Transformer Help??????????????
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 28th February 2014, 05:25 AM #1 diyAudio Member     Join Date: Feb 2014 Location: cailfornia Transformer Help?????????????? This is what I have going on I purchased a 700w mono sub woofer amp which need a 700w transformer 50-0-50 ac out so I decided to build my own transformer for this project I just want to make sure I am doing the math right transformer core area is 6cm X 3.5cm =21 constant of 42/21 = 2 v.x v. 117v x 2 =234 turns for Primary winding now for the gauge of the magnet wire this is where I am not sure of? I divided watts of the amplifier by the source voltage 700x117=5.9amps? so 15gauge magnet wire on my chart 6.6 amperage I don't think I am doing this part right. For the secondary winding 50v x 2 =100 turns for each 50v this is where I think the math is off it says take the watts of the amp dived it by the output voltage 700/50=14amps so I would need a 11 gauge magnet wire. So can someone tell me where I am going wrong?
 28th February 2014, 10:55 AM #2 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders When flux is 1T VA ~ core area^2 * 31, for sq inches. VA ~ core area^2 * 0.75, for sq cm. If you want a different flux then just proportion the result. eg. 6cm by 3.5cm = 21cm^2 @ 0.8T, the VA is 21^2 * 0.75 * 0.8 = 265VA or in sq in 2.36" * 1.38" = 3.255sq in VA = 3.255^2 * 31 * 0.8 = 263VA __________________ regards Andrew T. Last edited by AndrewT; 28th February 2014 at 11:02 AM.
 28th February 2014, 11:07 AM #3 diyAudio Member   Join Date: Jul 2003 Location: Dona paula, Goa Primary current will be less than the secondary current. I think u r confusing between them. 700VA=100V x 7A Gajanan Phadte
 28th February 2014, 01:46 PM #4 diyAudio Member   Join Date: Feb 2008 Location: Jackson,michigan AndrewT is that formula based upon 50hz or 60hz? Just curious. jer
diyAudio Member

Join Date: Feb 2014
Location: cailfornia
Quote:
 Originally Posted by AndrewT When flux is 1T VA ~ core area^2 * 31, for sq inches. VA ~ core area^2 * 0.75, for sq cm. If you want a different flux then just proportion the result. eg. 6cm by 3.5cm = 21cm^2 @ 0.8T, the VA is 21^2 * 0.75 * 0.8 = 265VA or in sq in 2.36" * 1.38" = 3.255sq in VA = 3.255^2 * 31 * 0.8 = 263VA
you are talking about the transformer core area value?

diyAudio Member

Join Date: Feb 2014
Location: cailfornia
Quote:
 Originally Posted by gmphadte Primary current will be less than the secondary current. I think u r confusing between them. 700VA=100V x 7A Gajanan Phadte
This is all new to me I think I have math right for how many turns for the primary & secondary but when it comes to the magnet wire size that were I get confused This is the site I got the info from Como calcular un transformador de corriente

Any help to get me on the right track would be appreciated.

 1st March 2014, 01:36 AM #7 diyAudio Member   Join Date: Aug 2010 Life is a enigma, In post 2 Andrew was trying to tell you that your transformer is to small for 700W. (His equation was not written properly) "6cm by 3.5cm = 21cm^2 @ 0.8T, the VA is 21^2 * 0.75 * 0.8 = 265VA" He is saying your transformer is good for about 265 Watts at .8 Tesla. You need a transformer about twice as big. (42 cm^2)^2 x .75 x .8 Tesla = 1058 W (35 cm^2)^2 x .75 x .8 Tesla = 735W (30 cm^2)^2 x .75 x .8 Tesla = 540W (21 cm^2)^2 x .75 x .8 Tesla = 264W So you have to find a transformer with a core area of at least 35CM^2 See if you can find this transformer and then i will help with wire size.
 1st March 2014, 01:52 AM #8 diyAudio Member   Join Date: Aug 2010 Life is a enigma, I just thought of something. This is for audio. You can get buy with some real junk for audio. Because of the mostly average and sometimes peak power needed you can probably get by with 1/3 the power rating of the transformer. So the one you have will be just big enough, if the windings fit. Do you have a bobbin for this transformer. If so what is the winding width and height.
diyAudio Member

Join Date: Feb 2014
Location: cailfornia
Quote:
 Originally Posted by powerbob Life is a enigma, In post 2 Andrew was trying to tell you that your transformer is to small for 700W. (His equation was not written properly) "6cm by 3.5cm = 21cm^2 @ 0.8T, the VA is 21^2 * 0.75 * 0.8 = 265VA" He is saying your transformer is good for about 265 Watts at .8 Tesla. You need a transformer about twice as big. (42 cm^2)^2 x .75 x .8 Tesla = 1058 W (35 cm^2)^2 x .75 x .8 Tesla = 735W (30 cm^2)^2 x .75 x .8 Tesla = 540W (21 cm^2)^2 x .75 x .8 Tesla = 264W So you have to find a transformer with a core area of at least 35CM^2 See if you can find this transformer and then i will help with wire size.
well that not good I appreciate the help from you guys. This do it my self project is being a pain in my butt. So does anyone know where I can get a E-I core kit that will fit my needs for this project?

diyAudio Member

Join Date: Aug 2010
Life is a enigma, Just to be sure there are no mistakes, this picture shows the core area we need for our calculations. The checkerboard area is the core cross sectional area that you measured as "6cm by 3.5cm = 21cm^2
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