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Old 2006-06-11, 08:09   #1
mfgoode
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Lightbulb Capacitor batteries



I have always been amazed by the silent action of capacitors (condensers) ever since I learnt about them from NRI Wash. in a course in Industrail and Military Electronics back in the 60's

They now seem to be used in the making of batteries in the near future
and thereby replacing the current chemical ones.

Heres a news item from Slashdot.

An anonymous reader writes "MIT's Joel Schindall plans to use old
technology in a new way with nanotubes. 'We made the connection that
perhaps we could take an old product, a capacitor, and use a new
technology, nanotechnology, to make that old product in a new way.'
Capacitors contain energy as an electric field of charged particles
created by two metal electrodes, and capacitors charge faster and last
longer than normal batteries, but the problem is that storage capacity
is
proportional to the surface area of the battery's electrodes. MIT
researchers solved this by [0]covering the electrodes with millions of
nanotubes. 'It's better for the environment, because it allows the user
to not worry about replacing his battery,' he says. 'It can be
discharged
and charged hundreds of thousands of times, essentially lasting longer
than the life of the equipment with which it is associated.'"

Links:
0.
http://www.sciencentral.com/articles...e_id=218392803

Mally
+--------------------------------------------------------------------+

Last fiddled with by alpertron on 2006-06-15 at 15:30 Reason: Correct title
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Old 2006-06-11, 13:55   #2
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All of the large value (1F or more) and small size (handheld equipment) capacitors I've seen always have severe limitations on ampere delivery capability. Thus limiting the use to SRAM backup and RTC circuits. If these capacitors can overcome that problem then that could be the killer product of the future. Also larger applications like electric cars could become commercially viable.
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Old 2006-06-11, 17:47   #3
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The largest Capacitors I know, that are mass-produced have 2700 F at 2.3 V. They have a Volume of about 300 ml and can be discharged with up to 400 A. If they are connected serially, the current can be kept at a low range.
Of course, they are still too large for replacing conventional batteries, but are already in use for Shuttlebuses that just need to cover a distance of 1-2 km.
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Old 2006-06-12, 13:41   #4
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Quote:
Originally Posted by biwema
replacing conventional batteries
You mean chemical cell based batteries. A 1.5v common "D" 'battery' is a single cell and not a battery of cells. A "B" battery is a battery of cells.
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Old 2006-06-13, 14:30   #5
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Quote:
Originally Posted by mfgoode
They now seem to be used in the making of batteries in the near future
and thereby replacing the current chemical ones.
While a chemical cell, due to the nature of the chemical process inside, have a fairly constant voltage through its useful life, the voltage of a capacitor is propotional with it's charge. A capacitor driven device will either have to work over a broad voltage range or include a hefty regulator to keep the voltage stable.
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Old 2006-06-13, 16:05   #6
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Quote:
include a hefty regulator to keep the voltage stable.
That is already happening with the ubiquitous switch mode DC-DC power supplies in almost everything electronic/electric.
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Old 2006-06-13, 17:38   #7
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Cool Ch. cells vs. condensers

Quote:
Originally Posted by S00113
While a chemical cell, due to the nature of the chemical process inside, have a fairly constant voltage through its useful life, the voltage of a capacitor is propotional with it's charge. A capacitor driven device will either have to work over a broad voltage range or include a hefty regulator to keep the voltage stable.

A chemical cell has an internal resistance (small though it may be) which drops the e.m.f. And as a condenser's voltage is proportional with its charge similarly a cell's voltage is proportional to the current and we have numerous devices which accommodate this anomaly and still last for the purpose it is designed for.
Cells also have to contend with local action over long periods of time so the condenser can rival the cell and can eventually be replaced.
Also consider the disposal of used Ch. cells. Their chemicals are still active when they have to be discarded and can be very toxic in large quantities.
Their shelf live is limited as a totally airtight seal is yet to be perfected.
Mally
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Old 2006-06-13, 18:11   #8
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Quote:
Originally Posted by retina
That is already happening with the ubiquitous switch mode DC-DC power supplies in almost everything electronic/electric.
Most of the battery driven equipment I own, like flashlights, radios, mini vacuum cleaner, drill, shaving machine, coffee maker for my car, etc, do not have builtin DC-DC converters.

Laptops and most other electronic equipment also have the luxury of a fairly constant input voltage from the battery or a wall wart, usually higher than the voltages needed at high current internally. A DC-DC power supply for a capacitor battery must handle both relatively high voltage (still at a safe level) and high current at low voltage on the supply side. And be small and efficient.
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Old 2006-06-13, 22:49   #9
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Most likely a battery of capacitors will have ribbon cable like lead (unless it is hard wired) with only one being a ground. With 35 cells or so, one could at first, with the solid state switch, bank cells in groups of 3, (remember that they all don't have to be live at once), then as voltage dropped, gang them in 4's, then in 5's, 6's and 7's. After that, you might be in emergency mode. A laptop would be shutting itself down and your e-car would limit you to 30-50km/h.

A proper filter circut would steady the voltages while the power switch played with the series/parallel issue. A single cap that kept the 'operating' voltage during the switching constant might be enough for a car or something that is not voltage critical, like a radio.
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Old 2006-06-14, 04:35   #10
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Quote:
Laptops and most other electronic equipment also have the luxury of a fairly constant input voltage from the battery or a wall wart,...
The wall wart you mention is really just a DC-DC converter inside also. The AC is rectified to ~300V DC then using switch-mode PSU down to whatever voltage is required. The presence of high or low voltages is not a problem for DC-DC converters, they can be sized accordingly. Most modern cell phones have multiple DC-DC converters for translation both up and down. Universal input (80v-AC to 270v-AC) equipment is also common and easy to design. I think essentially having a dimishing voltage would not be a difficult hurdle to overcome with a bit of modern electronics thrown in to compensate.
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Old 2006-06-14, 08:10   #11
mfgoode
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Smile Capicitors and size.


You all seem to be thinking in terms of conventional technology.

These guys at the M.I.T. are dealing in Nanotech and that makes the great difference.

Allow me to reiterate from the URL I have given.

"The researchers solved this by covering the electrodes with millions of tiny filaments called nanotubes. Each nanotube is 30,000 times thinner than a human hair. Similar to how a thick, fuzzy bath towel soaks up more water than a thin, flat bed sheet, the nanotube filaments increase the surface area of the electrodes and allow the capacitor to store more energy. Schindall says this combines the strength of today's batteries with the longevity and speed of capacitors."

Some type of Koch surface?

Mally
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