Chapter 2
Installation and Configuration
NI PS-15 Power Supply User Manual
2-10
ni.com
Back Feeding Loads
Loads such as decelerating motors and inductors can feed voltage back to
the power supply. This feature is also called return voltage immunity or
resistance against back-EMF (Electro Magnetic Force). The NI PS-15
power supply is resistant to this and does not malfunction when a load feeds
back voltage to the power supply, regardless of whether the power supply
itself is on or off.
The maximum allowed feed back voltage is 35 V
DC
. The absorbing energy
can be calculated according to the built-in large sized output capacitor,
which is specified in the
Output
section of Appendix A,
Specifications
.
Output Circuit Breakers
Standard miniature circuit breakers (MCBs) can be used for branch
protection. Ensure that the MCB is also rated for DC voltage. The
following tests show which circuit breakers the power supply typically
trips.
Note
Circuit breakers have huge tolerances in their tripping behavior. Therefore, these
typical tests can only be used as a recommendation or for comparing two different power
supplies. Furthermore, the loop impedance has a major influence on whether a breaker trips
or not.
Test 1
: Short circuit with S1 on the power supply end of the cable (loop
impedance approximately 20 m
Ω
). The input voltage was 230 V
AC
and the
load current was 0 A.
Figure 2-6.
Breaker Trip Test 1
AC
DC
+
–
Load
+
–
S1
Circuit
Breaker
I
Power
Supply
