10
STR2 Hardware Manual
920-0059A
4/20/2012
Choosing a Power Supply
When choosing a power supply, there are many things to consider. If you are manufacturing
equipment that will be sold to others, you probably want a supply with all the safety agency
approvals. If size and weight are an issue get a switching supply.
And you must decide what size of power supply (in terms of voltage and current) is needed for
your application.
Applied Motion offers three powers supplies that are excellent matches for the STR2 drive:
PS50A24 (24V, 2.1A), PS150A24 (24V, 6.3A) and PS320A48 (48V, 6.7A).
Voltage
Your motor can provide more torque at higher speeds if a higher power supply voltage is used.
Please consult the speed-torque curves later in this manual for guidance.
If you choose an unregulated power supply, make sure the no load voltage of the supply does
not exceed the drive’s maximum input voltage specification.
Current
The maximum supply current you could ever need is two times the motor current. However,
you will generally need a lot less than that, depending on the motor type, voltage, speed and
load conditions. That’s because the STR uses a switching amplifier, converting a high voltage
and low current into lower voltage and higher current. The more the power supply voltage ex-
ceeds the motor voltage, the less current you’ll need from the power supply. A motor running
from a 48 volt supply can be expected to draw only half the supply current that it would with a
24 volt supply.
We recommend the following selection procedure:
1. If you plan to use only a few drives, get a power supply with at least twice “per
phase” current rating of the step motor. Example: for a motor that’s rated for 2 A/phase use a 4
A power supply..
2. If you are designing for mass production and must minimize cost, get one power
supply with more than twice the rated current of the motor. Install the motor in the application
and monitor the current coming out of the power supply and into the drive at various motor
loads. This will tell you how much current you really need so you can design in a lower cost
