Welding Tips and Tricks

Ok guys,

I've heard that if your welding, say on a truck bumper, trailer hitch, bed, you should you disconnect the + battery terminal.

Something like, "weldering" current travels through some of the electrical components and could screw something up....

Any insight/theories/"horror stories you would like to share?

Thanks,

John

The idea is to protect the computers common in today's vehicles. They're all connected to ground, so disconnecting the battery ground does nothing.

I'm not sure whether there's any truth to the value of disconnecting the + cable, but since there's no harm on it, why not play it safe?

Steve S

Hey,

I always disconnect the batteries of any vehicles completely before welding on them, and then put the earth or work return or ground as close as possible to the area of welding. As Steve says, play it safe.

Mick

I worked on a truck putting a receiver hitch on the back, and I didn't disconnect the battery cable,
Later that week the guy noticed his radio was dead
could it of been my fault or just a coincidence ?

John

As you worked on the back of the car it seems like a coincidence if the grounding clamp was also fitted at the rear.

As a precaution, if you work on cars more often, it could be an idea to invest in a clip-on surge protector/supressor like this:

http://www.amazon.com/OTC-3386-Antizap- ... B000F5JLP0

Various types are available and they are usually also recommended in the official service manuals of various car manufacturers if any welding is being done on a car somewhere.

Bye, Arno.

thanks Arno.
I'll look into one....

John

Just keep the ground clamp as close as possible to the weld joint.

O try to remember to disconnect them especially when using foot pedal tig. I'm always concerned what the high freq will do.

I was assisting the welder at the one place I worked and we were building a water truck for oil field work and when we went to mount it to the truck we didn't unhook the battery on the International truck we were welding on. The next day our boss was contacting International. LUCKILY the truck was still under warranty. Now standard procedure in the shop is to unhook the batteries before hooking a ground to any vehicle.

I always unhook the battery on a vehicle I am welding on. Why take a chance at burning out the boards in the car? Its a simple thing to do. Why not prevent damage. Seams pretty stupid not too.

Hey, No name calling!!! (you might be right tho)
But, I was wondering if a guy could screw something up(like a radio) by welding on the back bumper?
It's a interesting theory.
I try and always unhook the battery, But you know in a hurry(duel battery's too), and I just didn't.
Anyone have any technical(advanced electronic physics) information on the subject?

~John

I don't know the technical explanation for it but I've been called stupid so many times, almost lost my job for it and will never weld on a vehicle without unhooking the battery. That was a big learning experience for me. Sometimes the best teacher is yourself.

If you weld on the back of the car, and ground on the front bumper, you run the risk of frying every electronics board in between. If the path of least resistance happens to be through your ECM, then electricity, the lazy bastard, will take it. Same as clamping on an axle tube and welding on the frame. You run a highly elevated risk of arcing between the bearings. Even if they don't weld themselves, that becomes a super hard spot compared to the surrounding metal. Just clamp as close as possible to where you are welding. As I stated before, electricity is lazy and will always take the shortest path of least resistance. No need to have an advanced degree, just basic electrical and circuit knowledge.

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Removed a couple of snapped exhaust manifold bolts from the head of a Dodge Ram a couple of months back. Disconnected the battery, switched to lift arc and connected my work clamp the the neg battery lead. No probs whatsoever. I won't use high freq cause it's basically intentional ESD.

I have seen where someone supposedly welded on a car with out disconnecting the batteries and it fried the gauges.
We use CAT engines on our equipment and our engineering department requires us to remove the computers if welding is to occur on the units. A little extreme but there are no mistakes that way.
The bearings on the car are the same as the crane. Even though it is highly unlikely to happen, never weld on a unit hooked up to a crane with chains or slings. Why risk it?
-Jonathan

Yup its not worth taking the risk. Unhook it all the way and play it safe. Frying any kind of electronics in a vehicle is just lazy on the person doing it too. Not to mention what could it do if it decided to travel through the wiring harness? How much would that cost to repair? As much as the comp board in the vehicle?

I was always told to never weld on a vehicle without hanging a chain from the vehicle and laying it on the ground(dirt). That goes back farther than I am old. I always do it anyway.

I would not worry about it at all i have herd the same thing but i have a 2009 f350 with welding bed and all kinds of extras on it. I have a ground clamp in side my lead box where i ground to the bed and work all over it and get ground threw the bed. IF its a one off time you work on it i would do it but im not unhooking 2 battries every thime i work off my truck lol

DCALLWELD wrote:I would not worry about it at all i have herd the same thing but i have a 2009 f350 with welding bed and all kinds of extras on it. I have a ground clamp in side my lead box where i ground to the bed and work all over it and get ground threw the bed. IF its a one off time you work on it i would do it but im not unhooking 2 battries every thime i work off my truck lol

I work off the back of my 02 f350 also with no problems. All i do off this rig is stick and scratch start tig. I just worry about the high freq tig units.

Are truck beds not isolated from the truck frame with grommets that the bed bolts go through? Perhaps there is not enough ground to travel through the frame.

A factory bed is grounded to the cap of the truck by a ground strap going from the cab to bed , if you look in-between the little gap in-between your truck and bed you can see it. then the cab is grounded to the frame and engine that is directly grounded to the batteries. ON most welding beds ( at least people I know ) will weld the bed to the truck frame. And im talking brand new trucks, granted you loose factory warranty these boys are not worried about that because they are chasing pipe all over the country and put 100k on a truck in a year and in about 4 to 5 years are in a new truck. MY bed is bolted to the frame but is still in direct metal to metal contact with the frame. If I go and weld on some one else's machine , Trash compactor in a landfill yesterday for instance , I disconnect the batteries just to be safe because I don't want to pay to put a computer in a have million dollar machine on the off chance something goes wrong.

Ok I get that you are comfortable with welding on your truck. The danger of that positive feed going through into the trucks computer system is reduced greatly. You are not welding on the actual truck. Much like you say you unplug any batteries on what ever you are welding as a precaution so should someone that is actually welding metal onto a car with computer boards in it. An older classic such as say a pre 80 Camaro or Mustang will not have computer systems in it. Unless it has been upgraded to MSD ignition. Anything after that its just a safety measure to make sure nothing happens to the car.

What does it hurt to make sure you don't blow out a $1000 computer board? I sure wouldn't want to find out the stupid car won't start and have to tow it to a mechanic and find out that is why.

I have a custom pipeline style bed that sits right on the frame.

Before I got into just welding as a profession, I spent a decade as an ASE certified mechanic, both on heavy duty diesels and automobiles. I can tell you with the full backing of every single OEM out there that you can do major damage to the modules in the vehicle if the ground lead is not disconnected prior to welding. High frequency TIG is particularly bad, but under the right conditions MIG or arc can do it too. Modern vehicles do incorporate surge suppression devices built into them, mostly for catastrophic surging of a failing alternator or some idiot hooking up jumper cables backwards, but they are not in every vehicle and cannot always protect to enough.

The major thing that fries out is the fact that most vehicle sensors use a 5v reference signal, which according to conditions experienced by the individual sensors send varying voltages or digital square waves back to the PCM which in turn converts that to known data and adjusts the parameters of the fuel and ignition accordingly in milliseconds. Things such as ignition coils, fuel injectors and such are not controlled by delivering power but by controlling grounds VIA the PCM. Now think of electricity as a hydraulic system, which is essentially the same principle. Voltage is pressure, amps are gallons per minute. If this vehicle was made to run on 12.6 volts (which is a fully charged battery of 6 cells contributing 2.1v per cell) and can tolerate 14.6v running (this allows for small voltage drops due to surge loads such as turning on the heater, headlights, etc.) then it was made to hold back 14.6v of pressure. Now hook in your MIG welder and run a pass at 21v or so. You have increased the pressure beyond design specs as surely as if you put 5000psi into a hydraulic system with hoses rated for 4000psi. You all know what will happen then.

By realizing that the average new vehicle contains at least 5 or 6 computer controlled modules (or more, a fully loaded 2012 F-150 can contain as many as 21 according to my SnapOn scanner that can access each and every one of them) and they use ground side switching, it makes sense that the practice of allowing the energy of a weld arc to surge through them using the path of a vehicle's connected ground lead not only can, but will cause severe damage to one or more systems in this vehicle. The biggest cause of damage seems to be from poor grounding, either from vehicles that had poor grounds themselves or a welder not bothering to make sure his ground was clean and tight first. Also, placing a ground at a random spot on a vehicle and welding some distance from it will cause the energy to flow through more of the truck. Batteries have a capacitance effect, and when electricity cannot flow through the path you chose due to resistance it will find somewhere it wants to go.

When I was a new tech at a Mack dealership we had a motorcoach for a race team come in for work. They wanted some things that needed welding. But anyone who has worked on a coach bus or motorhome can attest that because they are custom built to specs there are not only no wiring diagrams available for each one but that they also can vary by who was working at the factory on that day of the build. The owner had a very large plasma screen in it (this was 10 years ago when these things were VERY big bucks to get) and it got fried due to a ground to the power inverter being left on. Shop ate a 4 figure bill to replace it. Since then, I have seen many cars and trucks welded on by people who did damage by not unhooking the ground cable first. I took a few of the PCM's apart myself to prove they were bad and found ground side transistors fried out visibly. This is not an urban myth like leaving a battery on concrete, it is a proven fact. Just because it doesn't happen every time to everyone immediately after welding doesn't mean it will not. When one of these modules fails, if it is proven to be your shop at fault, the bill is 4 digits for a repair. That makes the bossman VERY mad at you.

One product I like which is also mentioned earlier in this is called anti-zap. You hook it to both cables and it is like a surge suppressor. Myself, I unhook every battery ground and make sure it cannot possibly touch the battery. Some are tight to move out of the way. Put an old welding glove on it. Do whatever you need to do to protect it. Nothing is worse than an angry customer except the angry boss that will follow him. Always pull the grounds off the battery of anything that you are going to weld on. I do that even when I weld on a muffler with a little MIG machine.

I was lead to believe it was a safety issue more then a wiring issue. Yes wiring could get damaged, but the battery could develop hydrogen gas witch could blow up. I have seen batteries blow up from a spark a big event indeed.