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Taco SR502-4 Switching Relay - Unable to Power Two Ecobee4's?

pburkepburke Member Posts: 2
edited June 2018 in Controls
Hello,

I tried researching this issue but the solution still seems somewhat unclear to me. I'm in the midst of a major renovation and have had numerous issues with both the plumber and electrician and as such am trying to solve this problem myself.

A new Taco SR502-4 Switch Relay was installed for two heating zones by the contractor. An Ecobee4 thermostat was installed in each zone by the contractor. One thermostat receives power while the other does not. I've traced the issue back to the Taco Switch Relay. On the upper left corner of the circuit board there are two connections to provide power to the "C" wire. One seems to be getting approximately 27 volts while the other connection doesn't seem to be getting any power.




Ecobee support believes that the transformer is not sufficient to power both thermostats and I need a more powerful transformer and an isolation relay. Is this correct? It just seems odd to me that the second terminal is showing no voltage as oppose to low/or insufficient voltage.



Thank you for your time and assistance and I apologize in advance for any improper terminology.

Thanks,
Pat

Comments

  • Jamie HallJamie Hall Member Posts: 13,417
    If I read that circuit board correctly, one side of that connector is labelled "24 vac" and the other side is labelled "Com". Common usually means a return, sometimes (not always) grounded, while 24 vac means just what it says.

    To what are you connecting the return from the Ecobee which works?
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ratioratio Member Posts: 2,563
    As Jamie said, you should be showing (a nominal) 24V between those two terminals, and if you show 24V between the "24VAC" terminal and ground/metal box and appx 0V between "com" and the same place that merely indicates that the common terminal is electrically to the box. If you have an ampy clampy, measure the current on the yaller or red wire from the xfrmr. if it's anything over about ½ amp, it's nearly certainly your issue.

    A 15 VA xfrmr is quite small and I have no trouble believing that it is unable power two Ecobee stats and the SR502. If it were me, I'd just replace the xfrmr with a larger one, but that would not do anything good for your warranty.

  • HVACNUTHVACNUT Member Posts: 3,517
    edited June 2018
    What are the Blue (24v) and Black (Com) wires connected to on the Ecobee's?
    You should only need the "Com" wire connected the the "C" terminal on the thermostats. The power (24v) is already there from the Red wires "R" terminals in the relay where the thermostat wires are connected. R-W. Nothing needs to be connected to the 24v terminal.
    Note: For HVAC low voltage control wiring, the power wire (24v) should be Red and Common wire should be Blue or Brown.
    The thermostat wiring should be simple.
    R- 24v
    C- common
    W- to heat heat relay (your SR502)
    G- to fan relay
    Y- to the A/C condenser
    O,B- if it's a heatpump system
    Zman
  • newagedawnnewagedawn Member Posts: 566
    you need at least a 40 va transformer for that application, maybe even a 75 va transformer, not to familiar with ecobee watt consumption check that
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • lchmblchmb Member Posts: 2,992
    edited June 2018


    you may need a resistor
  • Tim PotterTim Potter Member Posts: 253
    try switching places with the blue wires on the 24vac/com termial and see if the other t-stat powers up.
    Winter Park, CO & Lenexa, KS
  • ZmanZman Member Posts: 6,004
    @pburke
    HVACNUT said:

    What are the Blue (24v) and Black (Com) wires connected to on the Ecobee's?

    You should only need the "Com" wire connected the the "C" terminal on the thermostats. The power (24v) is already there from the Red wires "R" terminals in the relay where the thermostat wires are connected. R-W. Nothing needs to be connected to the 24v terminal.

    Note: For HVAC low voltage control wiring, the power wire (24v) should be Red and Common wire should be Blue or Brown.

    The thermostat wiring should be simple.

    R- 24v

    C- common

    W- to heat heat relay (your SR502)

    G- to fan relay

    Y- to the A/C condenser

    O,B- if it's a heatpump system

    Like he said :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • pburkepburke Member Posts: 2
    Thanks for everyone's insightful replies.

    So based on what I've gathered from everyone's replies and a little deductive reasoning, I ended up connecting both Blue "C" / Common wires to the "COM" terminal on the Taco's board. (Please see picture below). This seems to have fixed the issue as both Ecobee's are now powering up and currently seem to be functioning properly.



    Question being:

    Does anyone see any potential issues with the way I did this?

    Thanks again for everyone's time,
    Pat
  • ratioratio Member Posts: 2,563
    Functionally, it should work; but that xfrmr is very low power. It may not be able to provide sufficient current if e.g. both stats call at the same time. The easiest way to check would be to turn them both down so they call for heat & check the voltage at the 24VAC & COM terminals—you're looking for at least 24 volts at maximum load.
  • hot_rodhot_rod Member Posts: 13,850
    Up to 3.5 Va for the Ecobee draw. Plus whatever else is on the circuit.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • RandyCarusoRandyCaruso Member Posts: 1
    VERY similar problem with that Taco board, actually fixed via this info however: When testing for the 24v I got .3v - nothing more ever no matter how I tested. Basic Multi-meter settings but when I hooked it all up: poof! it worked. What the hell, is there a digital switch there I'm not aware of?
  • STEVEusaPASTEVEusaPA Member Posts: 4,420
    You shouldn’t use the word 'poof' when discussing wiring and electrical connections. 'Poof' usually means you let the smoke out...lol
    steve
    EdTheHeaterMan
  • EdTheHeaterManEdTheHeaterMan Member Posts: 802
    @STEVEusaPA I thought the same thing.... Poof and my gut went :s
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