Welding

[Captain13]

The problem lies with the ECU and the welder sharing a single conductor – the vehicle’s body. For the welder to push current through the body, it must impose a voltage across it regardless of how good your earthing is (Ohm’s law). With the battery connected there is a closed electrical loop where the voltage across the vehicle’s body COULD add to the battery’s voltage and cause an over-voltage condition at the ECU. With the battery’s negative terminal disconnected, the loop is broken, both terminals of the ECU will float to the same voltage and no over-voltage will occur regardless of the voltage across the vehicle’s body.

Look at various welder forums including American Welding Society, Miller, Hobart and you can see that the recommendation from the professionals is to remove the negative terminal.

 

[Henro]

Would love it if someone were intersted enough to take the time to produce an electrical drawing showing the dangers they perceive.

As far as which terminal of the battery to disconnect, what difference can it make? If either battery terminal is disconnected, the battery is removed from the circuit and is hanging in free air, so it should not matter which terminal is removed from the battery as far as welding goes.

Actually it should not matter as far as anything goes with respect to the battery, if you think about it. Remove the positive terminal connection, and short any wire to the frame and nothing happens if the tractor is not running. Remove the negative battery terminal and short any wire to the frame and nothing will happen if the tractor is not running.

 

[GeoHorn]

Negative terminal disconnection is best for a couple reasons:
1. It’s safer from the standpoint of using metal tools for the disconnect because of reduced possibility of shorting via the tool. In addition, some harnesses have a secondary circuit connected directly to the positive terminal possibly complicating that action.
2. Electrons flow from Negative to the Positive terminal. Disconnecting the negative terminal can be thought of as preventing any current leakage to the frame…and avoiding any capacitance via the battery case. (I have a hard time believing that myself, but that’s what my electrical-engineer son says.)

Be certain that when you disconnect the main battery…that you do so with the ignition and any electrical circuits in the OFF position (not active)… to avoid activating any back-up or auxiliary power sources. Otherwise their internal (backup) batteries will come into the circuit, even if discharged, and can provide an avenue for current flow when welding.

For example, per the 2019 Chevrolet Equinox service manual:

“For Vehicles equipped with OnStar® (UE1) with Back Up Battery: The Back Up Battery is a redundant power supply to allow limited OnStar® functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar®module). Do not disconnect the main vehicle battery or remove the OnStar® fuse with the ignition key in any position other than OFF. Retained accessory power should be allowed to time out or be disabled (simply opening the driver door should disable retained accessory power) before disconnecting power. Disconnecting power to the OnStar® module in any way while the ignition is On or with retained accessory power activated may cause activation of the OnStar® Back-Up Battery system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The back-up battery is not rechargeable and once activated the back-up battery must be replaced.”
Since the backup battery is active, any welding activity that breaches the circuit will overload the device and cause damage.

 

[Captain13]

Would love it if someone were intersted enough to take the time to produce an electrical drawing showing the dangers they perceive.

As far as which terminal of the battery to disconnect, what difference can it make? If either battery terminal is disconnected, the battery is removed from the circuit and is hanging in free air, so it should not matter which terminal is removed from the battery as far as welding goes.

Actually it should not matter as far as anything goes with respect to the battery, if you think about it. Remove the positive terminal connection, and short any wire to the frame and nothing happens if the tractor is not running. Remove the negative battery terminal and short any wire to the frame and nothing will happen if the tractor is not running.

Look at my earlier post with the link. It has a diagram of the circuits with and without the battery negative connected along with an explanation of how the ECU could be affected with the battery connected. Essentially, with the battery connected, the ecu or any other electronics could float to the welder voltage. Therein lies the issue. It may not happen. But think of it like changing out the starter. You can leave the battery connected and you may or may not short the battery cable going to the starter. removing the negative is quick and easy and may save a more costly repair by doing it. Remember, when the arc strikes with the welder, there is a large electromagnetic field generated. The EMF, although brief, generates spurious high voltage spikes that easily damage electronis made to run on 5 volts DC, not 30-100 volts with spurious signals riding on top of that.

 

[Mark_BX25D]

Would love it if someone were intersted enough to take the time to produce an electrical drawing showing the dangers they perceive.

It's been done. The danger is not "perceived", it's real. It's well researched, well documented. As suggested above, look up what the pros have to say about it.

Just because your uncle Billy Bob did welding and never had a problem doesn't mean the danger is made up.

 

[Captain13]

One of the welding forums was discussing welding on the bed of a truck. The welder with 20 years experience said he blew three throttle position sensors on his welding truck before he realized that it was doing the welding on the truck bed that was taking out the sensor. I would just disconnect the battery if it was me.

 

[GreensvilleJay]

re: (I have a hard time believing that myself, but that’s what my electrical-engineer son says.)

me too, as disconnecting EITHER terminal removes the battery from the circuit so ZERO current (electrons) can flow..no comes out, none go in....

In the past I've had to correct an EE with a PHD about a few things....

as for the Onstar ramble.....since the device has been 'selfisolated', nothing external should affect it.

 

[hagrid]

Welding with oxy/acetylene removes most if not all of these concerns.

 

[Henro]

It's been done. The danger is not "perceived", it's real. It's well researched, well documented. As suggested above, look up what the pros have to say about it.

Just because your uncle Billy Bob did welding and never had a problem doesn't mean the danger is made up.

I did not mean to use the word "perceived" as a value laden term, and was rather using it to distinguish between what someone thinks is happening as his own conclusion, as compared to simply believing what another has stated.

Missed that link you (Captain13) posted for some reason. But the analysis there is a bit simplistic. For example, with the battery disconnect they still show 12V being supplied to the ECU terminal, when in reality the battery can supply no voltage to that terminal, since it is hanging in the air, and the negative terminal is not connected to anything.

Also in that same (right hand) drawing, the welder can contribute nothing to the ECU because there is no return path for current flow with the battery disconnected.

BUT the right hand drawing actually does say something if you ignore the voltage values shown. Which is: If you disconnect the battery negative terminal, you separate the ECU from the welding circuit voltage. So this is the best one can hope for.

BUT there is still a possible risk, as if anything is connected between the positive circuit wiring and frame ground, then there is still risk of applying a reverse polarity voltage to such components, wherever they may be. This risk is actually there independent of the battery.

On the other hand, if one ignores the voltages show in the other (left) drawing, and just looks at the voltage developed across the welding arc, and ignores the effect of resistance in the frame between the ground clamp, and the welding arc/negative battery terminal, there is also an important message. The welding arc voltage will either add or subtract/add (depending if AC/DC arc) but regardless, the net voltage seen at the ECU 12V terminal will be arc voltage +/- battery voltage.) This cannot be a good thing.

Conclusion is: Disconnect the negative battery terminal if you are going to weld on equipment which has electronic circuitry.

Works for me...although with no electronics on any of my tractors, I do not think this is a personal concern, but I guess it could be...

Edit: I tried to add the image from Mark's link, but failed for unknown reasons...

2nd edit: It was captain13 that posted the link with drawings I was referring to.

 

[Captain13]

Hebro, the main concern if there is not a computer and digital display is the alternator. Other than that, you should be safe. Except, as I mentioned earlier about welding on the FEL bucket, we had damage to one of the loader arms due to the ground not being connected to the bucket but rather to the frame. Electric current will always find a home if given the opportunity.

 

[Henro]

Hebro, the main concern if there is not a computer and digital display is the alternator. Other than that, you should be safe. Except, as I mentioned earlier about welding on the FEL bucket, we had damage to one of the loader arms due to the ground not being connected to the bucket but rather to the frame. Electric current will always find a home if given the opportunity.

Diodes in the alternator are very likely able to withstand arc voltage if they are reverse biased I would expect. Now the voltage regulator circuitry…not sure What might go on there.

In heavy industry welding on overhead traveling cranes is a concern as welding current can damage wheel bearings, leading to premature failure. Buildings, cranes and everything else is often steel. So the easy way is to attach the ground to the building frame, and only pull the electrode cable up on to the crane. This is prohibited due to concerns of bearing damage from the return welding current flowing back to the ground clamp, if the ground clamp is not connected to the crane itself.

Always best to keep the ground as close to the weld as possible. This would be a concern with loader pivot points as well.

There will always be a voltage developed between the electrode side of the arc and the ground clamp. As you say, current follows the path of least resistance. And voltage develops wherever current flows.

 

[GeoHorn]

Is this Horse DEAD YET..???

DISCONNECT THE *&^$% … BATTERY BEFORE WELDING ON A VEHICLE/TRACTOR/COMPUTER/ETC/ETC.

 

[Henro]

Is this Horse DEAD YET..???

DISCONNECT THE *&^$% … BATTERY BEFORE WELDING ON A VEHICLE/TRACTOR/COMPUTER/ETC/ETC.

Ha ha, the best way to kill this thread in your mind is to stop reading it.

Some people do have intellectual curiosity, and try to reason out why something should be done...

Granted the conclusion reached looks like it makes good sense to disconnect the battery before welding on a machine that has electronic controls on it.

What is the problem with discussing the reasons?

 

[ctfjr]

. . . As you say, current follows the path of least resistance. And voltage develops wherever current flows.

This is one of those old sayings that never made any sense to me. Current will follow every path from a higher voltage potential to a lower one (yes the electron flow is negative to positive).
If you had a 12 volt source and a headlight with a resistance of 2 ohms connected to it the current flow would be 6 amps. At the same time if you had a running light connected with 24 ohms resistance, current would also flow through that (.5 amp)

 

[hagrid]

What is the problem with discussing the reasons?

Hang on... I'll channel SnideBarDrip:

"I'm the best welder in Michigan and probably the world I have a working farm in Michigan and I'm the envy of my neighbors I wouldn't bother welding on a BX or a B series those are toy tractors I have thirteen MX6000000 I earn my living with those my living is way betterer than your living you are poor I was crowned Michigan State Fair Queen because of my real tractors and my pre-64 Weatherby rifles made in West Germany and my old 7.3 PowerGoat F35000 with Gail Banks everything makes 2367 horse power and 56,761 foot pounds your truck and toy tractor sucks I am the greatest"

 

[Henro]

This is one of those old sayings that never made any sense to me. Current will follow every path from a higher voltage potential to a lower one (yes the electron flow is negative to positive).
If you had a 12 volt source and a headlight with a resistance of 2 ohms connected to it the current flow would be 6 amps. At the same time if you had a running light connected with 24 ohms resistance, current would also flow through that (.5 amp)

What you say is of course true. At least if the wiring were discrete.

BUT when the tractor frame is the return conductor, the majority of current will follow the path of lowest resistance. But parallel to that path, there will be other paths for some other current to flow. But they will not be the majority of the current in most cases.

Also each current causes voltage drops, which affect the other currents. Not a simple thing to figure out, and likely nothing that any tractor owner will ever figure out.

When the frame is the conductor for the return current path who knows how the total current flows? It is unlikely following only one path. The return current for whatever is connected to the system will likely follow MANY paths, but just as likely, one will be the primary path.

An interesting, but mostly unrelated, thing to me is the two ways one can view current flow. One is electron flow, and the other is conventional current flow, which is from positive voltage to negative.

Conventional current flow is used in engineering, at least was when I was a student. Electron flow works too, but then you need to figure out voltage drops across resistances due to electron flow. Not a big deal, but a step often better if not needed.

 

[Henro]

Hang on... I'll channel SnideBarDrip:

"I'm the best welder in Michigan and probably the world I have a working farm in Michigan and I'm the envy of my neighbors I wouldn't bother welding on a BX or a B series those are toy tractors I have thirteen MX6000000 I earn my living with those my living is way betterer than your living you are poor I was crowned Michigan State Fair Queen because of my real tractors and my pre-64 Weatherby rifles made in West Germany and my old 7.3 PowerGoat F35000 with Gail Banks everything makes 2367 horse power and 56,761 foot pounds your truck and toy tractor sucks I am the greatest"

Hagrid, you just put one well over the top of my head.

I love it but can't relate...Still laughing though, which might be a sign of dementia developing.

Hope not at my end!

Frankly dementia is a serious issue and I should not be making light of it... ...Apologies for that...

 

[hagrid]

Is it the lack of punctuation? I did that on porpoise.

 

[ferguson]

Lots of input on the WELDING ? In the time it took me to read all the input could have removed implement 1/2 doz times HAHA THANKS for all the input

 

[Lil Foot]

I doubt welding on my old B7100 would have much effect on it's electronics; not sure what it has would qualify as electronics; it barely qualifies as electrics.

But it is so easy to disconnect the battery, why would anybody chance it?