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  1. #11
    Nicholas Lindan's Avatar
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    One relay with a form A (Common/Normally Open) contacts.

    The output of Timer 1 drives the relay coil.

    The output of Timer 2 goes to the safe light on one side and the the relay C contact on the other. The other wire of the safelight is wired to the 'NO' contact of the relay.

    For the safe light to be one both timers must have energized their safe light output AC sockets.


    It is possible to do it with no relays - but you don't want to try it as it has a good chance of making a short circuit - and violates every wiring code on the planet.

    * * *

    The reason for switching the safelight off is to:

    1) Make focusing easier as there is more contrast on the paper

    2) Make it easier to position dodgers and burners

    3) Allow the use of meters and analyzers as the safelight illumination interferes with the readings
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  2. #12
    Sirius Glass's Avatar
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    Quote Originally Posted by Worker 11811 View Post
    Sirius, an engineer would be better. But any electrician worth his salt would have learned how to wire a three-way switch on his second week of tech school. This circuit is only half that. If you drew it out on a big piece of paper with a nice, big crayon I bet you could teach an electrician to do it. It just might take a while.
    But using an electrician would not be as much fun as watching a engineer solve your problem just to prove you are wrong. Both sides win that way.

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  3. #13
    Worker 11811's Avatar
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    Yes, the best way to get something done is to tell an engineer that it can't be done!
    Randy S.

    In girum imus nocte et consumimur igni.

    -----

    http://www.flickr.com/photos/randystankey/

  4. #14
    Steve Smith's Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    It is possible to do it with no relays - but you don't want to try it as it has a good chance of making a short circuit
    That was going to be my suggestion. You don't need anything extra, just modify the timers so both internal relays are in series.

    But as the op is asking the question I assume he is not interested or able to do these sort of modifications.

    Quote Originally Posted by Nicholas Lindan View Post
    and violates every wiring code on the planet.
    There are no rules in the UK to prevent you doing this yourself in a domestic situation.

    The other option would be a parallel connection with separate on/off switches for each timer so only one was powered at a time.


    Steve.
    Last edited by Steve Smith; 05-16-2010 at 03:03 AM. Click to view previous post history.

  5. #15
    Sirius Glass's Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    It is possible to do it with no relays - but you don't want to try it as it has a good chance of making a short circuit - and violates every wiring code on the planet.
    Short circuits do not violate any laws or codes. The lifetime of a short circuit is usually short due to fuses and circuit breakers. Short circuits can burn out, therefore the open circuit is more reliable and will not burn out.

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  6. #16
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Steve Smith View Post
    just modify the timers so both internal relays are in series.
    Wellllll, most timers only use one relay inside -- the NC contacts go the to safelight outlet and the NO contacts go to the enlarger.

    To do it with no relays you need to hook one timer up to the AC line in a backwards configuration (reversed Hot/Neutral or Brown/Blue wires) and then wire the safelight between the two Hot sides of the safelight outlets. Really not recommended.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  7. #17
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Steve Smith View Post
    There are no rules in the UK to prevent you doing this yourself in a domestic situation.
    Your insurance may balk at paying if dodgy DIY wiring is responsible for setting the house on fire. In the US the 'National Electrical Code' is part of the housing regulations in most states and cities.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  8. #18
    RalphLambrecht's Avatar
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    Quote Originally Posted by clayne View Post
    ...Another alternative would be to say screw it and leave the safelights on all the time.
    There you go!
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  9. #19
    Steve Smith's Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    Your insurance may balk at paying if dodgy DIY wiring is responsible for setting the house on fire.
    I'm sure they would (if they knew) but there is nothing to stop you connecting whatever you like to a socket. From incoming supply to outlet there are regulations but no one is going to check or test anything you connect to an outlet yourself.


    Steve.

  10. #20
    Steve Smith's Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    Wellllll, most timers only use one relay inside -- the NC contacts go the to safelight outlet and the NO contacts go to the enlarger.
    Yes that does complicate it a bit. So far, your single relay method seems to be the best solution..... other than just using one timer and only plugging in one enlarger at a time.


    Steve.

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