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Diode for thermostat circuit

Discussion in 'General Electronics Discussion' started by marklamberti, Nov 24, 2016.

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  1. marklamberti

    marklamberti

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    Nov 24, 2016
    Hello all,

    I have a 4 zone relay box controlling my boiler. It is controlled via 3 thermostats 1 per floor plus one for the domestic hot water tank.

    I want to tie all three heating zones together such that when the first floor thermostat calls for heat it will make all the zones fire. To do this i can simply run a jumper from one to each other on the low voltage side of the relay box. I am doing this to keep the boiler from short cycling and it makes the house more comfortable and i think may save energy.

    The problem is that occasionally I want extra heat in the basement or second floor. If I have those thermostats call for heat they will make the first floor zone also turn on by the current going in the opposite direction on the jumper wire.

    I know very little about electronics. I want to know what kind and size of diode i should use. The circuit is 24v .18amps.

    Cliff Notes:
    I need a diode to stop .18 amps at 24volts.

    Also if I am way off base and none of this will work let me know

    Thanks,
    Mark
     
  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    It appears that you have two conflicting requirements:

    1. All zones should operate whenever one is calling for heat.
    2. Sometimes, I don't want the basement or second floor thermostat to turn on the other zones.

    You cannot have both of these things without having an extra state, like a switch on the basement and second floor thermostat that says do not turn on the other zones that you can flip when you want extra heat there. And then you will need some logic to sort it out.

    Bob
     
  3. Audioguru

    Audioguru

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    649
    Sep 24, 2016
    Diodes will combine or separate the relays only if the 24V that turns them on is DC and is not AC. A diode connects the thermostat to a relay and each relay needs a diode. A switch or another thermostat connects directly to the relay you want to turn on separately. 1N4002 diodes will work well.
     
  4. Alec_t

    Alec_t

    2,862
    768
    Jul 7, 2015
    What type of thermostat? Does it simply close a pair of contacts when heat is demanded, or does it incorporate some fancy electronics to provide a signal? Can you post a link to the thermostat spec/datasheet?
     
  5. marklamberti

    marklamberti

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    Nov 24, 2016
    The thermostats are simple all they do i close contacts

    I do not want all zones to fire when one of them is calling for heat. I want all zones to fire when zone #1 is calling for heat.

    I believe it is an a/c circuit.
     
  6. BobK

    BobK

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    Jan 5, 2010
    OK, I misread your original post.

    So it looks like you want this:

    When zone 1 thermostat is on, zoner 1,2,3,4 all run.

    When zone 1 is off and zone 2 is on, zone 2 runs but not the others

    When zone 1 is off and zone 3 is on, zone 3 runs but not the others.

    Is that correct?

    Bob
     
  7. AnalogKid

    AnalogKid

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    661
    Jun 10, 2015
    OK, this is important. If the voltage on the relay coils is 24 Vac, you cannot prevent reverse direction current flow with a diode. If the relays are powered by 24 Vdc, you can. Got got gotta know which one it is.

    ak
     
  8. marklamberti

    marklamberti

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    Nov 24, 2016
    Absolutely

    I just double checked it is 24VAC. Makes sense that a diode would not work in this case.

    What are my other options? Obviously i know very little about electronics.
     
  9. marklamberti

    marklamberti

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    0
    Nov 24, 2016
  10. BobK

    BobK

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    1,686
    Jan 5, 2010
    I think what you need is an extra relay each for zones 2 and 3. The inputs of these relays would be the connected to their thermostats. And the outputs would be placed in parallel with the outputs of the zone 2 and 3 relays in the original controller. Then you link the inputs of the original relays to the zone 1 thermostat. Actually, you might want to use another relay in between because the thermostat may not be able to drive all 4 relays in parallel.

    Bob
     
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