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92DripCherokee
January 3rd, 2010, 22:39
What electrics need to be ungrounded before welding?
Don't want to cause a release of the magic electronic smoke.

I'm midway into tearing out the passenger rear floorpan, going to weld in a repro stamping.

battery
PCM computer grounds to driver's fender
alternator B+, and sensing

anything else? Fuel pump, or stereo?

DesertRunner
January 3rd, 2010, 22:42
ive only ever disconnected the battery. welded up a bumper and a tire mount reinforced the rear floor pan...

bcmaxx
January 3rd, 2010, 22:46
What electrics need to be ungrounded before welding?
Don't want to cause a release of the magic electronic smoke.

I'm midway into tearing out the passenger rear floorpan, going to weld in a repro stamping.

battery
PCM computer grounds to driver's fender
alternator B+, and sensing

anything else? Fuel pump, or stereo?
Hmm never thought it, Never unhooked anything before when welding. Have welded in replacement rockers, unibody stiffeners and rear chassis stiffeners and no harm done

92DripCherokee
January 3rd, 2010, 22:53
hey, that's easy enough with my marine terminals
After all this brutality on metal, the jeep has to come back to life

I actually do work from ya'lls advice here at NAXJA...and I've lived to tell about it.
I'm thinking of discharging a CO2 extinguisher into the fuel tank, before welding. Just to make the fireball a little less orange.:flame:

DesertRunner
January 3rd, 2010, 22:57
your welding on a fuel tank? if you are remove from jeep remove all sending units ect and full with water!

92DripCherokee
January 3rd, 2010, 23:08
oh no, not directly on the tank, not like the bro here.
http://www.youtube.com/watch?v=tD4KiQEnxwQ
- If you've never seen a sober man weld on a fueled tank, not many of these high powered mutants are alive at any one time.

just over the front spring hanger is the closest I'll be
welding near the fuel tank, probably close enough to need cross ventilation!


The rot in the rear pan will have to wait until I have a safe, distant place to keep the fuel tank.

DesertRunner
January 4th, 2010, 17:21
might want to go to harborfreight or somewhere similar and get a welding blanket.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95015

Brown Dog
January 4th, 2010, 17:43
Usually, I disconnect both the positive and negative terminals on the battery. Call me over-cautious, but I once had a very bad experience arc-welding on a VW. OK, it was over 30 years ago, and I didn't know what I was doing, but it made a lasting impression!

kastein
January 4th, 2010, 18:23
Don't bother ungrounding anything, but I'd pull the fuel tank and battery and stop off the fuel lines.

dgrigorenko
January 4th, 2010, 18:25
I have talked to people that have cooked their PCM by welding, I have also talked to people who have never unhooked anything and have never had anything go weong... That said, I disconnect both bAttery terminals just to be safe, I mean you might as well, better safe than sorry and it's quick

stroked88
January 4th, 2010, 19:51
Don't bother ungrounding anything, but I'd pull the fuel tank and battery and stop off the fuel lines.


dont listen to this guy... you will fry your ecu if you weld on the chassis. maybe not the first time but it will happen. unground the battery and then everything will be fine

pierceME311
January 4th, 2010, 20:03
dont listen to this guy... you will fry your ecu if you weld on the chassis. maybe not the first time but it will happen. unground the battery and then everything will be fine

"that guy" happens to be an electrical engineer if I'm not mistaken. Check out his threads because he is developing custom electronics specifically for our XJ's.

ECKSJAY
January 4th, 2010, 20:12
dont listen to this guy... you will fry your ecu if you weld on the chassis. maybe not the first time but it will happen. unground the battery and then everything will be fine

Deep breath...deep breath...

cmelo
January 4th, 2010, 20:44
Don't bother ungrounding anything, but I'd pull the fuel tank and battery and stop off the fuel lines.

If Ken is comfortable welding without ungrounding things I feel pretty comfortable. The consensus seems like if you're really worried just disconnect the battery cables. You seem worried, so unhook the battery cables...

kastein
January 4th, 2010, 21:31
dont listen to this guy... you will fry your ecu if you weld on the chassis. maybe not the first time but it will happen. unground the battery and then everything will be fine
:dunno: as long as you get a good ground on the frame and don't smack the welder into any wiring, you will be absolutely 100% fine. People have had lightning strike a car they were *driving* in, it went through the frame, axles, and tires to ground. Blew the crap out of their wheel bearings, diff carrier bearings etc but the engine continued running and the car kept driving. That's a few billion volts at a few million to a few billion amps; your welder is maybe 20 volts and a few hundred amps if you're hardcore. I'm 100% comfortable welding on my XJ with whatever the hell I want in it - including hundreds of dollars of extremely sensitive radios. Hell, I will bet you a case of beer I can throw a weld bead on a piece of 1/8 plate bolted to the side of a desktop computer case without damaging the computer internals at all.

"that guy" happens to be an electrical engineer if I'm not mistaken. Check out his threads because he is developing custom electronics specifically for our XJ's.
Correct, though I try not to toot my own horn that much :o. If old_man disagrees with me on welding without disconnecting stuff, I'd take it quite seriously as he has a lot more experience than I do, but I'd probably still try doing it again to test my luck. I've welded stuff on my axles, exhaust, and frame without even disconnecting the battery and had absolutely no issues; I likely will only disconnect the battery when I do new floorpans as I don't want welding heat to melt a wire and cause an electrical fire - I'd rather have it just melt a wire if I heat something up too close to one.

thechief86
January 4th, 2010, 21:38
oh no, not directly on the tank, not like the bro here.
http://www.youtube.com/watch?v=tD4KiQEnxwQ
- If you've never seen a sober man weld on a fueled tank, not many of these high powered mutants are alive at any one time.

just over the front spring hanger is the closest I'll be
welding near the fuel tank, probably close enough to need cross ventilation!


The rot in the rear pan will have to wait until I have a safe, distant place to keep the fuel tank.
i kept hoping for the kaboom, and it never came:(:flame:

JRW7072009
January 4th, 2010, 21:59
At work I always take off the pos side of the battery just to be safe and we are required too on customers vehicles. We also have a surge protector thing (not sure of the real name) to hook on the battery if we need to but I would rather disconnect the battery to make sure I know its not going to do anything.

helliphinon8
January 5th, 2010, 00:20
I think that the whole removing the positive battery cable comes from using a TIG welder. The high frequency arc start on these welders does weird things to electronics. I've always done it after I fried a Corvette C5 computer. Oops!! :laugh:

techno1154
January 5th, 2010, 06:58
I had good luck for awhile welding on heavy equipment with disconnecting the battery. One day my luck ran out. Using a stick at 200 amp to weld a boom. There was a kaboom, and a lot of smoke. The battery blue 2/3 of the top and all the factory smoke escaped from the alternator.

RCP Phx
January 5th, 2010, 07:10
The other key note is to place the welder ground clamp as close as possible to where you are welding and in a fashion that any possible currents would not pass thru an area that has electronics in it!

jeeperjohn
January 5th, 2010, 07:53
I only disco the battery when I weld. Never had a problem.

WebDog
January 5th, 2010, 10:17
The other key note is to place the welder ground clamp as close as possible to where you are welding and in a fashion that any possible currents would not pass thru an area that has electronics in it!

thats all i have ever done and no problems yet, and i have probably welded on my rig more then some of you...

go1lum
January 5th, 2010, 11:07
I think that the whole removing the positive battery cable comes from using a TIG welder. The high frequency arc start on these welders does weird things to electronics. I've always done it after I fried a Corvette C5 computer. Oops!! :laugh:

Ding ding ding. High freq from tig machines can mess with electronics. I have never unplugged anything when welding on cars. Keep your work clamp close to the area that you are welding. The electricity will take the path of least resistance.

jeeperjohn
January 5th, 2010, 15:05
Ding ding ding. High freq from tig machines can mess with electronics. I have never unplugged anything when welding on cars. Keep your work clamp close to the area that you are welding. The electricity will take the path of least resistance.
Whenever I push the button on my TIG welder without striking an arc, my sprinklers come on for just a second then turn off again. Wierd

kastein
January 5th, 2010, 15:11
Whenever I push the button on my TIG welder without striking an arc, my sprinklers come on for just a second then turn off again. Wierd
Probably the high frequency arc ignition circuit inducing a large amount of voltage in the long wires leading to the sprinklers, I'd bet. They work great as antennas for all sorts of signals not intended for them...

gollum's also got another great point, ALWAYS keep that ground clamp as close as possible to your work location. V = IR, the further the current has to travel, the more resistance it passes through, so the more of a voltage you'll be creating across your frame. This will both reduce the heat you get from the arc on your welder and increase the wacky signals you'll send to anything grounded to widely spaced locations on the frame. That's why a good solid ground connection for the welder is very important.