Applied Motion SV7-C-CE - Manual (Page 22)

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SV7 Hardware Manual 920-0012F
12/18/2014
Choosing a Power Supply
When choosing a power supply, there are many things to consider. If you are manufacturing equip-
ment 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.
Voltage
PWM drives like the SV7 work by switching the voltage to the motor terminals on and off
while monitoring current to achieve a precise level of phase current. Depending on how fast you
want to run the motor, you may not need a power supply equal to the rated voltage of the motor.
To get a rough estimate of how much voltage you need, multiply the voltage constant of the motor
(Ke) by the maximum speed required for your application. For example, if you want to operate
the M0100-103-4 at 4000 rpm, you’ll need V = Ke * rpm = (4.6V/krpm)(4 krpm) = 18.4 volts. To
produce any real torque at that speed, add 30%, for a total of 24 V.
Always check the “no load” voltage of the power supply before using it with the drive, to be sure
that it does not exceed 80 VDC.
Current
The maximum supply current you could ever need is three 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 SV servo uses a switching amplifier, converting a high volt-
age and low current into lower voltage and higher current. The more the power supply voltage
exceeds 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. Furthermore, the servo loop only commands the amplifier to provide as much current
as load conditions require.
We recommend the following selection procedure:
1. If you plan to use only a few drives, get a power supply with at least 3X the rated con-
tinuous current of the motor.
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 moni-