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Zone valves and transformers

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Dave Stroman
Dave Stroman Member Posts: 766
in THE MAIN WALL
Yes, a 75VA xfmr would work. And, yes, you can use 2 xfmrs in parallel.

Dave in Denver

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  • MD Shunk
    MD Shunk Member Posts: 14
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    zone valves and transformers

    Taco wants one 40va transformer for each set of three zone valves. Is there any reason why I can't use one, 75va transformer for 5 zone valves?
  • Rich Ferris
    Rich Ferris Member Posts: 72
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    That would be fine

    That is fine. The rule is .8amps per zone so in turn you are at about 20VA with three zone valves. The easy way is to use a 75VA but most of the time 2 40VA are tied in parallel at the outputs which is sometime tricky for homeowners to distingish the difference.

    Good Luck,

    Rich
  • MD Shunk
    MD Shunk Member Posts: 14
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    Rich, I appreciate your reply, but as an electrician I know that you CANNOT parallel AC transformers. Perhaps that was a bit of a slip? Perhaps you were talking about 2 banks of zone valves, each on their own 40va transformer?
    Thanks!
  • Larry C_5
    Larry C_5 Member Posts: 10
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    Parralleling transformers

    MD Shunk,

    I think most electricians might disagree with you on that statement. You can most certainly CONNECT two transformers in parallel. You just have to phase them correctly. I believe your statement is refering to parralleling transformers fed from multiple power sources.

    If the primaries are connected to the same source, and the transformers are the same size and type, when one side of each secondary is tied together, the voltage between the other secondary wires will either be twice the secondary voltage or zero. If it is twice the secondary voltage, the secondaries are hooked up in series. If it is zero, the secondaries are hooked up in parrallel.

    Respectfully,

    Larry C
  • MD Shunk
    MD Shunk Member Posts: 14
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    Oh, my....

    Larry... this is where I get off the bus. While I certainly appreciate your reply, you are absolutely dead wrong. While I don't mean to sidetrack my original query on using one large transformer in lieu of 2 smaller one's, I am very concerned about your very technically inaccurate response with regard to paralleling 2 AC (underscore AC) transformers. No two AC transformers are absolutely identical, and you're asking for big trouble by paralleling two. You can parallel a DC source, but not an AC source. Please disregard this area of discussion, as I'm only concerned with serving 5 Taco 570 series zone valves off one 75va transformer.
  • MD Shunk
    MD Shunk Member Posts: 14
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    You can't parallel (or rather, shouldn't) parallel AC transformers!!!!!


    Thanks for your reply, just the same.
  • Unknown
    Unknown
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    u mean that all the jobs

    U mean to tell me that all the jobs I did with multi transformers is done wrong and not working? I'll admitted that I burnt up a few due the secondary are not marked at all... Ease of wirings and hook up, I now use a 75 transformer with circut breaker
  • Rich Ferris
    Rich Ferris Member Posts: 72
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    O.K. Good Luck

    Either way a 75 VA will do the trick. I just thought I'd give you another option of adding a second tranformer. I think you may have Parallel and Series mixed up in your analogy.

    Rich
  • MD Shunk
    MD Shunk Member Posts: 14
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    Nope, not telling you they aren't working. The TACO diagrams with multi transformers are not transformers in parallel. They are two distinct and seperate groups, and the secondaries of those transformers are not interconnected... parallel, series, or otherwise.

    Thanks for your help, fellas!
  • Leo
    Leo Member Posts: 770
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    But

    Care has to be taken that the number one and two terminals of the zone valves are wired to the same side of each transformer so when they make the TT switch (from the 2 and 3 terminal) neither transformer bucks the other. Bucking blows transformers.

    Leo
  • Darrell
    Darrell Member Posts: 303
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    Or you could use a Taco ZVC 405 and solve the issue altogether...I believe it uses two transformers...in parallel from the factory with UL stamp.

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  • Big Ed
    Big Ed Member Posts: 1,117
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    VA

    It depends on the zonevalves that are being used. VA equals volt x amps . We know the voltage is 24 volts and you can get the amp draw from the valves Say three are .6A and two are .8A , total amp draw is 3.4 A . Then 24Vx3.4A equals 81.6 VA of tranformer needed .I would use a 85VA or higher for a margin of error .
  • heatboy
    heatboy Member Posts: 1,468
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    I use a 50 VA......

    .......when forced to use 3 of the 571 Taco valves. If you actually read amperage draw for the valves, it almost always exceeds the 21.6 VA they are rated. So yes, a 75 VA transformer will operate 5 valves with little difficulty (unless all 5 power open at the same time - highly unlikely).

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  • Big Ed
    Big Ed Member Posts: 1,117
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    How about....

    ..... after a no heat call in the middle of the Winter.The tech has the power off,.He fixed the burner and throws the switch ?

  • heatboy
    heatboy Member Posts: 1,468
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    Yep.

    In that instance the VA would be at least 110 for 5 valves. Fortunately, it's only for a few minutes, so if it's a strong transformer with little voltage drop...........

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  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557
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    I placed a quick call to Taco regarding the ZVC 405 panel. According to the tech support guy I talked to, this panel is powered by 2 field supplied zone valves and they are wired in parallel within the panel. I guess if Taco says they can be wired in parallel, then they can be.
  • Darrell
    Darrell Member Posts: 303
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    Yes, and every once in awhile, when you're really doing the control magic and you happen to be using the extra terminals onboard the Taco ZVC's to power, Oh say a tekmar something or other, you better make sure the polarity of each Taco ZVC matches all the others...they've been known to show up reversed...and once you let the smoke out of the box......

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  • Rollie Peck
    Rollie Peck Member Posts: 47
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    Dear friends:

    This discussion of transformers has overlooked one very important point so far: protection of the #18 or smaller size wire used to connect the various units. 40VA transformers are designed in a special way to limit the maximum amount of current they will provide in case of a short circuit and prevent the wire from overheating and starting a fire. Using a larger transformer or paralleled transformers defeats this protection. That is why equipment manufacturers generally specify multiple seperate transformers. This info is in the National Electrical Code.

    Respectfully submitted,

    Rollie Peck, homeowner.
  • Tekkie
    Tekkie Member Posts: 58
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    Parallel transformers

    Shhhh, don't tell the power companies you can not parallel transformers.
  • John Abbott
    John Abbott Member Posts: 356
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    Parallel Transformers

    Must be the geography. Iam a master electrian/ heating contracter and have been paralleling Taco 40VA transformers for 30 plus years never cooked one yet.I have had no issues in this regard and its pretty to argue with success.They certainly work in N.H. I wouuld not make the broad statement that you can paralell all AC transformers because I have only used Taco and similar 40VA transformers.Perhaps one of our engineering types or one of our friends at Taco could explain how this is possible.


    Most respectfully,
    John
  • Rollie Peck
    Rollie Peck Member Posts: 47
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    Paralleling transformers

    > Oh, my....

    >

    > Larry... this is where I get off

    > the bus. While I certainly appreciate your

    > reply, you are absolutely dead wrong. While I

    > don't mean to sidetrack my original query on

    > using one large transformer in lieu of 2 smaller

    > one's, I am very concerned about your very

    > technically inaccurate response with regard to

    > paralleling 2 AC (underscore AC) transformers.

    > No two AC transformers are absolutely identical,

    > and you're asking for big trouble by paralleling

    > two. You can parallel a DC source, but not an AC

    > source. Please disregard this area of

    > discussion, as I'm only concerned with serving 5

    > Taco 570 series zone valves off one 75va

    > transformer.



  • Rollie Peck
    Rollie Peck Member Posts: 47
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    Paralleling transformers

    A response to MD Shunk.

    I wanted to Email you directly, MD, but couldn't find your Email address.

    I'd like to show you why paralleling a couple of 24 volt, 40VA transformers is no big deal.

    Dividing the power, 40VA, by the voltage, 24 volts, gives us the current flow, which comes out to 1.67 amperes.
    Dividing the voltage, 24V, by the current flow, 1.67A, gives us the AC impedance of the transformer secondary, 14.4 ohms. Since the manufacture of the transformers is highly automated, the difference in output voltage between transformers is likely to be very small. Lets assume that the difference between our two transformers is one volt.
    One volt of voltage divided by 14.4 ohms of impedance gives us a current of .07 amperes. .07 amperes times one volt gives us .07 watts, hardly enough to overheat or damage anything. Even a ten volt difference between two 240 volt
    10,000 watt transformers comes out to only 17.6 watts.

    If you see a mistake in this logic, please let me know.

    Rollie Peck,

    Homeowner
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