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In a linear load, the Crest Factor is 1.414. However, in a general purpose SMPS, due to its non
linear nature, this factor will be much higher – in the region of up to 4. This will mean that for a
particular rated RMS current (applicable for a linear load), the general purpose SMPS will draw
much larger peak currents – approx. up to 4 times more than its rated RMS current.
Same kind of problem occurs even with electronic CFL lamps and electronic transformers used in
spot lights.
If an XM Series UPS is used to power the SMPS beyond its rated peak power capacity, it will be
forced to deliver higher peak currents resulting in triggering of the XM Series UPS’s over current
protection circuits. Thus, for safe operation, the continuous RMS current rating of the XM Series
UPS should be at least 2.8 times the continuous RMS current rating of the SMPS.
Peak current of XM Series UPS = Peak current of SMPS
Or
RMS current of XM Series UPS X 1.414 = RMS current of SMPS X 4
Or
RMS current of XM Series UPS = 4/1.414 XRMS current of SMPS
Or
RMS current of XM Series UPS = 2.8 X RMS current of SMPS)
Alternatively, the continuous power rating of the XM Series UPS in Watts / VA should be at
least 2.8 times the continuous power rating of the SMPS in Watts / VA
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General