|
The
Problem:
|
Screened
\ twisted \ bundled cables have significant parasitic capacitance
between the conductors. The capacitance increases with the increase
of the cable length. A typical value is 200 pF per meter or
60pF per feet.
Using long cables for the motor - amplifier connection might
cause short circuit condition in the power stage for short durations
of time. The magnitude of the short circuit depends on the capacitance
value and the operating voltage. |
| Those
short circuits cause: |
| 1. |
As
a rule of thumb we assume that cable length under 10 meters
(30 feet) do not cause any significant problem. |
| 2. |
In
those cases where a long cable is required, additional inductance
must be connected between the cable and each of the amplifier
outputs. An inductance value of 150-200 µH is typically
sufficient. This can also be acheived by winding each of the
cable conductor around a separate toroid. |
| 3. |
Using
separate conductor/cable for each amplifier's output. The conductors
must not be twisted or bundled together. |
| 4. |
Use
a cable with minimum parasitic capacitance. This is not a practical
solution as it is difficult to source such a cable and its cost
is very high. |
