Baldor 23H Series Installation & Operating Manual page 141

tions and current is calculated from the relationship:
T = K I
T
where K is the torque constant from Figure 5.
T
Figure 5. Relationship between KE and KT for a brushless motor when
driven with a DC control versus an AC control
Voltage constant is measured as V/KRPM peak (phase to phase). The RMS values are determined
by multiplying by the value in the table:
For DC drive
For Sine drive
As an example, suppose you measure the sinusoidal waveform as 75 V/KRPM peak.
For a DC drive, the equivalent voltage constant is 71.2 V/KRPM; the torque constant would be 96.3
oz-in/amp; and the current required to develop 180 lb-in of torque is:
T = K I
T
180 = 96.3 I
16
or I= 29.9 amps
For an AC drive, the equivalent voltage constant is 53 V/KRPM; the torque constant would be
124.2 oz-in/amps; and the current required to develop 180 lb-in of torque is:
T = K I
T
180 = 124.2 I
16
or I = 23 amps
Conclusion
Torques developed by the brushless motor depends upon the control technology used. An easy
way to determine the type of control is to look at the feedback scheme. The DC control typically
uses Hall sensors for feedback, where the AC control typically uses resolvers.
Application Notes
English
K 0.95 V/KRPM
E
K 1.285 oz-in/amp
T
K 0.707 V/KRPM
E
K 1.656 oz-in/amp
T
(Note: Divide 96.3 oz-in/amp by 16 to obtain lb-in/amp)
Page 21
Metric
0.009076 v/r/s
0.009076 N-m/amp
0.006754 v/r/s
0.011698 N-m/amp