Make Your Shop Vacuum Automatic!

Hi folks, this is a device that automatically turns on an outlet (usually to the dust collector/shop vac) when there is a lot of current draw on another outlet, like the table saw. You can buy one but I decided they were more than I wanted to spend. I also had a lot of the components already lying around so why not make it.

This is a simple project that I think most people can easily accomplish, however you will need to be familiar with connecting a household electrical outlet.

Bonus: I've seen some automatic vacuum switches that are a single plug which seems somewhat questionable if you're running a normal 20 amp breaker. Making it yourself you can run the saw and vacuum off of different outlets and avoid tripping a breaker.

Modules

• Current Sense Module
• Relay Module (rated for at least your vacuum amperage)
• Micro USB Jack or, any power supply that matches your relay.

Power Outlets

• 2 gang box
• Duplex power outlet for the saw
• Combined outlet and switch for the vacuum or...
• Single outlet and single switch
• An additional 1 gang box

Some 12-14awg cable and wall plug connectors

Some small hookup wire for connecting the modules

A few wire pass-thrus (wire glands) of your choice

Sourcing: Electronics pricing really varies a lot for each item. I got the modules a long time ago from aliexpress. Take a look at your local electronics shops, you pay a small markup but you can get it right away. For the power hardware any home improvement store will stock plenty of those. The bendy cable used for power plugs is called "portable cable" at my home depot.

The saw duplex outlet is the simpler of the two outlets. It is a normal outlet with one of the cables going through the hole in the current sense module. After stripping and crimping the terminals to connect the outlet I connected a hot wire extension about 20cm long that exits the box, goes through the current sense module, and then back to the outlet.

Wall outlet voltage can electrocute you, please be careful and if in doubt ask an electrician.

A lot of the work is already done for you if you buy a current sense module. It detects current going through the sensor and closes the two terminals it has if there is enough current. You'll have to turn this switch closing into something that your relay understands, in my case I have a 5V active low relay. So normally the input pin of my relay will sit at 5V because of a pull up resistor. When the switch is closed this will connect the input directly to ground and turn on the relay. A very small amount of current will go through the pull up resistor when the relay is turned on.

I made a little breakout board for this but I accidentally ripped the pads off when unplugging the micro-usb oops. There are so few components you can definitely get away with using hookup wire and some solderless connectors.

From here you can test that your relay is activating properly before hooking up power to the vacuum outlet. Plug your saw into the saw side outlet and when the saw turns on, the relay should trigger. Nice!

Finally, hook up the shop vacuum outlet. I did the switch first. Hot wire into the switch, when you flip the switch it connects the two sides and powers on the vacuum outlet. In my case there's an internal connection since the switch and outlet are one unit, but you can do the same thing with a normal light switch and outlet. You can use a multimeter to make sure everything is working right.

After I connected the relay hot wire. I went from the always-on side of the switch, through the relay, and then back to the vacuum outlet. Now there are two ways of turning on the shop vacuum, and the light switch will override the current sensor. Nice!

It's best to double check everything now before mounting the electrical box and closing the cover. I did some head scratching since there are now 4 plugs to sort out, among whatever power bars and extension cords you need.

Now turning on your saws automatically turns on the shop vacuum, simple as that!