Reply to post: Large bipolar electrolytic capacitors are always fun.

'The capacitors exploded, showering the lab in flaming confetti'

Morrie Wyatt

Large bipolar electrolytic capacitors are always fun.

Back in the late 70s, I was a young apprentice.

The company I worked for also imported cheap Taiwanese bench grinders.

One of these had been returned under warranty, so was on the department manager's bench with the base off to check the wiring. When nothing obvious presented itself the switch was turned on and we retreated to the office doorway. These grinders used a large capacitor and a centrifugal switch to energize the motor start winding with the resulting L/C circuit providing a phase shift to ensure the motor started in the right direction. The grinder started up and seemed to be running normally, until with a loud bang, the capacitor blew its lid, (through the small covered pressure relief hole in the end of the cap) blasting a jet of evil smelling vapor directly at all standing in the doorway.

We at least now knew what the fault was. The centrifugal switch "didn't", leaving the start winding connected. The start winding and capacitor weren't designed to run for more than about 10 seconds, so the capacitor overheated, boiling the electrolyte until the weak point cried uncle.

The office became almost uninhabitable for days, and took many months before the smell finally faded to barely perceptible levels.

I still work for the same company some 40 odd years later.

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