Tech Talk: Racing to Start-Stop
Guest post by Gale Kimbrough, Interstate Batteries® Engineering and Technical Services Manager
Just suppose you own a vehicle that would get 30 mpg at 65 mph, and you hit three traffic lights on the 15 miles to work. Every stoplight cuts your average gas mileage by holding the vehicle at zero mpg for about three minutes. At the end of the day, your gas mileage could be just 15 mpg.
Mandates on U.S. auto manufacturers require an average fuel economy of 35.5 mpg by 2016. To hit this target, vehicle manufacturers have three basic options. The most obvious two are hybrid or electric vehicles. But another, new vehicle option bridges the gap between a hybrid and a standard gas engine: start-stop technology.
Start-stop technology (sometimes called “stop-start”) turns a regular gas engine into a semi-hybrid vehicle. Basically, the engine shuts off anytime the vehicle idles, at stoplights or in traffic. While the engine’s off, the battery in the start-stop system sustains the entire electrical system. When the driver presses the gas, the engine starts right back up. Start-stop designs use a battery and a beefed-up starter motor that also acts as a generator. This technology, as simple as it is, cuts fuel consumption and emissions by 8% to 15%.
The battery is a critical component for start-stop technology. This fuel-saving system needs batteries ready for double duty: lots of starts and lots of reserve capacity. The battery needs a strong enough reserve capacity to sustain the AC blower, headlamps and multiple computers when the engine’s off. That means the battery would need to withstand 20% to 30% depth-of-discharge. A normal starting vehicle battery today only discharges to 3% to 5%.
Some start-stop designs use two batteries for the start-stop motor, but one large, reconfigured lead-acid battery could deliver the same performance. It may even use absorbed glass-mat (AGM) batteries.
French carmaker PSA Peugeot Citroën uses lead-acid batteries, but European BMW models use AGM batteries. The coming 2012 Chevrolet Malibu sports a lithium-ion battery. In the race to start-stop, no universal battery type has emerged. But know this: Start-stop designs are coming.
Some European drivers have already seen this technology in new vehicles. Regulations on carbon emissions reduction made start-stop popular in 2008. Already, new models like the 2012 Chevrolet Malibu, Buick LaCrosse, Buick Regal, Kia Rio and BMW 5 Series use start-stop technology. The transition to systems like these could happen faster in America than the transition to hybrids.
Battery manufacturer Johnson Controls estimates about 52% of the new cars available in 2016 around the world would use start-stop. That’s 8 percentage points more than in 2010.
As start-stop technology spreads, some shops could begin retrofitting older models with start-stop starters and batteries. Since the system only kicks in when the car stops, it would hurt quarter-mile times or engine performance. But it’s an endurance test on the alternator, starter and battery.
Obviously, city drivers would tax the batteries more due to the amount of starts and stops per day. As more American cars use start-stop, drivers will find out how long these batteries last. Many 2012 models may not need a replacement until 2014 or 2015. On average, AGM batteries cost twice as much as their flooded lead-acid counterparts, but they also offer additional cycle life.
It’s hard to say which battery type will come out on top for U.S. start-stop technology. But you can bet the team at Interstate Batteries is dedicated to powering that future with engineering expertise.
- N. American car battery shipments surge in March – Reuters (reuters.com)
- How idle-stop systems work (howstuffworks.com)
- My Demo Drive (johnsoncontrols.com)