Current operated auto switch?

I would like to turn on the vacuum cleaner every time I start the saw/sander/whatever. It's not a specialised cleaner - just a Henry.
ISTR current operated gadgets for this - a multi way socket strip which energises all the sockets if current is drawn from a 'master' one....
Anyone have any information/places to get them please?
--
Bob Eager
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Lidl had these on sale a couple of months ago at 6.99 each. Picked up a few for my computers, but had to return one only after a few weeks. The rest seems to be behaving for now.
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On Sun, 23 Jan 2005 23:56:21 -0000, "clueless2" <no.spam> wrote:

Won't work for machine tools though. The current, particularly the inrush on startup, will kill them if you use anything bigger than a detail sander.
If you have to do it with parts from Lidl, then try their remote-controlled sockets. 15 for four and a radio remote control, so you can even afford to kill the odd one ! Having _remote_ control of the dust collector is nearly as good as having automatic control.
Another way is some good ear defenders, so you don't worry so much about turning it off.
If you know some electronics, then a surplus (or even new from RS) current transformer and a simple circuit with a rectifier, op-amp and monostable delay can drive a contactor (big relay) for you. Mine is all junk-box parts. Don't forget that time delay to keep it running after switch off, otherwise it doesn't clear the last few chips out.
--
Smert' spamionam

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Or you can simply run the contactor from the flimsy autostart device.
Christian.
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On Mon, 24 Jan 2005 09:50:58 -0000, "Christian McArdle"
No, a woodworking machine (especially with a brush motor) will kill the sensing circuit in the Lidl auto-extension lead.
Most DCs that are switched on and off, rather than permanentyly plumbed and running continuously, are just quite small induction motors of 1/3rd or 1/2 horse. It might manage to survive those (marginal, but probable).
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There is a 2A fuse inside the Lidl thing. Unfortunately, I couldn't see an obvious way to upgrade the sensor socket to take 13A.
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wrote:

Hi,
Use the Lidl thing to drive a mains coil relay, something like RS 352-474 will do.
cheers, Pete.
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strung together this:

No, it's the sensor socket that is under-rated. That's the one that the powertool plugs into.
--

SJW
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On Mon, 24 Jan 2005 23:14:31 +0000, Lurch

Doh! >:|
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On 23 Jan 2005 22:27:36 GMT, Bob Eager wrote:

Seen in B&Q if Lide don't have any... but as others have pointed out watch the ratings, though a decent CRT has quite an inrush as the degaussing takes place.
CPC have a Velleman-kit module K8034 (CPC Part HK00779 15.97 + VAT) but looking at the picture and the spec this has changed between the 2004 cat and 2005. Looks like the max loads are now lower. 2A for the master and 5A for the slave, it uses a relay for the slave switching though... It also says "enclosure supplied".
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Simplest is take a relay, remove the winding and rewind it with thick insulated cpper wire. Once a certain current goes through that, the relay will close. You get around a 3:1 current operating range, which should be workable for power tools. Relays typically close at around half rated, and generally survive upto 1.5x rated. It is best to calculate wire size.
NT
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Relays cost around 1-2 a piece, or for 24v you can find them in various chucked out kit. Try to avoid rat shack etc.
NT
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For jobs like the vacuum cleaner/circular saw combination, you could make your own gadget if you're so inclined ( and this is a DIY forum after all ).
If you get a reed switch ( glass tube with a magnetically sensitive switch inside ) you can wind a number of turns of suitably rated wire around it and place it in series with the master load.
When the current flows, the reed relay closes and in turn operates a more powerful relay that works the vac.
Reed switches typically need about 30 amp/turns to operate, so if your saw draws 3 amps then 10 turns will do the trick. You can't harm a reed switch by exposing it to too much of a magnetic field, but they are very puny switches in an electrical sense, so make sure you get one that will handle the voltage and current needed for your chosen power relay ( the one that works the vac ). It's most unlikely that you'll find a reed switch that will work a vac directly without needing another power relay.
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Are you saying a reed switch will work with AC?
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*Why is 'abbreviation' such a long word?

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Check out CPC's catalogue ( page 2479 )
They have a range of reed switches rated up to 3A or 1500V ac, however the maximum VA is only 120, which is why you need a power relay for the vac, but to operate a power relay, you only need a lesser reed relay, which costs 68p. I would expect Maplin & RS to offer a similar range.
I use this reed relay trick to operate an extractor fan in a utility room where an old unvented tumble drier is located. Turn on the drier and the fan automatically turns on as well, but the fan can be run independently too if you wish.
I couldn't think of a simpler solution.
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snipped-for-privacy@Tesco.net wrote:

however
the
That's the contact rating.
I think the question was do they work with an Alternating field as you would get by winding mains supply to a power tool around one?
MBQ
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On 25 Jan 2005 07:53:48 -0800, snipped-for-privacy@Tesco.net wrote:

And protect it from the back EMF from the relay coil when it switches off. There is no switch off delay with this either, which your really do need for vac to clear the last lot of chips/dust WHY.
--
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Don't think it matters. ;-) I've got loads of assorted reed relays and they're all DC only.
--
*Xerox and Wurlitzer will merge to market reproductive organs.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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and
good point. Reed relays will typically switch upto a few hundred hertz. Although the bigger relay may not be too bothered by a chopped feed, it will reduce the life of the reed dramatically.
I'd rectify the feed to the reed and add a reservoir cap: this will also give run on after power off, as wanted by so many.
A small cap across the ac terminals of the 4 diode brisge will protect it against most spikes.
NT
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snipped-for-privacy@meeow.co.uk wrote:

hertz.
it
How do you rectify the feed to the reed? It's a magnetic field from a few turns of the supply wire to the load?
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