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RE: [TCML] Meters (was Variac)

Here is a brief AC meter tutorial.

AC Volt meters:
They measure voltage and do not know or care about current. Meters can be readily found with a 150 or 250 Volt scales as appropriate for your coil.

AC ammeters:
Similarly to the Voltmeters, these know nothing and care nothing about the voltage up to a certain HV point. These measure current. These can be readily found that can measure up to about 20 amps without any shunts or current transformers. Beyond about 20 Amps, you would normally use a current transformer with a standard AC Ammeter. These current transformers are described in a ratio relating the rated input and output current. For example, a transformer might be described as 100:5. In this case, with 100 amps input, you get 5 Amps output. This would usually be directly connected to a meter rated for 5 Amps full scale. It would have a face showing 100 amps full scale. It would also be possible to add a low ohm resistor in series with the meter and transformer that could be connected to an oscilloscope for waveform viewing. This would be useful to optimise your power factor which will minimize the current draw.

Just for the fun of it, I have installed a pair of 100:5 current transformers and 5 Amp meters with 100 Amp scales on my house AC in my circuit breaker panel. It is interesting some times.

Meters and current transformers of these types are readily often available on Ebay.

I have a few 100:5 current transformers that I am not using if anyone is interested. I can also provide any custom current transformers for smaller currents that could be made to work with almost any DC meter that you may have laying around.

Skip Malley

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