Brushless DC Motor
Maximum Continuous Stall Torque (T
C
) is the amount of torque produce at zero speed, which results in a 100 Cº
rise in temperature. Generally the highest operation temperature that should be allowed is 150 Cº and is a
combination of the ambient temperature and the temperature rise for a given operating condition.
Maximum rated Torque (T
R
) is the amount of torque that the motor can produce without demagnetizing the rotor.
The torque is only available for short durations. Also, it may not be possible to produce the Maximum rater torque
because of limitations of voltage and current (see peak torque).
Motor Constant (K
M
) is the rations of the peak torque to the square root of the input power at stall which 25 Cº
ambient temperature. The ratio is useful during the initial selection of a motor since it indicated the ability of the
motor to convert electrical power into torque.
K
M
= T
P
(Peak Torque / √P
P
(Peal Input Power)
Or
K
M
= K
T
(Torque Constant / √R
M
(Terminal Resistance)
Electrical Time Constant ( t
F
) is the ration of inductance (L
M
) IN henries, to the resistance R
M
IN ohms. This is
the inductance and resistance as measured across any two phases in a delta or wye configuration.
T
E
= L
M
/ R
M
Mechanical Time Constant (t
M
) is the time required to reach 62.3% of the motor maximum speed after the
application of constant DC voltage trough the commutation, ignoring friction, wind age and cross losses.
T
M
= J
M
* R
M
/ K
T
*K
B
Thermal Resistance (TPR) correlated winding temperature rise to the average power dissipated in the stator
winding. The published TPR assumes that a housed motor is mounted to an aluminum heat sink of specific
damnations. Additional cooling from forced air, water jacketing, or increased heat sinking decreases the motor
Thermal Resistance allowing higher power output then the published date.
Viscous damping (F
0
) gives an indication of the torque lost due to B.E.M.F in the motor when the source
impedance is zero. F
0
value can be represented as F
0
= K
T
Maximum Cogging Torque (T
F
) is principally the static
friction torque felt as the motor is rotated as low speed. The published value does not include the bearing friction of
a housed motor.
Number of Poles ( N
P
) is the number of permanent magnet poles of the rotor. For the QB Series this is generally a
total of six (three north and three south)
Design Voltage (V
P
) is the nominal voltage required to produce the peak torque when the rotor speed is zero and
the winding temperature is 25 ºC. as such V
P
is the product of I
P
and R
M
. at any temperature greater then 25 ºC, the
required voltage to produce peak torque increases due to the increase in winding resistance. The design voltage is
not a limit but a reference point for the date.
Peak Torque (t
P
) is the nominal value of developed torque with the rated current I
P
applied to the windings. For
each winding specified the product of peak current (I
P
) and nominal torque sensitivity (k
T
) gives T
P
unless the
maximum rated torque (T
R
) is reached.
Peak Current (I
P
) is the rated current used to obtain the nominal peak torque from the motor with nominal torque
sensitivity (K
T
). I
P
is generally the design voltage divided by the terminal resistance (R
M
).
Torque Sensitivity (k
T
) is the ratio of the developed torque to the applied current for a specific winding. K
T
is
related to the BEMF constant K
B
.
No load Speed (S
LN
) is the theoretical no load speed of the motor with the design voltage applied.
BEMF Constant (k
B
) is the ration of voltage generated in the winding to the speed of the rotor. K
B
is proportional to
K
T
.
Terminal Resistance (R
M
) is the winding resistance measured between any two leads of the winding in either a
delta or wye configuration at 25 ºC.
Terminal Inductance (L
M
) is the winding inductance measured between any two leads of the winding in either a
delta or wye configuration at 25ºC.
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