Welding on tractor advice

[k0ua]

And just to add some fat to the fire, I am going to state that electricity does not JUST take the path of least resistance, electricity takes all paths. Yes I know I just contradicted an old rule, but I say the old rule attempts to simplify a complex issue. I say electricity takes all paths and the amount of current that flows in each path is inversely proportional to the resistance of each path. For example, if you place 2 resistors in parrallel lets say a 1 ohm resistor and a 100 ohm resistor and apply 10 volts DC across them there will be a current flow in each resistor not just a current flow in the 1 ohm resistor. Yes much more current will flow in the 1 ohm resistor, ( 10 amps of current in this case and this is what most people would call a short) than in the 100 ohm resistor but you still have some current flowing in the 100 ohm resistor ( .1 amps in this case ). If a voltage is applied across a resistor and current is flowing thru it, then power is being dissapated in that resistor (P=EI) I am not saying that in practical life that you are going to fry your electronics by welding on some part of your tractor. Maybe you are and maybe you aint. What I am saying is that it is possible. And I am saying that electricity does NOT take the path of least resistance but it DOES take ALL resistive paths. Yes I know I come across in this discussion as speaking as an engineer without any practical experience and I am in no way trying to denigrate all of you guys with years of practical experience welding on things for a living, I am just attempting to set the record straight on using old simple rules to describe complex issues. Here is one link that does discuss this:

The Path of Least Resistance

Happy welding

James K0UA

 

[dex3361]

I have seen bearings damaged from electrical current flowing through it. It takes as little as 200 millivolt potential to cause a current flow across a bearing. Welding set up incorrectly will cause bearing damage but it is not usually apparent till later.:thumbsup:

 

[Baby Grand]

As Moored4 observes, if the primary current path is through the bearing, you will probably do damage to the bearing. James K0UA also brings up an interesting point about secondary current flows.

My test is this: would the dealership replace the bearings or electronics that were damaged if they knew you had been welding on the tractor? Would they repair or replace anything else on the tractor that failed in a matter completely unrelated to your welding (say an engine or tranmission failure) if they knew you had been welding on the tractor? Call them up and ask them before you strike that arc.

Not saying that this proves anything about the potential for damage - just suggesting you explore the consequences of your actions on any future claims before you try it.

When I have any doubt, I separate whatever I'm welding from what I want to protect. That's what I was instructed to do in welding school.

Troubleshooting - SKF.com / Products / Interactive Engineering Catalogue/5

Mechanical engineering other topics - Plain Bearing Damage

 

[mwb]

It is dangerous to remove the positive cable first; if you want to isolate the battery remove the negative cable first. While the negative is still attached you have a much greater risk of grounding the positive to anything metal. If you short between the neg and chasis it doesn't matter - you only have to avoid shorting to the positive post.

 

[zmansmac]

Thanks for all the replies guys. I see this thread got off on a tangent about the bearings but it is all interesting reading. I didn't mention that I will be using a mig welder but I don't believe that would make any difference. And since it's fairly easy to do I will disconnect my negative only terminal. After all, it's not like I'm going to lose any presets on a radio.

 

[Gary Fowler]

If you note, I didnt say it couldnt happen, but I can with authority say that if it happens, the welder is intentionally trying to mess up the equipment and should be fired immediately. About all I can say to folks who would ground to the shaft of a pump or any other rotating piece of equipment and then weld on the housing is they should get a Darwin award.
As I stated, to arc a bearing one would have to ground to the outer race, (housing) and weld on the shaft which is what you are saying happened. Anyone stupidly welding on their equipment and doing something like that deserves to have to replace the bearings.
I have never had a bearing failure because we preach constantly to correctly ground the weldment and in construction we have no need to be welding on the impellers or turbines of new equipment.

 

[Hollow]

I read a story not long ago where man had just bought a Ford truck and put a flat bed on it. When he went to weld something to steel bed without disconnecting the batteries it fried the computer in the truck. I forget exactly how much the fix was but I think it was in the $4,000 to $6,000 range.

 

[Gary Fowler]

That price sounds about right for total replacement. That is what my Chevy dealer priced me for computer replacement cost when trying to get me to buy and extended warranty. I didnt buy one and so far no issues with my 2007. Only been back to the dealer once to replace the broken tail lens from factory recall that they broke again when they replaced it. IF you tighten the screws holding in those tail light assemblies, they break. Of course I didnt see this for years. A little JB Weld and it is better than new now.
But that is getting off the subject matter.
You hear those tales and think if welding on something burns up the computers, then it would do it everytime someone struck an arc on a vehicle when they didnt unhook the battery but that doesnt happen. For it to do it once in 1000 times means someone did something very wrong that everyone else didnt do but just tells everyone that he was welding on a XXXXX.
If you worry that something will happen, just remove the ground from your battery and it is then isolated from the system. Just dont clamp your ground around a wiring harness, tail light wires, etc and short thru them because you are downstream of all the fuses at that point and a back feed is going to fry something more than the computers.

 

[Jerry/MT]

I have a FEL mounted snow plow, that unfortunately has had little action this winter in SE Michigan, and had the connection bracket for my power angle break. It's a bit of a hassle to remove the plow and I would prefer to make the weld repair with it still attached. I know this can be done but I'm not sure if I risk any damage to the tractor electrical system. To be safe I'm thinking I could just disconnect the battery but I'm not sure if I only need to disconnect the positive, negative or both. Any advice before our next "fantasy" snowfall would be appreciated.

JohnZ
B7500

I believe the key issue is to make sure the welder ground connection is right near where you are welding. As an exaggeration, Don't have the ground connection on the drawbar while you weld on the bucket in the front. obviously you also don't want to have your ground calmp around any wire bundles either.

 

[WilliamBos]

I'm doing it on a daily basis. Just put your ground cable as close to the area your welding and you'll have no problems at all. Good luck.

Disconnecting the battery a good idea? Will be doing some this summer.