Nilfisk SC370 43B Manual De Servicio página 37

Service Manual- SC370
34 Scrub System 36
34 Scrub System
Functional Description
The rotating brush system cleans the surface of the floor. The main component of the brush system is the deck
where brush or pad holder with pad whichever is suitable for the type of surface to be cleaned is installed.
Press the one-button start on Dashboard (EB1) to turn on the machine, and the brush motor (M1) is on standby.
When the safety switch is pressed, the control signal is transmitted to Control board (EB2) via port J1-5 (brush
PWM) to activate the output of brush motor. When the safety switch is released, the output is off.
The machine uses a current sense circuit to detect the current. Here is how the MCU knows how much current is
flowing through the motor. When the transistor (switch) closes to cause the motor to run, the current flows through
a shunt resistor, inside the EB2 control board, with a known resistance value before reaching battery negative. The
EB1 Dashboard has an internal "voltmeter" that measures the voltage drop across the shunt resistor. With the
knowledge of the resistance value and the voltage drop, the MCU mathematically calculates the amperage going
through the resistor based on Ohm's law. Think of the "current" wire as though it were the red voltmeter lead,
reaching out to measure the voltage just upstream of the shunt resistor compared to battery negative.
If the current exceeds the set value (25A) for 3 seconds, the MCU outputs control signal (low level) to logic driver
and transmit it to the gate of power MOSFET controlled by MOSFET driver on Control board (EB2) via port J1-5 to
stop the brush motor. When the current is greater than 30A, the output is turned off after 60 milliseconds. And the
one-button start LED indicator flashes in the meantime, indicating the circuit is overcurrent.