08-09-2024, 10:09 PM
Also piezoelectric!
A problem with many ceramic caps.
Charge up a 50 year old 1nF 5 kV cap and leave connected for 20 minutes Short it, isolate it. Come back 20 minutes later and measure the voltage. It will be 100s of volts. The 5kV deformed it. So later it "recovers" and voltage rises as it does. Even more "interesting" with 10 kV or 20 kV parts all in parallel on a soak testing tray. The solution is NOT to short the tray, but put a bleed resistor.
You can guess how I discovered this 50 years ago.
Smaller values work as poor microphones.
A problem with many ceramic caps.
Charge up a 50 year old 1nF 5 kV cap and leave connected for 20 minutes Short it, isolate it. Come back 20 minutes later and measure the voltage. It will be 100s of volts. The 5kV deformed it. So later it "recovers" and voltage rises as it does. Even more "interesting" with 10 kV or 20 kV parts all in parallel on a soak testing tray. The solution is NOT to short the tray, but put a bleed resistor.
You can guess how I discovered this 50 years ago.
Smaller values work as poor microphones.
