transformers

Discussion in 'General Electronics Chat' started by gofigure, Dec 13, 2013.

  1. gofigure

    Thread Starter New Member

    Dec 13, 2013
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    noobie here..
    uh i just wanna ask something. i have a problem using isolation transformers..
    i cascaded 2 transformers in order to form an isolation transformer, i used 220v->12v then cascaded it to 12v->220v (because buying a cascaded transformer is very expensive). i tested it w/o load, and the voltage picked up from the end of the cascade was 220v, it was fine. but when i put a load on it, as shown in the circuit below (right side of the circuit), i got a lower voltage on the two terminals of the transformer. anybody, pls help? badly needed. thanks!

    by the way, the circuit is for a soldering iron power control.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    What is the power/current rating of the two transformers?
     
  3. #12

    Expert

    Nov 30, 2010
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    1) you need a rectifier in series with that LED or the reverse current will pop it pretty soon.
    2) All transformers have resistance in the copper wire of the windings and some losses in the magnetic coupling. The question is, How much loss do you see? It would be about normal at 5% with a light load, 12% at a heavy load. (from practical experience)
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a simple soldering iron controller is a light dimmer, the kind you put on the wall to dim incandecant lights. resistance type soldering irons work fine with these. I dont know about the 220 volt ones, but I use one of the 120 volt ones here all the time. most use a triac inside and have a rating of 500 to 1000 watts.
    cliff
     
  5. gofigure

    Thread Starter New Member

    Dec 13, 2013
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    Current rating of both transformers is 1A
     
  6. gofigure

    Thread Starter New Member

    Dec 13, 2013
    3
    0
    uh, when the transformer is unloaded (meaning no circuit is present at the right side, 220v comes out from the transformer on the right, but when loaded (meaning the circuit is present @ right side), 78 v comes out [measured]
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,854
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    Normally we don't use that way, it just take two transformers away and then connecting them from left wires to the right wires.
     
  8. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I am guessing your 1 amp transformers are designed to put out 1 amp on their 12 volt side?

    If so your system is limited to about 12 watts of power at best which is why your output voltage drops off so far.
     
    #12 likes this.
  9. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    As tcmtech noted that transformer rating is for the output and thus are rated for 12VA, or 12W for the maximum power you can draw, and I assume your soldering iron draws more than that. Even at 12W there will be a significant drop in voltage do to the winding resistance since you have the two transformers in series and all the primary and secondary resistances contribute. You need transformers rated higher than the maximum load you want to draw.
     
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