Hochvolt-Fahrzeug freischalten (3D)
About this app
BEV-Unterbau in 3D: nach den fünf Sicherheitsregeln freischalten, Zwischenkreis entladen sehen, Spannungsfreiheit mit zweipoligem Prüfer feststellen, Fehlerfall klebende Schütze.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
De-energising by the five safety rules
Before work on the high-voltage system of an electric or hybrid vehicle, a qualified person de-energises it. The basis is the five safety rules in vehicle practice, as described in the German DGUV Information 209-093, together with the manufacturer’s instructions: disconnect, secure against reconnection, verify the absence of voltage, earth and short-circuit (usually not intended on the vehicle) and cover adjacent live parts. Touch voltages above AC 25 V or DC 60 V count as hazardous. Typical vehicle systems run at 400 V or 800 V direct voltage.
What the app shows
A generic electric car underbody in 3D: high-voltage battery with twelve modules, junction box with main contactors and insulation monitor, orange HV cables to the power electronics with the DC link capacitor and to the DC/DC converter, 12 V battery, service plug with pilot line and a two-pole voltage tester. Moving dots show where voltage is present. One panel guides through the work steps; another shows the DC link voltage, the waiting time, the curve U(t) with the 60 V limit and the five measuring steps of the tester. All figures are example values of a 400 V system.
Things to try
Switch the ignition off and then wake the vehicle with the charging timer: the contactors close again and 390 V is present. Disconnect the 12 V battery, remove the service plug and watch the DC link, which is still charged well above 60 V. Let the waiting time run in time lapse, then measure with the tester, which is checked on a known source before and after. For comparison, switch on the fault case “contactors stuck”: the tester shows 390 V and the app blocks further work.
Frequently asked questions
- Is an electric car de-energised with the ignition off?
- No. The main contactors usually open when the car is switched off, but the vehicle can wake up again, for example via a charging timer, and the contactors close once more. In addition, the DC link is still charged right after switching off, and the high-voltage battery itself is always live.
- Why do you have to wait after removing the service plug?
- The DC link capacitor in the power electronics stores energy and only discharges gradually through a resistor. The manufacturer specifies the waiting time. Afterwards the absence of voltage is still verified with a suitable two-pole voltage tester.
- How do you verify the absence of voltage on the HV system?
- With a two-pole voltage tester, for example to EN 61243-3, at the measuring points named by the manufacturer: HV+ to HV−, HV+ to ground and HV− to ground. The tester is checked on a known voltage source before and after the measurement. Some manufacturers specify the check with the diagnostic tester.
- What does the app show in the fault case?
- With “contactors stuck”, the main contactors do not disconnect. After de-energising and the waiting time, the tester still shows 390 V between HV+ and HV−. The app then blocks the next step: the vehicle stays secured, the responsible person is informed, and further action follows the manufacturer’s instructions.
Subject: Automotive engineering
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