Inductive triggered relay to start dust collector?

[JDuke]

I have a vac switch for shop vac that senses tool start and starts the vacuum that’s plugged in, also have festool vac and Fein vac built in functionality.

I’m still using remotes to trigger bigger DC due to higher amp draw of both tool and load.

I’m thinking I could make a small extension cord that has a wire wrapped around the hot leg to induce 24vac and then use a rectifier to make it DC then use this to trigger the coil of a contactor thus turning on DC, maybe even introduce a timer to keep DC on for 5-10 seconds after tool off.

Anybody done anything like this and have any learned gotchas?

Thanks
Duke

[Tapper]

Is it too much trouble to push the button on the remote? I use a Long Ranger for my Penn State 2 1/2 HP DC and it works fine for me.

I would be interested in the unit brand/model you mentioned for your shop vac that senses when the tool comes on, and activates the vac. Thinking of adding one for the shroud on my tablesaw guard.

Doug

[JDuke]

DGI I-vac auto switch is the one I have for vacuum.

No turning on the remote isn’t to much trouble, but sometimes keeping track of where it is located is more troublesome.

I made my own switch with a contactor that is energized by 110vac and use a cheap Christmas light remote to trigger it.

I like to tinker, and the mental exercise of design for something like this is why I build things.
Not everything has to have a “need”

Duke

[jteneyck]

DGI I-vac auto switch is the one I have for vacuum.

No turning on the remote isn’t to much trouble, but sometimes keeping track of where it is located is more troublesome.

I made my own switch with a contactor that is energized by 110vac and use a cheap Christmas light remote to trigger it.

I like to tinker, and the mental exercise of design for something like this is why I build things.
Not everything has to have a “need”

Duke

Keep the remote in your shop apron pocket.  Problem solved.  

John

[MstrCarpenter]

I have worked on larger vac.s that uses the same application to power 30a 240v equipment. On these units power is fed to the vac and a receptacle mounted on it for the equipment. A manual switch (on/off/auto) controls the vac. I just searched the web for the technical term for the donut shaped coil and what I found was "Toroidal inductors and transformers". One leg of the 240v passed thru the center of the ring and the leads from the ring went to a circuit board and relay. I understand how "I and E" transformers work, and that the alternating current passing thru the donut will induce a current in the winding around the donut. In fact, that's exactly how I measure current with my meters. I also see overcurrent protectors that use what appears to be similar physics to drop the power to the coil of the relay of the same conductor it's protecting. That's where I get lost.

Clamp on/around meters can measure voltage and current, so I know they're both there. I don't know if just wrapping a wire around a conductor will produce a lower voltage. In my mind I see a step-up transformer. I think you need to first sense there is current, and then use that to close a circuit to the coil of the relay that powers your vac. Best case scenario with an "I-E" transformer is 2X loops of the 240v next to X loops to get 120v A.C.. Then use a 30a dbl. pole relay with 120v coil. Beyond that is electronics that I'm not well versed in.

[JDuke]

I have worked on larger vac.s that uses the same application to power 30a 240v equipment. On these units power is fed to the vac and a receptacle mounted on it for the equipment. A manual switch (on/off/auto) controls the vac. I just searched the web for the technical term for the donut shaped coil and what I found was "Toroidal inductors and transformers". One leg of the 240v passed thru the center of the ring and the leads from the ring went to a circuit board and relay. I understand how "I and E" transformers work, and that the alternating current passing thru the donut will induce a current in the winding around the donut. In fact, that's exactly how I measure current with my meters. I also see overcurrent protectors that use what appears to be similar physics to drop the power to the coil of the relay of the same conductor it's protecting. That's where I get lost.

Clamp on/around meters can measure voltage and current, so I know they're both there. I don't know if just wrapping a wire around a conductor will produce a lower voltage. In my mind I see a step-up transformer. I think you need to first sense there is current, and then use that to close a circuit to the coil of the relay that powers your vac. Best case scenario with an "I-E" transformer is 2X loops of the 240v next to X loops to get 120v A.C.. Then use a 30a dbl. pole relay with 120v coil. Beyond that is electronics that I'm not well versed in.

My understanding is that when you wrap a wire around another wire how much current is induced is directly related to how many wraps you make around the wire, such that it should take approximately 1/5 the number of wraps to get 24vac that it would take to get 120vac 

I’m a little more comfortable working with low voltage DC, and already have some cheap timers that I may incorporate into this experiment. 

I’ll keep y’all posted on my experiments 

Thanks
Duke

[JDuke]

Experimenting has begun.

So wrapping an 18g wire around one of the hot wires to Sawstop was enough to induce 12vac between the wrapped wire and earth ground

Unfortunately I unplugged the saw, and even in absence of load 12v was still present. My understanding was that current has to be flowing to induce a current ?

Any suggestions on what I’m missing?
Duke

[Roly]

Experimenting has begun. 

So wrapping an 18g wire around one of the hot wires to Sawstop was enough to induce 12vac between the wrapped wire and earth ground

Unfortunately I unplugged the saw, and even in absence of load 12v was still present. My understanding was that current has to be flowing to induce a current ?

Any suggestions on what I’m missing?
Duke

 Try putting a small load on it such as the coil from a relay you are planning to use.  You will show 0 volts.    You are reading a phantom voltage which is a issue with the digital meters that are high impedance.
 Don't confuse voltage and current as they are not the same.   Roly

[MstrCarpenter]

Question; How many 18 ga. wraps around the hot wire to get 12v? And you said "one of the hot wires", so I'm assuming it's 240v. Relays with 24 vac are common on HVAC units. I would favor 24vac over 12vdc. That's what most thermostats use. You could also wire more low voltage "start/stop" switches (green=momentary on, red=momentary off) than you'll ever need with the same relay and have many tools turning the vac on. Your timer or stop switches would shut it off.

[JDuke]

Yes working with 220 on this.
It took 40-41 wraps of 18g to get 12vac.
I am planning on 24v dc for exactly the reason you mentioned the contactor with 24vdc coils are ubiquitous as a result of being common in HVAC.

I’m either going to use more wraps of the 18g or use a larger wire to get to 24v haven’t decided yet.

Also waiting on the voltage rectifier to arrive to test as mentioned whether the ghost voltage disappears when load is present.

Going to keep current 12v wraps until I test that and how well this works on Sawstop.

My concern with Sawstop is that there are 2 switches, one that turns on only the brains, and a second that turns motor on.

I’m going to need to test and make sure the brains don’t pull enough current to mess with the induction sensor. I can’t imagine it would but am going to test.

Duke