Diodes and fuse for a 120VAC circuit

Discussion in 'The Projects Forum' started by johntee, Feb 19, 2010.

  1. johntee

    Thread Starter Member

    Jul 20, 2009
    Hi folks. In the attached schematic, does anyone know what model/spec of diode I should add to protect the system from a collapse of the transformer's magnetic field? The transformer's Primary is a 120VAC line, and its secondary is 24VAC, 20 Watts).

    Also, what would be a proper model # for the Fuse? That's also a 120VAC line, off of a 20-Amp electrical circuit (12-gauge wire). Probably a 3- or 5-Amp fuse would be sufficient for the load this system will carry.


    Last edited: Feb 20, 2010
  2. DickCappels


    Aug 21, 2008
    I lost a lot of sleep over a similar question (how to keep from arcing the realy contacts), when I had to run 15 Amp 240V motor with a realy.

    Diodes are not the answer, though metal oxide varistors might work fine. The classic solution is an RC snubber, but those are difficult to design and can be rather bulky.

    In the end, I found a relay rated to drive motors at that kind of current, and its been cycling 2 x a day for over two years, without a problem.