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Capacitor across a solenoid valve. Why?

Discussion in 'General Electronics Discussion' started by roylaster, Oct 9, 2016.

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  1. roylaster

    roylaster

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    Dec 17, 2015
    I took apart an old glovebox, and I found these in there.

    They look like normal solenoid valves, but they all have a cap across them. I would understand if it would be a diode, but these i don't understand.

    Can anyone give me some insight about these?

    P.S. Secondary question would be what are the values prior to the TM30/24VDC (the D23/4.5/MG14/V) those vary among the valves. Do they have something to do with the cores specifications or maybe the valve design?
     

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  2. duke37

    duke37

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    Jan 9, 2011
    Are you sure it is a capacitor and not some form of voltage limiter.
    As you know, a diode is normally used but this needs to be connected the right way round and will slow the release of the valve somewhat.
    The higher the voltage that is permitted on switch off, the faster the current drops.
     
  3. Minder

    Minder

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    641
    Apr 24, 2015
    They look like a VDR/MOV to me.
    M.
     
    davenn likes this.
  4. roylaster

    roylaster

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    Dec 17, 2015
    Thank you, and yes they are. I apologize for my ignorance.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    I have seen caps used instead of a diode though .......
     
  6. oz93666

    oz93666

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    1
    Dec 7, 2014
    They look like VDR's , these are voltage dependent resisters , when voltage is low , their resistance high and it has no effect , but when the power is switched off from the valve a high voltage spike wants to appear across the valve due to the collapsing field of it's coil , at high voltage this VDR changes to lower resistance tending to short out this spike , and keep the voltage lower.

    A capacitor would do a similar job, any building voltage spike would be dissipated in charging the cap.
     
  7. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    The MOV is sometimes used on a solenoid to speed up the turning off in comparison to a diode. It does also depend on how large the coil is whether it's beneficial.
    Thanks
    Adam
     
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