PG DRIVES TECHNOLOGY I-DRIVE TECHNICAL MANUAL – INSTALLATION
There are two main methods.
1) Provide electrically conductive discharge or drain paths between the electrically conductive masses around the
machine.
This is best achieved by providing a drain wire, which connects all the electrically conductive masses around the vehicle
together. The path of the wire or wires should be kept as short as possible. In some applications a resistor of a suitable value may
be inserted in all or one of these lines. Varistors may also be used in some applications.
Resistors can prevent large ESD currents flowing that may cause unpleasant shocks to operators but at the same time prevent
differential charge build up occurring.
Varistors appear open circuit to battery voltages but will limit charge build up to a safe level. They can be used where a battery
ground circuit is the only drain path available.
2) Prevent charge build up.
The action of the vehicle travelling over certain surfaces or certain actions carried out by the vehicle (e.g. cleaning brush
operation) may cause a significant charge build up by all or part of the vehicle. Static dissipating straps, wheel materials or
careful material selection can reduce or prevent charge build up.
11.2.1 Control Panels
Control panels and their components should be made from non-conductive materials in order to prevent any form of
electrostatic discharge. This not only protects the control system but also prevents the operator experiencing shocks.
If the panels are made from a conductive material then a drain wire must be connected to the main chassis or other
conductive masses around the vehicle. On some designs the only available solution is to connect the panel to a battery ground
via a varistor. However, ESD may still cause disruption to the signals from the control panel as large discharges will cause
disturbances in the ground line.
Where conductive user control systems are used (e.g. metal toggle switches) the body must be connected to the panel
(assuming it is conductive). If the control panel is not conductive then the body of the control must be connected to the chassis
by drain wire or battery ground via a varistor. Some user control systems will be unsuitable, as they will provide an ESD path to and
from the outside world (perhaps by a hidden path) but no means of providing a drain path.
Membrane keyboards can provide a high degree of protection. However, they must be made of sufficiently thick material (the
supplier should be able to advise). Other design details such as ensuring the switch tracks are well away from the edge of the
keyboard and providing conductive barrier tracks can also improve reliability.
11.2.2 Electrical System to Chassis Paths
It is important to provide an ESD discharge path between the electrical/control system and any electrically conductive masses in
close proximity to it (chassis etc.). Failure to do say may result in uncontrolled flashovers leading to damage or malfunction.
All PGDT control systems incorporate conduction paths between the battery 0V connection and the heatsink/case. The screws
that mount the controller case or heatsink to the vehicle chassis or metalwork normally complete the circuit path between
electrical system and chassis. If the control system is mounted on a non-conductive surface then another means of providing the
circuit path must be provided.
PGDT control systems either incorporate an internal varistor or resistor in series with the battery 0V to heatsink/case connection. The
resistor is adequate for most purposes. However, if system ESD tests show a problem then a varistor should be fitted externally.
11.2.3 Electrical Components
Large electrical components such as motor casings can store appreciable amounts of ESD energy if they are not grounded. This
can flash over to sensitive circuitry. If a separate drain wire is not possible then a drain resistor or varistor connected to a power
circuit connection can be used. However, issues such as circuit isolation, potential standby battery drain and noise propagation
must be considered.
SK76977-07 57
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