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October 2004 SC2000 Manual – 177/52301 Rev G Page 27
10.1.21 Steering Potentiometer - For Dual Motor traction applications, the footbrake input can be
reassigned to be a steering potentiometer input.
10.1.22 Digital Switch Inputs
- The digital inputs on the controller can be configured as Active Low
inputs, where the switches are wired to B-ve, or as Active High inputs where the switches are
connected to B+ve. The SEVCON standard is Active Low, and is recommended for it’s low
impedance input stage and immunity to moisture related problems. Active High inputs are a
hardware option which must be specified when the controller is manufactured.
In addition a further configuration allows each input to be specified as normally open or
normally closed. Most switches are normally open, with the exception of the 2 speed cutback
switch inputs which are normally closed, so that a wire off type fault, or bad connection
initiates the cutback speed, rather than a higher speed. On compensated Pump systems the
Power Steer input can be conveniently configured as normally closed.
10.1.23 Contactors
- There are up to 8 outputs for driving contactors as described in previous
sections. It is also possible to reconfigure one of the outputs, normally contactor drive 8, as
an external LED or Lamp driver to allow dashboard indication of the controller’s integral LED.
The controller can diagnose open circuit (o/c) and short circuit (s/c) problems with certain
contactors, as described in the diagnostic section. Generally, following a request to open a
contactor, the controller will report a 4 flash fault and a calibrator message if a successful
operation was not detected after approximately 500ms. To help prevent against minor tip
contaminants causing spurious diagnostic trips when closing a contactor, if a closure is not
detected after 500ms, pulsing up to a maximum of 25% is allowed. This is designed to pass a
controlled amount of current to try and break through any contaminant present to allow
uninterrupted drive. If a closure isn’t detected on reaching 25%, then the contactor drive is
removed and a 4 flash fault is indicated.
An optional Line Contactor can be connected between the B+ terminal of the controller and
battery positive to help prevent large currents flowing through the battery connectors and into
the internal capacitors when the controller is first connected to the battery. After the keyswitch
has been switched, and once the capacitors have charged up (via internal resistance) the line
contactor will be energised. An internal diode fitted in the keyswitch line will prevent any
contactor energising if the polarity of the battery voltage is reversed. On Pump controllers the
Line Contactor also gives a mechanical break.
Under normal operating conditions contactors will operate without arcing. However, under
certain fault conditions, contactors may arc when opening. The Bypass contactor may also
arc during Bypass over-current drop out conditions.
10.1.24 Contactor chopping
- This feature allows 24 V contactors to be used at all battery voltages
24V - 96V, by continuously monitoring the battery voltage and chopping the contactor output
pins accordingly, to present an average voltage suitable for 24V coils. Chopping is selectable
by the calibrator. All the contactor drives will be either chopped or not chopped. It is not
possible to select individual drives to chop. Care must be taken to ensure that chopping is
always selected if 24V contactors are being used on battery voltages higher than 24V. In
applications > 24 volts contactors must be fitted with blow out magnets.
Chopping can reduce the overall dissipation in the coils and allows only one set of contactors
to be stocked for all battery voltages.
Chopping Frequency approx. = 650Hz (Slightly audible at higher battery voltages)
Typical contactor coil voltage during chopping = 16 volts.
Typical contactor coil voltage during energisation = 24 volts for 1 second.
There are 3 contactor chopping options available via the setup menu: Off, On and 24V. The
off setting is used for nominal battery voltage coils, and the On setting is for 24V coils on
higher voltage vehicles. Setting to 24V provides chopping for 24V coils and lamps without the
drop to 16V after 1s.
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