Tool-activated shopvac for dust collection? A relay for activating a shopvac for dust collection when a tool is started

Some expensive shopvacs can be "tool activated", meaning that the shopvac hose can be attached to the dust port of chop saw, sander, router table, etc, and the shopvac turned on or energized when a relay device detects that the attached tool is drawing power.  It saves trips between the shopvac and the tool, making automatic dust collection at the point of dust generation more practical.

Off the shelf solutions are $50 to $80, usually consisting of a short extension cord with two outlet sockets.  A power draw on one outlet energizes the other.  The theory is simple enough that I can't think of a good excuse for why it couldn't be done with stock components.  

Comments

[iceng]

You can expand the SAW outlet to the sander, router etc.
Each tool will start the shopvac...  .  .  A

[foxwoodfarm]

The coil on the relay would need to be large to handle the 5 or 10 amps that a saw could draw on start-up. Do they make a relay that could handle that much current through it coils. I realize the contacts are make for the current

[spstewart]

I just built a current sensing system for my shop-vac. Look here on instructables for "DIY Dust Collector"
Steve

[Quercus austrina]

I knew I had seen this somewhere. I believe it is what you want, albeit for 230 volts AC. I have no idea where you are in the world, so you may need to experiment a bit to get it right. Remember, MAINS eletricity is potentially lethal. Take all precautions neccessary to insure your safety and the safety of others.

Qa

[Jayefuu]

$50 seems pretty reasonable.

What've you found? If all of your tools are on one extension, you could put a split core current transformer around the supply to those tools, then condition the output of the current transformer to activate a relay to power on your extractor.

[seandogue]

If you want a dust collector to act on a group of tools, you could isolate the tool feeds from any other wiring on its circuit breaker and put the current activated switch in the main output line for the circuit. That way, operation of any device attached to the power outlets on that circuit will also activate the circuit which energizes the vacuum.