Below is part one of an interesting article on ultracapacitors which can improve battery life and range in EVs, HEVs etc.<br><br>It would be interesting to see the results of one installed in a Prius. Bet it would really launch it off the line.<br><br><a href=http://evworld.com/databases/storybuilder.cfm?storyid=178 target=new>http://evworld.com/databases/storybuilder.cfm?storyid=178</a><br><br>\ Ken (just improve your capacity)

Re: Ultracapacitors "It would be interesting to see the results of one installed in a Prius. Bet it would really launch it off the line."<br><br>The Prius "traction control" would prevent any noticable differences in off the line launches. The big improvement of an ultracapacitor on a Prius would be the 90% regen braking efficiency vs. the current 33%. Then it's just a matter of economics. Would you pay an additional $500-$1000 for the additional regen? Not likely if you do mostly highway driving. Possibly a good payback over the life of the car if you do mostly city driving. The other benefit is it eliminates the most stressful condition on the Prius battery, namely the high amp discharge when starting from 0 MPH while also starting up the engine. This could greatly extend the life of the battery. In 8 years or so we'll know if this would have been a good idea. Again, the city driver gets the most benefit due to the preponderance of stop lights/signs.<br><br>Robert Snyder<br>NJ-PIKACHU

Ultracaps will never see action in any EV/HEV for the simple reason that their energy density is and order of magnitude to low (5 wh/kg vs. 50+ for NiMH batteries) Ultracaps have been "on the verge" of a break through for a least 5 years. I am sure Toyota (and Honda, GM, Ford...) have tested ultracaps for vehicle applcations, including EVs, HEVs, and starting. But, the truth is that while ultracaps have working on a breakthrough, battery manufactures (Pb-Acid, NiMH, Li) have all developed high power batteries for all sorts of applications from power tools to HEVs .<br>Example: The first Japanese Priuses (Pri-i?) had cylindrical D size batteries in the HV pack. Panasonic removed a lot of mass and volume by switching to a prismatic design and pack size was reduced by about 50% while keeping the same power and energy. Toyota did a little development on the pack design too. ;) <br>Ultracaps do have there place it just not in vehicles.

You would not notice any differance in acceleration with ultracaps, but not because of "traction control". The limit would be the invertor and electric motor. The Prius motor is rated at 33kW, so even if the energy storage system (batteries, ultracaps, fuel cell...) could produce 100kW the invertor/motor couldn't transfer that much power to the wheels. <br><br>Also the regen effiecny of the Prius is not limited by the batteries. (At least not totally) The braking of 33% regen/67% friction brakes is set up in the control system to give the braking a feel that we are used to from years of driving "gas cars". All be it that it is still a little torquey in comparison, but that is the price we pay for efficiency. The regen could be set to 100% but, the torque would be big enough to give the driver a nice case of whiplash. :)

Maxwell Technologies<br><a href=http://www.maxwell.com target=new>http://www.maxwell.com</a><br>is a manufacturer of ultracaps. HEre is the first paragraph from their May 1, 2001 press release:<br>Wilmington, MASS - Solectria Corporation announced today that it has signed a strategic development and supply agreement with Maxwell Technologies (Nasdaq: MXWL) to collaboratively develop advanced hybrid electric drive systems incorporating Maxwell's PowerCache? ultracapacitors for energy storage and power delivery. The agreement calls for Maxwell to deliver several thousand ultracapacitor cells immediately.<br><br>No way would any car company buy several thousand of anything unless they were ready to put them into a production run.<br><br>Full press release here:<br><a href=http://www.maxwell.com/news/archives/2001/may1-01.html target=new>http://www.maxwell.com/news/archives/2001/may1-01.html</a><br><br>Rea\ d this story:<br><a href=http://evworld.com/databases/storybuilder.cfm?storyid=178 target=new>http://evworld.com/databases/storybuilder.cfm?storyid=178</a>

Nothing personal against Solectria and wish them the best. The more high efficieny vehicles on the road the better. <br>To my knowledge all the major car companies, the US Advanced Battery Consortium, and the PNGV have given up on ultracaps for vehicles applications for good reason.<br>Maybe Solectria knows something no one else does? If they can come up with a more efficient and cheaper energy storage system for HEVs more "power" to them.

Ok, I'll leave your original comments about ultracapacitors to others since I don't know much about them myself, but I have this uncontrollable need to address your comments about the Prius (it's a scary disease :-)<br><br>The "traction control" is absolutely the limiter on acceleration in the Prius at the low end of the speedometer. First of all, the batteries can provide a maximum of 21 kW to the motor, but power is not the dominant factor at very low speed, torque is; and the Prius traction motor can put out a tire smoking 250 ft-lbs. of torque at 0 RPM. The traction control limits output to keep the tires from smoking (and to protect the drive train which really isn't up to the task of racing).<br><br>Also, the regen efficiency IS indeed limited by the battery.<br><br>First of all, Toyota spent a good deal of effort to get as much out of regen as they could and to make the transition to friction brakes as seamless as possible. The hydraulic pressure is captured in canisters normally used for ABS systems and only released to the brake pads as needed to slow the car more than can be done using regeneration. There's no strict 33/67 split, everything goes first to regen, then the leftover braking needs are assigned to the friction brakes.<br><br>The batteries are absolutely the limit on regen efficiency. They can only absorb 15 kW of regeneration and the car returns much more power than that under normal braking. Keep in mind that the friction brakes can stop the car faster than the 70 kW engine + the 21 kW battery power can accelerate the car and its obvious that the bulk of any serious braking is done by the friction brakes because that's the only place it can be done. The current motor could provide up to 33 kW of braking if it had a place to put the energy. Even more if it were allowed to run it's output voltage up higher than the current battery rating (which I suspect an ultracap would allow). When you brake over a long distance (trying to keep the absorbed power at or below 15 kW), other friction sources (tires, bearings, etc. also bleed off a lot of kinetic energy). Even so, you actually probably could regen more than 33% of the kenetic energy, it would just be a really boring thing to do. Since almost nobody would actually do this on a regular basis, Toyota doesn't include that scenario in the regen statistics. Seriously screeching up to stop lights will get you far less than 33% regen, but they figure Prius owners aren't likely to make that a habit either. The 33% is not a hard and fast number, it's just a reasonable estimate based on reasonable braking behavior.<br><br>There's no way the electric motor could give you more whiplash than the friction brakes. Either one would stop the tires from spinning long before that happened and all you'd do is skid. At higher speeds the electric motor can't even stop the wheels from spinning, but the friction brakes sure can (until the ABS kicks in).<br><br>So in conclusion, ultracaps could not improve initial acceleration (although they probably could improve higher speed acceleration), and properly designed ultracaps could indeed allow more energy capture by regen (I have no idea if the 90% claim is legit though). The questions remaining are feasibility, cost, and longevity. I don't know from these.<br><br>Robert Snyder<br>NJ-PIKACHU

I just dropped about $1,000 in routine brake maintenance on my Passat -- at 35,000 miles. <br><br>I think improving the regen efficiency from 33% to 90% would be worth the effort. That means the brakes would be used 10% instead of 67%, leading to much longer brake life, plus less wear on the transmission and batteries, plus more fuel efficiency. I'd pay $1,000 extra for this feature.<br><br><br><br>I don't know much about HEV design, but I do dabble in computer design. This discussion reminds me of what we call the storage hierarchy, where more expensive, but higher-performing storage components are used to 'cache' data from the more cost-effective, slower components. Much of computer performance optimization is based on intelligent exploitation of cache. Hybrid vehicles do the same trick of caching energy, if you think about it. Here's an analogy, HEV regen to computer. (As the Germans say, this analogy limps a little -- but then all analogies do.)<br><br>Component Performance Description<br><br>CPU/MG Source/Sink data/energy<br>L1 cache/Ultracap 1nsec/? short term store<br>memory/traction bat 100nsec/15kw long term store<br>disk/gasoline 10msec/lots longer term yet<br>tape/oil wells 10sec/unlimited-ha!<br> <br>Actually, if somebody could do the math to get kilowatt-hours capacity of the ultracap, the battery pack, and a tank of gas, this comparason would be even more telling.