Author Topic: Using an AC Circuit to Turn on Another AC Circuit  (Read 4478 times)

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Offline dellsam34Topic starter

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #25 on: January 25, 2025, 07:46:31 am »
Here's a switch I built to turn on a shop vac being used with a power tool (bandsaw) whenever the saw was in use:



The SSR I used is plenty beefy enough to handle your fan as a load.

Of course, to use this with your stove you'd have to connect the switch between a plug and a receptacle for the oven plug, assuming the stove isn't directly wired into a junction box. (You probably wouldn't want to cut open the stove cord, although you could do that.)

Maybe this'll help?
This won't work for me, The stove is 220v.

Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #26 on: January 25, 2025, 06:24:05 pm »
Here's a switch I built to turn on a shop vac being used with a power tool (bandsaw) whenever the saw was in use:

The SSR I used is plenty beefy enough to handle your fan as a load.

Of course, to use this with your stove you'd have to connect the switch between a plug and a receptacle for the oven plug, assuming the stove isn't directly wired into a junction box. (You probably wouldn't want to cut open the stove cord, although you could do that.)

Maybe this'll help?
This won't work for me, The stove is 220v.

It'll work:



You can either power the fan from one of the legs of the 240 VAC (= 120 V), or run a separate 120 volt line in for the fan.

Ackshooly, the SSR has nothing to do with the ability to use this on 240 VAC. That's up to the current transformer, which can easily handle that. You just need to make sure that the conductor going through the transformer (just a piece of insulated wire) is a big enough gauge (10 AWG?) to handle the stove current.
« Last Edit: January 25, 2025, 06:28:15 pm by Analog Kid »
 

Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #27 on: January 25, 2025, 06:43:22 pm »
I've redrawn the circuit for your application:

 

Offline dellsam34Topic starter

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #28 on: January 25, 2025, 11:26:33 pm »
It is still invasive as it involves cutting wires, As you already know here in the US the 220V wires are too thick and I don't think they can be wired with spade connectors, it's a fire hazard waiting to happen, By the way the local code allows only twisted caps isolators, This is why I was initially looking for an amp sensing solution before I switched to heat sensing solution, I do really appreciate your effort to help.
« Last Edit: January 25, 2025, 11:28:37 pm by dellsam34 »
 

Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #29 on: January 25, 2025, 11:31:03 pm »
No cutting wires at all.
Notice the plugs and sockets on the schematic? This is a totally sef-contained "plug-n-play" thing.
I built mine in a square outlet box which will hold the two sockets (one for stove, the other for fan).
Two plugs emerge from the box, one for the 240 for the stove, the other for the 120 for the fan.
You'll probably have to go to an electrical supplier for the stove plug and socket, unless your local big-box home-improvement store happens to carry them. (There are several types.)

Here's an updated schematic making the wiring clear (no ambiguous grounds shown).

« Last Edit: January 25, 2025, 11:37:26 pm by Analog Kid »
 

Offline drksy

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #30 on: January 26, 2025, 03:13:40 am »
No cutting wires at all.
Notice the plugs and sockets on the schematic? This is a totally sef-contained "plug-n-play" thing.
I built mine in a square outlet box which will hold the two sockets (one for stove, the other for fan).
Two plugs emerge from the box, one for the 240 for the stove, the other for the 120 for the fan.
You'll probably have to go to an electrical supplier for the stove plug and socket, unless your local big-box home-improvement store happens to carry them. (There are several types.)

Here's an updated schematic making the wiring clear (no ambiguous grounds shown).

(Attachment Link)

OP may be confused looking at this picture since the wire going from the socket to the stove seems to be cut to passing through a transformer where you marked a star. It's probably more helpful to show how a current transformer looks, maybe with exact part numbers. The thick live wire carrying the current to the stove would simply pass through the center of a toroid, so it isn't being cut. It's similar to how AC current is sensed with a clamp meter.
 

Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #31 on: January 26, 2025, 03:26:26 am »
There's a picture in this post.
No part #, because it's cannibalized from a GFCI outlet, available everywhere.
The wire that passes through the current-sensing transformer is inside the box, between the plug and socket for the stove.
Plug the plug into the outlet the stove is currently plugged into.
Plug the stove into the switch box.

Here's a picture of another type of current transformer found inside a GFCI outlet:



The power line (in the schematic the line between the plug and the socket that goes to the stove) is the thick conductor through the center (there are two here, but you could just discard the other one for this type; you only need 1 conductor going through to form the primary side of the transformer).
The coil of fine wire is the secondary, as shown in the schematic.

Does that make sense to you?
« Last Edit: January 26, 2025, 03:36:16 am by Analog Kid »
 

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #32 on: January 26, 2025, 04:01:18 am »
This shows how everything fits into a box for my shop-vac switch:



Yours would be a bit tighter, since you need 2 outlets side-by-side (the 240-volt outlets are singles, not duplex), but I think you could cram everything into one of these square boxes. You might need to use a deep box.
The orange cord is the incoming power. You'll need 2 cords, one for the stove (240 volts), the other for the fan (120 volts).
 

Online inse

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #33 on: January 26, 2025, 06:19:36 am »
Educating the people to use the hood when cooking is not an option?
 

Offline dellsam34Topic starter

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #34 on: January 28, 2025, 08:33:23 am »
Educating the people to use the hood when cooking is not an option?
Me using the phrase "idiot proof" was not a coincidence.

Online Zero999

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #35 on: January 28, 2025, 09:49:35 am »
No cutting wires at all.
Notice the plugs and sockets on the schematic? This is a totally sef-contained "plug-n-play" thing.
I built mine in a square outlet box which will hold the two sockets (one for stove, the other for fan).
Two plugs emerge from the box, one for the 240 for the stove, the other for the 120 for the fan.
You'll probably have to go to an electrical supplier for the stove plug and socket, unless your local big-box home-improvement store happens to carry them. (There are several types.)

Here's an updated schematic making the wiring clear (no ambiguous grounds shown).

(Attachment Link)
A potential issue with that circuit is current transformers don't like being open circuit, so that  Schottky diode might be subject to high reverse voltages. A simple fix is to put another diode in the reverse direction, directly across the transformer.

The OP's cooker might also draw too much current for that tiny transformer to handle. Your saw is much lower power than a heating element. GFCI transformers are not designed to handle the full current continuously.

If breaking into the cooker wiring is impractical, then a split core current transformer can be used, which simply clips over the current carrying cable.

EDIT:  GFCI transformers are not designed to handle the full current continuously
« Last Edit: January 31, 2025, 08:58:25 am by Zero999 »
 

Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #36 on: January 30, 2025, 11:22:34 pm »
I have designed 2 devices that can accomplish this task.
Both are simple, reliable, and consume no standby current.

WARNING: One of the line wires for the stove must draw 0 current when the stove is off.
This will not work on stoves that don't utilise the neutral.

Determine which line does not power the clock and draws 0 current when the stove is off; this is is the line that is switched.
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Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #37 on: January 30, 2025, 11:40:35 pm »
No cutting wires at all.
Notice the plugs and sockets on the schematic? This is a totally sef-contained "plug-n-play" thing.
I built mine in a square outlet box which will hold the two sockets (one for stove, the other for fan).
Two plugs emerge from the box, one for the 240 for the stove, the other for the 120 for the fan.
You'll probably have to go to an electrical supplier for the stove plug and socket, unless your local big-box home-improvement store happens to carry them. (There are several types.)

Here's an updated schematic making the wiring clear (no ambiguous grounds shown).

(Attachment Link)
A potential issue with that circuit is current transformers don't like being open circuit, so that  Schottky diode might be subject to high reverse voltages. A simple fix is to put another diode in the reverse direction, directly across the transformer.

The OP's cooker might also draw too much current for that tiny transformer to handle. Your saw is much lower power than a heating element. GFCI transformers are designed to handle the full current continuously.

I don't think any of that would be a problem using this with a stove instead of my power tools.
It's true that the stove is going to draw a lot more current than my bandsaw, but as you wrote, GFCI transformers are designed to handle that kind of current continuously, so I don't see that as a problem.
Keep in mind that the high current is flowing through the "primary" which is just a thick piece of wire rated at the stove's full current (I'm guessing 10 ga. wire here), while the secondary really doesn't matter; its ratings aren't going to be exceeded at all.

So far as your first caution about open-circuit voltages, don't think that will be a problem either. The Schottky diode I used is rated at 40 volts, waaaaay above anything that GFCI transformer is ever going to deliver.

Worth a try in any case. So what do you say, OP?
 

Online Zero999

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #38 on: January 31, 2025, 08:56:34 am »
No cutting wires at all.
Notice the plugs and sockets on the schematic? This is a totally sef-contained "plug-n-play" thing.
I built mine in a square outlet box which will hold the two sockets (one for stove, the other for fan).
Two plugs emerge from the box, one for the 240 for the stove, the other for the 120 for the fan.
You'll probably have to go to an electrical supplier for the stove plug and socket, unless your local big-box home-improvement store happens to carry them. (There are several types.)

Here's an updated schematic making the wiring clear (no ambiguous grounds shown).

(Attachment Link)
A potential issue with that circuit is current transformers don't like being open circuit, so that  Schottky diode might be subject to high reverse voltages. A simple fix is to put another diode in the reverse direction, directly across the transformer.

The OP's cooker might also draw too much current for that tiny transformer to handle. Your saw is much lower power than a heating element. GFCI transformers are designed to handle the full current continuously.

I don't think any of that would be a problem using this with a stove instead of my power tools.
It's true that the stove is going to draw a lot more current than my bandsaw, but as you wrote, GFCI transformers are designed to handle that kind of current continuously, so I don't see that as a problem.
Keep in mind that the high current is flowing through the "primary" which is just a thick piece of wire rated at the stove's full current (I'm guessing 10 ga. wire here), while the secondary really doesn't matter; its ratings aren't going to be exceeded at all.
The secondary does matter.

The current flowing through the secondary is proportional to the primary current. Under normal operation in a GFCI, there are two primary windings, consisting of the phase and neutral, running through the middle of the current transformer. The currents through each primary are out of phase, so their fields cancel. Under fault conditions, the flux no longer cancels, a current is induced in the secondary, which triggers the trip mechanism that safely disconnects the power.

In your circuit, there is only one primary turn and the current continuously flows through the secondary. If the current is too high, for too long, then it will overheat.  The continuous secondary current rating is not specified. It might work in the original poster's application, or it might smoke.


Quote
So far as your first caution about open-circuit voltages, don't think that will be a problem either. The Schottky diode I used is rated at 40 volts, waaaaay above anything that GFCI transformer is ever going to deliver.
How do you know that? Have you connected it to an oscilloscope?

Isn't it easier just to add another diode (1N4148 will do) to avoid all doubt?


References:
https://www.google.com/search?client=firefox-b-d&q=current+transformer+open+circuit+high+voltage
 

Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #39 on: February 05, 2025, 02:19:32 pm »
Just use my design!

I will post an improved schematic later today.
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Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #40 on: February 05, 2025, 03:40:46 pm »
1N4148 are suitable for low-current only.

They are great and cheap and very reliable, but should never be used for power applications.

Use 1N400x or something.
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Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #41 on: February 05, 2025, 04:17:00 pm »
My website used to be www.getpacman.gq
It is now www.langdonstaab.ca
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Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #42 on: February 05, 2025, 10:43:52 pm »
Could you possibly make your schematics any more unreadable?
Heck, if you could supply a readable one I could draw a real nice standard schematic from it.
 

Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #43 on: February 07, 2025, 08:23:45 pm »
I'm a 16-year-old with a writing disablility.

Cut me some slack!

The V3 one is better.
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Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #44 on: February 08, 2025, 10:41:55 pm »
Perfect solution:

https://www2.langdonstaab.ca/files/Automatic%20switch%20schematics/Automatic%20fume%20hood%20switch%20V3.pdf

For resistors labeled a and b, use some resitive device that limits the voltage suppied to the relay.

A combination of a PTC thermistor and resistors should work (coils need more power to turn on)
« Last Edit: February 08, 2025, 10:49:53 pm by Langdon »
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Online Analog Kid

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #45 on: February 09, 2025, 02:42:43 am »
I see what you're doing there. Two relays, one self-activated by the oven, the other one controlling the vent fan.

Couple things: why two relays? You could just use a double-pole relay in the oven circuit to control itself (latching), with the fan switched by the other set of contacts.

Not sure why you have that "reset" switch which would de-energize the oven; is that some kind of safety feature?

Also not sure why you have the oven relay connected to both legs of the circuit through diodes; one side would suffice to energize the relay.

This would work. I still like my design better: uses no mechanical relays, which are expensive, noisy and harder to mount than my small solid-state relay.
 

Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #46 on: February 09, 2025, 06:35:21 pm »
I think one SPST 50A relay and one SPST 15-20A relay is probably cheaper than one 50A DPST relay.

For lower, equal amperages, one relay is fine.
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Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #47 on: February 09, 2025, 06:37:11 pm »
You press RESET when you turn "off" the oven.

The oven still recieves power through the line that is not switched and the neutral (for the clock and stuff).

RESET turns the fume hood off.

(You won't remeber to turn the hood off because it is noisy)

Technically, you only need 2 diodes, not five.
« Last Edit: February 09, 2025, 06:39:47 pm by Langdon »
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Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #48 on: February 09, 2025, 06:45:46 pm »
I see what you're doing there. Two relays, one self-activated by the oven, the other one controlling the vent fan.

Couple things: why two relays? You could just use a double-pole relay in the oven circuit to control itself (latching), with the fan switched by the other set of contacts.

Not sure why you have that "reset" switch which would de-energize the oven; is that some kind of safety feature?

Also not sure why you have the oven relay connected to both legs of the circuit through diodes; one side would suffice to energize the relay.

This would work. I still like my design better: uses no mechanical relays, which are expensive, noisy and harder to mount than my small solid-state relay.

You don't really understand how my circuit works, do you?

Obviously, you can substitue a solid-state switch for the relays in my design.

The relay is just a suggestion an equivalent is fine.

50A solid-state switches are not so cheap either.

But using a solid-state switch for the hood should be fine.
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Offline Langdon

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Re: Using an AC Circuit to Turn on Another AC Circuit
« Reply #49 on: February 09, 2025, 06:51:16 pm »
The GFCI transformer method proposed by Analog Kid should work fine too.

Just cut the wires that go through the coils and feed a thich stove conductor through the hole.

Though weird stray AC currents may sporadically turn on the fume hood for no reason (this device is perhaps a bit like the opposite of a surge protector).
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