Overloading capaciters

[MrWild]

I hear they tend to explode if overstrained. Not having had much excitement lately, I was looking at adding a third 12v 20A transformer for 36 AC volts before my rectifier and caps. The caps are rated for 50v DC (2x 10,000uf and 1 x 26,000uf in parrallel). The rectifier is rated 600v 30A. With just two transformers, I have 33v DC and any voltage spikes caused by the steppers is well in hand. Going to three transformers, I'd be right at 50v DC, and inductance generated spikes will be higher.

What I'm curious about is what are the fudge factors that manufacturers use when they build? For an example, my state posts speeds for corners that can easily be doubled in dry, and safely multiplied by about a facter of 1.3 in wet conditions. Other states are spot on for their dry conditions and woe be unto you for trying them in wet. I know it is a don't do this under dire consequences sort of thing, I'm interested in what have people done and gotten away with.

Any experiments would be done with the case closed to contain the shrapnel....

[epineh]

If you really want the electrolytics to pop, just wire them reverse polarity ! I have inadvertantly done this as a kid with small sized (100uf) sized caps, and it was like a small firecracker, I would try a large one but they are too expensive

I think the stuff inside (that will come outside in a hurry) is pretty carcinagenic, not to mention it smells bad...

As for the road speeds, coming from a motorcycling background, we used say that if you have got time to look at the speedo then you are not going fast enough, if you are scraping your exaust pipe and footpegs on a winding range road, (on a Jap bike) THEN you are going fast enough !

Russell.

[NC Cams]

Essentially, you're asking "how much can I cheat and still get away with it?"

In that respect the FOS (factor of safety) you're looking to find is going to be a sliding scale that is NOT really or readily quantifiable. Reason: the FOS's vary and can vary from manufacturer to manufacturer. They may also vary, to some extent, from batch to batch.

My personal FOS dos not involve EVER runing a cap at RATED voltage. I always run a votage rated higher than the anticipated circuit voltage for overvoltage protection reasons. IN that regard, I've never lost a cap due to overpressure. THen again, I haven't tried that hard....

[pastera]

The capacitor probably has a surge voltage rating of about 63 volts but don't rely on it for the long term. You will be repeatedly hitting the caps with an overvoltage and high ripple current, heating them up and causing a very reduced lifetime.

If you have a overvoltage dump circuit set for a couple of volts over nominal, then you would be able to get away with it short term (low lifetime on the caps).

You can get 27000uF 63 volt caps (ECE-T1JA273FA) for about $14 each. For $30 plus shipping you can replace what you have with the correct parts on not worry about failure.

Aaron

[MrWild]

Thanks! I probably won't go ahead and try, but my curisoity being what it is.... And these caps were FREE, but are my only ones at this power so I'll probably not waste them. Along with these, I also got lower voltage, high capcitance capaciters and I'm thinking I may run those in series for my higher power tests.

[vtxstar]

Originally Posted by MrWild I hear they tend to explode if overstrained. Not having had much excitement lately, I was looking at adding a third 12v 20A transformer for 36 AC volts before my rectifier and caps...

I'm not sure I follow your wiring idea. It sounds like you want to wire these transformers in series. Regardless, I regularly see 16V caps in circuits with 12V supplies. 20 to 30 % values over applied voltage is safe because the caps themselves are not terribly accurate and change with time.

Be careful. I've got a 450VDC cap here in the shop that let go in a system. Man what a mess. It dented the cabinet it was in and bent the buss bars connected to it like pretzels.

[rdpzycho]

3300uF at 50V rated voltage explodes like a firecracker. by the way, the intensity of explosion also depends on how you abused the capacitor. reversing it and charging to abnormally high voltages causes the largest explosion. slowly giving it peak voltages will just tend to heat it up, smokes come out of safety vents and the capacitor explodes.

300Vdc fed to a 33000uF 50V capacitor --- results in a small cloud like explosion in a nuclear bomb, probably because of the construction. we did'nt made it on purpose, two heatsinks (not insulated) just touch each other, then everybody just shouted "Oh God".

[neilw20]

Turn OFF MAIN SWITCH
Put a small 47uF 16v electro on the end of a SUICIDE LEAD.
Plug it in.
Stand behind protection screen like Mythbusters
TURN ON MAINSWITCH

Result:
Capacitor cannot be repaired
You can't get the smoke back in either! (LOL)
Should only be done under full supervision, or by a fully qualified sparko.


Don't try this. Just use your imagination.
Putting capacitors in series is also a good way to get LOUD surprises after some indeterminate time delay.

[rdpzycho]

Originally Posted by neilw20 Turn OFF MAIN SWITCH Put a small 47uF 16v electro on the end of a SUICIDE LEAD. Plug it in. Stand behind protection screen like Mythbusters TURN ON MAINSWITCH Result: Capacitor cannot be repaired You can't get the smoke back in either! (LOL) Should only be done under full supervision, or by a fully qualified sparko. Don't try this. Just use your imagination. Putting capacitors in series is also a good way to get LOUD surprises after some indeterminate time delay.

I already tried this quite a few times.

there are some capacitor charges that breaks open my circuit breaker.

some capacitors will no longer left traces of itself, just soot on your mounting and the remaining two pins. the film and the tin can can no longer be found.

the large ones can tear down metal chassis instantly when exploding.