Capacitor powered car to give 500 miles on 5 min charge

[Dean Huster]

A battery uses a chemical reaction (reversable in the case of a rechargable) while a cap simply passivly stores charge on the surface area of its plates.

A small correction here. The plates of a capacitor are merely conductors. The charge is actually stored in the dielectric as an electrostatic field.


Al, I was working from the charge cost figuring electricity at 0.06/KWH. Nine bucks equates to 150KWH used, which for a period of five minutes is 12.5KW used. That translates into 52 amps at 240v. So, the charge isn't bad electrically. I'm pretty dubious about the stored charge to horsepower output as others are.

Dean

[rshayes]

The patent seems to be based on using a 1/2 mil dielectric layer to withstand 3500 volts. This may be optimistic.

It also assumes that adding a coating to the particles in the dielectric material will not change the dielectric constant from that measured in thin films of barium titanate. This may be optimistic.

The coating may be only a few percent of the partical size, but its dielectric constant is much lower, probably by a factor of about 1000. This means that the electrical stress will be on the aluminum oxide film rather than on the barium titanate particles. It will also tends to reduce the capacitance by a substantial amount, since it will put small aluminum oxide capacitors in series with much larger barium titanate capacitors. The capacitance of series connected capacitors is always smaller than the smallest capacitor.

[MrAl]

HI again,

Dean:
Im not sure what you mean when you say:
"the charge isnt bad electrically".

In order to charge a 31F cap in five minutes from 1750v to
3500v you need a source of 181 amps. Since toward the end
of charge the voltage is near 3500v, the power supply needs to
be able to deliver 3500*181 watts, which is a heck of a
lot of power. Now calculate the input current at 240v.
Now because it only has to charge for five minutes, we might
get away with using a power supply which is rated less than
633500 watts, but the line still needs to deliver this power
somehow at least for the last minute or so of the charge.
Note that at the beginning of the charge cycle only 316750 watts
is needed, but that's still a lot of amps at 240v.

[jwax]

Doc, (ala "Back to the Future") needed 2.2 Jigawatts, available from a convenient lightening strike, for a charge. Same here.
As a matter of fact, we could solve the whole energy crisis thingy by capturing lightning in these amazing capacitors!
Discharge the caps into our cars caps. Or, just park your car outside with a kite or balloon attached.
Gives a whole new meaning to a "Lightning-fast car"!

[ringo47stars]

I used to think capacitors were different from batteries bacause they didn't explode or diminish in value (volts and amps) like batteries. So using them for an electric car is the same as saying "hey now they hold a charge just like a battery". Technically the volts and amps to do this ,as they say, makes me think they can still call this a capacitor because it will not overheat with that punishment to it. I guess it's all in the definitions of batteries and capacitors.

[Chris Smith]

Caps blow for the same and more reasons that batteries blow.

They are fragile.

The physics here is nice, electric motors are 2.5 times better than a gas motor for energy, the voltage is beyond outrageous, .....but who knows, the future is here.

Any thing beats a soldier in uniform in a false land and a false war.

[Dean Huster]

Al, my charge current calculation was based simply upon what the OP had quoted in the article (cost to charge), not upon the actual physics. The comparison was to point out that according to the OP quote, the charge current wasn't bad at all, no worse than electrically heating a house for the same period of time. However, I can't see how that power would ever translate into enough poopie to take that car down to the end of the driveway, let alone on a 500-mile trip!

I think too much here is based upon conception and dreams and none on an actual vehicle. So, all is moot, right?

Dean

[markp]

Until I retired, I did a lot of long distance driving - 1,000+ miles
per day. On our Interstates that can be done if you don't expect
to do it more than one day in a row. I've often wondered why we
don't put an electrified third rail in the left lane to allow hands-off
driving. A "smallish" electric motor and enough fail-safe
electronics to maintain the proper distance. Getting on and off
will require some thought but should not present an unsolveable
problem. There would be an enegy charge for this service which
would include a fee for the control sysem.

[Chris Smith]

Before anything smart can happen like that we need a real person in the white house with desire, insight, and who can do more than just tie his shoe with others helping him.

It can be done with the will of the people, and leaders with any IQ over 75.

Its not rocket science, just the desire to do things right.

[Bob Scott]

I'm pretty dubious about the stored charge to horsepower output as others are.

Dean,

I calculated that a 31 Farad cap at 3,500V has 52.74 KWH. Converting to horsepower by dividing by .746 leaves 70.7 Horsepower hours.

My Dad, an EE, always told me that gasoline engine horsepower was overrated by a factor of 3. That is, if you had a 1 HP electric motor operating a pump, you'd have to replace it with a 3 HP gas motor to get the same performance. So that 70.7 HPH converts to about 212 Automotive HP Hours.

If the 500 mi. trip took 10 hours @ 50mph, you'd have 21.2 HP available per hour for 10 hours. It looks do-able to me. Heck, when VW Beetles first came out they were only rated at about 40 HP, and you didn't need to floor the accelerator for full power to achieve 50MPH.

And charging the giant cap up to 3,500 cap would be easy with a large flyback inductor. Why not two flybacks alternately discharging into the cap, driven by two square waves synced 180 degrees apart in phase.
It is not pseudo science. It is realistic.

Regards, Bob

[Robert Reed]

Bob
I had read in an old Society of Automotive engineers (S.A.E.) manual, that it took 12 H.P. to keep a 4000# vehicle rolling down thew highway at 60 M.P.H. If your figures are correct, then this looks VERY doable.

[dyarker]

70HPH divided by the 10Hr it takes to go the 500miles (at 50mph) is 7hp; a lot less than a VW beetle. If the car is 2000lbs (vs 12hp for 4000lbs), then looks doable ... just... maybe ... barely. (no stops, no headlights, no music, and if cap can be drained to zero charge left)

[Dean Huster]

Bob Scott:

If the 500 mi. trip took 10 hours @ 50mph, you'd have 21.2 HP available per hour for 10 hours. It looks do-able to me.

Regardless of whether 21.2 hp (is that engine, drawbar, belt or PTO horsepower?) can keep the car going at whatever reasonable speed, the calculations are still based upon a level road, no headwind, no extra electrical demands whatsover (heat, A/C, wipers, lights, defroster, pointless audio system, any conversion losses, etc.), unearthing my Missouri roots. Show Me.

And harnessing that 3,500 volts doesn't sound like a walk in the park, either. And where was this marvelous capacitor coming from? I don't recall. If the best supercap available at 31F were rated conservatively at 10 volts, that's 350 caps in series for the voltage and 350 banks of those in parallel to get the capacitance back up to 31F -- a total of 122.500 caps. Is my math wrong here?

Dean

[dyarker]

Where did 21HP come from? To keep the units straight it comes to only 7HP for me.

Agree on the serial/parallel banks of caps math.

[zotdoc]

I think this whole idea is bogus due to the conservation of energy laws and the math already demonstrated in other posts, but safety keeps coming up, so I'm putting my 2 cents in. Gasoline has a flash point of -45 degrees F, and the fumes are explosive under certain conditions. If we can design a car that can use it as a fuel and is safe from explosions and fires such that the average houswewife or teenager should never expect any particular problems then why can't a car be designed that would be safe in an accident even with 3500 volts?