Trigger the same set of safelights from independent timers?

[Sirius Glass]

You need to use a relay for each timer and run the coils separately via each timer and the contacts (normally open) in series on the safelight power line. The safelight is plugged into it's own wall outlet and the safelight outlets on the timers power the relay coils. All power circuits are separate from each other and no chance of a short circuit.

I am not sure that is quite right. Could you explain in more detail so i [we] could be sure we understood correctly?

Steve

 

[glbeas]

Each timer has an outlet that energises for the safelight. Use this to energise the coil of a relay for each timer. The contacts should be wired to an outlet daisy chain style (in series) so both have to be energised for the safelight to be on. The safelight plugs into this setup. I'd put the relays in a project box with clearly marked cords for the timer connections and a power cord for the safelight to plug in the wall and an outlet to plug the safelight in to. Heres a rough sketch. I could put together a working circuit in minutes if I had the parts on hand.
It could easily be set up for a normally closed setup to actively turn off the circuit using the enlarger plug or with a normally open to use the safelight plug if available.

 

[clayne]

Each timer has an outlet that energises for the safelight. Use this to energise the coil of a relay for each timer. The contacts should be wired to an outlet daisy chain style (in series) so both have to be energised for the safelight to be on. The safelight plugs into this setup. I'd put the relays in a project box with clearly marked cords for the timer connections and a power cord for the safelight to plug in the wall and an outlet to plug the safelight in to. Heres a rough sketch. I could put together a working circuit in minutes if I had the parts on hand.
It could easily be set up for a normally closed setup to actively turn off the circuit using the enlarger plug or with a normally open to use the safelight plug if available.

Gary, similar to an earlier post with SPST relays as an example. Either way, your method also looks sound to me. I think the key factor here is the inline or serial use of relays to guarantee either timer will indirectly (via relay) create an open situation in the main circuit.

I'll rig something up in the coming months and let you guys know if I blew anything up.

BTW, given a typical US 120vac/15a circuit, I'd presume we wouldn't be drawing 15 amps through the control side of the relay, as that would be nuts. Is the solenoid (or similar) on the coil side of the relay the only limiting factor of current draw from it's source - or does it use some form of resistor?

 

[Sirius Glass]

Each timer has an outlet that energises for the safelight. Use this to energise the coil of a relay for each timer. The contacts should be wired to an outlet daisy chain style (in series) so both have to be energised for the safelight to be on. The safelight plugs into this setup. I'd put the relays in a project box with clearly marked cords for the timer connections and a power cord for the safelight to plug in the wall and an outlet to plug the safelight in to. Heres a rough sketch. I could put together a working circuit in minutes if I had the parts on hand.
It could easily be set up for a normally closed setup to actively turn off the circuit using the enlarger plug or with a normally open to use the safelight plug if available.

Thanks for your clarification.

Steve

 

[Steve Smith]

Whilst this two really version will work fine, Nicholas Lindan's single relay version is simpler and Sirius Glass's no relay version is simpler still.

BTW, given a typical US 120vac/15a circuit, I'd presume we wouldn't be drawing 15 amps through the control side of the relay

Or through the contacts unless you're running 1800 watts of safe light.


Steve.

 

[clayne]

I'm still having trouble wrapping my head around the single relay version, unfortunately.

The zero relay version I definitely won't be trying. If this were 5v and mAmps, maybe I'd be game - but we're talking line voltage here.

If anything, at least the thread is out there now. None of my previous searches turned up anything in the ballpark.

 

[Steve Smith]

I'm still having trouble wrapping my head around the single relay version, unfortunately.

It's simple. When neither enlarger is on, the outputs for both safelights are energised. This turns on the relay whose contacts then connect the safelight to the output of the other timer.

If timer 1 switches the safelight off, the relay disconnects the safelight from timer 2.

If timer 2 switches the safelight off, it doesn't matter where the relay is as there is no power being supplied to power the safelight.


Steve.