Roushon,
Magnetic shield is put on the outside of the transformer.
First, you have to put a belly band made from copper. Instead of the un-obtainium shielding material called the mu metal which needs to be anealed after reshaping, I am going to fix a casing around the transformer made from thick iron plates. As far as I can tell from the observations from the japanese stereos, you have to wrap it tight and varnish it so that it does not vibrate.
Additionally, you can also put your transformer in a faraday cage made from iron(thicker, the better).
Gajanan Phadte
Wrong connection on LM338 for even once, and they say goodbye.
Magnetic shield is put on the outside of the transformer.
First, you have to put a belly band made from copper. Instead of the un-obtainium shielding material called the mu metal which needs to be anealed after reshaping, I am going to fix a casing around the transformer made from thick iron plates. As far as I can tell from the observations from the japanese stereos, you have to wrap it tight and varnish it so that it does not vibrate.
Additionally, you can also put your transformer in a faraday cage made from iron(thicker, the better).
Gajanan Phadte
Wrong connection on LM338 for even once, and they say goodbye.
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Thanks Gajanan for the explanation. I think it is like we
see in valve products, those big transformers are
covered...
By any chance do you know where does one find copper
sheet in Mumbai. I looked around a bit in Lohar Chawl,
Mumbai but could not locate a source.
The LM338 I got from VISHA are weak physically, the
legs are almost hobbling. Did not expect from them.
Roushon
see in valve products, those big transformers are
covered...
By any chance do you know where does one find copper
sheet in Mumbai. I looked around a bit in Lohar Chawl,
Mumbai but could not locate a source.
The LM338 I got from VISHA are weak physically, the
legs are almost hobbling. Did not expect from them.
Roushon
The transformers I purchased from Vegakit (or may be
Gala, on the same floor as Visha) in LR are made of
NOT copper wire. Very strange! I am not sure what it is, it
looks like some white metal wire with a coating. Must be
some cheap replacement of copper wire. Also not
solderable well.
Roushon.
Gala, on the same floor as Visha) in LR are made of
NOT copper wire. Very strange! I am not sure what it is, it
looks like some white metal wire with a coating. Must be
some cheap replacement of copper wire. Also not
solderable well.
Roushon.
You seem to have singularly bad luck every time you go to Lamington road!
What you got is Aluminium wire. Few years ago when Copper prices went very high, people started making cheap transformers out of Aluminium wire. They have stopped that dirty practice now, but I guess there is still some old stock lying around ?
Frankly, I am surprised they sold it to you without warning you. I have never seen anyone sell those transformers without warning the customer first. Usually they offer the Aluminium transformers only after the customer complains about the high cost of the Copper one.
About your earlier question regarding copper sheet: You can buy it from the same shop that sells the EI laminations and Copper wire.
100% correct! Every time I need some parts first I try to be a `good citizen
of India' and try to purchase India made things but get a kick. Then, import,
costing me more...In any event, is there any (bad) side effect to use
aluminum wires in transformer.
Thanks for your reply....
Regards
Roushon.
There are excellent transformers made in India. In fact, several of the big name American/European manufacturers actually have their factories in India. It would be ironic if you imported a made in India transformer.
Aluminium has high resistance and corrosion/solderability (as you found out) issues, and it is fragile (it cracks).
Many years ago I got a transformer custom built by a guy in the lane that leads to the station (sorry I don't remember the name). It was very well done. If you can find the shop, I heartily recommend him.
Aluminium has high resistance and corrosion/solderability (as you found out) issues, and it is fragile (it cracks).
Many years ago I got a transformer custom built by a guy in the lane that leads to the station (sorry I don't remember the name). It was very well done. If you can find the shop, I heartily recommend him.
Did not have time, so thought of purchasing a ready made one. Now as I think
back the number of times I purchased ready made transformers, many a times I
found no tag board connection, instead rubber coated wire coming out of it,
these are exactly the aluminum wire's one I am sure now. I found out now as I
tried to unwind it to reduce the secondary voltage, otherwise would have remain
ignorant for ever....there is no end of learning in LR....such a waste of time and money!!!!
Roushon
back the number of times I purchased ready made transformers, many a times I
found no tag board connection, instead rubber coated wire coming out of it,
these are exactly the aluminum wire's one I am sure now. I found out now as I
tried to unwind it to reduce the secondary voltage, otherwise would have remain
ignorant for ever....there is no end of learning in LR....such a waste of time and money!!!!
Roushon
One more comment. It is true that there are manufacturers of things in India
and the products are excellent but they least care about or give a damn
about hobbyist or retail purchaser. I believe they make things here as it is
cheap labor but aim is to export in high cost or to supply bulk purchaser. I
remember when I was struggling to get some PCBs made. The companies
were willing but with a huge cost and many copies. (Now I mastered to make
fine PCBs at home.) Got made some very good toroid in LR in the past from
Radio Electric Pvt. Ltd. but they are unresponsive now to any queries, may
be they also have started to export....
Roushon.
That is a good idea to shield transformers, but I need it to
shield the digital section IC in my cd player also. There I need to solder it to the ground. Also not sure if aluminum
will be a very good shield. Have no knowledge about
the physics behind all these very much.
Roushon.
shield on transformer
Here is the transformer from a Sony MHC RV50. The mu metal on which the s. no. is printed has three turns of the sheet. The pin side was on the left side of the stereo, mounted on a pcb for voltage selection, the fuses and a small aux power supply. The right side of the stereo had the main pcb, towards the shield on the transformer.
Gajanan Phadte
Here is the transformer from a Sony MHC RV50. The mu metal on which the s. no. is printed has three turns of the sheet. The pin side was on the left side of the stereo, mounted on a pcb for voltage selection, the fuses and a small aux power supply. The right side of the stereo had the main pcb, towards the shield on the transformer.
Gajanan Phadte
Attachments
I believe mu-metal has no alternative name here and possibly very hard to get here. I don't believe it is made in the country as we import a lot of transformer lamination's. They are bought in bulk and punched to size over here. Thin copper foil is available from many shops selling metal sheets. Try smaller shops as they will sell small quantities.
Why do you need mu-metal in any case ? You should be able to get hum free audio designs using toroid transformers. In pre-amps you could put the transformer in a separate box like some high end companies do.
I felt a brief note to understand the different types of shielding in transformers would be useful to all and searched for a link on the Net.
Here is one:
( from : why shield are used in HF transformer? | LinkedIn )
Ray R. • There is a lot of confusion around this topic here.
There are two types of shields - one which is wrapped around the transformer after it is completely wound, and which is shorted to itself and to the core. This is sometimes known as a "belly-band" shield and is used to stop the core and outer windings from acting as radiating surfaces.
The other type of shield is used between windings to minimize interwinding capacitance. This is referred to as a faraday shield. It must not be a complete turn.
Thin foils are used for both types of shields for maximum effectiveness.
Proper grounding of both types of shields is crucial. They must be tied via a low impedance path to a quiet node of the circuit, otherwise their effectiveness will be compromised. The faraday shield is usually tied to a quiet node on the primary, and the intent is to return the high-frequency noise generated by primary switching, through as short a path as possible to either the + rail or the return path, which may well be another pin on the transformer.
For large transformers, shields are sometimes grounded at more than one point.
For ultra-isolation transformers, as many as three shields can be used to dramatically drop capacitance.
The shields are very effective at reducing EMI, especially common-mode. They are very common in medical supplies where input filter common-mode capacitance is limited by agency rules. Even very low-cost flyback for medical applications usually have faraday shields in them.
More information on high-frequency transformer design can be found at Ridley Engineering | - Solutions for Switching Power Supplies in the design center.
I hope this helps answer your question.
Ray R. • Negative aspects of shields (ie why we don't always use them)
1) extra process adds cost
2) maintaining isolation standards between primary and secondary is complicated by the presence of the faraday shield. foil must be completely insulated with tape, or appropriate margins applied.
3) termination of faraday shield is awkward - either the foil must be brought out of winding for large transformers, or wires soldered to the foil to terminate it.
4) leakage inductance is increased with the faraday shield. with a 1 or 2 mil foil, this increase can be manageable, and worthwhile for the big drop in capacitance and noise.
5) PCB transformers can benefit from shields, but i don't see this applied as often as it should be.
6) Just to iterate - be careful with where you ground them, as this can eliminate the effectiveness of the shields if not done properly.
Why do you need mu-metal in any case ? You should be able to get hum free audio designs using toroid transformers. In pre-amps you could put the transformer in a separate box like some high end companies do.
I felt a brief note to understand the different types of shielding in transformers would be useful to all and searched for a link on the Net.
Here is one:
( from : why shield are used in HF transformer? | LinkedIn )
Ray R. • There is a lot of confusion around this topic here.
There are two types of shields - one which is wrapped around the transformer after it is completely wound, and which is shorted to itself and to the core. This is sometimes known as a "belly-band" shield and is used to stop the core and outer windings from acting as radiating surfaces.
The other type of shield is used between windings to minimize interwinding capacitance. This is referred to as a faraday shield. It must not be a complete turn.
Thin foils are used for both types of shields for maximum effectiveness.
Proper grounding of both types of shields is crucial. They must be tied via a low impedance path to a quiet node of the circuit, otherwise their effectiveness will be compromised. The faraday shield is usually tied to a quiet node on the primary, and the intent is to return the high-frequency noise generated by primary switching, through as short a path as possible to either the + rail or the return path, which may well be another pin on the transformer.
For large transformers, shields are sometimes grounded at more than one point.
For ultra-isolation transformers, as many as three shields can be used to dramatically drop capacitance.
The shields are very effective at reducing EMI, especially common-mode. They are very common in medical supplies where input filter common-mode capacitance is limited by agency rules. Even very low-cost flyback for medical applications usually have faraday shields in them.
More information on high-frequency transformer design can be found at Ridley Engineering | - Solutions for Switching Power Supplies in the design center.
I hope this helps answer your question.
Ray R. • Negative aspects of shields (ie why we don't always use them)
1) extra process adds cost
2) maintaining isolation standards between primary and secondary is complicated by the presence of the faraday shield. foil must be completely insulated with tape, or appropriate margins applied.
3) termination of faraday shield is awkward - either the foil must be brought out of winding for large transformers, or wires soldered to the foil to terminate it.
4) leakage inductance is increased with the faraday shield. with a 1 or 2 mil foil, this increase can be manageable, and worthwhile for the big drop in capacitance and noise.
5) PCB transformers can benefit from shields, but i don't see this applied as often as it should be.
6) Just to iterate - be careful with where you ground them, as this can eliminate the effectiveness of the shields if not done properly.