This might seem silly, but I've tested how much voltage a secondary winding, different wire sizes, with no interleave insulation, can withstand by driving the primary with a 200 watt Nad amp at 1000 Hz.
The transformer has 30 prim turns, 1200 sec turns, no load and core area is 9 Cm2.
0.1 mm wire went up in smoke at around 15 volt RMS input, 0.15 about the same, 0.25 coped with 25 volts RMS.
And now the interesting part, I couldn't burn the 0.3 mm wire! Max amp output is 40 volt rms...
I did this experiment to figure out why toroidals can withstand those high voltages, I think it depends the rather thick
prim wires.
The transformer has 30 prim turns, 1200 sec turns, no load and core area is 9 Cm2.
0.1 mm wire went up in smoke at around 15 volt RMS input, 0.15 about the same, 0.25 coped with 25 volts RMS.
And now the interesting part, I couldn't burn the 0.3 mm wire! Max amp output is 40 volt rms...
I did this experiment to figure out why toroidals can withstand those high voltages, I think it depends the rather thick
prim wires.
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That's interesting, I beg your pardon if you already know what I am about to say.
Does your amp have 200W 40V 8 Ohm?
For 200W we'd have 5A rms primary => .25A rms secondary
0.13 wire has 0.01 mm^2 cross section
Current density is 12.5A per mm sq. It's way too high.
0.3 wire has 0.07 mm^2 cross-section.
Typical current density has to be around 3 for the power we are considering.
Also it might be insulation problem.
a) wind your transformer turn by turn, very meticulously, in regard to primary as well
b)do not do incomplete layers, if you can't add the turns - change the pitch or the distance between turns
c)make the rings out of thin (0.1-0.2 mm) cardboards that would cover top and bottom parts of the winding (for toroidal x-former) for each winding layer, even low voltage one. That would ease your work (inner diameter usually get smaller and smaller as you proceed). So you wind the layer, put rings on top and bottom, take scotch tape (the one without adhesive is better) about 2 cm wide and put two layers of it, making sure that no voids occur at the outer part of the wire to be covered. That means you will get almost 4 layers of tape on the inner part.Now you can wind another one.
d) I would suggest to put at least four layers of tape between the primary and the secondary.
e) be sure that the beginning of the seconadry (which is buried under) is the cold wire - so it has the lowest potential
f) do not forget to insulate well the beginning - it will be subjected to full secondary voltage. To do so use 3-5 layers of heat shrink tubing - it's easier to get then the silicon tube. You may as well solder the HV hookup wire to the very beginning of secondary before you start winding one. The key is the thickness of HV hookup wire insulation besides the rating. 3 mm are O'K 5 is better. The latter looks ugly but that's O'K.
Same goes for primary termination, as soon as it's the next to the core.
Hopefully this shoud fix your problem.
BTW 30 turns @ 9 sm sq iron core give you Lf power cutoff at 200Hz, so you are 270 primary and 11000 secondary turns shy for 20Hz
You easily find the formula at the web.
Sincerely,
Alex
P.S.It does require some practice to do it well. And do not attempt to wind 12000 turns at the first take.
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The way I see it it's small distance between wires with the big difference in potential. No load most likely breakdown or you was lucky
and hit the resonance.Alex
Very good pionts you have stated,Alex.
You can't expect a .1mm wire to handle 5 amps of current especialy when frequency goes up.
That 5 amps turns into 10 amps and 20 amps rather quickly.
If one uses a thick low dielectric contsant material between the core and the first winding layer and adjacent winding layers this would help a great deal in reducing the residual transformer capacitance.
If one could get it in the 100pf to 200pf range would be awesome.
However getting it below 100pf would be a hard trick to feat.
This is why it is called an art.
It still would be a vast improvment of the 400pf that I measured on my core ,which is still better than some of the other commercialy available products.
One the problems I am trying to solve is trying to drive my little panel of 31.5 square inches to match the effeciancy of an equivilant sized woofer.
This I have done,but the capacitance that the amp has to deal with is 7 times (total) that of the 70pf panel itself.
This wouldn't be such an issue the a larger panel of course.
But once all of these factors are straightened out and applied to a larger panel it should reveal a very very effeciant ,loud and great sounding system.
Not that it isn't already, but one that doesn't cause issues with your average cheapy off of the shelf amp of 40 watts to 100 watts.
My little panel should only present a minimum load of 3 to 4 ohms.
But because of the transformer it is way much less than that,like about 1 to .5 ohms or less.
Wasting alot of power that could be better put to use driving the panel it self.
I'll try too get the data together in a few days on what I have learned about leakage inductance and the custom wound primary,as I have about six or more things going on at once on top of every day life things.
Sometimes (but not too often) I get a little burned out and need to take a break once in a while.
I will deliver as I promised, as my next bit of info is going to shed some more light on the subject.
Once again I want to thank all of you that have helped and stuck by me in this vast learning experience.
I hope that when it is all said and done ,it will make it easier for all of those DIYER's new and old to be able to dive into the world of esl's with confidence as it truley is the most remakable type of system known to mankind.
Execpt plasma of course ,but that will be a whole another chapter . jer
You can't expect a .1mm wire to handle 5 amps of current especialy when frequency goes up.
That 5 amps turns into 10 amps and 20 amps rather quickly.
If one uses a thick low dielectric contsant material between the core and the first winding layer and adjacent winding layers this would help a great deal in reducing the residual transformer capacitance.
If one could get it in the 100pf to 200pf range would be awesome.
However getting it below 100pf would be a hard trick to feat.
This is why it is called an art.
It still would be a vast improvment of the 400pf that I measured on my core ,which is still better than some of the other commercialy available products.
One the problems I am trying to solve is trying to drive my little panel of 31.5 square inches to match the effeciancy of an equivilant sized woofer.
This I have done,but the capacitance that the amp has to deal with is 7 times (total) that of the 70pf panel itself.
This wouldn't be such an issue the a larger panel of course.
But once all of these factors are straightened out and applied to a larger panel it should reveal a very very effeciant ,loud and great sounding system.
Not that it isn't already, but one that doesn't cause issues with your average cheapy off of the shelf amp of 40 watts to 100 watts.
My little panel should only present a minimum load of 3 to 4 ohms.
But because of the transformer it is way much less than that,like about 1 to .5 ohms or less.
Wasting alot of power that could be better put to use driving the panel it self.
I'll try too get the data together in a few days on what I have learned about leakage inductance and the custom wound primary,as I have about six or more things going on at once on top of every day life things.
Sometimes (but not too often) I get a little burned out and need to take a break once in a while.
I will deliver as I promised, as my next bit of info is going to shed some more light on the subject.
Once again I want to thank all of you that have helped and stuck by me in this vast learning experience.
I hope that when it is all said and done ,it will make it easier for all of those DIYER's new and old to be able to dive into the world of esl's with confidence as it truley is the most remakable type of system known to mankind.
Execpt plasma of course ,but that will be a whole another chapter . jer
Jonas,I think your experiment is very interesting and significant.
As I have yet to find any major problems with the cores I have used in past test.
Except the they are not exactly matched from one to the other.
Running 80 volts P-P at 1:200 and upwards didn't seem to have damaged them when I tested them in normal service.
If there were any shorted windings, they would have burned up instantly,I believe.
I had found my last working meter a few weeks ago and I desperately wanted to know the resistances of all of my windings.
Very much to my suprise that the 120v windings were only 5.7 ohms.
In one of my tests (before the one were the two resistors burned up for no reason)they were wired for 1:400 and I had heard a loud snap and after I took them apart I found no evidence of any burn marks and put them back together.
That was when I proceeded to scortch three meters that morning( ha ha ha).
I also didn't relize the 32kv P-P I was dealing either.
So because of this I have been pondering the same question myself.
Great work . jer
As I have yet to find any major problems with the cores I have used in past test.
Except the they are not exactly matched from one to the other.
Running 80 volts P-P at 1:200 and upwards didn't seem to have damaged them when I tested them in normal service.
If there were any shorted windings, they would have burned up instantly,I believe.
I had found my last working meter a few weeks ago and I desperately wanted to know the resistances of all of my windings.
Very much to my suprise that the 120v windings were only 5.7 ohms.
In one of my tests (before the one were the two resistors burned up for no reason)they were wired for 1:400 and I had heard a loud snap and after I took them apart I found no evidence of any burn marks and put them back together.
That was when I proceeded to scortch three meters that morning( ha ha ha).
I also didn't relize the 32kv P-P I was dealing either.
So because of this I have been pondering the same question myself.
Great work . jer
The secondary current I've calculated is 5/40=0.125A. 5 is output current, 40 is turns ratio. Cross-section 0.01 sq mm => current density equal 12.5 A/mm sq.
Alex
BTW, reduction of capacitance is rather straightforward. The trick is to have low stray inductance and low capacitance simultaneously. Even then some topologies make capacitance somewhat irrelevant. Not easily applicable for high voltage. And even then you may look for so-called cable transformers. Huge core cross section of such transformers will force you to use exotic materials...
Alex
BTW, reduction of capacitance is rather straightforward. The trick is to have low stray inductance and low capacitance simultaneously. Even then some topologies make capacitance somewhat irrelevant. Not easily applicable for high voltage. And even then you may look for so-called cable transformers. Huge core cross section of such transformers will force you to use exotic materials...
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I'm sorry I misunderstood that the wire your were testing is that of the secondary and not for the primary,please exuse my ignorance.
125ma is kind of pushing the limits for .1mm diameter wire acording to the charts and if an arc should occour this would short the winding cuasing it to burn up.
however on my travels of looking for wire charts I found this interesting calculator that shows the effect of capcitance per inch vs wire size. jer
Wire Capacitance Calculator
p.s I'm not sure if it is acurate from some of spacings I have just tried?
It may not be applicable in this case. jer
125ma is kind of pushing the limits for .1mm diameter wire acording to the charts and if an arc should occour this would short the winding cuasing it to burn up.
however on my travels of looking for wire charts I found this interesting calculator that shows the effect of capcitance per inch vs wire size. jer
Wire Capacitance Calculator
p.s I'm not sure if it is acurate from some of spacings I have just tried?
It may not be applicable in this case. jer
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Tannoy do this in their dual concentric range and have done so for ~50yrs.
It is an easy (but expensive) way to tap off an adjustable voltage drive and compensate for different sensitivity drivers.
There are/were probably many others that do/did similar
Thanks Andrew!
I heard about it and even consider doing it on my JBL L300.
(was carefully asked ..newibe here
)Many people saying the the weak chain in L300's is the crossover.
As understand at the time L300 came out the marker , The heavy SS amp like Mcintosh 250W was very "IN".
So JBL design the crossover as "fuse" so it will protect the very effiecient drivers .
but ths "choking" the sound and make the speaker less detailed.
If possible , can some 1 please check the schema and advice if moving building new crossover for L300 basing transofmers will do good with them?
Case yes, please recommened on good transformer for the L300.
Thanks a lot!
Good thread! Some questions regarding the transformer design...
I have an opportunity to get these kind of transformers:
1) 2 x 30 primary turns on 10,5cm2 core, secondary 2680 turns = 1: 89,9 and calculated core saturation 9Vrms@50Hz for each primary.
2) 2 x 40 turns on 14cm2 core, secondary 3500 turns = 1:87,5 and calculated core saturation 15Vrms@50Hz for each primary.
I plan use two of either trafo's (per stat) with primaries in parallel and secondaries in series to get ~1:180 step up ratio. The panels will be crossed over at ~250Hz 1st order, and filter steepens to 2nd order at ~110Hz.
Some extra specs: trafo will have an electrostatic shield between pri and sec that supposedly reduces capacitive loading the trafo when connected to the center tap. The secondary will have some insulation layers between the winding layers to reduce the winding capacitance. There will be 6 layers of insulation between PRI and SEC to give at least 6kV insulation. The core will be grain oriented silicon steel with Bmin <1.7T. The winding wire is 1,2mm diameter on the primary and 0.28mm on the secondary and the wire is general 99,9% OFC. The core and the windings will be impregnated with some stuff so the trafo won't buzz (and offes some extra insulation).
The real question is, which one of the transformers likely has wider bandwidth (lower leakage inductance)? I would presume that the one with smaller core, but I was thinking that maybe they could be pretty close in the end because the bigger one has more primary turns and thus the core coverage and coupling might be higher?
The extra saturation headroom is not absolutely necessary, I would rather get higher bandwidth trafo if the other trafo put's the resonance to the audio band, but I'm just wondering if i could get the etra headroom and the same bandwidth... maybe. What do you think? My stats, with size of a regular door, have ~2,8nF capacitance.
Regards,
Legis
I have an opportunity to get these kind of transformers:
1) 2 x 30 primary turns on 10,5cm2 core, secondary 2680 turns = 1: 89,9 and calculated core saturation 9Vrms@50Hz for each primary.
2) 2 x 40 turns on 14cm2 core, secondary 3500 turns = 1:87,5 and calculated core saturation 15Vrms@50Hz for each primary.
I plan use two of either trafo's (per stat) with primaries in parallel and secondaries in series to get ~1:180 step up ratio. The panels will be crossed over at ~250Hz 1st order, and filter steepens to 2nd order at ~110Hz.
Some extra specs: trafo will have an electrostatic shield between pri and sec that supposedly reduces capacitive loading the trafo when connected to the center tap. The secondary will have some insulation layers between the winding layers to reduce the winding capacitance. There will be 6 layers of insulation between PRI and SEC to give at least 6kV insulation. The core will be grain oriented silicon steel with Bmin <1.7T. The winding wire is 1,2mm diameter on the primary and 0.28mm on the secondary and the wire is general 99,9% OFC. The core and the windings will be impregnated with some stuff so the trafo won't buzz (and offes some extra insulation).
The real question is, which one of the transformers likely has wider bandwidth (lower leakage inductance)? I would presume that the one with smaller core, but I was thinking that maybe they could be pretty close in the end because the bigger one has more primary turns and thus the core coverage and coupling might be higher?
The extra saturation headroom is not absolutely necessary, I would rather get higher bandwidth trafo if the other trafo put's the resonance to the audio band, but I'm just wondering if i could get the etra headroom and the same bandwidth... maybe. What do you think? My stats, with size of a regular door, have ~2,8nF capacitance.
Regards,
Legis
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Are these going to be custom made?
IMHO I am not so sure if the static shield actually will reduce the capacitance.
It may between the primary and the secondary winding, but increasing the thickness of the insulation of the secondary layers form the core, static shield or primary layers is/or the only bet to decrease the parasitic capacitance of the secondary winding.
Also don't use any bifilar winding techniques as well, As this increases the capacitance as well.
For instance when using a power transformer in reverse the primary is now the secondary and it is the winding closest to the core if the insulation between the core and the winding was thicker this would reduce the capacitance of that winding.
My transformers have two 120v winding's that are bifilar wound and the difference is like four fold,and is one of the main reason I have to use 4 transformers per panel.
On my transformers I use 4 sets of 10 turn winding's of speaker wire in parallel wound on top for the primary.
So the capacitance between the primary and the secondary is not the issue.
It is the secondary capacitance caused from being so close to the core.
It is the cause of all of that extra capacitance.
After measuring the capacitance of my transformers I plugged in the values of the surface area of the core and winding's and guessed what the insulation thickness would be about ,and,I'll darned if I didn't get the guessed capacitance right, nearly on the money of my measured value.
This is where I realized that if I were to make a transformer I would have to use a large core as this would allow me enough room for a thicker than normal insulation thickness in order to keep the capacitance on the low side.
Also using a larger core will allow for just one layer for the secondary as well as a lower saturation frequency point this is especially good for a full range design as well.
As far as the core size I would go with the bigger core.
This is because at 250Hz your edge of saturation point is going to be at 45v with the smaller core.
This maybe ample for most cases but may be problem if your amp is capable of large voltage swings when you might have the urge to crank it up once in a while.
The large core will allow you a more respectable 75V voltage swing at 250Hz this is where most of time the amp will be spending its time any how.
Remember ESL's have a higher output at the higher end of the spectrum for the same amount of voltage in and you won't get any saturation at all in the higher end of the spectrum, It is at the lower end where it will be heard.
I have noticed this with my cores as well, and is why it requires the use of 4 of my 210watt transformers instead of two or even one to keep my amp from shutting down with my little panels because of low frequency saturation, and, That is with a highpass filter at 80Hz and any other low frequency cut filter that I can use below 200Hz or so.
I also think that you will also have a lower leakage inductance with the two 40 turn winding's for the primary as well.
As this depends on the core area coverage.
Even though the leakage inductance is a big factor as your panels are quite large,I have found that reducing the capacitance of the secondary winding to be the utmost importance for a few reasons.
First it will increase the bandwidth of the transformer.
Second any extra capacitance in the winding makes for extra unneeded load on the amp and the power just gets wasted as heat in the transformer or actually the amp itself.
Lets say if your panels have 3nf of capacitance and your transformer has at least 1nf of capacitance or more than your amp will waste 25% or more power than needed to push the panel, And if you only have say a 100 or150 watt amp this is a lot of power wasted as heat that could otherwise be sound as an example.
And third of course it keeps helps the resonance higher than the audio band.
FWIW
Jer
IMHO I am not so sure if the static shield actually will reduce the capacitance.
It may between the primary and the secondary winding, but increasing the thickness of the insulation of the secondary layers form the core, static shield or primary layers is/or the only bet to decrease the parasitic capacitance of the secondary winding.
Also don't use any bifilar winding techniques as well, As this increases the capacitance as well.
For instance when using a power transformer in reverse the primary is now the secondary and it is the winding closest to the core if the insulation between the core and the winding was thicker this would reduce the capacitance of that winding.
My transformers have two 120v winding's that are bifilar wound and the difference is like four fold,and is one of the main reason I have to use 4 transformers per panel.
On my transformers I use 4 sets of 10 turn winding's of speaker wire in parallel wound on top for the primary.
So the capacitance between the primary and the secondary is not the issue.
It is the secondary capacitance caused from being so close to the core.
It is the cause of all of that extra capacitance.
After measuring the capacitance of my transformers I plugged in the values of the surface area of the core and winding's and guessed what the insulation thickness would be about ,and,I'll darned if I didn't get the guessed capacitance right, nearly on the money of my measured value.
This is where I realized that if I were to make a transformer I would have to use a large core as this would allow me enough room for a thicker than normal insulation thickness in order to keep the capacitance on the low side.
Also using a larger core will allow for just one layer for the secondary as well as a lower saturation frequency point this is especially good for a full range design as well.
As far as the core size I would go with the bigger core.
This is because at 250Hz your edge of saturation point is going to be at 45v with the smaller core.
This maybe ample for most cases but may be problem if your amp is capable of large voltage swings when you might have the urge to crank it up once in a while.
The large core will allow you a more respectable 75V voltage swing at 250Hz this is where most of time the amp will be spending its time any how.
Remember ESL's have a higher output at the higher end of the spectrum for the same amount of voltage in and you won't get any saturation at all in the higher end of the spectrum, It is at the lower end where it will be heard.
I have noticed this with my cores as well, and is why it requires the use of 4 of my 210watt transformers instead of two or even one to keep my amp from shutting down with my little panels because of low frequency saturation, and, That is with a highpass filter at 80Hz and any other low frequency cut filter that I can use below 200Hz or so.
I also think that you will also have a lower leakage inductance with the two 40 turn winding's for the primary as well.
As this depends on the core area coverage.
Even though the leakage inductance is a big factor as your panels are quite large,I have found that reducing the capacitance of the secondary winding to be the utmost importance for a few reasons.
First it will increase the bandwidth of the transformer.
Second any extra capacitance in the winding makes for extra unneeded load on the amp and the power just gets wasted as heat in the transformer or actually the amp itself.
Lets say if your panels have 3nf of capacitance and your transformer has at least 1nf of capacitance or more than your amp will waste 25% or more power than needed to push the panel, And if you only have say a 100 or150 watt amp this is a lot of power wasted as heat that could otherwise be sound as an example.
And third of course it keeps helps the resonance higher than the audio band.
FWIW
Jer
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Hi Jer, thanks for the reply.
Yes, the trafos will be custom made by TOROIDY.PL Transformatory Toroidalne Producent, Audio, Separacyjne, Trójfazowe, 230/110V, 110/230V, Na zamówienie. The primaries will be wound bifilar and the windings spread so the core coverage is best. I think bifilar primary is not bad but actually could be better than winding the primaries normally? If I read this correctly, it reduces leakage inductance (beginning of the second paragraph): Transformer and Inductor Design Handbook - Wm. T. McLyman, Colonel William T. McLyman - Google-kirjat
The manufacturer agreed to produce a prototype with the 40 PRI / 3500 SEC on the bigger core and measure it's primary's leakage inductance and secondary's winding capacitance. I let you know the values. I will use two trafos that have all 4 primaries in parallel and the two secondaries in series so I think the primary leakage inductances are added together and the secondary winding capacitances are added and then divided by 4... I can then simulate the response with my panels.
Yes, the trafos will be custom made by TOROIDY.PL Transformatory Toroidalne Producent, Audio, Separacyjne, Trójfazowe, 230/110V, 110/230V, Na zamówienie. The primaries will be wound bifilar and the windings spread so the core coverage is best. I think bifilar primary is not bad but actually could be better than winding the primaries normally? If I read this correctly, it reduces leakage inductance (beginning of the second paragraph): Transformer and Inductor Design Handbook - Wm. T. McLyman, Colonel William T. McLyman - Google-kirjat
The manufacturer agreed to produce a prototype with the 40 PRI / 3500 SEC on the bigger core and measure it's primary's leakage inductance and secondary's winding capacitance. I let you know the values. I will use two trafos that have all 4 primaries in parallel and the two secondaries in series so I think the primary leakage inductances are added together and the secondary winding capacitances are added and then divided by 4... I can then simulate the response with my panels.
I always do like this: Calculate the impedance of the ESL unit at 20 kHz, take the square root of this value, which gives You the step up value for one Ohm total impedance minimum for the complete speaker. In your case, step up = 1:53
When winding this kind of transformer, it's very important to keep individual turns and windings with high different voltages apart, so I'm not sure you should use bifilar winding.
When winding this kind of transformer, it's very important to keep individual turns and windings with high different voltages apart, so I'm not sure you should use bifilar winding.
Hi Jonas, trafo consists of 2x 40 turn primaries and 1x 3500 turn secondary. Only the primaries are wound bifilar, there voltrages are rather small. The secondary winding will have insulation layer between each layer ("interlayer insulation") and there will be 6 layers of insulation between pri and sec (instead of normal 3).
By normal transformation ratio calculation I think the transformation ratio will be close to 1:175 (minus the losses) with two such transformers primaries in parallel and secondaries in series. What does the 1:53 ratio mean exactly?
Regards,
Legis
By normal transformation ratio calculation I think the transformation ratio will be close to 1:175 (minus the losses) with two such transformers primaries in parallel and secondaries in series. What does the 1:53 ratio mean exactly?
Regards,
Legis
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