Wesley BC-620-4CA - Manual (Page 130)

Curtis 1234/36/38 Manual,
OS
11 B-3
Given the safety considerations involved in connecting electrical components
to the chassis or frame in battery powered vehicles, such filtering will usually
consist of a series inductor (or ferrite bead) rather than a shunt capacitor. If a
capacitor is used, it must have a voltage rating and leakage characteristics that
will allow the end product to meet applicable safety regulations.
The B+ (and B-, if applicable) wires that supply power to a control panel
should be bundled with the other control wires to the panel so that all these
wires are routed together. If the wires to the control panel are routed separately,
a larger loop area is formed. Larger loop areas produce more efficient antennas
which will result in decreased immunity performance.
Keep all low power I/O separate from the motor and battery leads. When
this is not possible, cross them at right angles.
ELECTROSTATIC DISCHARGE (ESD)
Curtis motor controllers contain ESD-sensitive components, and it is therefore
necessary to protect them from ESD (electrostatic discharge) damage. Most
of these control lines have protection for moderate ESD events, but must be
protected from damage if higher levels exist in a particular application.
ESD immunity is achieved either by providing sufficient distance be-
tween conductors and the ESD source so that a discharge will not occur, or by
providing an intentional path for the discharge current such that the circuit
is isolated from the electric and magnetic fields produced by the discharge. In
general the guidelines presented above for increasing radiated immunity will
also provide increased ESD immunity.
It is usually easier to prevent the discharge from occurring than to divert
the current path. A fundamental technique for ESD prevention is to provide
adequately thick insulation between all metal conductors and the outside envi-
ronment so that the voltage gradient does not exceed the threshold required for
a discharge to occur. If the current diversion approach is used, all exposed metal
components must be grounded. The shielded enclosure, if properly grounded,
can be used to divert the discharge current; it should be noted that the loca-
tion of holes and seams can have a significant impact on ESD suppression. If
the enclosure is not grounded, the path of the discharge current becomes more
complex and less predictable, especially if holes and seams are involved. Some
experimentation may be required to optimize the selection and placement of
holes, wires, and grounding paths. Careful attention must be paid to the control
panel design so that it can tolerate a static discharge.
MOV, transorbs, or other devices can be placed between B- and offending
wires, plates, and touch points if ESD shock cannot be otherwise avoided.
APPENDIX B: EMC & ESD DESIGN CONSIDERATIONS