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24 volt transformers

Mars_3Mars_3 Member Posts: 65
Hello Carol my name is Matt Rossi and I met you when I was working for Day P & H in Indian Hills, Bill Burnet was the owner. I have learnded quite a bit from your books and have a question for you. If I have two 24 volt 100 va transformers same manufacture same model, how do I wire them to get 48 volts. I hope you can give me some input on this question. thank you Sincerley Matt Rossi.


  • Empire_2Empire_2 Member Posts: 2,343
    Hello Mars?

    Although I'm not sure why you need 48 volts in the first place, the only way to achieve your scenario is to have the t-former rewound to give you the 48 vac. It's the wire turns inside the t-former that give you the step down whether it be 208 to 24 or 120 to 24vac etc... There is no special trick you can use to manipulate, change the 24 to 48 vac. If you look at a multi tap t former, you will see that different voltages are the result of where the taps are, off of the t-former. Posts or connections fall in different places on the winding inside. Easier to see on larger t-formers.

    Mike T.
  • bob_46bob_46 Member Posts: 813
    put the

    secondaries in series
  • carol_3carol_3 Member Posts: 397

    I do know Day P&H! Sorry, you can't increase the voltage.

  • Bob's correct. If you wire the 120V primaries in parallel, and the 24V secondary windings of each transformer in series and in the correct phase, you will get 48V. If the windings are out of phase, you will have zero output, in which case reverse the secondary terminals on ONE transformer.
  • Empire_2Empire_2 Member Posts: 2,343
    Mike & Bob?

    I am working on this,.So far the secondary in series will only increase the out put voltage by 20% which equals 28.8 VAC. Now maybe I'm missing something, but I think it's very good Question. It's called a "Boost transformer connection" referenced from "UGLY'S" electrical reference. To be sure without putting my foot in my mouth "I'll be Back"....:-)

    Mike T.
  • Mars_3Mars_3 Member Posts: 65
    After some trial and error I was able to get the 48 Volts.

    After I fiddled around with the transformers I did find that I was able to get the 48 volts I needed. In series worked, I just had to find it. Thank you all for your help. The 48 volts is for a radiant window from ME. Thanks again Matt Rossi
  • Mars_3Mars_3 Member Posts: 65
    Carol it was a pleasent suprise to see you this evening

    I had a good time talking to you this evening Carol. While you might not remember me, Bill Burnet sent me to one of your basic electrical classes at Honeywell when I was still green. I personaly thank you for all the training and efort you have given to people like me to get to the position I have been able to achive. I hope to see you again and hope all is well. Sincerley Matt Rossi
  • bo ramsourbo ramsour Member Posts: 6

    regarding tranformers ..iam trying to figure out a way to bench test the newer hot surface igition style gas valve e.g. a valve that has the p. c. m. 3 wire connection.. how can a test this when the standard transormer only has two leads?. i would think that i woild need a transformer with 3 leads .. any help would be appreciated..
    bo federal heating and cooling supply denver.............

  • What you are thinking of is a "boost connection", which would connect the 24V secondary in series with the 120V primary to add the voltages to give you 144V at the output.

    What we were talking about is connecting two separate transformers 24V secondaries in series, to add the voltages together to give you 48V.

    Kind of like connecting two 6V car batteries in series to give you 12V, although with AC transformers the phase is important. This is similar to the idea of the polarity of the batteries, where you have to connect the positive terminal of one battery to the negative of the other to get the full 12V. If you switch the polarity of one battery, the voltages will subtract instead of add and you will get zero output voltage.
  • Is it a Robertshaw

    720-079 valve? If so there is an adapter in the box that converts it to a two wire for use with Direct Spark Ignition and also Hot Surface Ignition. It is basically a Universal Replacement Valve the same as Honeywell VR8345M. When the adapter is in place and 24 volts applied the valve should be full open.

    The "P" on the valve is for Pilot Valve (PV on Honeywell) on Internittent Ignition, the "M" for main valve (MV on Honeywell) and C is common back to "C" on the transformer the same as MV/PV on Honeywell.
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