Auto switch on for extractors

[AndyBoyd]

I need to build a few of these as the 70€ price tag is a bit daunting for a Scheppach one of these.

I know Maplin used to slock a Master/Slave unit that could be used but discontinued it. Does anyone else know where I can buy a switching relay to handle a 1hp extractor, with ideally an off delay built in?

I thought of wiring a standard relay into my set up (in a box with in socket and out socket 220v- and a trailing cable with a plug to provide the switched power for the extrator.

But would I run into trouble wiring the coil of such a relay (240v version)
http://www.maplin.co.uk/module.aspx?ModuleNo=37514&doy=10m2&QV=P

Into the power feed for the machine from which the extraction is required?
So I turn e.g the saw on - the coil for the above relay is in the power feed to the saw, and therefore the relay activates, sending a seperate power feed via the relay contacts to the extractor.

Assuming I wire it all safely (boxed earthed proper sockets plugs, properly rated realy etc) is there any flaws in this logic?

 

[RogerS]

Andy

The problem you face, as I see it, is that you need to sense the current being drawn by your saw and to use this as your trigger to turn on the relay. That is exactly what the Maplin device did. There is a thread elsewhere on this same topic.

Your solution will work but you need to tap into the on/off switch of your table saw to pick up the voltage (when you turn the saw on) to provide power to the relay. I'm not sure (reading your thread) that that was what you were intending to do.

Also the spec for the relay has an error...the maximum load is stated in both cases as resistive and I suspect that one of them (the lower one) is for an inductive load which will be what your extractor will present and so the relay won;t be suitable I think...maybe Tony will be along soon to comment?

If the table saw power switch is an NVR then you can't turn the problem around the other way and use a separate switch to turn on, say the saw when the extractor is on.

 

[ike]

Andy,

Just a bit of lateral thinking here. You know those cheapy Performance Power Workshop vacs in B&Q for £34.99 (the black/red one about the size of a petrol can?

They have a PCB in them for autoswitching tools up to 2400W (the vacumm motor is rated 600W). The total rating is 3000W but I'm not sure if this means you can balance the loads in different proportion. Obviously it is designed to switch an inductive load.

Mine is knackered (the motor/fan bearings are almost shot). I replaced it with the bigger unit and I am going to hopefully salvage the electronics for an autoswitching box I can simply plug inline from a wall socket as required for various tools in the workshop.

Is it woth spending £35 to cannabilise an almost readymade solution that just needs an enclosure?.


cheers,

Ike

 

[Les1693]

I was looking for one of these last year. The only one I could find was from Axminster, a master socket with 5 slaves for just under £50. I thought this was too much and took the cheap option of being the slave myself by manually switching the dust extractor on and off.

Keep us posted if you do find one at a reasonable price.

 

[Les1693]

For info here's the link the Axminster Master/Slave socket.