View Full Version : Time delay switch for a fan

07-01-2011, 09:28 AM
I have my compressor in a small shed (just big enough for the compressor) that is insulated for noise. It is pretty well ventilated but yesterday it was around 90 deg and I was using the compressor a lot and it finally hit the temp shut off twice. At least I am pretty sure that is what happened. I want to install a 20" box fan mounted horizontally over the compressor to draw air from the lower vents, over the compressor and out the upper vents. I am having trouble finding a switch that I can wire in so it comes on when the compressor does and then runs for 10-20 minuites after it shuts off. I can't seem to find what I am looking for probably because I can't find the right search terms. I was hoping this would be a big box store type thing and hopefully it will be in the $10-15 range.

Any help is greatly appreciated.

Jack Olsen
07-01-2011, 12:15 PM
The simple way is one of the load-sensing switches that Craftsman and others sell that will turn the fan on whenever the compressor switches on. This will save you from having the fan running whenever the power for the compressor is on, but the compressor might just be sitting still.

What that doesn't get you is the delay. This makes me a little crazy, since the same thing would be handy for the bathroom exhaust fans that are wasting electricity in every house in the world. At least, I went looking for something like this for the fans in my house and came up empty (at least for an inexpensive solution).

Why can every garage door opener keep the light on for five minutes after you close the door, but every bathroom fan require me to either leave it running or come back in a few minutes to turn it off?

Wait, I'm talking way too much about my bathroom, here. :)

But I'll be watching the thread to see if there's a timed shut-off device that's available that I've missed. I could use it for my compressor cooling fans as well.

07-01-2011, 12:51 PM
I think a simple spring-wound timer would for for both you guys.
turbo6justin- this will require you to manually turn it on.

07-01-2011, 01:22 PM
I've got a similar problem with my new compressor (and the "closet" it's in). The on/off switch on mine is on top of the pressure switch that turns the motor on. I was thinking about putting a fan above the compressor and running power from the 240VAC side (on one of the power legs) to the fan. The fan comes on when the compressor starts and stays running while the compressor is running.

I like the idea of a delayed on/off and I know that there are devices that do this. I'm sure one of our "sparky's" will give us a source fairly soon.

07-01-2011, 02:57 PM
Why can every garage door opener keep the light on for five minutes after you close the door, but every bathroom fan require me to either leave it running or come back in a few minutes to turn it off?

I used one of these for the bathroom in the barn. Switch for light+fan with an adjustable delay to turn off fan after light:

Won't work for the OP, but great for the bathroom.

07-01-2011, 03:20 PM
You can wire up a "off delay" relay that automatically triggers when power is applied. I doubt you'll find a timer/relay in a big box store that does what you want. It'll be considered a process control part.

You could use a thermostat. Only comes on when needed. It's likely you won't need it in the middle of winter.

Milton Shaw
07-01-2011, 06:54 PM
you need a delay on off timer, they are used in heat and air work, somebody like Johnstone supply should have them. Gas heaters use them to keep the fan on after the flame has shut down to cool off. Works better than a thermostat for that application.

07-01-2011, 07:40 PM
You could also use a line voltage thermostat like this one:

When it gets to hot, it turns on the fan. Simple

Edit: Someone beat me to it. Oh well.

07-01-2011, 10:45 PM
They have fan timers. I have them in my 2 bathrooms. It's a normal switch but has a timer built in that comes on when you turn the switch off. 5-60 mins I think is the adjustment. They were about $40 each though.