Electric Cars

A Jones has written a cool article about electric cars.

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The author is a physicist and engineer with additional degree equivalent qualifications in accountancy, economics and management. He worked for the UK government (HMG) and in 1974 was transferred to a newly formed division considering how to mitigate the effects of the oil price shock which included examining all possible alternative sources of energy as to cost and effectiveness. In 1976 he became increasingly involved in the electric car team and was formally seconded to it in 1977 when it became the Electric Car Group, (ECG) which had a brief from HMG to develop and report on the technology of a practical small electric city car and provide technical support to British manufacturers. He retired some years ago. The views expressed below are entirely his own as are any errors.

Today, once again, there is much excitement about electric vehicles which were popular in the early days of the horseless carriage and still found niche applications in the UK in the 1970’s: such as the electric milk float. After the oil crisis of 1973/4 it was thought that a practical electric city runabout for UK use could be developed which would reduce dependency on imported oil since almost all electricity was generated by home mined coal or nuclear: and a new generation of nuclear stations, the AGRs, were coming on line.

It is important to appreciate that overall efficiency was not a priority, the aim was to utilise a then abundant resource, off peak electricity, with the bonus of reducing inner city pollution from car fumes. Studies showed the overall efficiency of an electric vehicle, whilst not good, was within limits, rather better than the internal combustion engine. This has an optimal efficiency of about 25% for a petrol [gasoline] Spark Ignition [SI] engine and 35% for a medium speed diesel, Compression Ignition [CI] one. In practice however because of the range of speed over which the engine must work, and depending on driving conditions, the overall efficiency is much less.

By comparison the then Central Electricity Generating Board [CEGB] reckoned the overall efficiency of its coal fired stations at 33%. From this must be deducted transmission losses, charging losses and the usual losses in the controller and electric motor giving an overall figure of a bit less than 25%. But unlike its internal combustion engine counterpart an electric car can more or less achieve this efficiency over a wide range of driving conditions, in theory it delivers only as much power as is wanted at any time, wastes none when stopped, and can recover some energy when braking or descending hills.

Moreover the UK, especially south east England, was densely populated with good paved roads, the CEGB was only too eager to sell overnight off peak electricity cheaply to keep its base load up and the whole country had more or less standardised on the 6kw domestic ring main at 230 volts/50hz, using a 13 amp square pin plug: which was ideal for electric runabouts.

In the 1950’s and 60’s British motor companies had been very adventurous is exploring new technology, such as turbines, and had essayed electric cars both in the form of what is now called a parallel hybrid in which a motor car also has a electric motor/generator which alternately drives or is driven by the transmission and series hybrids in which the engine and generator only serve to recharge the battery when needed: but with little result. They lacked a suitable battery.

A traction battery must meet several demanding requirements. Because it is part of the haulage load it must be light in weight for the energy stored, it must be capable of high rates of discharge, and thus almost by definition charge, it must be robust to resist both vibration in use and for the electrodes to withstand the great forces on them during high rates of charge/discharge: and it must also be able to tolerate many thousands of charge/discharge cycles with little deterioration: and ideally the change in cell voltage at various discharge rates throughout the cycle should be small.

At that time there was a cell devised during world war two which showed exceptional promise in terms of weight and cost but the technology to develop it into a practical commercial battery wasn’t available in the 1940’s or even by the 1970’s. The lithium cell was under development but not for traction purposes. Exotica such as silver/zinc or zinc/air were just that and although cheap the weight and lifetime of the lead acid accumulator was poor. Sodium/sulphur was a Ford dream back then and the NICAD too temperamental for traction use, and whilst expensive, proven and almost indestructible the Edison NIFE, although much used in early electric cars, could not meet modern traction requirements.

The solution was the little known but technically well proven Drumm cell, which like the NIFE used a nickel/nickel hydroxide electrode but instead of an iron electrode used a nickel mesh and an electrolyte of potassium hydroxide and dissolved zinc oxide. Charging caused the zinc to deposit on the nickel mesh and discharge the reverse. Although manufacture had ceased some time around 1940 it had been successfully used to power electric commuter trains in Ireland for many years and was in every way superior to the NIFE. As originally designed it was not ideal for electric cars but by making various changes the result was a most satisfactory if costly traction battery.

In part this success was due to the great care with which the ECG design committee [the Committee] drew up its requirements. They calculated that using a punt chassis and space frame construction with plastic body panels a complete car a little over 4 ft wide, a bit under 5 ft high and about 10 ft length using the standard 10 inch mini wheel with a slightly modified high pressure crossply tyre would have a tare weight of about 1200 lbs including a 500 lb 20Kwhr battery pack.

With hub motors and the battery slung below the floor pan this would easily provide for four seats, with ample leg room and up to six seats if required with a reasonable boot [trunk] to a maximum load of 800 to 1000 lbs: and could also be made into a two seat light commercial van. Total effective frontal area was expected to be about 18 sq. ft. and it was hoped if care was taken over aerodynamic design the drag coefficient, Cd, would be 0.33.

It was calculated that such a light small car should be able to maintain a speed of about 60 to 70 mph, the maximum UK speed limit, on about 12 KW, roughly 16 hp. Using 200 volts this was about 60 amps, with an intermittent load of 90 amps, 18 KW. The modified Drumm cell battery pack handled this perfectly well. Tests also showed an expected lifetime of 1000 deep (80% of flat to full and vice versa) charge/discharge cycles: and partial cycles had far less effect on cell life.

Thus allowing for gradients, load, weather and auxiliaries with a fully charged 20Kwhr battery pack at full speed the car would have a range of at least 60 miles and at moderate cruise, between 30 and 40 mph a range of about 120 miles. By comparison then half of typical UK suburban car drivers drove less than 100 miles a week, and 90% less than 200 miles.

The auxiliary power for lights, wipers and sundries was not a significant problem but there was difficulty about the heater. At that time the standard British car heater was rated at around 3Kw. There was no problem in building a heater of such output: it was merely the drain it would impose on the battery pack.

Ideas such a using a reversed air conditioner etc. were scouted but research showed that high heater outputs were used chiefly because many cars were left outside and started from cold and took a long time to warm up. A car needs little heat when stationary but much more at speed. So if the car were on charge a tiny heater of about 100 watts would keep it warm even in icy conditions and that if thermostatically controlled even at full speed heater demand could be kept down to below 1000 watts. Better still the driver got into a warm car with no need to defrost the windows.

The concept of the hub motor is very old but presents unusual design problems because by electric motor standards it turns over very slowly and so needs a multiplicity of poles if it is to achieve high efficiency: which was set at a target of 85% at medium cruise speed. The solution adopted was a multiple pole rotor and a complex wound stator, which, after steadily refining the basic design, eventually managed rather better than the target figure. Brushes were frowned upon so Hall effect devices were used to detect the rotor position and control electronic switching.

The best power transistor available then was the 2N3055 which could only handle 60V and 15 A, or about 900W as a switch. The solution was to split the 200V battery pack into 4 50 V units and the motor windings into 8 50 V sectors working in parallel: and for charging electro mechanical relays switched the cells into series.

These hub motors worked at high torques but low rotational speed and used relatively low voltage with high currents and so had a very low back EMF which presented problems for regenerative braking: as well as for the ‘tow to charge’ emergency facility proposed. There were various possible solutions but the one adopted used subsidiary low voltage battery packs to accept the charge which they could shuttle back and forth with the main battery pack using a chopper step up/down system: because in series they also supplied the industry standard 12V circuits for lighting and auxiliaries.

Thus braking was not only regenerative but a simple controller also provided speed and differential control together with anti lock braking and traction control for each wheel. This made the test cars, despite their small wheels, very sure footed in ice, snow and slush and capable of negotiating light, shallow mud: but the increased power demand in such conditions was heavy. It was also found in practice that the low rolling resistance high pressure crossply tyre initially specified offered negligible energy savings in general use compared to the cheaper industry standard low pressure radial which was adopted from then on.

Charging was straightforward, the 13 amp 230 volt supply was controlled by a triac before rectification, the controller and safety devices were simple and the whole battery pack could be charged from flat in a bit under the then 8 hour off peak overnight cheap rate from the standard domestic socket. The Committee decided to standardise charging at two rates, trickle at 3Kw and boost at 6Kw: to match the UK 3Kw socket and 6Kw domestic ring main.

In this they were chiefly influenced by restriction on cable size and current: ideas of recharging from flat to full in minutes would have needed currents of 500+Amps which was thought absurd both in terms of supply and cables. But they were also aware that high current density in charging might cause problems from uneven deposition of the zinc, producing dendrite growths, which could short out a cell: a problem which plagued the DEAC [NICAD] despite its different electrochemistry.

Although the use of a 3Kw cable and standard plug, attached to the vehicle so it could not be left behind, was cheap and practical for home use there was also a heavier external 6Kw cable and special plug. The need for public charging points was recognised especially for those who relied on overnight street parking, common in the inner cities, and at first it was imagined that users would plug into these and insert their pennies but from early on the idea of an electronic ‘purse’ built into the car which could automatically pay for both charge and parking and be regularly topped up by some kind of fixed price disposable one off key bought over the counter was mooted. This proved very easy to do and the 6Kw cable was provided with extra connections to allow this.

But the Committee was very unhappy about cables trailing all over the place, not least because of the risk of accident and vandalism, and hankered after some kind of automated connector so the user could, not too precisely, park within a designated bay to be plugged in. It was obvious that if this was to be then the connection would have to be made underneath the car by some kind of plug locking into a ground socket. In some ways this proved easy, robotic arms with a simple radio transmitter/detector could find each other and mate up but the ground socket proved very difficult. It couldn’t trip pedestrians, seriously impede a vehicle driving over it or be damaged by it and had to work reliably in all weather conditions, rain water of course but also ice and snow and not be affected by mud and grit. And it had to be intrinsically safe from inquisitive small children, or bigger bad tempered ones, as well as dogs lifting their legs over it etc. It took several attempts to get it right but finally it worked well.

This circuit was set at 6Kw. The ground socket was relatively cheap to make and install and further could detect whether a car was an electric: and so effectually reserve bays for electric users by triggering some kind of alarm.

It was hoped that since the automatic charging station was cheap to buy and install then commercial interests from hotels, pubs, roadside cafes [diners], private car parks and the like would find it attracted custom as well as making a profit from the electricity sold. And users could install it at home if they had hard standing or a garage and so select urgent or cheap overnight charge at the flick of a switch.

For the long haul user the Committee opted for rapid battery exchange, also a very old idea. Again in this they were influenced by a number of considerations. The nickel based battery pack was very expensive, and it was thought that buyers might be worried about battery life. Moreover a single defective cell can ruin a battery pack’s performance and on the bench failing cells can be easily detected and replaced: a commonplace procedure then amongst re-builders of lead acid car accumulators, and even today. It is also very economical because valuable materials from dying cells can be recovered and reused.

Original thoughts about battery exchange were fairly primitive of the drive a car over a pit and drop out the pack and lift in a new one kind much as New York taxicabs did back in 1900. But it was found that suspending the pack together with its electronic and relay controls on rails under the floor pan made it easy to slide out using a sort of manually operated version of a fork lift pallet handler. The method was developed with future automation linked to the automatic connector and ‘purse’ in mind: but this was never done.

So by some sort of battery rental and routine exchange and replace all such problems could be addressed easily at a very reasonable price whether for the short run, a yearly free change, or long haul users. The only problems with this were ensuring a watertight enclosure and that nefarious persons might not steal the battery pack for its nickel or indeed wheel away the whole car with the same intention. Scotland Yard had the answers to that.

Cost had always been in the forefront of the ECG’s concerns because it was felt that users would only adopt light electric cars if they offered cheaper motoring than conventional ones. Analysis of test vehicles showed this to be so, broadly when charged at home at off peak rates the fuel cost per mile was about one tenth that of similar petrol cars, so even allowing for buying electricity from public recharging points at perhaps three to four times the price they were still very economical.

In part this saving depended on the tax regime, petrol duty, but insurance would have been cheaper too, because from the first advice had been taken from Thatcham, itself a research facility created by British motor insurers, to develop ways to minimise the cost of accident repairs. Thus great care was taken to devise ways to protect vehicles from minor damage which would have been expensive to rectify in a conventional car.

Furthermore servicing costs were extremely cheap, the only major replacements were tyres, but with no clutch, brake pads/shoes, silencer [muffler] and the like to replace and no oil/filter changes and tune ups the savings were considerable: excluding tyres it was estimated these costs amounted to about one half the purchase price of a small conventional car over eight years, back then their typical lifetime. Of course today cars last longer and need less servicing.

Production cost and thus selling price were also a major concern and carefully studied. The ECG thought that early production might be a few thousand cars per year rising to tens of thousands a year within three to four years. So from the first the ECG looked for ways to minimise tooling costs and simplify assembly: and slowly learned, to its own experts’ surprise, that building an electric car is a very different process to conventional motor manufacturing.

This is because whilst both use vast numbers of components in a motor car there are very many types of component used in small numbers whereas in an electric car there are relatively few types of component but they are used in very large numbers. So the economy of scale in tooling and assembly is quite different between the two.

Once this had been appreciated and acted on it became apparent that low tooling costs, ease of assembly and the ability to cheaply automate many sub assembly processes largely offset the higher cost of materials and the associated lack of volume purchasing power to the point that the costs were competitive at small runs compared with mass produced motor cars. It also made it cheap for manufacturers to develop and produce a wide range of models. Again today automation is much more sophisticated, flexible and cheaper than back then.

Thus the hub motor proved a revelation, to provide the extremely close rotor/stator clearances needed a strong two part aluminium casing was devised using taper roller bearings which also provided the wheel bearings of the car outboard on a stub axle and inboard provision for a mechanical band brake to meet UK law: the latter serving as both a parking brake and available in an emergency.

Better still the hub motor casing could also serve as its own kingpin with the vertical centre of rotation set slightly ahead of the motor axis to provide the necessary degree of caster trail: which raised the question of four wheel steering. There was much debate about this because the small front wheels could be turned to steep angles giving a small turning circle.

But there were other concerns, notably that a light car with such a low centre of gravity but a high frontal lateral profile [fastback/rear chop body style] to get the best aerodynamic performance would suffer badly from side wind buffet. By providing limited steering at the back driven by an electric servo and coupling it to the suspension it proved possible to provide stability against this as well as better stability in cornering and improved ability to park in tight spaces.

The suspension itself was simple. The British motor industry had much experience in using rubber cones as springs sometimes combined with fluid coupling front to rear and/or with gas springs and this easily adapted to electronic control with the hub motors mounted on double wishbones. Thus it was possible to provide automatic variable spring rate and damping with effective anti roll provision without elaborate mechanical linkages. Self levelling was easy too as was varying ride height both automatically with speed and under the driver’s manual control to cope with road conditions.

Instead of a conventional chassis and glass fibre body the Committee had elected for a punt chassis, essentially a pressed floorpan reinforced by longitudinal box sections and a space frame above it on which body panels would be mounted because of concerns about the then new crash test requirements. As originally envisaged it would have been built out of welded steel but this proved unsatisfactory.

On the advice of the aerospace industry the solution adopted was to build out of standard soft aluminium strip which could be easily pressed, formed, anodised and primed before assembly on a precision jig using a micro-riveting technique: a sort of powered combination metal thread sewing machine with automatic thread cutting and stapler. All hollow sections were filled with foam and the outside painted. This not only produced a lightweight structure of surprising stiffness and strength but the tooling costs were very low compared to steel and whilst it was well suited to low volume manual techniques these could be easily automated if higher volumes were wanted. Furthermore it didn’t rust: a major concern amongst British motorists of those days.

Back then there were many British makers of plastic, usually fibreglass, car bodies and panels and with their help the ECG developed new techniques from quick and easy fastenings to simplify assembly, to moulding light assemblies and wiring looms and sockets into the panels and double sided moulding so that for instance the headlining could be moulded in as well.

Thus by the middle of 1979 the ECG had largely achieved what it had been set up to do. It could offer British manufacturers well proven electric car technology built around a standardised battery pack, charging and exchange system together with design and manufacturing processes and advice which they could easily adapt at little cost as might suit their prospective markets.

But by then the world had changed, the country was bankrupt and many of the small suppliers and motor Co’s that had been so enthusiastic had either disappeared or were in no financial condition to embark on new ventures. The semi nationalised car company had gone from haughty disinterest to outright hostility. Moreover the UK had ample North Sea oil and a new government which was suspicious of what it saw as a socialist experiment to foist electric cars on the public: and for which it would get no kudos if successful. So the ECG closed its doors and its people went their ways.

The author thought it a pity then and with hindsight an even greater one now. The intense interest of the British public a few years later in the Sinclair C5, which was announced as an electric car, quickly turned to derision when it turned out to be a toylike golf cart: which suggests they would have had an appetite for a real electric car. And there would have been a long window of opportunity for electric cars to become established, the then fashion for small economical cars persisted into the late 1990’s. Time enough for the necessary charging and battery exchange infrastructure to grow organically and become the way things were done.

So given the enormous hype and huge sums currently being thrown at electric car development what lessons can be learned from the ECG programme? The author thinks quite a few.

The first is that a battery powered car is much more constrained by its limited energy storage than a conventional motor car, broadly it has to be designed and built for a particular purpose: the idea that it can be, more or less, everything to anyone, and suitable for all things in the way most motor cars are within limits, the classic example being the model T Ford, is a chimera.

Improved battery storage would make it more versatile, back then the ECG reckoned an improvement of 3 to 4 times was needed, today a figure of 3 times is usually suggested. No matter, could that actually be achieved?

Despite all the talk of nanoparticles and such like fashionable technology the author doubts it. Unlike combustion an accumulator depends upon a reversible REDOX reaction and needs to incorporate both components of the reaction together with a necessary intermediary to function which makes it much heavier for the energy stored compared to any fuel.

For example the modified Drumm cell used by the ECG was a conservative design in case of unforeseen problems, but these did not eventuate, and it was thought back then that a further redesign could improve its capacity for weight by between 10 and 20 percent. It was not done. With modern techniques that might be 30 to 40 percent: a very respectable performance indeed even by today’s standards. And cheap by current prices too.

Can other cells do much better? Well Lithium is much touted but as a traction battery it has several drawbacks: certainly further development is needed. There are other technologies all of which have some promise but most are very expensive: although many analysts expect that prices will fall over time, a typical figure quoted is 6% a year. Nevertheless for practical reasons [ibid] recharging in minutes is likely to remain a pipe dream; Battery exchange seems the only solution and at least one company is trying to market it.

The fuel cell, about which there was much excitement some years ago, is a potential solution but it lacks an economical and pollution free source of hydrogen and the infrastructure to distribute it: not to mention a method of practical storage in the car itself.

The same problem of charging infrastructure is likely to hold back pure electric cars. Such infrastructure could be established by government fiat of course, at a price, but also requires a degree of standardisation to be effective of which there is little sign at the moment. A recent report for the French government suggested a time scale of 20 years at astronomical cost.

The logic of a parallel hybrid, of which there are various sub types, escaped both the ECG and the author back then and as far as he is concerned still does. What is the purpose of hauling around a heavy battery and motor generator system when you already have an engine and transmission suitable for road use? It is a vanity product both for motor manufacturers and buyers not a serious contender and, the author notes, does not appear to live up to the extravagant claims of fuel economy made for it.

A series hybrid is a very different animal because the engine runs at constant speed when required to charge the battery and so can be simple and easily tuned for maximum efficiency and minimum emissions. The ECG had two built using modified motor cycle engines and on motor only trial they had about half the fuel consumption of equivalent conventional small cars. An air cooled Wankel is the obvious candidate for the engine although the author thinks a lightweight turbine might be the way to go. If any hybrid has a viable commercial future the author thinks this is it.

There are other oddities in contention such as hydraulic [hydrostatic] drive systems using a hydraulic accumulator, an idea mooted around 1900 because it meant the electric motor and pump ran at constant speed to recharge the hydraulic system and so avoided the then complex and very inefficient switching to vary motor speed. It is not known whether any were ever built: but hydraulic [fluidic] drives were experimented with in the UK in the 1960’s, with little success.

So despite the huge sums being thrown at the problem the author is not sanguine about the results. Whilst many different approaches amplify ingenuity and competition a degree of standardisation especially over public charging/battery exchange facilities might well be needed for commercial success. Moreover the current view seems to be that usage would grow from the top downwards as cars grew cheaper and better with much talk of first adopters and killer apps. The author wonders.

The ECG understood that the success of the motor car was that it was far cheaper and better than horse drawn transport. By 1905 the motor cab [taxi] fares in London were only two thirds of the horse cabs. But a battery car has no such enormous commercial advantage today, whilst some of its costs are less, its fuel bill entirely depends upon the tax regime and in turn on political considerations.

Perhaps, as the ECG thought, in small urban areas a battery car could be cheaper and better. But could it master the wide open spaces of America? As modern cars do in what is called the driving season: and Ford’s model T before that. No. And can it do it more cheaply? No, it would require vast new extensive and expensive infrastructure.

But the ECG also remembered that the infrastructure to supply the motor car grew as demand required. Early motorists purchased their petrol [gasoline] in tins or cans which could easily be shipped and stored: the petrol pump and filling station only appeared later where sufficient regular customers made it financially viable. Their view was that only if simple and cheap recharging and battery exchange points were made profitable for the smaller business to buy and install, would natural growth to meet demand ensue.

Which is why the author thinks the series hybrid might have a future, it uses existing infrastructure both in terms of home electricity and filling stations. But in the end it would only succeed if it offered the user significant savings over a conventional motor car: of which fuel consumption and routine servicing are only a part.

The author doubts very much the lavish sums being thrown by American politicians at the electric car will produce any lasting effect. He also doubts whether it would or could continue, what politician looks beyond the next election?

For it is not clear that there is any long term pressure for change, the fantastical scare over fossil fuels and CO2 is fading fast and becoming conflated with energy security which dominated the 1970’s and 80’s: and is a different thing entirely.

With energy supply and security we have been there before and what didn’t work then won’t work now: the basic underlying physics and chemistry have not changed whatever the prophets of greenery may protest to the contrary with their windmills and such like. We tried all that before and we know all about it: and thirty years of improving technology has changed little in terms of efficiency, practicality or cost.

Moreover in the USA where the fashion is at its height, there is no problem bar political will to fossil fuel self sufficiency, apart from its ample oil and enormous coal reserves modern methods can tap huge amounts of native natural gas which is easily synthesised into clean liquid hydrocarbon fuels at a price well under the current oil price. There is enough of that for half a century or more. So where is the problem?

And finally, however vilified, as the Infernal combustion engine always has been and still is, it remains along with its liquid hydrocarbon fuel a faithful servant and a very formidable competitor when it comes to propelling motor cars. In the end it is simple, robust, reliable and cheap. It has been around so long that any mechanic from London to Outer Mongolia can twiddle, tweak and fix it. And behind these mechanics is an organised supply chain that can deliver spare parts almost anywhere, even Darkest Peru, within a day or two. And it has seen off its rivals, even those hardy perennials such as steam and electricity many times before and bids fair to do so again.

Do politicians really imagine, for all their delusions of grandeur, that by squandering a few billions of the taxpayer’s money, they can change a great worldwide industry overnight? That is for you, not the author to judge. He has his own view.

© ajgjones 2009 whose moral right is asserted. Free licence to reproduce, record or publish whether in whole or in part and by any means or in any form provided only that the reader is not charged for the copyright content itself: and further that authorship is acknowledged for fair use in short extracts therefrom and his copyright and moral right stated for extracts therefrom exceeding 500 hundred words in total whether in a single extract or a series of excerpts which together form an extract of the whole.