The Chevy Volt design....

Awl --
Recently, with the asshole extreeordinaire KiddingHisself, there was much acrimonious debate over the Volt, whose design I initially thought was Da
Bomb. Kidding, however, has pointed out that the design is, in fact, a kind of gratuitous silly complexity. Kidding dudn't understand this or any of the implications of his own research, but that's to be expected.
So the Q is:
If a diesel-electric locomotive uses a dert-simple diesel-to-generator-to-traction-motor design, with no intermediary bullshit, why doesn't the Volt do this as well? The only germane difference between the Volt and a diesel-electric locomotive (btw, virtually ALL locomotives are diesel-electric, so they just call the "diesels") is that the Volt has a parallel battery pack, for electric-only operation. No big biggie, in my mind. Well, big in the sense that this can avoid fossil fuel (Exxon/Mobil), but not big in the actual *design details*. After all, parallel is parallel, electrically speaking.
Think about how simple the generator-motor design is. Electric motors apparently no need no stinkin transmission, one of their big advantages. So all's you gotta do is hit the gas pedal, rev up the generator, to get accelerating electic power. Release, have some relays switch the motors to braking batteries, bang, you slow down. Switch over to batteries-only when they are available/charged.
So whazzup with all the rocket science (and rocket machining) in the Volt??
Dare I say it: RCMers could build/execute this basic design, and for a whole lot less than $45K. My 15,000 W genset (22 hp, and no bastion of technology) weighs a whole 220#. I'm sure that output could be at least tripled in 500# genset, what with Detroit know-how.
Oh, Kidding, please stay out of THIS thread, adults are tryna talk here....
--
EA



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No, they're not. You have obviously never heard of Voith who make hydraulic transmissions for diesel locomotives. There are also some manufacturers of mechanical transmission but these are only low powered (a few hundred horsepower) and not therefore mainstream.

Modern locomotives don't use generators any longer, they use alternators which are rectified then fed to an inverter which then powers (if modern) A.C. Three phase motors.

I don't want to rain on your parade, but I'm yet to come across any locomotive where the transmission will look after itself.

Locomotives would create too much power to store, regeneration is used where the power can be shunted away as in an electric locomotive which can either feed D.C. To the third rail or (I don't know about America, but here in Britain it 25,000volts at 50 Hertz) overhead catenary. Another locomotive on the same juice section might be drawing current and this negates the current draw from the power station.

You might be able to knock up something small like you suggest but remember that generator to traction motor is not very efficient (which is why the inverter/asynchronous motor of today), you're looking at about 15% losses in transmission.

--
Clive

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writes

OK, some clarifications:
First, I wasn't commenting at all about regenerative ng power in a locomotive -- or any rail car, as indeed, regenerated power from braking is enormous, and affects the whole signal system. In the NYC subway system all electric cars (not the diesels) actually use regenerative braking, but the power is disippated thru large banks of shunt resisters, not fed back to the system or grid. So I'm not making that particular analogy.
As far as transmission goes, and the definition thereof, yeah, there ARE gears between the electric traction motor itself and the actual wheel/axle of the carriage truck, so technically that IS a transmission... .. BUT not a transmission in the automotive sense, where it actually *changes gear ratios* or "speeds" -- at least not in the smaller diesels I'm familiar with --sub-1,000 hp utility diesels. I'm sure, in the 3,000, 6,000+ hp behemoths (which can't even operate on many sections of rail in the US), there is power-transmission rocket science going on, but I'm not talking about that. I'm talking about simple gas generator powered traction motors in utility diesels, where there is nothing between the wheel axle and the "generator" except the traction motor itself and mebbe a cupla reduction gears.
Btw, under-1,000 hp utility diesels are used for actual track work/construction, etc, not cross-country hauling. Thus, the operation is very simple: raise the rpm of the generator, send more voltage/current directly to the traction motors. No gear-shifting necessary. Just as there is no gear-shifting in all-electric cars -- altho one could effect a kind of gear-shifting by "shifting" motor windings.
I also use the term generator interchangeably with alternator, inverter, etc. But speaking of which, how efficient IS modern power transmission, from "generator coil to motor coil"? Ie, not counting the combustion process.
I believe overhead wires on the rails by me are 13,000 V. The third rail itself is 600-700 VDC. NYC has numerous substations around, which ostensibly convert the 13,000 V to 600 VDC, via hyooge two-story rotors/stators. At least they used to. You don't hear those spin much, anymore. Mebbe its straight transformer step-down, now.
--
EA





>> My 15,000 W genset (22 hp, and no bastion of technology) weighs a
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Back in the 1956/60s some main line locomotives did use a 4-speed constant mesh gearbox with the engine load being one permanently coupled torque convertor (Maybach-Mekydro) but I've not heard of those for several years now, and my experience is that the main ( not the only) maker of hydraulic transmissions is Voith, the layout differs between different models but the principal is the same. A torque convertor can multiply torque by up to five when the input shaft is driven and the output shaft is stationary. The input shaft connects to an impeller to throw oil outwards, the oil is directed by fixed blading onto the turbine which is coupled to the road wheels, the ideal behind the Voith transmission is to engage gear all you need to do is fill an empty converter with oil. If you gear three torque converters separately onto one output shaft and fill or empty them as needed you can see that three different ratios can be obtained, this is they way gears are changed. At idle, all three converters are empty and there is no drive, as you need drive so the first converter is filled, as speed increases the second is filled whilst the first is emptied and so on.

On an electric transmission, as you say, a generator is wired to the motor/s on the road wheels and some drive can be transmitted. However such a design needs modification to work properly. Firstly the generator needs the field to be excited to induce current flow in the commutator, the more the field is excited the higher the output from the generator for a set speed and it's this principal that can be made use of. Motors are very similar to generators and try to create a voltage opposing the driving voltage (called, back EMF) when turning, so the faster the motor turns the larger the back EMF, as it opposes forward flow of current, generator to motor, the prime mover (diesel engine) is off loaded. To keep the flow of juice constant the forward EMF needs to be increased and this is done by increasing the generator field to balance out. There comes a point at which you can't increase the field voltage without risk of flashover and on a lot of main line locomotives this is about 30 to 35 mph. The way around this, is to stop the motors generating some back EMF and this is done by weakening it's field, allowing the motor to take more current and drive to a higher speed, you might say this is the equivalent of an electrical gearbox. A locomotive would use maybe three different levels of field weakening allowing the motors to speed up and giving a higher top speed, the gearing between the motors and road wheels chosen for a mixture of either high tractive effort (pulling power) or top speed, or a mixture of both.

My understanding of modern three phase traction techniques is seriously limited and I'm not going to try to explain them other than to say, they are far more efficient and can turn in efficiencies of greater than 95%.

This is where a hybrid or range extended transmission can be used and frankly it's a case of personal preference. I'd like to make an observation and would welcome your feedback, I don't think there is such a thing as a free lunch and here in Britain, fuel can be or is 6.60UKP per gallon. It has been worked out that an electric car, whether pure EV or range extender needs to be charged and that electricity costs money, which has to be offset against the price of fuel to see if any gain is made. It turns out that the gain from using electricity is marginal at best or non-existent at worst, with the only upside being regeneration energy can be stored in batteries to help accelerate again. You would need to work out what it would cost you to drive one mile in both fuels (liquid and electricity) to see if it's cheaper to use one fuel over another, in the UK there isn't much in it. I know a US gallon is a bit smaller than an imperial one but the amount of liquid is the same, so it should be easy to look up the conversion factor and the financial exchange rate and get a figure for USD per US gallon.

See above.

I have read them. If you feel I am in error, please let me know.
--
Clive

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It is my understanding that virtually all American-made, for the domestic market, diesel electric locomotives consist of a diesel engine that turns a generator or alternator which drives electric motors attached to gear reduction drives that turn the wheels. This has been the main stream design since the late thirties.
Yes there have been locomotives that had gasoline or diesel motors attached to transmissions with drive shafts attached to differtials on the axles. Most of these were either home-brewed(Rio Grande "Galloping Goose" et al) or low powered low speed switch engines. Budd Railcars of the fifties were straight diesel engines with torque converters driving differntials on a single axle. One or two cars was about all they could pull.
In the late sixties/early seventies Southern Pacific imported a number of Kruass-Maiffi (sp) diesel hydraulic locomotives for use on some of the western mountain routes. They ultimately were considered failures because the temperature of the hydraulic fluid could not be adequately controlled causing motors and lines to burn up. And they were no more fuel efficient than diesel electrics.
The advent of alternators and AC motors increased the fuel effiency and tractive effort dramtically. The evolution of the controls to computer management has increased effiency even more. Thus the unit coal trains that shuttle between Wyoming and the Texas coast routinely consist of 125 cars(1.7 miles of 75 foot long cars), 15000 tons of coal, with 3(2 in front, one in back, pushing, remote controlled) locomotives( 6000 hp, six axle, Ac motors) traveling at speeds up to 60 mph.
Getting back to EA's original question of why not use this drivetrain, the usual answer is: the response time for intial acceleration is too slow for street/highway use.
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wrote:

Something that is often overlooked in the "it's cheaper to generate electricity" theory is that the THEORY is fine as far as how efficient it is AT the point of generation. But when you have to transmit that electricity over more then a couple hundred miles you start to get very large transmission losses. I forget the exact numbers but it's surprisingly large, you lose something like half the power by the time you send it 400 miles. This is one of the reasons super-cold superconductors have been a "hot" field of research, just eliminating that transmission loss would nearly double the available power from the current electric system.
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wrote:

Your numbers are WAY off - by roughly a factor of 10. California's grid is far from the best in North America, and they lost a whopping 6.8% of their power output in line losses in 2008.US average is about 7%. Better grids run closer to 4.2% , with Japan averaging about 5%
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wrote:

Yes, but the voltage has to be almost excessively high to get a sizeable difference.
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On Mon, 01 Apr 2013 19:47:58 -0400, snipped-for-privacy@snyder.on.ca wrote:

Yikes, Wiki confirms you. Wish I could recall the "expert" who spoke at a conference several years ago and imparted that info to me. He talked about superconductors and the line loses were one of his selling points.
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wrote:

You got it right - "selling points" Figures don't lie, but liars figure, and all that. Anytime someone quotes figures when he's trying to sell you something - even if it is just an idea, CHECK THE FIGURES. And you know the definition of "expert"? 1) - a guy from more than half an hour away carrying a briefcase, and 2) ex for Has-been, spurt for big drip.
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wrote:

It's still a pain to boost DC that high, and they couldn't do it at all till they came up with the high-voltage transistors to do it with. But the main reason for bothering with the HV DC Intertie lines is they are almost always transferring power between regional grids that are not normally in sync with each other. Ever seen what happens when you try to parallel two generators that aren't synchronized properly? There's always Lots Of Things Blowing Up, often very expensively.
The Southern California and Nevada and Arizona grid is taking it's frequency marching orders from Hoover Dam, and the PNW Region from Grand Coulee Dam - and it really doesn't matter if one's running at 59.99 Hz and the other is at 60.01 Hz, and the phasing is 180-degrees out at the moment they want to start the transfer - the DC converter stations are frequency locked to their own master sources at each end, and can compensate automagically.
Otherwise, they'd have to speed one grid up or slow the other down and get the phasing synced up perfectly (imagine the Synchrotron light bulb slowly pulsing...) before throwing The Big Switch to link them and start sharing energy - and then they'd have to break the connection with the other regions to their north and east, or get them to speed up or slow down too. That starts getting complex.
And if we get some Solar Flares that induce sneak currents on an AC Intertie, that can make things exponentially worse. DC it just compensates.
I got to run the telephone lines into the new section they added onto the LADWP Sylmar Converting Station, and that thing is a monster, all that gear inside a contender for Worlds Largest Faraday Cage. The old section was even more impressive - but it was running, and I know not to put my fingers anywhere near that...
--<< Bruce >>--
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Gunner Asch wrote:

Long AC lines turn into radiators: Think of it as a longwire antenna fed with 60 Hz. It is a poor match, but still emits a weak 60 Hz field.
The lower losses with higher DC voltages is simple Ohm's law. The current goes down as the voltage goes up for the same Volt-Amp. The current through a resistor is what causes the voltage drop, so the more you can reduce the current, the more you reduce the losses.
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You might be confusing a kid's ride at a carnival with a real locomotive that actually runs on track with a guage over 1 foot.
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I don't know about your neck of the woods but in mine a small gauge that runs in a fair is usually just a normal car setup.
--
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wrote:

Hydrostaic is common here for theultra-narrow-guage fair units. Often an adapted garden tractor.
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On Sat, 30 Mar 2013 13:24:31 -0400, "Existential Angst"

I think the primary reason why the basic design parameters of a diesel electric loco aren't used for an electric car are... .. A D-E is designed to mainly run long distances at more or less max output and fairly uniform speed, not a not of 0 - 70 mph and back over and over. .. Acceleration is not a critical factor to the "drivers" of them. It needs to be adequate but they don't need to provide for "especially quick starts", or passing slower traffic with a burst of speed. .. Each class of loco is designed for a specific basic function, switching, passenger service, freight being the main ones. So while a Passenger loco may be geared to run 90 mph, the freight version will be geared to run 60 mph and a switcher might be tuned for 30 mph being it's optimum. Sure they can be interchanged if needed in a pinch but doesn't change the basic premise. ... because of the above, and because the actual train is WAY heavier then the loco itself, the actual weight of the loco isn't all the big a deal, whereas for a car it's a huge factor in the overall design. In fact, for a loco, you don't want it to be too light, it needs a lot of weight to provide the traction to pull the heavy train.
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typed in rec.crafts.metalworking the following:

    Apropos of 'hybrid" cares and a similar set up, I recall a Pop Mech article decades ago, on a guy who was building an electric car "run off batteries" with a gas turbine engine to charge the batteries.     It would seem to me, that the "smart thing" is to have electric motors driving the wheels, and an gas/multi fuel engine to run the charger. [heck a stirling engine would work.] Optimize the engine/generator for efficiency and "Bob's your uncle!" -- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."
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On Tue, 02 Apr 2013 10:09:26 -0700, pyotr filipivich

that's pretty much what the Volt does I think.
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