Remotely controlled relay

[mklotz]

The original motivation for this relay-controlled outlet was for those evil tools (like certain Dremels) that have the speed control mated to the on-off switch. Every time you turn the device off you lose your speed setting and have to fiddle to recover it when the tool is turned back on.

The obvious solution is to power the device through an external switch to supply the on/off function while the speed control remains at your chosen setting.

At the time I built this I had another application that involved controlling a powerful AC spot light from a distant location. I did not want to run the AC line feeding the light back to a local switch because of the power loss in a long power cord.

So the solution to both problems was to control the device (Dremel/light) via a local high current relay and switch the relay via a low current, low voltage switching arrangement.

In the photo you can see the relay on the top of the box and the outlet it feeds on the side of the box beneath it. The small filament transformer on the top powers a simple diode & capacitor setup inside the box to provide 8 VDC. This DC is fed to a series of connectors on the side of the box - two pin jacks, a phone f jack and a switch - all wired in parallel. When any of these connectors are shorted the DC closes a reed relay inside the box to provide power to the relay coil and close the contacts to feed the AC outlet.

Because only very low voltage is used in the control circuit, any light wire can be used to short the connectors. Two strand bell wire is cheap and easily available. The foot switch shown, reclaimed from an old Dictaphone, plugs into the phone jack for foot control. When sitting on the workbench to control something like a Dremel, the switch on the box is used and nothing need be plugged into the other connectors.

Over the years, this device has proved useful many times. The convenience of being able to string any old, cheap wire to safely control potentially dangerous power is really great.

[DIYer]

Thanks mklotz! We've added your Remotely Controlled Relay to our Electrical category,
as well as to your builder page: mklotz's Homemade Tools. Your receipt:

Remotely Controlled Relay by mklotz

tags: electrical, switch

[Bony]

It's always interesting to read your posts Marv, thanks for sharing. No doubt your relay was conceived and constructed some time ago and what was had to then be done to remotely control a power point.

In the interests of assisting others with a need for remote switching another alternative nowadays of course is to use an inexpensive radio controlled remote switch which may be found in electronics stores and online. Eg. this one is less than US$15.

https://www.ebay.com.au/itm/35455692...Bk9SR4zilJm1Yg

[mklotz]

It's always interesting to read your posts Marv, thanks for sharing. No doubt your relay was conceived and constructed some time ago and what was had to then be done to remotely control a power point.

In the interests of assisting others with a need for remote switching another alternative nowadays of course is to use an inexpensive radio controlled remote switch which may be found in electronics stores and online.

Thanks for the kind words, Bony. Much appreciated.

Yes, I was aware of commercial remotely controlled switches when I built this. In fact, I had one of the earlier ones, built to control external Xmas lights, in use in the house to control an awkwardly placed light fixture.

A very great many of the ideas shown on this forum could be replaced with commercially available items. There aren't many problems that can't be solved by throwing money at them. It's best to view the forum as an idea fountain demonstrating how people solved a problem with available material, not necessarily in the most economical way. The focus should be to get you thinking about design features that could be used for your particular application

For instance, some takeaway points for my remote controller are...

Low voltage, parallel input capability so a number of simple low current switches could each could be used to control a large current. (I've never seen a commercial RC unit with a foot switch.)

Since a relay is used, the unit could easily be modified to control a large DC current.

The low voltage needed to close the relay could be supplied by batteries, thus making the entire unit independent of the mains.

In the event of a failure, a socketed relay is easier to replace than components on a circuit board.


I'm sure many folks who read my post would think, "Gosh, he could replace that honking relay with a triac triggered with his reed switch arrangement." They would be correct. In fact that's exactly how the light controller box, also homemade, in my bedroom is wired. (The noise of the relay clicking would have woken my wife.)