I thought I'd try to describe in a little more detail about power
transformer construction. I had received several e-mails asking me about
this so I hope this will help. Originally I didn't notice the size of
the capacitor and it is for power correction like was mentioned. Some
transceivers used RFI filters though on the lines using a couple of
chokes and some ceramic disc caps going to ground. The transformer core
size and number of turns are deduced from the frequency it will run at,
the power output needed, the voltage needed, and the flux density of the
laminates measured in gauss. For M6 lams made by Temple Steel, The flux
density runs about 70 gauss if I remember. Mild steel runs about 60
gauss and is what you use if you have unknown laminates. This would be
like using an old transformer or rewinding one. The higher the gauss the
less turns per volt needed and the physical core size drops. The five
square inches for 1000 watts is from using M6 steel and is about a
standard, especially in older transformers. Once transformers get over
1500 watts (1.5 KVa) they generally use Hypersil or other cores.
Hypersil has a higher flux density resulting in a smaller and lighter
core. These cores are known as "C" cores. The laminated steel cores
mostly used are called "E" cores. The reason for this is the shape of
the core material. The flux densities are obtained from the
manufacturers spec sheets which you should need in winding new
transformers. There is an easy formula to calculate the turns per volt
on any core size but you need to know;
Flux Density (Gauss)
Voltage In
Voltage Out
Frequency in Hertz
Number of Turns (Generally from 1.5 to 5 turns per volt)
Core size in square inches
Duty Cycle
The core sizes to not sized up linearly as the power goes up but form
something similar to a bell curve. There is a graph in most ARRL
Handbooks about this I've seen. The best reference material I have
found, and what I use, is a book published by Howard Sams named
"Practical Transformer Design". It deals with every aspect of
transformer, autotransformer, and choke design. Why there is not
anything published about transformer design is beyond me but this should
give you a starting point. If anyone else would like, I can send in the
basic formulas for the calculations. I would check with the local
library or electronics supply house carrying Sams publications for the
book. It was published in 1980 but is still obtainable. I hope this
clears up some things about transformer construction.
Will Matney
US Amp
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|