question about flyback diodes - AC/DC

Discussion in 'General Electronics Chat' started by dayman, Oct 29, 2015.

  1. dayman

    Thread Starter New Member

    Jul 29, 2013
    21
    0
    Im working at a plastics molding site and im working on creating as built drawings for some of their older machines

    Im seeing that the PLC output is controlling the 120V contactors
    24VDC and im seeing that theyre tied to a large diode

    IMG_1583.JPG

    IMG_1582.JPG IMG_1580.JPG

    the projects engineer said that it's a surge protector, I believe its working in the same way that a flyback diode does
    Im just curious as to why it would be used on 24 volts and not on 120 VAC coil, Ive seen a few contactors using AC but none of them used anything like this

    also the way its wired as ive drawn, should this be tied back to N, instead of just looping around just the coil?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,521
    2,369
    That looks more like an R/C snubber to me, usually associated with AC coils, if DC coils they should be a rectifier, 1n4007 etc.
    They appear to be Telemecanique contactors, they actually have suppresors that fit directly across the coil, no wire leads.
    Max.
     
    Johann likes this.
  3. dayman

    Thread Starter New Member

    Jul 29, 2013
    21
    0
    yes they operate with 120 V coils
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Only relay coils driven by DC will have a diode. AC relay coils will never have a diode by itself.

    If there is something across an AC coil, it is likely a low-value resistor in-series with a capacitor (shows open with an Ohmmeter), or a MOV.

    [​IMG]
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,521
    2,369
    You haven't confirmed the coil type, AC? DC?
    Your sketch shows DC but the component you point to is a RC snubber.
    Max.
     
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