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Reverse current

Discussion in 'Electrics UK' started by Mike2007, 24 Aug 2012.

  1. Mike2007

    Mike2007

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    I know AC is basically forward and reverse current, but if you only want "live" to be in one direction what can you do?
    I know on DC you can use blocking diodes, is there something similar with AC. Basically I have two circuits, one pump on either circuit and one boiler.
    When one channel is "live" then it starts pump/boiler, but it also makes the other second pump live!
    Any help welcome
    Cheers

    PS. I have been using a relay for this problem.
     
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  3. Spark123

    Spark123

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    Relays/contactors are good, using separate contacts for each device to keep the control signals separate.
    Motorised valves with microswitches may also used depending on the system.
     
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  4. SimonH2

    SimonH2

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    From the way you describe it, I'm guessing you have two circuits (eg heating in two parts of the house) with separate pumps and controls. You want it so that one set of controls (time clock, thermostat, whatever) to turn on it's pump and the boiler - and ditto for the other circuit ?

    What you need for that is two relays. Connect the coil of one relay across the circuit for one pump - so the relay turns on when the pump is running. Do the same with the other relay across the other pump. You now have two independent electrical circuits and "dry" contacts that are closed when a circuit is running.
    Now connect these dry contacts (ie a normally open contact on the relay) across the boiler run control - both in parallel so either relay can turn on the boiler.

    Depending on the circumstances, this can mean that the boiler, and the two circuits can be off different supplies. However, if this is the case, then certain precautions need to be taken for electrical safety. Most notably, you need to ensure you don't cross connect any part of the circuits across the relay isolation (eg sharing neutrals). And any enclosure with more than one supply into it needs to be clearly labelled so that no-one could open it and attempt to work on the circuits without being aware of the need to isolate multiple supplies.
    There may be more requirements in a domestic setup - I'm sure someone will chirp up if that is the case.
    Ideally, keep everything off one supply with a single point of isolation.

    BTW - straying off the electrical side ...
    You may also need non-return (check) valves in the plumbing. Without it there is a good chance that when one pump is running, it will push water not just through the boiler, but also in reverse direction around the other loop.
     
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  5. SimonH2

    SimonH2

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  6. ban-all-sheds

    ban-all-sheds

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    Ah - another post in the series of sad posts from a complete ******* who just will not accept that he is not competent to fiddle with the things he insists on fiddling with.

    I suggest anybody tempted to help him study his body of work here, particularly that on 3-phase.

    Hopefully you'll come to the conclusion that the only advice you should give is "get an electrician".
     
  7. ericmark

    ericmark

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    It is normal to use micro switches inside the motorised valves to activate the boiler rather then directly control the boiler.

    Clearly one does not want a pump to run or a boiler start if the liquid can't circulate and there is always a chance that although you have powered a valve it has not moved.

    There are a series of plans I think Honeywell designed them with labels W, S, Y etc which are normally followed so some one in the future has a chance of working out what you have done.

    Can't see point of re-inventing the wheel just select the most appropriate plan and use that.
     
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  9. SimonH2

    SimonH2

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    Those plans don't help since none of them address the two pump setup described.

    Now whether two pumps are neccessary or appropriate isn't an electrical question - that's a plumbing/heating design question.
     
  10. Mike2007

    Mike2007

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    Thankyou very much for the comprehensive replies, glad you all understood my query.
    I have been using motorised heads to get totally independent channels, but wanted to know what else was available.

    PS. You are on my ignore list "bas".
     
  11. bernardgreen

    bernardgreen

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    You also need to consider the boiler may require that the pump runs on for a few minutes after the flames have been turned off. If that is the case then you control the boiler and it controls the pump.
     
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  12. ban-all-sheds

    ban-all-sheds

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    Well - maybe somebody else will quote this so you get to see it.

    You are incompetent and out of your depth, and the questions you are asking are evidence of a truly scary level of ignorance in anyone doing electrical work.

    But you are so thick that you'd rather ignore people who tell you that than take on board the reality that you should get an electrician.
     
  13. vsynth

    vsynth

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    From the way you phrased your initial question,you don't know diddly squat about diodes, I believe most will be in agreement with bas.
     
  14. Spark123

    Spark123

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    I don't follow the argument, normal diodes are used in DC to pass current 1 way and block it from travelling the other way.
    They can't be used for the same purpose in AC control systems hence a different approach is required, the simplest in this instance is to use relays with dry contacts.
     
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