Neil,
If the power supplies are intended for audio equipment, where the peak
power required for some types of music can be 10 times the average
power, I could buy the manufacturer's explanation. Otherwise their
explanation of how they pass EN 61000-3-2:2000 sounds bogus to me.
An EN 61000-3-2:2000 harmonics test will usually take between 2.5
minutes and 25 minutes (Section 6.2.4, Test observation period).
Beginning 10 seconds after the EUT is turned on (Section 6.2.3.2,
Starting and stopping), the harmonic current drawn by the equipment
under test (EUT) is measured and analyzed in 1.5-second time chunks
(Section 6.2.2, Measurement Procedure).
Section 6.2.3.3, Application of limits, specifies that for an individual
harmonic current (one frequency), the average over the entire test
observation period must be under the specified limit. But the average
over a 1.5 second time chunk may exceed the specified limit by up to
50%.
This makes more sense when we read Annex C, detailing the test
conditions for various types of equipment. Audio amplifiers stand out
because of the wide normal variations in output-power, and thus current
draw. Similarly, washing machines stand out because certain modes may
require stopping and re-starting the motor, and starting an induction
motor can draw five to seven times its full-load running current.
A brief, infrequent burst of input current is not going to cause
overheating of neutral wires or power transformers, which is the major
concern of EN 61000-3-2. Do an Internet search for "triplen" if you
would like to read more about this subject.
John Barnes
dBi Corporation
http://www.dbicorporation.com/
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