| Electronics > Beginners |
| How is the current rating of a transformer determined? |
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| schmitt trigger:
There are of course, much better LED testers nowadays. But for my purpose, identifying the LED color, also a relative (visual) brightness check, it does its job. |
| IanMacdonald:
Main point to realise is that all rectifier and reservoir capacitor combinations have a less than unity power factor. The lower the series resistance of the winding and diodes, and the larger the reservoir cap, the worse this will be. Thus in real world use with a DC load the max current will be considerably less than with a resistive AC load. Modern tendency is simply to accept this situation, but in the early days the tendency was to use a 'pi filter' consisting of a small reservoir cap, series resistor or choke and smoothing cap. Which reduced the transformer loading for the same smoothing effect. I recall one model of portable TV that drew about 2A/12V but could easily burn out a 6A bridge rectifier. Reason was the use of huge reservoir cap and a transformer with very low winding resistance. Solution was to fit a 25A bridge. |
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