MOV's energy rating vs clamping voltage

Discussion in 'General Electronics Chat' started by alphacat, Dec 24, 2009.

  1. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    There is a rule of thumb that says that when connecting a MOV to the mains (110V/220V), its clamping voltage should be 300V-400V max.

    Is it possible to have a MOV with such clamping voltage, and with a very high energy rating - over KVJ?

    I cant find any high Energy rating MOV with low clamping voltage.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    It sounds as if you are really looking for a "crowbar circuit". Try Google on that term.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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  4. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    Thank you.
    So there's no such MOV with such high energy rating and low clamping voltage, right?

    I looked at some Crowbars' datasheets and there was no indication there to the energy rating of the crowbar circuit.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Check the spec on the SCR. The crowbar circuit is designed to trip the breaker or blow the fuse.
     
  6. Duane P Wetick

    Active Member

    Apr 23, 2009
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    See CKE (manufacturer), www.cke.com for MOV data. Their data sheets are reprints from old Westinghouse data (original makers) and require some interpretation and explanation. The usual selection procedure is to allow 12-15% overvoltage of the device you want to protect. For 115 VAC service, select a 130 VAC device. I have used MOV's in combination with other components; zener diodes and resistors for specific suppression needs.

    Cheers, DPW [ Everyone's knowledge is in-complete...Albert Einstein]
     
  7. alphacat

    Thread Starter Active Member

    Jun 6, 2009
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    Thank you!
    I checked the products of CKE.
    The thing is that all the high energy-rated MOVs there have a very high clamping voltage.

    Did you see there a 130V clamping voltage MOV with high energy rating?
     
  8. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
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    Ok, if you cannot find a MOV with the energy rating you want, add a power resistor in one leg of the MOV. That way, the transient's energy will be shared by the resistor and the MOV. It wouldn't hurt to add a zener diode (Vz cath.) at this juncture to the opposite MOV leg also. Observe the clamping action on a scope..thats the final test.

    Cheers, DPW [ Spent years making heaters out of op-amps.]
     
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