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Jump-Starting Dead Batteries

How to safely do a charging system Lazarus trick

Many people would rather call for roadside assistance than lift their own hoods. The rest of us know how valuable time is and know we can be back on the road in less time than it takes for assistance to arrive. Particularly when the problem is a dead battery, jump-starting it yourself can be more efficient than waiting for help.

Cable Comparo

Obviously, cables are a prerequisite for jump-starting a vehicle. Not all jumper cables are built the same, and you generally get what you pay for. The thicker the cable, the more electrical current can flow—and the higher the price of the jumpers.

Quality cables are available in thicknesses ranging from 10- to 2-gauge. Ten-gauge is usually sufficient for starting batteries in four-cylinder vehicles in warm weather. As the size of the engine increases and temperature decreases, fatter jumpers will do the job better. Large motorhomes or farm implements that need jumping in northern Minnesota in January are best served with 4- or possibly even 2-gauge cables. Thicker cables will also stay more flexible at colder temperatures than cheap, thin jumpers.

Word of warning: If the cables get warm during use, it's a sign of too much resistance. Either the cables are too thin for the job or they're possibly frayed or have rusty clamps.

Speaking of clamps, they also vary in configuration and quality. For side-terminal batteries, 45-degree-angle clamps often grip better than straight jaws. Like the cable itself, clamps also carry amperage ratings. Quality cables often have 400-amp-rated clamps, and industrial-strength clamps are even rated at 500 amps.

Cable storage is also critical. During jump-starting, the cables' jaws often pick up battery acid from corroded terminals. This acid is highly corrosive, so cable should always be stored in the bag that many higher-end models come in or at least in a thick trash bag. Otherwise, corroded cable clamps can slowly eat through your trunk. Furthermore, storage space often determines cable length—the longer and fatter the cable, the bigger the coil it makes. Jumper cables are generally available in lengths ranging from 10 to 30 feet.

Preliminaries

First, inspect the dead battery. If it's leaking excessively or the case is visibly cracked, abort the jump-starting mission and replace the battery. A damaged battery won't hold a charge anyway. Besides, attempting to charge a battery that has a split case can eject acid, and you'll end up reenacting the Wicked Witch of the West's death scene from the Wizard of Oz.

Next, verify voltage. While a good 12-volt battery can charge a dead 6-volt battery in an emergency, it can also fry the 6-volt vehicle's lights, gauges, and other electrical accessories. Also inspect the battery terminals. Corroded studs and battery-cable ends will impede the flow of electricity from the jumper cables into the battery, so clean the posts and cable ends as well as possible. Remember to keep even dried battery acid away from skin, eyes and lungs. Wearing eye and skin protection is always advisable whenever dealing with batteries.

Park the vehicle with the good battery within jumper-cable distance of the dead car. Make sure that the cars aren't touching. Both vehicles should be put in Park (automatics) or Neutral (manuals) with the parking brakes set and all accessories such as headlights, dome lights and radios off. Turn both ignitions to the OFF position. Unplug any cigarette-lighter accessories such as radar detectors and cell phones—jump-starting can send a voltage spike through the vehicles electrical system and burn out these gadgets.

At this point, if either battery has removable vent caps, pop them off and cover the holes with a rag. This allows hydrogen gasses to escape during jumping. If rags aren't available, then make sure that the caps are firmly seated.

After checking the caps, identify the batteries' positive and negative posts. (Many newer cars have terminal covers over the positive post; others that have tight-access battery locations use remote jumper studs.) Then prepare the jumper cables by uncoiling them and separating the positive and negative clamps. Remember that red or orange is positive and black means negative.

Cable Connecting

The Jumping Sequence (see Steps 1-4):

1.) Connect a positive/red/orange (+) jumper-cable clamp to the positive (+) terminal of the discharged battery.

2.) Connect the other positive/red/orange (+) cable clamp to the positive (+) terminal of the charged battery.

3.) Connect a negative/black (-) cable clamp to the negative (-) terminal of the charged battery.

4.) Connect the other end of the negative/black (-) cable to non-painted metal that's away from the battery, such as the alternator mounting bracket. DO NOT connect the negative/black (-) cable to the negative (-) post on the discharged battery—this can cause a defective battery to explode, particularly if the cables are connected incorrectly and polarity is reversed.

5.) Start the dead vehicle and remove the cables in the reverse order of the connections, taking care to avoid moving parts such as fan blades. Also, make sure that the cables' clamps don't touch until all four are disconnected.

If the final clamp connection produces a big spark, the polarity is likely reversed somewhere in the sequence. (Small sparks are normal and signify a good ground.) When starting the good vehicle, make sure that all electrical accessories (even the dome light) are off.

Let the bad battery charge for at least a minute before attempting to start it. If the dead car's dome light comes on, then the cables are connected properly. Also, if the victim vehicle is equipped with a voltmeter, turn the key to the ACC position and check the reading. Cars that have small engines and manual transmissions might start with as little as 10 volts, but 12 to 13.6 volts is the normal operating range.

Now try to start the car. If it cranks but won't fire, more charging time may be necessary. Revving the running engine will increase its alternator's output and send more juice through the jumper cables. Also check to ensure that the cable's clamps have a good bite, particularly on side-post batteries.

Troubleshooting

The best way to verify proper cabling connections is with a cheap voltmeter. When the dead battery is receiving a charge from the good battery, the voltage between the dead one's posts should be at least 12. If lower, wiggle the clamps to get a better connection. A better connection will also cause the running engine to bog down a little as it donates its voltage. The voltmeter can also be used to test the "good" battery. Any reading below 11.7 volts indicates that the assistance battery isn't holding a full charge and might be damaged by jumping another battery.

If all of the above fails, you can always call AAA.

Resources

Matson USA, www.matson-usa.com

Systems Material Handling (SMH), www.smhco.com

Philatron Products, www.philatron.com