Leaderboard

This SERIES snubber diode is to BLOCK the reverse EMF (voltage spike) created when the power is interupted by the thermo fan switch (current stops and the magnetic field of the DC motor collapses). In industrial applications with the control voltage circuits using 24 VDC, the relays will have a SHUNT snubber diode across the coil relay terminals (cathode on the + 24 v terminal and the anode to the - side..........that is put in backwards. The PLC's electronic driver switch, hates to have a back hit from the relay coils turn off (- spike components of the waveform) EMF spike. 120 VAC control voltage circuits relays do not require the diode (would fry on power up). A good visual example is to take an old style Ignition coil and feed 12 Vdc to the + post with and the - or gnd post tied to the - side. Coils were actually 6-8 V and the resistance wire in the harness (GM) or the Chrysler ballast block dropped the voltage to 6 V. Touch and remove the +12 v feed wire....notice the reverse voltage arc flash.....better yet, for a shocking example of what NOT TO DO is grab a good ground and touch the bare wire end of the feed when opening the circuit....the hole in your finger tip will grow back. The magnetic field from the current flow is stored energy........cut the current flow.....the energy has to go somewhere (other than to the high voltage side of the coil. That is why points burn up with a pit and a mound. The size of the capacitor (condenser) is "matched" to the ignition coils "L". The capacitor value size above or below the "ideal match" value will result in the deposit (triangle mound) to be on the base contact or the movable arm contact. The worst thing to do to an old points ignition motor.....TUNE UP. New points and condenser. If the points had little deposit transfer, the capacitor was a good match.......long point service life......only to be thrown away and a new RANDOM value capacitor installed THAT NIGHT NOT BE A GOOD MATCH. Time to quit.