other ideas to make this happen?


  2. mik3

    Senior Member

    Feb 4, 2008
    If you want to switch all the circuits with one relay, you can use a relay from an old car which can switch 35 Amps (some of them).
  3. kkazem

    Active Member

    Jul 23, 2009

    As a practicing and degreed engineer for over 30+ years, I highly recommend that if you're going to go thru the trouble to make this, then do it right. Although you could use a relay from an old car, it may not have all the poles you need and it likely will have arc'd contacts. Go online to or or and do a search on relays. They should all have a good selection and you can pick the type that's appropriate for your needs. Note that the contact ratings are based on current and not on power, so make sure you compute the maximum current needs for each pole and then get a relay with at least 15-20% extra current rating on each pole for a long-lasting circuit. If you drive the relay coil with DC, be sure an use a diode like a 1N4004 or similar across the coil inputs with the cathode side of the diode connected to the positive side connection to the coil and the anode side to the other coil input. If not, you'll likely burn-out whatever electronics your using to drive the coil. Usually a medium sized transistor or MOSFET will easily do.

    Good luck,
    Kamran Kazem
  4. Justpassinthru

    Thread Starter New Member

    Aug 13, 2009
    Sorry if I wasn't more clear. I edited the quote to clear things up.

    Thanks Kazem,

    I've never built a relay are there a DIY pictorial/exemplar that I can look at. I have very entry level electronics building skills but can usually figure things out.

    I would use multiple/separate 12v relays but I have a space limitation and a MAX 3 wire feed/trigger limitation.