BMW – no serious danger in KERS shock
What exactly happened in Jerez?
Markus Duesmann, Head of Powertrain: "The mechanic suffered an electric shock after touching the sidepod and steering wheel of the car. There was a high- frequency AC voltage between these contact points, the cause of which has been traced back to the KERS control unit and a sporadic capacitive coupling from the high-voltage network to the 12-volt network. The voltage ran through the wiring of the 12-volt network to the steering wheel and through the carbon chassis back to the control unit."
Note on capacitive coupling: this refers to an inadvertent transfer of electric voltage between two transfer media by inductive or capacitive coupling.
Was there a serious danger to the mechanic and the driver?
Duesmann: "No, as only a small amount of energy can be transferred through this capacitive coupling effect. However, the energy is sufficient to cause an extremely painful reaction. The driver was insulated against the car by his racing overalls and gloves and therefore not in any danger."
Why did the investigation take so long?
Duesmann: "It was not possible initially to reproduce the capacitive coupling effect in the car, as the problem was caused by a sporadic error in the control unit. Due to the extremely high frequency of the voltage in the steering wheel, the safety mechanisms and data recordings did not pick up on the error. In the absence of data, all the theoretical possibilities had to be systematically investigated and analyzed in tests. Furthermore, the capacitive coupling effect only occurs under certain conditions. Without the option of driving the KERS test car used in Jerez again, we had to reconstruct these conditions. We also had to develop a model to be installed between the steering wheel and sidepod which replicated the characteristics of the human body as an electric transfer element."