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Mechanical Batteries

01/13/2008 3:27 AM

The concept of energy storage has a long and somewhat clouded history. The possibility of a battery that can be recharged to full capacity in a matter of seconds eludes the Pink Bunny.

My question is this:

The technology has existed for 15 years. Some have tried to build this type of battery with metal flywheels. They have to this date never acheived the success of high speed composite energy storage devices.

The conversion of mechanical power to electrical energy has and always will be a matter of cost. So why do we have to wait for science and the military to allow us to continue this research and development?

Below are some links to help refresh you taste buds.

http://www.rense.com/general41/grat.htm

http://www.teslamotors.com/

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#1

Re: Mechanical Batteries

01/13/2008 3:54 AM

A flywheel has inertia ..so it's can't be recharged to full capacity in a matter of seconds . ....Ya cannae change the laws of physics

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#2
In reply to #1

Re: Mechanical Batteries

01/13/2008 11:28 AM

In 1996 a mechanical bearing flywheel at a dead stop (0 tip speed) can be fully charged ro 22.75 kilowatts in 15 seconds at 200,000 rpm. Discharging the unit to a dead stop and restarting took the same period of time. Laws of physics included. Remember tihis is mechanical and not chemical.

Tip speed (the outer velocity of the flywheel) of a fully mechanical bearing charged unit was Mach 6 (six times the speed of sound). You could hold the motor/generator in the palm of your hand. Then (in 1997) came along 3 dimensonal (tri-axial) magnetic bearings. Everything changed after that at 375,000 rpm for the same physically sized unit due to no restraints on bearings or cooling.

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#3
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Re: Mechanical Batteries

01/13/2008 12:15 PM

So 15 counts as a few?
I'd have thought <5 was few...maybe I should start a new thread on this?

Del

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#4
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Re: Mechanical Batteries

01/13/2008 3:42 PM

Del

You can recharge the flywheel in less than 5 seconds using another flywheel.

When we tested this in an automobile using AC/DC as the power source, 15 seconds would send you on your way for another 290 miles.

Keith

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#5
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Re: Mechanical Batteries

01/13/2008 5:15 PM

That's pretty cool...but it just made me laugh, although it does actually make sense it just sounds a tad loopy .

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#6
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Re: Mechanical Batteries

01/13/2008 5:26 PM

I think we were a tad loopy back in those days.

The new Tesla Motor electric car uses 4000 AAA batteries.

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#7
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Re: Mechanical Batteries

01/13/2008 11:07 PM

flywheels have been around for a while and are undergoing active research. They get better with time and are better than most batteries now.

Suitable for small trucks, busses etc there are a number runing now to gather data.

One risk is explosion, so they need a strong box.

http://www.accesstoenergy.com/view/atearchive/s76a4325.htm

Scienific American had an article a while back

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#17
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Re: Mechanical Batteries

01/14/2008 8:31 AM

290 miles is quite a spectacular range. F1 cars get a few hundred yards of boost.

Assuming a fleet average 20 mpg car, 290 miles would be 15HP at 60 mph for 4.83 hours: 72.5 HP- hrs. To recharge that in 15 seconds (1/240 hr) would require 17,400 HP ( = 12,980,400 watts). Was this the same flywheel system that would fit in the palm of your hand?

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#26
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Re: Mechanical Batteries

01/15/2008 8:04 AM

Compared to 4 hours, 15 seconds would be "a few", I think... How far is up?

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#28
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Re: Mechanical Batteries

01/15/2008 9:23 AM

6"

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#29
In reply to #28

Re: Mechanical Batteries

01/15/2008 10:38 AM

For some, perhaps...

As Mae West said: "Is that a banana in your pocket, or are you just glad to see me?"

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#10
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Re: Mechanical Batteries

01/14/2008 1:17 AM

In 1996 a mechanical bearing flywheel at a dead stop (0 tip speed) can be fully charged ro 22.75 kilowatts in 15 seconds at 200,000 rpm.

22.75 kilowatt-seconds, 22.75 kilowatt-hours? You are quoting a power, not an energy. Are you saying that the flywheel went from 0 to 200,000 rpm in 15 seconds?

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#11
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Re: Mechanical Batteries

01/14/2008 1:40 AM

Everything changed after that at 375,000 rpm

This would have to be an extraordinarily small flywheel. At Penn State they are working with carbon fiber flywheels, and 68,000 rpm is considered very fast.

The Wikipedia entry:

Advanced FES systems have rotors made of high strength carbon-composite filaments that spin at speeds from 20,000 to over 50,000 rpm [2] in a vacuum enclosure and use magnetic bearings. Such flywheels can come up to speed in a matter of minutes -- much quicker than some other forms of energy storage.[2]

Attempting to spin one of these up in seconds would shear the shaft. you can't enlarge the shaft without incurring more friction. Can you supply a technical article which described these ultrahigh speed flywheels.

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#18
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Re: Mechanical Batteries

01/14/2008 9:29 AM

IN a Wired article from 2000:

"Of all the advocates, Bitterly is least willing to accept size limits. "Some of the biggest flywheels were built in the industrial revolution," he says. "Since then, the trend is clear: They've been getting smaller and rotating faster. No one has beaten our pre-prototype for the space station, at 60,480 rpm, but you should be able to attain even higher speeds with smaller flywheels, and I foresee graphite fibers, in the next decade, that will be 10 times as strong, per pound, as they are now. I believe we'll be using those in the lab, and once something is in the lab, it always gets out of the lab if there's an advantage to it. Within 10 years I believe we'll see flywheels providing 10 times as much energy storage as they do today."

Kevin: is Bitterly lying here? You say that 4 years before this, flywheels were spinning more than 6 times faster. I'm anxious to see a technical report... or are you saying all this tongue-in-cheek?

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#19
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Re: Mechanical Batteries

01/14/2008 10:33 AM

It'll certainly get out of the lab if it pops off it's bearings!

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#23
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Re: Mechanical Batteries

01/15/2008 12:18 AM

Del

It did not get out of the lab or the containment chamber, but it did spin for 2 days like a toy top when we broke the first motor shafts until we learned how to brake the flywheel and control it's spin-up. That was my job. The composite flywheel does not fail outward, but inward unlike metal.

Keith

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#8

Re: Mechanical Batteries

01/13/2008 11:19 PM

Due to its large angular momentum, a flywheel usually is not very portable. Not important for stationary energy storage devices, but very important for portable storage, portability being one of the attributes usually associated with the word "battery".

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#9
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Re: Mechanical Batteries

01/14/2008 12:09 AM

they usually operate vehicle power flywheels vertically and they also have some gimballing to allow the axis to maintain it's vertical orientation on the hiles and curves the vehicle might find in it's travels

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#20
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Re: Mechanical Batteries

01/14/2008 2:16 PM

I started to think about that after I saw another post mentioning using flywheels in buses. I wonder if using a gimbal to allow the flywheel axle to move creates much of a challenge with the wiring between the flywheel and the rest of the vehicle?

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#24
In reply to #8

Re: Mechanical Batteries

01/15/2008 12:49 AM

Del

Does the BBW (British Bomb Works) still Exist?

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#25
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Re: Mechanical Batteries

01/15/2008 2:42 AM

Dunno...never heard of that one !

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#12

Re: Mechanical Batteries

01/14/2008 2:43 AM

Stationary flywheels are not really without angular movements!

You have to gimbal the housing (well above the center of gravity of the flywheel-housing assembly) to allow for a tilt (north-wise) that is generating a steady torque on the flywheel (in direction east-west) to let the flywheel (vertical axis) have a precession (turning) rate as the earth.

This is a true constant rate (called the gyro precession rate).

Then there is the small but not negligible angular vibration that may exist in any building and machine. Below the nutation frequency of the flywheel these vibrations require either freedom in the bearings (no problem with magnetics) or generate high bearing loads.

At nutation frequency the flywheel will be a high Q mechanical oscillator, so damping is a necessity to be introduced by the servos that act to stabilize the magnetic bearings.

Above nutation frequency there will not be big problems.

Nutation frequency is equal to ωN = (Jq/Jz)ωz Jq and Jz are the cross- and length inertia-moments of the rotor, ωz the rotation speed.

This is true if the stiffness of the suspension bearings is zero.

If bearing-stiffness is existing there will be a split of both the precession rate and the nutation frequency in two. So there will be 4 natural frequencies in a "simply" suspended flywheel. (Plus the axial).

This is rotor dynamics.

Looking at acceleration and deceleration this is only a question of torques.

But a fast acceleration is requiring a big motor - not very suitable.

There has been a passenger transportation bus driven by flywheels in the 60ties in Switzerland. They started with on flywheel only (vertical axis). As vertical axis does not remain vertical at hill-up, hill-down this introduced enormous torques (lengthwise) that brought the busses to dangerous tilts. Then they switched to two flywheels (counter-rotating) and thus canceling the torques. But at each flywheel the torque is still existing and was damaging the bearings.

There was an attempt towards energy storage and use on top of city area underground railways, they started with ball-bearings. One first failure at a test destroyed the test facility.

This event is introducing into another topic of design: fail-safe operation. We are dealing with a lot of energy stored. Naturally this can be dangerous.

So the electronics for the magnetic bearings has to be implemented threefold as in magnetic suspensions for high speed milling. And there has to be a supervising computer that is allowing one of these electronics to be active.

If there is an uncontrollable failure there have to be emergency bearings that live for minimum one rundown (preferably for more than one). This is known from the magnetic bearings of turbo-molecular vacuum pumps. In these constructions ball bearings are used for this purpose that are not rotating (separated from the rotor by a wide gap) at normal operation but if the magnetic suspension fails these auxiliary bearings will prevent contact of the rotor to the stator.

This may be pretty difficult with a large energy stored.

But lets try, high energy electric batteries have their risks too.

RHABE

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#21
In reply to #12

Re: Mechanical Batteries

01/14/2008 2:23 PM

Thanks RHABE, great details! I did not realize that stationary flywheels needed gimbals. Or that flywheels in buses presented such practical challenges. I agree that use of flywheels in stationary storage and in buses deserves further efforts. My original point had more to do with my doubts of trying to use flywheels as (small) batteries.

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#22
In reply to #12

Re: Mechanical Batteries

01/14/2008 3:30 PM

Excellent answer and I rated it as such.

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#27
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Re: Mechanical Batteries

01/15/2008 8:18 AM

Quite so - any form of stored energy can represent a potential hazard, whether heat, mechanical, chemical, electrical, atomic/nuclear, what-have-you. Some we understand almost intuitively and control well. Some we understand barely at all and control even less than that. Some we likely won't ever "control", but still may be able to make use of. If lack of understanding hindered development, we'd still be huddling in caves or mud huts with fires taken from lightning strikes or volcanic eruptions. After all, that's what science and engineering do - further understanding!

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#13

Re: Mechanical Batteries

01/14/2008 3:20 AM

what's the energy storage of a flywheel in watts per kg, and watts per litre??

There's a company that make flywheels that float between magnets, in a vacume to store energy for the grid. I don't know if they use this methode, but it sure seem simple and convenient! http://www.dvorak.org/blog/?p=6521

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#14
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Re: Mechanical Batteries

01/14/2008 3:59 AM

If it's floating between 2 magnets..how do you get the power out?

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#15
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Re: Mechanical Batteries

01/14/2008 5:54 AM

Mechanical energy storage systems: They will be in Formula one in 2009.

Google for KERS, Flybrid, Hykinesis

Flybrid is currently testing a unit.

The Unit already survived Formula One standard crash test.

The units are used for regenerating braking energy and take power from the transmission.

60kW power max allowed for the moment.

Only small amounts of storage allowed in the first year. To be increased later.

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#16

Re: Mechanical Batteries

01/14/2008 8:00 AM

04.01.1999

Spin, Baby, Spin

by Courtesy US Flywheel Systems and the NASA Lewis Research Center

Inventors Jack Bitterly and his son Steve of U.S. Flywheel Systems in Newbury Park, California, want to run internal-combustion engines off the road. They would rip out everything beneath a carĀ¹s hood‹engine, battery, and radiator‹and replace them with about a dozen 50-pound, carbon-fiber flywheels, each spinning 100,000 times per minute. After the Bitterlys were featured in our August 1996 issue, they had to shelve their plans to develop a flywheel-powered prototype car because no auto companies were interested. So they turned to building flywheels to replace chemical batteries on the International Space Station. They expect to see flywheels in satellites by 2002.

http://discovermagazine.com/1996/aug/reinventingthewh842

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#30

Re: Mechanical Batteries

01/18/2008 2:19 PM
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#31
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Re: Mechanical Batteries

01/18/2008 7:07 PM

Thanks Buzneg. Nice group of links.

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