We had one go off at my local radio club...it went off like a rocket! All the insides spooled off like toilet paper, and luckily no one was injured. Those electrolytics can be scary!
Especially for old ones, reforming caps (and carefully watching the current) is a good idea. Don't let it get past a few milliamps!
Kyle
Especially for old ones, reforming caps (and carefully watching the current) is a good idea. Don't let it get past a few milliamps!
Kyle
"I wonder what the exact reason was why it blew up in such a spectacular way. "
Some of those old caps have no vents and have gone so long without power that what used to be a capacitor with oxide film on the plates become more of a set of plates in an electrolyte which soon becomes partially vaporized from the part functioning mainly as a resistor.
They used to make hot water heaters without pressure release valves too. That was abandoned as well.
Some of those old caps have no vents and have gone so long without power that what used to be a capacitor with oxide film on the plates become more of a set of plates in an electrolyte which soon becomes partially vaporized from the part functioning mainly as a resistor.
They used to make hot water heaters without pressure release valves too. That was abandoned as well.
I've had a number of close calls with low power circuits and little reverse biased off-brand caps too. They are supposed to have vents but the stamping on the top of the can is critical and if they get some improperly adjusted dies the section that is supposed to rip doesn't and the whole can will jet right off the rubber plug. I've had them go past my face and stick right into the drop ceiling. You can always check for heat or unexpected current. It might take a few minutes for launch.
Yeah, the Mythbusters had some fun testing the hot water heater myth!
I think everyone should take a little more precaution in powering up vintage electronics with big caps, since we never know which ones will blow and which won't. A variac is a good tool to help, but without monitoring the current through the filter caps, you won't really know when they'll try to blow.
Kyle
I think everyone should take a little more precaution in powering up vintage electronics with big caps, since we never know which ones will blow and which won't. A variac is a good tool to help, but without monitoring the current through the filter caps, you won't really know when they'll try to blow.
Kyle
In a former lifetime I used to build computers for resale (the 286 era). Some friends and I pooled our money and bought out a vendor that sold components in the Computer Shopper magazine. There was a virtual mountain of returned goods in the back of the warehouse. I got at least a hundred "AT" power supplies. On the first pass I just tested them all using a car headlight for a load and sorted out the good ones. Later I opened each one and put a clip lead across the fuse (yeah even then I new better) and retested finding more good ones. Unfortunately I found one with shorted diodes and the result looked a lot like this, including the stuff stuck to the ceiling. It was one of those "ohnosecond" moments when you realize the instant the plug hits the outlet and the lights dim that you screwed up. Before the brain decides to yank the plug, and the body reacts and finds out that its welded into the outlet (the ohnosecond) the cap went BOOM!
After that I modified my technique to incorporate a 100 watt bulb in series with my clip lead "fuse".
As I recently found out even a vented cap can explode when the Big Dumb Blonde One sets a 1000 watt power supply on 600 volts feeding a circuit that has a 450 volt cap. There was a 10K resistor in series with the cap which exploded too. Blew the 47uF 450V cap completely in half, and there was only a black stain on the board where the resistor used to be! The amp was rockin before the cap came a knockin!
After that I modified my technique to incorporate a 100 watt bulb in series with my clip lead "fuse".
As I recently found out even a vented cap can explode when the Big Dumb Blonde One sets a 1000 watt power supply on 600 volts feeding a circuit that has a 450 volt cap. There was a 10K resistor in series with the cap which exploded too. Blew the 47uF 450V cap completely in half, and there was only a black stain on the board where the resistor used to be! The amp was rockin before the cap came a knockin!
I'm sure he's going to put the potentially go-bang parts under the cover next time around.
I had potential difference in a very long serial cable with no opto isolation blow up an UART once, it made a hole directly in the middle of the UART chip where the silicon die used to be. The cover was on fortunately. ICs (at least not the power stuff) are waaaaaay less prone to explosions than electrolytics but I learned my lesson.
If the die that punches the grooves for the vents isn't perfect, they will go boom. I have yet to blow up a cap in a tube amp. I have blown up a few in computers, especially cheap power supplies and VRMs. They use the cheapest caps they can find and they never seem to vent as they should after being cooked for years. A few times the PSU case was packed with aluminum foil and paper confetti after the bang.
Flamed plenty of tants, though. P U.
Flamed plenty of tants, though. P U.
I blew up a cap (C6) twice in my Tubelab-SE mono. Obviously something wasn't sized properly for this modification. Fortunately, the vent worked both times and ended up making a relatively small mess inside of chassis. Still not a good experience. The fume is nasty.
I blew up a cap (C6) twice in my Tubelab-SE mono. Obviously something wasn't sized properly for this modification. Fortunately, the vent worked both times and ended up making a relatively small mess inside of chassis. Still not a good experience. The fume is nasty.
That's good. I would expect the higher-quality caps that we generally buy from Panasonic and others to be built to better standards than the ultra-cheap ones found in most computers. I can't recall blowing any of these up, though.
I fried a whole bunch of tants one day as a teenager. I was inexperienced and didn't notice that the polarity marking on the body was for the POSITIVE terminal and not the negative like electrolytics (whose bad idea was that?). My dad got a chuckle out of that. Man those things stink, especially when a half dozen go at once.
I had a very similar experience with one of those small orange axial electrolytics made by Cornell-Dubilier about 30yrs ago. I was also quite lucky.
The capacitor was brand new, installed correctly and operating well within its ratings. I smelled something burning, and it was too late. The capacitor decapitated a transistor in a TO-5 can which was in the driver stage of a mosfet power amplifier, needless to say its failure took out the output mosfets as well. What a mess...
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