8 min Readtime
Published Jun 11, 2025
What happens when pressure builds up inside an electrolytic capacitor? Let’s find out — with a real-time safety-vent test that reveals how design saves circuits.
In this controlled experiment we intentionally stress an aluminum electrolytic capacitor to force internal gas generation. Under excessive heat, overvoltage, or high ripple current, the liquid electrolyte begins to decompose and produce gas (mostly hydrogen). Pressure rises inside the sealed can until the engineered safety vent — a scored or weakened section of the top — activates. The result is dramatic but deliberate: a rapid, directed release of hot gas and aerosolized electrolyte that prevents the can from shattering into dangerous fragments.
Watch closely: the early sign is subtle — the top cap domes and the seal bulges as pressure climbs. Then the vent opens at a predictable threshold; a puff of white/gray vapour and tiny droplets erupts, directed away from sensitive components. Because the vent is controlled, the can avoids catastrophic fragmentation and shrapnel hazards. Yet venting still sprays corrosive, hot material onto the PCB, so it’s not harmless: you’ll often see residue, discoloration, or burned traces around the vent area that require careful inspection and cleaning.
Why run this test? It’s a practical reminder that electrolytic capacitors are electrochemical devices — their failure modes are chemical, thermal, and electrical, not merely “mechanical.” A proper vent design saves boards; good layout practice and thermal management prevent reaching the vent threshold in the first place.
Design lessons from the demo:
• Leave vent clearance — don’t block vents with glue or potting.
• Avoid placing caps beside persistent heat sources or in sealed enclosures.
• Validate actual ripple current and thermal rise on the board, not just datasheet values.
• Consider polymer/solid alternatives in safety-critical or high-temperature locations.
This safety-vent test is both dramatic and instructive: the vent is the last line of defense, visible proof that smart mechanical design limits damage. Want to see the same test with different capacitor chemistries, or with thermal imaging and teardown analysis? Follow us and tell us which experiment next.
