See my post #25
So you claim. But, the folks from Beacon claim they have such a flywheel. Whether they do or not is irrelevant to the point of my post which was that if such a flywheel existed, putting it underground would make sense because there IS a risk of it flying apart or breaking free.
Well, duh.
Then why did you ask?
These guys are behind the times. The folks at MIT announced the development of a carbon nanotube ultracapacitor over a year ago:
"Joel E. Schindall, the Bernard Gordon Professor of Electrical Engineering and Computer Science (EECS) and associate director of the Laboratory for Electromagnetic and Electronic Systems; John G. Kassakian, EECS professor and director of LEES; and Ph.D. candidate Riccardo Signorelli are using nanotube structures to improve on an energy storage device called an ultracapacitor…
…This work was presented at the 15th International Seminar on Double Layer Capacitors and Hybrid Energy Storage Devices in Deerfield Beach, Fla., in December 2005."
At least the people at MIT have a solid reputation…
Hey, I’m not promoting the stock or the product. I am not shareholder and for good reason. It isn’t cost competitive with batteries and batteries will only get lighter and cheaper. Their niche is for locations where changing batteries out is extremely difficult or in which conditions are so harsh that batteries do not work well and that is a small niche indeed. But that speaks to the advances in batteries not to the false claim that “Nobody has ever designed a flywheel that can store a reasonable amount of energy, and still not fail catastrophically (and dangerously).” From Beacon’s website:
and from a linked page
All of which is a hijack from the op and just meant as a simple correction of a mistaken belief.
Enter the Flagon the issue isn’t if carbon nanotube ultracapacitors are possible or exist. The issue is if EEstor’s performance claims are real or even possible. MIT’s team claims they
(Maxwell, btw, is indeed using ultracaps in the Chinese bus market where their regeneration advantages with braking are a plus.) Meanwhile EEstor’s claims are not a just a several fold increase, they claim a whole 'nuther thing
So the questions are:[ul]
[li]Can they make it at all?[/li][li]Can they make it so that it will survive use in a car?[/li][li]Can they make it with the capacity as advertised at a price point that is competitive with Li-ion or Li-polymer batteries?[/li][li]Is their claim of a five minute recharge for 500 miles more than BS or minimally something that is theoretically possible but not ever going to be realistically possible in a home setting and maybe not ever even in a special power charging station setting?[/li][/ul]Making claims is easy. Making an ultracap that does what they say theirs will be able to do, that will be the hard part and they have not shown any evidence of having done so.
I don’t think that will make it anything but worse - counter-rotating wheels would aleviate torsion effects, but not the gyroscopic ones - which are rooted in the law of conservation of momentum - when you try to tilt a gyroscope, you’re essentially trying to divert a fast-moving object onto a different path.
Sure, it starts out that way, but next thing you know it hops up onto one tire and then throws itself right off the hill. Fucking precession!
Just out of interest, what it the likely effect of mechanical failure cause by damage to a hypothetical supercapacitor such as being discussed here? - let’s say one that it capable of storing enough charge to power a vehicle for 500 miles.
I’d have thought it would have to be a pretty big boom - more so than a fuel explosion, surely.
I’d be more worried about arcing in the case of voltage leakage and/or dielectric breakdown. You know the safety warnings about opening up a CRT-based televison or monitor and discharging the capacitors with a plastic handled screwdriver? Imagine a charge several orders of magnitude larger. That’ll straighten your curlies.
At any rate, a capacitor is really a poor way of storing and delivering energy for extended periods of time. It’s nothing like a battery or fuel cell, which upon closure of a circuit delivers current along a relatively flat voltage potential. You can get about 70% efficient recovery of energy from NiMH batteries, and >95% from LiON batteries and fuel cells. A capictor’s energy and discharge rate is related to the potential across it, however, which means that you have to either have a highly variable step-down to your operating voltage and a regulator that opens and closes the circuit to prevent unintented discharge, or a large bank of capacitors and accept a slower discharge rate. Capacitors are great for storing up a bunch of energy when you want a sudden burst of electrical power, as in a particle accelerator or Z-machine, or as an accumulator for charge but no so great at storing energy for long durations.
Stranger
Right on. As I wrote in a previous post, with a big enough capacitor and a voltage of 440 V you can store the equivalent of the available energy of a tank of gasoline by charging at 100 A for about an hour.
However the energy is proportional the the square of the voltage so when you have half emptied the “tank” the voltage is down to 0.707 of 440 or about 311 V. In addition, the lower the voltage left on the capacitor the more current you must take in order to maintain constant power. A pretty sophisticated motor control circuit is needed to accomodate the large difference in voltage input to the system.
I would be interested in seeing how those Japanese trial buses do it. Maybe they charge frequently at the stops in order to keep the “tank” nearly full and the voltage relatively constant.
That’s exactly what they do. IIRC they get partial charges along the route and then fully recharge when they get back to their home base.
-XT
Modern switching regulators can maintain >90% efficiency over a 4:1 input voltage range. I don’t think the discharge curve of a capacitor is a serious impediment.
A 4:1 range is rather limited, particularly if you want a very compact bank of capacitors storing a few hundred kilowatt-hours of energy at a charge. What about 50:1 or 100:1?
I’m not seeing the advantage over extant or near-future advances in fuel cells and NiMH batteries, unless these “ultracapacitors” are order of magnitude more efficient than such, and even then there are significant safety and operating issues.
Stranger
That means that in my example you could recover 94% of the energy before the regulator gave up. That’s pretty good. Shows what can happen to the state of the art in the 26 years that I’ve been retired. 
With a 4 to 1 range you can get 75% of the stored charge out of the capacitor and 93% of the energy. Because the energy proportional to the voltage squared. I don’t think there is a lot to be gained by bringing the voltage range for the regulator much passed 4 to 1.
I can’t vouch for a “super capacitor” battery but I’ve personally witnessed a capacitor battery that was in the exact shape/size as a “D” cell (might have been a “C” cell). What I saw was a demonstration of a cordless drill using these batteries. It took about a minute to recharge in the demonstration. The disadvantage was the amount of time the batteries would run compared to a regular cordless battery (about 1 to 3 ratio). The advantage, which correlates to the article, is the ability to fully recharge in less than five minutes. These batteries would run full strength until exhausted and they were much lighter than conventional batteries or capacitors. Imagine a much lighter power drill that will run hard for an hour and then recharge in a couple of minutes.
I’ve been looking for these things for over 3 years and haven’t found them for sale yet but I imagine they are in use today. The potential space available in a car for this technology is substantial. If the engine is replaced by small electric motors at each wheel then there is an engine compartment available along with the gas tank and axles. There is also a lot of space available in fender-wells and bumpers. If you turn the hood, trunk lid and roof into solar cells you have a car that gains better mileage while it sits in the sun.
I can’t attest to the cost or the cubic volume required for a 500 mile drive but I can guarantee that capacitor battery technology exists. I’ve been excited by this ever since I saw it demonstrated 3 years ago (NASA exhibit). It really left an impression on me for the very reason we are discussing it.
More on flywheels and ultracapacitors in one proposed vehicle! Who’d have thunk?
Do I ever expect to see it? No. But still a fun idea!
:dubious: