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Autotransformers

Discussion in 'General Electronics Discussion' started by William G Whitaker, May 18, 2017.

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  1. William G Whitaker

    William G Whitaker

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    Dec 27, 2016
    I am using an auto transformer and making a power supply that will have 3,5,9,12, or any voltage I want DC or AC. I want to use led's to tell me when a supply E is live. The AC led would vary from .01 to 110v ac. Also an led to show me that the DC is on, what ever the output.
    I realize the when the auto former is putting out less the 3 or 4 volts none of them will work. I think a zener circuit for each led would work . I need a suggestion and drawing of a circuit that will do what I want.
     
  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    What is supply E?
    An auto transformer does not give isolation so there is danger of shock.
    What is the input, is it mains?
    How do you get DC? Is this the input supply to an invertor?

    If the mains input goes to the transformer, then this will always be energised and a suitable led or bulb can give an indication of whether the circuit is live.
    Does the transformer have a variable voltage output like a Variac or Regavolt?
     
    hevans1944 likes this.
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    652
    May 8, 2012
    Post a link to the Autotransformer you're using. BTW, Duke gave you good advice regarding the none isolation characteristics of an Autotransformer. No one here will help you kill yourself.

    Chris
     
    hevans1944 likes this.
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    on it's own, this is really a bad idea

    as Chris did, I will also aim you back to duke37's post

    PLEASE use a mains isolating transformer between the mains input and the auto transformer, if you really want to use an auto transformer
     
    Harald Kapp and hevans1944 like this.
  5. William G Whitaker

    William G Whitaker

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    Dec 27, 2016
    Ah Nice try but this is a bench power supply and I'm using a power strip with on/off and light also the power Supply has an on and off so When I power up my bench power supply I can rectify and light an Led with approbate R included. Next I want to come off the center of the auto former Bridge rectifier cap and variable DC. So I am looking for a circuit to light an led when I'm 3 vDC and up to say 48 Vdc. Then I also have a variable AC out put terminals where I want to rectify + r=+led + circuit that would limit the I flowing through the AC output terminals. So its a little more then a battery or Breaker box AC on and off. Thanks for reading my request and see what Im talking about. I can sketch out what I' doing and where I need a circuit to limit I through 2 led's. The primary AC input Led I can handle.
     
  6. duke37

    duke37

    5,364
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    Jan 9, 2011
    Yes, please sketch a schematic to show us what you wish to do.
    Specify input power and outputs.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
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    Jan 21, 2010
    Please provide a schematic as requested above.

    If you're doing what I great you might be, the DC output will not be stable, it will vary with load.

    However, if the aim is to vary the ac voltage input to the rectifier/filter so as to maintain a reasonable overhead to a linear regulator, then it may work. I have linear power supplies which automatically select taps on a transformer to do this.

    I concur with all the warnings regarding autotransformers and shock hazards.
     
  8. William G Whitaker

    William G Whitaker

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    Dec 27, 2016
    To show a schematic or sketch will require me to clean it up a bit..time. Any way what is E? EMF need I ?? Any way How do I get the EMF DC? Full bridge and a filter or two. No sweat at this time for worries about EMF varying with the load. My tests will all be in a steady state mode. I'll force them to be in that state for initial testing.
    I am coming off a 15A circuit at the box to a std duplex receptacle, to a power strip w 10A resettable overload breaker I, then to a PS switch, then fused at 8A, then xformer, then to a rectifier and filter, then to another fuse (usually sized for the anticipated test load), then to a banana plug, then to my use building or trouble shooting things. Ok I want an Led just after each fuse to let me know when and if the device has exceeded my assessment (or name plate data) of I draw.at this time. I always have a handful of fuses. I tried to find a ckt breaker below 1 A but unless I pick a magnetic rather then thermal the price is way up there. Fuses and holders and led are much cheaper.
    Later I may want to add better output regulation but my PS/Variack has worked well for over 15 years without it). I only wanted to add DM's and get rid of analog meters and the project got out of hand (bigger). Maybe thats since things have gotten more complex? I always break down the functions (of a device) in to steady state before proceeding with other tests. That usually finds the problem, 99% of the time if a smoke test does not for trouble shooting. In design if I blow a fuse (goofed, replace it try again). If it still blows a fuse increase the EI size until it works.
    I'll sketch it up now but where and how do I include a drawing?
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    use the "upload a file" button to the lower right of the text box you write a post in ... to the right of the Post Reply button

    resize the file to a max of 1000 pixels and around 100 kb max
     
  10. William G Whitaker

    William G Whitaker

    14
    0
    Dec 27, 2016
     

    Attached Files:

  11. William G Whitaker

    William G Whitaker

    14
    0
    Dec 27, 2016
    I think I sent to much but this is not a small power supply' Ive used the Vareac and never had a problem.
    I'm redoing the supply with a digital display and other lights and fuses' Im doing this again since I have not heard anything on the forum.
     
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