Jumpstart: Why does BLACK get grounded and not hooked to NEGATIVE on dead battery?

What does electronic ignition and fuel injection have to do with a battery being drained to the level that it needs to be jumped???

The 1939 Chevrolet my dad owned had an emergency hand crank for starting the engine if the battery charge was low. I saw him start the car with the crank a couple of times. With the hand crank, there is no danger of the battery exploding when hooked wrong with the jumper cables. Of course, if the car was in gear and started, it could run over the person cranking the car. If the engine kicked back, you could get a broken arm.
The point is this: Nothing beats using safety precautions. In the hand crank days, you made sure the car was in neutral with the parking brake set and you held the crank so that if the engine kicked back, the crank would slip out of your hand and you wouldn’t break your arm. When you jump start a car, make the last connection to the car with the weak battery away from the battery. If there is a spark, there is no hydrogen gas to ignite. I think my previous minivan, a Chevrolet Uplander, had a positve point where one was to hook the jumper cable. The negative cable was to be connected to a point away from the battery. Therefore, there was no connection at the battery.

@MikeInNH For one thing cars start much easier in cold temps. nowdays. They require very little cranking before starting and rarely flood, unlike the old days of the carb. The less cranking = the less the battery runs down. At least that’s been my experience.

@DfromSD

But that’s not usually the cause of a drained battery. Most of the time it’s a light that’s left on.

I aggree on that point, Mike, especially nowdays. I was just thinking back to the days when cold snaps meant breaking out the jumper cables cuz you probably would be needing or giving a jump start soon.

I agree that what you’re saying could happen…But I’ve never seen it. Learned to drive in the early 70’s in upstate NY. We had some cold winters there. This was before multi-weight oil was popular. And points and before electronic ignition.

@DfromSD and @MikeInNH you both make good points, but I tend to agree with Mike. I too grew up and drove cars equipped with carburetors and and point type ignition systems. Most of the time then/today if a jump was/is needed it was either because some electrical devices had/have been left on such as lights or your battery was/is just weak and ready for replacement.

Wow. I’m stunned by some of the comments in this thread.

Back to basics: an electron is a negattively charged particle, a proton is a positively charged particle. A neutron has no charge.

Since an electron is negatively charged. an atom with a surplus of free electrons is called negatively charged. An atom with a relative deficiency of free electrons is called positively charged. In any cirscuit, electrons flow from the side with a surplus of free electrons to the side with a relative definciency of free electrons. They flow from the negatively charged side to the positively charged side. By definition, current flow being the flow of electrons, current flow is therefore from negative to positive.

“Ground”, in an automobile more properly called “chassis ground” is simply a common conductor (the car’s chassis) which serves as part of the circuit for most of the electrical curcuits and electronic devices. It’s that last part of the circuit after the loads have been applied. A vehicle can be designed to use either the negative or the positive part of the circuits as common ground. The automotive industry uses the negative side, and uses black to designate it as “ground”.

When you connect another battery to jump start a vehicle, you’re basically putting two batteries in parallell. That applies 12VDC to the vehhicle’s circuits. Connecting the batteries in series, one in fromt of the other, would apply 24VDC to the circuits…not a good thing.

And the only reason you use the car’s chassis to connect the black lead is to keep sparks away from the battery, as others have explained. The reason you connect it last rather than fist is that the last connection you make completing the circuit is the one that will spark, again as others have explained.

I tried to jump a car today.
I hooked the black on the dead cars frame, and no go.
I then hooked the black onto the dead battery’s negative terminal, and it fired right up.

What happened?

The car’s frame is usually grounded with a small gauge wire. The manufacturer’s only determine a small amount of amperage through the chassis to ground it, like in the 60-100 amp range. Next time, ground to a metal piece on the engine. The engine is grounded with the large lead off the battery and capable of 700-1000 amp loads. I always use a metal part of the engine to ground the dead car, not the body or frame.

You’re not supposed to hook the jumper cable to the dead car’s frame. You connect both cables to the dead car’s battery. You’re only supposed to hook the black jumper cable to the good car’s engine or chassis to avoid creating a spark near the battery of the good car.

Since the cables aren’t connected to anything when you hook-up the dead car, there is no need to worry about creating a spark near the dead car’s battery.

Yeah, some grounds are better than others. What with the move to cover damn near everything under the hood in %#€® plastic, getting a good ground isn’t as easy as it used to be. A hint that you’ve got one is the idle of the running car will change as alternator load makes the engine work harder.

The “worst case scenario” in hooking up both terminals on the good battery first is that the free ends short, weld together, and in a panic one doesn’t think to disconnect at the battery, but tugs fruitlessly at the weld as battery heads into thermal runaway…

Directions said to hook black to live cars negative terminal, and black to the frame of the dead car.

This is why I have come to favor jumper batteries, which have limited out put. With potential problems of damaging the jumper vehicle power supply, I would rather put a $39 jumper battery at risk. I have dumped my jumper Cables long ago in favor of a couple of these batteries. There are a great low power source with the battery in a self contained case you can use for a plethora of other things, more safely. If I need to use more power and cables, I call AAA.

On a recent episode of Ice Road Truckers, one of the drivers caused a battery explosion and got acid burns on his face. He had to be taken to a hospital.

He made the classic mistake of trying to jury rig a broken battery cable connection, which cause a spark right at the battery terminal. With his face right near the battery, which exploded.

So that’s why you never want to make a spark anywhere near a battery. And as has been pointed out above, a negative terminal can spark just as well as a positive terminal.

"Directions said to hook black to live cars negative terminal, and black to the frame of the dead car. "

Were these the instructions that came with the jumper cables? I think they’re wrong, regardless. The last connection should the black (negative) cable, made to a clean (unpainted) location on the engine.

The problem with ‘the frame’ is that it’s typically painted, and therefore a bad location to try and complete the circuit.

I guess the only difference is that my directions said the connect the dead car black last. You are saying to connect the live car black last. I don’t think it matters. The bottom line is the LAST black connector will spark, and therefore should be hooked to the frame. Of course, this never works, and so my entire life, I just connect it to both black terminals. Someimes, tiny sparks. Whatevs Never seen or heard of blown up battery except for urban legends.

You only need to have a battery blow up in your face once when connecting jumper cables to the negative terminal on the dead battery. And when that happens, you’ll never do it again.

Tester

I had a battery blow up in my face 42 years ago. @Tester is right when he says you’ll never do it again.

Concur with @Tester. I once had a battery explode and my good friend and neighbor found one of the battery posts in his driveway. His driveway was about 300 feet from the exploded battery.