Low Speed Relay

[Andreb6]

Hi , I need to make a safety circuit using a relay to cut the 220vac when one of 2 or 3(running simultaneously) PC cooler fans, get low RPM or stop rotation, using the tachometer wire.Any Idea?

 

[cjdelphi]

So you need a micro controller or frequency( or whatever it's outputting) to voltage converter, i have no clue what that pin outputs voltage wise?

Then use a single transistor to energize or cut power to the relay

 

[Kathy51]

That's a great idea..

 

[(*steve*)]

One obvious thing you'll also need is a method to override it for a short period of time. Without this you can't turn the PC on.

It could be as tricky as having the microcontroller turn power on, control the power on signal from the power supply, and wait some time for the fans to come up to speed.

Or it could be as simple as a momentary contact switch across the relay contacts.

 

[cjdelphi]

What if you rectified the pwm to a dc voltage and a drain resistor?

When the pwm is cut, the cap will discharge

 

[Bluejets]

air vane and micro switch with a start button over-ride.