OT:Switching line voltages

[Batz Goodfortune]

Y-ellow Y'all.
	Why not use an industrial relay. (Mains voltage) My whole studio is
switched on by an industrial motor contractor. Over kill I know and it's a
bit noisy mechanically but it's effective for the time being. All you do is
connect the mains up to the energizing terminals and it kicks in. The idea
is that you can use low current mains voltage to switch high current mains
voltage. In a similar way that you have a relay to switch your car
headlights on. So that you can have low current running through your
head-light switch and control the high current required by your headlights.
Or an ignition solenoid for that matter.

You should be able to pick up motor contractors surplus fairly cheaply. I
got mine that way. Mine has 3 terminals for 3 phase and switches about 100
amps @ 240 volts. Well over kill!

You can of course get smaller ones. But why use a golf buggy when you can
have a diesel electric locomotive. :)

Inside these things it's basically a normal relay coil designed to work at
about 380 VDC and a couple of rectifier  diodes. (rectifying 240 VAC
produces about 380VDC)

The way I do it is to use the neutral line to contact the relay. I use one
of the three  terminals to jam the relay on. So, there's a big green button
and you hit it and the studio turns on. Another big white button breaks the
circuit and turns it all off again. That way you don't have to hit 50 power
switches to get some action. And it's mighty impressive. When this thing
kicks in it's like they're frying Big Louie.

If that's no good to you, why not try SSRs. (Solid State Relays) These cute
little guys are a potted block with 4  screw terminals on them. You put
mains through one end and a control signal through the other. 

This explanation is a bit simplistic but basically inside, you have either
a triac or a pair of back-to-back SCRs. Basically any voltage between 3 and
40 volts will kick 'em in. They use an opto isolator at one end and are
completely isolated from the mains. Take the voltage away and they kick out.

Some do not kick out once they have been kicked in and require the mains to
be removed from the circuit before they disengage. Most kick in and out at
will.

Sometimes combinations of these devices can be used to do light dimming and
are often seen in lighting racks. The brand I use are called "OPTO22". Only
because I could get them at one time. There are other brands.

There are also devices called "Redacs" which are basically reed relays.
These also poses the  properties that they do not turn off once they are
turned on. However all the ones I've seen require around 32 volts to
initialize and are not as flexible as their solid state counterparts.

All of the above devices are good because you only need to wire them in.
You could use triacs and optos but you'd need to design an operating
circuit. After messing with triac based light dimmers years ago, I can't
stress how dangerous this can be.

What ever you do, remember, MAINS VOLTAGE CAN KILL! If not you, then
someone else operating the gear you've built. If you don't have a clue
about this stuff, don't attempt it in the first place. And as always a
disclaimer. If you fry your goldfish because of something said here then
it's you're own problem.

Hope this helps .

Be absolutely Icebox.

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