Do Capacitors Work in Reverse?

[mishalak]

I am not a technology geek. I do however have harebrained ideas. I know it isn't as simple as all that, because there are nitpicky design considerations, but I got to wondering if a type of capacitor could be designed that would take a large momentary charge and then bleed it off slowly rather than the usual take a small amount of current and deliver it all at once. See I was thinking if that was possible that enough of them could be hooked up together on one bus (I know just enough tech terminology to be dangerous to a science fiction story's plotline) that it could have enough capacitance to be as "attractive" as ground. Mad scientists will know where I'm going with this. Lightning in a bottle bled off slowly to turn a DC motor that turns an AC generator.

It is probably impractical if not totally impossible. But the thought experiment seemed to work... It would just need a mind bogglingly large amount of capacity.

Comments

in theory, yes, BUT...

[gomeza.livejournal.com]

Okay, here's the deal:

Capacitors resist a change in voltage by storing voltage in an electric field.

Inductors resist a change in current by storing energy in a magnetic field.

What you describe could be done (in theory only) with either type of component, using the appropriate additional components. The circuit is called an integrator, at least in terms of signals.

For serious power, what you are describing is impractical, because of the enormous values of current, voltage, and total charge.


The energy contained in an "average" lightning bolt (the number varies wildly, but you don't get to pick and choose among lightning bolts) is 215kWh, or 774 million joules.

To store that energy (assuming you could deal with it at all) using modern high energy density capacitors, would require 32 of the most powerful pulsed discharge machine ever created, the Atlas machine, shown here:
http://www.hytecinc.com/hei/app.html
Incidentally, the Atlas machine cost $43 million dollars to construct.

Or to put it into a different perspective (using older capacitor technology), you would need 43,000 capacitor banks the size of the one in my workshop. (the one in the big gray metal cabinet that weighs 3/4 of a ton)

Re: in theory, yes, BUT...

[mishalak.livejournal.com]

Figures there would be inconvenient facts getting in the way of the lovely idea of holding out a bucket for all that "free" energy. It is just frustrating on a stormy afternoon to be shutting off my computer because there is too much power floating about the atmosphere. I suppose it I wanted to make it far out possible in 30 years in a SF story no one could say for sure that it wouldn't be possible to build one for less. Of course by then electricity will probably be even less costly than it is now.

The only hope for this short story being close to the present rather than being the forever distant 30 years from now of room temperature superconductors and fusion power is if I can discover if building one of those mega masts like in North Dakota (http://en.wikipedia.org/wiki/KVLY-TV_mast) would make it possible to harvest power at lower densities than in a lightning bolt.

Re: in theory, yes, BUT...

[gomeza.livejournal.com]

Well, you had the right idea, everything I presented is just current engineering limitations. After all, there was a time when heavier than air flight was, in fact, quite impossible. The engineering and materials did not exist to make it possible. Same for space flight.

So don't give up hope. :)

However, I suspect putting money into other alternative sources of power would have more immediate benefit.

BTW, I never turn off my computer during stormy afternoons. Once you get a decent job again (and sooner or later you will) I can show you what to buy/do so you don't need to worry about surges, spikes, and power outages either.

(actually, I still have relatively unprotected phone lines - I really need to get on that)

Re: in theory, yes, BUT...

[mishalak.livejournal.com]

Part of the problem is that I now live out in IREA (Intermountain Rural Electric Association) territory. They do a good job and deliver moderately priced power but there are miles of wire between just the local substation and me. So every thunderstorm that comes close enough to hear the rumble will knock out the power for at least 3 seconds at one point if not for several hours. I've got the most heavy-duty surge protector I could afford, but I just couldn't plunk down the cash for a UPS. I'm not too worried on the data line score. We use microwave transmission to get from the house to a place on the other side of town. While theoretically possible I doubt the lighting will travel down the very slightly ionized path to the transmitter and receiver in the attic.

Re: in theory, yes, BUT...

[scottscidmore.livejournal.com]

Second tech point is that you wouldn't want to turn a moter to drive a generator, but rather use DC to AC conversion static invertors.

Re: in theory, yes, BUT...

[scottscidmore.livejournal.com]

Only I can not spell "motor"...

Another trick, assuming you could build capacitors, is to run a batch in series to collect the high voltage, then switch them into a parallel array to tap it at lower voltage.

Re: in theory, yes, BUT...

[mishalak.livejournal.com]

Well I'm really not up on tech. I thought a motor and generator set up was needed to convert from DC to AC. Hurm... I wonder if it would be cheaper to build a static inverter able to handle the enormous burst of energy and then step it down using ridiculously large transformers. Well the whole thing is impractical from the get go...