so far i have not needed to weld anything on a car that has working electrical systems in it. this is about to change since one of my projects is running and needs some pretty substantial welding done.
my question is, is it better for the electrical systems of the car (particularly ecu systems) to keep the battery connected in the car? or should i remove one or both terminals before i start to weld?
thanks!`
I've never run into any problems, but I try to always remove the positive terminal before welding. I have heard some other racers run into problems with messing up the ignition system. Better safe than sorry. To be doubly safe, remove both cables.
i generally disconnect the battery and whatever computers i can (challenge cars are easy), but i know for sure ive welded with everything connected before without issue, but yea, better safe than expensive.
I always thought the advice was to disconnect the battery...
I've welded on cars of all vintages, never disconnected anything, never had a problem.
YMMV 
acetylene...
/problems 
ansonivan wrote:I've welded on cars of all vintages, never disconnected anything, never had a problem.
YMMV
yea i havent damaged one yet, nor have i actually seen it happen but i have heard stories... perhaps just stories? i just figure a battery cable is easy enough to disconnect wheres the harm. but a buried computer can be a total PITA.
One note: TIG welders with high frequency start pose a much larger threat ecu's than low voltage MIG welders. I wouldn't try on board welding with a TIG without taking all the precautions.
It has happened to me.
I've done it before, and since with no problems, but I did have a battery blow up on me while arc welding about 30 years ago - and it EXPLODED.
We had to do some welding on my sons late model truck last week, and since it has computers, I made him disconnect the battery.
For something with electronics, I would never take the chance.
Zomby woof wrote: I've done it before, and since with no problems, but I did have a battery blow up on me while arc welding about 30 years ago - and it EXPLODED.
do you think that was caused by vented gas and spark or electrical reasons?
In reply to WilberM3:
No spark
I was nowhere near the battery.
Electricity doesn't always take the path expected. I would disconnect.
Just the other day while welding on a swing arm on a motorcycle I smoked the brake rod return spring. The ground connector was attached to the swing arm, I was welding on the swing arm, just a few inches away. Why the electricity felt the need to go up the brake rod spring and back down I've no idea. None the less, that's where it went. With the resulting damage.
As previously mentioned, torches don't have these electrical issues.
Be aware of where your ground clamp is. If you are welding on a differential, for example, don't put the ground clamp on the frame- its gotta ground from frame to trans through splines past ujoint...........If the ground clamp is on the item being welded, you will be fine.
ymmv.
You don't have to be near the battery for the gas to ignite. Although hydrogen is lighter than air (see the Hindenburg airship.) I think disconnecting the battery is a good idea. I've seen reasoning that goes like: Battery is +12v. You're messing with the ground level when you're welding on it and potentially raising that +12v to +12v + welding voltage of whatever (18, etc.) potentially apply 20-30+v to whatever components are live. They may or may not be able to handle that.
I've seen a lot of muffler shops welding with a MIG and have never seen one pull a battery cable. If they had a lot of problems buying new ECU's, I'd think they'd be pulling battery cables.
Safest, of course, is to physcially remove all the electrical components and put them in a grounded Faraday cage while your working on the vehicle. This may not be practical.
I know (as in i was there while they were doing it) of someone who was welding on a CJ5 without disconnecting the battery and the alternaor no longer worked when they went ot drive it home.
I've been working with a shop that accidentally fried an ECU while welding on the car. I didn't get a lot of details from them on exactly how they managed to do it, but it can be done.
The shop I used to work in always used one of these:
Costs around $60 and eliminates the need to remove battery cables. Maybe a bit much for a home mechanic but works great for a shop.
Having the boss buy a surge protector on Monday.
You can void your warranty on a MSD box if left connected when welding on a car. Apparently, the MSD box tend to get fried.
I've never had a problem either, but maybe I have just been lucky.
We welded a kickstand on a motorcylce once and the battery exploded, does that count? Since then I've kinda sorta decided if welding is done on the car anywhere near the battery, said battery comes out first. Ya know, just in case, cuz o' that whole igniting hydrogen fumes resulting in acid all over the place thing.
