Failed jump start

Thread Starter

nicksv

Joined Nov 22, 2019
15
I don't really know if this is the forum to ask this sort of question, and sorry if it ain't, but i'm curious, so here goes.

Today i pulled into a gas station, stopped mt car, when i got out again and tried it start, it was low on battery, so it would not start.
Asked some guy to jump start me, and he agreed to do so.
Pulled out my jumpers and connected them to my battery. he opened his hood and connected the positive to some positive connection on his engine, and then connected the negative to (what he thought was the negative on his battery, but was really possitive).

I did not know that now both jumpers from my car went to possitve on his car, so i got in my car and turned the key, but everything was completely dead. like there was 0 Volt on my battery :O

Jumped out and noticed that the one he should have connected to negative on his battery, was on the possitive.

I told him and he switched it around, then everything was fine, my car started up, and it looks like no damage was done.

My question is, in that situation what actually happens. does that just drain my battery, how does the power flow when both possitive and negative from my car are connected to possitive one his car?

All i know is that the jumper that went from my negative to his possitive got very hot *ouch*

Thanks in advance :)
 

SamR

Joined Mar 19, 2019
1,302
It shorted both batteries to ground hench the "HOT" cable. A common mistake and will burn up the insulation on cheap small gauge wire cables. Usually, other than ruining a set of cheap cables, not a real problem if corrected quickly.
 

Thread Starter

nicksv

Joined Nov 22, 2019
15
It shorted both batteries to ground hench the "HOT" cable. A common mistake and will burn up the insulation on cheap small gauge wire cables. Usually, other than ruining a set of cheap cables, not a real problem if corrected quickly.
So it is really just the jumper cable that suffer? And the batteries as well i guess?
Don't know if it was quick, but i guess the problem was sorted within 15-20 seconds
 

AlbertHall

Joined Jun 4, 2014
8,551
You shorted the flat battery in your car. It was just as well it was flat. If it had been a good fully charged battery it would definitely have released the magic smoke from the jump cables. Even then the battery would probably not have been damaged providing it was only for a short time.
 

dl324

Joined Mar 30, 2015
9,154
My question is, in that situation what actually happens. does that just drain my battery, how does the power flow when both possitive and negative from my car are connected to possitive one his car?

All i know is that the jumper that went from my negative to his possitive got very hot *ouch*
The good samaritan shorted your weak battery. Luckily it was weak.

Next time don't trust that they know what they're doing and check their work, do it yourself, or check that their connections are correct before connecting to your car.

If you battery is weak, replace it before it kills your alternator.

I drive my car so infrequently that the battery is often too weak to start it. I carry a lithium ion jump starter in our two cars; before that, I used the bulkier lead acid versions.
 

dl324

Joined Mar 30, 2015
9,154
Note the order of connecting and disconnecting the cables in the link below. This minimises the risk of magic smoke.
https://www.rac.co.uk/drive/advice/car-maintenance/how-to-jump-start-a-car/
It doesn't matter which battery you connect to first if you pay attention to not short anything and make the ground connection on the last connection to something metal; preferably as far as possible from the battery to avoid a potential explosion if there's an accumulation of hydrogen gas from the battery.
 

Thread Starter

nicksv

Joined Nov 22, 2019
15
The good samaritan shorted your weak battery. Luckily it was weak.

Next time don't trust that they know what they're doing and check their work, do it yourself, or check that their connections are correct before connecting to your car.

If you battery is weak, replace it before it kills your alternator.

I drive my car so infrequently that the battery is often too weak to start it. I carry a lithium ion jump starter in our two cars; before that, I used the bulkier lead acid versions.
Thank you all for your replies, i'm sort of a hypocondia, an was thiking it may had done some damage that was not yet apparent.

You are right, he was driving in some industrial cooling van, with work clothes, i figured he would be able to connect it properly.
but you are right, i should have checked how he connected before i connected to my own car. Just maybe a bit disrespectfull doubting his skills when asking a favor :D

And no worries about the alternator, it's been charging poorly for a couple of years now, it has been fine during summer time, but during winter i have had to make sure to turn off stereo and anything else that consume power 5 minuttes before i parked at home, else i would not be able to start the next morning.
I even have a new alternator that i should replace the old one with.

Only reason i have not done it yet, is cause.
Before the alternator went bad, the headlight bulbs only lasted like two months.
Then the alternator started charging poorly, but the headlight bulbs i'm using now worked for 2 years+
So i figured then i would just wait replacing the alternator until it was charging so poorly that my car would not start.

My car is an old Peugeot 206, and i think that maybe peugeot had a problem with headlight bulbs getting too much power on the 206. Cause i have very often seen peugeot 206's with broken bulbs.

That is just me guessing and i ain't the brightest bulb either ;)
 

SamR

Joined Mar 19, 2019
1,302
avoid a potential explosion if there's an accumulation of hydrogen gas from the battery.
I thought about mentioning that but with today's modern sealed lead/acid and GEL cells it is no longer an issue. Having a battery blow acid in your face was a real problem in the "old days".
 

Thread Starter

nicksv

Joined Nov 22, 2019
15
It is best to be diplomatic, but some people don't know much. I've had people tell me that jumping a vehicle could damage the ECU. Don't know how a myth like that got started.
You are right, i should have checked how he hooked it up before hooking it up on my own car, could have been even worse and he reversed the polarity :O

But thinking about what you said, with a bad battery killing the alternator, come to think of it, then maybe i actually killed the alternator my self, postponing a battery change :rolleyes:

Just did not know a bad battery could kill the alternator, is that because the alternator is charging all it's got all the time, or is it because the battery collapse and short circuit in some way?

thanks again :)
 

MaxHeadRoom

Joined Jul 18, 2013
19,198
You are right, he was driving in some industrial cooling van, with work clothes, i figured he would be able to connect it properly.
but you are right, i should have checked how he connected before i connected to my own car.
There is also a recommended way of removing/changing a battery.
Always remove the negative lead first.!
And connect it last on the new one..
This is in the event that when removing the positive post connection, if the wrench contacts chassis accidentally, there is no melted wrench!
Max.
 
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dl324

Joined Mar 30, 2015
9,154
Just did not know a bad battery could kill the alternator, is that because the alternator is charging all it's got all the time, or is it because the battery collapse and short circuit in some way?
The alternator is working harder than normal when the battery is dead or weak.
 

dl324

Joined Mar 30, 2015
9,154
This is in the event that when removing the positive post connection, if the wrench contacts chassis accidentally, there is no melted wrench!
It could be worse than that if the battery welded the wrench to the chassis and the battery exploded before you correct the situation.

The recommendations for connection order and location are to minimize the risk to people who don't know what they're doing.
 

Thread Starter

nicksv

Joined Nov 22, 2019
15
The good samaritan shorted your weak battery. Luckily it was weak.

Next time don't trust that they know what they're doing and check their work, do it yourself, or check that their connections are correct before connecting to your car.

If you battery is weak, replace it before it kills your alternator.

I drive my car so infrequently that the battery is often too weak to start it. I carry a lithium ion jump starter in our two cars; before that, I used the bulkier lead acid versions.
oh i did not even know theres a corrent order :oops:
I had allready connected both jumpers on my car before heconnected the possitive on his car to the possitve on my car, and then also possitive on his car, to negative on my car. And his car was running the whole time :oops:
 
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