I need a quick lesson on transformers - here's my questions:
1. What is the difference between magnetizing inductance and mutual inductance? Why do I ask? In spice, they model transformers as mutually coupled inductors. I don't see the relationship between mutual coupling and magnetizing inductance. Most people seem to spec transformers with magnetizing inductance, leakage inductance and turns ratio. I'd like to model this in spice, but don't know how to translate one to the other.
2. What does an air gap do for the transformer?
3. Any pointers to a good transformer discussion?
1. What is the difference between magnetizing inductance and mutual inductance? Why do I ask? In spice, they model transformers as mutually coupled inductors. I don't see the relationship between mutual coupling and magnetizing inductance. Most people seem to spec transformers with magnetizing inductance, leakage inductance and turns ratio. I'd like to model this in spice, but don't know how to translate one to the other.
2. What does an air gap do for the transformer?
3. Any pointers to a good transformer discussion?
go to
www.sound.westhost.com
see the articles section and find the topic on tansformers.read whole of the two part,very informative article which deals with technical as well as real world issues with transformers
www.sound.westhost.com
see the articles section and find the topic on tansformers.read whole of the two part,very informative article which deals with technical as well as real world issues with transformers
Transformer redesign
As far as transformer winding is concerned, I am confident that I could do it, (especially w/the magnetics design handbook link posted by carvin guy, it answers a lot of my questions) because I am already experienced in AC Motor rewinding. But all of my knowledge is industrial; I'm wondering what makes an output transformer "high end". What makes tranformer quality go beyond the formula "Turns in primary/Turns in secondary=V in primary/V in secondary"?
I don't have any projects on the agenda, but I was considering building my own amp sometime soon; and I was thinking that I would transplant and redesign the transformers from my current amp; if the cost should end up being less vs. the cost of brand new transformers.
So, what makes a transformer "high-end"?
As far as transformer winding is concerned, I am confident that I could do it, (especially w/the magnetics design handbook link posted by carvin guy, it answers a lot of my questions) because I am already experienced in AC Motor rewinding. But all of my knowledge is industrial; I'm wondering what makes an output transformer "high end". What makes tranformer quality go beyond the formula "Turns in primary/Turns in secondary=V in primary/V in secondary"?
I don't have any projects on the agenda, but I was considering building my own amp sometime soon; and I was thinking that I would transplant and redesign the transformers from my current amp; if the cost should end up being less vs. the cost of brand new transformers.
So, what makes a transformer "high-end"?
I assume that you refer to audio transformers not power transformers as used in power supplies. High end audio transformers follow conventional rules as far as turns and impedance ratio goes. Good low frequency performance hinges on a fairly high primary inductance ( set by the core size and primary turns). Good high frequency performance hinges on low interwinding capacitance and low leakage inductance. Both of these can greatly reduced by interleaving the primary and secondary windings, interwinding capacitance is also reduced by using low dielectric insulation between the windings. For anything approaching HIFI standard the primary must be split into at least 4 windings with the secondary split into 3 or 5 windings. eg. The windings being interleaved like this S-P-S-P-S-P-S-P-S . They are not hard to wind you just need care and PATIENCE. Guitar or PA transformers can get away with less interleaves eg P-S-P-S is usually sufficient.
Mutual Inductance essentially corelates to leakage inductance...with respect to just one winding, usually just the primary..even though it is a function of all windings that are coupled...
The highest "mutal inductance" would be UNITY, 1 ....this means a 100% coupling between primary and secondary, which is ideal...
You do not include copper or core losses in the mutual inductance.. although I sometimes do it that way to save time...
So, you may have a coupling coefficient or mutual inductance of .96 for example ...... The .04 would equate to leakage inductance..
Magnetizing Inductance... is usually refered to the primary winding in audio.... This is just straight up inductance....
The standard for magnetizing inductance is done at 60HZ over a sweep of Flux Density , which is essentially change in amplitude of the 60Hz signal....Data sheets will show this Magnetizing curve for various grades of core material....
The inductance is governed by several factors...
One is the Core Size.... second is the Number of Turns, third is the "effective" permeability of the core material....
Effective perm of the steel is the final perm of the steel after the transformer is assembled.... ALL transformers have an air-gap whether it's intentional or not...This reduces the perm of the steel, it needs to be calaculated ... Data sheets for perm of grades of steel are "perfect" Epstien ring samples that are a one-piece circular sample used for making the curves...usually all done in the 1940's and 1950's.... This perm number is reduced to the "effective" perm based on many factors....lamination type and shape, how laminations are stacked whether it is 1:1 or groups of 5:5, ect.., thickness of laminations, Flux levels you operate at...
The inductance of a transformer is usally not a single number...it does swing around...If your making a choke, you can gap it to try to lineraize it and keep the inductance swing to a minimum..
For a P-P Hi-Fi output transformer...the inductance will vary greatly depending on the power level you drive to...
The inductance on a C-core and toroid will peak roughly at the satuartion point of the steel...while in a E-I lamination the inductance will peak roughly at 1/2 the satuaration point..... This is something to consider..
Chris
The highest "mutal inductance" would be UNITY, 1 ....this means a 100% coupling between primary and secondary, which is ideal...
You do not include copper or core losses in the mutual inductance.. although I sometimes do it that way to save time...
So, you may have a coupling coefficient or mutual inductance of .96 for example ...... The .04 would equate to leakage inductance..
Magnetizing Inductance... is usually refered to the primary winding in audio.... This is just straight up inductance....
The standard for magnetizing inductance is done at 60HZ over a sweep of Flux Density , which is essentially change in amplitude of the 60Hz signal....Data sheets will show this Magnetizing curve for various grades of core material....
The inductance is governed by several factors...
One is the Core Size.... second is the Number of Turns, third is the "effective" permeability of the core material....
Effective perm of the steel is the final perm of the steel after the transformer is assembled.... ALL transformers have an air-gap whether it's intentional or not...This reduces the perm of the steel, it needs to be calaculated ... Data sheets for perm of grades of steel are "perfect" Epstien ring samples that are a one-piece circular sample used for making the curves...usually all done in the 1940's and 1950's.... This perm number is reduced to the "effective" perm based on many factors....lamination type and shape, how laminations are stacked whether it is 1:1 or groups of 5:5, ect.., thickness of laminations, Flux levels you operate at...
The inductance of a transformer is usally not a single number...it does swing around...If your making a choke, you can gap it to try to lineraize it and keep the inductance swing to a minimum..
For a P-P Hi-Fi output transformer...the inductance will vary greatly depending on the power level you drive to...
The inductance on a C-core and toroid will peak roughly at the satuartion point of the steel...while in a E-I lamination the inductance will peak roughly at 1/2 the satuaration point..... This is something to consider..
Chris
Transformer Help
I have recently purchased a Toroidal transformer and in use is making quite a bit of mechanical noise.
Aplication is a Large F5 with twin bridges and CRCLC filter
Specifications are
230 V 1000VA and twin secondary at 24 V with tap at 20.
When loading the transformer with 7 A on the 20 V taps it prouce a fair bit off mechanical noise.
I am the second house down from the mains distribution transformer and have mesured today 246 V ac (UK)
I am a bit concerned with the mechanical noise as eventualy the wires insulation will vear down and smoke
The suplier (will not name and shame at this stage) suggest that is the hi voltagge causing the problem as trafo was designed for 230 volts.
There is (preaty good meter) about 26 mv DC on the line but this seems not to be the problem as I have tried a DC filter (Bridge Diode and Large Caps)
Cecked the way is wired up and swaped vires around so definetly connected corectley.
First) of all tanks for posting the links (Rod site to the resque again)
Second) any Idea ?
Sugestion by traffo suplier is to get a new traffo made with specs for that volltagge.
But I am thinking
Bit strange that suplier blames hi voltagge al the rest of my stuff works no need for me to get any special order for tely or CD player and such realy.
I have recently purchased a Toroidal transformer and in use is making quite a bit of mechanical noise.
Aplication is a Large F5 with twin bridges and CRCLC filter
Specifications are
230 V 1000VA and twin secondary at 24 V with tap at 20.
When loading the transformer with 7 A on the 20 V taps it prouce a fair bit off mechanical noise.
I am the second house down from the mains distribution transformer and have mesured today 246 V ac (UK)
I am a bit concerned with the mechanical noise as eventualy the wires insulation will vear down and smoke
The suplier (will not name and shame at this stage) suggest that is the hi voltagge causing the problem as trafo was designed for 230 volts.
There is (preaty good meter) about 26 mv DC on the line but this seems not to be the problem as I have tried a DC filter (Bridge Diode and Large Caps)
Cecked the way is wired up and swaped vires around so definetly connected corectley.
First) of all tanks for posting the links (Rod site to the resque again)
Second) any Idea ?
Sugestion by traffo suplier is to get a new traffo made with specs for that volltagge.
But I am thinking
Bit strange that suplier blames hi voltagge al the rest of my stuff works no need for me to get any special order for tely or CD player and such realy.
Hi,
modern transformers are made to 230Vac or 115/230Vac or 115Vac.
These are for universal application on the respective 110/120Vac and 220/240Vac supplies around the world.
They should all work with any of those voltages within the tolerance range of each supplier.
But materials are expensive. Skimp on the copper and the primary turns run at near saturation when at the highest supply voltages. At highest power output the turns are drawing heavy current and that may be the vibration you hear.
modern transformers are made to 230Vac or 115/230Vac or 115Vac.
These are for universal application on the respective 110/120Vac and 220/240Vac supplies around the world.
They should all work with any of those voltages within the tolerance range of each supplier.
But materials are expensive. Skimp on the copper and the primary turns run at near saturation when at the highest supply voltages. At highest power output the turns are drawing heavy current and that may be the vibration you hear.
It is very likely that the toroid saturates with the high line voltage.
Toroidal transformers are efficient, but when they must work outside the specs they are a PITA.
That's why I only use c-cores for power supply transformers (minor airgaps to prevent line DC causing trouble; core excitation around 1 T for a quiet and cool transformer; electrostatic shield).
The last time I switched a toroid for a c-core power supply transformer on just a chip amp the sonic improvement was dramatic.
Toroidal transformers are efficient, but when they must work outside the specs they are a PITA.
That's why I only use c-cores for power supply transformers (minor airgaps to prevent line DC causing trouble; core excitation around 1 T for a quiet and cool transformer; electrostatic shield).
The last time I switched a toroid for a c-core power supply transformer on just a chip amp the sonic improvement was dramatic.
If the noise only happens at high load currents, it isn't a saturation problem.
It could be an electrodynamic effect (unlikely in a toroid), or improperly matched diodes in the rectifier bridge.
Toroids are extremely sensitive to DC bias, and some tens of millivolt difference between the two paths can begin to cause problems.
I'd try to replace the diodes from the bridge with properly matched ones.
If I understand well the F5 is pure class A, so there is constant current draw.
Normally the 1000VA transformer should function well as it is supposed to be able to deliver some 20 A.
When core saturation occurs high currents flow in the primary, also when there is no secondary load.
You could try how the transformer behaves under no load conditions.
Elvee Pieter T
Tanks for replies
Realy bugs me that when I asked for a quote I told the suplier that it was for an HIFI amplifier and that I wanted the best he could build.
As I got 2 of them one went back for suplier to do same work on it.
So I will let you know waht the score is.
But realy bugs me even more the fact that he was blaming the hi voltagge of my mains al the other stuf I got works fine.
One thing I have not tried is to use the 24 volts taps instead of the 20
I am prety shure that saturation of the core will be less on the 24.
Maybe tomrow I give it a go.
Tanks for replies
Realy bugs me that when I asked for a quote I told the suplier that it was for an HIFI amplifier and that I wanted the best he could build.
As I got 2 of them one went back for suplier to do same work on it.
So I will let you know waht the score is.
But realy bugs me even more the fact that he was blaming the hi voltagge of my mains al the other stuf I got works fine.
One thing I have not tried is to use the 24 volts taps instead of the 20
I am prety shure that saturation of the core will be less on the 24.
Maybe tomrow I give it a go.
Did you try how the transformer behaves unloaded?
Using the 24 volts taps instead of the 20 volts taps should not influence core saturation in your application (the problems are at the primary side).
Hi pieter
Traffo unloaded is quiet
I have changed the taps to the 24 V ac 35 DC no load 32 DC on load pulling now 3 A on each rail
Buzz maybe worst so more bull from traffo supplier (told me it would be beter at 24 taps as that is what is designed for) I will find out on Monday what development there are.
One thing for sure the amplifier sound even better at this voltage, is bit brighter and load more dynamics.
With 3 A I should get 36 watts in class A and after 12 V (more than loud enough) it will start switching over to class B.
I am playing at the moment a nice CD
Pavlov's Dog Pampered Menial
I could not find this on LP still David Surkamp voice is a must listen to
Traffo unloaded is quiet
I have changed the taps to the 24 V ac 35 DC no load 32 DC on load pulling now 3 A on each rail
Buzz maybe worst so more bull from traffo supplier (told me it would be beter at 24 taps as that is what is designed for) I will find out on Monday what development there are.
One thing for sure the amplifier sound even better at this voltage, is bit brighter and load more dynamics.
With 3 A I should get 36 watts in class A and after 12 V (more than loud enough) it will start switching over to class B.
I am playing at the moment a nice CD
Pavlov's Dog Pampered Menial
I could not find this on LP still David Surkamp voice is a must listen to
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