On Tue, 30 Oct 2007 08:51:25 -0500, Robert Swinney wrote:

"bob" sez:

"I think that you are mixing up size and efficency. The higher the
frequency the size for a certain power output decreases. But ! the
losses from eddy currents and the like increase. There is a crossover
point which was below 50 hz in the old days ...."

There is no specific coorelation re. size, frequency and efficiency. The efficiency of any
electrical device is a function of its design. i.e., efficiency is always a trade-off against cost,
performance, weight and a host of other things. Each device is designed to operate with a certain
efficiency (not always the maximimum efficiency) within certain boundaries, cost usu. being
foremost, among them.

Bob Swinney


A transformer's (or inductor's) core volume goes down as the reciprocal of
frequency for any given power level. Core materials can hold a nearly
constant amount of energy per unit volume, and the energy they must hold
is pretty close to power / frequency. This is why switching supplies (and
amplifiers) run as fast as the output transistors and catch diodes can go
-- they're trying to drive the transformer size down.

I believe that a motor's ability to transmit mechanical power follows a
similar trend, although the energy is stored in the gap between the
armature and coils -- I haven't done the math on this one yet.

So I certainly disagree as it pertains to transformers, and I think I do
for motors.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html