Creating Custom Motor Files
B-9
Installation Manual for Models ODM-005, ODM-005i, ODM-010, ODM-010i, ODM-020 and ODM-020i
Electrical Parameters
Resistance
The resistance value is the measured
phase-to-phase
resistance of the stator winding in Ohms. The
resistance is used to set the current regulator gains, and is critical to current loop performance. The
resistance value can be in the range from 0.0039 to 255.9961
Ω
.
The ratio of motor inductance to motor resistance is defined as the electrical time constant of the motor.
This value should always be checked to verify that it is in an acceptable range. Electrical time constants
less than ~1mS, and higher than ~50mS, present difficulties for current regulation and should be avoided.
Some manufacturers specify the resistance in Ohms/phase. The phase-to-phase resistance requested by
OMNI LINK is twice the per phase value.
Inductance
The inductance value is the measured
phase-to-phase
inductance in milliHenries of the stator winding.
The inductance is used to set the current regulator gains, and is critical to current loop performance. The
inductance value can be in the range from 0.0039 to 255.9961mH.
The ratio of motor inductance to motor resistance is defined as the electrical time constant of the motor.
Always verify this value is in a reasonable range. Electrical time constants less than ~1mS, and higher
than about ~50mS, present difficulties in the current regulator and should be avoided.
Inductances less than ~1mH suffer from high current ripple, and are not recommended for use with the
OMNIDRIVEs.
Some manufacturers specify the inductance in milliHenries/phase. The phase-to-phase inductance is twice
the per phase value.
Rating Parameters
Continuous Torque
Continuous torque specifies the rated current of the motor in peak Amps. (Note: Continuous torque is
peak Amps, rather than rms.) The drive uses the continuous torque current value in its motor thermal
protection software. The drive generates a fault if the square of the actual current, after passing through
a low pass filter, exceeds the square of the continuous torque current value. The square is used because
the power dissipation in the motor is approximated as I
2
R losses. The continuous torque value may be in
the range from 0.0078 to 255.9922 Amps.
Some manufacturers specify the rated current of a motor in rms Amps. To convert from rms Amps to
peak Amps, use the formula:
Occasionally a manufacturer specifies only the rated torque, and does not include the rated current spec-
ification. In such a case, the rated current can be computed using the rated torque and the torque constant.
A factor of 1.1 is included to allow for degradation of the torque constant at high temperatures, etc. The
formula, assuming the torque constant has already been converted to N-m/A(peak), is:
1 Amps
Amps(rms)
⋅
=
⋅
1414
.
I
1.1
rated torque in N m
K
RATED
T
=
⋅
⋅
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