Can we use capacitors instead of batteries?

[bossxero]

Hi All

My question is not that simple, but having look at all the ideas that we get on this boards.  I can see that there are lots of learned and sincere guys out there willing to help/share their knowledge and i felicitate them sincerely.

I want to know if we can use capacitors to store charge instead of batteries.  For example in a toy car requiring 9.6vDC.  All comments,ideas etc are most appreciated.

Please dont get too  technical.  Just go simple and its well understood :-)

thnx

Regards.

[wildbill hickup]

Well, you could if you wanted to however  :

http://www.fieldlines.com/story/2005/8/21/182926/768

lists some of the reasons you might not want to. They pretty much exhausted that question a few months ago.

Wildbill

[willib]

I've used an ultra cap , when charging NiMH batteries , with my old gen.

It did work .

By storing energy that the battery couldnt use when the gen was running fast , and putting it back in to the battery when the gen was running slower. When used in this respect, adding a 14 V ultra cap would  smooth out the charging process..

those Audio Caps for sale, even at pepboys , are ultra caps, ( with an ESR of 1 milli ohm)or less.

[Nando]

Presently, it is not possible to replace batteries with capacitors.

The storage capacity of the new capacitors is starting to get somewhat closer to the capacity of small batteries.

Example : capacitor with 1000 Farads Capacitor loaded with a 10 ohm resistor will drop its voltage to 37% of the initial value in 10,000 seconds or 2 hours, 46 minutes and about 40 seconds.

The same "time" size storage battery may be several times smaller in volume.

A 1000 Farads 2.5 Volts capacitor is big !. and the price bigger.

So the industry has not being able to replace the storage capacity of the chemical batteries -- one day may happen -- to some capacity.

A dream that many want.

We, in the electronic industry, have been using the large Farads capacitors, replacing Nickel based batteries, for low energy circuits, where the life of the capacitors DO out perform the batteries in charge cycles and energy storage without short time self discharge periods.

Nando

[Clifford]

Look at the NightStar Rechargeable LED Flashlights.

I haven't taken one apart, but I think they are somewhat simple...

• Coil
  
• Magnet
  
• Diode
  
• Capacitor
  
• LED
  
  

http://shakelight.notanumberinc.com/flashlight/

http://shakelight.notanumberinc.com/flashlight/techspecs.shtml

You shake it up (so magnet passes through the center of the coil) a few times, then turn the thing on.

According to the technical specs, it has a 1 Ferad, 5.5 Volt Capacitor as the element that you are recharging.

[finnsawyer]

Since the energy E stored in a capacitor is given by: E = 0.5xCxV^2, the trick is to maximize V(oltage) rather than C(apacitance).  This then creates the problem of efficiently converting the high voltage to the working voltage.  Perhaps some type of buck converter.

[terry5732]

The heart of most ultra-capacitors is aerogel foam which is extremely lightweight. If the capacity can be increased sufficiently, I see this being incorporated into lightweight electric cars. The body parts could be foam filled capacitors. Now if they are suddenly discharged in an collision........

[ghurd]

But how much volume would it take to supply 100ah between 12.6 and 11.9V?

[kirk]

http://www.skeleton-technologies.com/supcap1.htm

Be sure to notice "next" as the article is several pages.

Skeleton has used their technology to start diesel trucks in Alaska. As you know lead-acid batteries are not very good when cold.

Kirk

[pyrocasto]

Here's ya a nice cap to play with: http://www.maxwell.com/ultracapacitors/products/PC2500.html

;-)

That's getting closer to battery size, but for a battery pack the price would be ludacris!

[nanotech]

I work at New Flyer ( http://www.newflyer.com ) making transit busses.

Two of the models we do are Gasoline/Electric hybrid and Diesel/Electric hybrid.  On both of them the only batteries used are the conventional starter batteries.  The drive system uses HUGE capacitors on the roof of the busses.  I don't know the exact farad specs of them, but the motor voltage is 600VDC and I don't even want to KNOW what the amperage is to move a 7 ton bus to 55mph.......

[MountainMan]

Times they are a changing.

I remember a Popular Science article from maybe 20 years ago.  It was all about some crazy people who actually built a 1 farad capacitor.  At the time, it was considered impossible.  The thing was the size of a building.

As I understand it, the improvements have mostly come in the form of making dielectrics thinner without losing the ability to prevent the plates from (electrically) touching.  The capacitance of two parallel plates goes up as the inverse square of the distance between them if memory serves, so making the separator thinner and thinner makes bigger and bigger improvements in the capacitance.

Back then, it was two sheets of aluminum foil with a sheet of thin mylar in between as an insulator.  Then the whole things was rolled into a log shape.

Now I'm guessing they use some sort of vacuum deposition of an insulating layer onto the aluminum foil.

jp

[willib]

some form of carbon is used in super capacitors .

the next phase is to use carbon nanotubes all aligned perpendicular to the plates..

MIT has been working on it , so is everyone else i suppose.. the link was written back in february..

http://www.physorg.com/news3056.html

"Conventional, or "Faraday" capacitors, store electrical charges between a series of interleaved conducting plates. Because of their small size, the nanotubes provide a huge surface area on which to store and release energy, Pan said.

The new devices can produce a power density of 30 kilowatts per kilogram (kW/kg), compared with 4 kW/kg for the most advanced devices currently available commercially, Pan said. Other researchers have described laboratory supercapacitors capable of up to 20 kW/kg, he said. "

[wiredwrong]

I was wodering the same thing and came across this last night http://www.batcap.net/Indexnew5.htm

 I was going to post this and look for input from the board, so Ill toss it out here since you've already opened the door

[nothing to lose]

Lots of good answers.

Instead of replacing batteries I was wondering about grabing a fast charging source (high volts, high amps) with caps then releasing the stored power to charge a battery bank. Sort of like mentioned already about  smoothing the generator.

 Batteries only acept a charge so fast. So for an electric vehicle perhaps charge up a bank of caps durring braking and downhills, when power produced may exceed the rate batteries could absorb it, then either use the caps power durring excelleration again, or slowly release the power charging the battery bank.

We have alot of hills here I will have to ride, and I am building a electric trike (very slowly). With these hills rengenative braking would be a good thing to add to my little trike.

[asheets]

Maybe like charging a capacitor bank with a static electricity source (like lightning or a van der Graff generator), then discharging the bank slowly into a battery bank?

I did something very similar to this once when I was a kid -- I built up some sort of capacitor bank using my Radio Shack 75-in-1 kit, and charged it by rubbing my feet across the carpet, then touching my finger to a doorknob (which I had hooked up to the RS circuit).  The capacitors were then run through the kit's meter -- which took about 10 seconds to go from full deflection to 0.  

I also remember, though, that if I did it too many times, that it would stop working until I gave the caps a rest...