[Amps] current in primary of microwave oven transformer

[Dr. David Kirkby]

Angel Vilaseca wrote:
> Hi,
>
> I have a microwave oven transformer that I plan to use for my next HV 
> power supply.
>
> With the secondary unloaded and 220 V into the primary, I measured  670 
> mA through it.
>
> This is a 220 V unit so that means 147 Watts, with no load on the 
> secondary. Magnetic shunts were taken off.
>
> I have another two MOTs. Made the same measurement. They all behave the 
> same.
>
> On the other hand, the transformers do not hum, not smoke, not even get 
> hot, so I was wondering if this primary current could be "wattless" 
> current, that is a current that is out of phase with voltage.
>
>
> Should I worry about this amount of "idle current"?
>
> Is this behavior particular to microwave oven transformers?
>
> Is there a way to know what is happening here without using a double 
> trace oscilloscope?
>
>
> Vy 73
>
> Angel Vilaseca HB9SLV
>
>   
The power dissipated is V*I*Cos(phi) where phi is the phase angle 
between the voltage and current. (Assuming they are pure sine waves of 
course, which is not necessary so.)

There are ICs around which measure phase, but a scope is the easiest way.