1. System Installation Requirements
1-15
TI 32P01J10-01EN
Crest factor
The crest factor is the ratio of the peak value to the eective value of the device input current.
F010304.ai
Input voltage waveform
Approx. 5 ms
Input current waveform
Effective value
Peak value
Effective value
Peak value
Crest factor =
Figure Input Voltage and Input Current Waveforms
Crest factor = Peak value of device input current / Eective value of device input current
The crest factor must be considered for the input current supplied to every device connected to
the system when estimating the power output capacity in selecting the power unit.
Approximate device crest factors should be as follows:
100-120 V supply voltage: Crest factor About 3.
220-240 V supply voltage: Crest factor About 6.
Common Method to Determine Power Unit Capacity
The following shows the commonly used method used to determine the power unit capacity
taking the crest factor into consideration - the nal determination should be made in consultation
with a power unit manufacturer:
• If the specication of power unit crest factor (the peak current value allowable for the
eective current value) is larger than the above device crest factor, the power unit can be
used for up to full rated capacity. However, in-rush current, backup time, reserve capacity,
etc., must be separately taken into consideration.
• If the power unit crest factor is smaller than the device crest factor, the power unit capacity
needs to be calculated in the expression shown below. In-rush current, backup time, reserve
capacity, etc., must be separately taken into consideration.
Power unit output capacity = Total device power consumption x Capacity coecient
Capacity coecient = Device crest factor / Power unit crest factor specication
Nov. 27, 2015-00
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