It Went "POP" and Died

On Friday afternoon, while preparing for this week's in-water testing, there was a loud "POP", and a few seconds later the benchtop power supply's current-limit light turned on.

Uh oh.

Today we went about troubleshooting it. When we opened the main pressure housing, the smell of burnt electronics was noticeable (it soon dissipated).

The current limit on the benchtop power supply was lower than that of some of the fuses on the vehicle, so it was a simple matter of taking fuses out one by one to determine which component was shorting. It turned out to be one of the Parker Driveblok units.




The most likely explanation for the short was a failed capacitor. The Drivebloks have replaceable capacitor banks, so that was the first thing we checked.

This is the old capacitor bank, and the failed capacitor is quite noticeable. Not only does it have a considerable bulge overall, there is one spot with a prominent outward dent.

The reason for the failure is currently unknown. However, we did notice that the water blocks between each pair of Drivebloks were vapor locked -- the coolant enters and leaves on the bottom of each water block, and the top part had filled with air -- preventing any coolant from flowing. The rise in temperature may have contributed to the failure.

After putting in one of our spare capacitor banks, the system seems functional again.