[Amps] Transformers

[Will Matney]

Steve,

That's true. The only thing here in the US is every book that we use to teach with uses the CGS or inch system. I think though that the J&P Transformer book which is published and written in the UK uses the same thing. There's also a small paperback by Bandini that teaches this as well. Ferrites are a little different in that they have a really low flux density as compared to the high permeability steel alloys. I have seen Teslas used here, but the math was still the same. It's easier for some to say 1.3 Tesla that 13 kilogauss. There's several ARRL books on the subject by people like Doug DeMaw and others.

Best,

Will

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

On 7/16/06 at 11:46 AM Steve Thompson wrote:

>Will Matney wrote:
>> Steve,
>> 
>
>> First, everyone in the industry uses gauss. 1 Tesla is 10,000 gauss
>which he uses Tesla. You can use Tesla to shorten the number. However,
>when you read any book on the subject, the formulas use gauss. The
>magnetizing force H or Oersted has a lot to do with it too. As flux
>density rises, so does the magnetizing force. He also uses square meters,
>and where is a core a square meter unless in a huge transformer. Most all
>published formulas use square inches or centimeters. He also goes the hard
>way on the main formula using division after division ( t = V(RMS) / 4.44
>/ m^2 / Hz / T). It's much easier to multiply everything, and do one
>division. By the way, the 10^8 I show in the long formulas must be
>multiplied by the voltage so that it can be divided after multiplying
>everything.
>
>I can't speak for iron cores, but all the data I've been studying 
>recently for ferrites uses SI units - Teslas and m^2 or mm^2 - there 
>again, it's data from European or Japanese manufacturers. I guess cgs 
>units and inches might be more common in the US.
>> 
>> Also, the author never mentioned the watts per pound losses of the steel
>which rises with increased flux density. The short formulas I showed for
>core size from output power and the turns was developed from the
>experience of engineers years ago, and has been used ever since. They can
>be recalculated for different frequencies. All of this goes into the
>efficiency of the transformer, and has to do with its regulation too. I
>think he's over-simplifying the design process, leaving a little out, and
>making the math harder to do. There's just a little more to designing one
>in the real world than that.
>
>There's usually a bit more than anyone can put into a simple document - 
>but as someone who fits (or at least fitted) the description in his 
>opening lines, I found it very helpful. It's probably because the way he 
>puts things happens to 'click' with me.
>
>73, Steve
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