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Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
Backyard Skunkworks wrote ...
You may not have had any catastrophic failures from overcharging yet, but trust me, it will happen.
Overcharging a capacitor past 120% of its rated voltage is generally a good recipie for an explosion in short order.
Using caps at 90% or less of their rated voltage makes a very long life.
I guess its lucky I'm only charging them to 112% max then. It takes quite awhile to charge anyway so I usually have fired the coilgun at 300v - 330v anyway.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think if you are charging a capacitor beyond its rated voltage, it will just get hot. And a camera charger does not have nearly enough output power to heat a cap considerably...
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
When a capacitor is charged beyond its internal insulation capability the dielectric breaks down and it conducts. Yes, this causes heat, to start with. What happens next? Any capacitors in parallel with it will dump their charge into this low resistance path. This can boil the acid and steam pressure may cause it to explode. Some high quality capacitors are designed with a weak spot in the can so it leaks rather than explodes. But flash camera capacitors are made in the millions with the cheapest possible process.
Always build a capacitor bank into an enclosure for safety.
Cheers, Barry A chicken and an egg are laying down in bed. The egg is angrily muttering to itself, while the chicken is contentedly smoking a cigarette. The chicken leans over and says to the egg, "Well, I guess that answers THAT question..."
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Wood is good -- it's what I always use. A reasonable (not paper thin) amount of plexiglass or lexan or equivalent is fine, too. And plexi has the advantage of letting you see any bulges appear before a bigger catastrophe happens.
Cheers, Barry "I believe that religion is a serious neurological disorder." Bill Maher
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