Air Compressor Control

[Mike Henderson]

Like most or you, I suppose, I don't like to leave my air compressor on when I'm not in the shop. But I'd often forget to turn it off when I leave because it wouldn't be running (it'd be up to pressure). So I decided to rig up a way that it would only run when I'm in the shop.

I bought a contactor with a 125V coil that would switch both sides of a 240V line (my compressor is 240V). I rigged up a motion sensor to detect when I'm in the shop - the motion sensor provides power to the contactor coil when it senses motion. I thought there might be times when I would be using air and would be outside the shop so I added a switch that basically goes across the motion sensor. When switched one way, it always provides power to the contactor coil. I have the plate marked so I know which way to switch the switch for each function. BTW, you don't need the kind of switch I used - it's what I had on hand - a regular switch will do. The outlet is not needed.

Now, I can walk out of the shop and the air compressor won't run.

Mike

[Added note: The contactor is in a box close to the compressor. A wire (2 conductors) runs from the motion sensor to the box housing the contactor.]

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[Scott T Smith]

Great idea Mike - thanks for sharing.

Where did you source your contactor from?

[Stephen Cherry]

Sounds like a good concept. How long does the motion sensor stay active when it sees you move? My concern is that if you stop moving it would turn off the compressor before it finishes it's cycle.

Maybe it needs some sort of off delay to hold the signal active for long enough to fill the tank? (or maybe not)

[Bill Huber]

Sound like it should work ....

In my old shop I put a big P&B relay on the light switch that did the same thing, any time I was in the shop I had to have the lights on so the compressor had power whenever I was in the shop.

[Mike Henderson]

Great idea Mike - thanks for sharing.

Where did you source your contactor from?

I got it on eBay. It's easy to find contactors with 24V coils because those are used with air conditioners. But I did find one with a 120V coil and it wasn't very expensive.


Sounds like a good concept. How long does the motion sensor stay active when it sees you move? My concern is that if you stop moving it would turn off the compressor before it finishes it's cycle.

Maybe it needs some sort of off delay to hold the signal active for long enough to fill the tank? (or maybe not)

I guess the motion sensor takes about 5 to 10 minutes to turn off after it no longer senses motion. As long as I'm in the shop and in the field of the sensor it stays on. I've not had it turn off during the time it takes for the compressor to reach a full charge. But even if it did, I can't think of a problem with that. It would probably mean I'm not in the shop and not using the air.

I also have a separate sensor for the lights in the shop.

Mike

[Mike OMelia]

This is a great idea. My compressor scares the daylights out of my family when it switches on, but I'm not out there. Need to study this some more.

Thanks Mike!

Mike

[Jerome Stanek]

What I did was wire a light on one side of a 220 switch that goes on I can see as I leave the shop and turn off the power.

[Matt Meiser]

I did the same as Jerome.

Be careful using a motion sensor. I have one in the storage are of my shop. It works great 99% of the time. But I've been under the tractor at night and had it turn off. Good times! I've gotten in the habit of using the switch when I'm going to be working back there. Of course then I've also accidentally left it on. With the compressor I could see an issue if you were spraying maybe. Of course if that becomes an issue you can just use the switch like you said.

Another good source for contactors is http://www.factorymation.com.

[Mike OMelia]

Matt, is "relay" another word for "contactor"?

[Stephen Cherry]

I guess the motion sensor takes about 5 to 10 minutes to turn off after it no longer senses motion.

Mike

That sounds like a great solution then!

[Mike Henderson]

I did the same as Jerome.

Be careful using a motion sensor. I have one in the storage are of my shop. It works great 99% of the time. But I've been under the tractor at night and had it turn off. Good times! I've gotten in the habit of using the switch when I'm going to be working back there. Of course then I've also accidentally left it on. With the compressor I could see an issue if you were spraying maybe. Of course if that becomes an issue you can just use the switch like you said.

Another good source for contactors is http://www.factorymation.com.
I've had that happen when I'm working at night in a place in my shop where the sensor for the lights doesn't reach. I have to remember to turn on the bypass switch when I'm working in that location at night. When I forget, I have to feel my way to the light switch, feeling like an idiot.

Mike

[Mike Henderson]

Here's some pictures of the contactor box. The first picture shows the box closed (covered). The second picture shows the interior of the box, and the third just gives a better view of the plug.

One thing I'm going to change is to change the switch on the sensor part (see my first post in this thread). Right now, the switch is a switch and an outlet - that's what I had. I'm going to replace it with a dual switch. The second switch will be an off/on switch and will break the power to the sensor. That will allow me to turn off the air compressor from that switch.

Mike

[I changed the sensor area to include a switch that will turn off the air compressor. What it does is remove power from the sensor, which means the contactor won't engage so the air compressor is off. See last pix.]

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[Steve Kohn]

Sound like it should work ....

In my old shop I put a big P&B relay on the light switch that did the same thing, any time I was in the shop I had to have the lights on so the compressor had power whenever I was in the shop.

I did a similiar thing in my shop. Except I wired a 110 to 24V transformer to the lights and a 24 volt relay in the breaker panel that controls the 220V to the compressor. This way I was only running a low voltage circuit from the lights back to the panel. It meant I could use bell wire instead of conduit. Everything was sourced from McMaster for under $30.

[Patrick McCarthy]

Mike, I would be a LOT more comfortable if you had put all that into a metal electrical box. I don't know if you can arcing in there, but someone else around here more knowledgeable than me can comment . . . . . . but that makes me cringe . . . . .

[Mike Henderson]

Mike, I would be a LOT more comfortable if you had put all that into a metal electrical box. I don't know if you can arcing in there, but someone else around here more knowledgeable than me can comment . . . . . . but that makes me cringe . . . . .
It would take a lot to set that box on fire. I suppose the coil could short out and catch fire but I'll take the chance.

Mike

[Lornie McCullough]

Mike, I would be a LOT more comfortable if you had put all that into a metal electrical box. I don't know if you can arcing in there, but someone else around here more knowledgeable than me can comment . . . . . . but that makes me cringe . . . . .

+1.... Please make all of your electrical connections in code-compliant fire-proof electrical boxes. I like to see people doing their own electrical work, but the code is there for YOUR SAFETY.

Lornie

ps.... the motion senser controlling the contactor is very clever!!!

[Chris Padilla]

I have my compressor plugged into an old 24-hour mechanical timer so it only comes on during the day at the most. I got tired of hearing it kick-on in the middle of the night so I went this route. I like your idea, too, but will 2nd the metal box route.

[Jim Finn]

My compressor is in a different building not far away. I just put it on a timer. It comes on every morning at eight AM and off at five PM.