Jump starting cars and reversing the poles

Factual Questions
1

Without getting into details (read: airing my own stupidity), let’s say that while attempting to jump start a friend’s car, one were to reverse the positive and negative connections on the car doing the jumping. In other words, the receiving car is hooked up correctly, but the car providing the jump has the wires reversed.

Let’s further say the cables melted but were removed before anything could explode or anything like that. The donor vehicle is still running, and was able to be started after being turned off. There are no scary dash warning lights on, but there IS white powder on the positive terminal.

What are the chances that the donor car has been monumentally screwed up in some way that has yet to manifest itself? Is it likely the battery is now damaged? The charging system? Is there a period of time after which if nothing bad has happened I could feel better about my car’s long-term health?

2

Highly likely. Average cars are not grounded properly to give jumps, so even correctly jumping can damage a car, especially today when nearly all cars have an onboard computer.

If the donor car is a pickup truck or work vehicle, it may have proper grounding.

3

So when you say “highly likely”, highly likely what? The battery’s wrecked, the car’s electrical system… Help me properly calibrate my level of anxiety.

4

back 20 years ago, a friend I knew used to refuse to give boosts. He claimed that those sort of errors or more likely, shorting the wires by letting the dangling clips touch - would damage the alternator rectifiers with overcurrent. This would mean that they would fail a lot sooner. Of course in those days detroit crap needed new alternators randomly every few years anyway - usually because the rectifier diodes died; so it’s difficult to know if he was right. I t sort of meade sense, though.

Of course, draining and charging the battery to much is not good for it, but that’s more along the lines of the old “leave te lights on til the battery died” a dozen times in a summer. And, with today’s sealed batteries, you can’t just top up tthe water; and charging a battery in an enclosed space runs the risk of hydrogen production. One friend ended up in the hospital when he removed the charger clip from the battery post, creating a spark which blew a hole in the battery and splashed acid into his face and eye.

the real story is - don’t make a habit of it. Learn from your mistake(s).

This is why you first clip the grounds - chassis - together, not ground posts on batteries. Then connect the live (Positive, IIRC) from the running car to the dead car.

5

Thing is, I know how to jump a car (although I only ground to the chassis on the receiver’s side, on the donor side I connect to both posts.) What I’m looking for is more of a prognosis, or the likelihood that the donor is messed up to an expensive extent.

The jump start itself did not fail due to lack of knowledge, but lack of execution.

6

I hooked up jumper cables incorrectly once (If I had wiped more of the grime off the other battery I would have noticed the little pole identifiers). All it did was melt the jumper cables. But this was back in the seventies. Maybe GaryT will spot this thread and drop by to give us the correct answer soon.

7

Sparks happen when/where you make the last connection; in the above description, this will be at the dead battery. Bad juju.

What I was always told:

-connect positive lead to dead-battery+. (do not allow other end of positive cable to dangle and touch anything, since chassis=ground.)
-connect other end of positive cable to live-battery+.
-connect negative lead to dead-car chassis somewhere away from the battery.
-connect other end of negative cable to live-car chassis somewhere away from the battery.

If there’s sparks, they’ll happen when/where you make that last connection on the live car away from the battery.

Sparks may happen when you disconnect too, also, so disconnect in reverse order.

8

Great combination of user name/topic.

  • Theoretically *, you should be OK, in that all the current that you generated should have been confined to the loop consisting of the two batteries and the jumper cables. So it wouldn’t surprise me if you shortened the life of your battery, but they’re cheap, so that would be the least of your problems.

The battery you were connecting to was flat, so I wouldn’t think you’d have introduced a reverse voltage to your car (the other car is another story).

In the non-theoretical world, there might have been some kind of transients or voltage spikes introduced into the system, although I think any kind of major damage would show up almost immediately.

9

Thank you Finagle. That’s what I was looking for.

For the record, I follow Joe’s method of cable connection.

Never even thought about my user name when I was posting this- maybe I should change my name to Sparky, or Melty.

10

You’re lucky the car getting jumped wasn’t damaged. The charging car really shouldn’t be a problem. Crossing jumper cables can destroy radios, amps, blow fuses and in extreme cases even ruin an alternator, or worse, your car’s EFI or PCM (although they are usually protected with a relay that opens if reverse current is applied to it). Not mention you can blow up your battery.

11

I would be worried about the friend’s car. Do you know that it is OK?

From a similar stupid act (I installed a battery backwards) the following items had to be replaced: ($$$)

Alternator
ECU (engine computer)
Several expensive relays
Ignition module
Just about every fuse in the fusebox

Not recommended, especially if you drive a european car. Fortunately I was able to obtain junkyard replacements for many of these, and avoided spending $1200 on a new ECU, for example.

12

Oops. I may have gotten the live connect backwards - IANAM.

The alternator and overall electrical is in parallel with the battery, so if anything interesting happens, like too much current, you may have weakened the alternator rectifiers. I don’t know. The donor car is running, so as the voltage drops due to the shorted load, the alternator will try to put out more power to keep the voltage at optimal level…

Basically, if the boosting car’s alternator (or other significant electrical/electronic component) dies in the next 6 months, he may blame you… He may or may not be right.

13

How likely is this (preferably with an authoritative cite)? Likely enough that I should refuse someone who needs a jump, even at the risk of looking like an unhelpful a-hole? or that I should ask anyone else for one if I ever need one?

14

I’ve had my Ford E-150 van jumped at least 6 or 7 times in the past 8 years.

I always seem to forget to turn off the dome light.

Never hurt my van or the donor. It shouldn’t unless the cables get crossed like the original OP mentioned.

When I’m stuck in a parking lot, it’s cold and I need a jump. I hope people say yes. I’ve helped quite a few people in the same predicament.

15

Don’t know yet. Having melted our only pair of cables, getting his car out of the parking garage has been postponed for a day. Since I was ultimately the dillhole, I’d certainly offer to make good on any damage my helpfulness caused.

16

idiot proof jumper cables are great,
I picked up a pair of interesting ones from think geek recently that charge via the cigarette lighters. they also have some that you connect the clips to the batteries then connect the cables in the middle.

17

Any type of modern electronic device will have reverse polarity protection built-in, I am not worried about reverse-polarity.

Rectifiers, which are comprised of diodes, limit current flow to one direction. They usually have a reverse polarity voltage which is pretty high. A standard diode will usually have a reverse polarity voltage of 50. Sometimes it’s higher. But, that’s for voltage and not current. It’s the current that I am worried about…

The bothersome part is that the jumper cables melted and they are usually pretty thick cables. The melting indicates that a “short” was occurring, namely through the destination battery, and then the cables melted and that’s your hidden problem. Anything within that connected “short-circuit” will possibly have been degraded if not damaged.

I am an electronics technician and I dread seeing a power supply with similar damage. As it almost always means that whatever it was powering is now toast. They go hand-in-hand.

Obviously, your car is fine as it is running. However, your friends’ car may have suffered severe damage. Are there any different indications from before this experiment and now? Did any dash lights turn on? I guess it won’t be until you have your new set of cables and apply power will you know.

If you are somehow lucky: no damage.
At the very least depending on how robust the electronics are: damaged fuses, maybe a relay or two.
Worst case scenario: you blew out a lot of stuff during that “short” and it’s like what awldune said.

Until proper power is applied it’s all up in the air.

18

I doubt the current rating of a cigarette lighter can handle a starter for a car. Just look at the thickness of the wires going to your starter and that “cigarette jumper cable” and then a proper pair of jumper cables. There is a reason why they are so thick. If your car is weak that might work. But, if it is totally dead, I would not do that. I can easily see a blown fuse if not some toasted wires within the dashboard.

eb

19

Electrical engineer checking in here.

The cigarette lighter jumpers don’t supply anywhere close to enough current to start the car. They aren’t designed for that. What they do is slowly charge the dead car’s battery from the live car’s battery and alternator. Once the dead car’s battery has enough juice, you use it to start the car.

This has the advantage of being safer (you won’t blow stuff up if you connect it wrong or short something and it’s harder to connect it wrong anyway), but it has the disadvantage that it’s slow since you have to wait for the other battery to charge. It also won’t work at all if the dead car’s battery is completely shot and won’t hold enough of a charge to start the car.

You don’t have to worry about it blowing fuses or burning up the wiring because the thin wire is high enough in resistance to prevent a dangerous amount of current flow. It will let enough current flow to charge the other battery (slowly) but it won’t let enough current flow to be dangerous.

As to the OP, chances are if nothing is damaged now that you’ll be fine. You may have overstressed your alternator a bit, and there is a small chance that you may still see some damage later, but most likely since everything is ok now it will stay that way. Since the other car was dead, it probably wasn’t able to get a negative voltage onto your car’s electronics, which really would have damaged things.

The other car may not have fared so well. Since it was the dead car, it was much more likely to receive a reverse voltage to all of its electronics. As previous posters said, things like the engine computer, alternator, and other components including the wiring may have been toasted. The best case would be that they need a new battery. The worst case is that you are talking about several thousand dollars worth of damage.

Joe Frickin Friday’s instructions for how to make the battery connections are good. Technically you don’t need to make both negative connections away from the battery, but you absolutely want to make sure that you make the last connection to the chassis and not to the battery. Batteries tend to explode for two reasons. The first is that they produce hydrogen while being charged, and that hydrogen can explode due to a spark. The second reason is, if you’ve got a really dead battery or you’ve hooked them up backward, you can get an awful lot of current flowing (enough to melt the insulation off of pretty thick wires, as the OP discovered the hard way), and this excessive current can cause the electrolyte in the battery to boil with the result that the battery explodes. Either way, if you are close to the battery at the time you can get battery acid and bits of plastic and metal sprayed up into your face and eyes, which is just no fun at all.

20

After we were done, we pushed his car back into its spot. Not that it would take much juice or anything, but the remote trunk release still worked, and his headlights still came on.