See the picture. This little circuit was added to an older car clock
(electric wind by solenoid) to eliminate most current drain across the wind
contacts which tend to burn/pit over time. It worked just fine for 4 days,
then the solenoid went up in smoke and the mosfet shorted out ( I don't
know which event happened first)
Firstly..a fuse or current limited power supply would have been a good
idea hindsight is always 20/02...
[image: relay.gif]
They drive the solenoid very hard because it's only activated briefly every
2 minutes or so. .It's not designed for continuous operation of course,
just a lot of pull to kick the wind actuator. In fact, if the contacts
stick the coil gets HOT in a big hurry! The math says the current drain
would be ~5 amps continuous, the coil winding looks like 30 gauge wire.
When it was working I measured about 3.2 ohms across the coil.
My question is, do I need more protection for the transistor? Maybe a
diode? There is a 'flywheel' diode across the coil.
It's possible the coil simply failed after 50 plus years, it's also
possible the transistor failed and destroyed the coil. The transistor is
rated at 19 amps so one wouldn't think it would fail...
Thanks for any input..
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