Contactor burning

Discussion in 'Electrical Forum discussion & Blog' started by iwen, Jun 13, 2010.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Contactor coils do NOT like less than their rated input voltage (which may be a range). The contact ratings of the contactor power leads are a maximum, and using lower voltages (and current) on them than specified won't be a problem. Some motor designs will work and just run slower if you drop the voltage, some will burn up. If you are using DC contactor coils, you want to install a diode across the coil with it reversed, so during normal operation, there is no current flow (i.e., it is blocking the flow and not acting like a short across the relay coil - IOW, put the cathode on the plus side of the coil and the anode on the minus side). Then, when it is de-energized, the coil's induced voltage will be drained off, and not cause the thing to chatter as the spike decays. If the coil is big enough, there can be enough current generated when control power is removed to cause it to momentarily re-energize itself. the diode prevents that and lenghtens the life of the relay contacts for minimial costs.
  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, and I should have been more clear in the beginning.

    Where I worked, I always got corrected whenever I used the word "molds"! For whatever reason, "forms" are what they have there. But either way, most castings such as manholes, drywells, catch basins and just about everything else had forms/molds that opened up on the outside and were easily removed from the inside before the finished part ever got touched. With septic tanks, however, that would have been nearly impossible and completely impractical there since that would have meant flipping the one-piece (inner and outer) form/mold and tank half together in order to be able to remove the inside "plug" (my term), then flipping the form/mold back into place for the next pour. I once made a set of knock-down panels for forming square-and-vertical walls inside some custom 1000-gallon containment vessels, but that kind of thing would be far too labor-intensive in a production setting where the finished parts are going to be buried in the ground and filled with the stuff that typically goes into septic tanks.
  3. leejosepho

    leejosepho DIY scratch-pad engineer

    Well then, I must be picking the ones that do not! But yes, I have definitely seen low voltage produce heat and ruin motors.
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