[Greg From K/W]

Its not just the battery you can damage the wiring harness and the computer systems in a car if you don't undo the battery. It can pop resisters and diodes on a board. Chips can be blown and then your car is crap. Any body shop will undo the battery if they have to weld on the frame or the body panels.

Why take the chance in doing any damage to your car or someone else for the 2 seconds it takes to undo the clamps? If you don't then watch out.

[DieselD389]

I hate to burst everyone's bubble here but unhooking the battery alone to protect the computers from misplaced electrical current in the event of welding is an absolutely absurd idea. Most of the cars electronics do not ground through the battery but directly to the chassis of the vehicle so unless you remove every single ground on said vehicle removal of a battery terminal won't do squat to protect anything. As a few others have stated always ground as close as possible to the weld zone.

[Greg From K/W]

It was the fact that the entire electrical system is hooked up to both the ground and positive a the battery. By taking the leads off the battery it will prevent the juice from being back fed into the electrical system. That is what I was told in the welding course I was in and other welders have told me the same. Again Why take the chance that something could happen? If your willing to take the chance on it go for it. THat's up to you. I for one will not weld on a new vehicle with out that safety precaution.

[GreinTime]

I hate to burst your bubble, but you apparently have no concept of how a basic circuit works.

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[plantwelder]

@Diesel D389,

Sorry, but you're a little mistaken there. I've welded on the most up-to-date equipment and vehicles just by disconnecting the battery, and no issues. If you do have the twitches, all you need to do is disconnect the harness from the ECM, but you still need to unhook the battery to save your alternator.

[DieselD389]

My family has owned an auto repair shop for almost 40 years I have worked on cars my entire life and I can tell you that if a stray current is going to run into something it will definitely be able to do so through the ground side of things considering most newer pcms in vehicles do things by turning the ground on or off to operate solenoids and such. Unhooking the battery is a myth that's older than the hills.

[Otto Nobedder]

Here's the short-form from industrial construction.

The MOMENT the instrument technicians show up and begin wiring computers, you'd better have your ground firmly connected as close to your weld as practical.

Two conditions missed in this conversation are "static" electricity, which can be induced by eddy currents, and REMF, or reverse electromotive force, which occurs when you break your arc.

Steve S

[GreinTime]

My whole point behind the basic electrical circuit is that if the battery ground is disconnected, the chassis is not grounded. For a circuit to complete with the ground disconnected, it would physically have to jump an arc from the negative terminal to either the negative cable, completing the circuit, or to the body, whichever is closer. If you don't have a complete circuit, no electricity flows. Now is the point your trying to make is that by attaching a ground to the frame, and welding you are completing a circuit?

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[Arno]

An open circuit (eg. disconnecting a pole from the battery) will prevent large leak currents (eg. bad path from ground-clamp to electrode/torch) from directly damaging the electronics. That's the easy one..

But a more 'sneaky' killer are the various electromagnetic waves sent out from the welding process/arc itself.

These can induce small, but potentially damaging, currents and voltage spikes even in totally disconnected wiring/electronics. Some help can come from an array of capacitors attached to the cables to provide some suppression/dampening of these spikes, but if they occur close enough to the electronics themselves then they can stil fry.

Welding on a vehicle simply always has a certain risk. You can 'engineer out' most of the problems during the design phase, but they are simply not cost effective on your average car/truck.. Industrial machines like earth movers are more likely to have more 'resistance' built in as welding on the vehicle to repair or maintain them is likely in their future.. (and they can have plenty of computers on board these days too!)

You can reduce the risks by taking some precautions like making sure wiring is disconnected, supressor(s) installed and not welding in close proximity to wiring or electronic components. But unless sensitive parts are physically removed from the vehicle before welding, there's always some small chance they won't survive. Such is life

Bye, Arno.