Nilfisk SC370 43B Wartungshandbuch Seite 52

Service Manual- SC370
40 Recovery System 51
40 Recovery System
Functional Description
The recovery system removes dirty water from the floor and pipes it to the recovery tank. When the machine is
running, the dirty water on the floor is collected by the squeegee blades, and piped through the vacuum hose and
into the tank by the airflow created by vacuum motor (M2). The dirty water is piped into the recovery tank, while
the airflow continues to flow to the vacuum fan.
Press the one-button start on Dashboard (EB1) to turn on the machine. And press the vacuum button on
Dashboard (EB1) to turn on/off the vacuum motor (M2). Press the vacuum button for 1 second to switch between
normal mode (vacuum LED is on) and silent mode (vacuum LED flashes). The control signal is transmitted to
Control board (EB2) via port J1-6 (vacuum PWM) to control the on/off/vacuum level of vacuum output.
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 (20A) 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 J1-6
to stop the vacuum 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.