Danaher Motion
05/2008
Appendix B – Cables
S200-VTS Product Manual
119
APPENDIX B – CABLES
B.1
Long Cables
The DC resistance of long motor power cables steals some of the available voltage when motor
current is high. The principal effect of this is some reduction in peak motor power so
acceleration and deceleration times can be longer. The cable resistance has no significant
effect on lower speed torque or top speed. For most applications, the loss of performance is
small with cables up to the maximum cable length specification. Do not operate an S200 DC
Input Drive with long cables at the lower end of the bus voltage range because too much of the
available voltage is stolen by the cable resistance.
For S200 AC Input Drives, the DC resistance of the motor power cable is rarely an issue
because the voltage drop across the resistance is usually a small fraction of the available
nominal bus voltage.
For S200 DC Input Drives with long cables and demanding dynamics, the 14 AWG cable is
preferred over the 18 AWG cable. Cable voltage drop vs. cable length is shown in the table
below.
Cable Voltage Drop vs. Length
V
LOSS
in cable as
a percent of 75 V bus
Cable
Length
(meter)
AWG 18
2 x Rphase
(ohm)
V line-line
0-peak at 0.866
x 18 ARMS
AWG 18 cable
AWG 18 cable
AWG 14 cable
3
0.126
2.77
3.7 %
1.5 %
10
0.413
9.09
12.1 %
4.8 %
25
1.03
22.7
30.3 %
12.0 %
50
(50 m not recommended with
DC 6/18 ARMS)
N/A 24.0
%
B.2
Custom Composite Cables
A composite cable has both feedback and power wires within one overall cable jacket. One of
the critical requirements for a composite cable is to provide a high degree of isolation between
the power and feedback wires. With 240 VAC-connected drives the power wires can have up to
400 V
peak-peak
fast switching PWM waveforms that can couple to the feedback wiring. These
coupled signals can cause communication errors between the Smart Feedback Device (SFD)
and the drive.
Danaher Motion has developed and sells a composite cable that has very good isolation
between the power and feedback sections. It is strongly recommended that this raw cable be
used for custom composite cable designs. Contact your Danaher Motion sales representative
for additional information.
If this cable does not meet your specifications, the following are some guidelines for custom
composite cable development.
Due to the complexity of modeling and understanding cable coupling, a new composite
cable needs to be prototyped and tested to have confidence that it will be reliable.
1) Composite cable should have double concentric feedback shields – one shield within
another.
The raw composite cable that has been tested and is known to work well with the S200 has the
following structure:
double, concentric shields
around the feedback wires, plus an outer shield
around the whole cable (see diagram below). This type of raw cable is strongly recommended.
Testing shows double, concentric, shielding is ten times better than single shielding at reducing
coupling from the power wires to the feedback data wires.