# winding your own toroidal transformer

hello, I've just finished a module of Transformer theory in trade school and was hoping to try some of it out. I plan on experimenting with winding my own toroidal power transformer.
I require a 1:2 step up at 20V 150hz supply aiming at 150-300VA or so.
I have found a general ballpark equation to calculate primary turns for an EI type transformer which goes like this: is N = (E · 10^8)/ (4.44·f·A·B),
N= number of pri turns E= supply voltage f= frequency A= Cross sectional area of core (I think in square inches) B=max flux lines = rough figure of 60,000
Using a toroidal core with a CSA of 1sq" it gives me 50 turns for the primary.
Is this equaiton correct? Is the value of B ok for say a Mains 300VA toroidal core off the shelf? If anyone can help me answer these two questions, or point me somewhere that can I would be very greatfull.
Thankyou gavin.
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in article bkjntd\$g9t\$ snipped-for-privacy@lust.ihug.co.nz, gav at snipped-for-privacy@lost.com wrote on 9/21/03 1:38 AM:

Try it. Wind several with different numbers of turns. Your experimental results will be better than anything we can provide over the net.
Bill
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Gavin, my might want to check on the websites of producers of torroidal cores. It strikes me that trying to apply a solution for an EI core to a torroid might be a little dicey.
The name Arnold Magnetics springs to mind, but there are several other key players. Some of these have aplets for doing computations like this for their products online.
Possibly try:
http://www.arnoldmagnetics.com/products/powder/index.htm
Harry C.
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Thanks, plenty of usefull links there. gavin.
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The core material selected should be on par with the intended operational parameters of the transformer in use.
Powder may not be the optimal choice for the application in mind.
Be sure to research your desired application, and select the core material which will operate best for you in that application.