Step-up transformer design - Page 11 - diyAudio
Go Back   Home > Forums > Loudspeakers > Planars & Exotics

Planars & Exotics ESL's, planars, and alternative technologies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th March 2010, 07:24 PM   #101
bentl is offline bentl  Norway
diyAudio Member
 
Join Date: Apr 2009
Location: Norway
I am getting to understand the basics and a bit beyond regaring transformers.

One thing puzzles me; should one not design the transformer to be a optimal load for the amplifier? Reading other posts where people has taken a toroid and wrapped 10 turns of thick copper wire to make a new primay: in my head the stepup ratio will be as desired, but the amplifier will try to power a shourt circuit?

In relation to ribbon speakers/elements I come across "impedance matching transformers" where the goal is to make the ribbon a suitable load for the amp.

Just wondering...

(FedEx just reported that my transformer parts has arrived from Hong Kong to Norway)
  Reply With Quote
Old 11th March 2010, 04:29 AM   #102
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
I understand your concern as I have not yet had the time to write the last part of my article.
Today was the first day I had the chance to do some testing and will be doing alot more in the next few days .
I did, however ,try using 5 turns as a primary bringing my ratio up to 1:256 giving me much more efficiancy.
As long as my crosover was high enough, it did not saturate the transformer, however, it also refelcted a 3 ohm load at 20khz with my little panel of 40pf.
This would not be a problem with a larger panel as increased surface area would compensate for this.
My amp didn't like that at full power and would shut down on high peaks.But it worked fine at a nomal listening level with no audiable distortions. my next goal is to build an amp that can supply enough current for such a load.
Most of the research i have done on power toroidal transformers has found that manufactures use crgo steel in most all of them produced today.
Yes,i have found that 20 turns is probaly an optimum choice as far as a crossover of 300hz to 500hz is concerned for my particular core.
But the efficiancy suffers greatly and this would not be an issue if i had 1280 turn 240v windings instead of 120v 640 turn windings. But the idea is to use a stock transformer.
I could easly just rewind the whole thing ,but I dont want to go through all that trouble at moment.
Maybe at a later date I might.
I will see after I build a bigger amp. I'll keep you posted on what I find.
Just a thought I did find a 360v-0-360v toriodal transformer that might be better suited for this idea, but funds are lacking at the moment. jer

Last edited by geraldfryjr; 11th March 2010 at 04:35 AM.
  Reply With Quote
Old 11th March 2010, 05:57 AM   #103
diyAudio Member
 
kavermei's Avatar
 
Join Date: Jan 2005
Location: Lokeren, Belgium
Send a message via MSN to kavermei
Quote:
Originally Posted by bentl View Post
I am getting to understand the basics and a bit beyond regaring transformers.

One thing puzzles me; should one not design the transformer to be a optimal load for the amplifier? Reading other posts where people has taken a toroid and wrapped 10 turns of thick copper wire to make a new primay: in my head the stepup ratio will be as desired, but the amplifier will try to power a shourt circuit?

In relation to ribbon speakers/elements I come across "impedance matching transformers" where the goal is to make the ribbon a suitable load for the amp.

Just wondering...

(FedEx just reported that my transformer parts has arrived from Hong Kong to Norway)
An ESL panel is predominantly a capacitor, the reflected load at the primary will be a capacitance also. One can hardly say the transformer matches the load impedance to the amplifier, since the amplifier expects an ohmic load and certainly not a capacitance.
In the case of ESLs, it's easier to think of the transformer as a voltage-matching device rather than an impedance-matching device.

"When" a primary winding becomes a short-circuit to the amplifier, depends on the primary inductance and the frequency. The lower the frequency and the lower the primary inductance, the more the transformer acts as a short circuit to the amplifier.

Kenneth
__________________
Never send a human to do a machine's job. --Agent Smith
  Reply With Quote
Old 11th March 2010, 08:21 AM   #104
diyAudio Member
 
JonasKarud's Avatar
 
Join Date: May 2008
Quote:
Originally Posted by bentl View Post
I am getting to understand the basics and a bit beyond regaring transformers.

One thing puzzles me; should one not design the transformer to be a optimal load for the amplifier? Reading other posts where people has taken a toroid and wrapped 10 turns of thick copper wire to make a new primay: in my head the stepup ratio will be as desired, but the amplifier will try to power a shourt circuit?

In relation to ribbon speakers/elements I come across "impedance matching transformers" where the goal is to make the ribbon a suitable load for the amp.

Just wondering...

(FedEx just reported that my transformer parts has arrived from Hong Kong to Norway)
The inductive reactance of the step up transformer and the capacitive reactance of the stator to stator capacitance times the square of the step up ratio makes up the total impedance of an Esl speaker.

The amp sees almost zero ohms at dc, but just a few hertz from there, the inductive reactance of the step up transformer rises to sometimes over a hundred ohms.

The combined impedance peaks at a point where this inductive reactance is equal to the step-upped stator to stator capacitive reactance.

Shortly after this point, we have only the step-upped stator to stator capacitive reactance to deal with, which decreases as the frequency goes up, often down to one ohm or so at twenty kiloHertz.
  Reply With Quote
Old 11th March 2010, 04:13 PM   #105
diyAudio Member
 
bolserst's Avatar
 
Join Date: Jun 2005
Location: Fort Worth, Texas
Quote:
Originally Posted by bentl View Post
Reading other posts where people has taken a toroid and wrapped 10 turns of thick copper wire to make a new primay: in my head the stepup ratio will be as desired, but the amplifier will try to power a shourt circuit?
When trying to use a 10 turn primary you run in to two problems:

1) The load impedance seen be the amplifier may be too low.
2) Core saturation may occur at lower voltages and higher frequencies than desired.

Looking at these issues one at a time.

1)
You might review my earlier post(#40) ESL transformer load impedance
Step-up transformer design

With 10 primary turns around a toroidal transformer core of approximately 2.25 in^2 (14.5 cm^2) the primary inductance at low frequencies will be roughly 3mH for typical permiability of about 3500. This would result in load impedence of:

50 hz.......0.94 ohm
100 hz......1.88 ohm
150 hz......2.83 ohm
200 hz......3.77 ohm
250 hz......4.71 ohm
300 hz......5.65 ohm

So, you are correct that at low frequencies a 10 turn primary would pretty much look like a short circuit to an amplifier. But, if you plan to use the transformer to drive a hybrid crossing over above 300 Hz, the load on the amplifier would not be too low.


2)
You might review my earlier post(#37) on core saturation
Step-up transformer design

With 10 primary turns around a toroidal transformer core of approximately 2.25 in^2 (14.5 cm^2) the core will begin to saturate with voltage inputs of:

50 hz....... 3.5 Vrms (1.5W into 8ohm load)
100 hz...... 7.0 Vrms (6.1W into 8ohm load)
150 hz......10.4 Vrms (13.5W into 8ohm load)
200 hz......13.9 Vrms (24.2W into 8ohm load)
250 hz......17.4 Vrms (37.8W into 8ohm load)
300 hz......20.9 Vrms (54.6W into 8ohm load)

So IF you plan to cross over well above 300 Hz, AND you don't plan on using an amplifier rated at more the 50Wrms into 8 ohm, you can get away with using a 10 turn primary to get the high step up ratio you desire.

Otherwise, as your intuition led you to believe, you will need to use more primary turns.

Last edited by bolserst; 11th March 2010 at 04:17 PM.
  Reply With Quote
Old 14th March 2010, 08:00 PM   #106
bentl is offline bentl  Norway
diyAudio Member
 
Join Date: Apr 2009
Location: Norway
Default New attempt, bigger core

Hi,

I just triet to wind another transformer, after having rebuilt my winding jig with a stepmotor and a control that stops the motor at a preset count.

Interestingly, I ran into the exact same problem as with the smaller core; I went out of winding capacity on the coilformer.

The goal was to have 70 primary turns, 8.750 secondary turns for a 1:125 step-up ratio.

I used 0.71mm for the primary witch was exactly 1 layer, then insulation and then I had room for about 4200 turns of 0.25mm before the coilformer was 105% full.

So I ask again; is there a formula or table that can give a gestimate on how much wire a coilformer can hold?

Regards

bent
  Reply With Quote
Old 14th March 2010, 08:52 PM   #107
diyAudio Member
 
JonasKarud's Avatar
 
Join Date: May 2008
You can use .15 mm wire without problem, 0.1 also but it is very fragile.
  Reply With Quote
Old 15th March 2010, 09:17 PM   #108
bentl is offline bentl  Norway
diyAudio Member
 
Join Date: Apr 2009
Location: Norway
Hi,

it seems like the easiest solution to fit a lot of wire to a EI-core, is to stack to E-cores and use a coilformer with double stack height as suggested by geraldfryjr earlier.

I will start over with smaller cores and stack them, that should give sufficient space for a lot of windings!

regards

Bent
  Reply With Quote
Old 15th March 2010, 10:11 PM   #109
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
yes,this would allow less turns for the pirmary and more space for the seconary as thinner wire is just asking for an easy burnout if an arc should occour.
seeing that you only need about 5% more space ,by double stacking you might be able to get to the next octave lower (or close to it) and more power handling with less primary turns.
giving you the area you need for the secondary without sacrificing secondary wire diameter. jer

Last edited by geraldfryjr; 15th March 2010 at 10:17 PM.
  Reply With Quote
Old 15th March 2010, 10:19 PM   #110
diyAudio Member
 
Audiofanatic's Avatar
 
Join Date: Oct 2002
Location: The Netherlands, Utrecht
Default 0.1 mm

Quote:
Originally Posted by JonasKarud View Post
You can use .15 mm wire without problem, 0.1 also but it is very fragile.
That's right.

I use 0.1 mm for my transformers and it works perfectly well.

Audiofanatic
__________________
Be nice to animals.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Step Down Transformer Ropie Power Supplies 3 15th October 2006 09:42 AM
Can I use a step-up transformer as step-up? cviller Parts 5 6th September 2006 06:32 PM
help design SE preamp with mosfet buffer and step-up transformer. AudioGeek Solid State 0 19th January 2005 03:02 AM
Help Newbie Design X-over Step-by-Step Kongen Multi-Way 3 21st November 2004 02:32 AM
Using one transformer to step down another. Shoog Solid State 9 28th August 2003 10:00 PM


New To Site? Need Help?

All times are GMT. The time now is 12:48 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2