Hi AE.
A few weeks ago, in an electrical thread, you mentioned a “contactor” which is basically a relay that uses line voltage for both it’s coil and switched circuit.
I began wonding if such a device could be used for automatically switching on a vacuum when a too (sander?) was switched on. See attached drawing.
I’m pretty sure that what I’ve drawn won’t work, but I’m wondering if it’s even possible to do this without getting into solid state components. Whaddaya think?
Thanks a mil.
Scott.
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Replies
That's not going to work
You have both sides of the relay coil connected to the neutral. No significant current will ever flow through it. And you can't put a relay like that in series with the sensed tool receptacle because both the tool and the relay want to drop the 120v.
You want to have some kind of current sensing relay in series with the tool receptacle (on the hot side) that switches the load when the tool is begins to draw current. You'd probably also want it to be a timed relay, so the vacuum continued to run for a bit after the tool is switched off.
>>>current sensing
>>>current sensing relay
Thanks. Is such a thing readily available?
Looks like it's a pretty common item. Found this:
http://downloads.eatoncanada.ca/downloads/Logic%20Control/Relays%20and%20Timers/Sensing%20and%20Monitoring%20Relays/VSR%20Series%20Voltage%20Monitoring%20Relay.pdf
That's voltage sensing
You can't put that in series with another 120V load.
Scott
Sears had a switch box that you would plug in a table saw, sander etc into. You would also plug in the vac. As I've heard-powering up the tool would start the vac. Memory serves that that box was about 15 dollars. Don't know the amp rating.
Cool..thanks, I'll give it a look.
By the way everyone.... I costed out the Voltage Sensing Relay from Eaton-Cutler Hammer.
It was $597.00.
No thank you.
Here you go.
http://www.sears.com/shc/s/p_10153_12605_00924031000P
You're the best, thanks.
Nope,
Just a dumb carpenter, with a marginal memory................going fast.
Sort of
I would say what you want is slightly less than readily available. There are many AC current monitor relays on the market. A lot of them have a sensor coil that you'd pass the hot leg through, like a permanent clamp on meter. A lot of them are ridiculously expensive, like you could just buy the Fein autostart vac for less. You can find inexpensive ones designed to switch humidifiers on along with furnaces. I don't know if they'll be rated to swtich your vacuum. It might be hard to find exactly what you want in a single package. Maybe somebody makes a simple dust collection control box.
I've found a few sites with plans for this circuit, but it requires electronic skills and knowlege which I'm not up to. I might as well buy this:
http://www.leevalley.com/en/wood/page.aspx?p=63013&cat=1,240,41065&ap=1
That's perfect
I don't think you could make one that does all that for less than $45.
Yeah, I could pull together the parts for one, but not as cheaply as the Lee Valley unit.
Contactors are commonly used to accomplish exactly what you want to do: operate several things with one switch. Since you ask, I'll try to explain the idea a little better.
A contactor, as the name suggests, has a means to open or close a circuit. Just like a switch. Since we call the points where the circuit is interrupted 'contacts,' we wound up calling the entire thing a 'contactor.'
Instead of you standing there and flipping several switches, a contactor uses a magnetic coil (solenoid) to close multiple sets of contacts. Each set can control one wire. Contactors are available with as many as eight sets of contacts, and many have provisions for adding one or two more to them.
In a motor starter, the contactor opens all the 'hot' wires serving the motor. When you're doing lighting control, the contactor will use each set of contacts to operate a different set of lights.
The contacts are only half the story; they are the 'power' part of the arrangement (since they control power to the loads). The other half of the equation is the 'control' part; this is what controls the coil.
In the simplest arrangements, we use the power coming in for one of the loads to also supply the control circuit. After then, there is no direct connection between the control and power circuits. There is no reason that we "must" do this; in industry it is common for the control circuit to be 24 volts, and supplied from a completely different source than any of the loads.
When you use a contactor, ALL of your switches and push buttons are part of the control circuit. They no longer directly operate the equipment; they simlpl turn the coil 'on' and it is the coil that closes the contacts that allow the machine to start.
Let's imagine a contactor with three sets of contacts, that is used to supply a 240-volt saw. Two of the sets would be used for the saw (because you have two hot wires), and the third is not used. It's perfectly possible to pass the control circuit for the contactor that controls the dust collector through that third set of contacts. Start the saw, and the vacuum will start as well.
Perhaps you're now asking 'but wouldn't I need to have every machine running for that to work?' No, you would not. In a control circuit, all the 'stop' buttons are in series (they all must be closed for things to run), but the 'start' buttons are wired in parallel (closing any one will start the vacuum). Keep in mind that the 'control circuit' for the vacuum is not the same 'control circuit' that controls the machine.
>>>Let's imagine a contactor
>>>Let's imagine a contactor with three sets of contacts, that is used to supply a 240-volt saw.
Funny you mention that... I once had a single-phase saw starter with exactly that....three sets, which I wondered why they heck they did that. I bet it was for dust control.
Thanks for the great explanation.
Yeah, what you want is a current relay. They come in various configurations, some made specifically for starting dust collectors. Pretty sure I've seen these in a woodworker's catalog.