disconnecting battery terminal whilst welding

Bimmerguy2002 · Post by **Bimmerguy2002** » Jul 28, 2011 7:12 PM

Why is this a good idea?

Coldswede · Post by **Coldswede** » Jul 28, 2011 7:20 PM

Are you trollin' Matt?

Frybrid 524td · Post by **Frybrid 524td** » Jul 28, 2011 7:54 PM

Coldswede wrote:Are you trollin' Matt?

Never!

a · Post by a » Jul 28, 2011 8:09 PM

dont bother,if you have ecus to burn. When welding you are running lotsa amps through the body on the ground side . I 've welded and did no damage, but YMMV. Popping the connector on the ecu is easy insurance.

Bimmerguy2002 · Post by **Bimmerguy2002** » Jul 28, 2011 8:39 PM

hahah

Not trolling this time, just wondering why its recommended

Mike W. · Post by **Mike W.** » Jul 28, 2011 9:51 PM

All depends on what kind of welding. Oxy Acetylene and no reason to. But if you're talking electric, yes, there is a possibility of ECU damage. Disconnecting the ECU is probably more important than the battery.

booker · Post by **booker** » Jul 28, 2011 10:23 PM

How can you "force" current through an ECU?

slammin_e28 · Post by **slammin_e28** » Jul 28, 2011 10:29 PM

Why do you disconnect your welder while battering?

Hmmmmmm?

535is-pa · Post by **535is-pa** » Jul 28, 2011 10:41 PM

Mike W. wrote:All depends on what kind of welding. Oxy Acetylene and no reason to. But if you're talking electric, yes, there is a possibility of ECU damage. Disconnecting the ECU is probably more important than the battery.

batteries have hydrogen gas comming out of them and there is plenty of fuel to burn givin the circumstances a battery will explode. kinda like the hindenburg

http://www.youtube.com/watch?v=tC0UWIYs ... re=related

http://www.youtube.com/watch?v=pizFsY0y ... re=related

remvber the exploding laptop battery incident? thats with a small ass battery and look at that video you dont want a car battery doing that car batterys are a single cell not a series of cells.

Mike W. · Post by **Mike W.** » Jul 28, 2011 10:57 PM

booker wrote:How can you "force" current through an ECU?

Excessive voltage might exceed the rating of the P/N junction of a semiconductor and make it either a conductor or an insulator. Meaning kill it.

Xenocide · Post by **Xenocide** » Jul 28, 2011 11:25 PM

535is-pa wrote: http://www.youtube.com/watch?v=tC0UWIYs ... re=related

http://www.youtube.com/watch?v=pizFsY0y ... re=related

remvber the exploding laptop battery incident? thats with a small ass battery and look at that video you dont want a car battery doing that car batterys are a single cell not a series of cells.

Not even remotely relevant, those are sealed cell lithium batteries, totally different from lead acid batteries.

I understand the argument for protecting the ECU, but frankly the voltages you weld at aren't terribly high, and there's no good reason for the current to travel anywhere but from the torch to the ground clamp.

I have never disconnected a battery for anything I've welded on, but maybe I've just gotten lucky

Jsanders · Post by **Jsanders** » Jul 28, 2011 11:57 PM

I asked a welder at a body shop if I needed to disconnect the ecu or anything before I started reinforcing the subframe on my e46, and he had never in his entire career and never experienced any problems because of it.

535is-pa · Post by **535is-pa** » Jul 31, 2011 1:00 AM

Xenocide wrote:
535is-pa wrote: http://www.youtube.com/watch?v=tC0UWIYs ... re=related

http://www.youtube.com/watch?v=pizFsY0y ... re=related

remvber the exploding laptop battery incident? thats with a small ass battery and look at that video you dont want a car battery doing that car batterys are a single cell not a series of cells.
Not even remotely relevant, those are sealed cell lithium batteries, totally different from lead acid batteries.

I understand the argument for protecting the ECU, but frankly the voltages you weld at aren't terribly high, and there's no good reason for the current to travel anywhere but from the torch to the ground clamp.

I have never disconnected a battery for anything I've welded on, but maybe I've just gotten lucky

relevant....

the reason my father will not weld on cars is an incident where a coworker tried to weld a front bumper on a work truck. the battery exploded and scolded another person, the end result was a very complex lawsuit. and yes batteries lithium or acid/lead based do produce hydrogen and yes regardless there is fuel to burn and only more so with a car battery. and givin the amprage the discharge is more then enough to fear.

google...

Mike W. · Post by **Mike W.** » Jul 31, 2011 1:35 AM

Being an electrician with extensive electronics background too, I'll say this...

You probably don't need to disconnect anything, but if you do disconnect the battery and the ECU you're pretty damn safe. At least on an E28 vintage car. Get into newer stuff like I-drive and all bets are off. But there's still got to be a way to weld on them.

Xenocide · Post by **Xenocide** » Jul 31, 2011 1:41 AM

It is true that hydrogen can be produced when a lead acid battery charges (specifically over charges), but quantities are generally fairly small unless the battery is being dramatically over charged, and while I wouldn't leave one in a closed environment with an ignition source, it has nothing to do with the battery being connected during welding. The hydrogen has already been produced, disconnecting the terminal does nothing. An argument for removing the battery altogether could be made, but the battery being connected has no bearing. In this scenario the only potential ignition source is the arc from the welder, which has nothing to do with the battery.

I know of no lithium ion battery construction which produces hydrogen during charging. The fires and explosions referenced were the result of dead shorts causing lots of heat which increased pressure in the cells, which then ruptured, then the fluid inside them burned.

This is not relevant because there is no pressure vessel scenario here, most car batteries are vented. Even those that aren't have been designed to have safe failure modes. Even if they didn't, there's no way the battery could be charged by the welder unless you ran your ground clamp across the battery.

CoyoteStarfish · Post by **CoyoteStarfish** » Jul 31, 2011 6:33 AM

The only way I can imagine this damaging an electrical system is if the vehicles positive becomes earthed (to a grounding rod) or connected to the ground of the welder without the welders ground touching the vehicles frame at all. Then it will send whatever dc/ac current through the vehicles electrical loop and overvolt.

Tell the linemen who work on high voltage power lines with helicopters to dissconnect their batteries before linking to a 500kV line

MyE28.com

MyE28.com

disconnecting battery terminal whilst welding

disconnecting battery terminal whilst welding