Designing an Interstage Transformer - Page 5

popilin · 4th March 2013, 02:49 AM

Quote:

Originally Posted by TheGimp

What!

No sliderules?

Ah, come on, not that hard !
Making the simplification

B = B(AC) = B(DC) = Bt/2

Bt = 12000 Gauss = 1.2 Tesla

We can write

N = L x 10^8 i(DC) / (S B)

[L] = Henry, [i] = Ampere, [S] = cm^2, [B] = Gauss

The air gap is adjusted, measuring L, with the component i(DC).

Tony · 4th March 2013, 04:53 AM

Quote:

Originally Posted by TheGimp

What!

No sliderules?

i still have mine from the 70's...

Tony · 4th March 2013, 04:54 AM

Quote:

Originally Posted by popilin

Hi Tony
Nice to see you around here !

Look, I do what I can, I don't know what is a spreadsheet.

I always work with my old calculator.

What are you talking about ? Here valves are scarce and expensive, I have just a couple of projects for.

Once, I was tempted to get rid of my ECC82s, do you remember ?

After the overwhelming success of my last preamp and two class A monoblocks, I don't sell nor drunk.

BTW. All is here

Designing Transformers with J.C.Maxwell

i must have mistook you for someone else...

TheGimp · 4th March 2013, 12:48 PM

Poplin, from your formula using L=50H , I=10mA, and core cross section is =0.88sq-in:

N = (50 * 10^8 * .01A) / (.88sq-in * 2.54 cm/in * 2.54cm/in *6000gauss)

N = 1467.8 turns

Then after winding the transformer coil, assembling the transformer and adjust the gap to achieve 50H with 10mA dc bias through the coil.

Is this correct?

popilin · 4th March 2013, 01:10 PM

Quote:

Originally Posted by Tony

i still have mine from the 70's...

I have two that belonged to my grandfather and then my father, but I have no idea how to use it, but keep it quiet...

Quote:

Originally Posted by Tony

i must have mistook you for someone else...

Well, it happens, the forum is big and there are many people.

I live in a small town where everybody knows everybody, and it happens to me every day, so if is for concern.

TheGimp · 4th March 2013, 01:12 PM

Quote:

Originally Posted by GoatGuy

Dunno how you did your calcs there...

But I came up with 3800 turns. While that clearly is a high count ... it isn't outrageous. Just will take some time.

(I used u=2500, and H=432)

GoatGuy

GoatGuy,

Would you please post the formula(s) you used?

Thanks.

TheGimp · 4th March 2013, 01:14 PM

The comment on the slide rule was meant to be a joke. I still have two that work and one that does not (my fathers), although I've long forgotten how to use them. I vaguely remember using them in high school physics class in the late 60s.

popilin · 01:46 PM

Quote:

Originally Posted by TheGimp

Poplin, from your formula using L=50H , I=10mA, and core cross section is =0.88sq-in:

N = (50 * 10^8 * .01A) / (.88sq-in * 2.54 cm/in * 2.54cm/in *6000gauss)

N = 1467.8 turns

Then after winding the transformer coil, assembling the transformer and adjust the gap to achieve 50H with 10mA dc bias through the coil.

Is this correct?

Yes, this is correct.

As a rule of thumb, the wire (double or triple isolated) is selected for a current density of 3 A / mm ^ 2

You can play around with the numbers, maybe you can put more turns and approach the original target.

As insulation, you can use NOMEX, is very good insulator and for thicknesses of 0.08mm, has a dielectric constant lower than teflon !, very important to achieve low capacitance between windings.

iko · 4th March 2013, 02:10 PM

Calculating the number of turns this way does not take the gap into account. You can probably get away fumbling around with the gap after you wound your coil, for small currents like this example, but imagine you'll wind an output transformer for 100mA DC bias and as much as 260mA PP current. Then you might be sorry you didn't predict the number of turns, gap, and working flux density better. As they said, winding coils is labour intensive.

And even for this example, I'd do it right instead of playing with the core for the right gap. I'll be watching your progress with interest.

TheGimp · 4th March 2013, 02:13 PM

I was planning on using either Mylar or Kapton tape (.08mm) as I have both. However I'll start looking for Nomex.

I have double insulated magnet wire in sizes from 26 through 34 AWG. 34AWG is .02mm^2 so 60mA would be 3A/mm^2. Even 36AWG would be 38mA at 3A/mm^2.

EI-87 table shows a max of 5712 turns of 34AWG with 11 layers of .001" insulation. So I probably will get closer to 5000 turns total (2500 turns Pri, 2500Turns Sec) with .003" insulation.

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4th March 2013, 12:48 PM	#44
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Poplin, from your formula using L=50H , I=10mA, and core cross section is =0.88sq-in: N = (50 * 10^8 * .01A) / (.88sq-in * 2.54 cm/in * 2.54cm/in *6000gauss) N = 1467.8 turns Then after winding the transformer coil, assembling the transformer and adjust the gap to achieve 50H with 10mA dc bias through the coil. Is this correct?

4th March 2013, 01:14 PM	#47
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	The comment on the slide rule was meant to be a joke. I still have two that work and one that does not (my fathers), although I've long forgotten how to use them. I vaguely remember using them in high school physics class in the late 60s.

4th March 2013, 02:10 PM	#49
iko diyAudio Moderator Join Date: May 2008 Location: Toronto	Calculating the number of turns this way does not take the gap into account. You can probably get away fumbling around with the gap after you wound your coil, for small currents like this example, but imagine you'll wind an output transformer for 100mA DC bias and as much as 260mA PP current. Then you might be sorry you didn't predict the number of turns, gap, and working flux density better. As they said, winding coils is labour intensive. And even for this example, I'd do it right instead of playing with the core for the right gap. I'll be watching your progress with interest.

4th March 2013, 02:13 PM	#50
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	I was planning on using either Mylar or Kapton tape (.08mm) as I have both. However I'll start looking for Nomex. I have double insulated magnet wire in sizes from 26 through 34 AWG. 34AWG is .02mm^2 so 60mA would be 3A/mm^2. Even 36AWG would be 38mA at 3A/mm^2. EI-87 table shows a max of 5712 turns of 34AWG with 11 layers of .001" insulation. So I probably will get closer to 5000 turns total (2500 turns Pri, 2500Turns Sec) with .003" insulation.