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How to calculate Toroidal Core Maximum VA capacity

  1. Aug 30, 2016 #51

    jim hardy

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    i think so. It looks correct, with condition you won't get perfect lay on the wires so it'll usea kittke nore that 12.24 cm2
    Have you tried your spreadsheet , the one you used for your transformer ?


    0.395 volts per turn equates to how much flux ? 0.395 /100pi = 1.26milliwebers, in cross section of 1/800 m2 = only 1.006 Tesla RMS = 1.42 T peak.

    See if you can find a recommended operating flux for that core, or stick with 1T rms..
     
  2. Aug 31, 2016 #52
  3. Aug 31, 2016 #53

    jim hardy

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    Wow that'll be a challenging wind, manhandling 300+ turns of #12.
    For 230 to 115 I'd look into buying one. Try a search on THG step down transformer to see what's available in your part of the world.

    From your spreadshseet

    upload_2016-8-31_9-36-7.png

    great regulation,,
    2.6 turns per volt = 0.385 volts/turn
    0.385 / 100π = 1.22 milliwebers , in core area of 12.5 square cm
    1.22 X10-3 W / 12.5 X 10-4m2 = 0.979 Tesla, should be safe for most transformer cores i'd think , it's 1.39T peak

    Sanity check looks okay

    losses at full load show around 35 watts primary , 75 secondary ,,, so at 2kva it'll run warm..
    But i think it'll be a better transformer than you could buy . And you'll have fun.

    keep us posted ?
     
  4. Sep 1, 2016 #54
    Hello hardy sir
    Thanks for your thought.
    Sir how to calculate quickly both copper winding use how much mm redious of ID.Is that any formula.
     
  5. Sep 1, 2016 #55

    jim hardy

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    What ? To figure power I used volts drop (from your spreadsheet) X amps at 2000VA, 2000/230 for primary and 2000/115 for secondary
    i dont know what you are asking.
     
  6. Sep 1, 2016 #56
    I mean How to find both primary and secondary magnet wire use how much Inner diameter (not area in cm2)of the core?
     
  7. Sep 2, 2016 #57
    Hello hardy sir

    Which adhesive i should use on bare core before start winding because core is old and have some rust on core.I have standard Epoxy adhesive pack which contain 2 small tubes one is resin and other is hardener.with mixing two same quantity both tube.I got jelly type transparent liquid.Can i apply this liquid on bare core its got hard in 40 to 60 minit.But I don't know it's uses for electrical purpose.
    And can you suggest any insulating electrical tape for insulating primary and secondary winding like professional transformer use for their transformer.
     
  8. Sep 2, 2016 #58

    jim hardy

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    here's 3M's selection.
    http://multimedia.3m.com/mws/media/103938O/3m-oem-insulating-and-conductive-tapes-brochure.pdf

    myself i use mostly Scotch 27 glass cloth tape but only because i had several rolls of it . I'd like to try their polyester.
    How many layers of winding will you have ? What is thickness of wire ? Each layer will subtract that thickness from radius.
     
  9. Sep 2, 2016 #59

    jim hardy

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    Rust on core ? You want to arrest that before you cover it. I would apply a phosphoric acid treatment .
    It's in hardware stores as Naval Jelly or Ospho. It turns the rust black . Then apply your epoxy. I've never had rust eat through paint when i Ospho'd the metal before painting.
    Of course, wire brush or steel wool the loose rust away, and get it thoroughly dry before applying paint or epoxy.. I put my treated parts in the oven on "warm".
     
    Last edited: Sep 2, 2016
  10. Jul 26, 2017 #60
    Hello San,
    If I already have the transformer ready then how can I calculate the effective area Ac of the core?
    My core Dimension are OD=80mm, ID=46mm H=30mm, 100VA
    VA=5.0*J*Bm*f*Ac min*ID²*10-7
     
  11. Jul 26, 2017 #61
    Hello Jimmy Lalani
    Actual bare core dimension required for calculation, is your provided sizes are bare core or after transformer winding completed.please clarify.or proved primary and secondary VA rating.
     
  12. Aug 2, 2017 #62
    Hello San,
    The transformer winding is already completed.
     
  13. Sep 25, 2017 #63
    Hello Hardy Sir,
    I was just going through the conversation for calculating Maximum VA capacity. I found this conversation. In this you have taken e=230sqrt(2) cos(100t). I am a bit confused. Normally we take e=Em sinwt. Then why is it so here? Sorry , if it seems a stupid question to ask.

    Jimmy Lalani
     
  14. Sep 25, 2017 #64

    jim hardy

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    That was just an example of starting with an assumed flux instead of an assumed voltage.
    Flux and voltage have a derivative relationship, do they not ? One can ssume any flux one wants and voltage will be its derivative . I started with sine because its derivative has same sign. And san said he has 230 volts RMS.(not peak) where he is.
     
  15. Sep 26, 2017 #65
    Hello Hardy Sir,
    Thank you very much. Now it is crystal clear in my mind.
    However, if I assume Bm in order to calculate various parameters of transformer at the very begining, then later do I again have to find the new value? I asked few people and they said that my be I have to iterate until I get a suitable or final value? I could not understand what they meant? Can you please help me.
     
  16. Sep 26, 2017 #66

    jim hardy

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    I don't know why they said that.

    If you make a good guess at how much flux density your core will happily accommodate, then the magnetizing current required to produce it will be reasonable. For that reason you need to be aware of you core's flux capability when you choose your operating flux density.
    Since cores are available in discrete sizes and number of turns is an integer, you may have to adjust your Bm slightly to get your desired voltage with a standard size core .

    Here's an example from the internet, worked out by what appears to be a methodical student with a lot of common sense and a good "Do It Yourself" mindset:
    :
    :http://engineerexperiences.com/design-calculations.html

    here he shows pictures of the transformer he built and it's a pretty nice job................
    http://engineerexperiences.com/hardware-design-.html
     
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