Produce 1.21 Jiggawatts

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frezik
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Produce 1.21 Jiggawatts

Postby frezik » Thu May 07, 2009 3:39 am UTC

I rewatched all the Back to the Future movies recently. I think I was a kid when I last saw them, and it's interesting to find all the little jokes I missed back then.

Anyways, one thing I noticed is that, throwing away suspension of disbelief for the moment, the method of making 1.21 Jiggawatts in the first movie is ridiculously implausible. The DeLorean needs to hit the wire at exactly the moment lightning strikes, which brings up a lot of problems:

1) Doc says he's accounted for wind resistence in calculating acceleration. But there's a storm coming, and calculating this against gusting winds is impossible. Plus, nobody had really tried to apply aerodynamics to cars until the gas crisis of the '70s, and they found they had gotten it all wrong.
2) The exact acceleration could be off by at least a few tenths of a second just from tire wear (Doc did a nice little burnout just before he sent Einstein back in his first experiment) or Marty shifting a little early or late. Easily enough to miss the timing needed to catch the wire.
3) Attaching all that wire to the top of the clock tower likely would have changed the building's electric potential. Lightning may still have hit it, but not at the time originally expected.

Ignoring the fact that I'm suspending enough disbelief to allow for a working time machine but not for the above, how would you go about generating 1.21 Jiggawatts of electricity? You may use any means available to a wealthy, independent scientist living in 1955.
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douglasm
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Re: Produce 1.21 Jiggawatts

Postby douglasm » Thu May 07, 2009 3:50 am UTC

Make a note to go back and deliver plutonium to yourself 30 years later when it's easier to come by. :P

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Re: Produce 1.21 Jiggawatts

Postby Kizyr » Thu May 07, 2009 3:53 am UTC

What actually got me was none of that, but the fact that Marty only knew the minute that lightning struck the clock tower, whereas he would've needed to be accurate within at least 1/10th of a second.

But hey, it doesn't stop Back to the Future from being one of my favorite movie trilogies of all time. KF
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quintopia
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Re: Produce 1.21 Jiggawatts

Postby quintopia » Thu May 07, 2009 5:47 am UTC

Attach a van de graaf generator to the tower and make it so the pressure of the car on the wire closed the circuit and allowed the stored positive charge to flow up into the tower and further into the cloud. Also, put lots and lots of slack/springs in the wire so the car would remain in contact with the wire for like a whole 2 seconds (yes, i know that's probably 200 feet of slack, but the Doc was brilliant, yeah?)

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Kobayashi_Maru
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Re: Produce 1.21 Jiggawatts

Postby Kobayashi_Maru » Thu May 07, 2009 5:56 am UTC

Also, the Delorean stalls out for ten or fifteen seconds after Doc's carefully timed alarm clock goes off. So if Doc's calculations were correct, Marty should have been way late. If Doc's calculations were completely off, Marty rather arbitrarily manages to connect with the wire at the right instant.

In a basic attempt to answer your question: wikipedia says that the first nuclear power plant came online in 1954. In 1977 the Chernobyl Nuclear Power Plant's first reactor came online, producing about 1GW. Surely, Doc Brown would be able to engineer a 1.21 GW nuclear reactor in 1955, given the proper motivation. Indeed, in order to get 1.21 GW of electricity out of the plutonium in 1985, that is exactly what he has to do: build a nuclear reactor and a time machine out of a Delorean. I think most people completely disregard the former achievement.

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Zamfir
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Re: Produce 1.21 Jiggawatts

Postby Zamfir » Thu May 07, 2009 1:49 pm UTC

Why would he need a nuclear plant? A large 1950s coal plant surely has 1.2 gigawatt as output, and a lot less security issues. the Grand Coullee dam must have had several gWs of installed poer in the 1950s too.

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Re: Produce 1.21 Jiggawatts

Postby Tass » Thu May 07, 2009 2:07 pm UTC

Zamfir wrote:Why would he need a nuclear plant? A large 1950s coal plant surely has 1.2 gigawatt as output, and a lot less security issues. the Grand Coullee dam must have had several gWs of installed poer in the 1950s too.


Because it is much easier to fit a 1.21GW nuclear reactor on a DeLorean than a dam.

...Okay mayby not much easier...

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Re: Produce 1.21 Jiggawatts

Postby Kizyr » Thu May 07, 2009 2:17 pm UTC

Kobayashi_Maru wrote:Indeed, in order to get 1.21 GW of electricity out of the plutonium in 1985, that is exactly what he has to do: build a nuclear reactor and a time machine out of a Delorean. I think most people completely disregard the former achievement.

That might be because the latter achievement is way more awesome. I mean, if you're going to travel through time, you may as well do it in style. KF
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Velifer
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Re: Produce 1.21 Jiggawatts

Postby Velifer » Thu May 07, 2009 2:29 pm UTC

Grand Coulee generating capacity: 6,809 MW
Kashiwazaki nuclear plant total capacity: 8,212 MW
TVA’s Kingston Fossil Plant winter dependable capacity: 1,456 MW
1982 Delorian DMC-12: 1,210 MW

One of these would look pretty good in my back yard. One of these is in my Mom's backyard, and isn't quite so nice.

Kingston came online in 1955 and at the time was the largest coal fired plant in the world. It's been expanded since then I'm sure, so the largest coal plant extant in 1955 likely would have to be at all-hellfire capacity to perhaps squeeze out 1.21GW, if that was even possible then.
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idobox
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Re: Produce 1.21 Jiggawatts

Postby idobox » Thu May 07, 2009 8:04 pm UTC

The thing is, producing a lot of power is not that hard. Producing a lot of power for a long time is much harder.
A pretty feasible solution would be to build a hell lot of capacitors, take the time to charge them and connect them to a metal grid over a road.
From what I remember, the time machine needs something like 10s o work. If we make the hypothesis it consumes 1.2 gW for 10s, we get a total energy requirement of 12gJ. The energy stored in a capacitor is 1/2CU². With 100V capacitors, we need 0.6MF. A capacitor bank of this capacity could fit in a big house.

An other, easier alternative is to drive at a constant speed of 88mph with a kite or air balloon, thunder necklace-style.

I've also wondered : if the train didn't reach 88mph and the delorean fell, it would probably have achieved a falling speed of 88mph. In that case, would the Delorean have traveled back to the future before crashing?
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Re: Produce 1.21 Jiggawatts

Postby sgt york » Thu May 07, 2009 8:33 pm UTC

idobox wrote:I've also wondered : if the train didn't reach 88mph and the delorean fell, it would probably have achieved a falling speed of 88mph. In that case, would the Delorean have traveled back to the future before crashing?


Probably, but it would have crashed soon after traveling back. The cliff was still there.

Mr. Freeman
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Re: Produce 1.21 Jiggawatts

Postby Mr. Freeman » Fri May 08, 2009 5:22 am UTC

You don't need springs or anything really fancy.
Solution 1: Make the hook a slide, like a trombone, it'll remain in contact for a longer time.
Solution 2 (Preferred): Get a long wire and attach it to whatever the hook on the car is attached to. Doesn't matter where you are when the lightning hits, it'll still make contact.

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quintopia
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Re: Produce 1.21 Jiggawatts

Postby quintopia » Fri May 08, 2009 7:07 pm UTC

Mr. Freeman wrote:You don't need springs or anything really fancy.
Solution 1: Make the hook a slide, like a trombone, it'll remain in contact for a longer time.
Solution 2 (Preferred): Get a long wire and attach it to whatever the hook on the car is attached to. Doesn't matter where you are when the lightning hits, it'll still make contact.


That would be way uncool though. Where's the drama?

Also, how big does the cord need to be to minimize the induced resistance it will have to the sudden voltage input? Light enough that the DeLorean could drag a mile or two of it?


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