Iron Core Transformer Formula - Page 8 - diyAudio
 Iron Core Transformer Formula
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diyAudio Member

Join Date: Dec 2011
Location: Philippines
The Power transformer we are going to compute specifies 12 volts output with 750ma current (my Example) converting milliamperes to ampere will give us. .75a , multiplying voltage by current gives us wattage or power.

12x.75 = 9 watts

after having solved for the wattage of the transformer, which is 9 watts, look at Tables 1, where 9 watts is listed, follow the table horizontally and pick up the date for the center leg, thickness and turns per volt.

Center leg - 3/4
thickness - 3/4
turns per volt - 10

the nest step is to compute for the number of turns for the the primary and secondary coils respectively. the number of turns per volts in the primary is equal to the number of turns per volts in the secondary.

Primary coil - 220 volt (base our voltage rating in our country which is the PHILIPPINES)
Secondary coil - 12 volts
Number of turns (primary) = 220x10 = 2200 turns
Number of turns (secondary) = 12x10 = 120 turns

having computed for the number of turns in the primary and secondary coils. determine the sizes of wire for these coils in the next step . before computing for the guage or size of wire (AWG) must find out the current capacities of wires and their corresponding sizes. this data is provided in table 2 .

the power formula is used again in solving for the currents of wires in the primary and secondary. dividing the watts over voltage gives us the current of the wire:

I = w/e

I secondary = 9watts/12volts = .75 a
I primary = 9watts/220volts = .04a

after having solved for the currents of wires pick up the corresponding sizes of wires from table 2. choose the closest current listed in the table.

Size of wires (Primary) - #35
Size of wires (Secondary) - #23

in case of a multi-voltage secondary, the higher voltage should be taken for computation. if the transformer has multiple secondary coils, the wattage of each coil is computed and then summed up. in other words, the wattage of the primary is equal to the total wattage of all secondary coils.

if the secondary coil is only center-taped, half of the wattage and current is taken to compute for the wattage of that coil.

the primary is 220-0 volts, the secondary is 12-0-12 volts
Attached Images
 transformer coil mini.JPG (126.7 KB, 180 views) transformer coil table 2.JPG (144.9 KB, 169 views)

diyAudio Member

Join Date: Jun 2010
Location: Near the Mountain
Quote:
 Originally Posted by tranqspogi the primary is 220-0 volts, the secondary is 12-0-12 volts
Thanks tranqspogi, its useful for me...
our primary is the same that is good but I guess the frequency is different.
Right here in Indonesia that is 50Hz, so my trafo need more turn for same T.

Btw I want some opinion about the "red paper" that I attach,
I want to use it, or maybe you can tell me what paper did you use to make your transformer? or some picture of it

Regards
__________________
Thank you, I wish you happy
peace & G B U

 3rd January 2012, 01:01 AM #73 diyAudio Member   Join Date: Sep 2010 Location: Grove, Ok. Thank you tranqspogi for the great information and excellent examples. But I would like to know where I might be able to access the tables that you have pictures of??? I am sure the internet has them somewhere, but it would be bennificial if you could direct some of us laymen to the proper website. Thank you for your knowlege.
diyAudio Moderator

Join Date: May 2003
Location: Palatiw, Pasig City
Quote:
 Originally Posted by JOHN BALI Thanks Tony I find this paper Maybe it is can be used... my mother often use it in the kitchen to make some cake btw, now is mother's day here in my country Happy mother's day for my mom wish you all the best Then if we make trafo that run cool (below 1T) why we need so expensive insulator material? But if we run the trafo more than 1T that good insulating material must be used So if I go 0.8-0.9T & I use this paper I guess it just okay but if not okay please tell me... The trafo that I made earlier even not using inter layer insulator
you can use that paper.....make sure it is dry.....
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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....

 4th January 2012, 03:37 PM #75 diyAudio Member     Join Date: Jun 2010 Location: Near the Mountain ok... now I have better feeling about it I'll be back with my latest traffo build & a few more formula __________________ Thank you, I wish you happy peace & G B U
diyAudio Member

Join Date: Dec 2011
Quote:
 Originally Posted by JOHN BALI Does someone know the formula to get the best numbers of turn to this kind of transformer/trafo? I do have the 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... Wanted, trafo DIYers Thanks
salam kenal....saya arif dr jkt,
bli Nyoman pnya skema smps 500w ga?
tentunya sparepartnya yg mudah dicari di jkt.

 5th January 2012, 08:54 AM #77 diyAudio Moderator     Join Date: Aug 2003 Location: Sydney Blog Entries: 22 Riff This is an English speaking forum. Please post an English translation with your post. Silahkan posting terjemahan bahasa Inggris. __________________ Any intelligence I may appear to have is purely artificial! Some of my photos
 5th January 2012, 10:44 AM #78 diyAudio Member   Join Date: Jul 2004 Location: Gone on holiday again. back soon. Post79 shows a translation from english that appears, very unusually, to be much shorter than the english version. Is there something missing from the translation? __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 5th January 2012, 10:50 AM #79 diyAudio Moderator     Join Date: Aug 2003 Location: Sydney Blog Entries: 22 Hi Andrew the only part that was translated from English was "Please Post an English translation with your post" I find that the translation engines work best with simple sentences The translation engine did not do a particularly good job of translating the post I referred to though, so whether my message gets through I am uncertain, but putting the Indonesian back through (always a good test) returns "Please post the English translation" So I guess google simplified it Tony. __________________ Any intelligence I may appear to have is purely artificial! Some of my photos
 5th January 2012, 11:45 AM #80 diyAudio Member     Join Date: Nov 2011 Location: UK This question has been asked many times and answered almost as many times. During my HND training we were taught the following formula. Turns/Volt = (1 x 10e9) / (K * FF * B * f * Ai) Where FF is Form Factor - 1.11 for Sine Wave, 1.00 for Square Wave and 1.10 for Triangular Wave. K = 4 B = Max Flux Density in mT. (780mT is good practice but anything up to 1350mT) Ai = Area of magnetic CORE in square millimeters f = Frequency And for Ai: Ai = (Square Root W) / K Where W is 110% of the TOTAL secondary power K = 0.0086 for EI, 0.015 for TU and 0.035 for Ferrite type A13

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