Electronics > Beginners

Most good transformers I pull are "shorted", whats going on?

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perdrix:
60Hz transformers used on 50Hz will run hotter at the same voltage because they will pull more current.

Why - the inductance is the same but the current I = V/Z will be higher as Z will be lower (Z = 2πfL).

So if you need to use the same transformer for both 50Hz and 60Hz, you shouuld size the windings etc. for use at 50Hz.  It should then be OK to use at 60Hz (subject to saturation).

David

Zero999:
Small 60Hz transformer work fine on 50Hz because they have a high enough resistance to limit the extra current and they're also designed for a slightly higher voltage, than the rating. Note that the power rating will be halved, since the maximum current will remain the same. Incidentally, it's fine to run a transformer at a much lower frequency, as long as the voltage is reduced proportionally, so a 240V 50Hz transformer will happily run at 25Hz, but at a maximum voltage of 120V. It's also possible to run at a higher voltage, than the rating, if the frequency is increased, but only up to a certain point, when hysteresis and eddy losses or the maximum voltage rating of the insulation become limiting factors.

In this case, a switched mode power supply transformer will be designed for operation at >50kHz, so won't be able to be used for any serious amount of power at 50Hz.

Gyro:
I remember (or rather don't remember!) an HP or Tek scope that was prone to transformer failure due to saturation on 50Hz in Europe.

As I say, I can't remember the model, but it showed that even the 'big boys' could sail a bit too close to the wind at times.

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