Consider the arrangement shown above (Figure 1). A primary switching
cabinet (Application #1) is powered by a 480 W 24 VDC power supply
(the RACPRO1-T480/24V). A secondary switching cabinet (Application #2)
with a load of 5 A load is supplied from the same power source via a
25-meter-long cable. To enhance protection, the remote application includes a DC circuit breaker.
Problem: Voltage Drop along Long Cable
A 50-meter cable (25 meters there and back) with a cross-section of 2.5 square
millimeters has a total resistance of 174 milliohms. The fuse switch has an internal
resistance of 56 milliohms. Application #2 has a typical load of 5 A.
The voltage at application #2 is calculated as follows: power supply output voltage minus
R x I, i.e. 24 V minus (5 A x 230 milliohms). The result is 22.85 V. This supply voltage
is too low for a 24 V nominal supply.
Solution: Use the output voltage regulator RACPRO1
Vout to compensate for the voltage drop
The RACPRO1 series includes a front panel adjustment trimmer that allows fine-tuning
of the output voltage to offset voltage drops in long cables (Figure 2).
In this
example, the output can be trimmed up to 24.6 V, balancing the voltage drop.
Application #1 receives 24.6 V (600 mV above nominal). Application #2
receives 23.4 V (600 mV below nominal). Both supply voltages remain
1within an acceptable ±2.5 percent range.
Figure 2: Output Voltage Trim
