What to do with big capacitors?

[Kyle Love]

We use come big capacitors to make one kick'n ball.

[Richard Wallace]

Originally Posted by Doug G

If charged up at the max rating of 40 VDC - I don't think they will cause anyone that much harm. Resistance of people is on the order of 50,000 ohms - 500,000 ohms. Ohms Law says Current = Volts/Resistance, therefore... at 40 Volts and 50,000 Ohms, Current should be around 0.0008 Amps, which won't do much. It won't get your attention until you get up to 10 mA or higher. Maybe on your tongue will the resistance be low enough to give a good tingle. I use .1 Farad capacitors in my physics class and we charge them up with 9 V and the kids handle them without any shocks; they like putting tin foil on the terminals and watching sparks.

Human body resistance can be as high as you say, but can also be much lower depending on conditions. Look here or here for some interesting discussion and examples.

Originally Posted by Doug G

Power stored in a Capacitor is P = 1/2 * C * V^2, so 1/2 * .025 * 40^2 = 20 W in each Cap if its fully charged up to 40 V.

You mean energy, not power. The formula above gives stored energy in Joules. And 20 Joules is more than enough to stop your heart under the right (er, wrong ) conditions.

[Qbranch]

Originally Posted by lukevanoort

Rail Gun. Alright, they're a bit small, depending on your number and desired power. Then again, they might be just fine and I'm just crazy... most likely the latter, I had a railgun design I was going to make for Physics extra credit that had a theoretical 1MW output.

Actually.... if you tied these all in parallel and got a large wound electromagnet, put a steel magnetized ring over a pole, and discharged the caps into the magnet, it will shoot up pretty dang far!

btw can't take all the credit for that, i saw it at the carnegie science museum.

-Q

[MAteo9944]

http://www.youtube.com/watch?v=g9bnhJqWaR0

Here is a low power shot from one of my projects.
There were 9 more caps in parallel for use outside.
It was very amusing.

The most power I ever used was 1KJ

[Protronie]

Hey I got a really crazy idea

Why not just put them in a locker somewhere... and hang on to them .

You might come up with a good[/i] use for them someday.

[Matt Krass]

I say save them, you never know when a sensible, safe use for them will come up.

To all of you suggesting stupid, dangerous stunts, shame on you. When dealing with high powered devices the last thing on your minds should be "What stunts can I pull with this?"

Show some respect for the amount of damage you can cause to yourself when you're fooling around with stuff, this might be a relatively small capacitor, compared to say a computer monitor, but it can still hurt someone.

I'll never understand what's amusing about hurting yourself.

I say save em for a project, I bet you can come up with something cool. (And safe!)

[Alan Anderson]

Originally Posted by Qbranch

Actually.... if you tied these all in parallel and got a large wound electromagnet, put a steel magnetized ring over a pole, and discharged the caps into the magnet, it will shoot up pretty dang far!

btw can't take all the credit for that, i saw it at the carnegie science museum.

-Q

Are you sure the ring wasn't aluminum? That's what's used in the usual demonstration of such effects.

[Qbranch]

Originally Posted by Alan Anderson

Are you sure the ring wasn't aluminum? That's what's used in the usual demonstration of such effects.

it may have been aluminum, what I should have said was a metal ring, just saw the thing at a science museum, thought it was cool, and this thread reminded me of it, you are probably right.

-Q

[Doug G]

Richard,

True. Body resistance is much more complicated than that of a wire, which is why I used a range from 50k thru 500k Ohm. Measuring the resistance of a tongue and you get as low as 1-5k Ohm, which explains the tingly sensation of licking a 9 Volt battery. Also helps explain why it is common to see medical folks use a "gel" when connecting the terminals of a defibrilator to a patient. No doubt that gel lowers the resistance to help increase the current through the chest. I still think if someone charged up these caps and held them in your hand - the result is most likely not dangerous, probably more dangerous is the burn you may get from accidentally shorting out the cap's terminals. Also notice in your first linked website, that DC is somewhat safer than low freq AC, but then as the freq of AC increases the skin effect takes place and becomes a bit safer. Good sites - I will use them with my students!!

For the Power equation, I stand corrected, PE = 1/2 C V^2 and yes that ends up as 20 J not Watts.

[Doug G]

I've had this Cap for a while now and haven't decided what to do with it either - notice it's only 15 microFarad, but its rated at 3.5 kV. Possible PE = 1/2 * .000015 F * 3500^2 V^2 = 92 Joules. But touching this when charged when your body resistance is 50 kOhm results in up to 70 mA which is on the borderline of lethal. My only idea is to use a HeNe Laser power supply to build a charging circuit (need to research the feasibility of this) and then discharge the cap through some coiled up copper tubing wound around an Aluminum can (Can crusher). The brief max current through the tubing should be in excess of 10,000 A and will create one heck of a magnetic field. Hmmmm???

[Al Skierkiewicz]

Doug,
The gell used with defib actually decreases the localized current peaks to prevent burning by insuring that the current is spread out over the entire area of the paddle for much the same reason we are talking about. The skin resistance varies drastically over different areas and under different conditions. I am not sure what you are referring to with the "skin effect" vs. frequency. High frequency currents tend to move on the "skin" of a conductor but this has little to do with the effect on a body coming in contact with a high frequency voltage. RF burns are real and occur at relatively low voltages. I have some scars to prove that.
The big cap you have likely came from a high voltage power supply. I have seen these in old industrial strength microwave ovens, TWT amplifiers, transmitter power supplies and old style TV projection devices. Handle this one with care as it is oil filled and likely contains PCB if it was manufactured in the 60's or 70's.

[Salik Syed]

Nice Capacitor, don't let the physics kids get a hold of that one!
not that they'd know how to charge it ... but still.

Al:
I think it has something to do with the fact that as you increase frequency the current has more and more of a tendency to flow near the edges of the conductor. at high frequencies the Skin effect effectively increases the resistance of the conductor lowering the possiblity of damage to the body.
heres a webpage I found the info on
http://whatis.techtarget.com/definit...541369,00.html

[Al Skierkiewicz]

Originally Posted by Salik Syed

Al:
I think it has something to do with the fact that as you increase frequency the current has more and more of a tendency to flow near the edges of the conductor.

Salik,
This is true for current in a conductor and it also occurs with ever increasing voltage. This is why high tension lines are frequently made with a steel core for strength with a suitable high conductance outer shell. However, this effect does not take place inside the human body as current still travels through the path(s) of least resistance. On a wet body that may very well be along the outer surface but... The human body still operates with miniscule currents that control muscle function, nerve transfer and thinking. Large currents interfere and often fatally damage these transducers. In the case of many electrocutions, the heart is merely waiting for the next large pulse to beat. If other damage is minor and external means are used to keep breathing and blood flow moving, the heart can eventually return to operating on the miniature pulses it receives. This is why it so important to learn CPR. Of course, there is no substitute for learning safe operating practice and staying away from situations where harmful conditions can occur.
I have seen tissue damage from both high voltage and from RF voltage. As with lightning, the only thing that is predictable about body contact with these voltages is that they are unpredictable.
I forgot to mention that the caps in the power supply for one of the transmitters I work on are 4 mmf @ 50kV. The power supply is 30-35kV at 2 amps. The caps are about 6 x 24 x 40 inches, oil filled and reside in an explosion proof enclosure.

[Not2B]

Now I don't know much about electricity, but I can tell you...

Be careful!

The most painful wound I have ever had was an electrical burn from a capacitor when I was in middle school - and it was only the capacitor from a camera flash. (A 110 camera... no less). AND I thought it was discharged. (

Two fingers touched the leds... burned down deep... lots of smoke and burnt flesh... no blood because it was cotterized. I still have brown burn marks at the entry and exit points.

And to put this in relative pain terms, I also shot myself in the hand with an arrow in high school gym class (target tip lucky for me). Electical burn still worse.

[Salik Syed]

Originally Posted by Al Skierkiewicz

Salik,
This is true for current in a conductor and it also occurs with ever increasing voltage. This is why high tension lines are frequently made with a steel core for strength with a suitable high conductance outer shell. However, this effect does not take place inside the human body as current still travels through the path(s) of least resistance. On a wet body that may very well be along the outer surface but... .

I see now, It makes sense to me that the Skin effect wouldn't result in a significant palliative effect on the body , but why is it that the Skin effect does not take place at all inside the human body? I know current should take the path of least resistance, but the skin effect should still effectively lower the current flow since high frequency AC is still flowing through *a* conductor (the human body that is)? Is the skin effect not a simple property of AC regardless of the medium it is flowing through? I have no idea what i'm talking about so ...