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This morning a friend's car battery was flat and they needed a jump.
I left them to set up the leads and got in my car and started it. Within 30 seconds, I smelt and saw smoke. The jump lead was on fire.
Immediately after getting out of the car I realised negative was going to positive, positive was going to negative. We must have had this set up for 30+ seconds
Turned the car off immediately.
Once everything had cooled down, I started my car with no problems. No visual damage to the ECU, and everything seems to be working. There are no engine warning lights.
I just drove home (100+ miles) and haven't experienced any problems.
I'm incredibly worried I've done untold amounts of damage, but I would have expected to see problems immediately if that was the case. (If the ECU had burnt out I would have at least expected a light on the dash, and the fuses seem to be ok as everything electrical I am able to check is working fine)
Have I just been incredibly lucky and got away with it? Or could I have done damage that isn't noticablen yet and will come to haunt me.
I'll be taking it for diagnostics asap but I've got to drive another 100 miles tomorrrrow before I am able to.
Please advise! I appreciate any advice anyone can give!
Many thanks
 
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ruston

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Negative to negative and positive to positive is the correct combination .
It is likely that you have had a poor connection or inferior quality jump leads. Depending on the vehicle and the amount of discharge on the battery , you could be drawing in excess of three hundred amps on cranking , that is enough to fry any poor insulation on the jump leads.
If this was the case it is likely that this is all that would be damaged.
 
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  • #3
Negative to negative and positive to positive is the correct combination .
It is likely that you have had a poor connection or inferior quality jump leads. Depending on the vehicle and the amount of discharge on the battery , you could be drawing in excess of three hundred amps on cranking , that is enough to fry any poor insulation on the jump leads.
If this was the case it is likely that this is all that would be damaged.
Sorry! Edit made! It was connected Negative to Positive and Positive to Negative, causing a massive amount of current to burn the plastic on the leads.
 

ruston

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You have been very lucky then . It is a wonder that you did not have a serious incident on your hands. The battery could have exploded spraying acid on the person connecting the leads.
 
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  • #6
Is there any chance that damage has been done that isn't yet apparent? Or have I got away with it?
 
Original post now edited.
 

ruston

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If the battery you were trying to boost was completely flat you may have got away with it , and I suspect it was as the battery would have flashed over immediately the connection was made . The flat battery would take a reverse polarity charge and would likely be damaged.
 
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  • #11
If the battery you were trying to boost was completely flat you may have got away with it , and I suspect it was as the battery would have flashed over immediately the connection was made . The flat battery would take a reverse polarity charge and would likely be damaged.
Sounds like there were a few sparks intially (maybe not a fully dead battery). Any chance the good battery is damaged aswell or just the dead one?
 

ruston

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I would say your car and your battery would have a good chance of surviving , but how has the other car faired , did you ever get it started?
 
The cheaper your leads ,the better chance of no damage !
( ECU's spike even with the correct polarity )
Is his alternator still charging ? (is a good question)...
May have shunted -power !
..If drains quickly over night
a) Battery now shot
b) Something is damaged and taking power when off.. Alternator classic
 
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ruston

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Reversing polarity - the alternator in my recent experience is the usual victim.
 
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  • #15
I would say your car and your battery would have a good chance of surviving , but how has the other car faired , did you ever get it started?
The other car didn't start after that unfortunately. It's likely it's killed it. It's a £300 beater on its last legs, we are more worried about the damage that may have been done to my car.
The other car is pre 2000, so we are replacing the battery and ECU, if this doesn't work it'll be a scrap job.
 
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  • #16
The cheaper your leads ,the better chance of no damage !
( ECU's spike even with the correct polarity )
Is his alternator still charging ? (is a good question)...
May have shunted -power !
..If drains quickly over night
a) Battery now shot
b) Something is damaged and taking power when off.. Alternator classic
The alternator of mine (good battery) or the other car (bad battery) is likely to be the one that's damaged?
 
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  • #17
The cheaper your leads ,the better chance of no damage !
( ECU's spike even with the correct polarity )
Is his alternator still charging ? (is a good question)...
May have shunted -power !
..If drains quickly over night
a) Battery now shot
b) Something is damaged and taking power when off.. Alternator classic
The alternator of mine (good battery) or the other car (bad battery) is likely to be the one that's damaged?
 

ruston

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The other car didn't start after that unfortunately. It's likely it's killed it. It's a £300 beater on its last legs, we are more worried about the damage that may have been done to my car.
The other car is pre 2000, so we are replacing the battery and ECU, if this doesn't work it'll be a scrap job.
If after 100 miles you have had no problems and your alternator is not showing the warning lamp there is a good chance you have got away with it. It seems his car has taken the brunt of the reverse polarity.
 
If your battery was strong ,and his weak ,your battery probably will survive. His alternator is at risk , since his battery was most likely to reverse polarity !
As for your car charging -fans should speed up a little
and lights run brighter with engine running (..or a cheap
voltmeter ! rising to 14.0 14.4 ish ) and no warning light !
--
 
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  • #20
Really appreciate all of the help.
As soon as the bank holiday is over I'll be straight into an auto electricians. I'll keep you posted on the outcome of both cars.
 

telectrix

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start with just the battery, better still you can usually get a reasonable one from local auto breakers for a tenner or so. then if it works, consider a new battery.
 
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  • #22
start with just the battery, better still you can usually get a reasonable one from local auto breakers for a tenner or so. then if it works, consider a new battery.
Cheers will do. An ECU for her polo is only £20 on eBay, sounds like there isn't a lot to them and it's plug and play (she's got an X reg 6n2, no immobilizer or central locking). I think both for the peace of mind, but the car isn't worth as much as an alternator would be.

Are you recommending I also get a new battery on my car?
 
I think you've been lucky.....
PS just admit it was you......I know I wouldn't let anyone place the leads without checking before I crank it on.
 
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