How to blow (up) fuses

[Phil1977]

Hi,

I wanted to test an quite old high speed camera that is capable of doing 1200fps. So I thought let´s do something dangerous and load up a 350uF/1500V foil capacitor to 750V and short it with some glass fuses.

I switched it with a quite beefy contactor. The whole circuit has a resistance of around 0.3Ohm, so the short circuit current will be somewhere below 2.5kA. That´s a short circuit current that a low-impedance mains socket is also able to deliver, so the test parameters are not absolute unrealistic.

First I connected a 3A / 250V 5*20mm fast glass fuse. Surprisingly it succeeded to interrupt the current flow! The foil cap just discharged from 750V to 730V, the fuse was black but okay:





I wanted some fireworks, so I took a 20A/250V 5*20mm slow glass fuse. There the result clearly shows why this fuse can not get a higher CAT-rating:






It exploded with quite a bang, and the arc that is visible in the second last image discharged the cap down to 29V. It clearly was not able to interrupt the current flow.

PS: Please don't do these experiments if you have just a slight concern about your safety. Such a capacitor is roughly equivalent to a medical defibrillator - it can easily interfere with your heartbeat.

[tooki]

Very nice! Great demonstration of why we really do need $10 fuses in our multimeters!



Maybe the lead inductance was enough to slow current flow just enough for the fast-blow fuse to react in time?


The maximum current depends on the cap itself, too.

At work, my old boss built a doodad that uses two 2kV, 800µF electrolytics in parallel. Because the goal is huge currents, they were selected accordingly to have very low ESR, and each is the size of a 2 liter soda bottle.

When tested at 1.5kV, the discharge pulse peaked at 14kA. 

(And that's discharged through a little coil the size of the cap of a 2 liter soda bottle. They're potted in epoxy and cooled in liquid nitrogen, but still are basically single-use. )

[pcprogrammer]

The person of this youtube channel knows how to blow a fuse. 

[johansen]

The maximum current depends on the cap itself, too.

At work, my old boss built a doodad that uses two 2kV, 800µF electrolytics in parallel. Because the goal is huge currents, they were selected accordingly to have very low ESR, and each is the size of a 2 liter soda bottle.

When tested at 1.5kV, the discharge pulse peaked at 14kA. 

(And that's discharged through a little coil the size of the cap of a 2 liter soda bottle. They're potted in epoxy and cooled in liquid nitrogen, but still are basically single-use. )

i bought 40 8uF 4Kvdc caps for 5$ each back in 2010. wish i had bought 200 of them but i ended up buying the remaining 40 in stock.

they have a 50khz internal resonant frequency and so its practical for me to discharge them through a coil and get a 20Khz frequency. which is sort of still too slow for coin shrinking.

2560 joules at 8kv (or 4, if wired for 4kv)

I was able to bend a quarter but not shrink it. when i get around to it i'm going to make some coils and pot ceramic around them and then fire it in a kiln, and then press fit the ceramic tube into a copper pipe, to reflect all that good magnetic energy and also contain the coil.

i once wrapped the coil in 1/4" of fiberglass packing tape, and it blew it all up.

[tszaboo]

You can also blow up 3-5mm LEDs, with the right amount of voltage and current it might shoot off it's lens.
The worst mistake I saw was with a 10KA DC fuse, that someone blow.

[tooki]

The worst mistake I saw was with a 10KA DC fuse, that someone blow.

Go on...

[Phil1977]

Maybe the lead inductance was enough to slow current flow just enough for the fast-blow fuse to react in time?


The maximum current depends on the cap itself, too.

At work, my old boss built a doodad that uses two 2kV, 800µF electrolytics in parallel. Because the goal is huge currents, they were selected accordingly to have very low ESR, and each is the size of a 2 liter soda bottle.

When tested at 1.5kV, the discharge pulse peaked at 14kA. 

(And that's discharged through a little coil the size of the cap of a 2 liter soda bottle. They're potted in epoxy and cooled in liquid nitrogen, but still are basically single-use. )

The cap I´m using is specified for 25kA surge current and 1.9mOhm ESR. It´s a non-polar foil cap 8.5cm in diameter, 24cm long and 1.5kg (Electronicon E50.N23-354N50). I already did some short circuit tests with it and so far it´s capacity is stable - but I chickened out at 1kV so far, the energy and available power of this thing (>10MW peak power!!!) are nothing but scary.

[tszaboo]

The worst mistake I saw was with a 10KA DC fuse, that someone blow.

Go on...

It was with a lead acid battery, single cell about 20KG heavy.
Batteries do that. We were also making testers that went up to 4000A.

[schmitt trigger]

These hi-speed photos give one an appreciation on fault currents.
It would have been enlightening to actually see a video, but video cameras with those frame rates are devilishly expensive.

There is a YT channel of a pair of guys, The Slow Mo Guys, who specialize in very high frame rate videography and who love chemical explosions and bullets.
I ignore whether they have the knowledge to perform an electrical “explosion”.

[Phil1977]

In fact I took the pictures out of a video, but decided to just publish the stills because even in the 40x-slowmotion (1200fps record speed / 30fps view speed) everything happens more or less instantaneously. It´s quite obvious that the explosion of the 20A-fuse together with the discharge of the cap took something between 1 and 2ms.

Recording it with a Chronos or Phantom (as the SloMoBoys) would be great fun, but since I forgot to click order on bitcoins 20 years ago (yeah - my fault!) I can't do this right now. If someone in the area of Munich has a high speed cam of that type I´m readily available to blow something up.

And though it´s an ABB advertisement, there is at least one interesting high speed video of a circuit breaker available on Youtube: