Nilfisk SC800 ST User Manual

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

Form Number 56043150 Page 144

Drive Motor Controller Outputs

The primary job of the Drive Motor Controller is to operate the electric transaxle drive motor. It does this by regulang

current ow through the drive motor to control speed, and by changing polarity to control direcon. The secondary job is

to nofy the Main Machine Controller when the machine is moving and which direcon it is moving. The Main Machine

Controller uses this informaon to start and stop the soluon ow and scrub funcons.

To move the machine forward, the controller connects terminal M2 to baery negave AND connects terminal M1 to

baery posive. To regulate the speed, the controller pulses the baery posive voltage out to terminal M1 at a xed

frequency called a “duty cycle”. The greater the percentage of “on” me that the circuit is connected to baery posive,

the faster the machine will go.

To move the machine in reverse, terminal M1 is connected to ground and terminal M2 is pulsed to baery posive volt-

age. The speed in reverse is intenonally reduced.

The Drive Motor Controller tells the Main Machine Controller when the machine is moving and what direcon it is mov-

ing. Two circuits are used for this purpose, the FOR/REV and the REV circuit. Here is how the FOR/REV circuit works: The

Main Machine Controller sends 24 volts out through an internal resistor to the Drive Motor Controller. The Drive Motor

Controller has an internal switch to baery negave (B-). When the machine is not moving, the switch is open. There

is an internal voltmeter inside the Main Machine Controller that sees 24 volts on the circuit. When the machine moves

in either direcon, the switch closes and the voltage drops to 0 volts. This tells the main machine controller that the

machine is moving. However, the main machine controller does not know what direcon the machine is moving. There

is another circuit called the REV circuit that provides direcon informaon. It works similar to the FOR/REV circuit. When

the machine is staonary or moving forward, the switch remains open so the main machine controller “sees” 24v. The

switch closes when the machine moves in reverse, dropping the voltage to 0v.

• Staonary Machine - Both Inputs=24v

• Machine Moving Forward = FOR/REV=0v, REV = 24v

• Machine Moving in Reverse - FOR/REV=0v, REV = 0v

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Nilfisk SC800 ST Heavy-Duty Cleaning