Last night, for the 1st time in 40+ years of owning/using a soldering iron, I vented two power supply capacitors via reverse polarity error. I stuffed a power supply PCB backward. It was majestic and delightful to watch as though a genie was rising from a two-tower lantern, yet horrific and toxic. I'm fortunate they didn't explode in my face. Shame on me for not putting my VARIAC back together. I'll get on that asap.
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And when you get a variac for the bench you will still use the bulb. There are failure modes on untested DIY amp designs that come on so suddenly that a variac won’t save you. Looks like it’s working perfectly, then all of a sudden destructive oscillation with NO warning. Variacs also work both ways - you can overcome the voltage drop on the bulb and get it to normal voltage, while still retaining the current LIMIT feature. Invaluable for tube amps, where you want the full 6.3 volts on the heaters and the bias supply where it’s supposed to be. The combination is the perfect capacitor former, too. Turn it up till you see a little leakage, turn it back down and let it self discharge. Run the next cycle up a little higher. Repeat till it holds full voltage, then let it sit with the bulb in series for a while. Can walk away and leave it to do other things without worrying about burning the house down.
When doing destructive things (like blowing up or just sparking capacitors) I might use as many as 5 150 watt bulbs in parallel. You know what happens to caps that won’t properly form, now don’t you? No good anyway, might as well have some fun…..
When doing destructive things (like blowing up or just sparking capacitors) I might use as many as 5 150 watt bulbs in parallel. You know what happens to caps that won’t properly form, now don’t you? No good anyway, might as well have some fun…..
I bought a large unopened box of NOS 450 uF 35 volt electrolytic caps at a hamfest sometime in the early 1980's with intent on using them in a small electronic device that I was making and selling at the time. The date codes showed that they were about 5 years old at the time, and counterfeit caps were not a big issue yet. Unfortunately these caps were just crap. Not a few duds, but every one produced too much ripple for the 7815 regulator chip to clean up from a 24 VCT power transformer that produced over 30 volts due to a very light load (maybe 20 mA). New caps from Digikey worked fine.
The lead spacing was just right to fit in a US spec wall outlet, or a long outdoor extension cord. Place cap in cord, bury remote end a few inches deep in loose dirt, wait for unsuspecting stray critter to come by, plug cord into wall. critter sets new land speed record for its species. We lived about 1/4 mile from the edge of the Everglades swamp, so critters were varied and common. Some of the caps were so bad that they wouldn't even explode. Some vented slowly, some did nothing at all. I tossed the remaining stock when I moved out of Florida.
After hurricane Wilma trashed my backyard shed in 2005, I found a long forgotten audio "booster amp" that I had made in high school. Remember that this was made by a 16 year old kid from salvage yard parts in 1969. Yes, it is quite crude, ugly, and unsafe but it was LOUD through 2 big speaker cabinets with 4 12 inch speakers each when driven by a medium powered guitar amp. Power output was about 300 watts into 4 ohms. It hadn't seen power in 30+ years and was stored in that outdoor shed for over 25 years. What to do? Plug it in and see what happens, from a distance of course.
One of those big can caps made a good sized smoke cloud, but the little stud mount diodes shorted which made the power cord start to smoke. Plug was yanked. Game over. I saved the transistors and heat sinks, tossed the rest.
Side note: The salvage yard where I scored the old SOLA power supplies that gave up their caps was taken over by the FAA to store the pieces of Eastern Airlines Flight 401 that crashed in the everglades in 1972. A couple years later the yard was reopened to the public. But it had turned into a metal scrap yard with very little electronic scrap.
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I have never seen a big can cap like those SOLA's explode, but I did get to see the results of what was forever called the BIG BANG.
Many here know that I was a "Mr. Fixit" for the entire production floor on the evening (4 PM to midnight) shift at the Motorola plant in Florida where all of the police walkie talkies were made. That factory ran 3 shifts, 24/7. There was a small crew on the night (midnight to 7:30 AM) shift for about half of the production lines. There was no Mr. Fixit for that shift as there were plenty of open stations, and nobody that could do that job wanted to work those hours despite the higher hourly wage. There were two custom built automated test stations called Bigfoot 1 and Bigfoot 2, in the MX-300 radio product factory. Since the MX-300 was the top tier radio for Motorola at the time, every radio got stuffed into bigfoots face (a custom test fixture) where a printout of all of its test parameters was generated and shipped with the radio. Both Bigfoots were designed by in house Motorola test engineers and a full time in house HP guy.
The factory was in South Florida not far from the Everglades Swamp where huge thunderstorms grew and migrated east over the entire county on their way to the Atlantic Ocean nearly every afternoon in the summer. Power line surges, brownouts, and short dropouts were common despite a power company substation across the street. Bigfoot did not like this! To mitigate the issue a pair of custom large UPS systems were purchased, each taking up a 4 foot tall half rack that weighed several hundred pounds due to lead acid batteries.
Since I lived 3 miles from the plant I was the on call guy when something bad happened. Early one morning I got the " IT JUST EXPLODED" call. A night shift supervisor was so shaken that he couldn't even tell me what exploded, but one of the bigfoot stations was scattered all over the place. I got to the plant in about 15 minutes to see Plantation Fire trucks and police cars and most of the employees in the parking lot. With a fire department escort I was rushed to the scene, but I could "tell by the smell" that an electrolytic cap had been involved........BIG TIME. One of those half rack UPS units had a hole in its side and battery goo oozing out of the bottom. It indeed exploded. Some of the fragments had blown right through two layers of copper screen into an unoccupied RF proof screen room test booth nearby.
The offending UPS was disconnected and wheeled out to the loading dock to be relocated to an empty corner of the truck loading area. A cleanup ensued and everything, except the associated Bigfoot was back in operation.
A representative from the UPS company was dispatched to preform autopsy, and I was instructed to make the unit "safe" until he could get there. The instructions were to carefully remove a "link from the interconnected batteries" therby rendering the "energy source" inert. Why me. Well, my reputation preceded me. The sides of the rack lifted off and the links were copper bars connecting the 7 series connected 12 volt lead acid gel cells. It was easy to remove a link and to see the stupidest thing I had ever seen. There was 84 volts of "energy source" connected to a bank of electrolytic caps with heavy copper straps with the only fuse in the circuit AFTER the caps. Do electrolytic caps ever fail to a short? What would happen to one when it did and had nearly infinite energy connected to it? The BIG BANG happened. The rest was discussed behind closed doors, but those two UPS units went away in a couple days and were replaced with two units of a different brand with external battery boxes.
Many here know that I was a "Mr. Fixit" for the entire production floor on the evening (4 PM to midnight) shift at the Motorola plant in Florida where all of the police walkie talkies were made. That factory ran 3 shifts, 24/7. There was a small crew on the night (midnight to 7:30 AM) shift for about half of the production lines. There was no Mr. Fixit for that shift as there were plenty of open stations, and nobody that could do that job wanted to work those hours despite the higher hourly wage. There were two custom built automated test stations called Bigfoot 1 and Bigfoot 2, in the MX-300 radio product factory. Since the MX-300 was the top tier radio for Motorola at the time, every radio got stuffed into bigfoots face (a custom test fixture) where a printout of all of its test parameters was generated and shipped with the radio. Both Bigfoots were designed by in house Motorola test engineers and a full time in house HP guy.
The factory was in South Florida not far from the Everglades Swamp where huge thunderstorms grew and migrated east over the entire county on their way to the Atlantic Ocean nearly every afternoon in the summer. Power line surges, brownouts, and short dropouts were common despite a power company substation across the street. Bigfoot did not like this! To mitigate the issue a pair of custom large UPS systems were purchased, each taking up a 4 foot tall half rack that weighed several hundred pounds due to lead acid batteries.
Since I lived 3 miles from the plant I was the on call guy when something bad happened. Early one morning I got the " IT JUST EXPLODED" call. A night shift supervisor was so shaken that he couldn't even tell me what exploded, but one of the bigfoot stations was scattered all over the place. I got to the plant in about 15 minutes to see Plantation Fire trucks and police cars and most of the employees in the parking lot. With a fire department escort I was rushed to the scene, but I could "tell by the smell" that an electrolytic cap had been involved........BIG TIME. One of those half rack UPS units had a hole in its side and battery goo oozing out of the bottom. It indeed exploded. Some of the fragments had blown right through two layers of copper screen into an unoccupied RF proof screen room test booth nearby.
The offending UPS was disconnected and wheeled out to the loading dock to be relocated to an empty corner of the truck loading area. A cleanup ensued and everything, except the associated Bigfoot was back in operation.
A representative from the UPS company was dispatched to preform autopsy, and I was instructed to make the unit "safe" until he could get there. The instructions were to carefully remove a "link from the interconnected batteries" therby rendering the "energy source" inert. Why me. Well, my reputation preceded me. The sides of the rack lifted off and the links were copper bars connecting the 7 series connected 12 volt lead acid gel cells. It was easy to remove a link and to see the stupidest thing I had ever seen. There was 84 volts of "energy source" connected to a bank of electrolytic caps with heavy copper straps with the only fuse in the circuit AFTER the caps. Do electrolytic caps ever fail to a short? What would happen to one when it did and had nearly infinite energy connected to it? The BIG BANG happened. The rest was discussed behind closed doors, but those two UPS units went away in a couple days and were replaced with two units of a different brand with external battery boxes.