How to Hook up Jumper Cables
Jump-starting a car with a dead battery should be accomplished by keeping safety in mind at all times. Not doing this can have dangerous consequences. The number one danger is eye and face injuries caused by an exploding lead acid battery!
What causes a lead acid car battery to explode while jump-starting a car? The lead acid battery uses a chemical reaction between spongy lead, pure lead, and sulphuric acid, which is an electrolyte. During the charging process a small amount of highly explosive hydrogen gas is produced.
In the process of jump-starting a car safely, the most important safety precaution you should take is not to do anything that could cause a spark in the vicinity of the battery you are trying to charge!
The following is a safe way to proceed when trying to jump-start a car with a dead battery:
Park the car with the good battery near the car with the dead battery without touching them together. Put on a pair of safety glasses or goggles to protect your eyes. If a wire brush is handy, clean both battery terminals on the good battery. Clean the positive terminal on the dead battery. Why not bother to clean the negative terminal on the dead battery? Because you won't be connecting a jumper cable there. This is the key to safely jump starting a car with a dead battery.
Shut off the ignition switch of both cars and connect the jumper cables as follows:
First, connect one end of the red (positive) jumper cable to the positive terminal of the dead battery. Next, connect the other end of the red (positive) jumper cable to the positive terminal of the good battery. Connect one end of the black (negative) jumper cable to the negative terminal of the good battery. Then connect the other end of the black (negative) jumper cable to a bolt or other convenient location on the chassis of the car with the dead battery, away from the dead battery itself. Thus, when you make this last connection, which will complete the circuit, if you do cause a spark it should not cause the problem of hydrogen gas igniting near the dead battery.
Start the car with the good battery, but wait five minutes before trying to start the car with the dead battery. Why? Often an unknowing person will try to start the car with the dead battery immediately. But if the dead battery is completely discharged, the car may not start right away. So wait about five minutes to give the dead battery a chance to charge a little. Then try to start the car with the dead battery.If it starts OK, remove the jumper cables starting with the black (negative) cable connected to the chassis of the car with the dead battery and the rest in reverse order of how you connected them.
Drive the car that had the dead battery around for half an hour or so to allow its alternator to charge the battery.
If you have further problems starting the car you may want to do a quick check to see if the alternator is doing its job. Check the DC voltage across the battery terminals with a digital voltmeter or multi meter with the car running at idle (about 1000 rpm). If the meter reads 13.8 volts, your alternator is probably good. If it reads 12 volts or less, you probably have a bad alternator.
