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Green Wheels

Green Wheels: Stop-start tech useful, but flawed

Stop-start tech is currently under development, but faces a long road ahead.

Published July 6, 2012

In a few years, most new cars will come with stop-start technology.

This gizmo automatically shuts the engine when a vehicle stops at a traffic light, or in congestion or a drive-through line. When it’s time to move, a touch on the accelerator instantly gets things going again.

The system is now standard in hybrid vehicles and some gas burners, and optional on others.

But since it’s touted to improve fuel economy by up to 10 per cent, at a current cost of only a few hundred dollars, industry observers expect it to become a routine component as carmakers aim to achieve tougher fuel-consumption limits coming in 2016.

And the price should fall as it goes into increasingly mass production.

It sounds ideal. But — and if you’ve read enough of these columns you’ll have guessed it — there’s a hitch: Not a showstopper, but something to be aware of when you ponder the full-economy ratings of new vehicles.

Internal-combustion cars still run their stop-start systems on lead-acid batteries — improved versions of the type used since the dawn of automobile travel.

Stop-start requires too much from them. One study, presented a while back by Ford Motor Company and BMW, states that in a typical 25-kilometre commute, a battery running stop-start must do 100 times more work than one without it.

Alternators recharge batteries while a car moves. But current batteries can’t always receive a boost big enough to handle the next restart. As they age, the problem gets worse.

The Ford/BMW presentation notes that while it takes less than a minute for a new battery to absorb enough juice for a restart, the time stretches up to five for one with 8,000 kilometres under its belt.

The result: Chances are the battery will run short of restart power. If that happens, the system shuts off, which casts a shadow over those impressive fuel-consumption ratings: They lose much of their shine if they only apply to cars fresh from the showroom.

Currently available lithium-ion batteries could handle the workload better, except for one glitch: They’re unhappy in the high-temperature environment of a typical engine compartment and require overly expensive thermal-management systems to survive there.

Three alternatives are being tried.

One could rescue Massachusetts-based battery maker A123 Systems, which has encountered financial trouble because of slow EV sales and a recall of defective lithium-ion cells it produced for the Fisker Karma luxury plug-in hybrid.

The company has announced a “game-changing breakthrough” — a form of lithium-ion it calls Nanophosphate EXT, said to retain 90 per cent of its capacity after 2,000 full charge and discharge cycles at 45 degrees C, without thermal management. It has “10 times the life of lead-acid,” says an A123 statement.

Its main competitor is a variation on lead-acid known as lead-carbon that’s being developed by three companies, including giant Johnson Controls, maker of one-third of the world’s car batteries.

Both types offer similar performance. The lithium battery is lighter, but the weight difference isn’t enough to impact a car. And, at around $800, it’s now about twice as expensive.

The third player is the super-capacitor, which would specialize in restarts, leaving the battery to handle the stereo, air-conditioner, signals and the other electrical demands. It would require an initial jolt from the battery but, afterward, could collect enough power from the alternator to do its job.

All these are under development, with long testing ahead. And it will cost hundreds of millions to build commercial-scale production.

Eventually, they’ll be ready for prime time. Until then, consider stop-start a useful but flawed technology, and take its fuel-economy promises with a grain of salt.

The good news is that batteries don’t last forever and they’re not that expensive. So if you buy an imperfect version it wouldn’t be too taxing to replace it when something better comes along.

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