Adding another switch to a relay operated light switch

Posted by David Nebenzahl on September 13, 2008, 4:03 pm

On 9/13/2008 9:53 AM John Smith spake thus:

>> Your picture shows the two switches in series with each other. That
>> won't work. You have to install the second switch in parallel with
>> the first one, this way either switch will ratchet the relay one
>> notch each time it's closed

>
> Correct again. Looks like I have to do that. After following a lot of
> wires I still can't locate the original transformer.

RBM's correct: what you want, apparently, is a "wire OR" circuit (so
called because either one switch or the other will operate the device).
The way you have it wired is a "wired AND" circuit.

HOWEVER: if you're using transformers as power sources, there's an
additional problem. If you use more than one transformer connected
together, they have to be in phase, or they'll cancel each other out.
You could get around this by rectifying the current to DC, but then you
might have to use a DC relay instead of the AC one you have now.

--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire

Posted by Bill on September 13, 2008, 9:52 am

With a regular relay you could use two regular 120V 3-way light switches,
but connected to the 24 volt.

With a double pole relay, you could use one pole to latch on the relay and
use two normally open momentary push button switches wired in parallel to
turn the relay/light on, then two additional momentary normally closed
switches wired in series to the latching circuit to turn the light off.

Or use a certain type of toggle/switching relay and use two normally open
momentary push button switches wired in parallel to turn the light on/off.

"John Smith" wrote in message

> Light switch in my room is operated using a relay (rated 24v-8v). It just
> like in
> the picture http://home.howstuffworks.com/relay1.htm
> The top "battery" is ofcourse regular power. The bottom "battery" is
> operated by
> 24V transformer.
> I'd like to add another switch to the relay. How do I do add it to this
> system?
> I have another 24V transformer with a switch. If we have the
> http://home.howstuffworks.com/relay1.htm system as an example - could I
> add
> another switch+battery to the same coil? Actually the relay is a latching
> relay.

Posted by Kevin Ricks on September 13, 2008, 9:59 am

John Smith wrote:

> Light switch in my room is operated using a relay (rated 24v-8v). It just like

> the picture http://home.howstuffworks.com/relay1.htm
> The top "battery" is ofcourse regular power. The bottom "battery" is operated

> 24V transformer.
>
> I'd like to add another switch to the relay. How do I do add it to this

system?

> I have another 24V transformer with a switch. If we have the
> http://home.howstuffworks.com/relay1.htm system as an example - could I add
> another switch+battery to the same coil? Actually the relay is a latching

relay.

Depends on what you are trying to accomplish.

You could just add a 2nd switch in parallel with the 1st switch. But
then the 1st switch must always remain off for the 2nd to work.

You could add a second switch in series with the first, but now the 1st
would always need to be on in order for the 2nd switch to work.

If you want both switches to function independently then you would need
to change both switches to 3 way type.
Hook the battery to the common terminal of the 1st switch.
Run 2 wires (travelers) over to the 2nd switch.
Run another wire from the common terminal of the 2nd switch back back to
the relay coil.

Don't add any more voltage sources to the coil or you will likely burn
it out.

Get a book on basic electricity concepts. Then draw out your circuits on
paper.

Kevin

Posted by RBM on September 13, 2008, 11:28 am

> John Smith wrote:

>> Light switch in my room is operated using a relay (rated 24v-8v). It just
>> like in
>> the picture http://home.howstuffworks.com/relay1.htm
>> The top "battery" is ofcourse regular power. The bottom "battery" is
>> operated by
>> 24V transformer.
>> I'd like to add another switch to the relay. How do I do add it to this
>> system?
>> I have another 24V transformer with a switch. If we have the
>> http://home.howstuffworks.com/relay1.htm system as an example - could I
>> add
>> another switch+battery to the same coil? Actually the relay is a latching
>> relay.

> Depends on what you are trying to accomplish.
> You could just add a 2nd switch in parallel with the 1st switch. But then
> the 1st switch must always remain off for the 2nd to work.
> You could add a second switch in series with the first, but now the 1st
> would always need to be on in order for the 2nd switch to work.
> If you want both switches to function independently then you would need to
> change both switches to 3 way type.
> Hook the battery to the common terminal of the 1st switch.
> Run 2 wires (travelers) over to the 2nd switch.
> Run another wire from the common terminal of the 2nd switch back back to
> the relay coil.
> Don't add any more voltage sources to the coil or you will likely burn it
> out.
> Get a book on basic electricity concepts. Then draw out your circuits on
> paper.
> Kevin

Since he's using a ratchet relay, I'm guessing his switches are momentary
contact, "guessing" being the optimum word

Posted by John Smith on September 13, 2008, 12:51 pm

>Since he's using a ratchet relay, I'm guessing his switches are momentary
>contact, "guessing" being the optimum word

Correct. Switches are only momentary contact.

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