[Amps] Transformers

[Steve Thompson]

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