BIKERACE: Service & Maintenance Manual - rev. 1.1
Page 3.4
3.2. ALTERNATOR CONTROL
3.2.1. M
ECHANICS
The movement of the pedals turns the pedal crank which by means of a chain transmits the motion
to a pulley, which in turn transmits the motion to the alternator by means of a belt.
The pedal resistance perceived by the user results from a combination of 2 factors:
•
electrical component
: consisting of the resistance generated by the alternator, and which can be
measured as the electrical power dissipated on the resistor, also taking into consideration the
alternator efficiency;
•
mechanical component
: consisting of the mechanical efficiency of the linkages and more
generally of the mechanical friction of the system.
The alternator interface board is factory-calibrated by means of the 2 trimmers PT1 and
PT2 situated on the board itself. This is a purely electrical adjustment and should not be
modified, even in cases where the perceived resistance of adjacent machines is different.
3.2.2. C
ONTROL
To control the difficulty level of the workout, the machine adjusts the excitation of the alternator
which generates a resistance to the movement that is proportional to the excitation level. To do this,
the CPU board transmits a PFM (Pulse Frequency Modulation) signal. The alternator interface
board converts the PFM signal into an analogue signal which serves as the excitation signal for the
alternator. The higher the level of the alternator excitation signal, the greater will be the resulting
resistance.
The alternator rotates in the field produced by the excitation signal, generating electrical energy
which is dissipated by the power resistor.
There is a closed control loop between the alternator interface board, the alternator and the resistor.
In fact the alternator interface board regulates the excitation signal so that the voltage measured at
the resistor terminals matches the voltage programmed by the CPU board via the PFM signal.
If the excitation signal is not sufficient to generate the required resistance, the red LED
on the alternator interface board goes on.
The rotation of the alternator also generates a square wave signal proportional to its speed, with 6
pulses corresponding to one complete rotation of the alternator. This signal enters on the interface
alternator board where it is filtered and sent to the CPU board.
If the CPU board does not receive a speed signal greater or equal to 30 RPM, it does not
transmit any PFM signal. Therefore the alternator does not receive the excitation signal
and there is no resistance at all.
