But there is still the matter of EMI. Depending on the type of welder it could be inducing high frequency into wires if welding leads aren't routed sensibly. My hypothesis about leaving battery connected or shorting the leads together is meant more to address that.

So then you think welding something else in the garage with your car parked in it is going to fry the car? I have both a Tig welder with high frequency start, and a industrial type Mig welder with in 4 feet of a simple old boombox that's on while I weld, never any type of interference on the radio while welding. But did have a old bad florescent light that gave interference on the radio.

Welders made today have to pass federal standards as to radiated emissions. as to welding leads I've never routed the leads through anything when welding, so can't answer that one.

 

So then you think welding something else in the garage with your car parked in it is going to fry the car? I have both a Tig welder with high frequency start, and a industrial type Mig welder with in 4 feet of a simple old boombox that's on while I weld, never any type of interference on the radio while welding. But did have a old bad florescent light that gave interference on the radio.

Welders made today have to pass federal standards as to radiated emissions. as to welding leads I've never routed the leads through anything when welding, so can't answer that one.

Fair enough. I'm probably imagining a problem where there isn't one. I'm just making assumptions about the reasoning behind the recommendation to disconnect the battery and not questioning them. Glad you're here to question them for me .

 

Just because something is not obvious does not mean that it does not exist. And just because somebody gets away with taking a shortcut one time does not mean that there is no reason for the precaution. And just because there is an obvious current path in some welding operation does not mean that some accidental contact elsewhere is not possible. Errors happen occasionally, especially among those who see no possibility that anything could possibly go wrong. And theeffort to disconnect a battery lead is usually less than the effort yo replace some other part that was damaged.

 

Just because something is not obvious does not mean that it does not exist. And just because somebody gets away with taking a shortcut one time does not mean that there is no reason for the precaution. And just because there is an obvious current path in some welding operation does not mean that some accidental contact elsewhere is not possible. Errors happen occasionally, especially among those who see no possibility that anything could possibly go wrong. And theeffort to disconnect a battery lead is usually less than the effort yo replace some other part that was damaged.

Each additional post like this which insinuates that the decision not to disconnect the battery is one that can only possibly be made from a place of stubborn ignorance and laziness in lieu of putting forth any kind of technical justification for why it should be done, makes the act of disconnecting the battery look more and more like a superstitious ritual.

At best, it comes across like "It only takes a second to throw salt over your shoulder and it's cheap insurance. Just because you took the shortcut of not throwing it last time and you weren't hit by a bus, doesn't mean it won't happen this time. Someone like you who is too dense to believe in luck is the one most likely to walk out in front of a bus anyway."

There's no harm in throwing salt over one's shoulder (usually). But I suggested that disconnecting the battery might do more harm than good. Do you have a counter point to that? Are you sure you're not promoting the consumption of some chakra cleansing potion with unknown and potentially poisonous ingredients?

 

Here's a thought ... why not place a big 16V TVS diode (or a couple of large zeners back-to-back) between the poles of each battery? That should take care of any voltage spike that might damage the electronics of any of the two cars, letting the zeners absorb the kickback and turning it into heat.

 

Here's a thought ... why not place a big 16V TVS diode (or a couple of large zeners back-to-back) between the poles of each battery? That should take care of any voltage spike that might damage the electronics of any of the two cars, letting the zeners absorb the kickback and turning it into heat.

Now that you mention it, that seems like something that should should be installed on cars from the factory!

 

What I have seen on one welder was that the return lead, the conductor that gets clipped to the section of metal that is to be welded, was common with the safety ground connection (green wire) of the power source cable. In addition, the motor driven lift that the car that was to be welded on was also grounded.
So while proper procedure calls for connecting the ground side adequately, that connection may not always be perfect, and when a large weld current flows, even a small resistance can produce a voltage drop of several volts. And it seems that not all of the weld current may be flowing through the intended return connection. That is the technical explanation requested.
So while I am not claiming a shock hazard for humans, some vehicle electronic devices are subject to damage from excess voltages of random polarity. And I would not call every safety precaution a superstition just because I see no need for it.
See also post #3 for another example.

 

What I have seen on one welder was that the return lead, the conductor that gets clipped to the section of metal that is to be welded, was common with the safety ground connection (green wire) of the power source cable. In addition, the motor driven lift that the car that was to be welded on was also grounded.
So while proper procedure calls for connecting the ground side adequately, that connection may not always be perfect, and when a large weld current flows, even a small resistance can produce a voltage drop of several volts. And it seems that not all of the weld current may be flowing through the intended return connection. That is the technical explanation requested.

Thank you. I understand this fact and thought I demonstrated sufficient understanding of it in the OP.

There are only two ways I can conceive that welding could damage electronics:

1. By raising the electrical potential of one ground higher than that of another ground, causing current to flow through electrical circuits in ways that it isn't intended to flow. And I think that would happen whether or not the battery was connected. The best way to prevent that is to place your ground clamp as close as possible to the area being welded.

I don't question whether a danger to electronics exists while welding, I question specifically whether disconnecting the battery presents a positive, neutral, or negative measure of protection against this damage.

 

"connect to the frame not the battery" is another thing in the list of automotive advice I've heard, never understood, never followed, and never had an issue.

The reason one should connect to the frame is to control where the spark occurs as the last connection is made when jumping a battery. As people try to charge a woefully discharged or even damaged battery, a lot of hydrogen can be generated. By connecting the ground cable to the frame, and connecting last + disconnecting first, the spark will occur on the "frame" instead of right next to a battery vent where you can get a hydrogen flash. Note that hydrogen flames are not visible - (the burning skin of the Hindenburg made the flames visible). You typically hear a small poof if you ignite hydrogen. Most hydrogen rises so it's not typically a problem.

the biggest problem is finding a good place to connect on the chassis. Most is painted black or covered in plastic in a modern car. I generally just connect to the battery terminals.

 

When changing a battery It always makes sense, at least in my vehicles, to disconnect the grounded side first and connect the grounded side last. That is because of the likely-hood of the wrench accidentally touching some grounded body part during the process. That may not be an issue in other vehicles, but in the past dozen or so that I have owned it was a definite possibility, if not using a very short handled wrench. As for the hydrogen explosion hazard, assuring adequate venting and not making the change right after intense charge or discharge should be adequate. Also, avoiding sparking right next to the battery caps.

 

When changing a battery It always makes sense, at least in my vehicles, to disconnect the grounded side first and connect the grounded side last. That is because of the likely-hood of the wrench accidentally touching some grounded body part during the process. That may not be an issue in other vehicles, but in the past dozen or so that I have owned it was a definite possibility, if not using a very short handled wrench. As for the hydrogen explosion hazard, assuring adequate venting and not making the change right after intense charge or discharge should be adequate. Also, avoiding sparking right next to the battery caps.

That method has been re-iterated a few times here over the past.

 

What I have seen on one welder was that the return lead, the conductor that gets clipped to the section of metal that is to be welded, was common with the safety ground connection (green wire) of the power source cable. In addition, the motor driven lift that the car that was to be welded on was also grounded.

I call BS on all of that. You can go on both Miller and Lincoln and find their welder schematics online. The welder is a transformer and the secondary is completely separate from the primary and ground.

So what if the lift is grounded? The vehicle has rubber tires. For you information rubber is an insulator.

I haven't to this point in any thread been impressed with you knowledge of cars or anything connected with them. So BS is called yet again.

 

the biggest problem is finding a good place to connect on the chassis. Most is painted black or covered in plastic in a modern car. I generally just connect to the battery terminals.

One problem there is that many auto's now place the battery in not so easy accessible places, Two locations are usually fitted on or near the engine for jumper lead attachment etc.

 

Heres my reason for disconnecting the battery.

Imagine a rouge signal that turns on the base of every transistor at the same time. Lets say you have a push pull pair, what happens when they turn on at the same time? Smoke every time. So by disconnecting the battery, transistors that might see a spurious signal and turn on when they are not supposed to, do not pass current. The EM fields from the welder do not hurt the electronics directly as the coupled current is small, but if transistors turn on when they are not supposed to (with a current source connected), thats where the problems start. One needs to remember that the arcing is also producing RF of all sorts of frequencies (due to rise time and harmonic content) and even a foot of wire hanging out of a computer can be a good antenna. Auto computers were not designed with RF crosstalk and coupling in mind. If an RF signal jumps on a sensor wire, it can easily couple to other traces on the PCB. It doesnt take much to turn on a fet....

 

Heres my reason for disconnecting the battery.

Imagine a rouge signal that turns on the base of every transistor at the same time. Lets say you have a push pull pair, what happens when they turn on at the same time? Smoke every time. So by disconnecting the battery, transistors that might see a spurious signal and turn on when they are not supposed to, do not pass current. The EM fields from the welder do not hurt the electronics directly as the coupled current is small, but if transistors turn on when they are not supposed to (with a current source connected), thats where the problems start.

Hey, that makes sense! Can't argue with it, so I'll accept it. I now have a valid reason for not leaving the battery connected.

One needs to remember that the arcing is also producing RF of all sorts of frequencies (due to rise time and harmonic content) and even a foot of wire hanging out of a computer can be a good antenna.

To address this, do you think it is safer to leave the battery cables floating? Or short them together? Or would it make no difference? My thoughts are that tying the 12V rail to ground will not allow any EMI to be induced in the circuits. At least not any that are directly connected between 12V and GND. Plausible?

Thanks

 

I call BS on all of that. You can go on both Miller and Lincoln and find their welder schematics online. The welder is a transformer and the secondary is completely separate from the primary and ground.

So what if the lift is grounded? The vehicle has rubber tires. For you information rubber is an insulator.

I haven't to this point in any thread been impressed with you knowledge of cars or anything connected with them. So BS is called yet again.

None of the welders that I have investigated or used were close to new. All had been "worked on" by those people who believe in grounding everything. (Not Me) So why the ground connection was tied to frame ground I can not tell, I did not do it. BUT stuff does get grounded in some businesses. So while the manufacturer does not ground the return, other folks do.
Like I said, connections happen.
AND that motorized lift was supporting the frame, not the tires. Check the lifts at most tire sales places. It is difficult to change a tire when that wheel is supporting the car. And not all frame lift pads are rubber cushioned.

 

Hey, that makes sense! Can't argue with it, so I'll accept it. I now have a valid reason for not leaving the battery connected.


To address this, do you think it is safer to leave the battery cables floating? Or short them together? Or would it make no difference? My thoughts are that tying the 12V rail to ground will not allow any EMI to be induced in the circuits. At least not any that are directly connected between 12V and GND. Plausible?

Thanks

I dont think you should short them. Leave them float.

 

I dont think you should short them. Leave them float.

Why is that?

 

Check the lifts at most tire sales places. It is difficult to change a tire when that wheel is supporting the car. And not all frame lift pads are rubber cushioned.

Not going to argue on this. You can never admit being wrong. I'll leave you with a new part of my signature, and it applies to you, " WATCH OUT...THOSE WHO DO NOT KNOW, DO NOT KNOW THAT THEY DO NOT KNOW "

 

Why is that?

I was afraid you were going to make me share my unconfirmed reasoning lol... ok.

When you connect them, you create a loop. From there, I see two problems.

#1- If you cut a loop antenna, its not as good of an antenna any more. So it makes sense to not make a loop.

#2- By doing so you invite any currents acros the frame to pass through the computer ~ allow me to explain. Although it is generally said that electricity takes the shortest path (ground clamp to welding electrode in this example), there can still be issues with that. Consider if your ground clamp is closer to the negative battery terminal and the welder electrode is closer to where the computer bolts up. Whatever the resistance is between those two point, there will be a respective voltage proportional to the welding current. By connecting the positive and negative cables, it can now send a fraction of the current through the computer to get to the ground clamp. If that voltage (due to the welding current and path resistance) is high enough to forward bias anything in the computer, I'm going to let you guess..

Unlikely, yes, given the ground clamp is as close to your weld as possible, but I see absolutely no benefit to connecting those cables.