Give me the the Straight Dope on jump-starting cars

Hmmm. I’m not sure why this would be the case. Unless the running voltage for a car (which is usually around 14 V) is a tad bit too high for a motorcycle…

umm… no.

do you notice how the most expensive cables are the biggest gauge? 8 gauge cables are cheap, why? because they are itty bitty. they get really hot jump starting a car. 0/2 gauge cable is expensive… they dont get hot because they have a huge capacity.

those little cigarette lighter jokes? even if they had thick cable (and i have never seen one that does!), the wiring connecting your cigarette lighter is only about 16 gauge… dont even waste your time with those.

Here`s something I have learned by jumping many vehicles.

Turn the headlights on on the dead car after you think you have made a good connection with the cables. This will let you know if you are getting juice from the running car or not.

Also, if you have good connections with the cables the dead cars lights chould come on nice and bright and the car should start right away, not necessary to wait for the battery to charge up first.

Good advice, whuckfistle. Just remember to turn the lights out before you try to start the car.

Most advice here is pretty good. I will just add one caveat ( for the operator’s safety, not specifically necessary to start the car):

Do NOT attach the positive and negative cables to a single car first. If you do, and have the other set of clamps in your hands, your body could complete the circuit with a small slip off the insulation. Even if you do this on the dead car, while there might not be enough juice to crank the engine, there could easily be enough to fry you pretty good.

Do NOT attach the positive and negative cables to a single car first. If you do, and have the other set of clamps in your hands, your body could complete the circuit with a small slip off the insulation. Even if you do this on the dead car, while there might not be enough juice to crank the engine, there could easily be enough to fry you pretty good.

It won’t fry you. You probably wouldn’t even notice it. (You can check it out by touching the two posts of a 12 volt car battery simultaneously.) However, if the two clamps were to touch each other, the short circuit could fry an alternator or ECU (“computer”), and possibly arc weld the clamps together. If that happens, and those clamps make contact for very long, it could set the cables on fire. Not good.

I dont think you can get nailed this way. Put your thumb and finger on the posts of a car battery and you wont feel a thing. Even if they`re wet. Too much resistance in your body and not enough voltage in the battery.

Thanks GARYT.

Uh guys, be careful here. Remember that electricity follows the path of least resistance. So when you touch the posts of a battery the current already has a nice path and has no reason to use you. You’re not completing a circuit–it was already complete. This is not at all the same as having a positive cable end in one hand and negative in the other.

How much could it hurt you? I don’t know.

Huh? I don’t understand your point. What exactly are you saying is dangerous?

I just bought a cheap car for my girlfriend to get her to and from work. We went to the beach about a week ago and when we went to start the car the battery was dead. Being an auto we couldn’t jump it so I managed to get my hands on some jump leads and we did it that way.

We bought a new battery for it the same day but today the battery was dead again when she tried to start it up.

So I’ve come to the conclusion that either the alternator has had it or that something is draining the power once the engine has been switched off. Would the battery cope with over a weeks usage if the alternator had broken? If not what could be draining the power? I’ve fitted a new stereo but the original problem, when we were at the beach happened before this.

Any advice would be greatly appreciated.

The reserve capacity (how long the battery will supply power in the event of an alternator failure) is rated in minutes not weeks.
As far as what could be draining the power, almost anything. dome light, trunk light, glove box light, a stuck relay, a short in the wiring. Lots and lots of things.
If you do not have any electrical test equipment, then I suggest that you take the car to a shop to be checked out. (or perhaps back to where you bought the battery)

Sorry, but it is indeed the same. You don’t know what you’re talking about.

Well, Parthol are you just completely confused now?

Like I asked before…what make and model?

I’ve only used jumper cables to start about a thousand different vehicles (mostly older US manuf. vehicles) and have never blown up a battery or burned up an alternator and have hooked up both clamps to the vehicles one vehicle at a time most times. (my father and brother are both mechanics w/ their own garages) I’ve worked w/ them for 30+years…these guys are trying to scare the shit out of you.
(BTW some of the old Fords have a pos. ground)

NEW/LATE model vehicles: Check the owners manual…if you have any doubts.
The most frequent screw up is burning out the MAP sensor.

Here’s a good surefire way to jump off another car.

The dead car and the live car, both ignition switches off.

Hook up pos. clamps to dead car then live car.

Next, hook up neg. clamp dead car on frame…then hook up neg. clamp on live car frame.

drivers in each vehicle…dead car attempt start…if no good then driver crank live car…idle up for minute…attempt crank dead car…if not started after three attempts…go get GOOD battery and exchange
Unless your owners manual specifies different this has never caused a problem in my experience w/ the exception of not finding a good ground, in that case the battery’s neg will work.

Good luck…
(you guys):rolleyes:

I’d tell him how to jump it to the starter to avoid all of this BS but I’m afraid we’d all wind up in the pit…:wink:

Future Kid …unhook the battery when its parked until you figure it out.

or Start a new thread and ask this question again.

No need to worry about bigger capacities… I start my bike with a car battery in the sidecar- if the voltages were higher, it might make a difference. But they’re not.

You’re right that you definitely don’t need the car running, though.

Try it once. You could tap dance naked on that battery in or out of the car and you wouldn`t get shocked.

Extending the posts with the jumper cables and then completing the circuit is the same as just touching the battery itself.

True, if the battery is connected in the car there is a completed circuit, but have you ever heard of parallel circuits?

…if the battery is connected in the car there is a completed circuit…

Actually, simply having a battery connected to its cables does not necessarily complete a circuit (just one of Grapes’ misconceptions). Some electrical consumer in the vehicle must also be switched or wired on.* But you are quite correct in stating that one wouldn’t get shocked, there is no difference between touching the terminals and touching the ends of cables connected to the terminals (another misconception), and the presence (or absence) of one complete circuit is irrelevant to some other complete circuit (another misconception).

*In modern cars, with everything switched off, there would be wired on completed circuits to the ECU (computer) memory and radio memory, which perhaps you were referring to. Still immaterial to the question at hand, as you noted.

2 points, for additional info…

  1. It’s possible to jumpstart a motorcycle with a car. Nothing wrong with it at all, a lot of people seem to think it would be harmful to the bike. Although doing it the other way around would be a bad idea - the bike’s battery & alternator aren’t meant to put out enough current to start a car - I’ve successfully jumpstarted a huge Lincoln with a '78 Honda CB750. (The battery was just run down enough not to start the car, on a warm day - my friend had been working on the stereo & the interior lights drained the battery)

  2. All the worry about which connection to make first & attaching the negative clamp to ground & not the dead battery’s negative terminal etc. is just about safety…hydrogen & oxygen & a spark are a bad combo, as anyone who watched the Hindenburg disaster can attest. Also, if you’ve got both clamps on the “good” battery, there’s a chance both of the other clamps might touch a conductor, or each other, and cause a short circuit. Batteries can explode if this happens - it happened to a buddy of mine, fortunately the worst that happened to him was he didn’t grow any hair on a spot of his chin for about 11 years. It could have been much worse. Safety considerations aside, it makes no difference what order the cables are put on.


How many power generation technologies can you name that people want to put in their backyard?

  • Richard Chleboski

Good grief.

Quite right. Though in my own little world, where the discussion led my mind to wander about household wiring and I for some unfathonable reason carried that analysis back into the discussion it all made perfect sense. :smack: Brain fart. :smack:

At least the subsequent discussion was worth reading.