Jump starting a car...

[pdw709]

I had to jump start my car last night (a job that I have performed many a time in the past) and got into a debate with someone regarding the order that one must connect the jump leads. He insisted that it must be "+" to "+" first and then "-" to "-" with the last one being attached to the flat battery.

After since doing a internet search it appears that this is indeed the correct order and there are terrible warnings about battery damage if the order is not adhered to.

Being a skeptic, my initial reaction was bullsh*t - basically thinking that a circuit (indeed any circuit) is not complete until the final connection is made so the order should not matter. Being a scientest i'm curious to understand the reasoning behind the advice, and if there is a plausible reason then i'm curious to know what it is! To a certain extent I can see why connecting the "-" last could be reasonable as it's the one with the electrons flowing out of it, however what damage could be caused by doing it wrong?

I'm puzzled.......

[JohnG]

I haven't heard that. I always connect the positive and negative leads on the dead battery then connect the positive and negative leads to the live battery. Ultimately it is positive to positive, negative to negative, like you say, but the important order is from dead to live. My reasoning being that you don't want to be handling "live" cables any longer than you have to.

I was always taught that the main thing was to not accidentally get the leads mixed up and inadvertently connect positive to negative because the battery would blow up in my face.:eek:

I have no science to back this up, just 25 years worth of "field testing". My method has never resulted in an exploding battery or a failure to charge the dead battery, unless the cables were in bad shape or there was some other problem with the "dead" car (e.g., the alternator).

I too would like to hear a proper explanation from an expert. Sounds like a job for the guys on Cartalk or maybe even Mythbusters (I can hear it now... "Kari, Grant and Tori find out if it's really possible to cause a car battery to explode with improperly connected jumper cables!").

Here's a related useful tip/fun fact/trivia question related to this discussion; do you know how to recharge a dead car battery without jumper cables?

There's a couple of different ways to go about it, but here's one example. You have two cars, one car has a dead battery and the other has a live battery.

1. Start the "live" car and remove the battery with the engine still running. The car should continue to run as it should only need the battery to operate the starter, not to keep it running.

2. Remove the dead battery from the other car and hook it up to the running "live" car.

3. Wait for the formerly dead battery to get recharged in the live car, at which point you simply put both batteries back into their original cars.

I should say that I've never tried this, so I'd be interested to hear if anyone else has?

[Bob Blaylock]

As far as I know, the important thing is to avoid making a spark near the battery.

Connect the positive terminals first, connect the cable to the negative terminal of one battery, and the other end of that — not to a battery terminal — but to some grounded metal part of the remaining car as far as practical from the battery. This last connection is the one that will spark; and that is why you want it to be away from the battery.

Lead-acid batteries give off hydrogen gas when they are charged or discharged. You don't want the spark to ignite any hydrogen that might be hanging around the battery.

[Subduction Zone]

Let's see, you could always plug a couple of leads into a giant onion or lemon, oh wait no none of HH's videos ever work. As long as you make sure that no contact is made other than to the batteries it does not matter what order they are hooked up in, just be sure it is ultimately positive to positive, negative to negative.A point about your spoiler, in modern carss the battery is part of the voltage regulation system. Taking it ou while the vehicles is running can have bad effects on your complex electronics. You could fry your computer:eek: With a precomputerized car this should be no problem.

[JohnG]

Let's see, you could always plug a couple of leads into a giant onion or lemon, oh wait no none of HH's videos ever work. As long as you make sure that no contact is made other than to the batteries it does not matter what order they are hooked up in, just be sure it is ultimately positive to positive, negative to negative.A point about your spoiler, in modern carss the battery is part of the voltage regulation system. Taking it ou while the vehicles is running can have bad effects on your complex electronics. You could fry your computer:eek: With a precomputerized car this should be no problem.


A point about your spoiler: Good to know, thanks. Guess I won't be trying that trick on a modern car!

[pdw709]

Connect the positive terminals first, connect the cable to the negative terminal of one battery, and the other end of that — not to a battery terminal — but to some grounded metal part of the remaining car as far as practical from the battery. This last connection is the one that will spark; and that is why you want it to be away from the battery.



I can see the rationale for this, however doing an internet search the advice is not consistant on this issue - some say connect to the bettery "-" terminal and others say grounded metal in the engine.

[JJM]

If you make a spark near a charging battery, it may blow up (hydrogen venting). It is best to connect the negative leads to conducting pieces of the cars which are not close to the batteries. With all the plastic used in cars today, that may not be easy to do.

As for connecting negative to positive, sometimes it is difficult to predict when a battery will explode; what is sure to happen is it will fry the alternator of the car with the dead battery. I have not worked on a car in more than 25 years- crossing the cables may do more extensive harm to today's electronic components.

ETA, I see someone else posted on this. As for the confusion on the Net noted by pdw; you cannot go wrong if you connect to a piece of the car remote from the battery.

[Ivor the Engineer]

I imagine the reason for connecting the '+' terminal first is because the bodywork on the vast majority of cars is connected to the '-' terminal, there is therefore a greater risk of accidentally shorting out the battery if the '-' terminals are connected first and the '+' jump lead is touching or touches the bodywork of the car while being connected.

[69dodge]

I don't think it matters in principle.

There are some practical reasons to connect the positive terminals first, then the negative terminals.

Cars nowadays use a negative-ground system; this means that the negative side of the battery is always connected to the car's body.

So, if you connect the negative terminals first, then one positive terminal, and then, as you're trying to connect the other positive terminal, you accidentally touch the end of the jumper cable anywhere else on the car, you'll short out one of the batteries. That could be dangerous. (ETA: Hmph...Ivor the Engineer got there first.)

Also, as Bob Blaylock said, to avoid creating a spark near the battery, which could result in an explosion, it's a good idea to make the last connection somewhere else on the car instead of at a battery terminal. If you connect the positive battery terminals first, the last connection will be a negative one, so you'll be able to connect the jumper cable somewhere else on the car instead of at the negative battery terminal.

[pdw709]

Thanks for the advice.

It looks like the concensus is that in terms of battery preservation it does not matter which order to connect, but its more down to accidentally shorting by touching the bodywork.

Makes sense to me!

Thanks

[Dave Rogers]

I haven't heard that. I always connect the positive and negative leads on the dead battery then connect the positive and negative leads to the live battery.

That's only a good idea if the dead battery is really, really dead. Usually there's some charge left in it, just not enough to turn the engine over. It may still be enough to cause some damage if, after connecting both leads to the dead battery, you accidentally allow the trailing ends of both leads to touch each other. As you correctly surmise, the reason for the order is nothing to do with how the circuit is set up, it's purely a safety procedure to avoid (a) accidental shorts (hence, connect both ends of one lead before connecting either end of the other) and (b) sparking near a hydrogen source (hence, make the final connection from the negative terminal of one battery to some other part of the other car).

Having said that, I usually connect to the terminals, but always positive-positive then negative-negative, because I'm never entirely sure I've remembered it right about negative grounding. I connected one battery the wrong way round recently, because I misread the symbols in the dark; that was quite exciting for a few seconds.

Dave

[El Greco]

I connected one battery the wrong way round recently, because I misread the symbols in the dark; that was quite exciting for a few seconds.

I did the same a few years ago. In case it happens, remember to immediately wash everything that comes in contact with the really corrosive battery liquid, or else you will have destroyed a few clothes and a car paint. :D

[Starthinker]

My ex crossed the cables once and you be surprised how quickly a good set of jumper cables can melt away into nothing.

[EvilBiker]

I imagine the reason for connecting the '+' terminal first is because the bodywork on the vast majority of cars is connected to the '-' terminal, there is therefore a greater risk of accidentally shorting out the battery if the '-' terminals are connected first and the '+' jump lead is touching or touches the bodywork of the car while being connected.

Exactly!

To expand on the battery removal option as per the spoiler: the battery effectively acts as a filter (besides, obviously, supplying juice to start the car). It shorts any AC component that could sneak through from the regulator - this includes any spikes and transients that could be generated by the alternator. Removal of the battery while the car is running will allow those nasty little spikes and transients through to the harness, and anything which has a tight voltage tolerance will likely be toasted.

If by removing the battery, you manage to disconnect the regulator control voltage, your alternator can push out VERY high voltages, which will fry everything. On the other hand, you can also damage the alternator, even though your internal electronics survive.

The problem here is that this does not always happen. It only happens sometimes, so an inexperienced auto tech will disconnect it a couple of times, get no negative results, and assume it's OK to do it every time.

...until you happen to bring your Mercedes SLK 500 in. You know, the one with all the gadgets and mod cons. :boggled:

[Dancing David]

Another important tip, turn off the jumping car! As opposed to the jumpee car, which you are trying to start. And dc the thing as soon as you can.

My dad said you can surge the jumping car and fry the electrical and my techno friends says you can fry it even if it is turned off but it helps. Something about the surge when the jumpee car actualy starts.

Myth or mythtery?

[shawmutt]

Myth or mythtery?

Myth. Once the car is started the power comes from the alternator, not the battery. There is no "surge".

I worked on cars for about five years, and had a battery explode while connecting the negative for the dead battery. Ever since I make that final connection on a metal part of the car, not the dead battery.

[Rolfe]

Here's a related useful tip/fun fact/trivia question related to this discussion; do you know how to recharge a dead car battery without jumper cables?

There's a couple of different ways to go about it, but here's one example. You have two cars, one car has a dead battery and the other has a live battery.

1. Start the "live" car and remove the battery with the engine still running. The car should continue to run as it should only need the battery to operate the starter, not to keep it running.

2. Remove the dead battery from the other car and hook it up to the running "live" car.

3. Wait for the formerly dead battery to get recharged in the live car, at which point you simply put both batteries back into their original cars.

I should say that I've never tried this, so I'd be interested to hear if anyone else has?


I've got a good one similar to that.

I was driving my father's car from Scotland to Hertfordshire just after New Year, in about 1984. It was a fairly old car even then, a Datsun 100A. I had a crawling suspicion all was not well with the battery, so I had both jump leads and a battery charger with me, expecting I might have trouble getting going on cold mornings.

As it transpired, it was very lucky that I left early, and so I was nearly there by the time dusk fell and I had to switch on the lights. I had to stop at a big roundabout where the A414 joined the A1. The engine died on me, with all the symptoms of a flat battery. This was a bit of a bummer, as the family AA membership only covered my father as the named driver and not me. And I didn't have a spare bean to pay for a rescue.

Another motorist, also in distress having run out of petrol, helped me get the car off the road onto the grass verge just past the roundabout, then flagged down a passing vehicle. Darkness was falling and the car was very close to the traffic on the A1. Performing any sort of jump start would have been pretty dangerous.

The passing motorist took us both to a big garage a bit further up the A1. The other stranded guy got his petrol, but they didn't have any quick/cheap solutions for me. I therefore walked the half-mile to my home, and got my motorbike out of the garage. I then rode the bike to the nearby town centre where there was a big Woolco store which stocked motoring gear. I asked the assistant if they had a replacement battery for a Datsun 100A (because I really thought that was what the car needed), and was assured that the item proffered was the correct thing. It was sold ready-charged.

I strapped my purchase onto the bike's rear carrier and returned to the car. It was really dark by this time and the traffic was whizzing past only feet away. No way was I going to try to replace the battery there and then. I put the battery on the floor of the car, in the driver's foot-well, and opened the bonnet. I was able to connect the new battery to the old using my jump leads, trailing them in through the open side window, and then lowered the bonnet gently onto the leads without trying to latch it.

I got in the car and started it. No problem, first time. So I drove like that, with the window open, the mile or two back to my home. I then cornered a neighbour and begged a lift back to where I'd left the motorbike, and fetched it back home too. OK, it was a walkable distance, but did I mention it was dark and cold?

I then removed the old battery from the car and took it into the house, where I connected it to the mains-powered battery charger. However, I was unsuccessful in fitting the new battery into the car - it was slightly too short and too wide to fit into the appropriate space and fasten the clamp. And besides, it was pitch dark and freezing cold. I quit and went to choir practice (on the bike).

I left the old battery on the charger overnight. In the morning, I found it was absolutely sparking with charge, apparently raring to go. It really, really wasn't behaving like a dud battery. I still couldn't fit the new one into the car, so I put the recharged old one back. Car started, first turn of the key. So I drove to a nearby Datsun dealership.

There, the car was diagnosed with a dud alternator, which explained why the engine died the first time I tried to idle it after switching on the lights. There was nothing wrong with the battery at all.

I left the car there to be fixed, walked home, and got out the trusty motorbike again. I looked at the new battery. It was pristine. I still had all the packaging, and the receipt. I packed it back up in its original box and took it and the receipt back to Woolco, explaining (entirely truthfully) that I'd bought it the previous afternoon, but it was the wrong size for the car. They happily refunded my money.

I got to work on my motorbike for the next couple of days (the loan of the car was to save me having to freeze my extremities off on my usual form of transport during the dead of winter), until the car was ready. I then walked to the garage and collected it.

My Dad coughed up the price of the new alternator - it was his car, after all.

So the rescue from the side of the A1 in the dark cost me precisely nothing.

Rolfe.

[Dave Rogers]

Another important tip, turn off the jumping car! As opposed to the jumpee car, which you are trying to start.

Huh? Isn't there the danger there that if the battery of the jumpee car is really dead, you'll just drain the battery of the jumper car into it enough to leave that one effectively dead too? I always keep the jumper car running while I connect, so that even in the worst case scenario I have at least one car running.

Dave

[bruto]

Exactly!

To expand on the battery removal option as per the spoiler: the battery effectively acts as a filter (besides, obviously, supplying juice to start the car). It shorts any AC component that could sneak through from the regulator - this includes any spikes and transients that could be generated by the alternator. Removal of the battery while the car is running will allow those nasty little spikes and transients through to the harness, and anything which has a tight voltage tolerance will likely be toasted.

If by removing the battery, you manage to disconnect the regulator control voltage, your alternator can push out VERY high voltages, which will fry everything. On the other hand, you can also damage the alternator, even though your internal electronics survive.

The problem here is that this does not always happen. It only happens sometimes, so an inexperienced auto tech will disconnect it a couple of times, get no negative results, and assume it's OK to do it every time.

...until you happen to bring your Mercedes SLK 500 in. You know, the one with all the gadgets and mod cons. :boggled:

As an addition to the above, this problem can occur in milder form in a vehicle that has just been jump started with a very dead battery. A really dead battery doesn't accept a charge, and the engine will be running essentially on the spiky chopped DC output of the alternator. Some systems don't mind this, but others (90's era Mopar fuel injection being a classic example) won't run worth beans until you get a good battery.

WRT Dancing David's "surge," what really happens is the opposite of a surge. It's a sudden voltage drop. An alternator is not bothered by this, so there is no reason to turn off the donor vehicle. It's better to leave it running so as not to drain the battery, and to give the dead car higher voltage.

[ponderingturtle]

I can see the rationale for this, however doing an internet search the advice is not consistant on this issue - some say connect to the bettery "-" terminal and others say grounded metal in the engine.

It doesn't matter, as the negative terminal is generaly grounded to the frame. This is why order becomes important, as a + charged wire can spark to the frame but the - charged wire can not.

[Uncle Vanya]

I had to jump start my car last night (a job that I have performed many a time in the past) and got into a debate with someone regarding the order that one must connect the jump leads. He insisted that it must be "+" to "+" first and then "-" to "-" with the last one being attached to the flat battery.

After since doing a internet search it appears that this is indeed the correct order and there are terrible warnings about battery damage if the order is not adhered to.

Being a skeptic, my initial reaction was bullsh*t - basically thinking that a circuit (indeed any circuit) is not complete until the final connection is made so the order should not matter. Being a scientest i'm curious to understand the reasoning behind the advice, and if there is a plausible reason then i'm curious to know what it is! To a certain extent I can see why connecting the "-" last could be reasonable as it's the one with the electrons flowing out of it, however what damage could be caused by doing it wrong?

I'm puzzled.......

As someone who used to work as a mechanic, as well as someone who has melted several wrenches, take it from me, ALWAYS connect positive first then ground. When disconnecting wires from the battery, ALWAYS disconnect ground first, then positive.

Why? Very simple. Let's say you connected "-" to "-" first. OK. Now you're fiddling with the positive cables, you connect one end of the cable to the "+" on one side, you go to the other side and... whoops, dropped the cable and the alligator clip touches a part of one of the vehicle's chassis. You just made a short circuit between "+" and "-" (ground). Best case scenario, you melt some cables, worst case scenario your battery explodes (not likely, but who knows).

Like I said, I've melted a few wrenches when I worked as a mechanic, mostly due to laziness. I knew that I should disconnect ground first, but I was working on a battery where the + terminal was easier to get to, while undoing the nut on the terminal, my wrench accidentally made contact with the car's chassis. Yeah... let's say that wrench can't be used anymore.

[Bikewer]

"Jump starts" are one of the services we render; I've done hundreds; possibly thousands.

I agree with Uncle Vanya. I have always connected the positive first, then made the ground connection to some exposed-metal part of the engine. (the alternator mount is generally good.)
I always remove that ground wire first when the engine is running.

Sometimes, I've found that the "safe" ground connection will not work (likely corroded terminals) and I have to connect directly to the negative post, but I always try a remote connection first.

We use a system which has a receptacle permanently wired into the electrics of the police car. The receptacle mounts on the bumper. With this, it's nearly impossible to incorrectly connect the leads, and since you don't make the receptacle connection till last, no danger of sparking.

[MRC_Hans]

I imagine the reason for connecting the '+' terminal first is because the bodywork on the vast majority of cars is connected to the '-' terminal, there is therefore a greater risk of accidentally shorting out the battery if the '-' terminals are connected first and the '+' jump lead is touching or touches the bodywork of the car while being connected.This is the correct answer and also the reason you should always disconnect the '-' terminal first and connect it last when respectively removing and installing a car battery: A loose lead or a tool accidentally touching other parts of the car will not cause a short.

I have a nice story about that:

Way back when I was in the Air Force, a couple of my fellow technicians were to install a radio set in one of the big fire-trucks (an air-base has some really big fire engines). So one of them, being a true technician, reckoned that it doesn't matter where you break a DC circuit. So, he proceeded to unscrew the tightening bolt on the '+' terminal of the truck's 24V battery with a large spanner. In the process the other end of the spanner touched a (metal) hydraulic line running above the battery......

It was not a nice walk for him up to the rather choleric colonel, who was fire chief, to tell him that several inches of hydraulic pipe had evaporated from one of his precious fire engines :eye-poppi.

Hans

[Uncle Vanya]

"Jump starts" are one of the services we render; I've done hundreds; possibly thousands.

I agree with Uncle Vanya. I have always connected the positive first, then made the ground connection to some exposed-metal part of the engine. (the alternator mount is generally good.)
I always remove that ground wire first when the engine is running.

Sometimes, I've found that the "safe" ground connection will not work (likely corroded terminals) and I have to connect directly to the negative post, but I always try a remote connection first.

We use a system which has a receptacle permanently wired into the electrics of the police car. The receptacle mounts on the bumper. With this, it's nearly impossible to incorrectly connect the leads, and since you don't make the receptacle connection till last, no danger of sparking.

We used to have those things on the buses in our fleet... except there was one major issue... the buses had 2 12V batteries in series, so it was a 24V system, our maintenance truck was a standard Dodge Ram truck (12V), we unfortunately couldn't use that receptacle when we needed to jump start. We actually had to jump each individual battery from the maintenance truck.

[mender]

By the way, boosting a Benz is a slower process than most. The later ones with all the modules won't allow the starter to be engaged unless the battery has enough charge to keep the voltage above a specific threshold while cranking to protect the modules. The latest SLs have a separate battery just for that and to maintain memory. The booster cables will need to remain hooked up with the boosting vehicle for a while to partially recharge the battery. I was the shop foreman at a M-B dealership and one of the guys on call for the M-B techline.

[ElMondoHummus]

My ex crossed the cables once and you be surprised how quickly a good set of jumper cables can melt away into nothing.

Yeah. I've experienced that before. I was sitting in the "jumper" car while a couple of other friends were connecting the cables to the dead "jumpee" one. As soon as the wrong lead clipped on... well, let me just say that the light show was incredible. Sparks everywhere.

One of the friends saved the day by doing something incredibly stupid and reaching in to disconnect the lead. And then he turned to bitch out the other guy who clipped it in wrong in full bellow, since that fellow just jumped back and watched the sparks fly. While I'm grateful that the first guy prevented anything worse from happening, I'm not sure I agree with his loud complaint that getting the hell away was the wrong thing to do. But regardless, no permanent harm done to either person. The cables didn't exacly melt away, but you can tell that the rubber near the end melted a bit. Surprisingly little actually, considering the sparkage, but it was still quite obvious. Scary, too.

My car ran fine after that; the dead one did once we got it correctly jump-started. From all the sparks, I'm surprised nothing got shorted on either end, but my car didn't show any signs of problems after that.

[alfaniner]

One suggestion... if you are the one with the live battery, make sure you are the one making the connections. The other guy always says he "knows" how to do it, but rarely does. After all, he's the one with the dead battery.

[shadron]

As long as everyone is piping up about warnings, here is another one (Bob B ought to know all about this one): remove any watches or rings you may be wearing. There is a danger that such jewelry might get caught in something mechanically since one of the cars is running to charge the other (and so loose ties, cuffs, shirt folds, fingers and the like are also at risk), but when working with high-amperage circuits like car electrical systems, metal jewelry might also complete a circuit, and even if only for a very short fraction of a second, they can heat to incandescence. It isn't fun to speculate on the injuries to the skin adjacent if this should happen.

People often feel safe in low voltage situations like cars, because the voltage is insufficient to kill by shock. However, wrapping a wad of steel wool around an AAA battery will show what even very low voltage can do in a low impedance circuit. See http://www.alpharubicon.com/primitive/doubleajaden.htm .

[shawmutt]

As someone who used to work as a mechanic, as well as someone who has melted several wrenches...

Worst I've seen is a guy fuse his wedding ring to a wrench. One of those lessons ya learn watching from afar ;)

[CORed]

This is the correct answer and also the reason you should always disconnect the '-' terminal first and connect it last when respectively removing and installing a car battery: A loose lead or a tool accidentally touching other parts of the car will not cause a short.

I have a nice story about that:

Way back when I was in the Air Force, a couple of my fellow technicians were to install a radio set in one of the big fire-trucks (an air-base has some really big fire engines). So one of them, being a true technician, reckoned that it doesn't matter where you break a DC circuit. So, he proceeded to unscrew the tightening bolt on the '+' terminal of the truck's 24V battery with a large spanner. In the process the other end of the spanner touched a (metal) hydraulic line running above the battery......

It was not a nice walk for him up to the rather choleric colonel, who was fire chief, to tell him that several inches of hydraulic pipe had evaporated from one of his precious fire engines :eye-poppi.

Hans

It's generally a good idea to disconnect the negative battery terminal when you are doing any work on a car, truck, etc. One time I skipped this step when working on the regulator of a propane fork lift. I had a line disconnected from the regulator, and managed to touch a live electrical terminal with a wrench and strike a small arc, and ignited propane leaking from the line. Not a big flame, but bigger than I could blow out. I had to use a fire extinguisher to put it out. No damage done, but a reminder not to cut corners with safety procedures.

[CORed]

As long as everyone is piping up about warnings, here is another one (Bob B ought to know all about this one): remove any watches or rings you may be wearing. There is a danger that such jewelry might get caught in something mechanically since one of the cars is running to charge the other (and so loose ties, cuffs, shirt folds, fingers and the like are also at risk), but when working with high-amperage circuits like car electrical systems, metal jewelry might also complete a circuit, and even if only for a very short fraction of a second, they can heat to incandescence. It isn't fun to speculate on the injuries to the skin adjacent if this should happen.

People often feel safe in low voltage situations like cars, because the voltage is insufficient to kill by shock. However, wrapping a wad of steel wool around an AAA battery will show what even very low voltage can do in a low impedance circuit. See http://www.alpharubicon.com/primitive/doubleajaden.htm .

A former co-worker got a third degree burn on his finger by completing a circuit to a motorcycle battery with his ring.

[GreyICE]

ARGH!

When you "jump" a car, you are essentially connecting the battery of the live car to the starter engine of the dead car. This starts the car. Thus you connect + to + and - to - because you're just bypassing the dead battery and using the live one. The alternator is what does the recharging.

When you connect + to - and - to + you complete a circuit through the battery. If the gigantic spray of blue sparks doesn't warn you this is a hugely bad idea, the discharging voltage through the battery is going to heat both batteries up mighty quick. Hot acid boils, and boiling acid expands. This breaks the battery open, spraying boiling acid around.

This hurts. A bit.

[MRC_Hans]

ARGH!

*snip*
This hurts. A bit.

Only when you laugh.

Hans

[MRC_Hans]

It's generally a good idea to disconnect the negative battery terminal when you are doing any work on a car, truck, etc. One time I skipped this step when working on the regulator of a propane fork lift. I had a line disconnected from the regulator, and managed to touch a live electrical terminal with a wrench and strike a small arc, and ignited propane leaking from the line. Not a big flame, but bigger than I could blow out. I had to use a fire extinguisher to put it out. No damage done, but a reminder not to cut corners with safety procedures.Absolutely agree. For my first car, I actually puchased an official maintenance handbook. It had the kind of step-by-baby-step repair instructions, that for instance after procedures hat involved jacking up the car ended with the steps:

- Lower the car.
- Remove the Jack.

In one of the procedures, which had nothing to do with the electrical system, one of the first instructions was "Unconnect the positive battery terminal" (this was a British car, and back then the British thought "since we drive in the other side of the road why not also have the plus to chassis, just to spite everyone"). I thought WTF? But a later par of the procedure had me operating a wrench in a very confined space very close to the starter relay, so I was glad I had followed the instruction.

12V (or 24 for that matter) cannot kill you, but high amperage can BURN you. The average car battery has short circuit currents in excess of a thousand Amps.

Hans

[Uncle Vanya]

Worst I've seen is a guy fuse his wedding ring to a wrench. One of those lessons ya learn watching from afar ;)

When I was working as a mechanic, we had a dude start working for us, he had a bunch of piercings (lip, nose, etc.) and wore rings. I worked for an old school mechanic, like he started as a diesel mechanic when he was 20, and when I was working there, he was nearing retirement age, probably retired by now. The first day this guy came to work, my boss took one look at him and said "Son, if you want to work here, you're gonna have to take all that :rule10 outta your face."

That also reminds me of a safety story regarding this guy, he would fervently enforce the use of safety goggles whenever we were working underneath a vehicle. Turns out that the reason for this was because when he was younger he was working underneath a car and a sliver of rust fell into his eye and punctured something or another.

Moral of the story, if someone with experience tells you to do something one way, just listen to them. I have mounds and mounds of stories (some involving me) of people who ignored safety because of laziness or otherwise who ended up with everything from minor injuries to missing fingers and broken bones. Sometimes it's more prudent to listen to the experienced guy than to be a skeptic about something, not all safety regulations are intuitive.

[ddt]

By the way, boosting a Benz is a slower process than most.

This not only holds for Benzes. I have a 5-year old Renault Laguna (diesel) with all the bells and whistles. Last year, I had a dead battery - I had forgotten to turn off the lights.

At first, I didn't even realize the battery was dead - when I operated the remote control of my car key, and the lights didn't flash, I first thought the battery of the remote control had died. Then I had to fiddle out the emergency key to unlock the door. (Renault has a credit-card sized key which you insert in a slot in the dashboard. The key contains a traditional type small key in one corner, which you can insert in a lock hidden in the door handle).

Only when I inserted the key into the dashboard and saw no lights flashing on I realised the battery was dead. Fortunately, I heard another diesel car about to leave the parking lot - the battery of a petrol car is not sufficiently powerful to operate a diesel starter engine. I asked the driver to help me out.

So I connected the jump start cables, sat in the car and immediately pushed the 'start' button. A lot of flashing lights, and some strange sounds, but no start. I waited some more, and pushed the 'start' button again, with the same result. I convinced the other driver to wait some more - a couple of minutes - and then attempted again. Only then the car would start.

In the process, though, something had partly fried the air conditioning unit - I couldn't adjust its temperature anymore.

[EvilBiker]

12V (or 24 for that matter) cannot kill you,
<snip>

Hans

No? Oh yes it can - the only thing preventing 12V from killing you is skin resistance:

Disclaimer: Do NOT try this without medical assistance in the immediate vicinity. Actually, do not try this at all and take my word for it.

Stick pin into left forefinger, until you draw blood. Leave it there, and try not to whine. Stick pin into right forefinger in the same way. Keep it down, you're waking the kids.

Get your scantily clad assistant to connect one terminal of a car battery to one of the pins currently sticking out of your finger, using any conductive method to hand. Repeat with other pin. Die.

In all seriousness, you can actually try this, but NOT with a 12V car battery - an AA cell will not kill you, but it will make you feel extremely uncomfortable if applied to your body as described above. You don't even need to insert the needles very deep, just until you start feeling a little pain.

I would connect the battery first and then prick fingers with needles slowly...

[ElMondoHummus]

Moral of the story, if someone with experience tells you to do something one way, just listen to them.

AMEN!

In so many of the jobs I've been in before - from part time summer factory jobs back in high school to theater stage work during college through to professional white-collar work post college, I've discovered the wisdom of that suggestion over and Over and OVER again. When it relates to electric safety - something you deal with on a musical theater and opera stage - you listen very carefully. A simple, small PAR can is bad enough if you mishandle it, but a freakin' 2k fresnel, or better (or worse) yet, a big ole carbon-arc spotlight... Holy Jeebus... that's a lot of current. Much in the same way a dump truck's a lot of dirt: We're talking sheer amounts here. Even on a smaller scale, talking about my current surroundings, opening up an enterprise class server with their big, beefy (for computers) redundant power supplies puts you in close proximity to serious current. It may not be on the scale of theater lighting, but it's certainly still enough to cause serious harm or death.

[Uncle Vanya]

AMEN!

In so many of the jobs I've been in before - from part time summer factory jobs back in high school to theater stage work during college through to professional white-collar work post college, I've discovered the wisdom of that suggestion over and Over and OVER again. When it relates to electric safety - something you deal with on a musical theater and opera stage - you listen very carefully. A simple, small PAR can is bad enough if you mishandle it, but a freakin' 2k fresnel, or better (or worse) yet, a big ole carbon-arc spotlight... Holy Jeebus... that's a lot of current. Much in the same way a dump truck's a lot of dirt: We're talking sheer amounts here. Even on a smaller scale, talking about my current surroundings, opening up an enterprise class server with their big, beefy (for computers) redundant power supplies puts you in close proximity to serious current. It may not be on the scale of theater lighting, but it's certainly still enough to cause serious harm or death.

Interestingly enough, I used to work as a stagehand in college (I've been around, I know). Another safety story comes from my days as a stage hand. Crew chief says "go up to the catwalks, one of the PARs is out, here's a lamp, do not, I repeat do not touch the glass of the lamp, wear gloves, or don't take the bulb out of the plastic bag it comes in." (Anyone who's done theater work knows where this story is headed by now). So I've spent a lot of time in the catwalks at this point, and I've helped other people replace lamps before, never really payed enough attention to how they did it though. So I go to replace the lamp, and the cans are difficult to fiddle with and the lamp doesn't just go in, you gotta push it in and there's a latch... I don't remember how it goes, but let's just say its a hassle for anyone who doesn't do this regularly. Seeing as this is my first time doing this, I keep the lamp in the plastic bag, but it's not easy widgeting the lamp into the can, lo and behold I accidentally touch the base of the lamp. I figure, meh, I barely touched it, what can happen. So I radio down to my boss "fire her up." Hey look, it works... What's that smell?... *Lamp asplodes*

[MRC_Hans]

No? Oh yes it can - the only thing preventing 12V from killing you is skin resistance:

Disclaimer: Do NOT try this without medical assistance in the immediate vicinity. Actually, do not try this at all and take my word for it.

Stick pin into left forefinger, until you draw blood. Leave it there, and try not to whine. Stick pin into right forefinger in the same way. Keep it down, you're waking the kids.

Get your scantily clad assistant to connect one terminal of a car battery to one of the pins currently sticking out of your finger, using any conductive method to hand. Repeat with other pin. Die.

In all seriousness, you can actually try this, but NOT with a 12V car battery - an AA cell will not kill you, but it will make you feel extremely uncomfortable if applied to your body as described above. You don't even need to insert the needles very deep, just until you start feeling a little pain.

I would connect the battery first and then prick fingers with needles slowly...Well, yes, perhaps. IIRR, the resistance of a human, sans skin resistance is somewhere around 200 ohms. For 12V, that's 60mA. 60mA DC will give you a jolt you won't forget soon, but it is not likely to kill you.

Anyway your scenario is akin to say: Sure a 12V car battery can kill you, ... if it's dropped on your head!" ;)

Hans

[Smackety]

I got to work on my motorbike for the next couple of days (the loan of the car was to save me having to freeze my extremities off on my usual form of transport during the dead of winter), until the car was ready. I then walked to the garage and collected it.

Great story, but - it took a couple days to replace an alternator?

I have crossed the jumper cables before, and almost completed the connection, but the clamp was sparking off the battery post so much I decided I must have it on the wrong way.

[MRC_Hans]

Oh, missed that one.

Actually, the moment I read that your engine died after switching on the light, I thought "faulty generator". You see, as long as the generator (=alternator) works, once the engine is running, your battery can be as bad as it wants.

But I have another question:

1984, British, old bike. Old british bikes ...drool (and girls on bikes, of course, but ...).

What kind of bike was it, and do you still have it?

Hans

I've got a good one similar to that.

I was driving my father's car from Scotland to Hertfordshire just after New Year, in about 1984. It was a fairly old car even then, a Datsun 100A. I had a crawling suspicion all was not well with the battery, so I had both jump leads and a battery charger with me, expecting I might have trouble getting going on cold mornings.

As it transpired, it was very lucky that I left early, and so I was nearly there by the time dusk fell and I had to switch on the lights. I had to stop at a big roundabout where the A414 joined the A1. The engine died on me, with all the symptoms of a flat battery. This was a bit of a bummer, as the family AA membership only covered my father as the named driver and not me. And I didn't have a spare bean to pay for a rescue.

Another motorist, also in distress having run out of petrol, helped me get the car off the road onto the grass verge just past the roundabout, then flagged down a passing vehicle. Darkness was falling and the car was very close to the traffic on the A1. Performing any sort of jump start would have been pretty dangerous.

The passing motorist took us both to a big garage a bit further up the A1. The other stranded guy got his petrol, but they didn't have any quick/cheap solutions for me. I therefore walked the half-mile to my home, and got my motorbike out of the garage. I then rode the bike to the nearby town centre where there was a big Woolco store which stocked motoring gear. I asked the assistant if they had a replacement battery for a Datsun 100A (because I really thought that was what the car needed), and was assured that the item proffered was the correct thing. It was sold ready-charged.

I strapped my purchase onto the bike's rear carrier and returned to the car. It was really dark by this time and the traffic was whizzing past only feet away. No way was I going to try to replace the battery there and then. I put the battery on the floor of the car, in the driver's foot-well, and opened the bonnet. I was able to connect the new battery to the old using my jump leads, trailing them in through the open side window, and then lowered the bonnet gently onto the leads without trying to latch it.

I got in the car and started it. No problem, first time. So I drove like that, with the window open, the mile or two back to my home. I then cornered a neighbour and begged a lift back to where I'd left the motorbike, and fetched it back home too. OK, it was a walkable distance, but did I mention it was dark and cold?

I then removed the old battery from the car and took it into the house, where I connected it to the mains-powered battery charger. However, I was unsuccessful in fitting the new battery into the car - it was slightly too short and too wide to fit into the appropriate space and fasten the clamp. And besides, it was pitch dark and freezing cold. I quit and went to choir practice (on the bike).

I left the old battery on the charger overnight. In the morning, I found it was absolutely sparking with charge, apparently raring to go. It really, really wasn't behaving like a dud battery. I still couldn't fit the new one into the car, so I put the recharged old one back. Car started, first turn of the key. So I drove to a nearby Datsun dealership.

There, the car was diagnosed with a dud alternator, which explained why the engine died the first time I tried to idle it after switching on the lights. There was nothing wrong with the battery at all.

I left the car there to be fixed, walked home, and got out the trusty motorbike again. I looked at the new battery. It was pristine. I still had all the packaging, and the receipt. I packed it back up in its original box and took it and the receipt back to Woolco, explaining (entirely truthfully) that I'd bought it the previous afternoon, but it was the wrong size for the car. They happily refunded my money.

I got to work on my motorbike for the next couple of days (the loan of the car was to save me having to freeze my extremities off on my usual form of transport during the dead of winter), until the car was ready. I then walked to the garage and collected it.

My Dad coughed up the price of the new alternator - it was his car, after all.

So the rescue from the side of the A1 in the dark cost me precisely nothing.

Rolfe.

[pipelineaudio]

Regarding not connecting negative to the battery, but to the car body instead to ward off explosions, get rid of any battery you suspect could do this

Old timers around here tell us stories about batteries blowing up because of tumbleweeds caught on headers or sparking from rocks, but honestly, there are so many potential causes of sparks when you have a hood full of moving parts and road and debris flying by at 80 miles per hour

If you think your battery can blow up from having a spark near it ( which I do understand is the case with many battery types), it doesnt belong under the hood of a spark factory. Throw an Optima in there or something. People use them as on trail welders with sparks flying like mad

[CaveDave]

This not only holds for Benzes. I have a 5-year old Renault Laguna (diesel) with all the bells and whistles. Last year, I had a dead battery - I had forgotten to turn off the lights.

<snip>

So I connected the jump start cables, sat in the car and immediately pushed the 'start' button. A lot of flashing lights, and some strange sounds, but no start. I waited some more, and pushed the 'start' button again, with the same result. I convinced the other driver to wait some more - a couple of minutes - and then attempted again. Only then the car would start.

More likely, the lights being left on will take the battery down to an extremely discharged state (near -0- voltage), whereas a too-weak-to-crank battery still has several volts open circuit, but a high internal resistance (the voltage drops if you turn the key, but will then recover somewhat). A totaly discharged battery has to be recharged a while before the terminal voltage comes up enough to allow starting (the heavy load on the boost cables can't keep up with all that demand).

In the process, though, something had partly fried the air conditioning unit - I couldn't adjust its temperature anymore.

I would bet that the problem was that the lack of any voltage caused the A/C sestem to "forget" the blend door position and it just needs recalibrating. Most any late-model european cars (Saab, Cadillac Catera, etc.) use stepper motors for the blend doors and the position must be "known" by the controller at all times. On all the cars I have worked on with these, disconnecting the battery wipes the memory and you must go through a procedure such as:

1. Turn ignition on, engine off.
2. Press "off" and "auto" buttons on climate control head simultaneously, and hold for at least five seconds.
3. Listen for "clicks" behind dash or odd display on panel while calibrating (may take a minute to finish).
4. Start engine and test for proper functioning.

There are different "magic dances" for different cars.
Our information system is down right now or I could look it up and tell you (give me the year/make/model/engine size and I'll look it up tomorrow or whenever the system is fixed).

HTH

Dave

[luchog]

I worked on cars for about five years, and had a battery explode while connecting the negative for the dead battery. Ever since I make that final connection on a metal part of the car, not the dead battery.
When I was a kid, my dad managed to blow up a battery doing the same thing. Got some minor acid burns as a result.

He still insists on making the connections directly to the battery terminals. :rolleyes:

[shawmutt]

Stick pin into left forefinger, until you draw blood. Leave it there, and try not to whine. Stick pin into right forefinger in the same way. Keep it down, you're waking the kids.

Get your scantily clad assistant to connect one terminal of a car battery to one of the pins currently sticking out of your finger, using any conductive method to hand. Repeat with other pin. Die.

Clear cut case of acupuncture moving energy through the body :D

[MRC_Hans]

Regarding not connecting negative to the battery, but to the car body instead to ward off explosions, get rid of any battery you suspect could do this

Old timers around here tell us stories about batteries blowing up because of tumbleweeds caught on headers or sparking from rocks, but honestly, there are so many potential causes of sparks when you have a hood full of moving parts and road and debris flying by at 80 miles per hour

If you think your battery can blow up from having a spark near it ( which I do understand is the case with many battery types), it doesnt belong under the hood of a spark factory. Throw an Optima in there or something. People use them as on trail welders with sparks flying like madOh, I've had a car battery 'blow up' during charging because we were careless with wires (charging it on a table with some loose wires). All that happend was that part of one of the stoppers came off. Modern batteries rarely have them, but old ones had a screw-in stopper for each cell, so you could inspect and top up the fluid. They usually consisted of two parts: A bottom part which basically was the stopper, and a small coloured plastic lid. This explosion blew the small lid off. ... While gas/air explosions can be quite powerful, they do not produce a terribly high pressure, and they don't expand very fast (as explosions go), and I doubt they can actually blow up the casing of a car battery, which has to be quite strong to hold pounds of lead together while bolted inside a car.

Hans

[MRC_Hans]

When batteries do blow up, as some report, I suspect it is not just a gas explosion. The fluid heated to the boiling point, or an internal short-circuit is much more likely to do the job.

Hans

[CaveDave]

Oh, I've had a car battery 'blow up' during charging because we were careless with wires (charging it on a table with some loose wires). All that happend was that part of one of the stoppers came off. Modern batteries rarely have them, but old ones had a screw-in stopper for each cell, so you could inspect and top up the fluid. They usually consisted of two parts: A bottom part which basically was the stopper, and a small coloured plastic lid. This explosion blew the small lid off. ... While gas/air explosions can be quite powerful, they do not produce a terribly high pressure, and they don't expand very fast (as explosions go), and I doubt they can actually blow up the casing of a car battery, which has to be quite strong to hold pounds of lead together while bolted inside a car.

Hans

Don't kid yourself, Hans.

I made the same assumption when I first starting working on cars -- then I learned the hard way!

I had a pinch clamp bolt that was corroded too much to loosen, so I decided to cut the bolt with an abrasive cut off wheel in an air powered die grinder. As the cut was progressing, throwing sparks, the wheel cut into the three-cell vent/fill cap slightly, just enough to let the sparks enter the upper chamber.

The resulting explosion ripped about 80% of the cover off in sharp shards that cut my hand (holding the air motor directly above the battery) badly, threw acid in about a six foot radius, and bulged the case cracking it in several places. My hand stopped the bulk of the shrapnel and acid from hitting my face square on, but I was lucky to be only 15 feet from a wash sink and wearing glasses. My ears rang for fifteen minutes.

The battery was a Sears Die-Hard only a few years old and 5 of the 6 cells detonated.

DO NOT TRY THIS AT HOME!!

Dave

[MRC_Hans]

OK, I bow to experience. Gas/air explosions can be quite violent, but the free volume over the battery fluid is not very big. Since your sparks came from a tool that should prove that only gas was responsible for the explosion.

Hans

[bruto]

OK, I bow to experience. Gas/air explosions can be quite violent, but the free volume over the battery fluid is not very big. Since your sparks came from a tool that should prove that only gas was responsible for the explosion.

HansPart of the problem, I think, especially with older batteries, is that as the battery ages, and especially if it has not been maintained and kept full of water, there's more air space in the case to fill up with hydrogen, and of course it's just those poorly maintained batteries that are most likely to need a boost. It may be less of a problem with the "maintenance-free" batteries we see nowadays. These batteries are not actually capless, it's just that the caps are flush with the top, and usually covered with labels so that their separability is not obvious.

[skeptigirl]

...

There's a couple of different ways to go about it, but here's one example. You have two cars, one car has a dead battery and the other has a live battery.

1. Start the "live" car and remove the battery with the engine still running. The car should continue to run as it should only need the battery to operate the starter, not to keep it running.

2. Remove the dead battery from the other car and hook it up to the running "live" car.

3. Wait for the formerly dead battery to get recharged in the live car, at which point you simply put both batteries back into their original cars.

I should say that I've never tried this, so I'd be interested to hear if anyone else has?Sheesh, it's a lot easier to jump the dead battery and let that car charge it up. :rolleyes:

[skeptigirl]

I can see the rationale for this, however doing an internet search the advice is not consistant on this issue - some say connect to the bettery "-" terminal and others say grounded metal in the engine.When in doubt, look for the rationale. As has been noted here, connecting the negative terminal to the car frame directs any inadvertent spark away from the battery.

Also, in figuring out who is right when the instructions have people connecting the cables in all sorts of different order, look for the rationale. You want to avoid having the completed circuit to the live battery until you are ready for it.

This site (http://www.carbuyingtips.com/jumpstart.htm) included the rationale. That gets my vote. Why do the battery charger cables have to be connected in this order?
The reason why you connect the battery cables to the dead car battery first is you have 3 metal cable ends dangling and potentially touching metal car parts, so a dead battery is less likely to cause any sparking, since it has little or no voltage. So that is the safest starting point for your jumper cables.

The 2nd battery cable clamp goes to the positive end of the good battery instead to minimize completing any circuits until we are ready to. Then the 3rd end of the battery cable goes to the ground of the good battery. Remember, we still have not completed the circuit yet, until the 4th battery cable clamp is attached to ground. This is why this order of attaching the battery cables to your car batteries is the safest way to do it. It minimizes unnecessary sparking until the charging circuit is completed. This is good practice because excessive and unnecessary sparking could cause car batteries to fail.

Since the bad battery is weak, and to prevent exploding, it's ground clamp gets connected last, but not directly to the ground battery post. To prevent sparking directly on the battery, you connect the 4th battery cable clamp to a metal frame part of the dead car, which is connected to the minus pole of the battery. Many people are easily confused by this step. They cannot figure out how this completes the circuit to the battery. Car batteries have their ground cable also wired to the chassis of the car, so by clamping to a good metal chassis point, this is electrically equivalent to connecting to the ground post of your car battery.

[CaveDave]

OK, I bow to experience. Gas/air explosions can be quite violent, but the free volume over the battery fluid is not very big. Since your sparks came from a tool that should prove that only gas was responsible for the explosion.

Hans

Part of the problem, I think, especially with older batteries, is that as the battery ages, and especially if it has not been maintained and kept full of water, there's more air space in the case to fill up with hydrogen, and of course it's just those poorly maintained batteries that are most likely to need a boost. It may be less of a problem with the "maintenance-free" batteries we see nowadays. These batteries are not actually capless, it's just that the caps are flush with the top, and usually covered with labels so that their separability is not obvious.

Exactly.

The unit in question was a few years old (the summer heat around here kills most batteries in 3 to 6 years) and the car was old and had been having problems, which was why I needed to get the cable clamps off. I'm sure it was sulphated and had boiled out some electrolyte so it had more headspace for gas build-up. The tied-together vent caps must have allowed more cells to ignite than singles would have, too.

Dave