Patrick Lawler wrote: > > Recently, I asked a question concerning harmonic specifications and a > system containing a 120W switching supply in parallel with an intermittant > 450W resistive heater. I came up with two positions that support harmonic > measurement while the resistive load is powered on (the system passes test > under these conditions). > > Annex C discusses test setup conditions. The first paragraph states that: > " ... controls or automatic programs shall be set to produce the maximum > harmonic components under normal operating conditions ... " > > Case 1 - 'Control setting' corresponds to cycling between 120W and 570W. > Considering the radical change in input power (120W -> 570W), there might > be enough parasitic effects that increase harmonics slightly during the > high power heating period. Inherent distortion of the AC line voltage > alone would be magnified during the high power operation. The harmonics > are higher during high power operation, therefore harmonics are measured > at 570W. The less-stringent Class A limits are applied. > > A difference in harmonics could be generated on purpose by switching a 5W > dummy load onto the DC output of the switcher, concurrently with the 450W > resistive load operating. Again, because the harmonics are higher during > the 570W period, this causes the Class A limits to be applied. > > Case 2 - Normal operating condition: 120W or 570W? > The time when the resistive heater is on, and the system input power is > 570W, represents normal operation. This causes the Class A limits to be > applied. > This is supported by the safety report and nameplate rating that > reference an input power of 570W. The time when the resistive load is > off represents idle time, and is not representative of normal operation > (this product does function as a heater, after all!). > > Comments?
When someone asks me a question such as this, I always back up to - What is the purpose of using this product? Once past this point it's easy to decide what is the "Normal Operating Condition" and from there which 'worst case' scenerio. ************************************************************ ------------------------------------------------------------ The comments and opinions stated herein are mine alone, and do not reflect those of my employer. ------------------------------------------------------------ ************************************************************
