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How big a capacitor to run a bus?

12/06/2008 6:24 PM

So I'm watching the new lightrail train go by and thinking the only downsides are the rails themselves and the costs of stringing those powerlines above the road.

I'm admiring the silence as the electric train goes by, since beside me I have a typical noisy, smelly diesel bus idling at the light.

I thought how nice if the bus was electric, but there is the matter of running those poles and stringing lines, and tall trucks to worry about, etc.

Then it occurred to me; what if the bus was electric, and like my kids toys ran on an enormous capacitor? Then it could recharge at each bus stop.

Lunacy?

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#1

Re: How big a capacitor to run a bus?

12/06/2008 9:39 PM

Hello edignan

The present development of capacitors and super-capacitors does not permit them to be used to supply a passenger bus with a useful quantity of energy.

It is not generally realised that chemical storage of energy (Oil energy) is far more space efficient than storing the same amount of energy in the electrical charge form.

Any capacitor large enough to run the bus, would presently be many times the size of the actual bus, thus the capacitors would need to be in a string of trailers behind the bus to power it and leave room for the passengers.

If such a capacitor-powered bus was ever designed, then consider how damaging the energy stored in the capacitor/s, if a sudden short circuit developed - it would demolish several city blocks in the resultant explosion.

By comparison, energy stored in chemical form is far safer, small volume for large energy storage, easy to control.

You say: <"....like my kids toys ran on an enormous capacitor...."> There is also the matter of a large powerhouse needed to recharge the capacitors in a reasonably short period of time, plus the substation/charger unit to do the job.

So, for the meantime, we are still going to use those diesel engines, until something safer, cheaper and more efficient arrives.

As an aside, diesel engines can have a water scrubber fitted to the exhaust pipe, and then there are no particulates (smoke etc) which are ejected into the air, because they all end up in the water scrubber.

Water scrubbers for diesel engines enable use of these in mines and enclosed spaces, where people work, and the emitted fumes coming after a water scrubber are not dangerous to health, provided there is a fresh-air source.

Water Scrubber - refer: http://books.google.com/books?id=q3lS_AFL4-QC&pg=PA320&lpg=PA320&dq=water+scrubber+diesel+engine&source=web&ots=wlhy-qC1FE&sig=1vFWFSm6RBgHur73ZfR5VYCF02A&hl=en&sa=X&oi=book_result&resnum=10&ct=result

Kind Regards....

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#3
In reply to #1

Re: How big a capacitor to run a bus?

12/07/2008 11:38 PM

Spark,

You are correct about the present capacity of capacitors - they aren't ready to power a bus yet. I do remember a cartoon from an electronic magazine from the '60s. It showed a semitruck delivering a 1 Farad capacitor - with a caption saying that the ordering party had forgotten the "u" or the "F". Very funny back then. Not so funny now that 1F caps are small. But that shows the speed of development in capacitors.

Even though the day of bus capacitors (omnibus capacitor - for clarity) is not too far off, you make a good point about energy release in an accident. Petroleum fuel fires are limited by the amount of air that can get to the fuel. When all the fuel burns at once you get more of an explosion than a fire. This is called fuel-air explosive, or a "daisy cutter". A capacitor with a similar amount of energy would fail in a similar explosion.

There was a thread here on CR4 recently about incorporating battery cells into automotive body panels. This could work with capacitors and provide safety by using many small capacitors distributed so that and accident could only affect a few at a tiem.

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#10
In reply to #1

Re: How big a capacitor to run a bus?

12/08/2008 10:24 AM

Hey Sparky, I like your posts. Don't kid yourself though, ALL fumes from diesels are dangerous, filtered or not.

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#15
In reply to #1

Re: How big a capacitor to run a bus?

12/08/2008 9:33 PM

Rather than use the "many times the size of the bus capacitors" of sparkstations design, we opted for 4 capacitor series installation.

Alas, we had some center of gravity issues when a light breeze wafted across the road.

The authorities wouldnot permit them to stick out of the sides (something about the width of the lanes) nor would they let us put them inside the bus and the kids on the roof.

We were unable to get any funding from Krisdel TM venture capital either, so we're giving up for the time being. But hey, at least we tried!

milo

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#2

Re: How big a capacitor to run a bus?

12/07/2008 12:32 AM

edignan; they tried buses with a huge fly wheel & motor/generator mounted under the bus in a vacuum at some bus stops the had a power arm over the street that the bus made connection to chargec up the fly wheel that drove electric wheels to further stops but oil was so cheap. perry

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#4

Re: How big a capacitor to run a bus?

12/07/2008 11:46 PM

A bus has an engine capable of producing about 100kW, used for half the running time, over say 1 hour means it produces approx 180MJ

Capacitors energy = 1/2CV², using the caps over the range of 1000V to 800V, means you'd need 1000F

Although this is physically possible, it's not the best way (cost, size or weight) to store the energy, even lead acid batteries are better.

If you "google" you'll find a few capacitor powered vehicles have been built, but they wont be going into mass production any time soon.

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#21
In reply to #4

Re: How big a capacitor to run a bus?

12/28/2008 12:29 AM

A bus has an engine capable of producing about 100kW, used for half the running time, over say 1 hour means it produces approx 180MJ

Capacitors energy = 1/2CV², using the caps over the range of 1000V to 800V, means you'd need 1000F

Are you sure about that? I have a 350 F supercapacitor sitting on my lab bench (actually, 35 10 F caps connected in parallel), and even charging it to 1000 V, I find it hard to believe that it could provide 1/3 of the power needed to move a bus. And can capacitors be charged to 1000 V? Mine can only hold 2.5 V.

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#5

Re: How big a capacitor to run a bus?

12/08/2008 12:23 AM

You use the same technology that the modern train uses the diesel electric turns a generator that turns the wheels

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#6

Re: How big a capacitor to run a bus?

12/08/2008 5:02 AM

note also as the capacitor discharges, voltage across it will drop and this will require a very sophisticated control for the motor,

Better thing is to go for fuel cells- where the storage is in a compact area using chemical energy - at cost of efficiency of course and use regenerative braking. This if I am not wrong is the area of innovation now.

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#7

Re: How big a capacitor to run a bus?

12/08/2008 8:00 AM

Ed,

Electric propulsion aside, I think light rail is the wrong answer to mass transit. We have an existing road network for rubber wheeled vehicles. We have trucks on our highways pulling two and three trailers. Convert those trailers to passenger cars. And use smaller trams like Disney World. Use the roads and our existing technology to get a cost effective mass transit system up and running. The biggest barrier to mass transit is connectivity: how does one get there from here? Use of our existing roads will help to solve that problem.

Bob

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#8

Re: How big a capacitor to run a bus?

12/08/2008 8:48 AM

While they work well in Citizen watches, it would take one a little bigger than a bus to power a bus for a few miles. The power switched into the capacitors would be a very large and quick load to the grid. So far it seems to be fuel cells that hold vehicular promise of non-oil energy. Syngas fuels are also a front runner.

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#9

Re: How big a capacitor to run a bus?

12/08/2008 9:27 AM

Although as previously mentioned, flywheels offer the opportunity to recapture your losses. Buses spend almost as much time braking as accelerating.

I do agree on the smaller, faster concept. BART was a lovely example except for the rails thing. One of the serious downsides to buses the size we use is they are rarely run at capacity, yet you cannot downsize the expense to match demand. And unless turnouts are incorporated, they clog traffic; which is what they are NOT supposed to do.

Rails have the serious downside of being expensive to move when traffic patterns change.

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#11
In reply to #9

Re: How big a capacitor to run a bus?

12/08/2008 11:52 AM

A capacitor will work in a regenerative braking scheme as well or better that a flywheel. A flywheel will need a fairly complicated variable speed drive to allow energy transfer in both directions. A complex mechanical drive like that will also have bigger losses as it gets more complex.

A capacitor drive can go from driving to braking with a simple low-loss switch.

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#12

Re: How big a capacitor to run a bus?

12/08/2008 12:19 PM

I guess why I initially reached for capacitors; fast recharge, controllable discharge, and since I only have to make a few blocks to maybe a couple of miles between stops I had hoped to get a capacitor under the size of the bus itself.

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#13
In reply to #12

Re: How big a capacitor to run a bus?

12/08/2008 4:03 PM

Maybe forty years ago, I helped a guy put a capacitor power-pack on an overgrown golf cart. He had quite a bit of C on there, but the problem turned out (as noted earlier here) to be control due to the discharge curve of capacitors. He put the thing half-way through a wall on about the third trial. Modern power electronics would make this a bit easier, but it's still gonna be hard to compete with trolley wire or tracks.

Somebody around here is using flywheels to do sort of what you're looking for; they're making something like 30 or 40 minute trips on a flywheel that actually spins up (if I remember right) in about 15 minutes.

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#14

Re: How big a capacitor to run a bus?

12/08/2008 6:24 PM

I'll trust SparkStation on this score. With the risk of off topic I would like to comment on buses and transport systems in general. Here in Carrboro & Chapel Hill they are running some Hybrid buses with apparently some success. Population density is high and bus transport in the towns is free. I believe it is much used by the student and university employees. I believe the buses cost 800 thousand each. (a figure remembered from a Town Council Meeting I went to.) I think they got two of them. What that means is that the rest of the fleet are still old tech diesel powered, so overall I see no terrific advantage. In fact I myself am attracted to the diesel electric properly scaled and mature technologically as applied to trains. Still again the electric powered trolleys of the past were a good system, though inconvenient to automobiles and requiring a power "Grid". In Brazil they wanted to put in subways, but after crunching the numbers decided to simply make the buses act like subways, by dedicating a bus lane and building ramps and platforms at the stops both accessible to wheel chairs, at the same height as the bus door for loading, and where tokens or tickets were purchased relieving the driver of that chore. Providing an electric power grid for all vehicles appeals to me for I imagine if vehicles had battery power to get to the grid, the system would be flexible enough to satisfy individual destination needs. Overcoming the general disadvantages and dangers of live wires or the third rail, is done in the confines of the subway, below, and the trolley from above. How to make a power supply that powers a variety of shaped and motored vehicles is not yet a problem I have solved that would work as a retrofit to the infrastructure of urban, rural, and interstates for private and public vehicles. The most mature transportation infrastructure that used Diesel Electric (Long Island Railroad), Subway, Buses, Trucks, Cars, Passenger, Freight Trains, Ferries, Planes, and Helicopters), was in my living experience existing in Manhattan. I expect that whatever is most practical will be done and proved to be best, there, as we move forward. & P.S. SparkStation did say in his post that even with water scrubbers for diesel a supply of fresh air was essential.

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#16

Re: How big a capacitor to run a bus?

12/09/2008 7:43 PM

Consider this means of getting around in a city: To go from building A to building B you erect a trolley cable.The cable has a higher anchor point at building A than at the destination, building B.Building B has a similar setup, going to building A,that is higher anchor point than A. When the trolley at building A is full of people the trolley is heavy enough to carry itself and passengers to building B,since it is downhill, and mostly gravity powered. There should also be enough extra power to carry an empty trolley from A to the higher point on building B.When leaving Building B to go to A,you must take the elevator or stairs up to the higher trolley.When leaving building B,the full trolley has enough energy to carry the empty trolley back to Building A.Repeat the process as many times as necessary.There is no free lunch, because you still must take an elevator or stairs up to the trolleys, but horizontal movement would require no energy,the energy debt is paid at the elevator. The excess energy produced by the "falling full trolley" could be converted to power the empty trolley going the opposite direction. These cable trolleys could span many blocks, and alleviate a lot of street level pollution. Is this viable, or have I been partaking of the Scotch a little too heavily? ----(hic)------------------------------------------------------------------------------------------- HiTekRedNek

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#17
In reply to #16

Re: How big a capacitor to run a bus?

12/09/2008 9:08 PM

Hello Guest,

It would be far more efficient, energy-wise, for all those people to use bicycles, instead of climbing stairs to access a trolley-car as you suggest.

The bicycle is the most energy-efficient transport device for a person.

Give up the Scotch - try plain water.

Kind Regards....

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#18

Re: How big a capacitor to run a bus?

12/11/2008 5:31 PM

The idea was to reduce traffic at street level.Take an elevator to the trolley, and the trolley to your destination, as long as it is downhill from your starting point.It does not have to be building to building.

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#19
In reply to #18

Re: How big a capacitor to run a bus?

12/11/2008 6:46 PM

this technology is proven

no unnecessary moving parts.

milo

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#20
In reply to #18

Re: How big a capacitor to run a bus?

12/11/2008 7:40 PM

Hello Guest,

<"....Take an elevator to the trolley, and the trolley to your destination, as long as it is downhill from your starting point.....">

The method as you describe it, is not truly efficient, nor is it really eco-friendly.

The input to the elevator + the building in which it is sited + maintenance to all + energy inputs, added to the similar input to construct the trolley, the building in which it is sited + maintenance to all + energy inputs are quite excessive.

As was proven over 40 years ago, the most totally efficient people mover is a bicycle with pneumatic tyres (Invented by Robert William Thomson of Scotland, who actually patented his invention some 2 years before John Boyd Dunlop applied for a Patent, which was disallowed, but Dunlop took the credit none-the-less, on his development of Thompson's invention, and set up the Dunlop company..)

After the humble bicycle, the most cost-effective and energy efficient transport method is the railway, with steel wheels running on long-grain iron rails.

Kind Regards....

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