Ultracapacitors for Car Starting

[Foxpaw]

Right then. As you may already be aware, I somewhat favor ultracapacitors. Anyways, apparently some university students have found that using Maxwell's ultracapacitors, they were able to start an ICE with a regular starter 10 times at 20 degrees from a full charge, using an ultracapacitor pack weighing only 1.7 kilograms.

Such a pack would have an effectively unlimited lifetime and would be quick to recharge too. Anyways, I saw this on Maxwell's site so I thought I'd post the link:

http://www.maxwell.com/pdf/uc/app_notes ... 007240.pdf

There's two experiments done there, one using older, obsolete ultracaps to run the starter on a test bench, and a second using current generation ultracaps in a "real world" test inside a car.

[kapps]

Well the battery used in the insight is able to start the car fast enough for autostop but I'd be more interested in ultracapacitors being able to provide a very high current for acceleration purposes. They could also be used to store regenerative braking forces as the battery can't charge very fast. For a normal gas-only engine, an ultracapacitor might allow the introduction of auto-stop features but the alternator would have to pick up the slack when the ICE turns back on.

[Yves M.]

That is very interesting. Maybe an big enough ultracap for IMA can be in the commig

[Rick]

You know what application those would work really well in would be for portable jumper packs. My parents business goes through the current ones every couple of months because no one ever remembers to plug them back in so they are always left discharged for a while. These could be left discharged without a problem, plus they could be charged up in probably a couple of minutes when needed rather than hours.

That said I also did get to see in person a full electric drag vehicle that ran off of ultra capacitors. It was a donated stripped EV1 that went to BYU's engineer program. They willed the battery tray with a bunch of ultra capacitors. It wasn't super fast, but still had more than enough behind it to break their fat slicks loose.

[Foxpaw]

Portable boosting packs were actually explicitly mentioned at some point in that article. The main value that I would see in this for an Insight would be that the ultracaps would be able to cough up enough to boost other cars, they're about a tenth the weight, and their performance doesn't degrade in the cold. Plus they'd never need replacing. Unfortunately they do cost quite a bit more than batteries, at least for the time being.

Originally Posted by Yves M.

That is very interesting. Maybe an big enough ultracap for IMA can be in the commig

I'm not sure if I posted about this before or not. As you may recall, there was a post regarding the JEOL "nanogate capacitors." These capacitors presently hold roughly as much charge as NiMH batteries presently and are expected to be developed enough to almost hold as much charge as Lithium Ion batteries sometime in 2005.

Fortunately, it doesn't appear that this is purely lab work. JEOL has been teaming up with several corporations to bring these capacitors to the market. One of these corporations is Nissan Diesel Motor Co., Ltd, who apparently are planning to use the technology in the development of hybrid automobiles. The news release regarding this was in June of this year.

Or so I've gathered. The English in their news releases is a little broken.

References:
http://www.okamura-lab.com/pdf/040426_E ... SE_ENG.pdf
http://www.jeol.co.jp/english/newsroom/2004/040614.htm

[Mike Dabrowski 2000]

The main problem with ultra caps is that the energy is stored electrostatically rather than chemicaly like a battery. That means that as soon as you start drawing current, the voltage drops, and continues to drop as the cap is depleted. If a battery and cap are put in parallel, the cap will only supply power for the first few seconds, or minutes depending on the battery internal resistance.At some point the flat discharge voltage of the batterys takes over, and little help is provided by the cap. A car run off of the caps alone would lose power fast as the capacitor voltage droped off, and would need a fancy motor controller to deal with the wide voltage provided by the caps.
They are great for high current burst though. I helped my nephew design a robotic hackie sack throwing machine for a contest. The contest rules allowed caps, but only 2 AA batteries for power. I used three 22 farad supercaps to provide a super high current blast off. It worked quite well, but recharging the supercaps between runs depleted the AA's after about 3 runs.
A photo of the robot is on this page.
http://pages.cthome.net/genesisone/thin ... wheels.htm
Mike

[Foxpaw]

Batteries don't really have a flat voltage. They have discharge curves too, some of which are fairly linear. Now, the discharge curve of a capacitor is very linear, but that still isn't that big of a deal.

If we compare to the pack in our Insights, for instance, when we have discharged the pack halfway, we are at 50% charge. At this point our NiMH batteries are at about 80% normal voltage. However, because we can charge and discharge a capacitor pack completely, using the same amount of charge would put a capacitor pack of equivalent capacity at 70% charge. So the difference isn't really all that great, since we are forced to run our battery packs at lower voltages than their peak to conserve their life.

[clett]

So those students were using a 1.7kg Maxwell ultracap? Maxwells are about 5Wh/kg, but the JEOLS are up to 75Wh/kg (when news of that broke out in Japan their share price tripled overnight!) 75Wh/kg means they could have gotten away with a 120 gramme starter capacitor!

As for the issue of voltage drop, of course that's an issue but it isn't insurmountable by any means. I've seen many commercially available power conversion units for the specific purpose of converting a falling voltage capacitor draw into a steady fixed voltage at the other side - all they do is increase the current draw capacitor side as the voltage decreases and the efficiency isn't too bad either. Remember the Insight and Honda Dualnote were originally going to be ultracap boosted. Also, if you look down the list of companies forming close allegiances with JEOL, it's worth noting that Honda is one of them!

[ElectricTroy]

I'd like to see batteries replaced with capacitors. They weigh less, can absorb energy at a fast rate (braking), and don't wear out.

[fscott]

Has anyone done a comparison of energy stored per pound of equipment? That's what will tell you if an untracapacitor is better than a battery for vehicular use.