3 and 4 way magnetic switches?

[Kenton Keller]

I have a dust collector that I have set up with a contactor and remote switches, but about the only station it seems to work decently at is the 19/38 drum sander. The cnc router is so so, but the worst is the belt sander, the saw, and the band saw. I generally don't even use it on those three, partially because it doesn't work good, and partially because I don't have enough remotes to go around.

I picked up another shop vac at black friday and am in the process of adding a Thien baffle setup. I would like Y it off to those three machines. The problem is I would really like it if when I turned on any one of those machines, the vacuum would come on. Short of using standard light switches I have never seen or heard of 3 and 4 way switches preferably magnetic that would allow me to do that. So is my only option to use remotes again? I know me and if I was just making one or two cuts or using any of the machines for just a minute I would probably never turn on the remote.

Is there something I could hook up to each machine that would act like the remote when I turned on the machine?

[Jim Becker]

The "control of" the control circuit for a contactor can be pretty flexible...it only requires an "on/off" of the control voltage to flip the switch, as it were. The challenge that you describe is about sensing when a tool is active and that's a bit more interesting. You could key to the blast gates (assuming for DC) with microswitches or use current sensing technology to detect when current if flowing to a particular tool...which only happens when it's running.

That all said, I frankly tried the remote thing a number of years ago and chucked it all out in favor of a single, centrally located switch in my shop to trigger the contactor for my DC. It's cheap. It works reliably. And honestly, those 3 or 4 steps to get to the switch from anywhere in the shop really are not an issue. And if I'm bouncing between machines, I leave the DC run and just work the blast gates as I move from tool to tool.

For "shop vac" on small motorized tools, my vac is already tool sensing. (Festool system) Whatever tool is plugged in triggers the vac when I press the button to use it, whether it's a sander (connected most of the time) or a router or other tool.

[Tony Joyce]

I don't know if this relates to what you're asking, but I have a central dust collector with magnetic contactor and wired push button remote switches on three different machines. I can turn it off or on at any location. I didn't wire it, but my electrician did when I told what I needed. It shouldn't matter, but it's 3PH.

Tony

[Alan Schaffter]

I couldn't tell by your description what type of setup you currently have, or what you are trying to do. In any case, I think you can do exactly what you want with the correct type of circuit.

If just you want to manually turn the DC on AND off from each location you need a 3-wire control circuit and control stations that contain a normally open (N.O.) momentary START button and a normally closed (N.C.) momentary STOP button at each tool. You can have an unlimited number of control stations. The circuit is wired to a magnetic contactor which powers the DC (see the diagram below). It is easier and safer if you use a relay with low voltage coil and a low voltage three wire control circuit. My DC control circuit also incorporates a high dust alarm/DC shut-off feature.

If you want the DC to automatically turn on when a tool is turned on, that can be done with current sensing switches located at each outlet that operate a low voltage circuit that powers the main contactor relay (or most likely an intermediate low voltage relay or PLC because the internal switch in typical current sensing switches usually can only handle currents less than 100 mA and most contactor coils draw more current than that. To prevent cycling the DC motor too often, especially when jumping from machine to machine, the intermediate relay should be a "delay on off" type that you can set for anywhere from a few seconds to 5 min. delay or you can wire the current sensor switches to a latching circuit with manual off.

It was more important to me to have my blast gates open and close automatically. I have a version of the setup in the previous paragraph, except that my current sensor switches operate my pneumatic blast gates. A separate sensor, mounted to the transformer that supplies 24 volts to gate circuit senses when any gate opens and starts the DC. I intentionally decided against a delay on off because I sometimes let my machines run longer than most relay delays. When I am done with the DC I turn it off at any of a number of 3-wire stations around my shop.



Current sensor switch (toroid with NPN/PNP transistor) mounted in a box adjacent wall outlet. One leg of 220V (big black wire) passes through the toroid. Red/orange twisted pair are 'switched' wires:



Manual control station:

[Kenton Keller]

Thanks for the reply Alan, I am going to have to read this a couple more times to try to understand better. I am only turning on and off the shop vac, so it would just need a 110v contactor but other than that I suspect it would still be the same.

I had been thinking about it and got to wondering if I couldn't just use a contactor or solid state relay at each machine, hook the coil side up to each of the three machine switches, and the switched side to the vac. Wouldn't that work?

[Alan Schaffter]

Thanks for the reply Alan, I am going to have to read this a couple more times to try to understand better. I am only turning on and off the shop vac, so it would just need a 110v contactor but other than that I suspect it would still be the same.

I had been thinking about it and got to wondering if I couldn't just use a contactor or solid state relay at each machine, hook the coil side up to each of the three machine switches, and the switched side to the vac. Wouldn't that work?

There are a number of ways to do it. Before settling on my current system I experimented with or thought about doing it almost every conceivable way. What you suggest would work but requires some careful thought. You would need to tap into the machines start switch and if you decide to use a low voltage circuit, would need a small relay of some sort (and an electrical box.) You would end up with an extra 120V cord (or possibly even 220V one if the outlet or machine doesn't have have a neutral handy) or a low voltage cord running to the shopvac and a transformer. That can be a pain if your machines are mobile and you move them often. If you power the shopvac directly instead of using a relay and separate source of power, you must also consider current draw- are the switches (and pwr cords) on your machines heavy duty enough to handle the current draw of both machine and shopvac (and extra cord running to the shopvac)? For that matter, what about the outlet/outlet wiring? It can also be a real pain to tap into the start circuit if your machines have the current generation of self-contained, full-voltage magnetic starter switches found on many machines today. To use a low voltage circuit, you will need a transformer and another relay contactor (with a low voltage coil) to power the shopvac. If you were controlling a DC you would still need to address the issue of repeatedly cycling the DC motor- one reason I never put an autogate/DC start/stop circuit on my miter saw!!!!

I have a secondary, shopvac-based dust collection system for selected stationary/bench tools. I decided to control it with a very basic setup, however- mechanically latching push-on/push-off button switches at each drop, a low voltage circuit, and solid state relay. The setup uses a cabinet-mounted shopvac, mini cyclone, 2" PVC ductwork, manual blast gates, and, bench drops for my bench-top mortiser and mitersaw blade guard*, and a ceiling-mounted hose drop over my assembly table for my pneumatic ROSs, routers, biscuit jointer, etc. *I also have a 6" DC port behind/below the mitersaw. I must start and stop the shopvac from each location but they are only a few steps apart and I don't typically jump from station to station- no 3 wire circuit was needed here.