Best place for a switch...

I had a peak inside the switch / speed controller box on my scroll saw. It seems to be a NVR switch followed by a reasonably sophisticated electronic speed controller, with a two wire feed to the induction motor at the end of it (there is also a two wire connection to a 15uf high voltage cap that is housed in the same enclosure).
Now what would be nice, would be to add the capability to have a foot switch to stop / start the saw (momentary action - push to go, let go to stop kind of thing)
The NVR switch prevents the easy option of switching the mains in. So the options would seem to be:
1) Insert a switch between the NVR switch output and the mains into the speed controller.
2) Switch between the output of the speed controller and the motor
3) Combination of 1 or 2 above in addition to a foot pedal containing a suitable variable resistance to take the place of the speed selection knob - giving a sewing machine like control over speed.
1) seems like the obvious one, but can anyone thing of particular pros/cons of the options?
Next a suitable connector...
Can anyone suggest a suitable connector? I recall in the past there being a Telefunken style figure 8 socket that also integrated a switch that was actuated when the lead was inserted, but I can's find anything like that at the moment. It would be nice to have a smallish mains rated connector system that could be configured to leave the system running normally when the external switch is disconnected, but would automatically adapt to using it when plugged in. (and preferably with the female bit of the connector on the saw such that you can leave a pin live without risk!)
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John.
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On Saturday, February 1, 2014 4:57:45 AM UTC, John Rumm wrote:

Portable radios have long had a switched figure of 8 socket, so the battery disconnects when mains lead is in. But that leaves you live pins. If you used a relay you'd be down to low v on the pins.
If you used something like an 8 pin bulgin, plugging in could power up a relay that then switched mains onto other pins. Whats wrong with a simple fixed lead?
NT
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On 01/02/2014 07:04, snipped-for-privacy@care2.com wrote:

Yup it was kind of what I had in mind, but could not find an obvious source of those sockets either.

Fixed lead would actually solve some of the problems. Just a bit more hassle if one wants to move it about...
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On Saturday, February 1, 2014 5:46:16 PM UTC, John Rumm wrote:

theres always a dead radio :)

is it really?
I guess you can always add another box onto the machine for extra electronics.
NT
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A conventional motor starter can easily be fixed to do such a thing. Not sure if that's what you mean by NVR (No Volt Release?) http://www.indiamart.com/itcimpex/dol-motor-starter.html
The facility you want is called "inching"
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On 01/02/2014 09:23, harryagain wrote:

Er, no. I just want on/off control via a foot switch, not pulsed slow advance for the motor.
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There is no speed control effect. It is just a start button that you have to keep your finger on, the motor stops when you let go.
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Snag with that sort of connector is it's designed for mains in - to disconnect an internal battery. You need a gender reversed one for your application.
Is there lots of room inside the saw body? Room for a low voltage power supply and relay? With only low voltage going to the footswitch you'd have a wider choice of connectors - and in any case a much better way of doing it.
The Speakon/Mainscon range of connectors are reasonably cheap and very robust.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 01/02/2014 10:59, Dave Plowman (News) wrote:

Indeed and also I would not want to encourage anyone not informed to plug a normal mains lead into it.

Not really... Not my photo but:
http://img.auctiva.com/imgdata/1/2/7/0/6/1/webimg/664303492_tp.jpg
The plastic box with the mains lead going in is about 2" square, but its mostly full already with the PCB, NVR back projection, and the motor cap.

Yup agreed.

Something that is effectively shuttered or sleeved on both parts would be ideal.
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You could fix a second box alongside that one?

The Speakon type has the live pins on the plug reasonably protected - you couldn't touch them with a finger. Although they are different for in and out. I only suggested them because they are the strongest low(ish) priced connector.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 01/02/2014 04:57, John Rumm wrote:

I rigged up something similar using a pneumatic foot switch, operating an electric relay. It was a long time ago and I can't recall the make or type now though.
Colin Bignell
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On 01/02/2014 11:35, Nightjar wrote:

Now that is an option I had not thought of...
This kind of thing?:
http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/461128.xml
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On 01/02/2014 17:43, John Rumm wrote:

...

Very similar from what I recall.
Doing a Google search comes up with the spec sheet
http://www.herga.com/sites/default/files/6871_1.pdf
You may find the 6872 DPCO switches better suited to your needs.
Colin Bignell
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On Sat, 01 Feb 2014 04:57:45 +0000, John Rumm wrote:

4) DP Switch across the (DP?) NVR. "Switch" being a suitable relay with LV control or perhaps better a pneumatic operated one as has been mentioned.
Slight risk that the contacts across the NVR could weld into the "on" state but that would be fairly obvious as the thing wouldn't switch off...
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John Rumm wrote:

I'd suggest not putting any switching between the motor and the speed controller. The back emf when the switch opens just might damage the controller. Can't suggest a connector with built in switch but you could possible adapt a standard one to add a micro switch to one?
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