Anyone know anything about magnetic amplifiers?

[tim9000]

Hi,
I was wondering if anyone knew if you could use a magnetic amplifier:
http://en.wikipedia.org/wiki/File:Magnetic_amplifier.svg
as like a variable resistor for controlling current from the source to the load?
I imagine there would be a large voltage imposed across it when it is a high impedance.

Thinking just about the source and load electrical circuit: What sort of range of impedance would a magnetic amplifier have in this respect (as a variable impedance), could it go from acting like a really low impedance circuit component (of near zero ohms) to one in the M Ohms?
If so, if you've got a couple amps going through it and it looks like say 50 Ohms, is all that power being burnt up in the core of the Mag Amp in heat?
So the impedance of the Mag Amplifier being seen from the source/load side of the electric circuit, is that the magnetising branch impedance of the Mag Amp?

Thanks a lot!

 

[davenn]

did you read the actual wiki page on mag amps ? rather than just the image page ?

http://en.wikipedia.org/wiki/Magnetic_amplifier

 

[tim9000]

did you read the actual wiki page on mag amps ? rather than just the image page ?

http://en.wikipedia.org/wiki/Magnetic_amplifier

Hi,
Yes, I certainly did.

 

[jim hardy]

The magamp acts like a variable inductance and inductance doesn't dissipate heat. So they're pretty decent amplifiers but inexpensive thyristors drove them nearly extinct.

Add to your search the terms "self saturating"

self saturating magamp was the industrial workhorse before solid state power devices became available..

Be aware they are nonlinear, for what you're controlling is where in the sinewave its impedance goes to zero
my old WW2 era textbook says quite rightly they defy precise mathematical analysis.

They are enjoying a comeback and you'll find them as feedback elements in switching power supplies. They give galvanic isolation which is handy.
TI and Maxim have appnotes on modern ones. I'd have to search for them.

If i can find my magamp book will post its author, maybe some obscure bookseller will have a copy.

Meantime have a look here:
http://teslapress.com/magamp.pdf

and here
https://www.physicsforums.com/threads/search-for-magnetic-amplifier-circuit.654456/
http://d-amp.org/content/images/1067_mag3.PDF
http://stromrichter.org/d-amp/content/images/1067_mag4.PDF

Looks like there's a lot more interest in them of late !
I always liked them for their longevity . About all that goes wrong with them is the diodes.

 

[jim hardy]

ps here also http://www.tuks.nl/pdf/Reference_Ma...elf Saturating Magnetic Amplifiers - 1950.pdf

 

[tim9000]

Hi Jim, thanks for all the links, I will have a look through all of them (even after I find the answers I'm looking for). Hmm, ok that makes sense about regulating induction, but could you tell me if this is right:
During the high impedance (unsaturated) state it is acting like an inductor that is so big that practically all the voltage of the circuit is across it, so the mag amp is drawing serious VARs?
(if not that's fine, I'll read about it in your links regardless)
Thanks Jim!

P.S I'll keep that non linearity in mind

 

[jim hardy]

so the mag amp is drawing serious VARs?

think about it - it's a lot of inductance, so X_L is high, so neither much current nor very many vars can flow.
The ones i worked with, not huge maybe grapefruit size, could shut down to just a milliamp or two.

 

[tim9000]

Ah ok, cool.

Thanks