donalson SuperDork
Dec. 25, 2010 2:39 p.m.

I was on a web page that has a lot on energy conservation/solar etc... one bit they where talking about using a 1.5 farad capacitor to start car... hook it up in place of the battery and go...

anyone tried or thought of that?

just sounded interesting... perhaps less weight and cheaper for a challenge car?

i'll try to dig up the page (can't find it right now grr)

Mikey52_1
Mikey52_1 HalfDork
Dec. 25, 2010 2:46 p.m.

Okay, I'll bite...how does the capacitor get loaded?

integraguy Dork
Dec. 25, 2010 2:51 p.m.

"....how does the capacitor get loaded?"

wouldn't it be pretty much the same as a battery would get loaded?

(I'm assuming that the response you are/were looking for wasn't the punchline for a joke.) I imagine what would make this work for a "Challenge Car" is what would not work for a street car, and that is, a cap might not be able to take repeated starts.

Mikey52_1
Mikey52_1 HalfDork
Dec. 25, 2010 2:57 p.m.

I'm thinking more in terms of the wiring necessary...would it stand up to repeated bursts of hi amperage without melt-down?

Might work okay for a challenge car, but I wonder about a DD.

integraguy Dork
Dec. 25, 2010 3:16 p.m.

After thinking a bit more about this issue, you need to keep in mind that a battery isn't just used for starting a car...but for "working" the gauges and firing the ignition. I would think, that besides the question of wire gauge needed, what also would need to be worked out is providing the steady voltage to accesories if the race is "too long".

FlightService Reader
Dec. 25, 2010 3:32 p.m.

There is also the "dump" issue.

Capacitors will completely discharge instantaneously. I doubt the starter would act as a resistor enough to slow the discharge.

Then you have to recharge it.

I can see it being done but don't know why you would want to.

rustyvw HalfDork
Dec. 25, 2010 6:26 p.m.

It might help on a really high compression engine, if the battery couldn't get the starter to spin on its own.

cwh SuperDork
Dec. 25, 2010 6:34 p.m.

How big would said cap be? I'm used to little 1.5 microfarad ones. Never heard of one this size, but I know that military uses caps to fire linear accelerator cannons.

erohslc Reader
Dec. 25, 2010 6:50 p.m.

Such an ultracap could be useful if correctly integrated into the system. But do not consider it as a 'bolt in' replacement for a battery. Just like a battery, care and feeding (charging and discharge) must be done correctly in order to achieve long life. As mentioned, you cannot exceed the maximum discharge amperage without damage. And that max rate is determined by the specific design of the UC used. A capacitor does not discharge instantaneously, instead at the rate is mainly determined by the charge voltage, the load resistance, and the internal resistance. The internal resistance is determined by the design of the unit. High amp devices require specialized (more expensive) construction.

Most UC are rated at 2.5V max, so you would be looking at an array of devices hooked up in series

So a properly designed control circuit is required.

Check this out:

http://www.technologyreview.com/Biztech/18086/

And note this statement from the article:

'Where they're weak, however, is with energy storage. Compared with lithium-ion batteries, high-end ultracapacitors on the market today store 25 times less energy per pound'

That's vs lithium-ion batteries, doesn't say vs lead-acid. And then there's cost.

It will happen eventually.

Carter

donalson SuperDork
Dec. 25, 2010 7:24 p.m.
FlightService Reader
Dec. 25, 2010 8:20 p.m.

I have been hit by a 1 farad capacitor, don't tell me they don't discharge instantaneously, (ok let's use the word instantaneously as a colloquial term and not a technical one, yes it will take a second, but a battery won't fully discharge for a much longer time.) Like I said you need resistance to stop it. and I doubt the starter would provide enough.

You can get some at very high end car audio shops. They are good for stabilizing ultra high wattage systems from power spikes from hits from subs.

Never help a redneck with a stereo system that requires more power than the vehicle needs to move.

Dr. Hess SuperDork
Dec. 25, 2010 9:28 p.m.

Do the math. A Farad is a charge representing one amp in one second at one volt, or

(1 Amp / 1 second ) / 1 Volt

At 12V, 1.5 Farad ain't gonna start your car. It would be 18 amps (12*1.5) for a second. Your starter sucks down about 100 amps or better. So, 1.5 Farad would run your starter for a whopping fifth of a second. Give or take.

Dec. 25, 2010 9:30 p.m.

Farad... that sounds vaguely middle-eastern. I think its time for a cavity search.

donalson SuperDork
Dec. 25, 2010 9:51 p.m.

der i misread... it's not a 1.5 but a 150 farad... i think that changes things a bit...

Dr. Hess SuperDork
Dec. 26, 2010 7:23 a.m.

I always say "What's an order of magnitude amongst friends?" But I'm afraid I'll have to draw the line at 2 orders of magnitude.

internetautomart SuperDork
Dec. 26, 2010 8:42 a.m.

the cap will sure as heck be MUCH more expensive than a cheap battery. Most large audio caps I've seen are almost as large as a 51 series battery (honda civic size). Better off with a 51 batt than a cap IMO

donalson SuperDork
Dec. 26, 2010 10:00 a.m.

ya I missed the 150 and read it at 1.5... and I know you can get those down at walmart (prob crappy ones but whatever)... when it jumped by 100x the novelty idea changed lol...

kb58
kb58 Reader
Dec. 26, 2010 6:30 p.m.
FlightService wrote: ...Capacitors will completely discharge instantaneously. I doubt the starter would act as a resistor enough to slow the discharge...

A common mispreception. They're no different from a battery if you drop a wrench across the terminals. Both they and a battery provide as much current as their internal and external load resistance permits -> Ohm's law.

As was said, it's all about energy density, and since a capacitor is much less than a battery per pound, it's a pointless exercise. Just get a Odyssey PC680 and be done with it.

Zomby woof Dork
Dec. 26, 2010 6:53 p.m.

I drive a car where removing 25 lbs makes a noticeable difference, so I've been looking into lightweight batteries, and (being cheap) will build my own in a few weeks.

It should have no problem running the car, and will weigh about 2 lbs.

friedgreencorrado SuperDork
Dec. 26, 2010 7:02 p.m.
Zomby woof wrote: I drive a car where removing 25 lbs makes a noticeable difference, so I've been looking into lightweight batteries, and (being cheap) will build my own in a few weeks. It should have no problem running the car, and will weigh about 2 lbs.

Zomby, take pix and start a thread when it's done. That's going to be interesting.

erohslc Reader
Dec. 26, 2010 10:39 p.m.

Each homemade battery cell consists of a paper clip and piece of copper wire jammed into a Habanero pepper .....;)

How much energy do you suppose is stored in 2 lb of Habaneros?

kb58
kb58 Reader
Dec. 27, 2010 12:50 a.m.

Quite a bit. After eating a bunch of those, what happened 20-minutes later was rather... shocking.

Zomby woof Dork
Dec. 27, 2010 4:51 a.m.

Similar to this http://www.turntechbattery.com/TurnTech%20Battery/Welcome.html

The 5 ah will run my car. I'll build one for the bike first, and see how it works.

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