Can weldong with the battery connected damage anything?

[BlueMR2]

My car had some welding done with the battery connected and it stalled on the way home and had to be recovered as it wouldn't restart.

I need to try changing some relays which incidentally one was clicking like a nutter when you turned the ignition on, but has stopped if you try now. However it won't turn over at the moment.

I plan on removing the battery and charging it up, as well as pulling out all the relays and will check all the fuses as well, i'll change a few of the relays if needed as they are known to cause starting problems.

However could the welding have damaged something?

[davepoth]

Yes. The MIG needs an electrical circuit, and since it's attaching stuff to the car, you earth it on the car. The battery also earths on the car, so if you left it plugged in the MIG can make a circuit which includes the car, but also the battery and anything else connected.

[mwcr85]

I'd leave the relays until you charge the battery, a low voltage battery voltage can make them click. Sounds like you may have knackered the battery or alternator if it died while driving.

[v64paul]

On old school stuff, all you risked was the alternator. More recent stuff, lots of ecu's to throw a hissy fit. Sorry.

[XVar]

Can't see it being an issue as long as the ground clamp was directly connected to the part being welded. Electricity takes the path of least resistance so unless it had to take an indirect route it's unlikely to have caused any damage.

[redstu]

XVar said:

Can't see it being an issue as long as the ground clamp was directly connected to the part being welded. Electricity takes the path of least resistance so unless it had to take an indirect route it's unlikely to have caused any damage.

Thats my opinion as well, I have mig welded 3 cars without problems the last being a 98.
Maybe I'm just lucky!

[chryslerben]

v64paul said:

On old school stuff, all you risked was the alternator. More recent stuff, lots of ecu's to throw a hissy fit. Sorry.

Majority of modern ecu's are surge protected, Now reverse polarity there's a killer.

[BlueMR2]

Thanks for replying guys.

It's the 928. I think based on being driven out of the workshop daily and worked on in short bursts so to speak that it wont have been disconnected whilst welding. Also it was the very back of each sill, which especially on the passenger side is very near the underfloor boot mounted battery.

When the car cut out, it turned over 2 times, a bit of oil smoke the first and nothing the next, then it wouldn't crank at all. With the key turned round but not trying to crank it, it made a kind of thumping noise from where the battery is which i'm told could be due to the battery arcing? however it stopped doing that, then a relay sounded like it was clicking twice a second, which it no longer does either.

It shows over 12v when last checked at the battery but i haven't checked how low it goes when cranking as at the moment it wont crank for more than half a second however it seems to light up the dash lights correctly.

[Eggman]

Not cranking doesn't sound good. When was the timing belt last changed?

Assuming the belt checks out ok and the battery is charged, you could try shorting the starter solenoid to see if there's a problem with that.

[BlueMR2]

Eggman said:

Not cranking doesn't sound good. When was the timing belt last changed?

Assuming the belt checks out ok and the battery is charged, you could try shorting the starter solenoid to see if there's a problem with that.

The cambelt was changed last September just before it went to sleep over winter.

My Dads car battery is charged and in the dining room (not having much luck with cars the last year or 2) so i will try and use that as its a very similar size and see if it will crank at all.
Not too thrilled at the moment, expected it to be working and MOT'd a week last friday.