MIG welding advice

[Beastrider]

Hello - I have an area of rust on the rear crossmember where the bumper bracket mounts. It’s gone through at least 2 MOTs like this but I thought it could fail because it’s near the bumper mount. Otherwise the chassis is mint.
Anyway, I want to cut out the rot and weld in a 3mm thick repair patch. I’ve never welded on a vehicle before and am a bit nervous about causing an electrical problem afterwards.
I will ensure:
1. A good clean earth connection close to the welding area
2. Clean material
3. Batteries disconnected

Should I take any other precautions like disconnecting the alternator?

Any other advice?
Thanks

 

[Higgy]

Doing all 3 on the list will be fine,.....No need to disconnect Alt.... I was welding on my old Colorado all day once and completely forgot to disconnect anything. With no Ill affect... Remember there are rubber body mounts all over the place, If your welding the Chassis for instance, That Help prevent High currents zooming about, But its always best to be safe, Newer vehicles with complicated fragile electronics might Disagree...... Oh! and if its a Petrol make sure you have a quick exit route cleared and get ready to run ......Crack On!

 

[Shayne]

I used to disconnect the battery just in case until i forgot once and it did no harm so i don't bother any more .

 

[Chris]

You should be fine. Only other thing of course is wind and your shielding gas. You might need to turn the wick up a bit to maybe 15L/min

 

[Beastrider]

Thanks for your replies and reassurance. Good point about the gas - I haven’t welded outdoors before either.

 

[BobMurphy]

I'm in the process of welding my '100' (or would be if I didn't have daughter's car to fix first ).

I've got the batteries out and the battery leads shorted together - to earth any stray currents. Probably a total waste of time but better safe than sorry with all those ECUs about

I'm using MIG and TIG welders as appropriate.

Bob.

 

[Chris]

TIG? Show off.

 

[Beastrider]

Thanks Bob - just making sure I understand - do you mean remove both batteries from the vehicle and then have each negative cable attached to the corresponding positive?

 

[SteveJB]

Whether true or not was told if you earth at front of vehicle and are welding at rear best disconnect batteries but if earthing at back and say welding within a few feet then don't worry and as you are welding on chassis if you have some old carpet then put it across your chest and neck area should help reduce risk of burning injury and wear goggles when grinding and I bet quite a few can testify to that bit of advice

 

[Shayne]

I was arc welding a winch tray bolted to the chassis in place of recovery hooks directly below my 90 series battery , does it get much cruder than that ?

 

[Chris]

I have welded without disconnecting. Knowing that I should. But never had a problem. But I'd say DISCONNECT THE BATTERIES. It's not a myth and takes 60 seconds. Why chance it.

 

[Beastrider]

Thanks for the suggestions everyone. I’ll take the cautious option and disconnect.

 

[BobMurphy]

Thanks Bob - just making sure I understand - do you mean remove both batteries from the vehicle and then have each negative cable attached to the corresponding positive?

That's the way .

Bob.

 

[BobMurphy]

TIG? Show off.

I didn't say I was any good at it .

(its an R-tech 170 AC/DC jobbie - more buttons than a Jumbo Jet ).

Bob.