TESTING A SMART ALTERNATOR

1 Consult your car’s wiring diagram to identify the charging system circuit. This graphic shows not only the wiring but also the points at which to connect the Picoscope.

2 As in Step 1, the wiring that leads from the alternator to the ECU is backprobed and earthed, while the other ends of the leads are connected to the Picoscope.

3 The clamp is zeroed, then fitted over the positive battery to alternator cable. The Picoscope scale is set to 200A.

4 On this professional equipment, the realtime oscilloscope readings are displayed on your PC monitor.

5 Start the engine with all electrical ancillaries switched off. The waveform shown above indicates that the alternator is producing current of around 14 amps (blue line). The alternator feedback is operating (red line) but, although the command signal (green line) is present, the signal is idle.

6 With all electrical ancillaries activated and the engine speed increased to 2500rpm, the blue line shows that the alternator output has risen to around 70 amps. The green line (command signal) is now active, which results in the alternator responding with a higher output. The duty cycle of the red line (alternator feedback) increases with alternator output, as intended. This alternator is working correctly.