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oscilloscope probing on mains voltage through transformer
OwaisAhmed:
can i probe secondary side of transformer on oscilloscope. or does it still count as short through earth to neutral
mansaxel:
If it is a full transformer, no problem.
The waveform might not be 100% accurate; a transformer has distortion.
Do note that a typical Variac and all forms of Autotransformers not qualify as safe to do this on; since they're not galvanically isolated.
When in doubt, measure resistance (preferably with an insulation tester so test voltage will be closer to working voltage) betweeen primary and secondary. On a transformer not connected to the mains of course.
NiHaoMike:
One thing you can do is to use a transformer rated for a higher primary voltage (for example, 240V transformer on 120V mains or 380V transformer on 240V mains) so that it would be a lot more linear.
Kleinstein:
Especially small transformers (< 5 VA) often rund quite close to saturation and may show quite some distortion. Instead of 1 transformer for a higher voltage one could also use 2 transformers with a similar secondary voltage: primary in series and secondary in parallel.
The nominal transformer voltage is with nominal load. The no load output is a bit higher than the nominal voltage ratio.
Another alternative way is using the transformer as a current transformer with a relatively large resistor in series to convert mains voltage to current and than back to voltage on the secondary. So something like 100 K in series to the primary and than a rather low resitor (e.g. 10 or 100 Ohms - depends on the transformer ratio, aim for a low output voltage) at the secondary. I have not tested this, but it could work resonable well even with a relatively small transformer.
Zero999:
Yes, it will work. A step-down transformer is ideal, for low frequencies.
The secondary voltage is normally a little higher than the rating. Connect it to the mains, measure the actually primary and secondary voltages and calculate the scaling ratio.
Over what bandwidth? I've found small mains transformers to be fairly linear up to a few tens of kHz, with a sharp resonant peak at around 100kHz.
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