Ultracapacitors show promise
SUPERCHARGED VERSIONS of the capacitors commonly used in electronics are approaching the storage density of conventional batteries and could replace them for many uses.
The big advantage of the devices, called ultracapacitors, is that they can be charged and discharged rapidly, although they can give a steady, longer term, more battery-like flow depending on the load.
One possible long-term application is a laptop battery that can charge in as little a minute – the speed would be dictated less by the ultracapacitor than by the size of the mains adapter required to deliver the charging current.
Capacitors store charge and smooth out current flow in circuits in much the same way as a lake in the course of a river steadies its flow and acts as a reservoir. Except that most capacitors are more like tiny ponds, with a capacitance of billionths or millionths of a farad. A conventional capacitor with a rating of one farad would be massive.
The charge density of ultracapacitors is orders of magnitude higher. One already on the market, about the size of a D-cell battery, has a capacity of 350 Farads. Like other ultracapacitors currently available it is based on activated carbon, which has a structure like a sponge with nanoscale pores providing an enormous surface area to which charge adheres.
Researchers led by Joel Schindall, associate director of the Laboratory for Electromagnetic and Electronic Systems at MIT, are developing ultracapacitors with an even greater surface area using carbon nanotubes rooted on an aluminium substrate, like threads on a think-pile carpet.
“We have already achieved [two times] the energy density of activated carbon and within weeks or months we expect to get [five times],” Schindall said at the Emtech conference.
That would give ultracapacitors 25 per cent of the energy density of a standard Li-ion battery. Schindall said that for some heavy duty applications that is better than it sounds because the batteries used for them operate in the range of only 50 per cent to 60 per cent of their capacity and so actually have far less available energy than their theoretical storage capacity.
The rapid charge and discharge rates of ultracapacitors make them suitable for driving electric vehicles and regenerative braking, whereby kinetic energy is stored during deceleration so that a vehicle wastes less energy.
This task also exploits another advantage of the new ultracapacitors – they can be recharged more than a million times without deteriorating. Effectively that gives them an indefinite working life, says Schindall.
In the shorter term they could be used in rapid-charge auxiliary batteries for laptops and other electronic equipment. But Schindall says these are early days and energy densities could rise still further, which could make them a viable replacement for Li-ion batteries.
He said, “When digital cameras came in I wondered if they would ever match the resolution of film. How many people use a film camera now?”
The hope is that the cost can also be brought down to that of conventional batteries. But Schindall points out that even if they are much more expensive they could work out cheaper in the long run because they would not need replacing. µ
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DIY Rail-gun, here I come.
...to get rid of these evil Lithium-Polymer batteries!
Heavy crap...Why does battery tech seem so slow compared to the massive jumps of solid state integrated chips lol.
Saying that, I wonder how long a 1980's laptop would last on a modern day high capacity battery :)
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until then, deleted from bookmarks and off to tg!!
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There are a number of private companies working on the same problem. If some of their claims of energy density are true electric vehicles could be a reality. Expect some NDA's to be opened up a bit before the end of the year.
EESTOR FTW !
One common criticism of green power generation schemes is that the sun may not be shining or the the wind may not be blowing when we need electricity. With capacity in the hundreds of farads, perhaps banks of these devices could serve to store juice produced by windmills or solar systems until it is needed.
LiPol batteries are the lightest there are. If you want heavy batteries, you should try packing some NiMH, NiCad, or even worse, lead-acid batteries.
As for 1980s "laptops" I have an old Eagle "luggable" with a full-sized keyboard as its base, a monochrome CRT monitor, two disk drives, and amazingly, a hard drive too. I doubt it'd run long at all on modern batteries, especially since it was designed to plug into a wall.
So be thankful for what you have!
" ...like threads on a think-pile carpet"
Who's your shag?
The fundamental difference between capacitors and batteries is that batteries can maintain a (mostly) constant voltage during most of their discharge cycle, while a capacitor suffers an exponential falloff in voltage as it discharges.
Correspondingly, you can charge a battery with the same voltage, while the capacitor needs an exponentially increasing voltage to pack in more charge.
Do they have regulators that can deal with this? Alternatively, you can get around the problem by varying the capacitance as it charges/discharges. I’d give more details, but ... Hanc marginis exiguitas non caperet.
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...the days of being able to charge my mobile phone using the three-phase outlet will be here. :)
Lawrence, not so fast.
You've assumed a resistive load (exponential discharge). These days gizmos use switching regulators. As well as being far more efficient than linear regulators, the operating input voltage range is very wide (step up and down), hence regulation isn't really a problem.
"the capacitor needs an exponentially increasing voltage to pack in more charge"
Not so. The relationship is entirely linear (Q=CV). More significantly, the energy (the useful bit) is proportional to the square of the voltage (E=0.1CV^2), so in practice is actually the reverse of what you stated.
"350 Farads" for a D sized cell might sound impressive, but it means little without knowledge of the operating voltage range.
I think it's neat that they're considering storage mechanisms that in case of a fault could theoretically discharge say 90W-hrs
over the course of a fraction of a second. Or is there more internal resistance in these things than that?
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If these get good enough, would be interesting to see if there's any benefit/savings that could be had by having an intelligent electricity supply for the home - the system could charge capacitors during the night when electricity is cheaper and use the stores during the day. When combined with home generation of solar/wind power, could be a massive improvement for our national electrical grid
The ads put money in your journalists' wallets so that you - and also manufacturers who want to have their products lied about favourably - don't have to.
So how big a battery can be currently replaced, or for how much money, or by when? And yeah, that much energy in one place could be released by a short-circuit - any store of energy short of hydrogen or helium for atomic fusion is subject to that. Even fission nuclear reactors catch fire. But maybe you could divert the ultracapacitor discharge into an EMP instead.
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