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Old 7th December 2002, 09:05 AM   #1
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Default Winding torroidal transformers

Hi, I am considering building the m250 amp that I have seen on these pages, and I'm thinking about winding my own transformer for this project. Does anyone have any information on doing this before I get started? Thanks
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Old 7th December 2002, 10:13 AM   #2
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If you mean winding your own toroidal power transformer, don't.
Instead, if you mean winding your own toriodal output transformer, don't.

Sorry to say, but this is probably one thing which you are almost definitly better off to purchase from a proper reputable company. Your time would be much better spent designing the circuitry and layout, or spending your money on better coupling capacitors and/or otherwise.

Adrian
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Old 7th December 2002, 12:20 PM   #3
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Yup, for safety (mostly) and noise, winding your own tranformer is very difficult.

However it is feasable to unwind some of the coils of a secondary to reduce the output voltage, if you have a traffo that is rated too high for your requirements.
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Old 7th December 2002, 04:10 PM   #4
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I have made a toroid inductor with 10 meters 2 mm copper wire! Real heavy work!

The big problem (besides winding) is to calculate how long wire you need. Not very practical to realize the wire is too short....

As a conclusion: Don't make a toroid transformer by yourself.
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Old 7th December 2002, 04:32 PM   #5
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Thanks...I was afraid that that was the type of responses I would get! Does anyone know of any good dealers for transformers? Most of the companies that I have found on the internet don't seem to have what I'm looking for(or they're quite expensive). Oh, by the way,I was talking about power transformers. I found a company that has one for sale (surplus), and my idea was to re-wind the secondaries to accomplish my desired output. This is something that has always interested me, but maybe you're right, I should be spending my time learning more about amplifier design.
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Old 7th December 2002, 04:40 PM   #6
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It is a good question, and I'd like to know too. I've seen two resources on hand rolled transformers of the three leg laminated variety, which for the most part agree with each other. I haven't seen anything (yet) on two leg types (but I haven't looked too hard for that). I've found a few services for custom toroids, but didn't see any of the math behind it.
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Old 7th December 2002, 04:46 PM   #7
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Default Whaddya mean DON'T

Kiwi man -- oftentimes the only way to get the transformer you need is to roll your own -- this is particularly true from SMPS supplies for which inductance, leakage are important. But generally, if analyzing the problem as time = money, it's easier to just pull what you need from a catalog.

But, it's not that difficult. If you think of the "shuttle" used in weaving, you fashion one which will slip in the donut hole and you're good to go.

At any rate, I am blue in the face from recommending the ARRL handbook in these matters. They have a SMPS design with excellent directions for winding a multilayer torroidal transformer for a high power transceiver supply.
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Old 7th December 2002, 05:07 PM   #8
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If it is not absolutely necessary to have a toroid, it should be
considerably simpler to wind an ordinary EI-core transformer.
I have seen kits sold here in Sweden where the primary is
factory wound and you do the secondaries yourself. This should
be much simpler since you assemble the core after winding.
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Old 7th December 2002, 07:26 PM   #9
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How much power do you want to put out, at what impedance, and how many channels?

I have piles of power supply stuff, heatsink, transistors etc.

I live in Iowa so freight would be minimal.
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Old 8th December 2002, 06:53 PM   #10
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Toroid Corp of Maryland (http://www.toroid.com) sells power transformer kits. The 80 VA kit for example is $27 and comes with the primary and thermal breaker already installed. Wind on your secondaries, add leads to the secondaries, wind the finishing tape and you are done.

I have done this with good results a number of times. For a description of the transformer I use with my TubeDAC, take a look here:

http://quadesl.com/pdf/trans_inst.pdf

Now, having said that, I'll also say that it's a real pain. Low voltage windings like heaters or IC type levels, are fairly easy wth something like 40 turns. but a tube B+ with like 1500 turns is laborious, thumb muscle cramping work. But I've built some very complex transformers with many taps that would cost several hundred dollars for a custom unit (or you'd be using many descrete transformers). The TubeDAC transformer has a center tapped +-15 volt pair of windings for digital chips an idential pair of windings for analog chips, it's got two idenital heater windings that can be put in series or parallel for differnet output tubes. It's also got a 250 volt B+ winding. I put all that together for about $50. And I've still got a bunch of magnet wire left over for other transformer winding needs.

Sheldon
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