You could have simply said that the power factor of the load was low. The
power meter on your house measures loads as if the power factor is 1.0. The
power factor of an old power supply that has jumper selectable voltage
inputs is probably 0.65. Modern power supplies that have univeral
(85VAC-270VAC) inputs have power factor correction circuits to correct the
power factor to nearly 1.0.

At 03:00 AM 10/25/02 +0200, der Mouse wrote:
>> Wouldn't it be easier to just use an ammeter?
>
>When the load is not simply resistive, multiplying RMS amps times RMS
>volts will mis-estimate actual power consumed, sometimes drastically.
>(For example, if you have a purely capacitive or inductive load,
>current will be 90 degrees out of phase with voltage, and power
>consumed will be zero, even though current is flowing.  Power consumed
>is the integral of instantaneous current times instantaneous voltage;
>with an inductive or capacitive load, RMS volts times RMS amps will
>overestimate actual power drawn.
>
>Now, when the load is a switching power supply, current drawn consists
>of a spike at the peak of each voltage half-cycle, rather than anything
>even close to a sine wave.  In this case, actual power is something
>more like RMS amps times peak (not RMS) volts; measuring the current
>and multiplying by the nominal voltage will *under*estimate power
>consumed....
>
>Or, of course, I could be burbling nonsense.  Any power engineers here?
>
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Michael Thompson
E-Mail: M_Thompson@IDS.net