Re: Rebuilding an OBIT

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Luc by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<ludev-at-videotron.ca>
> 
> Hi Ed
> 
> May be I make a mistake but the formula I have for the numbers of turns  in
> a primary of a
> transformer is different.
> My formula is:  N = (E · 10^8)/ (4.44·f·A·B), where N=Number of turns;
> E=Primary Voltage;
>        f=line-frequency; A=core cross-section Area; and, B=max.flux, in
> lines. Assuming 60,000
> lines of flux...
> or N = (k·E)/ A, where k=6.256 when f=60 Hz., or, k=7.507 if f=50 Hz.
> 
> My formula could be no good, I never wound a transformer myself but on a 2
> square inch cross
> section core you have for 110V 55 turns and with the formula I have 344
turn .
> 
> Please tell me I'm wrong : It will be less work to wind a transformer !
>
	Sorry, but you're NOT wrong; your value IS correct!  It does take a lot
of turns!!!!!!!  I use a 60 Hz factor of 6.5, which is slightly more
conservative.  With modern steels your value of 6.256 is just fine.  In
a copy of the ARRL "Radio Amateurs' Handbook" for 1933 the recommended
value is 7.5, but transformer steels have been improved since that time.
 
> Luc Benard
> 
> P.S. I extracted this formula from a link post last week on the tesla list.
> The link is call:
> "Roll Your Own Power-Transformers! " I don't remember the URL I just copy
> the documentation...

	I have that URL saved somewhere.  It is a very good source of CORRECT
information on transformer design.

	Bottom line is that in designing transformers you can't cheat Mother
Nature!  You need enough core area and turns or you are in trouble.

Ed