consider that the internal resistance of a reasonably healthy 12 volt automotive size battery

{underline / italics edit for focus} When designing a system to be used by commoners, one should always consider worst possible case. Not everybody has a "reasonably healthy 12 V battery".

The recommended method of jumpstarting a modern car is to connect both vehicles, start the car with the good battery and let it run 10 mins to charge the battery of the other vehicle somewhat, then stop the car providing the jump and remove the cables. The car with the flat battery should have enough charge to get started.

I'm aware of a time where two guys (at work) one had a dead battery and needed a jump. The other guy gave a jump. The guy giving the jump was a pretty sharp guy who knew how to connect jumper cables, positive battery post to positive battery post, THEN negative to ground on the dead car, then neg. to ground on the source car. After getting the dead car started the source car then had a dead alternator.

I carry one of those portable boosters. This is the one I have. I've given them to friends and my son-in-law and told them "Charge them every three or four months or when you need them they won't work." My neighbor/friend always retorts "I check the battery and it always says it has 12 volts." Though I've tried to explain to him that the voltage is not the important factor but rather the battery's ability to deliver a charge. Worst case - he doesn't get it. And he's asked for jumps in the past. Old batteries are among the things he collects and stores without charging them periodically. Then doesn't understand why they don't work.

I don't give jumps when I don't have to. Rather, I'd prefer to carry a battery charger and plug it into my inverter. I haven't done that, but this thread has me thinking of doing just that. Along with the self contained portable booster.

As a side note - a few weeks ago I came upon a Vietnam Vet with one of those Rascal chairs. He was just sitting there about a quarter mile from home. Pulled over and offered him to plug into my inverter and charge his batteries. We spent about 15 minutes charging his chair, then he left. So the booster for my truck, which hasn't yet been needed but once for my wife's car, and maybe a good 12V charger for someone in need of a quick top-up of their battery.

As for the device, though some have explained why it's needed - or not needed, I can read what someone says but that doesn't always mean I accept their point of view. Not because I don't respect their POV but rather because I don't fully understand the point being made. We can talk Nuclear Physics, but since I have virtually no understanding of the subject I can "Hear" what you say, but that doesn't mean I can "Understand" what you say. You may be right. But then again; "No one has a more powerful network" (Thanks for that one Pan). So accepting what someone says doesn't always happen just because of my lack of knowledge or understanding on a subject.

 

Unfortunately, in the past, some automotive companies did not adequately design their systems to survive the "Load Dump", which is that short term over-voltage that happens when an alternator delivering a high current suddenly has the load removed. At that point the rotating field current is still quite high, and the magnetization is very strong. So it takes a short bit of time for the output voltage to drop. Some systems did not include adequate protection against this.
A similar thing would happen when the alternator was powered during the engine cranking time, if the charging connections were not good enough. The system voltage would drop while the engine was cranking, and so the alternator would be working at maximum output. Not only did this add to the load the starter motor had to spin, it also assured a voltage surge when the driver released the start connection and the starter motor was disconnected. The result was not an inductive spike at all, it was the alternator at max output suddenly not having much load, and the regulation not being nearly fast enough.
It is also the reason that it is incredibly stupid to race the engine the instant it starts.
The best solution, adopted by many but not all, is to not enable the alternator until the engine has started running. That delay of just a few seconds solves the problem.

My Volvo has that delay.

 

Certainly it is important to know how to correctly and safely use jumper cables.No question about that! There are a number of errors that will instantly cause serious consequences, and a couple of hazards that are vastly overstated. An accumulation of hydrogen gas on a breezy day with the hoods open is not likely at all. And mostly, the recipient battery is not stone dead, just a bit to weak to crank, or to crank and provide spark at the same time. In addition, having the supply battery vehicle running only at idle will assure that no huge alternator voltage spike is likely, unless one has a system designed for full output at idle. On some vehicles knowing which connection is positive can be a big challenge, especially in the dark.

 

Important tip when using jumpers, connect positive first.

 

Connecting:

Positive first, negative last.

Disconnecting:

Negative first, positive last.

Same applies when installing or removing a car battery from a vehicle.

The reason for connecting the positive battery terminal first is that if the wrench accidentally touches chassis ground, with the negative terminal NOT connected, there will be no sparks or excitement. But if the negative is connected and you touch positive to chassis ground - please make a video. That'd be entertaining.

 

I stopped helping people with car trouble because I don't want to get robbed or stabbed. Now I have the rational excuse of not wanting to damage my vehicle!

And yes someone tried robbing me after I gave them the time one lovely evening...

 

For those who might still have a positive ground electrical system the attachment/detachment sequence should be reversed. The main point is to make and break the connection by clipping onto a part of the chassis that is not close to the battery, the idea being that a spark near a battery could set off a hydrogen pop. Has anybody ever experienced that?

 

Has anybody ever experienced that?

I have. My first car and the battery froze. So after work my buddy the took me to work helped me jump my car. Smoke/gas started coming out of the cell caps and not knowing better I pulled the jumper off of the battery. A spark and a very loud explosion was the result. Battery acid all over my coat and hands.

 

The main point is to make and break the connection by clipping onto a part of the chassis that is not close to the battery, the idea being that a spark near a battery could set off a hydrogen pop. Has anybody ever experienced that?

I apparently went to a similar school as shortbus. I was a kid, maybe 16 working at the local Exon station. Put a new battery in a car and back then we added the electrolyte and charged the batteries. Battery had the small vented screw on caps. Turned off charger and disconnected it. Connected negative post first and when connecting positive post my wrench bumped chassis. Big spark and battery exploded. I was lucky to come away with just a messed up set of coveralls and fortunately my vision. Sad part is I knew better and still managed to destroy a battery and damn near myself. Lucky also I did not destroy the customer's car. Bought a battery out of my next paycheck. While not jumping a car same effect, hydrogen is not friendly.

<EDIT> Fixed the connection sequence, thanks Tony. </EDIT>

Ron

 

@shortbus
@Reloadron

My father had that happen also. Spark set it off. He was wearing glasses, luckily.

I read you are supposed to connect the ground lead last, to the bumper so sparks wont occur close to the battery. Dont think all bumpers are metal anymore so have to find somewhere else to connect.

 

The last three models of car I owned did not have bumpers.

 

Going back many years as a kid if a set of cables wasn't long enough we would just get the bumpers tight against each other and place two jumper cables in series and only connect the positive terminals. Then too that when cars actually had bumpers.

Ron

 

The last three models of car I owned did not have bumpers.

Oh that's interesting too, where did they go?

 

Going back many years as a kid if a set of cables wasn't long enough we would just get the bumpers tight against each other and place two jumper cables in series and only connect the positive terminals. Then too that when cars actually had bumpers.

Ron

That's a cute idea. Now if i can just get someone to jump my Tesla EV (ha ha).
i hate to think of what kind of explosion we could get with battery packs that large.

 

Going back many years as a kid if a set of cables wasn't long enough we would just get the bumpers tight against each other and place two jumper cables in series and only connect the positive terminals. Then too that when cars actually had bumpers.

Ron

I've never had (nor seen, that I recall) a set of jumper cables that weren't joined together. Knowing me, if I had such a pair then I would probably only be able to find one of the cables when I needed them.

 

a spark near a battery could set off a hydrogen pop. Has anybody ever experienced that?

I haven't. Wouldn't have thought it was that much more common a thing since I had heard a warning about that happening but have never experienced it, nor had any of my friends. And largely our friendship centered around our cars. With steel bumpers. And yes, I helped a friend on the freeway. Jumper cables from battery to battery was not possible. But since the cables I had at the time were not the sets where both wires are joined in the middle. Bumper to bumper, jumper end to jumper end and connected the dead battery first then the running 72 Chevy Nova.

Connected negative post first and when connecting negative post my wrench bumped chassis.

If your negative post created a spark when bumping the chassis it must be a positive ground system. Either that or you mis-spoke. I've seen positive ground cars before, maybe twice. I know they did exist but don't know if they still do. And yes, what

For those who might still have a positive ground electrical system the attachment/detachment sequence should be reversed.

is 100% absolutely correct. In short, regardless of positive or negative chassis ground, that ground is always the first off and the last on.

 

I've never had (nor seen, that I recall) a set of jumper cables that weren't joined together. Knowing me, if I had such a pair then I would probably only be able to find one of the cables when I needed them.

Hi,

I had a pair long time ago not sure if i have them anymore i got a much much better pair with heavy gauge wire and very durable alligator clips. The old pair was a cheapie so maybe that is why they were separate. They were twisted together a bit though.

But i think i just got your sig line. I must have read it too fast in the past. I think that is very clever. It's subtle so i wonder if anyone else got it (that is, understand it entirely) i'd love to hear other members thoughts on that so i wont say anything else about it just yet.

 

There are 10 types of people in the world: those who understand binary, those who don't, and those who can work in any number base. Author WBahn unless he heard it from somewhere else.

Yeah it took me a few seconds to get it. But I got it. 10 Boolean for 2.

 

There are 10 types of people in the world: those who understand binary, those who don't, and those who can work in any number base. Author WBahn unless he heard it from somewhere else.

Yeah it took me a few seconds to get it. But I got it. 10 Boolean for 2.

Well, 10 is binary for 2 (Boolean is not the correct word to use), but the statement is describing 3 groups of people and using 10 as the representation for 3.

It's not original to me -- I don't know where I first heard it, but I've seen it on a T-shirt at the Colorado School of Mines.

A very common statement that I had seen many time before was, "There are 10 types of people in the world: those who understand binary and those that don't." So seeing the same representation used in a statement that had three categories immediately caught me as being very clever and cute.

 

Well, 10 is binary for 2 (Boolean is not the correct word to use), but the statement is describing 3 groups of people and using 10 as the representation for 3.

It's not original to me -- I don't know where I first heard it, but I've seen it on a T-shirt at the Colorado School of Mines.

A very common statement that I had seen many time before was, "There are 10 types of people in the world: those who understand binary and those that don't." So seeing the same representation used in a statement that had three categories immediately caught me as being very clever and cute.

Oh that's very big of you to admit you found it somewhere else, but it's still cool.
In a drastic update to it may be:
"There are 10 people in the world, those who understand binary, those who dont, and those who's names are too numerous to mention."
(implying that 10 could be a number in a base system that is VERY, VERY large, maybe 2.828 billion <chuckle> (square that and get the approximate number of people in the world in base 2.828e9 which would be 10) )
Maybe reaching for too much though there