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A diode for my heating/hot water?

Discussion in 'General Electronics Discussion' started by dnalevy, Nov 16, 2011.

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  1. dnalevy

    dnalevy

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    Nov 16, 2011
    Hi, new to this site-looks very interesting!

    I have a central heating and hot water controller which turn on the HW and CH independently. The HW gives a 240V signal to the boiler whilst the CH part gives a 240V feed to power a valve to turn on the heating. The central heating will only work if the hot water is on.

    I've recently installed a wireless thermostat between the CH controller and the valve but as it stands I have to leave the HW on 24/7 so that the CH can be activated at any time.

    Ideally Id like to set the HW controller to come on at particular times in the day to heat enough hot water in the tank and have the thermostat wired into the HW so that when the CH needs to come on, the HW will be activated by the same 240V from the CH controller.

    However, this would mean that whenever the HW is set to come on the CH will be activated as well.

    My assumption is that I need to fit some sort of diode between the thermostat and the HW signal ensuring a signal only passes from the thermostat to the HW and not from the HW controller across into the CH valve.

    So...my question is: am I correct that the solution is a diode?
    If so my real problem is that I have no idea what type, rating etc of diode I would need?

    Ive attached a really lame diagram just to clarify the question.

    Thanks so much for your help!!!
     

    Attached Files:

  2. davelectronic

    davelectronic

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    Dec 13, 2010
    Central heating

    Hi dnalevy.
    Welcome to the forum.
    I am thinking you are in the UK, voltage and system description, unfortunately i would like to help with a component selection, but if your not aware curtain laws regarding gas central heating systems means i cant make a suggestion for you, UK IEC regulations are changing all the time.

    Its hard to keep up with the government legislation, on this occasion i would call in some professional help, fire is a risk if you get it wrong, no one wants that, so i would try and call in some top help, other members may see it different, but better safe than sorry.
    Dave.D :)
     
  3. duke37

    duke37

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    Jan 9, 2011
    Take note of what Dave D says.
    Your simplest solution is to insulate the hot water tank properly so that it does not matter that the heat is on all the time.

    You cannot use a diode to make a one way control on AC, you will need to use a relay which is wired correctly, get the wires crossed and you will have trouble. AC relays can buzz and will need to be installed safely - not a little job.

    Duke
     
  4. dnalevy

    dnalevy

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    Nov 16, 2011
    OK thanks so much for your help!
     
  5. jackorocko

    jackorocko

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    Apr 4, 2010
    So leave the HW on 24/7 and then use a relay that is triggered by the valve power to control (turn on, 'NO' side of the relay) the HW power. Done deal and it shouldn't cost you an arm and a leg. A relay will not draw that much extra current to close under mains voltage so I wouldn't worry about the controller not having enough power.

    I guess I can draw you a picture if you need it. As dave eletronic said, if you are in the UK depending on code you may not be qualified to do the job, If you are in the states, unless some local code prevents it, you are free to do as you please. But remember you must follow the boiler installation guidelines or you will void that warranty on your boiler. Sometimes the best place to ask this question is with the manufacture.


    What boiler are you using? Domestic hot water water supply? Low volume system? I don't understand why you have a tank to store HW unless it is for domestic use
     
    Last edited: Nov 17, 2011
  6. dnalevy

    dnalevy

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    Nov 16, 2011
    Yes im referring to my own home CH/HW system. A picture would be excellent!
     
  7. jackorocko

    jackorocko

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    Apr 4, 2010
    You still haven't answered my question. Does this system have a domestic hot water supply? Your drawing labels "HW Boiler". This confuses me, because most boilers I know of don't have storage tanks. You are not using a hot water tank as a boiler (for your central heating) and a domestic hot water supply are you?
     
  8. jackorocko

    jackorocko

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    Apr 4, 2010
    Here is what I had in mind. The relay will be energized when the CH pump comes on, this is why the coil of the relay is in series with the CH controller and the CH pump. Then on the other side of the relay, the NC (normally closed contacts) will be in series with your HW timer and the HW boiler. Then the NO (normally open contacts) will be in series with mains power.

    This way the HW boiler will be hooked up to mains power through a timer, until the time comes that your thermostat kicks on and turns on the CH pump, when this happens the state of the relay changes and directly causes the HW boiler to come on to heat the water till the room is warm enough (thermostat shuts down CH controller which shuts off CH pump and relay), then everything goes back to the way it was before.

    this will not work if you need on demand domestic hot water. My drawing is very simplified, a double pole double throw relay (DPDT) will need to be used at the very least for mains power, which will depend on if it is 3 or 4 wire 240V service.
     

    Attached Files:

    Last edited: Nov 18, 2011
  9. duke37

    duke37

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    Jan 9, 2011
    The pump will not run with a relay coil in series with it.
    What proposals do you have for safe installation of mains supply?

    Duke
     
  10. jackorocko

    jackorocko

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    Apr 4, 2010
    Parallel? If I remember correctly you can buy multiple zone controllers, one thermostat per zone, but why not use one thermostat with a two zone controller. Just tie the thermostat to both zones on the input. The output of the CH controller is probably not mains voltage, but the OP says it is.

    But that does bring up another question, what voltage is the output of the HW controller, he says 240V? Lot of unknowns still and that is primarily the OP's fault. I still haven't figured out if he is using a gas boiler or a electric hot water tank.

    My drawing assumes that the HW boiler is electric running off 240V and was nothing more then a concept of what could be done. For safe installation I would hope he would follow local electrical code, unless you mean something in particular.
     
    Last edited: Nov 18, 2011
  11. davelectronic

    davelectronic

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    Dec 13, 2010
    Hi again.
    I am only stating the obvious, if you go ahead and alter the function or configuration of your central heating and gas boiler be it standard or combination systems you will be in breach of uk safety regulations, this is not me poking my nose in, more if an accident occurred you would be solely responsible in a uk court of law, and on a personal level, if you stuff up, and there was a house fire, could you conscious deal with the aftermath of a serious mistake, worse case scenario.
    I wont look in again, but think about it. :eek:
     
  12. jackorocko

    jackorocko

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    Apr 4, 2010
    I understand this and it should be valid if the OP is in the UK. But where I live you can make any modification you want to any system in an existing structure (occupied) without having it approved by code enforcement (electrical, gas, water, waste.) The only time it would matter is when you are calling the insurance company, if it was not installed properly then you will be looking at a very empty wallet. Also, where I live code is normally only a guideline, 99% of the time manufacture installation instructions override code, but every appliance you buy in america should also be UL listed.

    Only time I can see this being an issue, where neighboring structures might affect another structure. Which mainly applies to fire code. NOTE, I am no expert on code, but it is my experience
     
    Last edited: Nov 18, 2011
  13. davelectronic

    davelectronic

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    Dec 13, 2010
    My last on this thread, its entirely up to the OP, but in the UK a mistake and fire from messing with ANY part of the heating system electricals gas etc can lead to a custodial sentence, ive seen in our BBC news whole family's killed by mistakes, the UK rules on gas fired, and electrical hard wired instantiations are very rigid, but it the OP's call on the best way forward, mine is only sound UK advice, as you say other country's have there rules or be it not so rigid. :)
     
  14. dnalevy

    dnalevy

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    Nov 16, 2011
    Thanks for all the replies!
    Sorry for not being clear: my hot water is an old style cylinder system heated by a gas boiler, not on demand.
    The controller in the airing cupboard gives a 240v signal to the boiler.

    Just to calm some of your nerves, I'm perfectly competent to carry out this kind of installation. I've done many mains voltage installations as well as tidying up the mess of a job the 'qualified electricians' left here.

    Anyhow I do understand the risks and liability in question.
     
  15. dnalevy

    dnalevy

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    Nov 16, 2011

    So this one should do fine.... (the last 1 on the list for £5.09).
    http://www.maplin.co.uk/10a-dpdt-miniature-relays-37518

    One thing I didnt understand in the drawing is the box marked 'timed' in the top right corner?
    Theres is only 1 time controller for hot water.
     
  16. dnalevy

    dnalevy

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    Nov 16, 2011
    Looking through it again, why wouldn't a SPDT relay do what I require?
     

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  17. jackorocko

    jackorocko

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    Apr 4, 2010
    Well because quite rightly you don't explain anything. I assumed your HW controller was not a timer. If you call a timer a HW controller, then that is my confusion. As stated by duke, you can not run the relay coil in series with the pump. So that will need be in parallel. Thirdly, your thermostat can not be in-between the CH controller and the pump (you don't want your thermostat turning on 240V, not very smart), that makes no sense to me at all. Only thing a thermostat is used for is to tell the CH controller when to activate the pump. The thermostat should send out it's own 'high' voltage signal to the controller which will turn on a relay and power the pump.

    because if it is 240V on the output of the controllers and you are in the UK then there should be 3 wires coming from your main supply? Ground you can connect all together, but you will need to switch the other 2 wires. This means you need at the very least a DPDT. Does the UK use a neutral tied to ground? I guess if it did you would only need switch the live wire. http://www.veris.com/docs/Datasheets/v300_400_d07101.pdf something like this would allow you to connect it to a box and have all your wiring inside a junction box. Or you could mount an open screw terminal relay inside a grounded box.
     
    Last edited: Nov 20, 2011
  18. dnalevy

    dnalevy

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    Nov 16, 2011
    Ok to clarify:

    1) First 2 pictures are what I'm calling my CH and HW controller with its wiring diagram. Pin 3 gives a 240V feed to the boiler, pin 4 is supposed to give a 240v feed to the CH valve (3rd pic below), but the thermostat has been wired in between.

    2) Let me get to the parallel issue in my next post....

    3) Sorry my mistake I meant to label it a CH valve (3rd pic below) not pump in my first diagram. They have wired the thermostat to cut in between the 'controller' (referred to in 1)) signal and the valve in the pipe that switches the hot water flow to CH. (See picture 3 below). So that the CH is meant to be left constantly ON from the controller and the thermostat opens and closes the circuit as necessary.

    I'm trying to be as clear as possible so please bare with me...
    thanks
     

    Attached Files:

    Last edited: Nov 20, 2011
  19. dnalevy

    dnalevy

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    Nov 16, 2011
    Re your second point above:
    Can the relay coil be run in series with the CH valve as so:?
     

    Attached Files:

  20. dnalevy

    dnalevy

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    0
    Nov 16, 2011
    Well I can only work with what I have. As you can see only 3 and 4 in use....
     

    Attached Files:

    Last edited: Nov 20, 2011
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