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Torroidal transformer details need

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thannara123

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Hi experts ,i want to know the details of toroidal transformer.How it works ?
Can i make it at home for learning purpose ?
Is there any tutorials regarding toroidal transformer ?
Thanking you
 

andre_teprom

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There is no special electromagnetic ability on geometry of transformers.
However, some details are considered in choice of type format :

MECHANICAL: EI cores offers protection to windings at center. Assembling is easy.
ESR: POT cores are self-shielded once magnetic flow over reel is confined inside pot. Are very expensive.

I don´t know exactly the advantage to use TOROID type.
In fact, opositelly, there is more dificult to wrap windings.

+++
 

bjuric

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I'm not sure we're allowed to post direct links to other sites, so google for "toroidal transformer basics", the first result should get you started on the basics.
If it's calculations you want, google for "design of toroidal transformers for maximum efficiency", there should be a nice pdf on top.
Wikipedia is also a good source to start.

Toroidal transformers offer many advantages over standard laminated power transformers.... Toroidals provide quiet, efficient operation with very low stray magnetic fields.... More efficient use of the core material in a toroidal can result in a size and weight reduction of up to 50% (depending on power rating).... The windings are evenly wrapped over the entire core allowing the transformer to operate at a higher flux density than in standard transformers.
 

chuckey

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Toroidal winding machines are very rare, so winding have to be put on by hand with the required length of wire wound on to a bobbin that will pass through the centre hole. I used to work for a company that had the only toroidal winding machine in the UK (1964), - made in the USA.
Frank
 

andre_teprom

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..."Toroidal transformers offer many advantages over standard laminated power transformers..."
It makes no sense :

1 ) There is possible to build an Toroidal transformer even laminated.
2 ) Lamination reduces Foulcaut losses effect.

Sometimes Wikipedia may not be a good real reference.

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RCinFLA

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You need to understand the requirements. There are basically two kinds of design. One is for power coupling, the other is energy storage and transfer. The core design for these two applications are different.

Power coupling uses a high permeability core material to provide tight coupling between winding. The core does not have ability to store much energy. The B-H curve is very steep and core is easy to saturate.

An inductor or Flyback transformer relies on the core to store energy and discharge it to another winding. It uses a lower permeability core or a higher permeablity core with an air gap. Since you don't generally put a gap in a torroid, it must have lower permeability core in this application. The B-H curve has a lower slope allowing more energy storage.

Torroid generally provide low flux leakage but are more difficult to wind wire on them.
 

bjuric

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It makes no sense :

1 ) There is possible to build an Toroidal transformer even laminated.
2 ) Lamination reduces Foulcaut losses effect.
Here's a full quotation so that I don't say something wrong.

To construct the core, grain-oriented silicon-iron is slit to form a ribbon of steel which is then wound, like a very tight clock spring. The result is a core in which all of the molecules are aligned with the direction of flux. Molecules not aligned with the flux direction increase a core's reluctance (the capacity for opposing magnetic induction), degrading performance to the level of common steel when the molecules are 90 degrees out of phase. EI laminated cores, which are stamped from grain-oriented Si-Fe, may have as much as 40% of the total core area perpendicular to the ideal grain direction, with another 40% acting only as a return flux path. This more efficient use of the core material in a toroidal can result in a size and weight reduction of up to 50% (depending on power rating)
There's a company here that winds high quality toroidal transformers (power and audio). First time heard about the toroidals and talked to the guy I was kinda cautious thinking he's just trying to make a sale, but it turned out to be true.

In this pic, you can see how the core looks similar to standard laminated cores, to avoid Eddy currents
 

andre_teprom

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hi bjuric

The text above seems a little bit confused and I wish know the reference. The numbers seems exagerated. There are not magic in the geometry difference.
I worked many years ago with power electronic in development of UPS and SMPS and my opinion was based on self experience.
For instance, the size of transformer is obtained for AC 60Hz main frequency is obtained from :
Ae = SQUARE_ROOT ( P )
P - Output power [watt]
Ae - Effective area of cross section[cm2]
So, it´s visible just looking at each type, that don´t have substantial difference in size.

The fact is that beyond the advantages highlighted above other points that must be considered are ( I had not pointed above ) :
> Winding must bo performed aroud ring structure, being more vulnerable to mechanical shock than EI
> Space inside Toroid type (hole) is wasted, in oposition to other types
> Due it rounded aspect, without plane surfaces, it is hard to place, and is needed a bracket.

+++
 
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bjuric

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I guess posting links to refferences you ask for would break several forum rules, but I'll indulge your curiosity.

I'll make this my last post to answer your questions, since any further posting on the subject won't be any productive nor helpful to the OP, beside the point of this thread and considered a direct thread hijacking.


... I wish know the reference...
The quote I posted is from here: Toroidal Transformer Basics
The company that makes high quality toroidals I was talking about: Trafomatic - production of toroidal transformers / izrada transformatora

The numbers seems exagerated.
In some cases, toroids can be much much smaller than laminated EI, since for the core area the windings are also taken into account, and core can be very small inside. The core itself is one piece which is grain oriented in the direction of the flux, which allows for higher flux, in turn allowing for much more power for it's size.

I worked many years ago with power electronic in development of UPS and SMPS and my opinion was based on self experience.......
Actually your background does explain your point of view a lot, since toroids are almost never used in SMPS design. It's hard to spread few turns of wire around the entire toroid. And winding of the wire gauges used are virtually impossible to automate.

The calculation you gave is true for laminated EI-core type transformer.
For toroids, the effective area of the windings is also taken into account. They don't scale like EI types.

The fact is that beyond the advantages highlighted...
There are many advantages of EI types over toroids, and you've missed almost all of them. Like how the air gap in the EI type helps filter out the 'dirty' mains power. How EI cores can deliver much more current in peak because of their higher inductance. Or how the toroids are much more affected by the DC offset in the mains (from switches, motors, etc...). And so on...

Winding must be performed around ring structure, being more vulnerable to mechanical shock than EI
True. And production is very hard to automate, in some cases virtually impossible (like in SMPS mentioned above).

Space inside Toroid type (hole) is wasted, in opposition to other types
Yes and no. Yes from a mechanical point of view. No from the electrical. But smaller overall size makes up for it :wink:

Due it rounded aspect, without plane surfaces, it is hard to place, and is needed a bracket.
Actually no. They are easy to mount. They are squeezed between a plate on top and a casing (or where it is mounted) on the bottom, with rubber sheets in between. Just one screw trough the middle and your set. And there is no worrying about the noise because toroids are not susceptible to magnetostriction like other types.
 
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FvM

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Many points have been already clarified, some possibly need supplementing.
- There's no doubt, that grain-oriented silicon-iron is superior to standard transformer cores. I'm not exactly sure about the 40% weigth saving, but the number sound reasonable. Besides wound tape toroidal cores, you have also SM cut tape transformer cores. They combine the advantages of grain-oriented magnetic material with a more conventional winding design.
- I know several companies making toroidal core transformers in Germany, and I'm rather sure that there also many in the UK. Remember that most current transformers and adjustable transformers are of the toroidal type. I agree however, that they are not particularly preferable for DIY. The basic relations (volts per turn, wire gauge versus current rating) are basically identical to standard transformers. The only special thing is in fact the winding technique.

Some special comments in addition:
There are many advantages of EI types over toroids, and you've missed almost all of them. Like how the air gap in the EI type helps filter out the 'dirty' mains power.
I'm not aware of standard power supply transformers utilizing an air gap. Strictly spoken, toroidal transformers also have a small built-in air gap, by the small non-magnetical spacing between band windings.

Toroidal cores are also used in SMPS, at least high power medium frequency applications. A customer of mine e.g. uses 60 KW 10 kHz toroidal transformers, they are however made of special "amorph" alloys rather than standard silicone iron. The number of turns is at least managable for high voltage designs.
 

andre_teprom

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hi bjuric

I wish say sorry to you and others concerning above posts if it seemed confrontational.
But performing a more accurate analysis I got the results above wich confirm some points :

At reference bellow was comparised 2 similar parts :
http://www.ferroxcube.com/appl/info/PSG2003.pdf

TOROID : T 140/106/15 # Ae=422[cm2] / M=800[g] / MaxDimension = ~106[mm]
EE : E 55/28/25 # Ae=420[cm2] / M= 130*2[g] / MaxDimension = ~56.2*2[mm]
In fact if we perform that analysis with few size parts, Toroid type give best score.
But to largher power rating EE wins. I really don´t know why.

Anybody know what is the reason ?

+++
 
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