Technically, I’m not aware of a reason why other than as a safety precaution. AFAIK, it’s done to minimize the chances of a spark near the battery, where there’s the potential existence of explosive gasses.

 

In all of this there was only one (AFAIK) answer to the original question: "Anybody know why the negative jumper cable should NEVER be connected to the battery?"

AFAIK, it’s done to minimize the chances of a spark near the battery, where there’s the potential existence of explosive gasses.

This -^ is one reason. A very flat battery can discharge hydrogen gas. By making the connection farther from the battery you minimize chances of a spark igniting the hydrogen. This is a pretty minimal risk in my book.

A better reason:

By connecting the ground jumper cable directly to a designated chassis ground you may (likely will) created a better ground path. Connected to the dead battery, the ground path has to go through the dead battery's terminal clamp and then the car's battery ground cable. Jumper cables' conductors are often larger in diameter than the typical car's battery ground cable and therefore have lower resistance.

The order in which you connect cables can be debated forever as there are many permutations to weigh. If you have actual jumper cables independent of the 'starting device' it is always best to start with the dead-car end of the cables.

And never drop the other end of the cable one you've made the first connection. If perchance one of the connections is difficult to make without a risk of accidentally contacting something other than the intended connection then do that end of the cable first.

Last, from Gtk:

"Let the engine of the donor vehicle run at a higher engine speed."

This is a good way to risk damage the alternator on the donor car. Best to just use the donor's battery with the donor's engine switched off.

I really don't understand your post.
Wrong thread for me or you ? This thread is about jump starts as I understand , that's what i referred to. It's not about just connecting batteries .
It's in the picture and in the YouTube video.

You're right my bad. The thread title is about jumper cables. However, the initial posts describe connecting - a device - portable jump starters to a dead battery.

Both the picture and the video states the same , start with the positive cable first (battery to battery) then go with the negative but the negative goes to the depleted car's engine block or predefined negative jump start point.

Again my bad: I misread the first diagram. Yes, they are the same.

 

Not sure about most, but the ones I have used can easily reach a suitable spot on the frame in any car I have experience with. You don't connect to the negative terminal because as Bob said there is a slight risk of explosion and there is no need to - the negative terminal is connected to the chassis which is the ground in this case. Any bare metal will do.

 

Found this.

The issue has to do with the fact that the computer progressively raises the charging voltage to the battery as the battery ages. This is why one has to let the computer know when a new battery is installed, because if not it will apply too high a voltage to the battery reducing the new battery's life span. Connecting the charger directly to the negative terminal bypasses this system and could cause the computer to erroneously overcharge the battery, reducing its lifespan

The reason I ask is most portable jump starters have short leads that only reach to the battery terminals, and therefore cannot be used.
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Also saw something about coulomb counting for auto stop/start on the neg terminal

 

The safety issue is what used to be said. It still makes sense. I'm not sure of the computer argument. If the negative terminal is connected directly to chassis ground then it shouldn't matter where you connect a charger.

 

It is also safest to connect both ends of the positive cable first then the negative ends. This is to prevent, a dropped positive end, from accidentally touching the body and causing a wicked short under the right conditions. If a negative cable is dropped and touches the body it does not much matter.

 

Actually the exact opposite of that.

Connect the ground first. Then you can drop the positive cable anywhere except on the positive battery terminal without creating a circuit with voltage.

If you connect the positive cable to the positive battery post then the negative cable is ready and willing to suck charged-battery-potentional electrons out of anything it touches. And THAT may cause damage if you drop it on something that is grounded that isn't intended to be an unfused battery ground.

 

my neighbor used to be one of these types that knew better than everyone else and did things how he wanted over any instructions and believed in jumping cars by connecting positive to positive and neg to neg and running the car to charge the dead battery faster. after damaging several alternators doing that, he started following the directions for jumping cars.

 

All the instructions I ever saw said to connect the positive terminals first.

The safety question was more about disconnecting than dropping. The reason for connecting ground away form the battery is, or at least was, that the disconnect could cause a spark. If the battery had been giving off a cloud of hydrogen a spark could ignite it. So you wanted to be able to disconnect something away for the battery. I never knew anyone who had such an experi

 

The traditional advice was positive good to positive bad; negative good to dead car ground IIRC.

 

I was thought that positive first

I think Bosch knows something 🙂about batteries and car electronics .

 

For my part, usual point of a jump is for a start. (BAT is by definition out of reach if the frunk is the goal.) Battery defect may be corroded leads or other high resistivity creating issue or ?; after all the BAT is dead for some reason. So, a direct connect to (through) the battery may fail as well. Chassis connect bypasses the defective BAT. Starter doesn't care where the (-) is as long as there is a complete circuit. FWIW, done it both ways numerous times with analogue and digital cars, conventional and zero maintenance batteries and never fried a computer, blew up the BAT, or incurred the wrath of any of the major automotive gods.

 

From the Good to Know App:

When jump-lead starting, never connect the black negative cable directly to the battery. Always connect the black negative cable to the ground point B (Fig. 36).”

Porsche actually provide a separate ground point on the left side of the car (as viewed from the seat.)

And from further in Good to Know:

Open front luggage compartment lid.

Please see chapter "Emergency unlocking of the luggage compartment lid".

Remove cover in front luggage compartment.

To remove the cover: Please see chapter "Removing and stowing tire sealing compound or tool box".

Connect the red positive cable to the positive terminal A of the flat battery.

Connect the red positive cable to the positive terminal of the donor battery.

Connect the black negative cable to the negative terminal of the donor battery.

Connect the black negative cable to the ground point B.

Never connect the black negative cable directly to the battery.

Let the engine of the donor vehicle run at a higher engine speed.

Start the engine. An attempted start using jumper cables should not last more than 15 seconds.

Then wait for at least one minute.

With engine running: First, disconnect the black negative cable from the ground point B then from the negative terminal on the donor battery.

With engine running: Disconnect the red positive lead from the positive terminal on the donor battery first, then from the positive terminal A on the flat battery.

 

Yes, I was wondering if there are pitfalls with a portable battery jumper. They look pretty cheap and easy. Just need to keep it charged. So you get to your car and its dead, defcon 1. Then your frunk doesn't open, defcon 2. Nobodies around for a jump defcon 3. You can call AAA if you have cell coverage and wait for someone to arrive, or use a portable jumper if it is charged. The jumper sounds a bit more convenient. It will open the frunk via the fuse box and also jump the battery. If the frunk does not open, defcon 4, and you need a tow. But the tow hook is in the frunk, defcon 5. Seems like a lot could happen.

 

DEFCON One is the most serious, not Five.

 

This thread is like a skit from the Three Stooges.....thank you for the entertainment.

Mike

 

This thread is like a skit from the Three Stooges.....thank you for the entertainment.

Mike

Who's on first??

 

As Boxsteiner mentioned, use a jump starter instead of jump starting from a donor vehicle. Only trick to this is having one charged and available when you need it.

NOCO - Boost UltraSafe Lithium Jump Starters

BOOST - Discover portable lithium battery jump starter packs. Powerful battery booster jump box for jump starting cars, trucks, boats, motorcycles and more.

no.co

 

I've had a NOCO for about 5 years. I charge it twice a year (New Years and July 4th) inside and leave it my car year round. Only used it once and worked like a charm.

 

Interesting approach about not running the donor car.
This is also how I learned and did in the previous decades. Make sense not to run, not to put additional stress to the generator. Luckily never had any issue with it.

 

This is also how I learned and did in the previous decades. Make sense not to run, not to put additional stress to the generator. Luckily never had any issue with it.

I learned to do it the wrong way as a kid. Only since I've owned and worked on Porsches have I learned that it's not the best way.

The best way to deal with a dead car battery is to fully charge it - with a charger - before attempting to start.

If you jump-start a dead-battery car, and drive away with a mostly-depleted battery you'd better drive directly to a store and buy a new battery. Very-depleted batteries subjected to the vibration and shock of being driven around have a high-probability of being damaged such that they won't hold a charge later even when fully charged.

That last bit is not my theory: I've witnessed this on numerious occasions and technical explanations exist.

If, however, is not convenient to charge the battery then...

So you are saying one should not do what the GTK manual says to do??? And also not do what people have done for years, run the donor car's engine at all??

Yup.

The way people have done it for years is to set up the jump with the donor car running, start the receiving car, disconnect the cables and let the receiving car then re-charge its own battery. The donor car never "donates" for more than a few minutes.

This is my understanding of the issue (which is subject to debate and/or correction...)

Have you ever heard that you're never supposed to disconnect the battery from a running car? The alternator is what powers the car after start up right? So why do you need a battery. The battery provides a reference voltage for the alternator and acts as a "capaciter" for transient voltage spikes that occur when various bits of the car start or stop consuming power. Without a reasonably well-charged battery the alternator can "go wild" and either damage itself or cause transient over-voltage spikes to electronics (which don't like them at all.)

A dead battery that's just been jump-started is a poor "capacitor" for the alternator.

On the other side of the cables, the running car has just started a dead-battery car's engine, and the running car's alternator is powering both vehicles, charging the the other car's dead battery, and topping-off its own battery. The 'dead' car's alternator may or may not be 'helping' depending upon the voltage it sees as a reference.

Now, when you abruptly disconnect the two batteries, the running car sees a huge change in alternator load that can cause transient voltage spikes. And the 'dead' car's alternator may suddenly go from doing almost nothing to running an engine and charging a deeply discharged battery and thus also have voltage spikes.

I had one occasion long long ago where the tiny battery and alternator in my Datsun 510 could not provide enough juice to turn over a much larger engine with a very dead battery. A much larger vehicle had no trouble with it though. But I've never had that process damage the donor alternator. I doubt the GTK manual would say to do it if it was so risky.

I think that - just like connecting the ground cable to the negative battery terminal might cause an explosion - the risk of alternator (or eletronic module) damage is probably small. The risk of alternator damage, from what I understand, is proportional to the age of the alternator (wear and tear.)

 

I never really thought about it, but it does make sense that there should be no need for the donor vehicle to be running just to jumpstart the other car.

 

Here is the latest update from Scotty!

Never Jump Start Your Car Like This

Never Jump Start Your Car Like ThisSubscribe for more daily vids ►https://www.youtube.com/channel/UCuxpxCCevIlF-k-K5YU8XPA?sub_confirmation=1⬇️Scotty’s Top D...

youtube.com

 

Spin against each other 🤣

 

Boxsteiner, here's the reason to never connect the negative cable directly to the battery, and why jumper boxes have really short cables, 1) When you're boosting off a vehicle, the vehicle doing the boosting should never have the negative cable hooked directly the its battery terminal because the vehicle being boosted may have a shorted alternator, and if it's shorted it will short out the alternator on the car dong the boosting. 2) Booster boxed have short cable because the shorted path is best, so connecting directly to the battery is best, and you don't have to worry about a shorted alternator.

 

i would like to add this Turn off the radio and any other elelctronics in the car before you jump start I blew up my daughters factory nissan stereo in her maxima by not shutting off the tunes