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Cap bank "Big Bang" explosion to open Cosmology Gallery

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LAN_403

Tesladownunder

Mon May 12 2008, 07:14PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

On Thursday 16th July, the Cosmology Gallery at the Gravity Discovery Center in Gingin, Western Australia will be opened by the Premier and assorted dignitaries.
In keeping with the Cosmological theme, I felt a "Big Bang" was needed rather than a heap of Helium balloons. Accordingly I offered to bring my big cap bank up there. (215uF total 12kV max)
The plan is to fire off perhaps 4kJ of energy into some steel wool and aluminum foil to give an explosion similar to the last picture.
To do this safely, I need to consider
1 The sound level: I have done sound level check with the output of my sound level meter. About 120dB peak (just clipping) at 10 m into my shed unshielded. See pics below.
2 The flash: I will shield the direct effect with some aluminum sheet.
3 Electrical safety. I will use my remote triggering with a string as before.
4 Sparkles protection.

To limit the sound and improve fire and electrical safety I will have the acrylic lifter enclosure which is about a 6 foot cube. The acrylic should not be damaged (I have tested this).

There were a few challenges. Particularly convincing 300kg to get onto my trailer. I used a block and tackle arrangement. I hope it will survive the 6 hour round trip.

TDU

1210618891 10 FT0 Pulsecapssteelwool2kjpre

1210619470 10 FT0 Pulsecapssteelwool3kjhiresside475

Tesladownunder

Fri May 16 2008, 12:12PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Got it on to a trailer for a test drive. Also wanted to go to higher energies without disturbing the neighbours so took it to an isolated industrial site driveway at night.

Here is 5kJ. Went to 10kJ but HV meter was running down and the shot was not as impressive for some reason. Wanted to try to fully charge the caps to 12kV but the HV meter was needed to make it safe so I've left that for another day.

Power was from a 300W generator and trickled in with a variac.

TDU

ea6b607

Fri May 16 2008, 12:26PM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
Location:
Posts: 67

Wow, those are some pretty wicked sparks!

Dragon64

Sat May 17 2008, 02:25AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

how long did it take you to load all the capacitor bank?

Tesladownunder

Sat May 17 2008, 07:27AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Theoretically only 25 seconds or so to charge 5kJ from 300W. The charger can supply more but it has resistive limiting to prevent damage during voltage reversals during ringing.
In practice just left it on while setting up the camera.

TDU

dingo27

Sun May 18 2008, 02:32PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

you caugh a ghost on left :)

nice sparks

Tesladownunder

Mon May 19 2008, 12:18AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

dingo27 wrote ...

you caugh a ghost on left :)

Interesting that I didn't see that earlier in the shot with the car. I had tried to get myself in the photo.
There are actually 3 light events. A camera flash at the start and end of the exposure plus the sparks from the explosion. Unless you are in all 3 you will be transparent to some degree. I was only caught by the final flash. I forgot to bring my long range IR remote that would have allowed me to be in all three.

The shot in the first post of the explosion has me in it which is real.

What do we call these trails of molten metal in an explosions. Should it be sparks, sparkles, sparklers or what?

Peter

Dragon64

Mon May 19 2008, 05:16AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

I guess we should call it sparks since the definition suits it the best.

Definition: A spark is a small airborne ember or particals of glowing hot metal.

Wavetuner

Sat May 24 2008, 05:14PM

Registered Member #1500 Joined: Sat May 24 2008, 04:38PM
Location: Ojai, Ca.
Posts: 44

Dr T. Can you show a picture of how your cap gap switch works. I have been wasting alot of time trying to design an adjustable inonized fired gap for various large dischage caps.

Tesladownunder

Sat May 24 2008, 06:29PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Switch is here. It seems to have functioned well after perhaps 50 shots. There is a few mm of erosion on the edge of the contact but there is a lot more mass to go. The other key feature is that I have designed it to be low bounce with a neoprene buffer.
My guess is that the arc forms at 5kV a couple of mm before contact is made but the solid force from the trampoline springs overcomes the explosive effect and forms a solid contact in a ms or so later.
It would be really interesting to know if this is really a self triggered gap or a contacting switch as the first discharge is over in 30us. I should do a voltage vs light intensity reading simultaneously on the CRO to look at that.
The other key thing about the switch is the heavy copper braid that provides the switch flexibility. You could use battery connecting braid (from an auto store) in several layers. Also the final current path is straight to reduce inductance.

TDU

1211653607 10 FT45143 Pulsecapsswitchclose

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