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.
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.
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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