Charging System: Testing and Inspection

Capacitor Box: Measurement Of The Ripple Of The Vehicle Voltage

The voltage supply of some components is provided via a power distribution box at the front that is connected to the positive battery connection point. To reduce the ripple caused by the alternator in the vehicle voltage, a capacitor is installed in the power distribution box.
The capacitor, fuses and power distribution box together form the capacitor box.

Cables used
Measuring cable with crocodile clips.

Testing instructions and procedure
- Connect the measuring cable for voltage measurement to the Integrated Measurement Interface Box (IMIB). Connect the crocodile clips to the jump start terminal points in the engine compartment.
- Oscilloscope with Record mode: Select TIME/DIV: 50 micro s/Div
- Start engine.
Switch on a large number of electrical consumers (heated rear window, defrost function, seat heating, etc.). Maintain the engine speed at 3000 rpm during measurement for several minutes.

- The measurement is performed once with the capacitor box and once without the capacitor box (removed capacitor box).

Test results
The following graphic shows the voltage curve of the vehicle voltage at the jump start terminal points with the capacitor box.

Oscilloscope settings:
CH1: Measuring cable, offset 0 %, selection 0.2 V/Div, coupling AC
Display: Record
Cursor: CH1







The following graphic shows the voltage curve of the vehicle voltage at the jump start terminal points without the capacitor box.

Oscilloscope settings:
CH1: Measuring cable, offset 0 %, selection 0.2 V/Div, couplingAC
Display: Record
Cursor: CH1







Ripple of vehicle voltage
The signal frequency is approx. 14 kHz.
Calculation of the frequency f in kHz with the time difference delta t in ms (time difference between the beginning of two voltage peaks: See the cursors in the previous graphics): f = 1 / delta t
See the following graphic: Calculate the signal level from the two measurements.







Execute the following procedure and enter both determined levels: Capacitor box.
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