What to do with big capacitors?
 

I've got a couple 25,000uF 40VDC capacitors. Is there anything cool I can do with them?

Re: What to do with big capacitors?
 

Charge them up, short em out, run.

:)


Well, you could use them for some high powered audio system.

Or you could make a giant tazer.

Better yet, charge them up and leave them on a bench top for some unsuspecting victim to touch. :)

My dad said back when he had electronics shop they would charge up little caps and leave them laying around for freshman to pickup.

Re: What to do with big capacitors?
 

A tack welder. Maybe even a mobile one!!!

Re: What to do with big capacitors?
 

Electrical socket + long handled needle nose pliers + safety goggles + a clear path + big capacitor under-rated for said electrical socket = Bottle Rocket++ :ahh:
-Eric

Re: What to do with big capacitors?
 

-tesla coil

-charge it up, grab a couple of friends, and take turns putting the ends on your tonge.

-same thing, but nostrils

-get some raw chicken wings and make it dance

-get a volenteer to allow the ends to be stuck in his head. (have emergency crew stand by)

-put the two ends in the pool when someone is swimming (may be dangerous)

-try to light stuff on fire with the spark (is there a spark?)

-charge it up, grab some old electronics, and watch the magic smoke!

-sell it on ebay

-compare the shock bettween that and the shock that you get from a disposeable camera flash capacitor

-give it fully charged to the newbies

-mount it on the wall, and claim you shot it when you where hunting in south africa

-chuck it at my head to disable me from comming up with any more ideas

Re: What to do with big capacitors?
 

haha please wear goggles and some thick fireproof clothes when exploding them. I exploded a tiny 100uF cap and it was messy. :eek:
Save them for some electronics projects lor.. 25mF @ 40V can power a circuit for quite a while..

Re: What to do with big capacitors?
 

0.025 Farad x 40 Volt = 1 Coulomb electrical charge.

That's one Ampere flowing for one second, or 10 mA for 100 seconds, assuming a load circuit that will draw a constant current. So yeah, that capacitor can power a small logic circuit, through an appropriately designed regulator, for at least a minute or so.

More realistically, a load circuit equivalent to a constant 2000 Ohm resistance (the path from your left index finger to your right index finger, through your body, under some conditions) would initially draw 20 milliAmperes, and this would decay exponentially with a 50 second time constant [ i(t) = 0.02 x exp(-t/50) where t = time in seconds and i(t) is current in Amperes ] so that after 2.5 minutes the current will be less than 1 mA and the voltage less that 0.5 Volt.

20 mA is not enough current to send your heart into ventricular fibrillation, but enough to get your attention. Look here for more on electric shock.

Re: What to do with big capacitors?
 

Staying alive near them would be pretty cool. ;)

Re: What to do with big capacitors?
 

I wouldn't do any of these things! Rule of thumb...if it sparks don't put your face and especially your tongue near it!

Those are some serious caps, might make a spectacular linear power supply.

Re: What to do with big capacitors?
 

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.:ahh:

Re: What to do with big capacitors?
 

Those are overkill for a small railgun... There are a few sets of plans out there that can launch 1x1mm steel balls at 30+ m/s and are made out of 5 or 6 disposable cameras, I'd love to see what you can make with those!

Re: What to do with big capacitors?
 

Disposable camera capacitors are like 400 uF, I think. So with those you could make something very nice!

Re: What to do with big capacitors?
 

sorry i have no idea the power that this capacitor can dish out. I was just comming up with some random ideas that I wouldnt want anybody to take seriously.

Re: What to do with big capacitors?
 

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.

Tesla Coil = NO (Voltage is way to high on a Tesla Coil)

Many of the other ideas mentioned just won't work with this voltage rating of 40 VDC. You can charge it up at 6 V and run a DC item for a while. I bet it could run an iPod Shuffle for a little while??

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.

Re: What to do with big capacitors?
 

One word: Boom. But if you do anything destructive, please... remember the rule of boom: If you can see it, it can kill you. So be safe in your haphazardly destructive rampage (if you're going to do that, that is).

Re: What to do with big capacitors?
 

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

Re: What to do with big capacitors?
 

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.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:ahh: ) conditions.

Re: What to do with big capacitors?
 

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! :ahh:

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

-Q

Re: What to do with big capacitors?
 

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.:D

The most power I ever used was 1KJ

Re: What to do with big capacitors?
 

Hey I got a really crazy idea :eek:

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. :cool:

Re: What to do with big capacitors?
 

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!)

Re: What to do with big capacitors?
 

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

Re: What to do with big capacitors?
 

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

Re: What to do with big capacitors?
 

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.

Re: What to do with big capacitors?
 

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???

Re: What to do with big capacitors?
 

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.

Re: What to do with big capacitors?
 

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

Re: What to do with big capacitors?
 

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.

Re: What to do with big capacitors?
 

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.

Re: What to do with big capacitors?
 

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 ... :D

Re: What to do with big capacitors?
 

Uh, I could be wrong, but I believe the "skin" effect applies in a more measurable amount when considering a homogeneous conductor. When considering a conductor with varying resistance- and also at work, I believe, in the steel-high conductance wire, electricity will flow through the path of least resistance. The skin effect is really not powerful enough to override the tendency of electricity to flow through low resistance areas in such a case. Like your soft, squishy insides!

Re: What to do with big capacitors?
 

It certainly is a very confusing issue. Here is another question though about cars and lighting strikes. Is that the skin effect?

Re: What to do with big capacitors?
 

Guys,
As I understand the skin effect, the higher voltage or the high frequency voltage causes such an elevated state at the atomic level that the atoms actually are trying to push apart, like charges repelling. In a conductor that naturally causes them to move farthest from the inside of the conductor or to the "skin". For many applications, the conductor has so little current flowing at the interior that it is actually made of pipe to save weight and material. High power tranmission coax is made this way. Common VHF transmitters use a 6-1/8 outer pipe and a 1-1/2 or 2" inner pipe with dry air as the dielectric and teflon spacers at regular intervals to hold everything in place. Since the human body is not a conductor in the true sense, it is difficult for the current to obtain the skin effect. What does occur in high voltage contact is current passes through the body at the least resistance points where there is a high volume of liquids. The liquids turn to steam and explode causing the current to seek a path in adjacent tissue. Eventually, as all moisture is turned to vapor, the tissue starts to burn causing a carbon path for the current to flow. In lightning strikes this occurs rapidly because of the intense pulse. Remember that a direct contact is not needed to cause injury or death. Because of the ground resistance, it is easy to have a lethal voltage develope between your legs as the current passes through the ground. Should you ever find yourself in a position where a power line has fallen and contacted the ground, DO NOT RUN! Keep your feet together, on the ground and shuffle away from the source. If you are with someone, don't touch them while moving away. If in danger of a lightning strike, crouch on the ground and keep yourself rolled in a ball until the danger passes. This will make you less likely of getting a direct strike or of serious injury from a nearby strike. Stay away from trees and the same explosive events occur from a strike and many injuries are a result of flying wood splinters.

In cars (as in airplanes) there is some debate as to what actually occurs. Many people believe that the conductive frame acts a Faraday Cage. You occassionally will see a Faraday Cage in old photos of Tesla experiments.

Re: What to do with big capacitors?
 

Ahh.. it makes sense now.. Thanks

Re: What to do with big capacitors?
 

I think the best example has to be the giant bird cage in the Science Musuem in Boston. In fact the original Van da Graaf generator resides there. You can effectively hold your hand on the inside of the metal posts as six feet electrical arcs strike the other side. I think the conducting spheres on the generator also doubled as a cage/office space for Faraday.