Welding - do you need to disconnect battery?

[MozzGTI]

Hey guys was chatting with a mate tonight about some welding exhaust work he's going to do on my GTI and he asked about disconnecting the battery as he did it so as to not fry the computer. Does this sound right?? also is there anything special you need to do to connect the battery and reconnect?

[h100vw]

You should disconnect the battery. Although some shops have a a protection device that goes across the battery.

protection - Protecting electronics against welding damage - Electrical Engineering Stack Exchange

[Lucas_R]

Not necessary, but wont hurt either. If you do decide to do it, just undo the negative terminal. When you connect it back up afterwards, you will get an airbag and esp warning light on the dash, but it goes away within about 100m of driving.

[MozzGTI]

thanks guys! Lucas why only negative terminal?

[Brendan_A]

Also put the earth lead of the welder as close to the area your welding.

[bazzle]

Not necessary. The battery can help to absorb the higher voltage spikes.
And do as Brendan said with the welder earth.

[MozzGTI]

Thanks all!!

[Notso Swift]

You only remove the earth lead because once a circuit is broken it is, well... broken
The fry the computer thing is sort off understandable... but... the main battery isn't the only one, ECU have back ups, so if it was gong to fry there is still a circuit!
Personally I still do it out of habit but it isn't needed

[DV52]

Wow- some really interesting responses here to a very good question!

Not sure that removing the battery negative lead (or the battery positive lead) does anything. If you think about it, there are very few electronic components in the car that are actually connected to the battery with the ignition off. So all these components won't be helped by removing the battery lead (IMO).

In fact there is a case to be made for switching-on the ignition while welding and leaving the battery connected. Turning-on the ignition means that the battery's low internal impedance will be connected across each connected component (albeit there may be some "electrical distance" between many of the components and the battery impedance). The big problem of course is avoiding large voltage spikes that can appear from the quick rise-time of the electric arc. Anything that has an AC impedance (like circuit inductance) will absorb these voltage spikes - and if the spikes are large enough, will destroy them. It's true that most car electronics these days have in built protection circuits to guard against spikes, but I'm not sure if the designers contemplated the rise times that came from arc welding!

Placing the earth lead from the welder as close to the item to be welded is a good idea (IMO)

[any001]

Projecta make a unit that just clamps onto the battery terminals. Almost all automotive parts places sell Projecta. They would just need to order it in.

http://www.projecta.com.au/Products/BoosterCables/SurgeProtectors.aspx