What's a current robbing thermostat? (2024)

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What's a current robbing thermostat? Vision Pro 8000 Backligfht issues vBulletin Message

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  1. 09-15-2010,03:03 PM #1

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    What's a current robbing thermostat?

    I read in a manual, "unit is compatible with almost all thermostat that is not of current robbing design".

    Well, the unit offers common connection for thermostat and I hooked up Vision 8000 for line operation so the back light stays on. Since its being powered by 24v instead of battery for routine operation, doesn't that make the thermostat current robbing?

    I don't see how it would be an issue if the power was getting sapped from R and C, and not bleeding between R and W or Y.

  3. 09-15-2010,03:33 PM #2

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    Current robbing means, that it is a digital tstat that doesnt need a common to operate, but must have batteries in order for the relays to operate correctly.

    If I would of killed my wife when I first met her, I'd be out of jail by now!

    GET SOME!!

  4. 09-15-2010,05:56 PM #3

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    What's a current robbing thermostat? (15)

    What's a current robbing thermostat? (16) Originally Posted by doubledueceWhat's a current robbing thermostat? (17)

    Current robbing means, that it is a digital tstat that doesnt need a common to operate, but must have batteries in order for the relays to operate correctly.

    If it's operating thermostat relays off of batteries, then why would it be current robbing?

  5. 09-15-2010,08:54 PM #4

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    There are some digital stats that are what the instructions say and how you stated. They rob current on the r to y or w connection. No common 24v conection is required for them to work. I've seen a few that function in this way. Honeywell makes a digital T87 that function this way. The "digital round" is the only one I remember off the top of my head that works that way. I'm lucky to deal with a conventional thermostat twice a year so I'm sure there are allot of others out there. It sounds like your thermostat is fine.

  6. 09-15-2010,10:17 PM #5

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    What's a current robbing thermostat? (27) Originally Posted by willf650What's a current robbing thermostat? (28)

    There are some digital stats that are what the instructions say and how you stated. They rob current on the r to y or w connection. No common 24v conection is required for them to work. I've seen a few that function in this way. Honeywell makes a digital T87 that function this way. The "digital round" is the only one I remember off the top of my head that works that way. I'm lucky to deal with a conventional thermostat twice a year so I'm sure there are allot of others out there. It sounds like your thermostat is fine.

    Yep, think a current robbing t-stat refers to a stat that uses 24v power to operate itself rather than batteries.
    Ive had some t-stats that only require batteries if amp draw on w or y on call for heat/cool are below a certain amount.

  7. What's a current robbing thermostat? (33) Originally Posted by doubledueceWhat's a current robbing thermostat? (34)

    Current robbing means, that it is a digital tstat that doesnt need a common to operate, but must have batteries in order for the relays to operate correctly.

    INCORRECT

    UA Local 141

  8. 09-17-2010,06:34 PM #7

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    Carrier makes a bunch of them and you put a resistor across r and w to draw power for the display. Bad part is you lose programming when you lose power and this includes unocc/occ etc.

    UA Local 141

  9. 09-19-2010,06:08 PM #8

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    It means that it will use the 24 volts that comes in on R or RH or RC and use that to run the thermostat without a common wire being connected, it drains the common to a heat sink.

  10. 09-19-2010,06:54 PM #9

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    What's a current robbing thermostat? (48) Originally Posted by MikeSands02What's a current robbing thermostat? (49)

    It means that it will use the 24 volts that comes in on R or RH or RC and use that to run the thermostat without a common wire being connected, it drains the common to a heat sink.


    Huh

    Explain that one to me please, how do the electrons flow?

    Kevin


    Controls is a lifestyle not a job

  11. 09-19-2010,07:48 PM #10

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    They explain it here, it's a voltage drop, it doesn't take much power. Only the 24 volt hot wire is needed to power up a power stealing thermostat. No need for a common wire, I happen to know that the heat sink is used as a drain for the small amount of power consumption.

    http://customer.honeywell.com/techli...0s/50-8433.pdf

  12. 09-19-2010,08:02 PM #11

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    i see nothing in the link about heat-sinks, it describes the way I understood them to work, by using the W or Y wire to provide a return path.

    Some thermostats come with a resistor that you can put between the common terminal and either W or Y to allow them to operate as a power stealing thermostat.

    Kevin

    Extract from the link.

    "The methods for powering an electronic thermostat from the
    transformer with a single direct wire connection to the transformer is called “power stealing”. The thermostat “steals” or
    draws its power during the “OFF” periods of the heating or cooling system by allowing a small amount of current to flow
    through it into the load coil below it’s response threshold (even at maximum transformer output voltage). During the
    “ON” periods of the heating or cooling system the thermostat draws it’s power by allowing a small voltage drop across
    itself. This voltage drop will not cause the load coil to dropout below it’s response threshold (even at minimum transformer
    output voltage)."


    Controls is a lifestyle not a job

    See Also
    Thermostat Keeps Resetting Itself? Here's What to Try

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  14. 09-19-2010,08:15 PM #12

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    What's a current robbing thermostat? (64) Originally Posted by klrogersWhat's a current robbing thermostat? (65)

    i see nothing in the link about heat-sinks, it describes the way I understood them to work, by using the W or Y wire to provide a return path.

    Some thermostats come with a resistor that you can put between the common terminal and either W or Y to allow them to operate as a power stealing thermostat.

    Kevin

    Extract from the link.

    "The methods for powering an electronic thermostat from the
    transformer with a single direct wire connection to the transformer is called “power stealing”. The thermostat “steals” or
    draws its power during the “OFF” periods of the heating or cooling system by allowing a small amount of current to flow
    through it into the load coil below it’s response threshold (even at maximum transformer output voltage). During the
    “ON” periods of the heating or cooling system the thermostat draws it’s power by allowing a small voltage drop across
    itself. This voltage drop will not cause the load coil to dropout below it’s response threshold (even at minimum transformer
    output voltage)."

    Well I guess we are both correct, the old ones operated as you say they did and the new ones use the circuit card as the common, its the last paragraph.

  15. 09-19-2010,08:44 PM #13

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    So, according to your understanding of how they operate. You could connect 24v to the R terminal, and not connect any other wires, and the thermostat would be powered up ?

    Kevin


    Controls is a lifestyle not a job

  16. 09-19-2010,09:10 PM #14

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    What's a current robbing thermostat? (75) Originally Posted by klrogersWhat's a current robbing thermostat? (76)

    So, according to your understanding of how they operate. You could connect 24v to the R terminal, and not connect any other wires, and the thermostat would be powered up ?

    Kevin

    Yes,

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  18. 09-19-2010,09:42 PM #15

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    What's a current robbing thermostat? (82) Originally Posted by klrogersWhat's a current robbing thermostat? (83)

    So, according to your understanding of how they operate. You could connect 24v to the R terminal, and not connect any other wires, and the thermostat would be powered up ?

    Kevin

    NO You have to hook up either the Y or W wire to complete the circuit for the current robbing.

    UA Local 141

  19. 09-19-2010,09:56 PM #16

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    I think you need at least three wires to work.

    The old Honneywells some times needed a relay put in between two of the wires. I think it was r and c but don't remember exactly. Really odd to open the blower compartment and see a relay there not "doing anything".

    I also think they use a Wheatstone bridge circuit to make it work.

    I know some of the Pulse's didn't like power stealing stats.

    Beware of advice given by some guy on the Internet.

  20. 09-20-2010,05:50 PM #17

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    What's a current robbing thermostat? (93) Originally Posted by berg2666What's a current robbing thermostat? (94)

    NO You have to hook up either the Y or W wire to complete the circuit for the current robbing.


    Exactly, I fully understand that, I was trying to get Mike to understand that as well. The way he is describing the operation some magical heat sink is somehow transmitting the electrons thru' the air to complete the circuit !!!

    Kevin


    Controls is a lifestyle not a job

  21. 09-21-2010,02:40 PM #18

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    Search ASIC on the PDF, anyway I don't have a lot of time to talk about it, its how the newer ones work you will just have to trust me.

  22. 11-30-2010,03:58 PM #19

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    Vision Pro 8000 Backligfht issues

    ICanHas, you have the common problem that new digital thermostats are creating when used with relays like the Taco SRs or if you are simply using a 24v transformer to power you system.

    In the old days thermostats did not use any power in and of themselves. So, they were not current robbing. The vision Pro 8000 and many of the new thermostats require up to 750ma of current to operate the back light feature. If a Taco relay is used then you must do surgery on it. The Taco relay comes with a 15va transformer which is not strong enough to power the thermostats when certain programmed features are used (backlight). Also, you must remember that when you wire an 8000 thermostat the C terminal in the base must go to the common on the secondary of the transformer that is supplying the power to the Rc terminal, you cannot simply use another transformer.
    To fix the issue use a high va(40 or better) transformer to power a site built relay system or if you are using a Taco you must remove the transformer from the board by cutting the contacts uder the board. Then you mount a high va transformer near it and run the secondary wires to the 24 volt power terminal which is just under the old transformer base.
    Then you will have enough power to run the backlights and keep the common C wire in the same ciruit as the W wire is and etc.
    Cheers

  23. 11-30-2010,04:55 PM #20

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    They are life savers.
    You have a homeowner who has an existing T-87 stat (Yo Yo).
    They want an energy saving programmable digital stat.
    The only problem is that they do not have that fifth wire for the common to
    power The stat's electronics.
    And forget about running a new T-stat cable.We are talking deeply embedded
    in a maze of walls and pipes.
    The solution is the current robbing T-Stat.It works fine with the existing 4 wires.

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