Battery Jumping: The Process Explained

[Beowulf]

Ok, a guy at work was very proud of his daughter for jumping her car on her own away at college. He stated that he forgot to ask her if she did a Positive to Positive and Negative to ground or P-P and N-N. This brought on a nice little quandry from the both of us on the reason for taking the negative to ground. I have allows just gone straight p-p and n-n. Never negative to a ground. He asked me why going Negative to Negative could make batteries explode and I did not have an answer for him.

So the question: Why go Negative to Ground and not Neg to Neg? What would cause a batter to explode? Is it the off gassing that can ignite? Is it the battery getting to hot?

Would and does this still apply to new AGM batteries?

 

[240sxguy]

The spark from the jumper cables igniting the gasses from the battery... that's the reason.

 

[mayday0017]

It is because of the gassing that can ignight from the spark. Always connect positive first then negative and connect negative to chasis away from battery.

Don't think it can happen with AGM but why risk it?

 

[9C1]

Ok, a guy at work was very proud of his daughter for jumping her car on her own away at college. He stated that he forgot to ask her if she did a Positive to Positive and Negative to ground or P-P and N-N. This brought on a nice little quandry from the both of us on the reason for taking the negative to ground. I have allows just gone straight p-p and n-n. Never negative to a ground. He asked me why going Negative to Negative could make batteries explode and I did not have an answer for him.

So the question: Why go Negative to Ground and not Neg to Neg? What would cause a batter to explode? Is it the off gassing that can ignite? Is it the battery getting to hot?

Would and does this still apply to new AGM batteries?

And ALWAYS wear safety glasses or preferably a face shield. Those of us who have had a battery explode and kept our eyesight will remember and practice this easy method of protection.
Terry

 

[pepi]

I find to battery jump, one should get a good running start gain and obtain the proper velocity. Before attempting to reach the proper and necessary attitude for a successful crossover and landing.

"Always connect positive first then negative "


No spark is the reason the above, is the correct procedure plain and simple.

Using the poles of the battery is the best practice, you are assured of a good ground.

The disconnect, is negative first positive last, again prevents spark.

The reason no path to ground, open circuit no spark

 

[justsam]

Not sure I agree with Mr. Pepi.

Completing the circuit, whether it is at the positive or negative terminal will produce a spark. That is why completing the circuit at the chassis, somewhere away from any potential battery fumes is the proper procedure.

I do agree in terms of electrical conductivity, that connecting directly at the post will offer the least resistance, just not the safest.

 

[George in Rancho Cordova]

I happened upon two guys trying to jumpstart an old Corolla.
One had a doctorate in political science; the other was an electrical engineer & MENSA member. A genuine recipe for disaster!
They had the polarity reversed, but the circuit was incomplete because one connection was made to something mounted in rubber.
Once that was rectified and the car started, I explained the problem to both of them.
The political scientist pretended to understand, and the MENSA member held his head & shouted: "OOH, my diodes".

 

[alan_3301]

It's best to use to proper jump start terminals. Most cars these days have places under the hood to hook up jumpers away from the battery, and usually a direct path to the starter B+ supply and engine ground. It keeps the current path short and makes starting easier.

 

[In My Garage]

And if it isn't a weak battery that you are needing a boost for, its probably a high resistance point (battery clamp and/or starter terminal) that is the issue.

 

[JMcFly]

I do know my MINI has a positive terminal in the engine compartment and one of the engine support arms has a big "-" cast into it. Kind of makes it way I jump the car since the battery is in the trunk.

 

[Thruxton]

I happened upon two guys trying to jumpstart an old Corolla.
One had a doctorate in political science; the other was an electrical engineer & MENSA member. A genuine recipe for disaster!
They had the polarity reversed, but the circuit was incomplete because one connection was made to something mounted in rubber.
Once that was rectified and the car started, I explained the problem to both of them.
The political scientist pretended to understand, and the MENSA member held his head & shouted: "OOH, my diodes".

 

[In My Garage]

One had a doctorate in political science; the other was an electrical engineer & MENSA member. A genuine recipe for disaster!

Were they holding tools? If so, run for cover.

I had my share of them as flying students. God, I hope they never made it to the airlines.

 

[jd_1138]

Not really to do with the OP's question which has been answered, but "Red Dead" is a good way to remember the order of operations. Connect the red cable to the dead battery's "+" post, then continue holding the red cable and connect it to the good battery's "+" post, then stay at the good battery and connect the negative to the "-" and then walk over and connect it to the chassis of the vehicle with the bad battery. Some newer cars have a specific spot labeled for this chassis connection.

 

[teamextreme]

The order is not important. I doesn't matter which is first or last, positive or negative, just that the last connection being made, the one that completes the circuit and causes the spark, is made to chassis ground away from the battery. If you connect the chassis ground first, then the remaining 3 you haven't accomplished anything in terms of being safer.

 

[kbs2244]

Isn't most battery jumping done on cold, windy days or nights?

 

[gpflepsen]

The order is not important. I doesn't matter which is first or last, positive or negative, just that the last connection being made, the one that completes the circuit and causes the spark, is made to chassis ground away from the battery. If you connect the chassis ground first, then the remaining 3 you haven't accomplished anything in terms of being safer.

I've always considered it best when connecting the dead car, to do the + first, then the - on the chassis. If you do the - first, then the positive cable clamp, being connected to the good battery, can cause a short on any chassis point. If you connect the + first, the only point to cause a short is the negative cable clamp and the positive post.

 

[pepi]

Not sure I agree with Mr. Pepi.

Completing the circuit, whether it is at the positive or negative terminal will produce a spark. That is why completing the circuit at the chassis, somewhere away from any potential battery fumes is the proper procedure.

I do agree in terms of electrical conductivity, that connecting directly at the post will offer the least resistance, just not the safest.

You do not have to agree, you are just wrong and that is fine by me.

 

[pepi]

Not sure I agree with Mr. Pepi.

Completing the circuit, whether it is at the positive or negative terminal will produce a spark. That is why completing the circuit at the chassis, somewhere away from any potential battery fumes is the proper procedure.

I do agree in terms of electrical conductivity, that connecting directly at the post will offer the least resistance, just not the safest.

You do not have to agree.

 

[teamextreme]

I've always considered it best when connecting the dead car, to do the + first, then the - on the chassis. If you do the - first, then the positive cable clamp, being connected to the good battery, can cause a short on any chassis point. If you connect the + first, the only point to cause a short is the negative cable clamp and the positive post.

I guess I worded that a little awkwardly. I think we are in agreement. Bottom line, make the chassis ground connection last.

Sorry Mr Pepi, justsam is correct. You will get arcing on making the last connection, regardless of the order you do it in. There are 4 connections. It won't arc on the first 3, but the 4th will always arc. Doesn't matter what order. Just because the positive connection is made first doesn't mean it won't arc when the negative is connected.

 

[kraneman]

When performing a jump start you're essentially connecting two batteries in parallel , + = +, -= - This maintains the circuit voltage but provides additional amperage to the discharged battery, Remember when a battery is being charged or discharged highly explosive HYDROGEN gas is produced ,as a result of the hydrogen gas ,oxygen in the air and an ignition source (spark) this forms a fire triangle ,and a lethal one at that. If the ignition source is removed , by making the final connection a ground (negative) and placing the connection point on a remote location away from the battery, it reduces the risk of a fire or explosion.

 

[UpstateNY]

You do not have to agree, you are just wrong and that is fine by me.

BSEE here, regrettably it is you that is wrong sir. The last conection is going to spark, every time. Ergo ipso facto, don't spark near the battery - make that last connection away from either battery .

 

[ChevyEFI]

Just remember red to dead is first.
black to ground is last.

 

[tcianci]

I find to battery jump, one should get a good running start gain and obtain the proper velocity. Before attempting to reach the proper and necessary attitude for a successful crossover and landing.

"Always connect positive first then negative "


No spark is the reason the above, is the correct procedure plain and simple.

Using the poles of the battery is the best practice, you are assured of a good ground.

The disconnect, is negative first positive last, again prevents spark.

The reason no path to ground, open circuit no spark

Sorry Skippy, but you're flat out WRONG. It's basic electricity and the order of connection makes no difference whatsoever. Once you make the last connection, since the voltage of the good battery is different than that of the weak battery, current will flow. The connection that starts the flow of current WILL spark whether its on the good battery, the dead battery, positive or negative. The most important thing is to be sure the hoods of both vehicles have been open for a bit to dissipate the hydrogen gas that is common around an automotive battery and to make the final connection away from either battery. That's why it's most common to do the negative connection last since you have many options of where you can make that connection that aren't near the battery.

I think we can agree that being adamant about bad science is a hallmark of internet thread participation.

 

[3xpendable]

This all sounds great but if the battery is dead and in need of a jump wtf is the gas.

 

[rslaback]

This all sounds great but if the battery is dead and in need of a jump wtf is the gas.

The cable will also spark when it is removed. Once your dead battery is now in a charging cycle since it has now started and the alternator is in high gear you are releasing hydrogen. Pull the cable and go boom.

 

[3xpendable]

The cable will also spark when it is removed. Once your dead battery is now in a charging cycle since it has now started and the alternator is in high gear you are releasing hydrogen. Pull the cable and go boom.

Pics or it didn't happen

 

[pattenp]

Here's a video for you.

Pics or it didn't happen

 

[James E]

Connecting both the neg and pos at either battery can cause problems when the loose pos and neg ends at the other end of the cable are invariably touching each other as they lay on the ground or touching something metal.

Doing red-dead then moving to the good battery will help keep this from happening.

And arguing that any method will totally prevent a spark assumes that there is no short anywhere. I've had a spark at the very first connection. Don't know if it was static or a short and maybe the terminal grounded through the cable because the other end was touching something conductive--hell if I know. I don't think there's any totally foolproof method for avoiding any spark at all.

 

[larry_g]

This all sounds great but if the battery is dead and in need of a jump wtf is the gas.

Your assuming that all connect to the dead battery last, The rig you have just started and pulled over to get the jump from is in charge mode to replace charge used to start the motor and producing h2. A spark at its battery chances an explosion. I learn that one as a youngster the hard way.

lg
no neat sig line

 

[Chilliwack Murray]

I guess I worded that a little awkwardly. I think we are in agreement. Bottom line, make the chassis ground connection last.

Sorry Mr Pepi, justsam is correct. You will get arcing on making the last connection, regardless of the order you do it in. There are 4 connections. It won't arc on the first 3, but the 4th will always arc. Doesn't matter what order. Just because the positive connection is made first doesn't mean it won't arc when the negative is connected.

Either Positive (if there is a suitable point) or negative (to a substantial engine part like a lifting bracket) can be connected last AND removed first so the the inevitable spark which will be the same either way will be away from the battery and the associated gasses.

The reason to make the negative connection last is that if you should accidentally touch some other part of the vehicle with the clamps, there is no circuit if you touch positive to ground and it is the first connection. If negative is last and you touch, it is nearly the same potential and will make a small spark, not a dead short.

Always a good plan to not be near the battery when you do attempt to start the car since there is a good chance the connections will arc a little as can the internal connections and it isn't likely you'd be wearing a faceshield or safety glasses on the side of the road or parking lot. I've had more than one battery explode during cranking when it wasn't being jumped and it's not something you want your face near... Seriously.

don't even get me started on positive ground! (pun intended)

 

[KEH]

Watching a dirt track stock car race years ago. A car going around the track had a battery explosion. They ran cars then without generators to keep from having a drain on power from running the alternator.

KEH

 

[5mall5nail5]

All of my older (mid 90's) BMW's have their battery under the rear seat and there are jumper terminals up under the hood. Never have to deal with thinking about this lol.

 

[Big Bad Dad]

Please caution your daughters and sons to use eye protection when jumping a battery! I saved a guys sight once while I was setting at a traffic light. He was broke down and jumping off an old Monte Carlo, and the battery exploded. The acid went straight into his eyes, and he was SCREAMIMG! We were on the upper level of an overpass at the time. I had some beer in my truck, and was able to wash his eyes out enough with the beer to save his sight until real help could arrive. He would have probably been blinded otherwise. I have been real cautious about jump starting ever since!

 

[jayz66ragtop]

Probably going to be told it's the wrong way but I've always done it this way:

1. connected the positive to the dead battery
2. put the other positive in my hand and keep a hold of it the rest of the time
3. connect the negative at the dead battery
4. connect the positive (still in your hand) to the good battery
5. connect the negative to a good ground or if you HAVE to on the negative post of the good battery

Some people want to help me BUT this way I insure it is connected properly and nobody to blame but myself if it's wrong. I also make sure that if the good battery is in a vehicle to have the vehicle running and the vehicle being jump started should have a blower motor or something electrical left on when starting.

 

[larry_g]

...snip... and the vehicle being jump started should have a blower motor or something electrical left on when starting.

Can you explain the thinking behind this? Never heard that before and I'm curious why.

lg
no neat sig line

 

[jayz66ragtop]

Can you explain the thinking behind this? Never heard that before and I'm curious why.

lg
no neat sig line

I don't have empirical evidence but for EFI cars I was told that sometimes a jolt of voltage gets absorbed by the only thing "on" when you turn the key on. If nothing else is on to absorb it, the computer gets it and could cause it to be DOA. I suppose it could be that the alternator voltage jumps over 13.5VDC? I don't have first hand experience but it came from a GM mechanic in the mid 80's who told me he saw it more than once. So I always switch the blower motor on PRIOR to hooking up the jumper cables just in case. Sorry I wasn't as clear about when to turn it on in the prior post.

 

[ddawg16]

urban myth....the battery is one of the best loads you could have at absorbing any spike....in relative terms of resistance, it's the lowest resistance in the car....unless it has an open cell.

Besides....there will not be a spike greater than the voltage of the car being used to jump the dead car...

Now, in them old days when cars had metal bumpers.....we would put the cars bumper to bumper for the ground and use both battery cables on the positive....because us kids were too cheap to buy good cables.

 

[jayz66ragtop]

urban myth....the battery is one of the best loads you could have at absorbing any spike....in relative terms of resistance, it's the lowest resistance in the car....unless it has an open cell.

Besides....there will not be a spike greater than the voltage of the car being used to jump the dead car...

Now, in them old days when cars had metal bumpers.....we would put the cars bumper to bumper for the ground and use both battery cables on the positive....because us kids were too cheap to buy good cables.

Like I said, I have no empirical data but I've always done it this way without issue. Yup, know all about touching bumpers for the ground and using both cables on the positive. Seen this done on large diesel pumping equipment as well, touch the metal frame with the front bumper and use both cables on the positive side of the battery.

 

[ovilla]

Never Leave Ground Alone


That's the way I was taught to use jumper cables. This always forces you to attach the red (+) cables first and remove them last.

 

[Davefr]

While we're on the subject of battery jumping, is there a good way to jump either to or from a GM vehicle with these little side terminals?

I've even tried the special jumper cables but have never gotten a good enough connection to supply a healthy dose of starting amps.

What's the best procedure for these side terminal batteries?