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Saturday, February 15, 2014

Recycle Transformers

Let's save our mother earth -> recycle transformers. Before we go further, I'd like to thank GS Ch'ng as this article is contributed by him. I've done some minor editing to make it better for Web presentation.

Recycle Transformers
Above are DIY tube power transformer using recycled transformer cores!
  • The bigger is version is a 100VA transformer. Input is 230V, output are 200V 0.5A, 6.3V 4A, 2.5V 7A and all used aluminum magnet wire.
  • The smaller transformer is 50VA. Input is 230V (copper), output are 300V-0V-300V (copper), 5V 2A (aluminum), 6.3V 2A (aluminum). 
I like to use aluminum wires because they are cheaper. Therefore, I can use for practices without burning my pocket.

The above 100VA power transformer operates at 1 Tesla and 50VA power transformer operates 1.2 Tesla. Usually this is the standard. The formula for turns ratio is as follow:
Volts per turn = 4.44 x AC x Freq x Tesla
  • AC = magnetic path cross section area in meter square
  • Freq = operating frequency 50Hz / 60Hz
  • Tesla = magnetic flux density.
    • For very old poor core, it can be set as 0.8 Tesla.
    • Normally I set as 1 Tesla. 
    • Some better core materials can operate as high as 1.5 Tesla.
Example, for EI57 core and stack up of 20mm,  we have about 20mm x 20mm of magnetic path cross section, converting to meter square = 400um2.

4.44 x 400um2 x 50hz x 1tesla = 88.8mV per turn
1 Volt = 11.26 turns (assume 11 turns for easy calculation)
  • For input voltage of 230V, # turns = 230 x 11 = 2530 turns
  • For output voltage of 12V, # turns = 12V x 11 = 132 turns
The wire size is depand the current density, typically what I found is 3A/mm2. Some can be as high as 6A/mm2.

The lower the Tesla value is set, the more turns it needs, making it hard to fit the core. For higher Tesla value, the Eddy current is higher due to core loss is higher and therefore it gets hotter during operation.

This article is to encourage more (transformer) DIYer to convert the junk steel cores to valueable tube parts.

*** Extracted from GS Ch'ng's posting.

If you've any questions or comments, please use the form below and perhaps GS or we can help to answer them when available.

J&K Audio Design
16 FEB 2014.

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* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.

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