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Help with AC switch - how can I make it gradually turn voltage up?

Discussion in 'Electronic Design' started by [email protected], Jan 12, 2006.

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  1. Guest

    I have a pump which runs on AC. When I flip the power switch on, I
    need pump to slowly turn on. So I basically need the AC voltage to
    gradually go from 0V to 120V (rms) over the course of around 1 second.
    But I cannot do it manually (I cant use a turnpot or anything like
    that). It needs to be done all on its own, just by flicking the AC
    switch on. What is the easiest way to do this? Thanks.
  2. Guest

    Easiest way is with a thermistor. When cool they're high resistance,
    so the load gets little current. But with almost full line voltage
    across them they heat up mighty quickly, within a second is typical.
    Look in the digi-key catalog, they have scads of them. Pick one that
    will handle the expected running current.
  3. Ian Stirling

    Ian Stirling Guest

    The thermistor suggestion - probably - won't work.
    Most AC pumps are synchronus - and only really work at all at near
    nominal voltage.

    What sort of pump is it?

    It may be possible to slowly ramp up the speed using a $100 (assuming
    you're in the US) or so controller.
    It may be more practical to do hydraulically.
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