Thanks. Back ~40 years or so ago, when I did know a little about electric motors, such sophisticated controllers for induction motors did not exist, Hell, even BLDC motor were uncommon. Again thinks for helping update my knowledge.
Electric cars are a pipe dream
- Thread starter Syzygys
- Start date
You know I just goggled it, I was not going to talk out of my ass because you have been teaching me the folly of doing that by glorious example, so we have both been learning things, thank you.
None taken. You might look at:
http://www.sciforums.com/showpost.php?p=2681666&postcount=32
which concisely restates my POV about China. The OP of that thread is my review / analysis of the Just released CBO's economic projections for the US to 2021. Read that OP and learn (again) with recent facts, why I grow increasing sure that the US will soon collapse.
Join in the discussion and vote in that thread's poll.
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That's the key. If you are operating the motor at high power levels you can't beat a BLDC for efficiency; you don't need to waste power generating a field. However, at lighter loads, there will be cases where BLDC's are better and cases where induction motors are better, since a vector-drive induction motor gives you independent control of stator and rotor fields.
For zero-speed traction applications (i.e. locomotives) induction motors can't be beat. For systems that average higher speeds (i.e. bicycles) BLDC gains you efficiency. Also, you can overload an induction motor until it melts; a BLDC motor will degauss its magnets when you get it hot enough.
Is that true? The street trolies used DC because that had the high torque they required even though they needed a reostat to to control the current with its losses.
It is hard for me to believe that the average torque on a DC current carrying wire in a strong magnetic field can be bet by an AC current in that same field.
Well, AC vector drives were not available back then, so it's hard to do an apples to apples comparison.
Also, DC train motors tended to use separately excited DC motors rather than permanent magnet DC motors for the same reason that modern trains use AC motors with vector drives - more control available. They would use tricks like first switching the stator current via a crude PWM circuit, then connecting the stator coils in series to the rotor, then switching the connections on the stator from one circuit to multiple smaller circuits, thus weakening the field and allowing a higher top speed. This was accomplished via a very large, complex and often balky electromechanical controller with a lot of relays, contact points, springs, cams etc. This also resulted in a small number of power choices to the driver, but by using tricks like alternating between the two top power settings, he could set speed to whatever he desired.
They were willing to put up with all of that (plus brushes besides!) because they needed to get as much power out of those motors as possible over a wide speed range. A straight permanent magnet DC motor would have had too _much_ torque at low speeds and would not have had the range to make it to a decent top speed.
On a per-amp basis, it can't. However, on other metrics AC wins hands down. For example, on weight and size, AC motors win bigtime since they do not have to carry magnets and they don't have to keep them cool.
Thanks also to you. I was not assuming that a train or trolley would use permanent magnets instead of coil generated B field. In fact, I think the reostat was in series with the B field coil to avoid whip-lash injury to the trolley passengers when a stopped trolley started to accelerate and then had the resistance decreased as the back EMF began to limit the coil current. (or something like that).
As ElectricFetus has explained to me, PM motors, despite no energy cost for making the B field, may not even have average better efficiency and probably have more capital cost and weight (but weight reduction is not very important for train) than modern AC vectored motors, which I don't quite understand* (and probably will not try to.)
*I recall that Edison never understood how an AC motor could work and greatly underestimated the advantages of AC's ease of voltage changes by transformers for transmission but unlike Tessla, he was well connected to the financial powers of his day (especially Ford & Firestone); so was able to install DC power stations every few blocks for low transmission losses and the higher torque (of that day) possible with DC motors. I guess that by not trying to understand vector AC motors, I am like Edison - stuck mentally in a older technology which is more simple. As they say: Science advances one death at a time.
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Jesus, again the links suggest average efficiency can be better then a PM motor, and what makes you think its capital costs be more? Sure the electronics need to be more complicated but it does not have expensive rare earth magnets. Finally weight, lets see Tesla engines weighs 70 lbs and can put out 248 hp (185 kW), a ratio of 2.64 Kw/lb, also 380 Nm of torque, sure just maybe a PM motor could do better but that performance is fucking awesome as is. The only big advantage of a PM motor I see is one that only been proposed but not yet implemented: Wheel hub motors, PM motors could operate without gear box and could be place in the wheel hub. GM experimented with it, they weighed 33 lbs and put out 25kw, a ratio of 0.76 Kw/lb, and reducing the hub weight is critical in order to keep the suspension system working.
I don't. Read more carefully what I said:
"PM motors, despite no energy cost for making the B field, may not even have average better efficiency and probably have more capital cost and weight"
I.e. all this is speaking of PM motors.
Fair enough, but one must be objective in all this, if induction motors have such advantages over PM motor, why do so many hybrids and EVs use PM motors? I would assume it has something to do with PM motors being electronically much simpler to operate, To make an induction motor have high variable torque and rpm efficiency, high torque at zero rpm and generator capabilities and operate from and charge to a DC power supply (battery) all requires specialize electronic solutions, while a PM motor can do so natively or with much simpler electronics. Tesla (the company, not the man, solid state variable inverters and FETs making this possible came long after his death.) proves it is possible, Heck even the old EV1 used an induction motor, so I'm guessing the choice of PM motor verse Induction economically is up to the price difference between fancy electronics verse rare earth permanent magnets, and the price difference can't be much considering companies like Tesla investment in them. So its clear rare earths pricing are not a major concern, they can be circumnavigated in the event of high market pricing, either directly with induction motors and indirectly with re-opening of non-Chinese mining and processing of them.
One year when I was an undergraduate, I shared a room with a mechanical engineer who was a real car nut - designing cars for fun, not homework.
If the words "un-sprung weight" did not come out of his mouth at least once per day I knew he was either sick or had some girl problems. I think that should be as low as possible so a higher percent of the car's weight is "sprung" for a better ride. - The motor must accelerate 100% of the car weight sprung or un-sprung. I think some of his designs had bicycle like tires filled with helium! That is both lighter and conducts heat from the flexing rubber to the metal hub better for any tire pressure. Perhaps He is actually used in some racing cars?
I have personnel experience with He's amazing heat conduction. One summer job at Haloid, which was developing a Battel institute patent that later became Xerox machines, they had a small contract from USAF, to develop that process for testing / evaluating high frequency printed circuits (The black "tonner" is a plastic and a great acid etch resist.) I made copper or silver wires, chrome resistors, and even condensers by multiple evaporation of layers of metal and stanous chloride as the dielectric. For them I need to open the vaccuum bell jar often each day and filled it with He before cranking it up 10 inches or so - enough to get my arms under the lip and change the evaporations masks. (The He protected the circuit I was building from oxidation.) Although it was at least at room temperature it really feels cold to stick your arm into an He atomosphere! These experimental circuits were such high frequency that the exact layout of the circuit was critical. I did not design that or evaluate the final units - I just made them and learned a lot about vaccuum technology that summer. But the most interesting thing was how badly we all (about full time 10 men and me in this research group) underestimated the market for Xerox.
Making a Xerox copy back then was an all manual process with many (15 or 20) separate steps. It took about five minutes for each copy if you were good at it. We all thought the main market would be making custom designed T-shirts at the beach etc. Who would spend five minutes making a copy when you could have several copies immediately with with carbon paper? :shrug: Another small group was trying to automate the process. Their first machine was about 8 feet tall, nearly a yard wide and at least as deep! I thought that effort was a crazy waste of money!
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Consumer Reports tests the Volt:
http://detnews.com/article/20110228/AUTO01/102280401
The review isn't very favorable, in the very harsh winter the range went down to 25-27 miles....
"questioning whether General Motors Co.'s flagship vehicle makes economic "sense."
"it doesn't really make a lot of sense. The Volt isn't particularly efficient as an electric vehicle and it's not particularly good as a gas vehicle either in terms of fuel economy,"
"The magazine has put about 2,500 miles on its Volt. It paid $48,700, including a $5,000 markup by a Chevy dealer.
Champion noted the Volt is about twice as expensive as a Prius."
"He was said the five hour time to recharge the Volt was "annoying" and was also critical of the power of the Volt heating system."
"Despite his criticism of the Volt, Champion praised its acceleration and acknowledged that under certain driving cycles, consumers could mostly avoid using gasoline. The magazine noted the Volt is nicely equipped and has a "taut yet supple ride.""
http://detnews.com/article/20110228/AUTO01/102280401
The review isn't very favorable, in the very harsh winter the range went down to 25-27 miles....
"questioning whether General Motors Co.'s flagship vehicle makes economic "sense."
"it doesn't really make a lot of sense. The Volt isn't particularly efficient as an electric vehicle and it's not particularly good as a gas vehicle either in terms of fuel economy,"
"The magazine has put about 2,500 miles on its Volt. It paid $48,700, including a $5,000 markup by a Chevy dealer.
Champion noted the Volt is about twice as expensive as a Prius."
"He was said the five hour time to recharge the Volt was "annoying" and was also critical of the power of the Volt heating system."
"Despite his criticism of the Volt, Champion praised its acceleration and acknowledged that under certain driving cycles, consumers could mostly avoid using gasoline. The magazine noted the Volt is nicely equipped and has a "taut yet supple ride.""
I've had an assortment of hub motor bikes, and they work OK as long as the wheel isn't sprung (i.e. it's the rear of a front-suspension-only mountain bike.) Since the one I have now will make it to 40mph it can rattle your teeth a lot at top speed. I originally had a battery in the front hub (which _is_ sprung) but that presented enough problems that I gave up on that and moved the battery to the frame.
It's telling that by far the most 'nimble' (i.e. best handling, most comfortable) ebike out there now is the Optibike, which has both wheels sprung and the motor/battery in the frame.
And yet I think that's the entire point of the car. It doesn't do either very well - but it does both, and beyond the Prius PHEV no other cars can do that.
I already mentioned this problem, BillyT did story about it, It good to see people re-enforced noted facts of no relevance to the current discussion. Wheel hub motors is a possible advantage, given wheel weight can be kept down, unless you disagree and believe that the possibility does not exist I don't see why people need to talk about it.
Just relating my experience with hub motors. Sorry if I made you angry.
You would probably enjoy this link
http://www.globalwarming.org/2011/02/22/can-electric-vehicles-change-the-game/