I wanted a fully automatic dust extractor switch unit that starts up when any tool is operated, and shuts off with a delay when the tools stopped, but for a semi fixed system.
Being a yorkshire man, i wasn't going to pay out for a ready made unit.
I did some re-wiring of the garage when turning the back half of it into the wood working area (split it to 2 seperate ring mains, one for dads model railway and the tumble drier in the back half, and the front half of the garage is for the woodworking machines.. which also got a type C breaker... dosen't trip when big machines are started up like a type B does... i.e. a dust extractor starting at the same time as a table saw)
i also fitted a few sockets that are just for the dust extractor to plug into.
i use a shop vac type with the 4 inch hose and move it to the machines i'm using atm, i'll add a fixed piping system later,
i didnt want to have to keep plugging the machines into the dust extractor, and my extractor didn't have the power take off facility anyway.
So, the 'heart' of the system is a 'current sensing switch' <£10>
https://www.amazon.co.uk/Current-Sw...=current+sensing+switch&qid=1603758370&sr=8-7
This i mounted in the consumer unit, and all i had to do was feed the 2 brown/live wires from the ring main that the machines plug into through the current switches centre after they exited the breaker.
This unit is a current transformer, which produces a voltage proportional to the current going through it, but it's got an adjustable triggered switch built in, and is totally self powered by the current going through it, the switch part is only good for 300mA.. hence the next bit.
I then added a 20 amp contactor <£5>, and the dust extractor's circuit breaker is powered via that,
i could have left it at that.. the dust extractor will start up whenever any tool is started that's plugged into the woodworking areas wall sockets, and will shut down when the tool is shut off (the current switch is adjustable, so it can be set to not trigger for small hand tools.. tho some modern fixed tools have motors the size of hand tools in them nowadays)
However, i wanted the dust extractor to keep running for a short time after the tools stopped, so i added a run on timer to the circuit <£7>, and adjusted that to give me a 3 second run on delay (i used another of these units for my battery tools charging station, to make it so they can't be left on overnight, just press the start button and the chargers get power for 90 minutes then shut off)
https://www.amazon.co.uk/Rockyin-10...ywords=fan+delay+timer&qid=1603756578&sr=8-97
I then made a control unit, which is a 3 position rotary switch <i already had this, but could have used a couple of rocker/toggle switches> and a couple of panel indicator lights <~£3 ea>, all mounted in a box <£4> that housed the timer module, this is mounted on the wall in a convenient place, needs 4 wires between it and the consumer unit:
Turning the switch to AUTO, the orange light 'Waiting for tool' flashes and it just sits there... waiting.
When a tool is started up, the dust extractor starts up and the green light comes on (i'll add a relay later to turn the orange flashing light off when a tool's triggered the system)
Stop the tool and 3 seconds later dust extractor turns off and the green light goes out.
Turn the switch to ON, and the green light comes on and the dust extractor starts up, this is so i can clear up the mess the mitre saw leaves chucking it's dust everywhere but up the extraction hose it seems, or for vacuuming the floor.
Turn switch back to auto or off, and the extractor turns off immediately.
Total cost for this was £35 - £40,
It is obviously in no way a plug and play solution, but it got me exactly what i wanted and i had fun making it.