Any point in disconnecting the battery when welding on a vehicle?

Thread Starter

strantor

Joined Oct 3, 2010
6,338
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.
Hmmm.... interesting. I need to let this percolate. Thanks for the input, this is a stimulating discussion
 

Halfpint786

Joined Feb 19, 2018
105
there would be enough inductance in that loop connecting them that it wouldn't "short out" anything RF anyhow. Edit: not only that, but shorting the positive means the positive is also at ground meaning transients on a sensor or control wire would have MORE paths to ground, more targets to destroy!!! Just let them float for sure.
 

cmartinez

Joined Jan 17, 2007
7,881
Now that I think of it, what's the difference between the scenario being discussed and that of a bolt of lightning hitting an airplane?
 

Thread Starter

strantor

Joined Oct 3, 2010
6,338
It only takes disconnecting one battery cable to open the circuit. This goes back to day one of the basic electricity class.
How do you figure that? The battery is just one of many components and circuits that exist between the +12v rail and ground. It isn't even the main power source. The circuit starts with a 3 phase generator (alternator) followed by a 3ph bridge rectifier circuit, followed by a battery where the main capacitor would be in power supply circuit. I don't understand how removing that capacitor (battery) from the power supply circuit somehow isolates the rest of the components from changing ground potential and EMI threats (other than shoot-through caused by EMI as described by @Halfpint786 )
 

dcbingaman

Joined Jun 30, 2021
799
I am getting ready to do something similar. I have a trailer I am converting into a camper. I have to do some welding on the external frame for adding solar panels among other things. My plan is to get all the welding done before I add any of the solar system, charge controllers, inverters etc. to avoid this type of problem. Interesting discussion. I do a lot of welding with a wire feed welder. I also use Oxy-Acetylene torch occasionally. Most of the time I don't have a lot of sensitive electronics connected to the same frame as the welder. This is my first time dealing with this sort of problem.
 

dcbingaman

Joined Jun 30, 2021
799
The difference is almost a million volts, and many thousands of amps. And many more cubic feet of hot plasma.
I live on a ranch with off grid power. A 3600 watt solar system. We had a lightning strike a few years back. It destroyed the inverter, one charge controller, 2 computers and various other electronic equipment that was plugged to 120V inside the house. It cost over $8,000 to repair, the inverter alone cost over $6,000. It did not damage the panels or the battery bank for what its worth. Not a pretty sight, but I don't think any type of protection can stop that sort of thing from happening. I hate lightning!
 

MisterBill2

Joined Jan 23, 2018
13,804
I live on a ranch with off grid power. A 3600 watt solar system. We had a lightning strike a few years back. It destroyed the inverter, one charge controller, 2 computers and various other electronic equipment that was plugged to 120V inside the house. It cost over $8,000 to repair, the inverter alone cost over $6,000. Not a pretty sight, but I don't think any type of protection can stop that sort of thing from happening. I hate lightning!
In regards to lightning strikes, I have had two direct hits on my antenna tower. Some damage, the worst being a computer power supply.
So for protection on a ranch: hopefully you have some portion quite far away from any electrical anything. That would be the location to erect a decoy for future lightning strikes. A discarded antenna tower, the higher the better, with a pointy pipe at the top. The object being simply to attract the lightning to a much less valuable point. There is a consensus that a tower protects objects withing a diameter of twice it's height from direct strikes. It odes make sense, and it certainly would be the preferred point for the charge cloud on the ground to jump up to the cloud.
 

dcbingaman

Joined Jun 30, 2021
799
In regards to lightning strikes, I have had two direct hits on my antenna tower. Some damage, the worst being a computer power supply.
So for protection on a ranch: hopefully you have some portion quite far away from any electrical anything. That would be the location to erect a decoy for future lightning strikes. A discarded antenna tower, the higher the better, with a pointy pipe at the top. The object being simply to attract the lightning to a much less valuable point. There is a consensus that a tower protects objects withing a diameter of twice it's height from direct strikes. It odes make sense, and it certainly would be the preferred point for the charge cloud on the ground to jump up to the cloud.
That is a nice idea! It may work out well for me. We are on the side of a hill (700 feet from the top). Placing a tower at that point might be best for my situation. Knowing the power of lightning, not sure how far away is best? Thanks for the suggestion!

According to your recommendation:

"There is a consensus that a tower protects objects within a diameter of twice it's height from direct strikes.". I would estimate the top of the hill alone is at least 200 feet higher than the house and is linearly 700 feet from the solar system. So it probably would not have to be to high not sure though maybe 700 feet away is to far for protection. Not like you can just go verify it works. :)
 
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cmartinez

Joined Jan 17, 2007
7,881
The difference is almost a million volts, and many thousands of amps. And many more cubic feet of hot plasma.
The difference is actually several hundred million volts, and tens of thousands of amps. But that was not my point. My point is that in both scenarios one has an external source of electrical power traveling through the chassis (or in my example, fuselage) of the vehicle in question.

I know that a plane is supposed to behave like a faraday cage whenever it encounters such scenario. But (to my knowledge) nevertheless it does have internal components protecting it from said surges. And I would very much like to know how they're arranged. Maybe a similar arrangement could be applied to a car's electronics.
 

Halfpint786

Joined Feb 19, 2018
105
In regards to lightning strikes, I have had two direct hits on my antenna tower. Some damage, the worst being a computer power supply.
So for protection on a ranch: hopefully you have some portion quite far away from any electrical anything. That would be the location to erect a decoy for future lightning strikes. A discarded antenna tower, the higher the better, with a pointy pipe at the top. The object being simply to attract the lightning to a much less valuable point. There is a consensus that a tower protects objects withing a diameter of twice it's height from direct strikes. It odes make sense, and it certainly would be the preferred point for the charge cloud on the ground to jump up to the cloud.
Although I believe it has been discussed elsewhere, I'll mention it here.

A tall pointy object does not necessarily "attract" lightning to it. It is quite the opposite in fact. Lightning rods prevent strikes by disspiating the approaching charge as it is arriving. When lightning hits a tower, it is because not enough (grounded) pointy objects were nearby. Check this out.

Part 1 (good demonstration of how lightning rods work at 4:45)
Part 2 (why sometimes lightning rods do get hit)
 

shortbus

Joined Sep 30, 2009
9,762
All of this extreme case scenario stuff. Can anyone point to even one(1) example of welding on the frame of a vehicle that disabled it? I don't think you will find one, unless it's one of those, "here, hold my beer",situations. I've stick welded and Mig welded car, truck and farm vehicles all without messing one up. If you take even the simplest precautions, like moving any wiring out of the way your going to be fine.
 

Halfpint786

Joined Feb 19, 2018
105
All of this extreme case scenario stuff. Can anyone point to even one(1) example of welding on the frame of a vehicle that disabled it? I don't think you will find one, unless it's one of those, "here, hold my beer",situations. I've stick welded and Mig welded car, truck and farm vehicles all without messing one up. If you take even the simplest precautions, like moving any wiring out of the way your going to be fine.
It happened to me once, and I never let it happen again.

If money is no object to you, go ahead, cook a $1200 computer just to find out for yourself.. The price of that auto computer is about the same as a really nice oscilloscope. If I had $1200 laying around, I'd rather be buying a new scope.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,338
All of this extreme case scenario stuff. Can anyone point to even one(1) example of welding on the frame of a vehicle that disabled it? I don't think you will find one, unless it's one of those, "here, hold my beer",situations. I've stick welded and Mig welded car, truck and farm vehicles all without messing one up. If you take even the simplest precautions, like moving any wiring out of the way your going to be fine.
I've only welded on a late-model (computerized) cars 3 times that I can think of ('93 Chevy pickup, '99 trans am, '02 Chevy cavalier). In none of those instances did I disconnect the battery, and in none did I have a problem. I do not consider 3 experiences to be enough to speak with authority on the topic, hence why I'm sticking more to the theoretical side of the discussion.

I did place my ground clamp right near the welding spot, as I am in the habit of doing that any time I weld, and not necessarily because I was cognizant of the risk to the electronics at that time. So I can't say that I've ever witnessed anything that we are discussing. I merely saw the recommendation repeated many times and could not understand the reasoning behind it.
 

dcbingaman

Joined Jun 30, 2021
799
Although I believe it has been discussed elsewhere, I'll mention it here.

A tall pointy object does not necessarily "attract" lightning to it. It is quite the opposite in fact. Lightning rods prevent strikes by disspiating the approaching charge as it is arriving. When lightning hits a tower, it is because not enough (grounded) pointy objects were nearby. Check this out.

Part 1 (good demonstration of how lightning rods work at 4:45)
Part 2 (why sometimes lightning rods do get hit)
Very informative! Thanks!
 

Thread Starter

strantor

Joined Oct 3, 2010
6,338
The difference is actually several hundred million volts, and tens of thousands of amps. But that was not my point. My point is that in both scenarios one has an external source of electrical power traveling through the chassis (or in my example, fuselage) of the vehicle in question.

I know that a plane is supposed to behave like a faraday cage whenever it encounters such scenario. But (to my knowledge) nevertheless it does have internal components protecting it from said surges. And I would very much like to know how they're arranged. Maybe a similar arrangement could be applied to a car's electronics.
I did attempt a bit of research last night after reading your comment. My thought was that "surely airplanes don't use chassis as current carrying conductor like automobiles do." I could not find anything that confirms my suspicions. Most of what I found was not very technical or specific, and was meant to address the question "how are airplanes earthed" to which they explained that the plane's circuits are grounded to the chassis. I'm not sure that means the chassis is a current carrying conductor though; after all, the the electrical circuits in our homes are also grounded, but ground is not used as an intentional current carrying conductor.

In my opinion I've always seen automobiles' one-wire circuits as a bit of a hack. I would be surprised to learn that indeed planes have the same vulnerability of having any wire that might rub through against anything that it might have the opportunity to rub against, cause loss of function.

Do you know for a fact that they do?
 
I won't lie I didn't make it all the way through the first page before I got the sense an argument was brewing instead of a civil discussion and skimmed / skipped over most of the rest. I have always kind of wondered the same myself, but took the time to disconnect the battery or batteries just because it sounded like a good idea. I don't like to make thousand dollar plus mistakes if I can avoid them.

There are probably instances where mechanical neglect, lack of adequate preparation of the weld area, and / or lack of gray matter have caused problems and as a general rule it's always been taught to disconnect batteries and people just generally don't question it. I once witnessed a new guy at work try to ground on a random piece of pipe (cheater bar) laying on the floor... some people have no idea how electricity works (FNG!)

Part of me was wondering about if running some sort of reverse polarity or A/C welds would cause problems, or back in the days of positive grounded vehicles, but even then it's going to take the right conditions that shouldn't even exist in the first place.

It seems like the real problem would be to have your ground (or work lead to be proper) on a different part than you are welding on and not having the conductive connection between the two you assume is there... a common rookie error. It's still doubtful in that instance if disconnecting the battery will really be a benefit except for the ultra rare most ideal circumstance possible.

Long story short I don't have an answer either, but thanks for asking the question.
 
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