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  1. #1
    Join Date
    May 2004
    Posts
    26

    Hmm

    I would like to wire two transformers both Pri: 120 Volts ,. Sec: 24 Volts. in order to get 48 volts at the low side. Should I just wire the primaries in parallel and the secondaries in series? Or do I need to be concerned with polarities ( Additive or substartive ). I'm bringing this thread because of the fact that one of my co-workers said to me that he found two transformers in this system and that the contactor ( outdoor unit ) was making a lot of noise because its coil was at 60 Volts Ac. From where this 60 volts comes from ? I kept on telling him that the max. Secondary voltage he could get is 48 volts from these two transformes..right ? Or I'm Wrong. All I need to prove this is to hook these two transformers that I'm talking about but I can't come up with the time to do it.
    Thanks for your help, ahead of time.
    Rooky.

  2. #2
    Join Date
    Aug 2000
    Location
    USA
    Posts
    4,979

    48V coils?

    The system youve got has dual transformers, ones for heat and ones for AC. You need a split subase for this aplication. Ask at the supply house and see if you can buy a 48V compressor contactor. Normaly when I find these messes Ill change it to a single trans at the heater and junk the second one. Its usually quicker to rewire it using one trans then dik around trying to figure out who butchered up what. JMHO
    Your poor planning does not constitute an emergency on my part!!!!

  3. #3
    Join Date
    Nov 2002
    Location
    emerald city, sc
    Posts
    1,469
    just remember to put fuses in the circuit so as not to burn up the transformers. transformers aren't like batteries you can't just hook them what ever way you want to. the 60 volts could be coming from a feed back, or a transformer breaking down.
    i wanted to put a picture here

  4. #4
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,012
    I've never tried this but if you put two transformers in parallel and phased correctly you can add the VA.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,824
    Before trying this, go and check the coil voltage yourself.

    I think abs gave you the right answer.
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  6. #6
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Originally posted by beenthere
    Before trying this, go and check the coil voltage yourself.

    I think abs gave you the right answer.
    He did. At least, that's what I would do. I see no good reason to run two xformers on warm air/ac in 99% of the cases. It adds nothing to the overall system except spaghetti.

  7. #7
    Join Date
    Dec 2000
    Location
    alabama
    Posts
    214
    what kind of system is it (gas) fan limit may have been changed. they have a jumper that should be remove on a four wire hook up. this will feed high voltage to low voltage side of system.

  8. #8
    Join Date
    Jan 2001
    Posts
    6,719
    Originally posted by rooky
    I would like to wire two transformers both Pri: 120 Volts ,. Sec: 24 Volts. in order to get 48 volts at the low side. Should I just wire the primaries in parallel and the secondaries in series? Or do I need to be concerned with polarities ( Additive or substartive ). I'm bringing this thread because of the fact that one of my co-workers said to me that he found two transformers in this system and that the contactor ( outdoor unit ) was making a lot of noise because its coil was at 60 Volts Ac. From where this 60 volts comes from ? I kept on telling him that the max. Secondary voltage he could get is 48 volts from these two transformes..right ? Or I'm Wrong. All I need to prove this is to hook these two transformers that I'm talking about but I can't come up with the time to do it.
    Thanks for your help, ahead of time.
    Rooky.

    yep...you can wire two 24 volt transformers in series and get 48 volts.....more under no load conditions as most transformers produce anywhere from 26-28 volts no load. If the transformers are not exactly the same or even if they are the same...the VA rating will be only as good as that of the lesser transformer....two 40 va transformers in series will give you 48 volts but the VA rating is still 40

    Now if you take those same two 40 transformers and wire the secondaries in parallel you will have the equivelent of a 24 volt 80 VA transformer.....

    Though I dont know why you would ever want or need to...you can also wire the secondary of transformer in series with the primary and boost the voltage by the amount of the secondary.... a 120 pri/24 volt sec becomes a 144 volt autotransformer...by phasing the windings differently this same transformer can be used to buck the voltage down by 24 volts...making it roughly an 86 volt autotransformer......

    If this system has two transformers and they are tied together...something is wrong...Ive seen the old mobile home units done like this but the secondaries never come into contact with each other.......the thermostat keeps them seperated....looks like someone either did some wiring wrong......or something....


  9. #9
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,960
    Actually the VA for 2 transformers wired in series WOULD go up. VA = Volts X Amps. If voltage doubles and current remains constant VA doubles.

  10. #10
    oil-2-4-6-gas is offline Professional Member b&M _email server rejected
    Join Date
    Aug 2003
    Posts
    294
    how is he testing the transformer --r-c or each leg individually to ground

  11. #11
    Join Date
    Oct 2001
    Posts
    2,095
    Rooky,


    What kind of system was your co-worker talking about.
    Noisy contactor usually is caused by supplied voltage
    much bellow coil rated voltage.
    If this coil was rated for 24 V, then 60 V would release
    magic smoke from it.
    Something is telling me that this is not a residential system, and coil is rated for 120 V.

  12. #12

    jumper

    What is the purpose for wanting 48 volts. Sound like its not hooked up right.. pull the jumper off the t-stat if you are running 2 transfomers. RC & RH. This seperates the heat and the cool side. I dont think the transformer will survive being tied together.

    It would be eisier to use only one transformer.

    regards,
    Klyons20

  13. #13
    Join Date
    Oct 2001
    Posts
    2,095

    Re: jumper

    Originally posted by klyons20
    What is the purpose for wanting 48 volts.
    Rooky’s question was how to wire two 24V
    transformers and get 48 V out of this combination,
    just to prove that this is possible. He does not want to use
    it in the system. He also wants to know where this 60 V
    came from. Unless he asks his co-worker more question
    about this system, we all will be guessing.




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