What to do with bad caps? - Page 1
Forum section: electronics / projects

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: December 17, 2016, 10:35:26 am
content: The town fathers of my pueblo have asked me to coordinate a fireworks show. They will provide the incendiaries but want me to run the show.My question is can electrolytic capacitors of say about 50 microfarads be used as a charge to set off the display in a coordinated way using a pic microcontroller, some relays, and ac voltage?Thanks in advance.

author: Rerouter
author_rank: Super Contributor
timestamp: December 17, 2016, 10:47:14 am
content: capacitors pressurise and pop / explode from the steam pressure inside them, as its a wet explosion it will not ignite a fuse, and would be a rather unreliable ignition source,Far better to use conventional heater igniters (Take a high current source like a car battery, run the wire to the exposive (through relyas or however you prefer), neck down the wire to 1-3 strands of thin wire, and wrap it around the fuse multiple times, the idea is the thin strands failure temperature should be more than the fuses ignition temperate.

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 11:02:26 am
content: If electrolytic capacitor has already lost it's capacitance because dried out/vented, it won't explode. There isn't electrolyte inside to cause pressure build up and cause explosion. Generally you want to apply reverse voltage or AC to blow a capacitor. Some are almost instant to blow, some are not. But if you apply something as mains AC voltage, low voltage capacitors should blow up almost instantly. Be ware that you may cause circuit breakers to trip, and that capacitor shell may become a projectile which will fly directly in your face.BTW, old capacitors without any safety vent explode much better than newer ones.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: December 17, 2016, 11:03:18 am
content: Thanks for the swift reply. Using a furnace igniter seems like a pricey solution. Is this how its done by commercial fireworks contractors?

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 11:07:35 am
content: Quote from: joseph nicholas on December 17, 2016, 10:35:26 amCapacitors are useful only as fireworks by themselves, there won't be any fire (unless you apply really high energy to them). Just buy electric ignitershttp://www.ebay.com/itm/E-match-100pcs-lot-11-81in-For-Fireworks-Firing-System-Electric-Igniters-display-/131738535564?hash=item1eac3a868c:g:6S0AAOSwzgRW0qS4

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: December 17, 2016, 11:09:19 am
content: I've had a few blow up in my face already, they seem to explode in all directions, and leave alot of paper around the lab. A real trauma when you don't expect it.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: December 17, 2016, 11:13:23 am
content: Quote from: wraper on December 17, 2016, 11:07:35 amPretty sure these thing woun't make it through coustoms (sp?).

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 11:17:24 am
content: Quote from: joseph nicholas on December 17, 2016, 11:13:23 amWhy won't it?

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 11:21:42 am
content: There also are more convenient ones with pegshttp://www.ebay.com/itm/60pcs-0-3M-wedding-stage-connect-wire-Safety-igniter-fireworks-firing-system-/222255036692?hash=item33bf6eb914:g:f4gAAOSwll1WxrMG

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: December 17, 2016, 11:25:50 am
content: Quote from: wraper on December 17, 2016, 11:17:24 amAnything that is faintly explosive will probably throw a red flag to the authorities. Like waving a red cape in front of a bull.

author: wraper
author_rank: Unknown
timestamp: December 17, 2016, 11:36:32 am
content: Quote from: joseph nicholas on December 17, 2016, 11:25:50 amAnd how they will know it's explosive? Will look just like a bunch of wires under X-ray.

author: Yansi
author_rank: Super Contributor
timestamp: December 17, 2016, 11:37:44 am
content: It shouldn't. These aren't classified as explosives. These are igniters. They just burn, do not explode.Do a quick googling, ya'll find some local suppliers of these in your area too for sure and maybe the price will be lower. For example I can buy igniters from a local company for half that price on ebay. (We have used them for some airsoft games and occasional small fireworks).

author: DaJMasta
author_rank: Super Contributor
timestamp: December 17, 2016, 05:45:16 pm
content: Quote from: joseph nicholas on December 17, 2016, 11:25:50 amDon't know if you can get model rockets in local hobby shops, but those electric match igniters are basically the same thing as what you put in a model rocket to ignite the engine.It would probably raise more flags doing this if you're caught, but these igniters are often just a bit of nichrome wire and an accelerant that ignites at a reasonably low temperature - even just wrapping the end of a fuse in nichrome and running some current through it would probably do the trick.

author: Ian.M
author_rank: Super Contributor
timestamp: December 17, 2016, 06:30:38 pm
content: Assembling an electric match with performance comparable to a commercial one is entirely DIYable. There's a good reference here:http://www.skylighter.com/fireworks/how-to-make/electric-matches-for-July-4th.aspInstead of the pre-made uncoated match blanks, you could make your own using offcuts of double sided PCB and fine iron wire. To make the iron wire solderable, degrease it and dip it in conc. copper sulphate solution to 'flash' it with a layer of copper plate.

author: orolo
author_rank: Frequent Contributor
timestamp: December 17, 2016, 07:36:47 pm
content: When in doubt about moonshine, fireworks or dubious ebay products, I always defer to Big Clive's wisdom.This can be done at 12 volts, just a battery. Safer and cheaper. Of course, there is the mains voltage version: