Any Help???

Discussion in 'General Electronics Chat' started by Dr.killjoy, Mar 10, 2014.

  1. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    I tried getting a 24v toroid transformer and when I got it was the wrong one ..Its a brand new 0-277v pri and sec 0-12v 4.167A but is there anyway I could use it on 120v AC or am I better off selling it or trading for the right one ???




    Thanks
    Jason Sr
     
  2. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    It will work on 120. but the outputs will scale:

    277/120 = x/12

    So, you will get less than half of the 12V rating.

    You should not exceed the current rating of the secondary.
     
  3. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    How hard would it be to rewind it for my application ???




    Thanks
    Jason Dr
     
  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    I think I'd get the right transformer.

    The general eqns are n1/v1=n2/V2 where n is the number of turns.

    I've only wound a few torroids in my life and they were maybe less than 100 turns with fairly large wire. Typically you Bifilar wind them or wind two wires at a time.

    The larger core xformers can be wound using a sort of stick where the wires are placed on and then wound off as you pass it through the core.

    Face it, you screwed up. Buy the right xformer.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The 12v winding will be around 20-24 turns so take that off, count the turns and this way you will know how many to remove off of the primary.
    Wind a 24v secondary back on.
    Max.
     
  6. #12

    Expert

    Nov 30, 2010
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    Certainly there is a way to rewind it yourself, but it's not fun, it takes a lot more time than a trip to the post office, and the finished product will not be as reliable as when the pros do it. I used to do everything electrical in a power supply factory except wind the transformers. My transformer man would have taught me the whole operation if I asked, but it was obvious to me that his tools, materials, and methods were so specialized that it wasn't feasible to achieve that quality for a DIY situation.

    Still, you're free to try. All it takes is a lot of labor and picking up some of the tricks as you unwind the original transformer.

    Cute story: My transformer man said engineers think a transformer is made of steel and copper, but there are a lot more pieces of tape and paper than there are pieces of steel and copper. Watch as it comes apart and learn as you go.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also on just removing primary windings, technically you would need to remove all and wind on a suitable gauge to suit the transformer va size, but if you do not intend to use it at the max va for your application, then just remove sufficient windings and use the present reduced winding for the primary.
    Max.
     
  8. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Ok so what's worth ???
    I am really torn what to do with it ... I was thinking to cut the copper off and throw the ring away or just throw the whole thing away or sell it but not sure who uses 277v ???
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Wouldn't take much to modify for 240vac. But fairly small at 48va.
    Max.
     
  10. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    OK but I live in the USA and 240 vac is useless to me..
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
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    How much of the hole in the center is still open? If there is enough room, double the number of turns for the secondary, using the same size magnet wire. Motor rewind shops should be able to help you with the wire.
     
  12. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Face what I didn't do anything but buy the right transformer and got sent a different on then was display .. So I am stuck with this one .. How hard would it be to cut the secondary off and maybe remove some of the primary for use with 120Vac and then wrap for my secondary but not sure how much..
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
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    Look at post #11. You really shouldn't need to do anything with the primary if you double the turns on the secondary, as I see it. If I'm wrong, edgumacate me.
     
  14. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    What I am trying to do is make a power transformer with specs of ..

    Primary-120VAC
    Sec-24 or 30 VAC with 2 or 3 amps


    But I am trying to do some research but have been coming up with nothing so far that I can understand or where to even begin to rewind this ..

    I am not sure at all..
     
  15. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Transformers are all about ratios. Like BillB said use the 220V primary as wound, and double the number of wraps on the secondary. Made up numbers follow since I dont know actual wrap numbers. At 220V primary is 20 wraps, and secondary 5 wraps. To use on 120V, and get same output, you would have original 20 wraps on primary and then you need 10 wraps on secondary.

    Is your primary center tapped (three wires on the primary)? If so you could use the center tap and one of the other primary leads. This effectively cuts the primary in half. Making the correct voltage at the secondary.


    Maybe you could give a link to the transformer you bought?
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Post #5 & #7, Or place 10 turns on and power the transformer from 120vac, measure the voltage to obtain the turns/volt x2, this if removing primary turns for 120v operation..
    If powering it from a 220v outlet then no x2.
    Max.
     
  17. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Pics added


    The transformer is made for 270VAC and I am using 120VAC
     
    shortbus likes this.
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The problem with adding more turns to the secondary without modifying the primary is that, for a 48VA output the primary winding will have to carry ~twice its design current if run on 120V. I smell smoke.
     
    Last edited: Mar 25, 2014
  19. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    My plan was rewind the whole thing to my specs instead of throwing it out ...
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the primary wire gauge is sufficient for the va rating using 120 instead of 240, it would be a case of removing pri turns instead of the whole Pri.
    My post #16 was to find out the turn/volt ratio.
    Max.
     
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