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 Winding Transformers for valve radios.
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 Return to top of page · Post #: 1 · Written at 5:23:16 PM on 29 August 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

Hi All, here is a bit of a ramble about winding trannys.
There is so much one could tell, but it is not a book!
You can read a book somewhere else about it.
This is my practical take on doing stuff.


Cheers, Fred.

Transformer Winding At Home


 
 Return to top of page · Post #: 2 · Written at 8:42:43 PM on 29 August 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6354

Document uploaded.

This takes me back to my days at tech. One of the lads in my class decided to clean off the laminations in the acid bath. It cleaned them up alright, to the extent outlined in Fred's article. The transformer didn't heat up but only because the teach sprung him before final assembly!


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 3 · Written at 10:20:19 AM on 30 August 2020.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 942

Its over 50 years since I studied this but my recollection is that the steel core is laminated to minimise eddy currents normal to the magnetic field induced by the AC current in the winding. If there is no insulation, laminations become a block, eddy current increased and heat produced reducing efficiency. A good insulator needed as what is insulation isn't iron to carry the magnetic flux.

There was also a calculation relating frequency, and perhaps magnetic properties, its a long time ago, to enable the optimum lamination thickness, comprising steel and insulation thickness, be determined.


 
 Return to top of page · Post #: 4 · Written at 8:06:36 PM on 30 August 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

Yes STC there are all the off the planet calculations you can do when you read books and learn about the theory.
The best text book I have ever read was written about 1890, probably Oersted and Henry and Ampere were still alive and they were hand beating the wire and laminations!
Meanwhile in the real world in 1955 or so, young Fred wound his first transformer for a guitar amplifer and it hummed badly and overheated!
Thus I learnt about turns too low, too high an excitation current and saturated iron!
THEN I used the classical calculations, learnt a lot and the second winding had double the turns and worked perfectly!
Never had another dud!.
Fred.


 
 Return to top of page · Post #: 5 · Written at 10:29:20 AM on 31 August 2020.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 942

If rewinding a transformer we are in the lucky position that someone has already done the lamination thickness calculation so we go with what we have got. The important thing is to know the importance of the insulation between the laminations.


 
 Return to top of page · Post #: 6 · Written at 12:15:18 AM on 1 September 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4351

The steel is not ordinary steel either. Its Electrical Steel, aka Silicon Steel, aka Relay Steel....


 
 Return to top of page · Post #: 7 · Written at 9:37:22 AM on 1 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

A little story about EDDY currents.

In the design shop we were working on a Synchronous electric motor for a specific piece of machinery.
The motor had a rotor with solid pole pieces, not a squirrel cage, and could be locked into syncronism by driving DC current through the pole windings. The stator was your normal wound 3 phase 4 pole thing.
The motor was started up in the normal way by shorting the rotor pole windings, star delta starter and then spin as an induction motor at slip speed or synced in at line frequency when required. (Efficiency and power output were not material).

After some running the motor exhibited an alarming temperature rise (smoke).
Stop and dismantle to inspect.
The stator winding was perfect, but, the pole caps of the rotor were BLUE in colour and the pole windings BLACK.
Some wretch had fitted machined SOLID pole caps to the poles, and why not, as the poles were DC were they not?
NOT SO young Fred!
A set of LAMINATED pole caps were fabricated (welded together and bolted) and fitted in place of the solid caps.
Normal operation was then restored, the motor performed with NO SMOKE and was passed for use.

And someone learnt a hard lesson about the power of EDDY currents!

Fred.


 
 Return to top of page · Post #: 8 · Written at 9:22:02 PM on 1 September 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6354

There's a lot of things to do with electric motors that confuse some people, and perhaps rightly so because on the face of it there isn't a lot of logic to it unless one is well versed in electrical theory. Here's one that gets many people - in a DC motor, when one reduces the voltage on the armature, the speed increases! Yep, not a misprint - though when the speed is increased, the torque decreases. That's the trade off. Though it is the case that people are more likely to believe that when a motor is pumped with as much juice as possible it will perform better.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 9 · Written at 11:32:50 PM on 1 September 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4351

When you look at what goes on in motors: It causes you contemplate the brain of Tesla, who designed the 3 phase motor whilst apparently walking through a park, & then went home & built it.


 
 Return to top of page · Post #: 10 · Written at 12:06:14 AM on 2 September 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6354

It is the best kind of motor in my opinion. One moving part and if failing bearings are replaced before the motor starts poling, should last for 100 years.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 11 · Written at 7:34:30 AM on 2 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

I was very thankful for my time in the "research and design" departments.
There was nothing like actually building various motors and transformers for applications.
I made DC motors and generators, AC motors and generators, transformers, chokes and Magnetic amplifiers.
Having to meet a design requirement and go from raw material to test bed was the best experiance in the world.
All that went poof in the late 60's and I moved onto to Electronics and left magnetics to the over seas suppliers!
The knowledge never leaves you and I am comfortable when playing with copper wires and bits of steel.
Fred.


 
 Return to top of page · Post #: 12 · Written at 2:05:44 AM on 3 September 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4351

TLC does work wonders tractors starter & generator have been serviced as necessary but are 1951. The ceiling fan in the chaff shed that has virtually never stopped for any length of time since 1982, has had the bearings repacked a couple of times. As noted a few times, never been able to track down its actual age but I suspect circa 1930's. Marelli (Breezo) Italy.

Marc


 
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