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itsarebuild
itsarebuild Reader
12/10/10 1:15 p.m.

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!`

ncjay
ncjay Reader
12/10/10 1:25 p.m.

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.

WilberM3
WilberM3 HalfDork
12/10/10 1:30 p.m.

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.

BoxheadTim
BoxheadTim Dork
12/10/10 1:40 p.m.

I always thought the advice was to disconnect the battery...

ansonivan
ansonivan HalfDork
12/10/10 1:43 p.m.

I've welded on cars of all vintages, never disconnected anything, never had a problem.

YMMV

Pumpkin Escobar
Pumpkin Escobar SuperDork
12/10/10 1:48 p.m.

acetylene...

/problems

WilberM3
WilberM3 HalfDork
12/10/10 1:55 p.m.
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.

ansonivan
ansonivan HalfDork
12/10/10 1:59 p.m.

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.

Zomby woof
Zomby woof Dork
12/10/10 2:19 p.m.

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.

WilberM3
WilberM3 HalfDork
12/10/10 2:31 p.m.
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?

Zomby woof
Zomby woof Dork
12/10/10 2:37 p.m.

In reply to WilberM3:

No spark

I was nowhere near the battery.

foxtrapper
foxtrapper SuperDork
12/10/10 2:48 p.m.

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.

Streetwiseguy
Streetwiseguy HalfDork
12/10/10 2:48 p.m.

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.

Dr. Hess
Dr. Hess SuperDork
12/10/10 2:48 p.m.

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.

Travis_K
Travis_K Dork
12/10/10 3:08 p.m.

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.

Keith
Keith SuperDork
12/10/10 5:43 p.m.

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.

Marty!
Marty! Dork
12/10/10 6:05 p.m.

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.

ansonivan
ansonivan HalfDork
12/10/10 8:38 p.m.

Having the boss buy a surge protector on Monday.

hotg54b
hotg54b New Reader
12/10/10 8:38 p.m.

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.

Jensenman
Jensenman SuperDork
12/10/10 9:25 p.m.

I've never had a problem either, but maybe I have just been lucky.

Jay_W
Jay_W HalfDork
12/11/10 8:16 a.m.

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.

dinger
dinger Reader
12/17/13 8:16 a.m.

I've never had a problem, and I've always followed two simple rules: 1) Disconnect the battery, it's only two bolts; 2) Get the ground as close to the joint as possible to keep stray current to a minimum.

pinchvalve
pinchvalve MegaDork
12/17/13 8:27 a.m.

Never removed the battery, never cleaned up leaky gas, never moved oily rags away, never wore sleeves or shoes, never had a problem. But it was stupid and I am lucky to still have a house. Next project, all precautions will be taken.

Giant Purple Snorklewacker
Giant Purple Snorklewacker MegaDork
12/17/13 8:28 a.m.
ansonivan wrote: 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.

I think the risk is pretty low provided you don't forget to hook up the ground, make sure it's good and close to the work - for the same reason you don't get electrocuted touching the car.

That said - I still disconnect batteries and pluck out ECUs when I can because atleast 10x every cage I knock the ground off and don't see it or forget to connect it before I step on the pedal. Electrons looking for holes will definitely wreck some E36 M3 using alternative exit routes. I can tell because of the way my heart tickles :)

iceracer
iceracer UberDork
12/17/13 9:23 a.m.

As has been said, Be sure the welder ground cable is on the part being welded.

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