Electrical Question: Using a contactor in-line with a tool to control my dust extraction

[sams93]

I'm re-doing my dust extraction set up. I won't be doing it like described below, but I am posing a theoretical question to help me understand.

I'm trying to work out, if I set up a contactor such as the one below in-line with my tool, will it work to switch when the tool is in use.i.e cut the live to my sander, and connect it to A1, then continue to my sander from A2.

Would it then close the contactor when there is current passing along the live wire to the tool?

 

[MikeJhn]

Most contactors work from a momentary switch and will probably burn out the coil if power is applied constantly, only a thought.

I use these in my workshop: https://www.amazon.co.uk/HBN-Progra...-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

 

[Gordon Tarling]

You wouldn't burn the contactor out, but by putting the contactor coil in series with the load, your sander will run very slowly, if at all.

G.

 

[sams93]

Makes sense, I assumed there was a good reason why this wouldnt work but didnt realise what it was - thanks!

In the end I have gone with one of the KEMO M103N master/slave control modules. It is rated for 16A, but that is shared across both the master(Machine) and slave(extractor) circuits. The KEMO M103N also switches instantly whithout any delay.

I need to decide if I should use the KEMO to switch a contactor or relay for the slave(extractor). I was also considering a time-delay to allow me to set the extraction to remain on for a few seconds after the machine turns off.

One of these:
Delay Relay - GRT8-B1 Mini Power Off Delay Time Relay Timer Relay DIN Rail Type AC 220V

 

[deema]

So far all of the answers you have got are incorrect. It’s perfectly feasible to use a contactor to start up another machine, it’s a very simple circuit. You wouldn’t put it in series. I never give technical details on electrical stuff, because if you need to ask this level of questions you don’t poses the necessary knowledge to do it safely. You should never ever tinker with electrics unless you know what your doing. It kills if you get it wrong.

 

[sams93]

So far all of the answers you have got are incorrect. It’s perfectly feasible to use a contactor to start up another machine, it’s a very simple circuit. You wouldn’t put it in series. I never give technical details on electrical stuff, because if you need to ask this level of questions you don’t poses the necessary knowledge to do it safely. You should never ever tinker with electrics unless you know what your doing. It kills if you get it wrong.

I think this applies to almost everything to do with working with tools and machines that we discuss on this forum as well doesnt it - it can hurt and kill you if you get it wrong?


I asked the question to try and learn more about if/how contactors are used in these circumstances.

 

[deema]

Electricity is one of the most dangerous things you can play with. Mechanical stuff moves, you can see it. Gas you can smell long before it gets to a concentration where it may explode. All of these provide you with a warning that something is wrong. With electricity, you can’t see it, feel it and it acts instantaneously. You wouldn’t t dream about doing your own gas fire plumbing for instance!

 

[MikeK]

One of the electricians put signs similar to this on the electrical distribution panels at a facility under construction.

 

[Spectric]

Most contactors work from a momentary switch and will probably burn out the coil if power is applied constantly, only a thought.

If the coil is not powered then the contacts will drop out and the load is no longer powered. The momentary switch circuit as found in DOL starters just uses an auxilary set of contacts to maintain power to the coil until the circuit is broken by the stop button.

 

[MikeJhn]

Got my latching relays and contactors mixed, its an age thing or need to take more tonic with it.

 

[Sideways]

If it were necessary to slave a dust extractor to a properly high current machine, the / one of the live wires to the machine can be monitored with a current sensing transformer, and the necessary modules to support that and operate a separate contactor feeding the extractor. A timer would be involved to run the extractor for a while after the machine stopped in order to clear the ducting.

Like @deema, I won't explain how, but it can be useful to know that this problem is easily solved by an industrial, not domestic, electrician. It would cost two to three hundred (?) in parts and some more to have them build it for you.

 

[scholar]

Not sure about the use of contactors - why not use the thing designed for the job https://www.manomano.co.uk/p/automa...r-scheppach-ha1000-woova-30-woova-70-36424639
I have had one of these for many years and it works really well - there is a delayed start on the extractor, to allow the main machine to run up first, and then there is delayed switch off of the extractor to clear the dust outlet.

I built mine into a Commando socket wiring enclosure and connected it to multiple outlets

This way the main machines and the extractor can be permanently plugged in - obviously, this setup is only suitable for my small home workshop as theoretically more than one machine could be turned on together. The main input to this fancy “extension lead” comes from a 16A isolation switch outlet with interlock and that is run off a dedicated 16A circuit.

The three-position (20A) switch for the dust extractor is very useful - with this I can turn the extractor on on its own eg for the floor gulper - it can run on auto as described above, or it can be turned off so it is not triggered when one of the main machines is turned on - this is helpful as my big planer draws a lot of current when cold and the auto switch kicks in the extractor just a little too early so it can trip the 16A MCB, even with a C-Type.

Cheers

 

[Sideways]

@sams93
The kemo module you bought is a good unit.
I've used them to add auto switching to a quiet commercial vac.
You have 16A available, less typically 5A for the vac, leaving 11A or essentially 2.5kW for the power tool.
That's enough for most uses.
Don't use these with induction motor machines. Those draw a 5x to 8x current surge on startup and the little relays built into the kemo won't be rated for that type of inductive load. It may work but I wouldn't expect it to last.

The problem is easily fixed. Use a radio remote on off switch for the vac instead of trying to fully automate by sensing the current through the machine tool. A keyfob remote is super easy to operate manually and really no less convenient than a full auto solution.

 

[Yojevol]

The problem is easily fixed. Use a radio remote on off switch for the vac instead of trying to fully automate by sensing the current through the machine tool. A keyfob remote is super easy to operate manually and really no less convenient than a full auto solution.

Totally agree with you on this Sideways. I've been using this system for years. I can never understand the search for auto start in systems with multiple machines. When you move from one m/c to the next, eg, saw to planer, you need to manually shut/open blast gates and with remote-manual control you can keep the vac running.
My remote has recently failed after 15 years use (stopped transmitting) and has been replaced with a new one costing £10, which is considerably cheaper in real terms than the original.
Mine is simply set up to switch on the vac contactor solenoid coil so no high currents involved.
Brian

 

[Sideways]

I've been using a remote switch that I built up from leftovers :
A 12V plugtop power supply
A 12V car electric window radio remote control
One big relay and a couple of components.

It gets left plugged in all the time so probably has 5x365x24 hours of idle time on its clock without any issues.
But these are so cheap it makes absolute sense to buy one and use it exactly like Brian has

 

[thikone]

Makes sense, I assumed there was a good reason why this wouldnt work but didnt realise what it was - thanks!

In the end I have gone with one of the KEMO M103N master/slave control modules. It is rated for 16A, but that is shared across both the master(Machine) and slave(extractor) circuits. The KEMO M103N also switches instantly whithout any delay.

I need to decide if I should use the KEMO to switch a contactor or relay for the slave(extractor). I was also considering a time-delay to allow me to set the extraction to remain on for a few seconds after the machine turns off.

One of these:
Delay Relay - GRT8-B1 Mini Power Off Delay Time Relay Timer Relay DIN Rail Type AC 220V

Yes, that might work. I recently installed GRT8-B1 in my box inline with heating after I forgot to switch off heating and it burned electricity for two weeks...

There are two variants, A and B, and then number of contact pairs. A is for delay on - it switches on after delay, and B is for delay off, it switches off after delay. There are also devices specifically for dust collection that combine delayed on and off for slave device.

I did my dust extraction automatics with a PCB from such device: Automatic switch-on 3Ph-400V / 230V with selector switch hand-0-auto for extraction https://amzn.eu/d/9O670SM

If I would do it now I would prefer this: Anlaufautomatik mit verzögertertem Auslauf für 1-8 Maschinen
It uses coils like this to detect current: Wandlerspule für Anlaufautomaten

But since you asked about connecting in series relay coil and load... I would suggest to delegate wiring to someone who knows better

 

[thikone]

I used this PCB: CCST with variable switch-on and switch-off times and switch-on threshold - Article number: 87005931
And this relay: Contactor KB-04 - Article number: 86010740