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step-up transformer design problem

Discussion in 'Renewable Energy' started by georgetwo, Oct 15, 2011.

  1. georgetwo

    georgetwo Member

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    Hello!
    I have been involved in building inverters for quit a some time, and i have noticed some things about my step-up transformer:
    1) the efficiency is less than 60%
    2) the current drown at no load is more than 2.5A
    3) A 2kva inverter cannot feed a load of 1.2kw (it starts smoking)

    I Need you guys to pleas help me with all necessary calculations needed to achieve the turns ratio, number of turns and swg of the coil for a particular power of transformer?
    I'm using 220v as inverter output voltage and 60Hz frequency
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    We need a lot more info, preferably a schematic, before we can diagnose the problem.
     
  3. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    What are the transformers actual physical size and saturation characteristics of the iron being used?

    Low efficiency of transformer can easily be caused by undersized core and/or poor magnetic properties or massive losses due to excess eddy currents in the core itself from improper laminating of the iron sheets.
     
  4. dave

    Dave New Member

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  5. georgetwo

    georgetwo Member

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    i added two more fets to both sides of the fet cct to achieve enough power to drive my 1kv transformer of which I am having problem with winding and calculation.
     

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  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    For starters if you are trying to drive a 1200+ watt load with a 1 KVA transformer thats why it starts smoking after a bit.

    Second a 2.5 amp idle load at 12 volts with a reworked 1 KVA iron core transformer and being driven with that circuit is not bad at all.
     
  7. georgetwo

    georgetwo Member

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    oh surry! In the first post, I was talking about a 2kva I previously built. There is on 2kva inverter I am presently working on, with 8 irf540 (4 up, 4down) same cct but transformer I used was xtracted from a bad 2kva transformer. I realy need a calculation guide to turns and wire gauge. Cos i need to do this one perfectly.
     
  8. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    If the voltages where known for the old winding configuration and the number of turns as well then it would have been easy to calculate what the new ratios would have needed to be.

    What did the old transformer come from and what method of disassembly and rewind did you use?

    Still thats a rather poor circuit to use to drive inverter from being there is very little time delay for the switching devices to turn of and transfer to the other half of the cycle. A 5 - 20% dead band between cycle halves helps greatly with efficiency and power control on 50 - 60 Hz transformer based inverter designs such as this.
     
  9. georgetwo

    georgetwo Member

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    I think I saw that on a book but don't know how to make the delay with this ic. As for the transformer, I got it from a stabilizer rated 2kva
     
  10. georgetwo

    georgetwo Member

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    can any one help me with any info for transformer winding calculation!
     
  11. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    As far as IC's for inverters go using something deigned for inverter and other similar types of switch mode based power supply circuits is far better!

    These LM3524 and LM3525 IC's are still around and cheap and easy to buy new or scavenge from circuit boards.

    View attachment LM3524 PWM regulator.pdf
     
    Last edited: Oct 17, 2011
  12. georgetwo

    georgetwo Member

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    thanks, Im on it.
    ILL get back to you when the cct is working.
     
  13. HIZIBIZI

    HIZIBIZI New Member

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    Post the specifications of your system, like input voltage, output voltage, primary and secondary wire gauges and no. of turns, core and window area. Efficiency of around 80 % with used cores at 1 kVA power level is doable. You also have to provide snubbers in the primary side to compensate for the high leakage flux associated with low voltage winding.
     
  14. Glentech4

    Glentech4 New Member

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    Do you have a transformer you need to redesign ? If so what is the size of the core
     
  15. William I. Behen

    William I. Behen New Member

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    Current drawn at no load is "magnetizing current." If the input side parallel inductance is Lm, then the current drawn is I = V/X where V is the input voltage and X = 2pifLm where pi = 3.14 and f is the switching frequency.

    Also be sure the two transistors are not ON at the same time, even for a short part of the cycle, as this shorts the transformer with much current drawn from the source!
     
  16. szhighstar

    szhighstar New Member

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    V=Li*di/dt=N*Bs/dt, you can get turns of winding accoring to the formula.
     

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