Bought huge capacitors

[ritaismyconscience]

http://imgur.com/gallery/OcA4IgW

I bought these 15600uF 2800v for 50 dollars each and I was wondering what kind of project I should build with them. I probably won't be able to afford scrs and switching 100kj is likely not easy. Any ideas?

[Mads Barnkob]

First, congratulations on a bargain buy there! I will buy them off you if shipping isn't a killer!

I got some good papers collected on high current discharges, especially the one on erosion is interesting when it comes to designing spark gaps: http://kaizerpowerelectronics.dk/tools/file-archive/?drawer=application_notes*pulse_power

One of these capacitors is obvious choice as DC bus capacitor in a large DRSSTC, as in serisouly large, multiply 600-1200A IGBTs in parallel, 5-6 meters tall, so might not be the project you are looking for. Or build your own electric car.

Ring launchers, can crushers etc. utilizes lower voltage better as you have less flash-over of the work coil, so there is always that.

[Hydron]

My 2c:
- very nice score!
- take those safety warnings seriously
- play around with mechanical switching, triggered spark gaps etc. This sort of energy is probably beyond normal SCR territory anyway!

[ritaismyconscience]

One of my other concerns is that my neighbors would get mad at me (it'll probably sound like an explosion)

[Mads Barnkob]

One of my other concerns is that my neighbors would get mad at me (it'll probably sound like an explosion)

More in the region of gun shot, it does not get that deep boom from a huge displacement of a lot of air, it is a sharp metallic snapping from the intense and short lived short circuit energy discharge.

With some soft materials around, which can also act as blast shields, you can absorb a lot of sound. Even just a closed door to a garage will take most of it.

Also, take safety serious as Hydron says, these energy levels can remove your hand or any other flesh that becomes a conductor.

[badpeter]

This immediately reminds me of youtuber "PhotonicInduction" who does all kinds of very odd things with crazy parts like that!

[Max]

Some time ago I visited a high voltage lab. Beside highly interesting things like a 900kV transformer they also had a few serious cap banks. One of them was used to blow up an Aluminium wire with 30kJ. We stand a few meters away and the "boom" was deep and intense enough to be felt in the whole body. There was much more energy released because the aluminium reacts with the oxygen - and as it's evaporated and very hot it does this rather quickly

Outdoors the sound might be sharper, but it definetly has nothing to do with your <5kJ home made cap banks.


Kind regards,
Max

[MRMILSTAR]

Switching a high energy at low voltage like that is definitely a challenge. My quarter shrinker uses 2 brass electrodes, each of which is 2 inches in diameter. I can move them as close as 1 mm with good precision but that is not good enough for your low voltage capacitors unless you can make a switch with enough precision to achieve sub-millimeter spacing without touching. Normally, you don't want the electrodes to touch when firing to prevent welding. I only see 2 options for your low voltage: triggered gap or contact switch.

I haven't seen any triggered gaps that operate at these low voltages (<2500 volts). You may be able to build one but it would take some experimentation.

The other option is a contact switch. You can make a sacrificial switch that welds each time it is used. This is not very attractive because it would have ti be replaced after each firing. Another possibility is the use of pure tungsten electrodes. These might be able to make contact without welding. I don't know. Even if it would work, large tungsten electrodes would be expensive. Perhaps you could cut up some tungsten welding rods and use the rods in parallel to make a large electrode.

[dexter]

in a 2015 post from 4hv by Kizmo about triggered spark gaps he says it works at any capacitor voltage even as low as 20V
https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=171055#post-171722

also saw some russians playing with a homemade taser on the mains wiring of their house which had the same effect as a triggered spark gap

[MRMILSTAR]

Triggered spark gaps make me nervous. They don't seem to be extremely reliable. Most of the time they fire but sometimes they don't. When they don't, you're sitting there with a huge capacitor with massive energy stored in it. Then you have to figure out a way to discharge it. That's why I use a simple 2-electrode switch that depends only on proximity to fire. Of course any impulse energy device such as this should have a way to safely and slowly discharge a fully-charged capacitor bank. I use a group of power resistors.

Given your low maximum voltage, a triggered spark gap may be your best option if you can make it work reliably and without destroying the trigger circuit.