Old Jumper Cables and New Cars | What to know to avoid damaging your vehicle's electrical system.

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Old Jumper Cables and New Cars

It's five a.m. on a cold, snowy morning. You're about to leave for the airport to catch an early flight. Your car won't start. The battery is dead.

You grab your trusty jumper cables off the shelf and-wait! You vaguely recall a story on PBS TV's "Motorweek" about jump-starting modern vehicles. Car-care expert Pat Goss had held up a set of conventional jumper cables and said, emphatically, "Throw these away!"

Why? Because, he said, they can damage your vehicle's electrical systems.

Really? The few times you've jump-started a battery in recent years, your old cables had worked just fine. But Goss had demonstrated a set of new "Smart Jumper Cables" from tire manufacturer Michelin and said you would need something like those to prevent potentially expensive damage.

Nice to know, you think, but all you have on this bitter cold morning are your trusty old cables. And you really need to catch that plane. So you use them, more carefully than usual, and you're soon on your way. But you can't help thinking about Goss' warning. How serious was it? Are traditional cables really likely to damage a modern vehicle's electrics, or is using "smart" cables merely advisable just in case?

We contacted Goss and asked him. "I would consider the warning to be quite strong," he responded. "Back before computers and sophisticated electronics on cars, there wasn't much of an issue other than folks getting hurt from exploding batteries. Today is a very different world, and there are thousands, if not millions, of cars damaged by old fashioned cables every year."

You properly hook up the old-style cables, he explained, and get the car with the dead battery started. Now you have one vehicle with a strong battery and one with a dead one, both running, with their electrical systems hooked together. Both alternators are working hard trying to charge the dead battery and replenish the energy drawn from the good one.

"As long as the cables are connected," Goss continued, "the two batteries act as buffers to contain maximum voltage rise. But as soon as the first cable end is removed, the systems go nuts. When the first cable is removed, the voltage reference is gone. It instantly changes from the level of two batteries and two alternators to one battery and one alternator.

"During this period of adjustment, the voltage regulator allows the alternator to climb to a very high voltage level. The alternators of both cars are unregulated for a few milliseconds, and during that brief time, the alternator can produce several hundred volts of low-amperage electricity. This high-voltage spike shoots through the electrical systems of both cars."

This is like a voltage surge running through a computer. It usually doesn't destroy anything instantly but can weaken components of both vehicles, including the engine control computer, alternator, sound system or any of the dozens of electronic modules in modern cars.

Because these parts are merely weakened, not destroyed, there are usually no immediate symptoms. But as the vehicle is used, those weakened components will eventually fail. And since it may be weeks or months later, you never realize that it was caused by your use of conventional jumper cables.

Goss also explained that so-called "smart" cables have built-in surge protectors like professional units used in auto shops for many years, which dampen voltage spikes to prevent surge damage to electronics. An added bonus is that they also have automatic polarity adjustment to eliminate the possibility of damage (to you or the vehicle) from the sparking or shorting that can result from hooking up cables backwards, positive to negative.

We obtained a set and-fortunately or unfortunately-had a real-life opportunity to try them one very cold morning. They come neatly coiled and packed in a compact, hard plastic case, yet were long enough to reach car-to-car with ease. With the plus-minus polarity sorted out within the surge protector at their center, there was no concern about which clamp to attach where: either one on one end to a battery-positive connection on the dead-battery car, the other to a solid ground, and the same lack of concern clamping the other end to the running car's system.

Despite the bitter cold, they stayed flexible and tangle-free. Our only complaint was that the spring-loaded, insulated clamps took a strong hand to spread. Once all four clamps were in place, the unit's two LEDs were lit to show that everything was properly connected. We cranked the dead-battery car, and it started right up-presumably with no future damage to either vehicle.

Why do car batteries go dead, sometimes without warning, and how often? Many factors can cause a battery to fail," says Alexia Hayes, a product development engineer for Pylon Manufacturing Corp., the aftermarket supplier responsible for distributing and marketing Michelin's Smart Jumper Cables (and premium wiper blades) in North America. "The combination of performing many starting cycles, coupled with short run times, can leave a battery below the ideal charge specification for most of its shortened life."

That multiple-short-trip duty cycle pretty much sums up the working life of the typical family vehicle. And temperature extremes can further shorten battery life. Experts say the life expectance of a typical auto battery is three to five years in average climes, but just two to three years in areas with high heat or extreme cold. And there's the ever-present possibility of leaving lights (or something) turned on and consuming energy when the vehicle is parked. Which none of us would ever do, right?

Our purpose is to enlighten you about the potential danger of jump-starting modern vehicles with old-style cables, not to sell you Michelin's (patented-technology) Smart Cables. They're available at stores for about $40, and we recommend checking them out, as well as suitable alternatives. Given our test experience, we'll keep our set and toss our old ones, and keep one good set of old-style cables around for occasional use on older (non-computerized) vehicles.

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