car electrics and welding

[zardoz]

these days with all automobiles having little computers inside them and all sort of expensive e.c.u. boxes etc. Is there any fear of zapping them dead when welding. I am of course thinking of MIG and TIG, in the olden days, all you had to worry about was the gas flame setting fire to a carpet or some insulation etc.



ps:On a totally unrelated matter. I have never seen the Spell checker on the top right of the text entering box, until just now!

 

[Hitch]

Its always a good precaution to disconnect the battery- lead, and many people will say unplug ECUs aswell.

I've done welding on specialist vehicles (lots of electronics, plcs etc) in the past, without doing so, and never had a problem though. Often weld things up sat on forklifts, again, not had any problems there either.

For the extra effort it takes, only a couple of mins, its worth it imo.

 

[Glyn]

I always used to disconnect the - lead because I was told to. I sometimes didn't bother but once on a transit pick up, I had a bad earth while welding the chassis and I'm sure I heard a pop from the front. I started it up and the charge light was on. The auto spark said I'd fried the diodes in the alternator. But why?

 

[craig8661]

one thing is take both battery leeds of ive seen batterys explode with just the earth left on

 

[JayRS4]

I just disconnect the ground, remember, not all cars have a negative earth, just most of them. On the odd occasion that I have forgotten i`ve never had any problems though.

Just make sure you`ve got a good earth and that it`s as close as possible to the part you are welding. A bit like with a shock in a person, a zap from your elow to hand might not hurt much, but from one hand to another (across your chest) is a whole different story.

 

[shenion]

It is best to disconnect both the battery wires and connect them together. Next is to disconnect one lead and leave it floating, that allows the electrical system to float and accept induced voltages.

The biggest issue is leaving it connected is safety, you stand the chance of melting the starter lead. Then you find out how good an arc welder 400 cold-cranking amps is There are many other wires that are still powered. The next issue is if you connect the welder wrong and induce a spike on the line, the alternator diodes will avalanche and become a short until power is removed.

Keep the ground lead close to the work and on the same system. For example, when welding a frame, it is real easy to clamp to those big ears on the transmission. The engine and frame are isolated by rubber dampers and usually only a small braid connects them. That is usually corroded so you now have the welding voltage induced between the engine and frame with the ECU connected to both; poof.

Same for welding exhausts, usually isolated system, the best return path to ground is through the oxy senser and ECU.

Again, suspension is isolated also. Ground to frame and weld suspension and the return path is through the ABS sensor and ECU. I remember an old car that had radio static caused by the rear axle getting a static charge and arcing. Took a long time to find that one.

I seem to remember the GM/Ford service bulletins said bolt both batt leads to the frame.

 

[madkayaker]

killed a electric gate PCB with a stick once welding a repair onto a toothed rail didn't clean the galve off before putting earth on so had rubbish earth