60Service Manual – SC900 34 - Scrub System, Cylindrical
Circuit Overview
The brush circuit has several prerequisites
to operate. All of the following must to be
true for the brushes to run:
• Key switch on
• Battery Voltage not low
• Machine in motion (even if zero speed)
• Brush deck lowered.
Starting at the motors and working back
toward the batteries; the brush motors are
connected directly to battery negative. On
the positive side, each motor has its own
circuit breaker, which is downstream from
the K2 relay contact.
The control coil of the K2 relay is in series
with the brush (deck lift) switch and the
K1 relay. This circuit receives power from
the Drive Controller’s Brake output, which
is active only when the drive controller is
commanding motion. The positive side is
always energized when the controller is
enabled, and the negative side is switched
to ground voltage when the machine is in
motion.
This circuit of the K2 coil, Brush Switch,
and K1 relay, along with the Drive
Controller’s Brake output, provides the
fundamental control of the brush motor.
This circuit is active only when all 4 of the prerequisite conditions mentioned above have been met.
The control coil for the K1 relay is in series with the hour meter. This aspect of the circuit provides the
low-voltage cutout feature to disable the scrub system when the batteries are running low. The hour meter
contains a Field Effect Transistor (FET), which is active (conducting) when the battery voltage is sufcient
for operation. The FET acts like a switch which connects the negative side of the relay coil to ground.
When the key switch is off, it disables the drive controller and also the K1 relay. This effectively disables all
machine functions.
BLK
BLK
PNK/WHTVIO
PNK/BLU
VIO/WHT
PNK/BLU
VIO
PNK
PNK
S1
SW, SPST KEY
S4
SW, BRUSH
RELAY, LVC
1
2
3
4
5
6
CURTIS 1228
KSI
5
BRAKE-
6
BRAKE+
14
D2
K1 RELAY, LVC
BATTERY GAUGE WITH HOURMETER
FET DRAIN
3
B-
4
D1
36 VDC
+ -
K2
COIL, BRUSH
K1
RED/GRNWHT/RED
WHT/RED RED/BRN
M
M2
MOTOR, BRUSH LEFT
- +
M
M3
MOTOR, BRUSH RIGHT
-+
CB3
25A
K2
BRUSH CONTACT
CB2
25A
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