AMCI SD4840EK, User Manual

Page: 82 / 104

M
OTOR AND
P
OWER
S
UPPLY
S
IZING
SD4840EK User Manual
ADVANCED MICRO CONTROLS INC.
82
1.4 Power Supply Sizing
The power supply can be sized based on the power the motor must generate during its operation. As a general
guideline, your supply should be able to produce 150% to 175% of the power the motor can produce. The
power and torque curves on the previous pages can be used to determine the maximum power the motor can
generate over its speed range.
Note that the power value that you should use is the
maximum
power value over the range of speeds that the
motor will be operated at. The power generated by the motor decreases towards the end of its usable speed.
Therefore, the power generated at your machine’s operating point may be less than the maximum the motor
can generate at a lower speed.
Example 1:
An SM2340-130 will be running at a maximum of 7 RPS and a 48 Vdc supply will be used. Based
on the power curve in figure T1.1 on page 80, the combinations will generate a maximum of 40
Watts. Therefore a 48 Vdc supply with a power range of 60 W to 70 W can be used in the applica-
tion.
Example 2:
An SM2340-240 will be running at a maximum of 9 RPS and a 24 Vdc supply will be used.
Based on the power curve in figure T1.2 on page 80, the power at this speed is 45 W, but the
maximum power over the entire speed range is 55 W, which occurs at 7 RPS. Therefore, the 55
Watt value should be used, and the 24 Vdc supply should be able to generate 83 W to 97 W.
The two tables below shows the suggested power supply sizes based on the maximum power the motor can
generate over its entire speed range.
Table T1.1 SM23 Suggested Power Supply Ratings
Regeneration (Back EMF) Effects
All motors generate electrical energy when the mechanical speed of the rotor is greater than the speed of the
rotating magnetic fields set by the drive. This is known as regeneration, or back EMF. Designers of systems
with a large mass moment of inertia or high deceleration rates must take regeneration effects into account
when selecting power supply components.
All AMCI stepper motors are low inductance motors. Back EMF is typically not an issue unless there is a
gearhead attached to the motor and it is driven by hand. In these instances, the motor acts as a generator. With
the speed of the motor multiplied by the ratio of the gearhead, this can lead to large enough voltage spikes to
damage the attached power supply.
The first line of defense against regenerative events is an appropriately sized power supply. The additional
capacitance typically found in a larger supplies can be used to absorb the regenerative energy. If your applica-
tion has high deceleration rates, then a supply that can deliver 175% of peak motor power should be used.
The second line of defense is a regeneration resistor, also known as a braking resistor. Braking resistors, and
their control circuitry, are built into AMCI AC powered drives. They are not included in the SD4840EK prod-
ucts because of the limited ability to dissipate the heat generated by the resistor. An external braking resistor
and control circuitry can be added to the system if needed.
SM2340-130 SM2340-240
SM34-450 &
SM34-850
Motor
Power
150%
Supply
175%
Supply
Motor
Power
150%
Supply
175%
Supply
Motor
Power
150%
Supply
175%
Supply
Supp
ly
Vo
lt
a
g
e
24 Vdc 53W 80 W 93W 57 W 86 W 100 W Not Applicable
48 Vdc 105 W 158 W 184 W 135 W 203 W 237 W 135 W 203 W 237 W