The modular car

Publication date: 18 May 2006.
Last modified 03-Dec-2011.

I'm frightfully pleased with myself, because I know how to make an electric car you'd actually want to own.

Electric cars have not, as you may have noticed, been doing all that well since about 1900. Here in Australia, normal battery electric vehicles pretty much just don't exist. I've looked high and low, and once you rule out the little scooters and hideous specialised commercial vehicles and hilarious is-that-thing's-aspect-ratio-right Noddy cars (which let you pay used-Corolla prices for pensioner-scooter performance...), there's nothing. The Australian Electric Vehicle Association Web site is a land of blowing dust and bouncing tumbleweeds. Apart from a few proud DIYers, we got nothin'.

The Australian EV situation is unusually lousy, but general purpose consumer EVs are unpopular world-wide, and you all know why. It's because the darn things keep falling into one of three categories.

Category one: Slow and hideous.

Category two: Fast (or, at least, fast enough), but not enough range.

Category three: Wow - that thing looks great! And it's fast! And its range is excellent! Look at all the fancy toys! How much does it cost? Oh.

But it doesn't have to be this way. No bleeding-edge technology is needed, no mansions need be mortgaged, to get good electric vehicles into the hands of consumers.

You just have to cheat a bit.

Most car trips taken by most people, even in a big country like Australia, aren't very long. An electric car with a hundred kilometre urban range between charges is more than adequate. Heck, 50 kilometres of non-stop range will do most people for everyday use - especially if the car includes a bank of supercapacitors for effective regenerative braking, which'll give you much of that 50km range even if it's all in stop-start city traffic.

(Range depends on speed - a given EV may get its best range if you trundle along at a constant 50km/h, with a lot less range if you double or halve that speed.)

An electric car with 50km range is an easy engineering problem, even with current technology. Any half-competent mechanic can take a Hi-Lux with a blown engine and use off-the-shelf components to turn it into a 50km-range lead-acid-batteried Electric Vehicle that can struggle its way up to highway speed - 75km, even. And possibly still have some room in the bed for cargo. The thing'll handle like a boat and something really interesting will happen to it and its occupants if they crash into a brick wall at speed, but just making a vehicle that can go the distance is not, itself, hard.

Problems arise when you want more range. More range means more batteries, more batteries mean more weight, and more weight means more power consumption, so each new battery does less good. One day we'll have feather-light electron-buckets that charge in ten seconds, last for ten thousand cycles and cost close to nothing, but we're definitely not there yet. Just loading up on today's batteries, even today's best and lightest batteries, leads to diminishing returns.

The obvious solution is to slim down the battery, install an engine, and start making advertisements for your new hybrid vehicle that include a lot of peaceful greenery. But then you're burning petroleum for pretty much every trip again, and a hundred kilometre highway cruise now uses about as much fuel as it would if you were in an ordinary car.

The solution is simple, if strange: Make the engine optional. And put it in a little trailer.

Suppose you're in the market for a new car, and you only need short range, and you're happy to plug your car in overnight to charge it. In this case, you just buy the electric car without the engine-trailer. If and when you want to do long trips, you buy the engine. Or just rent an engine, not a whole car, when necessary.

The trailer won't just have the engine in it, of course; it'll also need a generator of some kind, and maybe inverter and charge control hardware as well. It'll be some kind of "genset", in other words.

This amazing idea is, you'll be relieved to know, not my own creation. Vehicles composed of gensets and electric tractors have existed for some time. Diesel-electric locomotives, for instance, usually roll it all into one ball - engine, generator and motors all in the one module, much the same sort of thing Ferdinand Porsche kept trying to put in a tank - but can also have separate generator and traction modules.

In the electric-car department, there's the AC Propulsion "tzero" (they don't believe in capital letters). It's a super-performance electric that's been making headlines for, oh, about a decade now, without getting any closer to market (this tzero FAQ still says it's "expected to begin deliveries in 2002"; this other one admits it's not really a product, but says something really great will be coming along in, uh, 2005...). But the tzero does have a smooth and shiny little trailer-engine of exactly the kind I'm talking about. Shame about the whole vapourware thing.

Back in the real world, the towed-engine idea is practical enough that the same schlub who electrified his Hi-Lux can do this, too, albeit in a goofy Honda-generator-in-a-wheelbarrow sort of way.

It's surprising how small an engine can be and still be perfectly adequate to give an electric car unlimited cruise range, fuel permitting.

A large-ish "portable" generator - which is to say, not so portable that you're in any danger of some dude sneaking onto your building site, grabbing it and running away - will weigh in at about a hundred kilos, and deliver about 9000 watts (9kW) for about six hours from about 30 litres of diesel. This sort of thing. Petrol versions don't run as long from the same volume of fuel, partly for the reason people think - because diesel engines are more efficient than petrol - but mainly for the reason people forget - because diesel contains more energy per litre. Here in environmentally enlightened Australia diesel is taxed more heavily than petrol, so there's close to no economic difference unless you start fuelling up behind burger joints.

Aaaanyway, 9kW is about 12 lousy horsepower, and if you think that's not going to deliver scintillating performance, you're right. A very boring modern small car engine can output 60kW, mainstream family cars these days are commonly driven by 180kW-ish powerplants. Even the Model T had 15kW.

But a piddly 9kW motor actually can give you good cruise speeds, if your car's light and slippery enough. Not to mention ultra-low fuel consumption compared with a normal vehicle.

Little engines don't have the torque for acceleration and hills, but if your trailer-hybrid has any battery charge at all, you'll be OK; most electric motors have torque to burn, which is why electric cars with miserable top speed can usually get away from the lights surprisingly smartly.

Realistically, though, highway cruising with a small-trailer-engined hybrid is likely to slowly run down the batteries. Actually, if it doesn't, I think that means you're lugging around too much engine.

If your trailer-engine doesn't have enough poke to keep you at 110km/h (around 70mph) for more than four hours without a break - well, you shouldn't be driving for that long without a break anyway. Park, leave the trailer poketta-poketting while you have lunch, then off you go again, with more than enough charge to smoke the tyres on the way out of the rest stop.

The trailed-engine design also allows even more configuration variety, and easy upgrades. There could be only one actual model of car, but your trailer could contain whatever kind of engine you like - a simple petrol engine, a mildly more efficient diesel, a fold-up wind generator (no, you couldn't use it while you were rolling...), or indeed the fuel cell or ultra battery pack of the future.

But hang on, I hear you say - won't the trailer jack-knife on you if you reverse with the care and skill expected from normal drivers?

Yes, grasshopper, but this problem is eminently avoidable, especially when the trailer's a tiddly little thing. Which also ought to let you get your slim-'n'-sexy electric vehicle, with trailer, into normal parking spaces.

(Here's an impressively engineered towed-engine arrangement that gives unlimited range and also gets around the jack-knifing problem, with a fancier solution. And then there's this, which apparently works. For some reason.)

It's all quite worryingly sensible sounding, if you ask me. It could really work.

The standard vehicles would, of course, have current limiting hardware to prevent burnouts. But if you just hold Delete during startup...

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