- 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).
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.
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 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.