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1450 lbs of HV capacitors - gloves and boots?

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LAN_403

Hydron

Thu Feb 20 2014, 09:21AM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

At uni the HV lab had a 50+ kJ cap bank, which is in the same voltage and energy ballpark as what you have here.

For charging they had a commercial HV meter on it to monitor the voltage - one day this silently failed (read lower than actual) and they ended up with some of the caps rupturing. I saw the aftermath - not pretty, insulators and oil everywhere. Don't trust just having a meter across them, it's not enough!

What they did always do was have a bunch of chicken sticks with grounded earth hooks at the end to make the bank safe after discharge. I think they had two per node just to make darn sure it was grounded.

They also had a large resistor to discharge the bank slowly if needed - you don't want to short out a 50kJ bank! I believe they connected it to the bank (with a fail-safe knife type switch held open by electromagnet) as an automatic part of the firing sequence, minimizing the opportunity for human error. This system was DIYed by some postgrads and a lecturer and worked well, so it is possible to do these things yourself (it also included a triggered spark gap, and was all isolated fiber-optically).

The last thing was that they never got near it while it was energized - no messing about with gloves is needed if there are a few meters, earth hooks and an automatic discharge system between you and the danger. At a minimum everyone was at a safe distance wearing face shields and earmuffs - there is an explosion hazard as well as an electrical one when dealing with this stuff. I wouldn't even contemplate getting within glove distance of these energies without being specifically trained to, and I sincerely hope you don't either.

See attached pic - in background on left is the cap bank, behind the tripod is on of the chicken sticks with earth hook (will have been a few more of these out of shot). Just above the exploding wire on the left the open knife 'blade' can be seen.

Edit: have a look at this thesis:

It contains a rundown of safety procedures they used and pictures of the setup, as well as some very impressive wire explosion pictures in chapter 6 which are probably of general interest (60 meters of plasma!). My pic was from an earlier setup - the later stuff in the thesis was after I left uni. There are probably more publications of this stuff too if people are interested. It was certainly interesting working near these guys - you got used to hearing big bangs going off in the building next door, and I'd pop by occasionally to check it out.

Mads Barnkob

Thu Feb 20 2014, 12:16PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Thanks for the description and link to the thesis, just browsed through it, looking forward to read it through, later when I get home.

The construction details for all the DIY parts is amazing :)

seveerz

Thu Feb 20 2014, 11:39PM

Registered Member #8993 Joined: Mon Dec 24 2012, 11:21AM
Location: Yukon, OK USA
Posts: 3

would you say that's a current shunt on the table (left side behind what looks like film cans) in Hydrons post

Dr. Dark Current

Fri Feb 21 2014, 10:34AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Do people have common sense today? Just don't go near it when it's charged. And install safety discharge system.

Tetris

Tue Feb 25 2014, 12:14AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Proud Mary wrote ...

Stella's opinion: Not necessarily fatal, not fatal in every single case that is, but if you survive the Lichtenberg figures experience you'll be able to dine out on it for a year:

1391884435 543 FT161143 Lichtenberg Figures On Skin

PS You will defo need ear defenders when those bad caps crack over.

Hey, at least it leaves you with a really cool fractal tattoo, and better to get a sharp pain done and over with rather than have a lesser pain drag out for hours and days!

GammaRay

Wed Feb 26 2014, 08:55AM

Registered Member #5323 Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104

The safety discharge 'crow-bar' system is a good idea. But which of the several crowbar designs out there, particularly the components, would be best suited/able to safely discharge a capacitor bank of (10) 41kV caps @ totaling 70.5 uf ? I've looked at a few designs, but could use some guidance from those who have built/used crowbar systems themselves.

Kizmo

Wed Feb 26 2014, 01:18PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I have some experiece with my deadly dangerous electrolytic capacitor bank (80kJ at 11mF @ 3850V)

This capacitor bank is made from 8 series connected smaller banks of 30 lytics in parallel (whopping 240 capacitors total).

My safety discharge system is made like this: 30 capacitor "sub banks" have 150ohm 100W ceramic resistor in series with homemade pneumatic knife switch. Switches are spring loaded NC type so they will close as soon as pneumatic pressure is not present. I can use either compressor or bicycle pump to arm the bank right before charging and after more or less successful discharge i just let the air out and bank will discharge to safe state.

Also all 8 sub banks have indicator lights that tell me if there is more than 20Volts present.

Things like these are damn scary. No matter what kind of safety thigns i have, the feeling is like standing right next to a armed bomb. Remote voltage indication and discharge does help but still..

Stay safe!

EDIT: This is an example what happes when you bodge things together: (and this is when I started to take safety more seriously..)

Voltage doubler failure
Video evidence..

It took 4 hours to clean up that mess. And new pair of underwear was needed because i was standing right next to the doubler that blew up. I did test the doubler up to 60kV without load but then it blew up at around 30kV. Luckily no one was hurt but i did feel the heatwave from that fire ball...

Main reason for this failure was bad build quality and lack of charging resistance. Once doubler shorted for some reason, there was nothing to limit the current from capacitors to the obviously shorted doubler...

Newton Brawn

Tue Mar 04 2014, 01:32PM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

How many grams or paound of dynamit is nescessary to produce 50kJ ??

Mads Barnkob

Tue Mar 04 2014, 06:13PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Newton Brawn wrote ...

How many grams or paound of dynamit is nescessary to produce 50kJ ??

Did you Google it first?

10 gram

quicksilver

Tue Mar 11 2014, 07:39PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Without being overly dramatic, 8 grams of RDX is generally used in "toe popper" mines & Cluster bombs & things of that nature leaving traumatic amputations of legs, etc. so from an energy stand-point you are working with a "too late to say your sorry" issue. {Remember the caps are encased in metal as well.}

I once did some things at a radar station back in the 1970's and "space-suits" and extremely heavy grounding were the norm.The "chicken sticks" and knife-switches were very professional grade (for that time) and 3 men lost their lives in that room. The caps were of a type somewhat similar to what you have there. There really are few experiments that you can't do with substantially less.
Unless you have the funds to seriously invest in the correct type of materials, I would not work with them as they offer opportunities to get hurt & if you are alone; to experience a tragedy.
The type of materials are really NOT MADE to be worked with alone & thus the expense gets greater & greater.

Please be careful.

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