Tag Archive for capacitors

Bleeding it dry


Cor blimey I nearly blew my head off. Shorting capacitors, particularly large ones is a very scary experience. I had removed the rectification board from the mains board of the power supply project. Read more


Finally, it happened. I busted a cap. No, this has nothing to do with firearms.

I’ve oft been entertained by youtube videos showing exploding capacitors but had yet to witness one in person, thankfully. Here’s what happened.

I was playing around with my voltage control board using my new transformers. I used pretty much a standard rectifier design to get my DC out, and all was well through several tests. I used a 1000µF cap as a filter and it was working through the short power up tests I was doing. As I progressed, I left it on for longer and longer. At one point, with no warning, it just went BANG and scared the living crap out of me.

At the time, i was using my finger to test the temperature of my trimmer pots and resistors in my voltage divider for the 24V Vset reference because I was having some heating issues. I did notice that the first resistor and trimmer was too warm for comfort when I hard a bang and my head was enveloped in smoke.

After I coughed my lungs out from the noxious electrolyte vapour, I was worried that it was my trimmer(s) that died on me but was puzzled to find them fine and operational. Then I looked a bit left and noticed the deformed case of my filter cap.

What had happened was I mistakenly chose a 1000µF cap with only a 25V rating when the voltage across its pins was about 35V. Surprised it lasted as long as it did really.

Moral of the story: pick a cap with the proper voltage rating for heavens sake! At least it wasn’t a tantalum cap which are prone to catching on fire. Still, scary. Breathing the vaporized electrolyte wasn’t good for me either.