Welding without frying

[k0ua]

I still don't see how disconnecting the batt isolates the PCM from the welding voltage??? It disconnects it from the batteries 12v, but the PCM still has wires hooked to the chassis and various other sensors that may be conducting the welding voltage

I have always though the same thing, not to mention those sensors are connected by wires, and those wires lay next to the chassis that could have current flowing thru it. (if you are dumb enough not to put the clamp as close to the weldment as possible) and if there is current flowing in the chassis and a copper conductor is nearby, a voltage can be induced into the conductor by induction. And Mosfets and other semiconductor devices sleeping quietly in their beds could possibly be damaged. I am of the OK, a powered down semiconductor is probably less susceptible to damage than a powered up one, and disconnecting the battery terminals sure can't hurt, but I am not so sure it is the panacea that some have alluded to. So I think disconnect the battery, both leads, and make sure they do not touch the chassis, and put the "ground" clamp as close as possible to the weldment, to minimize current flow in the chassis of the vehicle, and hope for the best. I sure don't claim to be an expert in this, but those are my thoughts.

James K0UA

 

[LD1]

OK to make sure the positive don't contact the chassis, but the other end of the ground is directly connected to the chassis, so weather it touches.......

 

[Herkypilot]

As a side note, the major welder manufacturers have e-learn sections on their web sites to get free advice on welding. Also you can find many Youtube vids on welding. I'd look at some of that prior to getting started. I took a basic MIG welding class at a community college which all we did was weld on scrap mild steel for each 2 hour class. Money well spent. I just modified some of my Wildkat implements last weekend to make them fit properly on my Kubota quick attach loader. They fit great now.

 

[k0ua]

OK to make sure the positive don't contact the chassis, but the other end of the ground is directly connected to the chassis, so weather it touches.......

good point!

 

[DwightD123]

Good stuff guys. Making sense. Let me ask a question off topic but within the responses of the
thread. If I were to buy a diff welder it would be the small Lincoln one. Getting the one I could probably afford right now in a MIG says it will weld 1/8 mild steel. This is less than the Chic Elec claims. Is that because it is MIG not arc or is it over claiming on part of Chic Elec part?

 

[Arc weld]

I briefly scrolled through this thread but thought it important to respond. Any type of welding that uses an electric arc is arc welding. Many people think arc welding refers only to stick welding. There's SMAW (stick), GMAW(MIG), GTAW(TIG), FCAW(Flux-core), SAW(Sub-arc), etc., etc. The common denominator is the AW stands for arc welding.

If you are going to buy a welding machine, DON'T waste your money on an off brand 90 amp machine or even a higher amp off brand machine. You'd be better off waiting till you could afford something better or looking for a good used machine like an Idealarc 250 or Dialarc 250 for stick welding. Having a poor machine to start with will make welding very frustrating! I think an Everlast or Longevity machine would certainly be worth considering though. They obviously have been around long enough that they aren't some fly-by-night outfit with no way of contacting them after they take your money. They have received some excellent reviews as well. Don't let the odd bad review scare you away. Lincoln and Miller have had warranty issues as well on some machines. You want something you can get parts for 3,5,7 years down the road. Don't be worried that their machines are made in China. Go look at one of the most respected names in cutting torches what it says on most of their boxes. Yes, most Victor torch sets, except for the real pricey sets, are made in china.

 

[jwmorris]

My thought of disconnecting +\- cables was just to isolate RFI not current. Haven't ever had any problems like that welding but...

Connecting the ground to the part you are welding back on like the hitch itself would be an easy solution.

If you get the little Lincoln get a 230v machine, they work well despite a short duty cycle.

 

[gwdixon]

Since you asked...I have a Everlast PA 200 (stick only...well, and I hear TIG with some effort) machine that will do just about any welding job found around the farm. Plenty of amperage, 5 year warranty, good duty cycle, and will even do 3/16" hardfacing. The price is very reasonable and TBN members get a discount (usually).

The Longevity basic stick machine also gets good reviews at a reasonable price. I think it is the 250 model. Contact Shield Arc since he has hands-on experience with both machines.

You will NOT be happy with the weak Harbor Freight or other obscure brands once you get to a serious project in my opinion. It will be worth the little extra money that will be spent to get a powerhouse machine...well, at least enough power for the farm.

The big names come with big prices. Great reliability for the professional but one pretty much has to be making money with the machine to justify the expense.

 

[yomax4]

It never hurts to double ground as well. I always have an extra ground hooked to a rod driven into the earth. Undo battery too. Why not do everything you can to prevent issues. I always weld on my plow mount on my ATV's instead of the bolt on version that comes loose all the time.

 

[Jorville]

The last two trucks I've bought, both cab & chassis. A 2004 F-550, and a 2007 Dodge 3500, had an envelope in the glove box addressed to the upfitters. Both manufactures said to disconnect both batteries before doing any welding on the truck. The Ford had a start up procedure, the Dodge did not. The Ford I built a dump bed for, I had to weld the hinge to the frame. The Dodge I made a sub frame and used holes already in the frame to bolt the sub frame, so I didn't have to weld to the truck.
Best advice has already been given, disconnect the battery, and keep the ground clamp as close to the welding as possible.
I've always wondered about Tig welding using high frequency on a car / truck with on board computers?

My son is taking an auto body class at a tech school. They give three welding classes oxygen/acetylene, ARC, and MIG. The instructor said there will not be a TIG class because of the electronics on all of the new cars today. So I am assuming the high frequency will damage the newer cars electronics. Wether that is fact or just their opinion I do not know.

 

[firemanmike69]

I still don't see how disconnecting the batt isolates the PCM from the welding voltage??? It disconnects it from the batteries 12v, but the PCM still has wires hooked to the chassis and various other sensors that may be conducting the welding voltage

Just did some welding on a brand new paver at work with the factory rep from Sweden, his words were " when you weld on my machine you will disconnect battery shut off switch and remove harness from machine controller" that would eliminate any way that stray voltage could find the control computer and damage it. On the other hand on our other equipment it is also the manufacturers recommendation that the controllers be separately unhooked and we never do that, just unhook the batteries and weld away with no problem

 

[IslandTractor]

My son is taking an auto body class at a tech school. They give three welding classes oxygen/acetylene, ARC, and MIG. The instructor said there will not be a TIG class because of the electronics on all of the new cars today. So I am assuming the high frequency will damage the newer cars electronics. Wether that is fact or just their opinion I do not know.

I don't know about high frequency starts but the basic TIG welding process is no different than any other arc weld with regard to how electric current flows. Why would lift or scratch start TIG differ at all from SMAW with regard to car electronics?

 

[Shield Arc]

Only reason I'm curious about high frequency on a vehicle, I have an aluminum flatbed on my 2007 truck. So far I have not damaged it, but it is a matter of time! Also been thinking of ways to build a lumber rack for it, but haven't come up with a design yet. I can always take the bed off, but that would be a lot of work, truly would be the safest way to go.

 

[LD1]

Unplugging the harness from the controller (pcm) makes sense. That would isolate it for sure. But simple unhooking the battery to prevent damage to the computer has me baffled??

But also keep in mind that most modern cars have more than one computer. Most also have a BCM (body control module) that would also need unplugged if you are that concerned with it.