Switch before or after the transformer?

Discussion in 'The Projects Forum' started by MarzSocks, Jul 14, 2011.

  1. MarzSocks

    Thread Starter New Member

    Jul 14, 2011
    Hi everyone,

    I have built a simple circuit consisting of a transformer, switch and LED strip. The transformer is AC 240V -> DC 12V, (18 Watt).

    My question is should the switch be before or after the transformer?

    My concern is that if the switch is after the transformer (ie on the 12V circuit), there is still power going through the transformer even when the switch is off, making it a zombie appliance. Is this reasoning accurate?

    Thanks in advance.
  2. mbxs3

    Active Member

    Oct 14, 2009
    Personally, I think I would put the switch after the transformer. We use transformers all the time that are plugged directly into the wall outlet(in my case 120vac), that have no switch. I just unplug them when not in use.

    Another thing you need to look at is the switch itself. What are the specs on it? Can it be used in either of the positions you are contemplating? You need to verify that the switch can handle the electrical requirements that you will be placing it in to.
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
    Personally, I think that all wall transformers should be built with switches that would disconnect the 220V/110V. This would save the country a whole lot of useless energy, but cost and space restraints generally inhibit the manufacturer from doing so. Thus in my opinion I would place the switch before the transformer and you will save yourself a bit of energy/$$.
  4. debjit625

    Well-Known Member

    Apr 17, 2010
    I will go with iONic...
  5. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    I would consider the location of the transformer. If it's not a wall (receptacle) mount, then switch it on the supply side. Make sure however that your switch / transformer is fully encolsed, and your enclosure if metallic, be bonded.
  6. RiJoRI

    Well-Known Member

    Aug 15, 2007
    I put my power switches (DPST) between the power source (mains) and my circuit. I also power my projects through a 15A power strip. Fires, or even the release of Magic Smoke, is so blase', and I just don't care to waste my time cleaning up. (The missus would CERTAINLY agree.)