16Service Manual – SC900 20 - Wheel System, Traction
Circuit Description (Idle)
Main battery power is always
present at the speed controller
from the battery, but the controller
remains inhibited until the KSI
input is brought to positive battery
voltage. When the main key switch
is closed, positive battery power is
provided to the KSI input on the
drive controller, and also enables the
positive side of the reverse switch on
the drive handle.
In this state, the drive controller is
enabled, but is not active until one
of the drive switches is closed. When
the drive controller is enabled but
not active, its outputs are set as
follows:
• Pot-Lo = 0V
• Pot-Hi = 5V
• Brake+ = 36V
• Brake- = 36V
Because there isn’t a voltage difference between Brake+ and Brake-, none of the scrub system components
will be energized.
Because all of the Go switches are open, no current will ow through the Speed Pot (R1), and therefore it
will have no voltage drop. This causes all of the R1 terminals to be equal to the 5 volts of the Pot-Hi output.
Specically, the Throttle-Pot input is high (5V), which is the command for “No Throttle”. (Note that the
throttle input is inverted, as described previously.)
Even though this open circuit results in the Speed Limit to be commanded to maximum speed, the throttle
input remains off. So no motion is commanded.
POT.
5K OHM
RED/GRN YEL/BLK
BLK
RED
PNK/BLU
GRA/VIO
BLU
WHT
ORN
YEL
PNK
S1
Key Switch
S7 GO RT
S2
GO MID
BRUSH
S3
S, REV
P1
CURTIS 1228
POT HI
3
THR POT
4
KSI
5
POT LO
13
BRAKE-
6
REV
17
B+
B-M1
M2
M1
M2
SPD POT
18
BRAKE+
14
S6
GO LEFT
R1
M
M1
MOTOR, DRIVE
-+
36 VDC
+ -
VIO
Detergent Pump
Solution Solenoid
36V
36V
36V
5V
0V
Closed
Open
Off
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