Changing Driving Behavior Or How People Use Cars

There are dozens of good commercial and government applications for electrical vehicles, and some of them even make economic sense:-) The truth about battery powered electric cars for private ownership is that without a major and unexpected breakthrough in battery technology they will never be more than urban, short-haul vehicles. For many observers, this means that battery powered cars have no place in the American setting, but I believe they could prove a valuable lever for changing driving behavior. The problem, from the standpoint of a small government advocate, is that it would take a massive government intervention, in the form of electric car subsidies and gasoline taxes to bring it about.

Americans are rich. You can argue that we’re poorer than our parents generation, and in some ways that may be true, but we’re all rich compared to the average Joe of 100 or more years ago who spent most of his time worrying about getting enough to eat or wear. The problem with this wealth is that people can afford to indulge in bad behavior, like driving overweight, overpowered, inefficient gasoline vehicles. As the recent price bump in gasoline demonstrated, doubling the price from around $1.50 to $3.00 a gallon had only a modest effect on changing American’s driving behavior – we’re addicted to gas.

But what if the government slapped a $3 per gallon tax on gas, bringing the price up to European levels. I’m not suggesting that the price paid for gas in England or Germany is in any sense a "correct" price, but I’m pretty sure it would be enough to start changing the driving behavior of people at the lower end of the income scale. Unfair? Absolutely, which is why the government should take that money and spend it on subsidizing electric cars, so the people who can no longer afford a gas guzzler will have little choice but to buy one.

So why do I think it’s a good idea to essentially force a segment of the population into a technology that’s more expensive than running gasoline cars on an unsubsidized basis? Because the limited range and charging requirements will actually start changing the way those people use cars. The private car won’t be some sort of get-away toy for them, it will be a way to commute to a fairly close job or school. People will be forced to learn to make one or two intelligent shopping trips a week, rather than jumping in the car for the mall every time something comes up, and the rest of the time they’ll be stuck with public transportation or walking.

I’ll be one of those people if the day comes, it won’t be out of economic need (hopefully) but because I believe in the limited use model. I rarely drive my own car more than once a week, unless I’m helping friends with a construction project out in the sticks. Somehow, we’ve gotten stuck on the notion that an unlimited cruising range car is a right, in the constitutional sense, when it’s only the last hundred years that the car has been around. There are plenty of cost effective alternatives to owning a gasoline car for the occasional long haul trip most people make, like car clubs or rentals. Technology isn’t just advancing at a rapid pace, it’s pretty good already. It’s our driving habits that need improving.

Electric Motor Horsepower Rating for Automobile Use

In my first blog post I looked at the horsepower rating for the killer app of cars, the Model T, and found that it took America by storm on 20 HP. That’s a lot of horses of the flesh-and-blood variety, but not so many by automobile standards, where most vehicles produced have at least 100 under the hood. When I started running web searches on motors for use in electric cars, I found that they their power ratings tend to be in KW, with the simple conversion factor that . 1 hp = .746 kW. However, the more I read about motors for electric and hybrid vehicles on the web, the more I see references to the rated horsepower – and ignoring it. The logic runs something like this.

Electric motors are rated for continuous output, connected to a power source, they should be able to deliver their rated horsepower until the cows come home. In order to compare them with internal combustion engines, which are rated for peak power, you have to know what maximum horsepower an electric motor can put forth for a short period of time without melting something or catching fire. I know that sounds like a pretty inexact description, but I haven’t come across any sites giving a rationalized rating system, like (the following is made up)

Rated 10 HP
Delivers 20 HP for two minutes
Delivers 30 HP for one minute
Delivers 40 HP for 20 seconds

Not to mention a nice curve showing horsepower vs time through the longest range you’d want to consider. While two minutes is much longer than you’d hope to need for acceleration when entering a highway, it’s nothing when you consider some of the hills you encounter even just in New England. I’m going to keep searching, but I’m getting tired of seeing rule-of-thumb statements that vary from "Electric motors can deliver over twice their rated horsepower for short periods of time" to "… five time their rated horsepower…" That’s a big spread.

As to how the motors are coaxed into delivering the extra horsepower, that’s entirely in the hands of the control circuitry. I’m as innocent about solid state power controls as I am about electric motors, so I have no idea if some of them do this through current regulation or if it’s a simple question of upping the voltage. Maybe in motors that use electromagnets rather than permanent magnets, they overdrive the electromagnet windings rather than the armature windings. I’m not even sure if the failure mechanism is always heat, it could be that the insulators fail and you get arcing at higher voltages, or maybe the air-gap is idealized for a lower voltage. Much more research to do, but I hope I find some primary electric motor vendors who have better specs.

Rectification in Motors and Generators

Ideally, the motors used in an electric vehicle will be able to function as generators when during braking, with the current generated going to recharge the battery. Sounds like a simple enough concept for an electrical engineer to be dealing with, but frankly, I doubt I ever understood the basics of how an electric motor worked when I was at university. It seems to me there was a senior year course elective called "Power Engineering" that wasn’t in my concentration, and maybe that’s where they taught basic electromotive concepts, but I doubt it. I remember friends telling me that it was all math, like most of our courses.

I searched around the library today for a nice basic text on motors, and came across "Electrical Machines" by Kostenko and Piotrovsky. It’s a fun read because it was written as a textbook during the communist era in the former USSR, and therefore, Russian inventors are much lauded and capitalist exploiters are blamed for the early lack of progress in that country. However, it does have an excellent explanation of the basic concepts of a motor/generator right in the first chapter, using a two magnetic poles and a Faraday loop. My ability to produce illustrations while I’m traveling is pretty limited, so I’ll stick to a text commentary.

If you picture two permanent magnets with a nice cylindrical channel cut out of each, oriented across from each other so that the North pole of one faces the South pole of the other, you have set up a nice continuos magnetic field. If you introduce into that field a loop shaped conductor, the armature, you’ve essentially placed two conductors in the magnetic field, which happened to be made from one piece of wire that forms a "U" on one end. As that armature is spun between the two magnets, a current is induced in the conductors (Faraday’s Law). The free ends of the wires are attached to a split cylinder, or commutator, where the current is drawn off each half on the commutator by a brush, forming a circuit with whatever load is put between them. The function of the split cylinder commutator and brushes is to rectify the current so that it always flows in the same direction, though the magnitude will be very sinusoidal. The brushes are fixed in position, one so that it always draws the current off from the conductor near the South Pole, the other from the North. The whole arrangement is rather magical, and proves there is beauty in electrical engineering.

The design formula for electric motors, which are far more complex in practice than our simple loop with two magnets, are highly idealized using rules-of-thumb and cookbook methods. The reason is that the motor components themselves have geometrys that just aren’t describable with continuos functions. I suppose you could do something with numerical methods to describe the flux through the odd shaped windings and magnets, but since motors and generators are built for practical purposes, practical solutions built upon existing data rule the roost. If instead of turning the armature with an external mechanical force (generation) you cause a current to flow through it from an external electrical force, it causes the armature to spin between the polls and you have a motor.

The reading has me itching to build a couple crude DC motors of my own when I get back. I wouldn’t dream (at this point) of actually designing and winding my own motors and generators to build an electric power train for a car. It wouldn’t be practical or cost effective, even if I knew what I was doing, and would add a couple years of lead-up to my first go. It does bring back memories of a few weeks I spent winding transformers some twenty years ago. They were custom transformers with a special ferrite core, a split secondary with multiple taps and a bifilar wound primary, meaning the primary winding consisted of two identical length conductors wound the same number of turns, side by side. I was actually pretty good at it, when the inductance (or was it reluctance:-) was checked by test equipment.

Why an Electric Powered Car

Why an electric powered car? All right, fair question. Electric drives are pretty much universal in super-heavy equipment, such as train locomotives and mining trucks, but unlike early trolley car attempts, they aren't battery powered. The standard approach is to run a diesel motor generator, a sort of onboard DC power plant, to drive large electric motors on multiple wheels. Electric motors are relatively simple, can deliver maximum torque without having to get revved up, and don't consume any power when they aren't running. They are also pretty scalable, so an onboard generator combined with battery assist can deliver more peak power than a direct drive diesel. You can think of locomotives and massive dump trucks as hybrids, but I'm not that ambitious.

What attracts me most to the electric powered car, even with all the drawbacks inherent in battery technology, is that they don't care how you make the electricity. Whether you go whole hog with PV panels charging up the battery pack and not driving unless you've had a few days of sun or whether you use off-peak nuclear generated power to charge up, you're doing the environment and the economy a favor. I suppose you could even hook up a bicycle generator to your car and ride for a few days in order to drive a few miles, the important thing is not to burn fossil fuels.

Once the batteries are charged and you start driving around, electric cars are far more energy efficient than their greenhouse gas breathing brethren. Regenerative braking turns the motors into generators when you want to slow down, recharging the batteries instead of wasting the energy in friction heat, as do standard braking systems. As with the super heavy equipment, electric powered cars don't waste any energy idling when you're stuck in traffic, they just sit there. The main efficiency complaint about electric cars is that they spend so much of their energy hauling around the battery pack, but you can reduce that waste by settling for a shorter range, according to the habits of the particular user.

But what really attracts me to electric cars is that line the kid medic delivers to the painless dentist in the original movie version of Mash -"But you're throwing away your whole education." I spent six years grinding through a couple electrical engineering degrees with little but a lack of appreciation for education to show for it. Twenty years later, I'd like to see if there's anything left, and I can understand the manuals that come with the motor controllers, maybe make a few modifications. Hopefully I'll find something at the library tomorrow to get started on DC motor technology, from the beginning.

Rechargeable Lead Acid and NiCd Batteries in Vehicles

Finished the Schallenberg book today, a bit anti-climactic in the sense the battery designers never come close to solving all of the problems that make battery use in electric vehicles problematical. In the best tradition of a technology in search of an application, electric batteries were tried in just about every application where electricity was used, showed great promise on paper, and failed to deliver in the field. Obviously, lead-acid batteries did find a place in everything from car starters to powering submarines, and of course providing back-up to critical systems, but on the whole, storage batteries had enough going against them that they never took the world by storm.

It’s interesting to look at all of today’s battery powered technology and realize that it’s been made possible not by vast improvements in battery design but by vast improvements in solid-state electronics. It’s the low power demand of the devices that make them practical, not the high capacity of the batteries, though rechargeables really have made a difference in markets like power tools, cameras and cell phones.

Oddly enough, one of the first jobs I had as a co-op student in electrical engineering was helping a consulting firm determine why the NiCd battery packs of a major manufacturer were failing to perform well with their medical tools. Unlike many non-critical applications, it’s a bit inconvenient to have your drill run out of juice when you’re making holes in somebody’s skull or sawing through a tibia. The power packs were very similar to today’s power tool batteries, containing a large number of low voltage cells in series to make up the proper voltage and capacity, but the application called for fast recharging. A little processor controlled charger would track the charging current and look at the first derivative to see when the curve bellied over, but it didn’t work for beans. The problem turned out to be that individual NiCd cells charged at different rates, in part according to their individual state of discharge, introducing all sorts of sub-inflexions on the curve, and in the worst cases, reverse polarizing the cells. The only solution offered was to make sure battery packs were fully discharged before attempting to recharge, and then doing that on a timed basis.

It was interesting to read that some Edison utilities, in the in the second decade of the 20th century, actually constructed recharging garages where they would recharge electric vehicles during off-peak (night) hours for the sake of load leveling. They did so at a reasonable monthly fee that would be cheaper than the customer buying electricity directly from the utility. Such solutions would actually work well today in areas with a high percentage of nuclear power, like New England, since it’s highly advantageous to run those plants near their peak output. But, I suppose the grid is such that New England nukes probably provide power up and down the East coast at night while fossil fuel generating stations are taken off line.

Batteries for Load Balancing and Locomotion

I read through the middle third of Schallenberg’s "Energy in a Bottle" today, which focused primarily on the use of lead-acid batteries as electrochemical transformer devices and short term storage for load balancing in the early days of the electrical distribution industry. As the AC vs DC debate raged around the end of the 19th century, it was found that large scale AC distribution systems could easily incorporate existing DC systems by using the AC to run a motor/generator set. Efficiencies above 90% were possible, which wasn’t too far off the AC transformers of the day. It reminded me of a suggestion I made back in the early 90’s to an engineer who had charge of a large PV pilot installation on a school roof, on the order of 100 kW if I recall. The project was rusting away because the inverters had failed early on, and the money (grant) wasn’t their to replace them new solid state inverters. I suggested adapting a surplus motor/generator set, but he rejected the idea out of hand thinking it inefficient and I suspect, not sufficiently elegant for a PV installation.

Schallenberg wrote on the subject of using batteries for anything other than energy storage, "Despite their illusory simplicity, storage batteries are inherently expensive devices, both in capital and maintenance costs. Electromechanical or electromagnetic devices are almost always cheaper and better than electrochemical ones, if both can be used for the same function." It’s also interesting to note that lead-acid battery capital costs don’t seem to move at all, with whatever minor price reductions we may see coming from more efficient retailing rather than manufacturing. Power tool prices have dropped like a rock in my lifetime, by well over 50% on average, while battery prices have remained fixed.

The early generation and distribution engineers soon discovered that sizing systems with an inconsistent load led to tremendous inefficiencies (i.e., costs). R.E.B. Compton coined the term "load factor" which was defined by the average demand over the peak demand, and found to his dismay that the load factor on any given day for some installations was as low as 5%! Batteries were used as a temporary solution to this problem is some places for a few decades, but improvements in loading (round the clock demand) combined with other electromechanical fixes made them an expensive option.

At the dawn of the automobile, the most promising application for storage batteries seemed to be trolley cars. Although these systems had been tried with miserable results for decades, the rapid growth of cities and the inability of horse draw trolleys to keep up with demand helped the idea current. In the end, electric trolleys were a big winner, but the power source was overhead wires or conduits. Schallenberg wrote, "Therefore, the chief reason that the battery car turned out to be almost as expensive to run as the horsecar is the battery suffered from the same technological limitation as the horse… The cars needed to go faster and carry more passengers as the cities expanded. The horses could not do this without shortening their lives to an unprofitable extent."

The main failure mechanism of these batteries was the peak demand put on them during acceleration. Drawing too much current from a battery, any battery, will adversely effect it’s life. Trolley requirements did bring about the development of the deep discharge battery, essentially a heavy duty version of the lead acid battery that could be exhausted without great harm, though at a cost of a heavier battery and greater size. These same problems remain with lead-acid battery systems if used to build an electric car today, though I wonder if some of the peak demand couldn’t be addressed with lightweight super capacitors.

Energy in a Bottle

I’ve been reading a book titled "Bottled Energy" by Richard Schallenberg because I’d like to design a car that runs on single malt Scotch, but only if I get a government subsidy to buy the whiskey. Actually, Schallenberg’s book is a tour-de-force presentation of the history of battery technology, focusing on the lead-acid battery, its proponents and uses over the first century and a half or so of its existence. As he points out, one of the early obstacles to battery development was the lack of practical uses for the thing, not to mention instrumentation for measuring the output. Early researches mainly relied on putting the wires on their tongues and trying to gauge the galvanic taste/ The more advanced instrumentation consisted of the effect of the current on a frog’s leg. I got this mental picture of an automotive instrument cluster, where the indicator needles are all frog’s legs that kick out over the scale.

The idea of using batteries to drive motors for locomotion was apparently pretty widespread amongst anybody using batteries in a process that required a dynamo to charge the batteries. If the drive shaft was disconnected from the dynamo, the batteries tended to run them backwards, which would make a light bulb go off in any engineer’s head, though apparently, that took a little longer. The initial "practical" application from batteries was mainly found in telegraphy, but it eventually moved to mixed electrical lighting solutions that are similar in conception to solar systems – charge during the day (but with a dynamo) and illuminate at night. They remain with us in the form of emergency lightning.

Because of the relatively low voltages and heavy battery weights, the original attempts as locomotion with batteries seems to have been focused on a replacement technology for horses on horse-drawn trams. The economics looked promising, but the battery technology was so primitive (they failed very quickly) that none of the systems stayed in service for any amount of time. About half the payload for most of these trams was the batteries themselves, and even though they were easily hidden below the seats, it wasn’t a terribly efficient use of energy.

I have one complaint about the book, which is Schallenbergs repeated comments about how demanding battery development was. One quote, "Storage battery engineering is an inherently demanding skill requiring full-time specialization to produce a commercial product. All those companies which succeeded in the field were specialists." Aside from the fact you could say that about any technology (though it wouldn’t be so as the many great inventors and technologists of the century showed) , it appears to be a case of the author attributing a mystique to a beloved research project that just doesn’t appear to the critical reader (ahem).

At the point this comment appeared, I can only think of two companies he’d described working in battery technology that could be described as "commercially successful" and then only in a small way. There seemed to be a dearth of interest from the serious electrical engineering concerns of the day in batteries, which just weren’t viewed as that important, and many of the researchers who Schallenberg describes were essentially dilettantes. To this point in the history of the battery, it strikes me as a case of the only companies that could be bothered to keep working with the things were those who had no other products. If I change my mind by the end of the book, I’ll gladly retract:-)

Basic Power Conversion

When we’re talking about electricity, we talk about power in terms of Watts (W) or kilowatts (kW). The Kilowatt Hour (the power of a kW used for one hour) is a measure of how much energy is used, and also how your home electric bill is computed. Now when’s the last time you heard somebody say about their car, "this baby has 200 kW under the hood!" Probably never.
Horsepower (hp) is also a unit of power, so it can be directly converted into kW, and vise versa. The conversion factor is:

1 hp = 745.7 W, or 0.746 kW

Since car buyers and manufacturers who pay attention to horsepower tend not to care about fuel mileage, it’s not a standard thing to think in terms of how much energy is used, or horsepower hours, because after all, you can just refill the tank when you run out. When people do think about fuels in terms of available energy, the traditional unit is the British Thermal Unit (Btu), and it’s a little smaller than the Watt:

1 Btu = 0.293 Wh or 1 kWh = 3412 Btu

Just for reference, a ton of coal contains about 25 million Btu or 8076 kWh. A barrel of crude oil contains more than twice as much energy, about 58 million Btu, while a cubic meter of gas contains just over a thousand Btu.

When we’re talking about energy available to do work (to produce a force through a distance), it’s critical to know not just how much energy is available from a generation or storage system, but how quickly it can be drawn. One reason gas guzzlers are so popular is because they can produce their peak horsepower just by revving them up to the right RPM range and dumping the clutch. Batteries, on the other hand, will overload and fail if you try to suck out all of their available energy at once through a short circuit, and will produce less energy when drawn on heavily rather than moderately.

The Model T as the Killer App of Cars

E-mail was the killer app (application) that made Internet access "must have" for modern man and the Model T was the killer app that made the automobile a "must have" in its day. Neither technology was a new invention, both had existed in various forms for at least a decade before their broad public introduction. The thing that made them killer apps is that they had arrived at the evolutionary stage where they were seen as practical and cost effective. E-mail got there with the 14.4 Kb/s dial-up modem, remember those? I’ve had a decade long career as an Internet publisher, and I’ve been on dial-up for all but eight months of that period. The Model T became the killer app of the automotive world with 20 horsepower engine and a 1200 pound curb weight, and it likewise showed it’s worth for over a decade.

The world may have changed quite a bit between now and then, but I have to believe if people could buy street legal Model T’s to tool around the country for $850 (their introductory price), there would still be a market. What that tells me about automotive technology as a starting point is that you can get by with 20 hp. I’ll get into what a horsepower actually is in the next post, but for the time being, lets look at some comparisons. I’ve seen SUV’s advertised on TV with 300 horsepower engines, talk about a waste of resources. On the other hand, a 125cc Honda dirt bike with a total weight of 180 pounds could also boast 20 horsepower a couple decades ago. I rode a 100cc Honda for a few summers, it had plenty of power to go wherever you wanted, though it got blown around a bit by passing trucks.

The relationship between horsepower generated by a motor and speed achieved by a vehicle depends on several factors, the gearing in the drive train, the friction losses in the drive train, the aerodynamic losses to wind, even the rolling friction of bearings and soft tires. Well, that’s not exactly right either, since a small horsepower engine can move a car along just as fast as a large horsepower engine, particularly if the car isn’t very heavy and you don’t exceed the speed limit by an excessive amount. The main difference horsepower makes in this case is how quick you can get up to that speed. If you drive like an idiot and never learned how to merge, horsepower can be very useful, but in most cases, it’s just not necessary.

So, our adoption of the Model T as the killer app of cars means if we build a 1200 pound electric car and put 20 horsepower of motors into it, we should have the start of a useful car. Whether or not it will have a useful range with the number of batteries we can afford to carry to keep the weight down will be another question for another day, but it’s a start. For what it’s worth, I expect we’ll be able to get more useful work (speed and acceleration) out of our 20 horsepower than the Model T did with its two speed transmission.