
Home  Forums  Rules  Articles  The diyAudio Store  Gallery  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
20th November 2011, 11:31 AM  #1 
diyAudio Member
Join Date: Jun 2010
Location: Near the Mountain

Iron Core Transformer Formula
Do you know the formula?
to get the best numbers of turn to this kind of transformer / trafo? I have over simplified formula, but maybe some other formula to compare with This my formula for EI trafo for 50 Hertz frequency primary winding n = 45 * V / A secondary winding n = 49.5 * V / A n = number of winding turn V = voltage input or output (volt) A = core area (cm square) Maybe someone help to add another formula here, please... I want to make right trafo this time Thanks Last edited by JOHN BALI; 24th January 2012 at 05:30 PM. 
20th November 2011, 11:37 AM  #2 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

the secondary shows a +10% correction for loaded output voltage.
I suspect this is a guesstimated value for regulation of the final transformer build. Regulation can vary from <=3% to >=30%. A fixed turns ratio correction of +10% is not appropriate to all transformers.
__________________
regards Andrew T. 
20th November 2011, 11:44 AM  #3 
diyAudio Moderator
Join Date: May 2003
Location: Palatiw, Pasig City

are you winding on an EI core or torroid?
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus.... 
20th November 2011, 11:46 AM  #4 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

__________________
regards Andrew T. 
20th November 2011, 11:51 AM  #5 
diyAudio Member
Join Date: Nov 2011
Location: UK

This is OVERSIMPLIFIED.
The important thing to learn is the magnetic properties of the transformer that you are trying to wind. The first formula is A = Square Root (W) ..........= mm2 ................K Where W is the Secondary Power + 10% K = 0.0086 for standard E & I laminated sheet 0.0150 for T & U laminations. Once you've got the correct iron work for the transformer. Turns / Volt = 1 x 10e9 .................. ...................K x B x f x A Where K = 4.44 for a SINE wave, 4.00 for a SQUARE wave. B = Max Flux Density  780mT is good for reliabilty, hoever this can be pushed to 1350mT f = Frequency 50Hz or 60Hz (Unless you are design SMPS then its kHz) A = The Core Area as discussed above. Once you know the Turns / Volt its a simple case of working out the Primary and Secondary Turns. Last edited by KatieandDad; 20th November 2011 at 11:54 AM. 
20th November 2011, 12:22 PM  #6 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

Is the first formula?
A = sqrt(W) / K where W is the input power in Watts and K is 0.0086 for EI. The answer in mm^2 (sqmm) Is the second formula? Turns/Volt = 10^9 / [ K' * B * f * A] where K' = 4.44 for sinewave, B = 780mT for EI to stay cool and avoid the saturation knee on high mains voltage, f = mains frequency, A = core area in sqmm Inserting values into that first equation gives the same answer as: Watts = 31 * [Core Area (in square in)]^2 using 100W and 1160sqmm = 1.8sqin Inserting values into the second formula for 4.44, 780mT, 50Hz, 1160sqmm, gives 5T/V resulting in 1145T for 230Vac @ 100VA Whereas, John's first formula result in 892T for 230Vac with 1160sqmm. This seems to confirm that Johns' first formula has assumed B=1000mT = 1T Have I got this correct?
__________________
regards Andrew T. Last edited by AndrewT; 20th November 2011 at 12:49 PM. 
20th November 2011, 12:57 PM  #7 
diyAudio Member
Join Date: Nov 2011
Location: UK

1000mT is fine for commercial design.
If you've got the core material I would reduce the Magnetising Force (B). You can ALWAYS increase the Turns / Volt, NEVER reduce them. 780mT is what the MoD employ. It also allows for Mains Transients of over 100%, not that the windings wouldn't take that for a short time anyway. For SMPS designs the B figure needs to be MUCH lower. Last edited by KatieandDad; 20th November 2011 at 01:03 PM. 
20th November 2011, 01:00 PM  #8 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

But, have I interpreted your formulae correctly and drawn the correct conclusions?
__________________
regards Andrew T. 
20th November 2011, 01:07 PM  #9 
diyAudio Member
Join Date: Nov 2011
Location: UK

Looks fine to me.

20th November 2011, 01:46 PM  #10 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

I have only done it once so far, but would testing for the knee in the B vs V curve give confidence in having guessed at the correct identification of the core material?
I found that plotting for Vac from 10Vac to 260Vac showed that the tiny 3VA transformer was being run at far too high a voltage. 160Vac would be far cooler than running it at a nominal 240Vac, even though it is rated as 220/240Vac. Lies!! or the cheapskates thought I couldn't care about being burnt by the surface of the EI core
__________________
regards Andrew T. 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Where you buy iron transformer core for DIY audio transformer  tarsik  Tubes / Valves  10  27th December 2011 09:15 PM 
Which, Foil Air Core or Iron Core Inductors  slhijb  MultiWay  16  20th November 2009 04:12 AM 
Solen Air core inductors, Hammond Iron core.  gnomus  Swap Meet  0  30th July 2004 02:28 AM 
Iron Dust Core Transformer  Hemal  Car Audio  0  7th June 2004 04:43 PM 
Air core vs Iron core  Ilianh  MultiWay  5  2nd January 2003 02:36 PM 
New To Site?  Need Help? 