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Transformer Windings

Discussion in 'General Electronics Chat' started by Divendra Nath, Sep 5, 2017.

  1. Divendra Nath

    Divendra Nath New Member

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    How to calculate windings on a transformer 120/240 input and secondary with multi voltage:33v 0v,13.5v 0v,2.7v 0v 2.7v,9v 0v 9v.
    Total consumption is 28watts only .How to calculate windings for all secondary and how to workout Amps for VA?.
     
  2. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    First you would need to know the magnetic properties of your core and to what physical dimensions you would need to meet all the combined VA loads of each winding set.

    Realistically you would start with a already made transformer that has the correct primary winding in place and that has a VA rating equal to or exceeding your estimated power draw requirements then wind each secondary set as needed to get correct voltages you need at whatever loads each set has to support.
     
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  3. Divendra Nath

    Divendra Nath New Member

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    Thankyou sir for your kind response.I am from Fiji Islands,i live in USA.The transformer was sent to me from Fiji but I did not receive it for last 8months.I know it is lost.So and there is none available I was ready to buy it from any where I cant find it the factory no longer makes any.
     
  4. dave

    Dave New Member

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  5. Colin

    Colin Member

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    To start with, there are no transformers made with 120v 240v primary. Although it can be done, you need to series or parallel 120v primaries.
    Decide which input voltage you want and get separate transformers for a few dollars each. There are multi tap transformers but not with centre taps
     
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  6. chemelec

    chemelec Well-Known Member

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    "Hammond Transformers" in Canada, Does Make transformers with Both the 120/240 Primaries.
    They also make CUSTOM Transformers, Even for a Quantity of just needing ONE.
     
  7. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    We are probably talking apples/oranges but:
    upload_2017-9-6_12-40-49.png
     
  8. dr pepper

    dr pepper Well-Known Member

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    You design a transfrmer by selecting a suitable core, usually silicon steel laminate for mains transformers, the primary is then calculated, this done so that the magnetic field ustilises the core fully but doesnt saturate it, then its just a matter of turns ratio and wire size for the secondary.
    You can get transformer design calculators of the net.
    If you want a particular transformer a good way to start is to get a transformer kit with a pre wound primary, you just wind the secondary for the voltages and currents you need, equations come with the kit.
     
  9. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Most hobby people get a transformer that is close to what they want and modify it.
    Get a 28 watt transformer! with the primary you want. In your case a 120 and 240 inputs. (secondary voltage is not important)
    Then unwind the secondary while counting turns. You need to know turns/volt. example 10T=5V
    Do not touch the primary and insulation.
    Now put back the secondary with the turns you want.

    In your case I would; start at 0, wind to 2.7 come out to a pin then back in, wind to 9V, come out to a pin. Probably change to a smaller wire size, back in and wind to 33V. (repeat for the other secondary except wind the other direction)
     
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Just a few quick notes here...

    First, i have a transformer myself that has a 120v/240v primary and you get this by either series or parallel connections of the primary.

    Second, when the voltage on the secondary is calculated it is usually at the expected load of all secondaries. The primary resistance and the secondary resistances affect the output voltage due to the winding resistance.

    Third, the secondary on most wall warts is physically separated from the primary in that it is not wound on top of the primary but wound next to it instead, with a physical gap between them. This adds to the safety by providing a physical isolatino between windings.
     
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  11. chemelec

    chemelec Well-Known Member

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    The Total wattage may be 28 watts. So Maximum Primary Current is about 233 mA. with 120 VAC in.
    or about 117 mA with 240 VAC in.
    But for determining "Secondary Wire Gauges", you need to determine What the Output Currents are on each output:
    33v 0v
    13.5v 0v
    2.7v 0v 2.7v
    9v 0v 9v
     

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