Relay back EMF question

Discussion in 'The Projects Forum' started by TAP, Jan 17, 2011.

  1. TAP

    Thread Starter New Member

    Jan 17, 2011
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    Attached is a schematic that demonstrates the proper method for back emf surpression. Is D1 necessary, and will D1 alone surpress the back emf if D2 is not installed? I think it will not due to the reverse politary of the induced voltage at disconnect.
    Thanks,
    TAP
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    928
    D1 will prevent the battery from being used in reverse polarity and drop about 1/2 a volt while it is in operation.

    D2 is arranged properly for back EMF protection, but this simple schematic has nothing that needs protecting. ;)
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    2,534
    To add to what Kermit said, relays are generally turned on/off with transistors. D2 is correct, and will protect said transistors.
     
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