My car is blowing up batteries! =/ Bad alternator?

[VAG-Abound]

The diagrams I found have a 2.5mm wire from starter motor to a 10-pin brown connector (amongst yellow, blue, white, etc) on left of engine. Position 4 is a red / white wire to ignition switch on manual or starter inhibitor on an automatic. Can you match that to your wire, and hence check for short in engine or further back? Is the can manual?

[mikeote]

Heya VAG-Abound, the smaller cable is connected to the larger cable right at the battery post terminal connection. The smaller cable is definitely from the factory.

"Although now disconnected from main starter cable that smaller wire presumably still has a short to ground?", yes it's definitely that smaller cable with the ground.

"BTW, you're mixing terminology a bit. Nothing is high voltage, just high current." I originally thought that there may have been AC voltage from the alternator going to the battery which killed it, which has turned out not to be the case.

"If starter relay was stuck starter motor would keep turning even if not needed." The short killed the battery completely so the starter has no power to turn.

" It sounds like you've managed to get a short between the high current starter motot cablr and the small cable which has a path to ground witjout going through a fuse" Once the smaller cable and the larger cable are disconnected at the battery post terminal there is no longer a short on the larger cable, once disconnected I believe the two cables are on separate circuits separated by a relay which may have gone bad.

Perhaps there was originally a short on the larger cable (starter motor for example), which fried the relay on the smaller cable circuit causing it to provide it's own short. I'll need to fix the short on the smaller cable circuit then re-install the starter and check if there is a short, if there is I'd replace the starter.

"To get hot, etc you'ryou're probably dumping 10A to 20A though a 1 Ohm or so path which may damage but not destroy that smaller wire. Be sure to replace it even if it seems you've fiund a rub point that you can reinsulate." That's good advice, happily I realised that there was a problem pretty quickly so removed the battery cable before it got too hot. It wasn't quite so hot that I couldn't hold the cables. I think the smaller cable contains several cables which go to the relays, so perhaps I should cut the insulation to see if the smaller cables have been melted ... I'll do that after I've checked the relays.

Cheers!

[VAG-Abound]

Something doesn't make sense to me there. If the smaller wire was creating a short from battery post to earth then there would be no need for current to go through the thicker starter motor cable. If the starter relay was being controlled by the thinner wire it could be implicated in forming both paths, but in an unenergised system disconnecting the thinner wire will have no effect on the relay, and if it was a stuck / welded relay it also wouldn't change the multimeter resistance readings.

[Roverfan]

You have a short on one of the circuits powered by the smaller cable or the smaller cable or its spliced connections is shorting itself before it gets to any gadgetry.
Follow this smaller cable back where ever it goes

[] Watch out for melted insulation, signs of over heating electrical wires or connectors, damaged insulation

Edit: Sorry mate, just realised you wanted to cut into loom insulation to see the cables. Yes but with a plan for how you are going to reprotect the loom after.

[Roverfan]

Something doesn't make sense to me there. If the smaller wire was creating a short from battery post to earth then there would be no need for current to go through the thicker starter motor cable. If the starter relay was being controlled by the thinner wire it could be implicated in forming both paths, but in an unenergised system disconnecting the thinner wire will have no effect on the relay, and if it was a stuck / welded relay it also wouldn't change the multimeter resistance readings.

Afaik he was measuring at the battery terminals, so measurements were taken here. He was getting a short till he removed this smaller b+ wire. So the short is through this smaller wire or it's circuits. It's only connection to starter motor wire is that it was attached next to it on battery post. As for stuck closed relay this is a guess on where the short was coming from.

[VAG-Abound]

Afaik he was measuring at the battery terminals, so measurements were taken here. He was getting a short till he removed this smaller b+ wire. So the short is through this smaller wire or it's circuits. It's only connection to starter motor wire is that it was attached next to it on battery post. As for stuck closed relay this is a guess on where the short was coming from.

I'm assuming it was the thicker battery cables which were getting hot, so carrying high current. No need for the current to go through there if the short is in the thinner wire.

[Roverfan]

I'm assuming it was the thicker battery cables which were getting hot, so carrying high current. No need for the current to go through there if the short is in the thinner wire.

Iirc the actual cable getting hot was not specified. Just that one of the cables in the pack were hot making the area of those cables hot and we assumed it would be one of the larger cables. At least that is my understanding it.

[mikeote]

Found the problems!

Quick version: Problem one: Alternator wire which is attached to the starter was routed wrong at the starter causing it to rub against motor mount causing the short.
Problem two: Short in the smaller wire from the battery ended up being in the rear left bulb holder.

Longer version:

Yesterday:
I followed the smaller wire (which is attached to the positive battery cable terminal) under the steering wheel to the relay board. I removed all relays one by one checking to see if the short disappeared after each one removed, no luck.

I removed the same wire going to the relay box from the relay box and the short disappeared, I then reattached the wire and followed the same wire from the relay box to the interior fuse box. I put my multimeter on ohms beep mode (produces a continuous tone until continuity broken) and attached it to the two battery cable terminals, then removed each fuse from the inner fuse box until the tone disappeared; it was a short in the bulb holder of the left rear light unit. I removed that bulb holder and ordered a replacement. Seemed very strange that a short in a light unit would be both significant enough to explode a lithium battery jump starter and instantly kill a brand new battery without even blowing it's fuse....

Today:
I reconnected the starter motor wiring and checked again for a short in the larger positive battery cable, there was none so I proceeded to install the starter motor and checked again once installed; a short in the larger battery positive battery cable appeared! I loosened the starter motor bolts and the short went away...

I removed the starter motor again and re-inspected the wires going to it, and found that the alternator wire which is attached to the starter had rubbed against a motor mount causing the insulation to wear away right next to the cables end terminal. I removed the wires from the starter and reattached them with a different routing. The starter has a piece of plastic where the cables attach to the starter with two paths, it seems that you would attach one cable to each path but if you do this one of the cables will rub against the motor mount; so I routed both cables in one path. I had originally removed and reinstalled the starter motor (and f'd up the wire routing) when I replaced the clutch, moral of the story; always take a photo of the wires routing before you disassemble!

I reinstalled the starter motor again and there was no longer a short on the large battery cable. With the short resolved on the smaller positive battery cable yesterday and the short on the larger positive battery cable resolved today I no longer have any shorts! I reckon the short in the larger battery cable probably resulted in the short in the smaller battery cable.

The bulb holder looks mint though, can't see any signs of burning or where the circuit has been pinched together.

Tomorrow evening or Saturday I'll have time to put the car back together and replace the failing alternator and a couple of other bits, I'll post again when it's all working as it should (fingers crossed).

Thanks for all the help guys!!!
Mike

[mikeote]

The car's all back together and working nicely Thanks again for the help guys.

[elitclark]

My car is blowing up batteries! =/ 2003 VW Passat 1.9 litre TDI, 140,000 miles.


Hey guys, have you seen this before? I was driving down the road and my car just died, no warning, no nothing every thing just turned off. Luckily I was able to pull over to a parking space. I checked the battery which had zero voltage so I thought the battery had an internal short 192.168.1.1. To verify I plugged in a small cheap car just starter which instantly exploded!


I thought that this was just because it was a cheapo jump starter which couldn't handle being plugged into a shorted battery. I took the bus to my local auto place and bought a new battery. As soon as I connected the battery cables to the battery there was a fizzing sound, so I disconnected the cables and checked the voltage on the battery which was previously 12 volts and now zero volts! =/


So I'm thinking that it's not a battery problem... After doing a little research I found that if a diode has failed inside the alternator, the alternator can flood the cars electrical system with alternating current; which is my best guess so far. The alternator was on it's way out any way (I got it from a scrap yard) 192.168.100.1, when I revved hard a warning showed up on the dash "alternator workshop". I checked the alternator a few times when it was running, and when at idle it was fine; so I thought it was just losing a bit of power generating capacity when the car was revved hard so kept using it.

Can any thing else cause the instant death of a battery? Could it be a short in the system? I've ordered a multimeter (lost my last one) to check for AC in the system. If there is AC coming from the alternator how can I get rid of this to make it safe to remove the alternator?

PS. I definitely did not put the battery in backwards.

Thanks!
Mike

I have same car as you, but never had an issue with it, good luck bro.