Nilfisk SC800 ST User Manual

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Service Manual: SC750, SC800, SC 750 ST, SC800 ST

Form Number 56043150 Page 142

Wheel System, Traction

Functional Description

A permanent magnet motor transaxle is used to propel the machine in both forward and reverse direcons. The con-

trols for forward, reverse and speed are dierent between the “ST” (SC 750 ST, SC800 ST) and “Non-ST”(SC750, SC800)

Models. The SC750 and SC800 models use a drive paddle with an angle sensor (potenometer) as an input for forward

and reverse with a variable speed signal. They also have a separate speed limit potenometer to control the maximum

speed. The SC750 ST and SC800 ST models use a combinaon of two switches. There are 2 “Palm Drive Buons” and a

Reverse Buon. When either palm drive buon is pressed, the machine will go forward. If the reverse buon is pressed

while a palm drive buon is pressed the machine will move in reverse. ST models also have a separate speed control

potenometer. It controls the speed of travel. On both models, the speed in reverse is intenonally less than in forward.

The Drive Motor Controller varies the amount of voltage it applies to the drive motor to control speed. It reverses the

polarity to change direcon. The Drive Motor Controller is capable of informing the Main Machine Controller that it sees

a problem, but there are no specic drive system codes to retrieve.

Drive Motor Circuit Description - SC750 ST and SC800 ST models.

Powering up the Drive Motor Controller:

The controller is connected directly to baery posive (B+) and baery negave (B-). These supply the power that the

controller uses to send out to the drive motor. The controller “wakes up” when it receives voltage from the key switch.

On machines with an oponal on-board baery charger, the voltage rst goes through the key switch and then through

the interlock circuit in the baery charger when the charger is not plugged into an AC power supply. When the charger is

plugged in, the voltage is interrupted by the built in interlock relay and the drive system will not wake up even if the key

is turned on.

Drive Motor Controller Inputs

To drive forward, the operator presses either palm drive buon and rotates the speed control potenometer to achieve

the desired speed. The drive motor controller has internal “voltmeters” that are monitoring 3 inputs.

1. Palm Switches - To know when to move.

2. Speed Request - To know how fast to move

3. Reverse Switch - To know which direcon to move

The palm drive buons are fed 5 volts from the controller. When either switch closes, the 5 volts goes through the switch

and back to the controller where an internal voltmeter “sees” the 5 volts and “recognizes” it as a request to move. (Note:

There is an internal “diagnosc voltage” of a lile more than 2 volts that will be seen when both switches are open.)

The speed limit potenometer is fed 5 volts from the controller on one side of its resisve strip. The voltage goes

through the resisve strip and returns to baery negave inside the controller. The “wiper” inside the potenometer will

return a voltage back to the controller as a speed request input. If the wiper is close to the supply side, the voltage will

be high (4.6v = Maximum speed request). If it is close to the baery negave return side, the voltage will be low (0.2v =

Minimum speed request).

The reverse switch provides the “direconal request input.” Here is how it works. The Drive Motor Controller sends ap-

proximately 2.8v through an internal resistor out to the reverse switch. An “internal voltmeter” monitors the voltage.

When the reverse switch is open, 2.8v is seen. This is interpreted as a “forward direcon” request. When the reverse

switch closes, it connects the voltage to baery negave through the Drive Motor Controller. This drops the voltage from

2.5v to nearly 0v. This is interpreted as a “reverse direcon” request.

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Nilfisk SC800 ST Heavy-Duty Cleaning