Wanted: Indicator Lamp on Thermostat

Discussion in 'The Projects Forum' started by Big Al MA, Mar 8, 2013.

  1. Big Al MA

    Thread Starter New Member

    Jan 31, 2013
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    I have a wood boiler in my home. There are several Aquastat thermostats involved in controlling the pumps which circulate the hot water. The heating system is 24 VAC nominal. Actual voltage is 28 volts, more or less.

    I would like to add an indicator lamp at one or more of the Aquastats, which would come ON when the themostat is closed.

    I am thinking that I could break one leg of the thermostat wire, and put a bulb in series at that point. When current is flowing (thermostat is closed), the bulb would light.

    I'm thinking that if the bulb was low wattage (maybe LED?) that the bulb load would not affect the circuit in any detrimental way.

    Does this sound like a decent way to do it? Would any of you have suggestions as to what type of bulb to acquire for this purpose, and/or a way to mount it to or near the thermostat?

    Your help and suggestions would be most appreciated. :)
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
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    Depends on what thermostat it is, how much current flows through it etc. Any component connected in series with thermostat will have a voltage drop. The thermostat probably turns on a relay (just guessing). Therefore you will have less voltage available at the relay coil (or whatever the load is) when the thermostat is closed.

    You could post a photo and a simplified circuit diagram. A LED could possibly work, maybe with some diodes in parallel.
     
  3. Big Al MA

    Thread Starter New Member

    Jan 31, 2013
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    Thanks for the reply.

    Yes, your guess is right, the thermostat/Aquastat trips a relay at the Taco SR504 switching relay, activating the pump.

    Some pictures below might help to illustrate what I'm dealing with.

    First of all, here is a picture of the inside of the Aquastat (100-240 deg. F). Two wires, red and white, are tied to terminals which close upon temperature rise.

    [​IMG]

    Secondly, the outside of the SR504 switching relay control box.

    [​IMG]

    And, third, here is the inside of the SR504. Thermostat wires (24 VAC) come in at the top, relays are in the middle, and outgoing 120 VAC wires come out the bottom and go to pumps....

    [​IMG]
     
  4. Big Al MA

    Thread Starter New Member

    Jan 31, 2013
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    I think I have (somewhere) an induction type current meter, the kind that surrounds the wire and measures the magnitude of the magnetic field that is generated by the current. The clamp plugs into my multimeter. Would you recommend using this tool to measure the current in the thermostat wires?
     
  5. Retiredguy

    Member

    Feb 24, 2007
    28
    5
    What I would do is use some LED's in parallel with the relays to indicate if the Thermostat is activating, this would not show if the relays were working only if they were receiving voltage. Since this is AC current, the LED's would flash at 50 to 60 Hertz, much faster than the eye could detect but from what you described should suffice. You would need a resistor in series with each diode (about 2000 ohm) and the LED would need to have a PIV ( peak inverse voltage) rating of at least about 50 volts. If you cannot find one with that high a PIV place a regular diode in series with it also that has that high of a rating.
    Retiredguy
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Exactly. I would do the same thing. +1
     
  7. Big Al MA

    Thread Starter New Member

    Jan 31, 2013
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    Thanks for the recommendation, Retired Guy. I'm not sure it will work.

    Because, there are actually two aquastats connected in parallel at the "Zone 1" thermostat connections. The "primary" aquastat (what I'll call A1) is controlled by a thermostat in our living room, and activates the pump for that zone when the temperature is below the target temperature. The "secondary" aquastat (A2) is installed as a safety measure, and handles the condition when there is more heat being generated by the wood boiler than can be used by the various loads (heat zone 1, heat zone 2, domestic hot water, etc.). It "dumps" heat to Zone 1.

    So since there are two aquastats which can cause the same relay to trip, putting an LED in parallel at the relay won't indicate to me which of the aquastats have activated (A1 or A2). In fact, you'll see on my picture of the SR504 switching relay that there is already an LED light installed for each of the zones (the light for Zone 1 is ON in the picture).

    Can you think of a way to modify your suggestion so that I can achieve the desired result?
     
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