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  1. #1

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    Electrical help, please

    There seem to be a number of electronic-savvy members of this forum, and I wonder if they could help.
    I have motorised rockers for my trays (see Thread: Motorised Tray Rockers in this forum). Currently they are connected to clockwork timers, and they are powered separately by 115 volts AC from a single transformer.
    Problem is they only time up to 60 seconds, and I now want to lengthen that time, because the cellar darkroom now gets cold in winter (new efficient boiler) and one minute is no longer enough for dev and fix for RC when the ambient temperature is down to 16 degrees C.
    Now I have 2 electronic timers which can switch 240v AC, standard UK voltage. But they don't work on 115 volts so I can't use them directly to control the rocker motors. But it occurs to me that I should be able to switch the 115 volt motors on and off using separate relays switched by the 240 volt timers. The timers are enlarger timers and therefore should, I imagine, be able to switch up to 300 watts at least. The motors are quite powerful, about the size of a DIY electric drill motor, rated at 0.3 amps.
    I could alternatively, I suppose, double up on the transformer, but I would like to explore the possibility of using relays.
    Can anyone help me by saying 1. Whether it is possible? 2. If it is what sort of spec should I be looking for for the relays? 3. A circuit sketch would be helpful.
    I can use a soldering iron, drill holes in cases, and have a pretty good idea how to avoid electrocuting myself.
    Richard

  2. #2

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    Richard,

    You say you are using a 115 volt transformer to power the rocker motors. Why not power the transformer from the 240 volt timer? If you need the transformer for other stuff, your relay idea is fine. Ice cube relays with 5 amp contacts will probably work fine. Get relays with 240 volt AC coils.

  3. #3

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    It's definitey possibe. I think the easiest way is to plug the transformer into the switch output of the timer and power the rocker with the output of the transformer.

  4. #4

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    Quote Originally Posted by Chris Douglas View Post
    Richard,

    You say you are using a 115 volt transformer to power the rocker motors. Why not power the transformer from the 240 volt timer? If you need the transformer for other stuff, your relay idea is fine. Ice cube relays with 5 amp contacts will probably work fine. Get relays with 240 volt AC coils.
    Because I want to be able to control the rockers independently, a timer for each.
    What's an ice cube relay?
    Richard

  5. #5

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    Quote Originally Posted by Chan Tran View Post
    It's definitey possibe. I think the easiest way is to plug the transformer into the switch output of the timer and power the rocker with the output of the transformer.
    See above
    Richard

  6. #6

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    You have 2 rockers, 2 timers and 1 transformer?
    Ok, In that case you can use the relay. I got it. It's possibe. But let me find a way that you can do it very easily

  7. #7

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    That would be great.
    Richard

  8. #8

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    After doing some research I don't find anything premade. So you will have to make it yourself. Get some small relay (they call them ice cube), socket, wire, male plug and outlet and some enclosure then you're good to go.
    Something like this relay http://www.ia.omron.com/product/item...05d/index.html and the correct socket would do.

  9. #9
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    Yes, this is very doable but I (as an electrical engineer) have to say that where mains electricity is concerned, "if you have to ask how to do it, you should not be doing it". The risks for fire and electrocution are significant and there are subtle things that can go wrong that you won't know you've done wrong until they kill you.

    Plugging a transformer into the output of a timer module is completely fine. Once you start cutting and soldering and decide you need to put stuff in a box though, that's a recipe for trouble and I would suggest that it's much cheaper, easier and safer just to buy a second transformer to run off the output of your second timer. Hell, the second transformer costs on eBay about what you'd spend for a decent box.

  10. #10

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    I agree with polyglot. This is not something you want to take lightly. It can kill you. I am a licensed electrician.

    Well.... it's technically possible but it's not worth the trouble. It's far easier and cheaper to just buy another transformer. It's also safer. You said yourself, you are not families with electronics. You will be using your creation near water and at 240 volt potential. It's not safe - worse, you won't know it when something isn't right - until you get a shock. That may very well be the last shock you get....

    With that said...

    I understand you want to control a 115 volt circuit using TWO 230 volt timers. (or is it just one timer?) Then what you do is... buy two relays that works on 230 volts AC (not the DC kind). Connect each relay's coil windings to its respective timers. Now you have two relays that goes on and off via two timers.

    Now, take those N.O. (normally open) side of relay switches and tie them in parallel. Put that in series with the 115 volt circuit. This way, if one of the timer sends ON signal, the motor starts.

    If you just want one timer, then forget the parallel part.

    Please PLEASE be careful with this. You'll need to carefully ground all human contactable metal surfaces. None of the circuit should be at or near water area.
    Develop, stop, fix.... wait.... where's my film?

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