Simulating an Automotive Load Dump

From this StackExchange post.

Load dump is primarily an inductive phenomenon, and it would probably be easier to simulate it that way, too. You don’t really need to simulate the full energy of an actual automotive load dump; you just need to create the same voltage waveform across the supply terminals of your device.

Put a largish inductor (on the order of 1H, perhaps the primary of a large power transformer) in series with your device (i.e., connect the device to the power supply through the inductor). This represents the inductance of the automobile charging system.

Put a few µF of capacitance across (in parallel with) your device; this represents the distributed capacitance of the automobile wiring, and helps to limit the risetime of the load dump event. Make sure this capacitor is rated for a few hundred volts.

Put a 120Ω resistor in parallel with your device, too. This represents other loads within the automobile, and will set an upper limit on the peak voltage that the load dump creates. (This resistor will be drawing 100 mA and dissipating 1.2W.)

Now, connect a low-value, high-power resistor across your device, in series with a switch. This represents the load that is going to get “dumped”. The value of the resistor should be such that the DC current doesn’t exceed the power supply’s capability, and you can adjust the current with respect to the value of the inductor to dump a specific amount of energy (0.5×I2×L). For example, if your inductor is 1H and your resistor is 12Ω (@ 12W), you’ll be drawing 1A, and the stored energy will be 0.5 Joules.

Close the switch, then open it — there’s your load dump event. With these resistor values, the peak voltage will be on the order of 100-120V. You can use different resistor values to simulate different kinds of events.

(If any of this isn’t clear, let me know and I’ll make a diagram.)

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