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Old 26th March 2013, 02:38 AM   #431
AJT is offline AJT  Philippines
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Quote:
Originally Posted by gorgon53 View Post
Hi Tony

I hope you where not trying to tell me that loading the secundary would
would lower the frequency?
of course not.....

Quote:
Now to the flux-thingy, as I see it, please correct me if you thinck I am wrong.
If we connect a load to the secundary this will cause a current to flow. This current produces a secondary fluxfield that OPPOSES the primary fluxfield, therefore it CANCELS some of the primary fluxfield. Since now LESS flux is surrounding the primary the counter emf is reduced and more current is drawn from the source. In other words, the current taken by the primary increases and generates more flux, ALMOST reastablishing the original flux BUT IT CAN NEVER EXCEED IT. Therefore, the highest flux is when the secundary is unloaded.
some explanation here... Magnetic Hysteresis Loop including the B-H Curve
Click the image to open in full size.

magnetic field strength relies on the current flowing in the coils, since the number of turns is fixed, the magnetic path length is likewise fixed, so that the only varialble left is the current in the coils....

when i make my traffos, i make sure that i operate well below the knee of the magnetization curve, when unsure of the quality of the iron i have on hand, i operate at 0.6T, when using M6 i go to as high as 1T, this is so that i can avoid saturation conditions....
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Old 26th March 2013, 09:08 AM   #432
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Tony, when Pat Turner does his calcs he uses values as high as 1.5/1.6 tesla, this would be the highest grade material ? .. yet his transformers are quite large .. ??
Do you know of a really good book that actually explains the magnetism side of this rather than transformer construction ?
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Old 26th March 2013, 09:25 AM   #433
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Quote:
Originally Posted by donnyab View Post
Tony, when Pat Turner does his calcs he uses values as high as 1.5/1.6 tesla, this would be the highest grade material ? .. yet his transformers are quite large .. ??
Do you know of a really good book that actually explains the magnetism side of this rather than transformer construction ?
yes, those values are for highest grade materials, but even then i still will not use them as such...

truth is, there are more than a dozen ways to build your transformers, it is entirely up to you....there are guidelines and they are not set in stone.....

Patrick Turners' writings are what i really consider seriously...there is also Norman Crowhurst and the RDH3 and 4....

more than the numbers crunched in these write-ups, there are bits and pieces to be gleaned, you just need to alert about these....

and if you have been building traffos, you will recognize them as you see them...
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Old 27th March 2013, 11:36 PM   #434
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strip wound C cores and toroids can be run as high as 1.7T with regular iron.

losses are relative
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Old 28th March 2013, 01:34 AM   #435
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Default Commercial considerations

Quote:
Originally Posted by Tony View Post
yes, those values are for highest grade materials, but even then i still will not use them as such...

truth is, there are more than a dozen ways to build your transformers, it is entirely up to you....there are guidelines and they are not set in stone.....

Patrick Turners' writings are what i really consider seriously...there is also Norman Crowhurst and the RDH3 and 4....

more than the numbers crunched in these write-ups, there are bits and pieces to be gleaned, you just need to alert about these....

and if you have been building traffos, you will recognize them as you see them...
Tony, I really respect your work and all of the transformer projects that you have shared in this thread. If I ever get the bug to take on another obsession, it will surely be winding transformers!

I will add that commercial vendors probably push their cores to the limit - especially the "less expensive" transformers available commonly on eBay. I have seen numerous references to transformers running "warmish", and based on your descriptions I really do suspect the manufactured products (especially the lower-cost versions) tend to load up the transformers with little or no margins.

I have experienced this myself with simple EI core transformers that, when run for long periods, get unreasonably hot when loaded anyway near the rated outputs.

The custom designs you create take advantage of the experience you've learned (no doubt the hard way ), and I really do respect your giving generous margins on the designs. After all, if a person is going to invest the hours and hours of labor to wind their own transformers why take the cores to the limit? You are certainly not doing it to save money, especially on a production line - but rather to get EXACTLY the worry-free performance you want in your designs!

Please keep inspiring us with your designs and knowledge - your skill is in danger of becoming a "lost art" and it's dedicated folks like yourself that keep important aspects of the electronics world alive!

~ Sam
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Old 28th March 2013, 02:07 AM   #436
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Quote:
Originally Posted by johansen View Post
strip wound C cores and toroids can be run as high as 1.7T with regular iron.

losses are relative
thanks for the heads up, as i said i work with mostly surplus cores, the new virgin cores available here are the lowest grade steel there is, that is why i run them at 0.6T up to about 0.9T depending on applications...

while C cores are to be found here, without knowing the source it is is hard to say they can do 1.7T so i always assume they can not....
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Old 28th March 2013, 02:11 AM   #437
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Quote:
Originally Posted by rfengineer2013 View Post
Tony, I really respect your work and all of the transformer projects that you have shared in this thread. If I ever get the bug to take on another obsession, it will surely be winding transformers!

I will add that commercial vendors probably push their cores to the limit - especially the "less expensive" transformers available commonly on eBay. I have seen numerous references to transformers running "warmish", and based on your descriptions I really do suspect the manufactured products (especially the lower-cost versions) tend to load up the transformers with little or no margins.

I have experienced this myself with simple EI core transformers that, when run for long periods, get unreasonably hot when loaded anyway near the rated outputs.

The custom designs you create take advantage of the experience you've learned (no doubt the hard way ), and I really do respect your giving generous margins on the designs. After all, if a person is going to invest the hours and hours of labor to wind their own transformers why take the cores to the limit? You are certainly not doing it to save money, especially on a production line - but rather to get EXACTLY the worry-free performance you want in your designs!

Please keep inspiring us with your designs and knowledge - your skill is in danger of becoming a "lost art" and it's dedicated folks like yourself that keep important aspects of the electronics world alive!

~ Sam
thanks, back in the 70's i wanted to have a made to order power traffo for a simple ss amp, since tubes were still very much in season then, the shops i went to, said they could not do it and thought i was crazy.....that started me in the traffo making hobby.....

DIY'ers are not concerned with the same issues as commercial offerings, that of engineering economics and profits.....

btw, i have enlisted the hep of my wife, she stacks E-I's for me nowadays...
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Old 4th April 2013, 07:17 PM   #438
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Hey guYs, sorry for the off topic, could you please tell how I could detect if a traffo is burnt or not? i mean without put power on it. Theres some test with DMM i can do on it?
Thanks for any help!
nick
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Old 4th April 2013, 07:43 PM   #439
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might have been Lundahl, but I read somewhere that you can damage a trafo simply by trying meaure with digital ohm meter
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Old 4th April 2013, 09:07 PM   #440
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Originally Posted by tinitus View Post
might have been Lundahl, but I read somewhere that you can damage a trafo simply by trying meaure with digital ohm meter
extremely high permeability cores with 0 airgap would inreversible detoriate whit the the slightest trace of dc magnetisation
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