Is it Dangerous to Jump Start a Dead Battery

[brinkja]

@BubbaDog

In this column -Is it dangerous to jump start a dead battery - Cecil verifies that connecting directly to both battery posts of the dead car battery may cause an explosion due to leaking hydrogen gas from the battery.

I was hoping our brave leader would comment on the some changes in battery design.
Compared to years ago many car batteries are sealed instead of open. They neither require the addition of water nor do they appear to have the ability to vent hydrogen gas.

So what’s the scoop?

Cecil,

You missed out something big in your reply. You focussed on hydrogen and exploding batteries, but there is another reason to jump-start a car carefully. Your original questioner had the keyword in his question: VOLTAGE SURGES. According to an article in a Dutch paper I recently read modern cars with the complicated computers and other electronics on board are extremely susceptible to voltage surges. If you just jump-connect another battery to a dead one the surges can fry your electronics and then you really have a dead car. Some modern cars according to the article need to be taken to a dealer if the battery is dead.

Johnny

[WVBrady]

@foolsguinea

I once mildly electrocuted myself

I suspect that reports of your electrocution have been greatly exaggerated.

Brady MSEE

[WVBrady]

I can vouch for the danger of improperly jumping a car battery. Before I was the victim of blatant age discrimination by the local electrical utility, among my other duties, I taught Basic Electricity to various groups.

Once, with a group of mechanics, we were discussing the dangers of improperly handling the jumping of batteries when one of them related how a battery had blown up in his face. He had been charging the battery and just jerked the leads off before turning off the charger. Fortunately, he was right beside the washroom, and was able to make it to the sink and wash out his eyes. He lost about half the thickness of his cornea, but suffered no permanent loss of vision. I do not know if the cornea will regenerate in this situation or not.

I did see a battery (several years ago) blow all six battery caps out of the battery when the guy tried to start the car, using a jumper. They ricocheted off the hood (up at about a 45 degree angle) and across the street in a most impressive fashion.

I think the biggest danger is not in the making of the original connections, but when removing the connections from the dead battery (or ground connection). Initally there should not be much hydrogen gas present; it would be produced when the dead battery was being recharged by the good battery and the alternator.

What I do not understand is why the directions always call for removing the ground connection for the dead battery** first**. It would seem to me better to remove the ground connection from the good battery first, because as mentioned above, most of the production of hydrogen gas would be at the dead battery. (The reason for removing the ground connection first is that if you accidently make contact with the metal body of the car, you will not created a short circuit. If you remove the positive lead first and accidently contact the metal car body, you will make a dead short. This was my first experience with welding. )

The recommendation to wear goggles is a good one. Also, if you have an old carpet or something similar, that is good to lay over the dead battery, just in case it should happen to explode.

If someone is helping you, make sure that they do not “test the connection” by shorting the two clamps together. It makes pretty sparks, but is death to voltage regulators. :smack:

I had not heard of turning on the fan to prevent voltage spikes; makes sense! I myself do not make any connections or disconnections while my car is running; I figure my electronics are protected if the switch is off.

[happy_days]

@audiobottle

My girlfriend’s battery died the other day, and I attempted to jump it using my car. I connected + to + and - to her engine block. It wouldn’t start. Then somebody else came along, connected + to + and - to - and voila! Car started! So what happened there? Why didn’t he blow up and why wasn’t I the hero?

Most likely, the engine block connection you made was not electrically connected to the negative battery post. Starting a car requires a surge current of about 20 amps. Using Ohm’s law, this means that the resistance between your point of contact and the negative battery post must be less than 0.6 ohms. A little engine block dirt is more than adequate to keep you from being a hero.