High Energy Discharge Experiments

Turning the 'buzzzz' of electricity into 'BOOM's

 

Welcome to one of the scariest and most dangerous sections of the world of electronics. Consequently, this is also one area which I enjoy thoroughly!

So everyone knows that electricity goes 'fizz' and 'crackle' and 'bzzzzzzzzzzzzz', but something go 'KABOOM' isn't something you hear everyday. Well electricity has that potential, and it's just a matter of converting that stored energy into sound.


Capacitors... realise the energy!


Typical photoflash capacitor

This is actually rather simple - it utilizes the principles of one of the most common electronic components: the capacitor.

Capacitors store electric charge. The amount of charge they can store depends on their value of capacitance and their rated voltage. In short, the energy stored in a capacitor (Joules) = (1/2) x Volts^2 x Capacitance (Farads).

To the left is a typical capacitor found in a camera flash unit. These capacitors have extremely low ESR (equivalent series resistance), meaning they can discharge at very high currents. That's why we use them in these experiments...

People who work in the electricity industry will tell you that 16 joules is enough to kill a human. And that's very easily achievable with capacitors. Don't be surprised if your wife asks you to break out the annuity calculator and review the life insurance policies if you consider trying these experiments!

The capacitor bank that I use in these experiments consists of 5 paralleled photoflash capacitors, giving a total of 550uF at 330V. This rounds off to about 27 joules, so technically very dangerous.

Initially, I had put together a much larger capacitor bank, however the resultant explosions were difficult to capture on camera due to the sheer intensity of light involved. Hence I have found this setup to be the best demonstration circuit.


My collection of photoflash capacitors


The schematic... click on the picture for a higher resolution version.

Although 27 joules is nowhere near enough to do can crushing and railgun work, some interesting results are achievable. The aim of this simple, ultra small scale experiment was to see what happened when a couple hundred amps was passed through strips of different metals.

The very simple circuit to the left was designed. As you can see, I am being rather safe in that there are no direct mains voltages present - rather a 240/12V transformer run in reverse off a 12VAC supply. Switching is performed through a large relay that (in a past life) was probably used on a railway switch circuit.

Of course, a much neater alternative would be to use some kind of electronic means of switching, such as an SCR. But since we are here to destroy things anyway...

For safety's sake, the whole setup was enclosed in a tough industrial plastic case, just in case the capacitors decided to blow on me. The important features of the circuit are labelled on the image to the right. This is as crude as a pulse discharge circuit can get!

I decided to test the effects of the circuit on a few different metals; aluminium, copper, and steel. Strips of each were secured to the discharge terminals, then the capacitors shorted straight through the poor little strips.


The setup - messy, but functional.


The discharge terminals alight!

This is a strip of aluminium being vapourised on the discharge terminals. Vaporising aluminium produces a very intense light, and in fact it is commonly used as an ingredient for this purpose in flash grenades.

I like this image because it just looks like some kind of atom collision. The way the molten particles spread appears rather chaotic.

This is again a strip of aluminium being vapourised, but during an earlier test run of the circuit.

The multimeter serves no purpose other than tell me how many volts are left in the capacitor bank after discharge, potentially saving me from a nasty bite afterwards. Also barely visible in the foreground is the battery (12V, 7AH SLA) for energizing the relay.

Another strip of aluminium. Notice how the spark trails of aluminium are relatively straight, indicating that the residual aluminium is travelling at high velocity.
In comparison, this is steel wool vapourising off the discharge terminals. Very clearly this produces a different effect. The combustion is not as bright as aluminium, and the steel particles are relatively heavier as clearly evident in the parabolic spark trails.

This is a single strand of steel wool placed across the discharge terminals. Again, the molten projectiles are heavy and fall very quickly with a highly pronounced parabolic effect.

A good replacement for fountain fireworks, perhaps?

A copper strip over the discharge terminals. Not very interesting is it... probably due to the higher conductivity of copper (I couldn't find a thinner strand at the time). Also note how the explosion has a green shade... Copper oxide burns green.

 

Video frame captures

I managed to capture some of these discharges on video, and these are the frames captured during two explosions.

The first is of a strand of steel wool. Clearly evident in frame 1 is the green copper tinge of the stressed relay contacts uncontrollably arcing over.

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The second video involves a setup of a strip of aluminium of roughly the same thickness as the steel wool above. Frame 2 is seen to be completely saturated (hmm I'm not sure if this is great for the camera), whilst the ghostly artifact in frame 1 also gives the feeling that the camera is about to undergo some kind of serious torment.
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