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what type of switch and wiring arrangement would I need?

Discussion in 'General Electronics Discussion' started by jon5500, Nov 20, 2020.

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  1. jon5500


    Oct 31, 2020
    I have a standard PC power supply that I am using in another application. I would like to be able to use a switch to switch between the 5, 3, and 12V voltages to an attached load (I have single, high gauge wires coming from each voltage and one from the ground as well). The switch would need to be able to handle 12VDC @ 15A. What type of switch would I use and what wiring arrangement? Thanks.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    You would need a single pole 3 position switch. I know of no switch of that type that is capable of handling 15 A.
    The switch arrangement would be like this - if you should find a suitable switch:

    When you don't find a suitable switch, relays can be used to do the heavy switching with a 3 pole switch to select the relay:
    Here the switch is connected to the 5 V supply only. All relays have 5 V coils. If you use 12 V relays, connect the switch to 12 V.
    By moving the switch into one of its three positions, either relay coil 1, coil 2 or coil 3 are activated. The respective relay contact is closed (shown above for 12 V), all others are open (3.3 V, 5 V). The output is supplied by the selected voltage.
    Of course the relays used need to be able to support 15 A on the contact side. Automotive relays will possibly be good candidates as in a car high currents are often switched. The relay coil is then a 12 V coil (typically) and the 3 position switch needs to be connected to 12 V , too.
    davenn and bertus like this.
  3. jon5500


    Oct 31, 2020
    Harald Kapp, thank you. I had completely forgotten about relays as I never use them, but definitely will be advantageous here.
  4. AnalogKid


    Jun 10, 2015
    Another option is p-channel power MOSFETs for the 5 V and 12 V, and an n-channel MOSFET for the 3.3 V (since you have 12 V available to drive its gate). A 30 A power MOSFET probably is chaper than a 20 A relay.

    For the relay, consider the T90 or T9x series from Tyco (used to be P&B). Developed by Bosch for automotive use. 12 V coil, 30 A contacts designed for DC. Omron makes them in a field-wiring package.

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