Tony's latest traffo DIY build

You are still missing the point of my questioning.
How do we know whether the Bmax is correct, or well chosen, or badly chosen?
If we know the number of primary turns and we know the range of mains' (line) voltage and we have tried to measure the thickness of the core material sheet, then how do we know it is right or wrong?
 
You are still missing the point of my questioning.
How do we know whether the Bmax is correct, or well chosen, or badly chosen?
If we know the number of primary turns and we know the range of mains' (line) voltage and we have tried to measure the thickness of the core material sheet, then how do we know it is right or wrong?

If you all know this (and also Afe which is net iron area) the easiest part remains, and that is the calculation by means of some well known formula.
My calculation is based on the formula provided by Vacuumschmelze, which is for strip wound cut cores, also known as c-cores, quality Trafoperm N2, which is good quality corn oriented M6, strip thickness 0,35mm:

50 45
B = --- x ------------- x U.
f Afe x N

f = frequency in Hz;
U = rms value of voltage in V;
Afe = magnetic core cross-section in cm²;
B = flux density amplitude in T;
N = number of turns.
 
Andrew,
When designing a power supply transformer I apply this formula to stay very much on the safe side as fas as core saturation is concerned (by choosing 1, at most 1,2 T).
When you have a transformer there and you'd like to check if core saturation occurs, maybe looking at the 50 Hz "sinus" on the oscilloscope is an option?
You must use a probe I guess, and a variac would come in handy.
 
thanks to all who tried to help.

I will summarise what I think has been said on checking that core flux has not entered the saturation range.

Measure the primary current for a specific mains input voltage. Repeat for a variety of supply voltages covering the whole range of suppliers voltage tolerance.
Plot a Ipri vs Vpri
Read the graph to identify where, if any, knee occurs in that IV plot.
If the knee is above maximum supply tolerance then the core is below saturation flux. If the knee is well above the maximum supply voltage then the maximum flux is well short of what the transformer can be pushed to, i.e. it is bigger and heavier and more expensive for that VA.

Does any one disagree with this summary?

What design parameters would require, or benefit from, running well below the knee of the IV plot?
 
Last edited:
How do we know whether the Bmax is correct, or well chosen, or badly chosen?

we don't to an exact figure.....

but we know we made a right choice when we have a traffo that doesn't heat up much, or is efficient just as we designed it to be.......below the knee of the saturation curve there is a wide curve one can operate with, i have my preferences but you can have yours too...........there are a lot of other issues to contend with.....depends on the goals you have set out at the start of your traffo building.....

the thing is, the core materials available to us are of unknown manufacture and so we can not find the curves for them....vut we can guess and the results of our guessing can be verified by the outcome, the traffo that was built....
 
Last edited:
but we know we made a right choice when we have a traffo that doesn't heat up much, or is efficient just as we designed it to be.........
how do we know what is acceptable heating or what is acceptable efficiency?
there are a lot of other issues to contend with.....depends on the goals you have set out at the start of your traffo building.....
that is my final question. What or when is it a benefit to run at a voltage well below the knee in the IV plot
the results of our guessing can be verified by the outcome,
This is the point exactly. How do we verify?
 
Last edited:
sir tony
any link on RDH4/RDH3

here: Technical books online

Radiotron Designer's Handbook, Third Edition, P. Langford Smith, 1941, 352 pages
The quintessential vacuum tube design handbook,. This is the older, and smaller, third edition... at least I didn't have to pay $150 for a book to cut up and scan! Covers all the essential of tube electronics design, including the basics, tube theory, load lines, amplifier design, etc.

Download full text with index, 16MB PDF file

Radiotron Designer's Handbook, Fourth Edition, P. Langford Smith, 1953, 1,498 pages! - MANY thanks to Keith Carlsen!
The later and much more comprehensive version of the RDH3 above, this is probably the best book out there for the casual vacuum tube circuit designer. Coveted by the audio guys, it also has plenty of info on the design of radio receivers. This version is one I have scanned myself, in one file, with added nested PDF bookmarks so it's easy to find things. There are PDF versions already floating around the web... but I never figured out who scanned what, and there are a couple of versions that people are trying to sell, so I've not posted any of them here.

Download full text with index, 25MB PDF file

Electronic Transformers and Circuits, Reuben Lee, 1955, 349 pages - Courtesy of John Atwood
This book is a "reference on the design of transformers and electronic apparatus". It covers the design of power transformers, chokes, and signal (audio) transformers. It also talks a bit about circuitry, as it relates to transformers. Enough theory to understand what's going on, as well as practical info on how to construct transformers.

Download full text, 24MB PDF file
 
converting japan traffo to 220 volts...

i got a cd player from the pier, it has a 100volt "japan standard" power traffo...
now as a rainy day project, i decided to convert it to 220 volts...

after dismantling the traffo from the cd player, i dipped the traffo assembly into a can full of lacquer thinner, but first i also dismantled the mounting brackets...i left it to stay for more than 48 hours...


Turned out that the traffo had 848 turns or turns per volt = 8.48, now the average voltage at my sockets is 225 so therefore i needed 1908 turns. The original wire size was #30, therefore i needed to use a #33 wire, rule of thumb, is 3 wire sizes thinner to convert to local voltage.
 
Thank you.
Now, how do I check that I have not exceeded the Bmax of the core material?

Here is the post of some scope samples of when I tested a toriodal power transformer for step up use on an ESL by adding turns as a new primary and number of turns vs voltage and frequency against core saturation,

http://www.diyaudio.com/forums/planars-exotics/161485-step-up-transformer-design-5.html#post2194027

This is a very long thread and the process was compleatly documented and should be given a good read.

Although I was learning along the way I was able to determine the full specs of my core and what it could and couldn't do.

I did have a few complications along the way,But this was mainly due too being a step-up configuration and extremely high voltages were involved.

The resonances of the transformer caused some Tesla actions when the amplifier driving it had lost control at the crossover point of the transistors (dead spot) due to the very low impedence that it was trying to drive.

http://www.diyaudio.com/forums/planars-exotics/161485-step-up-transformer-design-4.html#post2137648

http://www.diyaudio.com/forums/planars-exotics/161485-step-up-transformer-design-3.html#post2133865

High Voltage RF had burned up some resistors and cheapy meters when they should not have failed at all.

If you stay away from the resonate frequency of the core that you are testing you should have any of these issues.
But core saturation does impose a high current demand on the signal source so keep that in mind.

Here is where I had plotted the chart of saturation data of the core that I was testing,

http://www.diyaudio.com/forums/planars-exotics/161485-step-up-transformer-design-2.html#post2103369,

I had started this study here,

http://www.diyaudio.com/forums/planars-exotics/158115-material-esl-3.html#post2085791

http://www.diyaudio.com/forums/planars-exotics/158115-material-esl-4.html#post2086879

and ended up here,

http://www.diyaudio.com/forums/planars-exotics/161485-step-up-transformer-design.html#post2088330

I hope this is of some use to you,enjoy!!

jer :)