Curtis PMC 1209B/1221B/1221C/1231C Manual
11
Forward/Reverse Contactors
The forward/reverse contactor coils must match the vehicle
’
s battery voltage. The
maximum allowed coil current for each contactor is 1 amp. Use of a changeover
contactor set
—
such as the Albright SW202 (available from Curtis)
—
is recom-
mended. Alternatively, two single-pole, double-throw (2
×
SPDT) contactors may
be used. Although inexpensive
“
can
”
type solenoids may be used, their ratings are
typically not suf
fi
cient for long life.
A coil suppression diode should be used on each of the forward/reverse
contactor coils. Curtis PMC p/n MP-1 (rated at 100 volts, 3 amps) is appropriate
in systems up to 72V. In systems with nominal voltage >72V where the contactor
coils are energized from the battery pack, diodes with breakdown voltages of at
least 200 volts should be used.
Forward/Reverse Switches
The forward/reverse contactor coils can be operated by any type of single-
pole, double-throw (SPDT) center-off switch capable of switching the coil
current. Toggle or rocker switches are generally used.
If your controller has the optional high pedal disable (HPD) feature and you
plan to wire it for freewheeling, the best switch to use is a double-pole, double-
throw (DPDT)
“
hesitation switch
”—
a toggle switch with a mechanism that
forces it to stop in the center (neutral) position before going into the opposite
direction. If a standard switch is moved quickly from one direction to the other,
it may not be in neutral long enough to actuate HPD, and the motor will plug
brake instead of freewheeling. The switch must be in neutral for several millisec-
onds to actuate HPD.
Keyswitch and Interlocks
The vehicle should have a master on/off switch to turn the system off when not
in use. A keyswitch is typically used for this purpose.
Various other safety and convenience interlocks may also be used to prevent
motor operation during certain conditions. For example, a battery charger
interlock can be used to prevent operation during charging. Similarly, a seat
switch can be used to turn the vehicle off when the operator gets up from the
driver
’
s seat. The contacts of these switches should be rated for the total coil
currents of all the contactors they operate.
Keyswitch Relay
A keyswitch relay is recommended for use in high voltage systems. This relay
prevents the full battery pack voltage from being brought into the operator
compartment through the throttle microswitch, potentially exposing the operator
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