Designing Transformers with J.C.Maxwell
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 13th January 2011, 07:06 PM #1 popilin   diyAudio Member     Join Date: Oct 2010 Location: Traslasierra Designing Transformers with J.C.Maxwell As a DIYer, all your work with a solder, (and all Classical Electrodynamics too) whith exception of Thermionic Effect and Semiconductor Theory (Quantum Mechanics), came from only four equations and two constitutive relationsand You must at least see them one time in your life. Eq.(1) to (4) are called Maxwell Equations due to his creator James Clerk Maxwell. If You are afraid of Mathematical Physics, skip the Theory after take a look on Maxwell Eq.!-Mandatory- Well, go to Transformers Eq.(51) is the well known Np = (Upx10^8)/(√2 π f S B) Where: Np=Number of primary turns Up=RMS Primary Voltage in Volts f=frequency in Hz S=Area of the core in cm2 B=Magnetic Field in Gauss Nothing to say, all You must Know it. Eq.(37) can be placed in the form Lp = (4 π μ S Np^2)/(9 lx10^8) Where: Lp=Primary Indutance in Henry μ=Permeability of the Core l=magnetic path length in cm No Matter What You do, PP or SE Transformers, is very important because of bottom end response of a Transformer.We tend to think high u exotic materials can help...Wrong, u is a fuction of almost everything, like frequency, temperature, oil price, etc. and at low frequency generaly is low, furthermore if You have an air gap μ(Real World)=(l μ)/(l+le μ) Where: le=Air Gap in cm Much lower yet!!! If You think making PP donīt have an Air Gap, You must have perfect lamination!!! The only way is as ever, bigger core or more turns.Because the number of turns is squared, has more efect on L. For SE lovers, OPT are PIA, donīt worry, I had deduced a long time ago Eq.(41) Np = (Lp iDCx10^8)/(S B) Where: iDC=Primary DC current in Amper B=Half allowable B of the core in Gauss Recipe:Choose the bottom end frequency, with Eq.(53) can calculate Lp, iDC is given by the operation point of your output valve, B is obtained in the lamination datasheet, and S... is given by "Art of Transfomers" For a 30W SE 211/VT4C/845 16cm2 and a good standard GOSS is enough. Check the turns with Eq.(37) and choose the bigger. Estimation formulae for S are all "Rule of Tumb", the correct calculation is a bit dificult. The rest of the story is "The Art of Transformers":Winding Techniques to reduce L disperse, capacitance, increase insulation, and many more. In coclusion: Donīt waste your money, standard grade GOSS (M6) is enough, if double-C much better, You only need High Flux to avoid saturation and a thin hysteresis curve for best linearity.The thinner the lamination the less energy loss. Cheers! __________________ I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe He has the most who is most content with the least. - Diogenes of Sinope Last edited by popilin; 2nd June 2012 at 12:58 AM.
popilin
diyAudio Member

Join Date: Oct 2010
Location: Traslasierra
Something was wrong with the .gif
Here are.
Sorry
Attached Images
 Eqn1.gif (31.9 KB, 804 views) Eqn2.gif (29.1 KB, 731 views) Eqn3.gif (18.4 KB, 722 views)

Last edited by popilin; 13th January 2011 at 07:16 PM.

 4th April 2015, 09:19 AM #3 scobham   diyAudio Member   Join Date: Mar 2008 Location: Merseyside Hi popilin could you give the full titles of the books you mention with ISBN numbers if they have them. Thanks.
 4th April 2015, 08:27 PM #4 Merlinb   diyAudio Member     Join Date: May 2006 Location: Lancashire Oh look. Popilin has posted his equations again.
popilin
diyAudio Member

Join Date: Oct 2010
Location: Traslasierra
Quote:
 Originally Posted by scobham Hi popilin could you give the full titles of the books you mention with ISBN numbers if they have them. Thanks.
Sorry, but I did not mentioned any book.

Quote:
 Originally Posted by Merlinb Oh look. Popilin has posted his equations again.
Sorry, not again, this is an old thread, the more complete with more equations here

http://www.diyaudio.com/forums/loung...mplifiers.html
__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

 6th April 2015, 08:00 AM #6 TrippleM Banned   Join Date: Oct 2014 "In coclusion: Donīt waste your money, standard grade GOSS (M6) is enough, if double-C much better, You only need High Flux to avoid saturation and a thin hysteresis curve for best linearity.The thinner the lamination the less energy loss." Maybe a detail but for a thinner hysteresis curve M5, M4.... M0 would be a better choice. The effect of thinner laminations are not so big as people might think. At 400Hz 0,5T (an unrealistic high flux density for an audio transformer) the differance between 0,3 mm SiFe (Vacuumschmelze Trafoperm N2) and 0,1mm is [2,9-3,8] = 1,1 W/kg. And at 50Hz there is almost no differance. At higher frequencies the flux density for a audio transformer wil be smaller and smaller, its not a power transformer! *source: Vacuumschmelze, Stripwound cut cores p65
popilin
diyAudio Member

Join Date: Oct 2010
Location: Traslasierra
Hi, is you, Martin?

Your writing style reminds me of a friend...

Anyway, as I said before, this is an old thread with early results, see the next thread cited before for a deeper analysis.

Quote:
 Originally Posted by TrippleM "In coclusion: Donīt waste your money, standard grade GOSS (M6) is enough, if double-C much better, You only need High Flux to avoid saturation and a thin hysteresis curve for best linearity.The thinner the lamination the less energy loss." Maybe a detail but for a thinner hysteresis curve M5, M4.... M0 would be a better choice. The effect of thinner laminations are not so big as people might think. At 400Hz 0,5T (an unrealistic high flux density for an audio transformer) the differance between 0,3 mm SiFe (Vacuumschmelze Trafoperm N2) and 0,1mm is [2,9-3,8] = 1,1 W/kg. And at 50Hz there is almost no differance. At higher frequencies the flux density for a audio transformer wil be smaller and smaller, its not a power transformer! *source: Vacuumschmelze, Stripwound cut cores p65
Of course, better materials give better transformers, but a poor design can give horrible transformers, no matter how good are its cores.

Remind you that losses are related with linearity, because the area of the hysteresis curve represents losses, so using a higher grade lamination with a higher thick is, in general, a contradiction.
__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

nec3
diyAudio Member

Join Date: Jun 2005
Location: Ankara
Quote:
 Originally Posted by popilin The rest of the story is "The Art of Transformers":Winding Techniques to reduce L disperse, capacitance, increase insulation, and many more. In coclusion: Donīt waste your money, standard grade GOSS (M6) is enough, if double-C much better, You only need High Flux to avoid saturation and a thin hysteresis curve for best linearity.The thinner the lamination the less energy loss.
Good summary.

I got a conclusion after many simulations in LTspice with various values of scattered capacitance and leakage inductances. The latter was of the key determinant to the frequency respond. IRL it must not be so much different.

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