Welding on cars

[Furry Freak]

Guys, there are many out there who seem to have MIG as their choice for car body work. One of my requirements is to weld on cars, but not actually bodywork. I have searched previous posts, but can't find anything about welding on cars per se. Now, fire, fume, fuel and electricity I'm well versed in, but what do I need to do to protect the car's sensitive bits like the ECU. Is disconnecting the battery sufficient? Are there any major DON'Ts? I may use a stick and my MIG to weld brackets, tow hitches etc .

FF

 

[peterd51]

Hi,

you'll find two definate 'camps'...either leave the battery connected but be carefull where you place the earth (not on the engine to weld the body, etc) or that you should always disconnect the battery and maybe even connect the battery leads together.

If you're welding tow-brackets (not sure, but I think that's not allowed now...tow-bars should all be approved types), you connect the earth lead to the bracket and it's a good connection then I'd say it's unlikely that you'll damage the engine management. But that just my opinion!

On my old Mondeo I don't bother disconnecting the battery but on a newer car, Pug, Citroen especially, or on my wifes newer Skoda I would disconnect the battery and connect the leads together. There's a lot more electronics on these cars and if it goes wrong it's horribly expensive.

Regards
Peter

 

[Furry Freak]

Thanks Peter. That's really helpful. I think I'll go for disconnecting. But not sure about connecting the two leads together. Don't see what that does. I'll certainly earth to something solid and local to the weld point, like the chassis.

Sorry, to be clear, I'm not welding tow bars, I'm welding tow bar attachments, like winch carriers and recovery points. Mostly for an off-road vehicle. These slot into a universal receiver in the tow bar. They can be welded 'off vehicle' in the main, but some bits need adjusting or tacking whilst in place.

Incidentally, there is a time limit on approval types for tow bars. ie if fitted to a vehicle pre 19XX (can't remember) the new legislation doesn't apply. Mine is before that day anyway.

FF

 

[Justme]

But they do now come under the scope of the MOT

 

[michael1703]

i always disconnect a lead from the battery, its not worth taking a chance for the sake of loosening one nut on a terminal

though.... a lead i had disconnected did flop back onto the terminal once and i effectively welded the car with the battery connected and did no damage

if you have seen 'the long way round' you would know that the welding carried out to one of their bikes caused damage to the abs

 

[pedrobedro]

It's always been advised to disconnect the earth lead from the battery and some recommend removing the alternator plug as well. I only ever saw one battery related problem on an old Mini being arc welded and it split the battery when the rod stuck.

 

[pommy]

try one of these from draper

 

[martinez]

try one of these from draper

what is it ?

 

[Wozzaaah]

It's a Draper VSP12

 

[gavuk]

thats what i use ,haven't messed up a car yet (not electrically anyway)

 

[pommy]

sorry it`s a battry safe i use one all the time it stops the surge from the welder
good if you work on cars all the time for around £7 it`s money well spent

 

[Iain Westland]

I use one of his big brothers, only problem I have had in 6 1/2 years has been on a vitara and to be honest I think it was just the straw that broke the camels back

Iain

 

[engybenjy]

Hi,

I would disconnect the battery and connect the leads together.
Regards
Peter

As far as Ive ever been told and understand it this is what you DONT want to do as it completes the circuit round the car - which kinda negates disconnecting the battery in the first place

I have always disconnected both battery leads and tucked them out of the way, and have not had a problem with that. If I am welding near the ECU I remove it - better safe than sorry, especially when you think that an ECU could end up costing £2000 or more!!!!! and some have to be re-coded to the rest of the car

HTH, Ben

 

[peterd51]

Hi,

well, I used to disconnect the battery and leave the leads free but a number of people have suggested that I was wrong to do that.

Regards
Peter

 

[gavuk]

Stick to the surge protector then you have something to blame if anything goes bang!

 

[ATGNI]

The answer is this.

if possible you should disconnect both the battery leads and connect them together. If you do this any voltage that gets onto the positive supply will be similar to any voltage on the negative or any other wire. There is now no potential difference therefore no current flow therefore now damage.

The reason that it may not be a good idea to connect them together is that many cars have memory devices that rely on being powered constantly such as adaptive engine management systems. Depending on the design of these memory devices removing power or shorting leads together may wipe the memory. I am sure many of us remember all the problems with the codes on the old ford stereos needing resetting.

What the device from Draper does is it actually connects the battery leads together, but only at some voltage above lets say 15v. I very much doubt the "battery saver" type devices actual work as the normally inductivity of the cabling will probable prevent the device from actually even seeing the high speed transients let alone clamping them to a safe level.

Designer are much more aware of EMC and ESD than we were 20 years ago and although the cars have much more electronics in them, circuit are much better protected. (Electro Magnetic Compatibility) (Electro Static Discharge)

Remember to ensure you take time to fit the earth clamp to completely clean metal as close as possible to what is being welded. Don't use some big crocodile clip type crap, it must be a really good clamp. If you do this you will have much less chance of doing any damage.

I would however say that its probably even worse idea to employ any equipment that uses HF starting and would include the cheap plasma cutter, where the pilot is partly struck to the metal being cut.

Regards Chris.

Not a Welder - Electronic Design Engineer.

PS: I agree - if you can disconect the ECU then do it. You only have dash board controller, abs system, air bag, climate control, and radio to destroy now.