Alternator / Resistance Testing
The colored connections to the alternator are as follows:
White-B+
Alternator output voltage
Brown
Field, Alternator Control Current
Black
Ground, Alternator return
Blue
Tachometer, velocity signal back to console
Resistance over gravity is performed by the alternator in the StepMill. When the console senses a user with
staircase movement, the console should be enabling full field current to the alternator. Field current is provided
from the external power supply, through the console, into the lower board and wired into the alternator’s field
terminal. Under this condition, the console should also be driving the lower board's J1 pin 1 low, switching the
.5ohm load resistor onto the alternator’s B+.
The alternator’s B+ should rise as a result of field current, but its voltage will depend on the weight of the user
and resulting velocity. Resistance is achieved by the oppositions of internal magnetic fields when field current
is applied. The user’s weight will affect the alternator’s RPM under this condition, and under full field current
conditions the voltage is not controlled. But, with the large gear ratio and full field current applied, the
resistance should be at maximum, and the step rate should be at a minimum.
Once a user starts a workout, the console controls the alternator’s field current attempting to maintain the
desired step rate. This signal is Pulse Width Modulated (PWM) from 0V to 12V, the level of the loaded external
supply. If the step rate is fast, the console will deliver field current longer, if the step rate is slow, it will deliver
less field current.
The only situation where no field current would be present during a workout is if a very light weight person was
attempting to achieve a step rate that could not be achieved by their weight overcoming the frictional
resistance of the system. In this case, the console would keep field current off, or no induced resistance.
During workouts the alternator’s B+ increases as a function of speed and user weight. For high level workouts
with heavy weight users, B+ levels of 20V could be witnessed.
Power entry is at the bottom of the unit. The 12V 2.5A supply enters via the main power harness, and enters
into the PCB via J2. LED2 indicates power is present, but 12V should still be confirmed with a volt meter.
Power and control interface to the console is provided at location J1. 12V is provided up to the console at J1
pin 4, and GND pin 5.
In addition to alternator field current, the console controls the loading of the alternator’s B+ with the .5ohm
resistor which is switched by the lower board's relay. When the console detects a user has stepped on the
staircase, it immediately applies full field current, and turns on the power relay to load B+ with .5ohm. LED1 is
an indicator the console is attempting to close the relay, but this should be confirmed with a VOM.
If no resistance is felt, confirm 10V to 12V is being applied to the alternator’s field. This should always be
present once a user is detected, and before a workout has begun. Confirm the additional load is being
switched also, which is controlled by a low voltage on J1 pin 1. The operation of the power relay can be
confirmed by unplugging the unit, and removing the console connection at J1. Install external power again, and
an ohmmeter should show continuity from B+ to field on the 23545's terminal strip.
Last revised 10/5/15
