3000 Farad ultracapacitors, cheap used surplus

Gold mine does that often. New items tend to be "on sale" a week or month later too.

I'm curious to know how you plan to use them and (if in series) how you plan to balance the charge?

A couple of AA batteries can do that!

John

Huh? :)

Eveready says 'short circuit' current for their AA cells can be as low as 5 A and still be within spec. Thats about what, 0.23% of the capacitor peak current?

--Winston

--
How many cells in the batteries?

Google results:

'shop "AA cell"' gets 28,500 hits 'shop "AA battery"' gets 470,000 hits

The motion is carried 16.5:1 One cell per battery.

(You had a witty response, though.) :)

--Winston

It just means ignorance overrules intelligence 16.5 to one.

--
Thank you for that, and welcome to the melee. ;)

--
Whoosh...

Nope. I got the import of your question instantly. Larkin clearly meant to say that two AA *cells* were capable of the same level of pulse current as were the 3000 Farad lytics.

They still aren't. Whoosh yerself. :)

--Winston

Using these in series is simply asking for a catastrophic failure mode to present itself.

He would have to actively watchdog circuit monitor each cap individually.

Same paradigm for batteries.

Simple math here. Just compare the Watt/Hour ratings of each.

The 3.04 wins. Also, I would imagine that it could pulse better too as it is made for delivery upon demand, whereas a battery is meant for long slow, steady draw, and hard hitting pulses kill 'em quick(er).

Odd that my camera accepts both Alkaline batteries at 1.5V each and NiMh at 1.2V each. The odd part is that the alkalines begin declaring low battery after a mere ten minutes of camera use, and the lower voltage set runs for days with whimpering once. It all has to do with the output consumption curves. I guess the extra .3 V means that it will simple end up avalanching sooner for the same W/Hr rating.

-

AA cells at two kiloamps? Um.

The 3000B spec says 0.00029 ohms max ESR. At 2.7 volts that gives

9,000 amps shorting current. A friend just reports that he's had his up to 5V without damage. Try 17,000 amps shorting current.

How about a mass driver using a droplet of liquid Galinstan metal and a nearby supermagnet?

I meant the energy storage. The peak pulse power could be handled with a much smaller cap. There's a small window of applications where such supercaps are sensible.

John

Come back when you can store and deliver the kinds of pulses needed to shrink coins.

http://205.243.100.155/frames/shrinkergallery.html

Like ~1610 Farads to get the necessary 5859 Joules? That is *tiny*. :)

I'm really feeling my age. 0.1 F used to be a "HUGE" cap!

--Winston

att-

But suddenly we can have Kiloamps for seconds, rather than mSec. I suspect that most of the fun will involve b-fields.

Yeah: physics lecture demonstrations, and low-volt hands-on science education. The whole point of buying $20 ultracaps is to do some niche interesting odd things, odd things which otherwise could only be done expensively if at all. If we all feel a need to badmouth the whole idea and prefer 12V car batteries instead, well, there's a certain narrow class of fun and messing around that we'll be missing.

In the long term I think it's quite unwise to habitually badmouth new types of electronics fun. But perhaps that's one of the unwritten requirements for surviving on SED?

Hmm. Maybe they'd let us change the pole patterns on Neo supermagnets. Or be good for spotwelding platinum electrodes!

(((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty

beaty, chem washington edu Research Engineer billb, amasci com UW Chem Dept, Bagley Hall RM74

206-543-6195 Box 351700, Seattle, WA 98195-1700

I used to magnetize/reverse alnico magnets when I was a kid. A cap bank was a dozen or two TV filter caps charged to 350 volts or so, discharged into a 10-turn coil of #14 wire, something like that. Bang. Seemed to saturate anything I had.

What would be cool would be to take a couple of hundred surplus electrolytics and parallel them using sheet conductors, to keep the impedance down. I'm not sure what you'd use for a switch. A high h-field could have some interesting optical effects.

The supercap voltages are kind of low to get extreme peak currents. $20 suggests that their use is rather specialized.

John

o

Hah, quartershrinking was invented locally by Dale T., see http://205.243.100.155/frames/Shrinking_History.htm

Later I heard an interesting (possibly even true) story from a Boeing guy that came to one of our meetings. He said the energy storage capacitors were on the local surplus market because the head of the Boeing dent-puller design project had been killed by a capacitor discharge. They were getting rid of the lethal things and switching over to banks of electrolytics running at well below 1KV.

From the high-speed videos of quartershrinking,

h?v=3De4W7VBl5mEg it looks like the compression happens over incredibly brief time. This suggests that HV capacitors may have a big downside re. efficiency, and not be well matched to the load. Design a very brief pulser which smashes quarters without then later destroying the work coil?

(((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty

beaty, chem washington edu Research Engineer billb, amasci com UW Chem Dept, Bagley Hall RM74

206-543-6195 Box 351700, Seattle, WA 98195-1700

The resonant frequency of these things is on the order of 50kHz, with a low Q, so most of the energy will be delivered in about 50us, or about nine frames at that speed (180kfps = 5.56 us/frame!).

Interesting that there seems to be a bright white spot in -95564; implosion heating? Perhaps analogous to cavitation?

It's too bad the rest of the video is all white-out from the huge plasma ball. Would've liked to see the coil fracture. All I can see is one crack, bridged with plasma, then whiteout until it subsides at the end.

Excellent video!

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms