Dust extractor automation, 240 volt, current sensor in the consumer unit?

[gazz292]

Converting half a garage into a woodworking area, i have a single dust extractor (4 inch hose type), and a few machines that chuck out a lot of sawdust,
the dust extractor does not have a power take off socket on it.

The woodworking half of the garage will have a single ring main feeding all tools (yes i'm in the uk)

I'd then put a couple of single sockets on a radial circuit on it's own breaker around the walls for the dust extractor to plug into,

i'd have a current sensor around one of the live wires feeding the ring main inside the breaker box (or should i have it around both live wires?)

so that whenever the current on ring main goes above say 450 watts (largest tool draws 3kw, but obviously has a large start up surge) a contactor switches the dust extractor sockets on...

BUT it does so 1/2 to 1 second or so after the tool that triggered the relay turns on, just so there's not a large current surge of 2 motors starting together.

Then when the tool turns off, current goes below say 450 watts, the relay stays on for 2 seconds, then drops out, to clear the pipe of dust as the tool spins down)

i know you can buy automated dust extractor boxes (for about £100!!!), but i really want to build this into the fixed circuits, i'd have a small box for the arduino to live in, with a suitable psu running it, and a couple of wires from that box going into the breaker box for the current transformer and contactor, i'm imagining it'd cost 20 quid to build this.

Are there current sensors that interface with an arduino easily? i imagine i don't want to be feeding in an AC signal to an analog pin, but i could be wrong.

As always with me, doing the physical wiring and that is easy, the software will stump me, so once i have the hardware, how do i go about the software that will monitor the voltage from the current transformer, and output when needed ?

[JCA34F]

At 240VAC 450W is about 1.9 Amps, what is the MAXIMUM expected current / Wattage?

[gazz292]

about 12.5 amps, 3kw.

[JCA34F]

Some ideas, should work with Arduino:

CrocSee Miniature Current Switch, CS-TS0, Normally Open Amp Sensor Monitoring...

Suncourt SW100 Current Switch: Hvac Controls: Amazon.com: Industrial &...

Current Sensing Switch, Normally Open Current Sensing Relay Adjustable AC 0.2A...

[gazz292]

Wow, thats awesome, thankyou for those suggestions.

i can actually do this without an arduino, all working at 240v

For current sensing of a tool turning on, i'd use an SZC23 current sensing switch, set the current to what i want on it, and it closes contacts whenever the current goes over the threshold i set, turns off when it drops.

Then feed the switched output from the SZC23 to a ''GRT8-M1 Multifunction Time Relay'' set in 'on - off' mode, ok i wont get the 0.5 second on delay 2 second off delay, but i'll settle for a 1 second on and off delay to keep things simple... the dust extractor takes about 5 seconds to spool down anyway, so will still be sucking dust for a few seconds after powered off.

Then use a contactor to switch the dust extractor sockets.

Maybe a simple switch to bypass the current sense and time delay to use the extractor with the floor nozzle atatchment to suck up stray sawdust, few panel lights to show what's going on, and a box to mount it all in,

[gazz292]

If anyone's interested, here's a schematic for how i did this using off the shelf parts.

I used a "Rockyin AC 100-220V Delay Timing Relay Module Delay Timer Board" for the switch off delay, they are about 10 quid on amazon or ebay, and the text in quotes is the text to use to search for them.

The current sensing switch is the one i mentioned, that costs £15 - £20, and
"Current Sensing Switch-AC 0.2-30A SZC23-NO-AL-CH Normally Open Current Sensing Switch Adjustable"
Is the term they are sold under.

So in the end i didn't bother with switch on delay, as having the dust extractor and the tool's ring main in the garage on separate MCB's stops the issue with 2 motors starting up at once tripping a type B breaker.
But i also use type C breakers now on any circuit where any big tool will be used, as they can handle a much higher switch on surge than the standard type B breakers can, my welder will only run on a circuit with a type C breaker due to it's transformer pulling so much current at initial turn on and arc strike.

First pic is how i have it in my garage, the switch i used is a rotary industrial one with customisable contacts, so it switches 3 lines on when switched to the right, that's auto mode... giving a flashing 'waiting for tool' light, middle is off, and to the left is on... used when cleaning the floor around the tools.

And here's how to do it with a standard DPDT switch, but no 'waiting for tool' light when in auto mode, you could easily implement this if you get a contactor with an auxiliary contact, most contactors can have them fitted, they just clip to the side of the contactor and a pin on the contact block goes inside the contactor and moves with the main contacts.

I found out that you can't back feed any voltage on the 'fan' terminal, or the relay on that module chatters like mad,
And it will trigger and not turn off if you back feed voltage on the L2 terminal,
hence the convoluted way with the switches and relay.. the relay is there so the 'waiting for tool' light goes off when the dust extractor is started up automatically.

[Paul_KD7HB]

MY brother, also a woodworker, uses a much simpler method. He has a remote control switch on the vacuum and turns it on with a fob attached to his shirt. Can turn it on/off from anywhere in his shop.

Paul

[gazz292]

Oh yeah, there's loads of ways to do this,

i wanted to just plug any tool in any socket and have the dust extractor start up automatically so i went with this method,
it's basically like those shop vacs with the power take off socket on it, but with 10 sockets that operate it and no current limit.

other ways are when you have a fixed dust extractor ducting to the tools, opening the blast gate operates a micro switch and turns the extractor on.

and of course there's loads of ways to do it with an arduino like i originally wanted to, but with 2 modules that run directly on mains voltage it was easier this way i felt.