sporqster Posted October 8, 2007 Share Posted October 8, 2007 As good general practice, I always disconnect my engine ECU from the harness and remove the ground from the battery before welding on the frame. I always ground my welder as close to the place I'm going to be welding as practical. A coworker seems to think disconnecting the ECU is way overkill, if you're already disconnecting the battery. There are some components that use chassis ground - so I can't think the entire electical system is electrically isolated from the body.... but I do agree that it is difficult the imagine a whole crew of welding electons marching their to ground through a piece of electronics with the battery ground disconnected.... but I'm not confident enough to risk my ECU for it... Just wondering - what do you do to protect electronics (if anything) before welding on the frame? Link to comment Share on other sites More sharing options...
BobDrye Posted October 8, 2007 Share Posted October 8, 2007 Do not disconnect the battery!!!!!!!!!!!!!!!! It will act as a capacitor. Link to comment Share on other sites More sharing options...
slngsht Posted October 8, 2007 Share Posted October 8, 2007 Do not disconnect the battery!!!!!!!!!!!!!!!! It will act as a capacitor. I've done welding on at least 50 cars over the years, mostly in the early 90's when I owned a shop. All we ever did was disconnect the battery. We never fried anything. Link to comment Share on other sites More sharing options...
powderbrake Posted October 8, 2007 Share Posted October 8, 2007 I have a TIG welder in my garage, and it has popped the GFI socket that the radio in the garage is on, so I have taken to shutting down my large screen TV and my computer when I am welding. I have not welded on my car ( I would hate to do so with a powdercoated frame) but I would disconnect the computer if I had to weld on it. Better safe than sorry!! Link to comment Share on other sites More sharing options...
Arya Ebrahimi Posted October 8, 2007 Share Posted October 8, 2007 I've done welding on at least 50 cars over the years, mostly in the early 90's when I owned a shop. Really? You'd never know looking at your welds :lol: :rofl: :lol: All we ever did was disconnect the battery. We never fried anything. Welded on many vehicles as well and all I've ever done was disconnect the battery. Never had any problems, and they've all been modern EFI computer controlled vehicles. Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Share Posted October 9, 2007 Really? You'd never know looking at your welds Where's the BAN button :cuss: :lol: When you weld the same thickness metal over and over again, it's hard to screw it up. Link to comment Share on other sites More sharing options...
locostv8 Posted October 9, 2007 Share Posted October 9, 2007 Kin ya ban kin???/ Link to comment Share on other sites More sharing options...
BobDrye Posted October 9, 2007 Share Posted October 9, 2007 I've done welding on at least 50 cars over the years, mostly in the early 90's when I owned a shop. All we ever did was disconnect the battery. We never fried anything. All that I'm saying is that you do not want to disconnect the battery. Just ask yourself "what does a battery do?" Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Share Posted October 9, 2007 well, the battery stores energy. Let's say the battery acts as a capacitor. A capacitor only stores energy when there is a charge differential across its legs... I could be wrong about this (there are some brainiacs here who will correct me), but you can supply +12V or +12000V to a battery or capacitor all day long, but if the other side isn't connected, it's not really +anything, because there is no voltage differential across its legs. Link to comment Share on other sites More sharing options...
BobDrye Posted October 9, 2007 Share Posted October 9, 2007 well, the battery stores energy. Let's say the battery acts as a capacitor. A capacitor only stores energy when there is a charge differential across its legs... I could be wrong about this (there are some brainiacs here who will correct me), but you can supply +12V or +12000V to a battery or capacitor all day long, but if the other side isn't connected, it's not really +anything, because there is no voltage differential across its legs. Kinda like if it's not a complete circuit there is no difference in potential? This issue was beat to death with the Bimmer Tech Group in the past year. How many pages of engineering posts do you want me to send you? Link to comment Share on other sites More sharing options...
slngsht Posted October 10, 2007 Share Posted October 10, 2007 none :lol: their conclusion was that the battery acts like a capacitor when only one terminal is connected? Link to comment Share on other sites More sharing options...
Arya Ebrahimi Posted October 10, 2007 Share Posted October 10, 2007 I just remove the battery completely. That way it's not a factor in the equation Link to comment Share on other sites More sharing options...
BobDrye Posted October 10, 2007 Share Posted October 10, 2007 I just remove the battery completely. That way it's not a factor in the equation Sorry, but your missing the point! Link to comment Share on other sites More sharing options...
sporqster Posted October 10, 2007 Author Share Posted October 10, 2007 So what are you saying Bob? Just grind off the paint and get to welding? Don't disconnect anything? Cranked all the way, my little cheapo chinese mig dumps about 20AMPS at 20V into a weld. How much damage could I really do with that?!? 20V prolly wouldn't blow up anything instantaneously, right?!? I welded up new trailing arm attachment brackets (going to rod ends to make more room for rubber under the fenders) with the battery disconnected, left the harnesses to the computer under the dash alone. http://www.savannahoosiers.com/schemat.JPG Link to comment Share on other sites More sharing options...
BobDrye Posted October 10, 2007 Share Posted October 10, 2007 That is what I'm saying. The battery provides protection and doesn't cause damage. The voltage used in Arc, Tig welding isn't high enough to do any damage. They actually sell capacitors to use when welding on a car. I don't have the time to dig up the article as I will be in BMW School for the next 4 days, but I will post it next week. Link to comment Share on other sites More sharing options...
slngsht Posted October 10, 2007 Share Posted October 10, 2007 That is what I'm saying. The battery provides protection and doesn't cause damage. The voltage used in Arc, Tig welding isn't high enough to do any damage. They actually sell capacitors to use when welding on a car. I don't have the time to dig up the article as I will be in BMW School for the next 4 days, but I will post it next week. Oh, that's not how I understood your first post. I thought you were saying even leaving one leg of the battery hooked up will cause damage. I think the rationale for disconnecting the battery is that it will actually isolate many circuits in the car that have keep-alive functionality. Link to comment Share on other sites More sharing options...
stevet Posted October 11, 2007 Share Posted October 11, 2007 Man this is a tough post. What's a battery Link to comment Share on other sites More sharing options...
JohnK Posted May 11, 2008 Share Posted May 11, 2008 That is what I'm saying. The battery provides protection and doesn't cause damage. The voltage used in Arc, Tig welding isn't high enough to do any damage. They actually sell capacitors to use when welding on a car. I don't have the time to dig up the article as I will be in BMW School for the next 4 days, but I will post it next week. Coming to the issue late: OK, so do you still have the article you mention? I understand that, with the battery connected, you've got a complete circuit for any introduced current to flow through. The voltage isn't high so you can, what, charge your battery a little? If the battery when disconnected acts as a capacitor wouldn't that be, as a capacitor is, a shock absorber? The factories must know about this stuff, so it would make sense to hear about that - "practice" trumps theory. My concern is what is introduced and how. If your TIG machine has high-frequency start couldn't it induce current in your harness, or voltage as in a transformer/coil? Also, if you're welding any aluminum on your car you're faced with even more potential for induced current with the AC. On the other side, an ordinary working automotive electrical environment is horribly noisy not to mention things caused by the occasional negligent mechanic. ECUs must be pretty much bullet proofed for general consumption. I've been removing my ECU and the Immobilizer on the ignition switch when I do any welding out of general paranoia. Anybody here a member of the American Welding Society? Link to comment Share on other sites More sharing options...
haiku88 Posted May 14, 2008 Share Posted May 14, 2008 Interesting question, just did some MIG welding on my car yesterday, removed the ECU and disconnected the battery first per conventional wisdom. But earlier I'd bought some parts at a busy exhaust shop and saw a lot of welding going on, and AFAIK they were not disconnecting anything....next time I'm there I will ask what they know about this, if some cars are damaged by welding they would know about it. BTW, drove the 7 there and thought that might help as I was only buying a few parts and it seemed to, got 2' of straight pipe, a bend done, a flange, and 2 kinds of clamps for $18... Link to comment Share on other sites More sharing options...
southwind25 Posted May 14, 2008 Share Posted May 14, 2008 I have Mig'd ,Tig'd, arc'd and rig'ged without disconecting anything.. havnt had a problem yet. yet. :leaving: heres one tidbit though....dont hold metal in place with a magnet while tigging..wow what a light show Link to comment Share on other sites More sharing options...
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