StopClock and Omega Super Chromega F

JackRosa · Jan 6, 2014

Please forgive me if this topic has already been discussed. Not knowing anything about electric connections, I am hoping I can get some help.

My darkroom setup includes an 8x10 Omega F enlarger (Super Chromega F head + Fotar chassis). The Omega F head has a 1,000-watt lamp-house (4 lamps, 250 Watts ea.). My timer is a Lektra TM8, which can handle the 1,000 watts no problem. I am seriously thinking about going the RH Designs' StopClock route but know their meter is rated for 500 Watts. In reviewing the Omega F's User's Manual, I see that I can use an Omega Power Relay (or some other type of contractor/relay) to absorb the high load and be able to connect any enlarger timer to my setup. The Omega F Power Supply controls not only the lamp-house but also the fan (that cools the lamp-house). When one turns on the power button (on Power Supply), the fan automatically goes on [a safety feature, I believe].

Can I simply connect the StopClock to the relay and the relay to the power supply and make the ensemble work with the StopClock? Does anyone have experience with this type of set-up?

Thank you in advance for your kind help.

Jack Rosa
jack.rosa@me.com

ic-racer · Jan 6, 2014

Yes, using a relay would be safest for the Stopclock.
I don't recall how the F power supply deals with the fan, but the D power supply drives the fan from the power supply AC cord and powers the enlarger lamp from the timer input receptacle.

JackRosa · Jan 6, 2014

Thanks ic-racer. I think I understand that using the relay would protect the StopClock (from getting fried by 1,000 Watts). Adding the StopClock to the circuit would not change how the Omega F Power Supply turns on the fan, correct? I want to make sure that when I turn ON the Power Supply, the lamp-house's fan goes on and that the StopClock simply turns on/off the lamp-house.

wildbill · Jan 6, 2014

I have the same setup (chromega head, fotar enlarger) and I was worried about a timer as well but ended up getting a Kearsarge timer (without relay) that I believe is only rated for 500watts. Someone had been using the same timer on their 1000w chromega w/o any issues so I went for it. Not that you should risk a pricey timer by trying it.

Ian C · Jan 6, 2014

From page 8 of the Super Chromega F manual:

“Any accurate enlarging timer can be used with the Super Chromega F enlarger. However, an electronic timer is recommended. Used in connection with the Omega Power Relay [Catalog number 412-022], this combination provides an ideal timing system for the most demanding requirements. Note: the power relay must be used with timers rated below 1000 watts (minimum 100 watts).”

Properly connected thorugh the relay, the timer never receives the transformer current, so any timer of at least 100 watts capacity will work.

ic-racer · Jan 6, 2014

I found my schematic for the Chromega F unit. Indeed one needs to power the lamp through the timing circuit (with or without relay). The main AC plug for the unit is not connected to the timer. That way the fan is not affected by the timer. Do you have the manual that shows how to hook this up?

JackRosa · Jan 6, 2014

Thanks ic-
I do have the manual showing the electrical hook-up; just did not know how to interpret it. Your insight reassures me that I should be OK with the StockClock if I use a power relay (contractor) to connect it to the power supply. THANKS much!

JackRosa · Jan 6, 2014

contactor, not contRactor

Erik L · Jan 6, 2014

I have the same setup except with a darkroom automation timer and I made a relay with the following McMaster Carr part numbers. Just needed to get a few feet of electrical cord and some plugs. It was very simple to do.
7384k21 and 7384k45

JackRosa · Jan 7, 2014

Thanks Erik and thanks to ic-racer, Ian C, and wildbill for contributing to this thread. I am now convinced that this is "doable" and will go ahead and pursue. I will report back, once I have received the StopClock and connected it to the Omega F. The Lektra TM8 has been a workhorse for me but it is time to move into the 21st century.

JackRosa · Jan 10, 2014

Progress Report I: purchased parts from Mcmaster-Carr and wired per drawing Erik L sent me. It was a breeze! Tested tonight (using an old Kearsarge timer, just in case) and the ensemble worked like a charm. A big thanks to all and a HUGE thanks to Erik L. The StopClock is on order!

JackRosa · Jan 15, 2014

Progress Report II (and final report): StopClock arrived and was connected to the enlarger via the power relay (as detailed in the enlarger's user's manual). The ensemble works perfectly.

Thank you all for your kind insight and help.

End of report

Fotocat2 · Jan 15, 2014

Another approach

Attached is an image of how we did it. As mentioned above, the relay is safest and allows use of almost any timer, but we were lucky enough to get one of the high wattage timers.

JackRosa · Jan 16, 2014

Thanks for sharing! I have the exact same enlarger set-up … a Fotar armed with a Super Chromega F head. A workhorse!

THGPhotography · Aug 1, 2018

I realize this post is a few years old, but hope the op is still available.

Would you be kind enough to send me, or post, the instructions for making the power relay with the McMaster parts, please?

I am waiting to plug my new stopclock into my super chromega f. The power relay from khb is nearly $600, so if there is a safe & less expensive option I'd like to explore that before writing a rather large check (after having just bought a brand new stopclock pro).

Thank so much!

Chan Tran · Aug 1, 2018

wildbill said:
I have the same setup (chromega head, fotar enlarger) and I was worried about a timer as well but ended up getting a Kearsarge timer (without relay) that I believe is only rated for 500watts. Someone had been using the same timer on their 1000w chromega w/o any issues so I went for it. Not that you should risk a pricey timer by trying it.

You can use a timer rated for 500W with an 1000W enlarger for quite sometime without problem but I wouldn't recommend doing so. Generally most timer are underated in their output power but still it's much better to use a relay in between.
When I had my Besseler CB7 with it's dichroic head which has 2 200W 24VDC lamp. I installed 2 24VDC 10A power supplies and 2 25A solid state relay. I modified my timer to send out only 24VDC to switch the relay on.

carlj · Nov 13, 2022

Again, also realize this is an old post, but does anyone have the wiring diagram for making the power relay (parts are still available)?

thanks

ic-racer · Nov 13, 2022

You will have a hot line coming to the coil of the relay from the timer that turns the relay on and off. The relay's contacts will control the power to the enlarger through another hot line coming in. Each relay is different, so you will have to look at the spec sheet to see which wires go where on the relay. This one is plugged into a socket that has screw terminals to make it easier to wire up.

carlj · Nov 18, 2022

Thanks, that's helpful and much appreciated.

I'll look again at parts and see what we can do.

carlj · Jan 5, 2023

Update. I'm ordering the parts listed above (from the 2014 post) from McMaster. It's a medium current relay and a cover. No expert but I'm willing to give it a try. I'll have to figure out what connectors are needed (you have 3 wires coming into/out of the box) when I can go take a closer look at the enlarger power supply.

https://www.mcmaster.com/7384K21/ - medium current relay.

https://www.mcmaster.com/7384K45/ - cover for 1 and 2 circuit medium-current relay.

Thanks

StopClock and Omega Super Chromega F

Privacy & Transparency

Privacy & Transparency