Specifications
Form Factor
NOTE: THE DASHED LINES (---) ON THE CURVES ON
THE GRAPH, RIGHT, INDICATE WHEN THE DRIVES ARE
OUT OF THEIR OPERATING RANGE.
orm factor is a figure that indicates how much the
current departs from pure DC. Mathematically,
form factor is the quotient of RMS current and average
(AVG) current.:
RMS Current (AC)
AVG Current (DC)
Unity form factor represents pure DC. Values greater than
one indicate increasing departure from pure DC. The
practical effects of larger form factor input into a motor
include increased heating, decreased brush life, and
diminished motor and system efficiency. The form factor
rating of a motor defines the maximum form factor for
which the stated motor ratings apply. The output form fac-
tor of the drive should never exceed the form factor rating
of the motor.
An unfiltered SCR drive output is not a fully rectified sine
wave at maximum speed. Form factors of approximately
1.37 are typical for an unfiltered SCR drive operating at
full speed. At lower speeds, the form factor of the arma-
ture output increases. The published form factor rating of
an SCR drive indicates only its best (lowest) form factor
value.
The form factor of filtered SCR drives at full speed can be
as low as 1.05, but the typical value is closer to 1.10.
Filtering raises both the RMS and the average current val-
ues and it reduces their difference. Filtered SCR drives
exhibit less deterioration in form factor at lower voltage
outputs than unfiltered SCR drives, but the form factor
does rise with reduced speed, further reducing motor effi-
ciency.
The form factor of filtered PWM drives does not exceed
1.05, nor does it deteriorated as speed reduces. The form
factor rating of PWM drives is valid over the entire speed
range, which accounts for the larger speed range of fil-
tered PWM drives. The low form factor can be a substan-
tial system advantage over SCR drives in terms of efficien-
cy of operation and lower maintenance costs.
Reference
Maximum Output Voltage
(115 VAC Input)
A 75 VDC
B 90 VDC
C 115 VDC
D 130 VDC
F
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REFERENCE