Need 24 Volt Transformer Info

Discussion in 'General Electronics Chat' started by hooperdoski, Feb 14, 2011.

  1. hooperdoski

    Thread Starter New Member

    Feb 14, 2011
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    I just put in a gravity flow hot water recirculation system in my home. I now have instant hot water at my kitchen sink, which is about 50 feet away from the water heater. Because the recirculation system runs 24 hours per day it causes my water heater to use more propane. I would like to put a timer and 24 volt solenoid valve into the system so I can control when the water is being circulated. I know how to do this, but I don't know what considerations need to go into choosing a transformer to convert the 120 AC volts to 24 DC volts. Can someone tell me what I should be concerned about when providing 110 volts to a 24 DC volt transformer to run a 24 volt solenoid valve?

    Thanks.
     
    Last edited: Feb 14, 2011
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Find out what current is necessary to operate the valve. Get a transformer rated somewhat above that for some overhead.

    It may be you can look around for a 24 VDC wall transformer that will work. That is almost the least expensive way to go. Make sure the wall wart has some extra capability, too.
     
  3. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Why not use an AC solenoid? Skip all that DC stuff.
    If you are stuck with a DC solenoid then you must take into account that rectified AC will not be at the same voltage as the transformers secondary.
     
  4. hooperdoski

    Thread Starter New Member

    Feb 14, 2011
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    Beenthere said: Get a transformer rated somewhat above that for some overhead.

    Jaguar said: you must take into account that rectified AC will not be at the same voltage as the transformers secondary.

    I don't understand what's being said above. Can someone explain in detailed lay terms what is meant by the above?

    So everyone knows, when it comes to transformers and talk about them you're dealing with a guy that is totally ignorant about the subject.

    As for going to a 110 solenoid, in my research I was drawn to looking at dc solenoids, but I'm not sure why. It's probably because they're more expensive, harder to find or they're not as common when hot water is involved and maybe more than one of those things apply.

    Thanks to both of you for your help.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Be big step is in finding out the current rating of the solenoid. Having the ability to supply a bit more current is useful as the solenoid needs more current to pull in than to stay energized.

    As to the transformer mystery - AC is measured differently from DC. The idea is to be able to relate the work that can be done with either kind of voltage. The AC voltage is the root of the square of the mean voltage (RMS). When you convert to DC and filter to smooth out the AC variations, the resulting voltage is almost 1.4 times the RMS value.

    So if you get a wall transformer with a 24 volt output, all you need to know is if it can supply the necessary current.

    It never hurts to know something about electricity, though. You might take a look at our Ebook (links at the top of the page).
     
  6. hooperdoski

    Thread Starter New Member

    Feb 14, 2011
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    Beenthere, thanks for the info, but it's still a little over my head although I did get some of what you wrote. A big part of the problem is that the solenoid manufacturers do not give any specs on what the necessary current is.

    I did take a look at the ebooks, but being 66 years old I just don't have the desire to go through the learning curve on this one. However, after doing more research I have come to a conclusion on this; in order to avoid guessing on which transformer is right I've decided to go with the 110 volt solenoid. That takes away all the questions.

    Thanks for the help.
     
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