[Amps] Transformer construction information

[Will Matney]

Ok,

As promised, I'm going to give two sets of short formulas here for 50 and 60 Hz transformers. These were calculated by using the long formulas at 12 kilogauss. 12 kilogauss is used as an in between so it can be used on CRGO or CRNO silicon steel from say M-22 or M-6. M-19 and M-22 are Cold rolled non-oriented silicon steel like used in most regular transformers of decent efficiency. M-8 to M-6 (actually on up to M-2) is Cold Rolled Grain Oriented silicon steel. M-6 and Hipersil are the same alloy. M-6 is pretty expensive and on up to M-2 really expensive. Most all power transformers are made using M-22, M-19, M-15, or M-6. M-22 to say M-15 has a maximum flux density of around 15 kilogauss. However, it's best to run them a good bit under this, especially the lower grades. 12 kilogauss is chosen as it's good if your using an unknown steel which could be something like M-50 (but with higher losses). It works OK with M-6 too but the core will be some larger. M-6 and Hipersil can be ran to a maximum of about 17 kilogauss, but after 15 kilogauss the magnetizing current raises rapidly. So it's better to really run it at 15 kilogauss or under. Again the below formulas use 12 kilogauss;

For 60 Hz

TPV = 4.85 / A

A = 0.172 x sq rt of P

--------------------------------

For 50 Hz

TPV = 5.82 / A

A = 0.206 x sq rt of P


A = Core area in square inches
TPV = Turns per volt
P = Power in Volt Amperes or Watts if load is resistive.

Figure power transformers around 85% efficient, and use around 800 circular mils per ampere on the wire size for say a duty cycle of 75%, and about 1100 circular mils per ampere for a 100% duty cycle. You may have to fudge around the first core design to get all the coil to fit into the windows. Generally, it's better to go to the next size larger lam to get a larger window, if the coil wont fit in the windows, than to cut back the number of turns, and raise the flux density. The insulation paper (fish paper) needs to be rated at least 100 volts per ever 2 mils thickness. Between each winding of the coil, and the bobbin, use at least 0.020" thick paper. The paper between the layers of each winding is sized by the voltage of each layer. Leave margins of at least 1/8" at the top and bottom of the coil. I'll show the long formulas tomorrow if wanted.

By the way, I found the old short formula listed in a lot of books to be off, and not for 12 kilogauss. They always said approximately 12 kilogauss, but it was actually for about 11,600. For 60 Hz those were;

TPV = 5 / A

A = 0.16 x sq rt P

Best,

Will


*********** REPLY SEPARATOR  ***********

On 2/7/06 at 1:04 PM Will Matney wrote:

>John,
>
>You can do a search back in the archives on here where I have shown how to
>do this, or wait until this evening and I'll try to show here what you
>want. First, I need to know what primary voltage you want, and what the
>secondary volrage(s)/current(s) you want. Also, what is the application to
>figure the duty cycle and efficiency.
>
>The book you mention I have and it goes more into the theory of how the
>formulas were contrived and to me is not a good book on how to calculate
>transformers. About the best one is named Practical Transformer Design.
>Try a seach for it.
>
>Best,
>
>Will
>
>*********** REPLY SEPARATOR  ***********
>
>On 2/7/06 at 11:04 AM John Darwin Powers wrote:
>
>>To fellow electron herders,
>>
>>Does anyone have any references to building high-current transformers.
>>Would anyone also know if there is an online version of the book  
>>"Transformers for Electronic Circuits" by Grossner?
>>Any online references to transformer design and construction would be  
>>appreciated.  Thank you.
>>
>>John
>>
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>
>
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