Re: Electric shutter circuit question - ready for timer?

Nicholas O. Lindan wrote:

The "standard" way to connect this circuit to an enlarging timer would be to leave the switch closed and plug the 120V leads into the timer. This may not work very well.

If the timer controls the 120V then the capacitor doesn't get fully charged and the shutter solenoid doesn't get a high voltage kick to slam it closed. Without the higher voltage the solenoid may not work or work sluggishly and erratically.

You need to wire a relay where the switch is located - the coil of the relay goes to the timer and the relay contacts are wired across the switch. You need a SPST relay with a 120VAC 60Hz coil. You can get one at Radio Shack.
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Indeed, you need that initial higher voltage to "kick" the solenoid, then hold it with a lower voltage. The above solution using an interposed relay is the correct way to do the job. Not complex, just a bit more wiring. I also concur about the need for a fuse, and the higher voltage rating of the capacitor. I would use a full wave rectifier. For this service, they are about 3/8 inch in diameter, and 1/4 inch high, having four leads; live, neutral, plus and minus. It would be good to know the DC resistance of the solenoid coil. With that information we can check the sizing of the resistor in terms of Ohms and wattage rating.
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Regards / JCH
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