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Old 25th February 2010, 11:44 AM   #51
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I didn't answer your question about interleaving. It is true that a 1:120 turns ratio is much higher than what you'll ever see in, for example, a tube amp output transformer. So it is harder to interleave. Still it would be best to interleave as much as possible. At the same time keeping the secondaries as electrically symmetrical as possible. Use your imagination

Quote:
Originally Posted by bentl View Post
Transformer parts is not easy to order in small quantities, and you can't experiment much before the cost exceeds buying off the shelf trafos.
Very true. It's the major thing holding me back...
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Old 25th February 2010, 12:02 PM   #52
bentl is offline bentl  Norway
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Hi,

getting the seconadries symmetrical is not a big problem if winding with two wires simultaneously as described in the link i posted earlier; the will be of equal length and the centertap will be...in the center.

I have bought some standard 230v/6v 100VA EI84 transformers that I have rippet apart. The manufacturer had WELDED the laminations together to reduse mechanical noise!

Bent
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Old 25th February 2010, 12:20 PM   #53
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thanks every one for all the tips.I wasn't exactly sure what some of the keys do, as they do weird things some times when you hit them.i thinking about starting a thread just to practice on. (he he he) .

i once had a thought of taking two identical transformers and rewinding them with the two cores stacked together on paper it showed it would work good but i never got the wire to wind them.as stacking the two would give 4x the power capabilety and the added iron would allow more primary inductance with the same amount of turns for a lower frequency. they were the radio shack 25.2v 2amp ones. i also used the same type to wind a ribbon tweeter transformer. i think that one worked, but it got put on the back burner too, and never got fully tested.

I'll have my results posted later today .you might want to take a look at, before you go spend big bucks on some ready made ones. jer
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Old 25th February 2010, 12:30 PM   #54
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back in 2004 i searched the world over for E-I core supplier.and i got lucky i found a local shop on thomas net that made motors and transformer and was willing to sell me more than enough iron to build a couple of 500 watt transformers for like $20 bucks.
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Old 26th February 2010, 09:15 AM   #55
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hi everyone sorry for being late on the data i promised to have by yesterday .I had to double check everyhing because the sweep rate switch on my scope has been giving me some problems lately.i have only had the covers off of it three times in the last 25 years and it is still acurate and works great when it's not acting up.

First,let me clarify some things in my last test. a couple of things might have been misunderstood.the 10hz to +100khz were done with just the signal generator only and no amp.however, when i did use the amp it worked at a very low level and i didn't understand why it was shutting down (which i'll explain in a bit).it was becuase the transformer was saturating (i had a feeling this was happening) at the lower frequency's.the sweep test consisted mostly of high frequency's and didnot seem to impose much of a problem.

second:the meter i have only reads ac average and not true rms which was throwing me way off from my scope readings.but the pics are true and i was getting 600v plus at 300hz and above and flat to 10khz with a drop to 20khz of not more than -1.5db,with only 10 turns for a primary

my study has found that a toroid power transformer will work very well to drive an esl by just winding a new primary to get a desired ratio.this will only work in a hybrid system unless you have a realy realy big core.

so, my main point is, rather than buying four transformers. buy two and get the biggest ones you can afford. i will explain this process later today (or tonight).right now need to get some sleep i have been working on this, 23 hours just today alone.

It has been a grand learning experience and some thing i needed to do for a long long time now. hopfully it will be easier (and cheaper)for all of you and any one conteplating on building an esl system to do so.

i would like to thank; charlie,mavric,calvin,capaciti,few,wachara,kaverme i,andrew,jonas,alexberg,analog_sa
and bentl for starting this thread and especialy bolserst for pointing out and reminding me ofsome very important issues of transformer design and any one else i may have forgotten.
I'll be back!!!
jer.

Last edited by geraldfryjr; 26th February 2010 at 09:17 AM.
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Old 28th February 2010, 12:49 AM   #56
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Hello diy’ers, as promised, I will try to explain how to calculate a new primary for a common toroid core power transformer there are actually two ways to go about this. The cut and dry method, and the find the saturation level first method. I prefer the latter as it will allow you to utilize the fullest potential of your core material.
In this tutorial I won’t be going into calculating gauss and B-H curves of the core material. This is just to learn how to find the number of turns on a toroid power transformer and how to find a saturation level of it’s core and its relation ship to frequency and voltage level compared to the number of turns of a winding, on a core of unknown material and size.To create a new primary to drive an electrostatic loudspeaker system.
The reason for this method, is to not have to tear apart the transformer in order to find the exact core cross section area, and that not all cores use the exact same type of material.
The first thing you have to find out is the number of turns that already exist on the core this is done by adding a winding of known turns .in this case I choose to use 20 turns. You can choose any number of turns you wish. The higher the number the better your accuracy may be, Due to a higher voltage from the winding.
You then excite a winding with a signal generator. I chose to use the existing 13.8 volt winding. The reason being, knowing that the transformer was designed at 60hz,it will not go into saturation at that voltage level and particular winding. Also, I knew that my amp could produce 13.8-volt signal without hurting itself.
***DANGER***
You could also use the line connected to the original primary.
THIS IS VERY DANGEROUS!
If the 20 turn winding some how got shorted you would have an arc welder running wide open on your bench!
The winding would melt down faster than you could turn the thing off and destroy the transformer. It would be very very ugly and not good,
Plus, the fact, that you could very seriously injure yourself or cause death.
***DANGER***
Besides this being a safer method, you will need a variable level to perform these tests, as you will find out as we go.

With my amp input connected to the signal generator set at 60hz and the output connected to the 13.8 volt winding. I adjusted the level until I got 120vac on the existing 120v primary using a a.c. voltmeter.once this was achieved I then double checked the other existing windings to make sure they too were in the range of the voltage that they were designed for. In my case it was the 16-0-16 and the other 120v primary winding, they were all at the proper voltage range.
I then drew a diagram of a transformer with the windings I was working with and wrote down all of the voltages on each individual winding especially the new one I created.
This is the most important one so be as accurate as you can (see ratio chart picture). By knowing the voltage value on the new winding and its number of turns you can calculate (with exacting accuracy to your measurements) the turns of every winding on the core.
Some of you already know this procedure but for the sake of being complete I’m going to take the time to explain it for those who don’t know. For accuracy my meter is only good to .1 volt.
Whatever unit you use to measure with the result is the same. It is the accuracy of the measurement that counts!
Here’s how:
To keep thing simple and fairly accurate I will set my signal generator so that the amp outputs 15V into the 13.8v winding. I will label this winding A.
My 20-turn winding is labeled B.
The 120v winding is labeled C.
The 16v-0-16v windings are labeled D1 and D2.
You may find your meter might bobble as I did. To combat this I just used a higher frequency. You may also find that your drive level had changed at a different frequency. This also is normal. Just reset your drive level at whatever frequency you choose and leave it there and the level won’t change as long as the frequency stays the same. I used 180hz.
My results are:
A= 15.0V
B= 3.7V
C= 121.7V (average between the two windings of 121.6v and 121.8v)
D1, D2= 17.6

The formula: Ns/Np=Vs/Vp

Where: Ns is turns secondary
Np is turns primary
Vs is volts secondary
Vp is volts primary
Rule of thumb: the one thing to remember is, the winding you start with becomes the primary winding and the other winding or windings your comparing it to, becomes the secondary winding or windings, regaurdless of which one you start with, As you will see.

The goal: the goal here is to determine the number of turns for each 120V winding (oop’s did I forget to mention that there two of them, sorry about that).

Using the formula:
By substituting Av for Vp
Cv for Vs
We get 121.7/15=8.11333
1:8.11333 is the ratio between windings C and A. we’ll call it 8:1.
To check this I reset the level so that the voltage at winding C was 120V and the measured on winding A (the amp), it was 14.8V a -.2V difference. This is probably due to the windings not being exactly a completed turn, as we will see in a moment, or maybe the losses within the transformer itself.

But how do we find the turns?
This is where our 20-turn winding comes in to play.

Again, by substituting Bv for Vp
Cv for Vs
We get 121.7/3.7=32.8888
To test this, this time I raised the level on C winding to 160v and got exactly 5V on winding B, as 160/32=5.
So the ratio between windings C and B is 32:1

Now that we know our voltage ratio we can calculate the turns on our 120v windings with the formula (Vs/Vp)*Np=Ns .so, (160/5)*20=640 turns for the 120v winding.

Remember the two 120v windings with to different voltage readings?
Here’s why, 121.8/121.6=1.0016447 the ratio between the two voltages times 640 turns =641.052608. So one winding has an extra turn. This is very common.

We can check our work by back tracking with the 13.8v winding (A),
Its turn’s ratio with C winding is 8:1. So, the turns of 13.8v winding is Ns/(Vs/Vp) or 640/(8)=80 turns. Now that we know this, we can then determine the ratio between winding A and B to be 80/20 or 4:1.since we had winding A set at 15v, winding B should be 15/4=3.75v, which on the meter it is at 3.7v. This is almost exact. This why you should have as accurate measurement as you can. Reading down to .01 volts is good but .001v (millivolt) is much better but you can get by on .1-volt division if you have to. As to that effect, I took extreme care this time around as my original calculation was 704 turns for a 120v winding 10% more than it really is. I confirmed a 32:1 ratio between the 120V winding C, and winding B of 20 turns using my oscilloscope.
This is the first part of my study and we have found the exact number of turns of the two 120V windings that will be used as secondary to drive an esl panel the next report will be how to plot the saturating voltage level vs. frequency using 10,20,30 and 40 turns as a new primary. Sergeant Schultz: ”trust me, it will be very interesting, vedy inter-res-tink“. Jer. p.s. is this a little better for you all to read, diy’ers?
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Old 28th February 2010, 01:22 AM   #57
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Hi Jer,

It really is a lot easier to read now.

Thanks for your tutorial. I'm looking forward to reading your next one.

Wachara C.
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Old 28th February 2010, 03:03 AM   #58
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thanks.it took me al day to write that one.the format is not the same as the original though.when i am done ill post the whole document as a downloadable file. jer
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Old 28th February 2010, 04:02 PM   #59
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Default Audio transformator for ESL

This audiotransformator band operating frequencies of 100 Hz - 20000 Hz
Load capacitance 820 pF, transformation = 100, Input Voltage = ~ 30V. output = ~ 3000V.
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File Type: jpg transs.JPG (723.4 KB, 151 views)
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Old 28th February 2010, 04:16 PM   #60
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Hi Statics Man,

Thanks for sharing your transformer design.

Wachara C.
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