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Spikes, Surges and Danger

Q. It is my understanding that if you connect jumper cables directly from battery to battery it is improper and one can damage an alternator on the car giving the jump. The alternative, as I understand, is to ground the negative cable to the chassis of the car being jumped.

My question is, how does the first method differ from the second and what is actually happening that makes it safer?


A. This is an interesting question and I'm glad you asked it. People for years have been connecting jumper cables from battery to baterry without any problem. And I must confess, so have I. You can do it a hunderd times with no problem but there is a risk, a potentially dangerous risk.

Batteries produce explosive gases and contain sulfuric acid. If any gets on your skin or in your eyes, flush immediately with water and seek medical help.

When you connect jumper cables directly from battery to battery, you have a very good chance of creating sparks. Batteries create hydrogen gas which is very easy to ignite, so if we connect the positive cable to the battery and the negative to the block, if we get a spark, it will be far enough away not to create an explosion hazard. This is the main reason why you connect to the block.

Whenever you connect two batteries with jumper cables you will get a voltage spike. This spike can damage electronic components. Not just the alternator, but sensors and computers. That's why you plug your computer into a surge protector at home. You'll get a voltage spike no matter where you connect. Fortunately most electronic parts in the car have surge protection built in.

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Additional Information provided courtesy of AllDATA and Warranty Direct
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