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Old 12-15-2017, 03:22 PM   #1
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When Welding; Battery Disconnect Switch good enough?

I'm going to have some HD rollers welded on the very back of my 5th wheel lower frame. Question, is the Battery Disconnect switch good enough or does the negative leads have to come off the batteries directly.

TY!
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Old 12-15-2017, 03:32 PM   #2
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I might answer my own question here...

The Battery cuttoff switch is just the Positive (I believe), so then in fact, you should lift the ground off the battery bank(s).
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Old 12-18-2017, 06:43 PM   #3
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While the disconnect might be fine as the means of disconnect, I would pull the cables and also make sure that the shore power is disconnected. I might even consider pulling the reverse polarity fuses on the converter.
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Old 12-18-2017, 06:55 PM   #4
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My first question is why?

Unless you're willing to go to every single electronic device and disconnect the grounds from them (almost all ground to the chassis or grounded part of body) you really aren't accomplishing anything.

When welding any current flow is localized between the area being welded and the welder's ground clamp. Welding on the rear of the frame won't bother anything at all. I spent some time in the Paccar research facility and we welded all the time on the truck chassis under development and never disconnected batteries. (Paccar builds Kenworth and other large trucks, all of which today are loaded with computers and "electronics".

This "disconnect the battery" business is a holdover from the days when people though computers were magic boxes and were afraid of even touching them.

If it makes one feel better, run a jumper cable from frame to a ground like a cold water pipe (metal of course).
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Old 12-18-2017, 07:16 PM   #5
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My first question is why?

Unless you're willing to go to every single electronic device and disconnect the grounds from them (almost all ground to the chassis or grounded part of body) you really aren't accomplishing anything.

When welding any current flow is localized between the area being welded and the welder's ground clamp. Welding on the rear of the frame won't bother anything at all. I spent some time in the Paccar research facility and we welded all the time on the truck chassis under development and never disconnected batteries. (Paccar builds Kenworth and other large trucks, all of which today are loaded with computers and "electronics".

This "disconnect the battery" business is a holdover from the days when people though computers were magic boxes and were afraid of even touching them.

If it makes one feel better, run a jumper cable from frame to a ground like a cold water pipe (metal of course).
Used to disconnect the positive wire off the alternators to keep from frying the built-in voltage regulators. I think it is still standard practice.
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Old 12-18-2017, 07:24 PM   #6
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I consider it insurance and it only takes a couple minutes to disconnect them. One loose welding ground lead and while it's not likely that anything will happen, there's a possibility that it could.

Ever seen what a battery will do when ~90 volts is applied across the plates? I have, and it ain't pretty.

Is the possibility remote, maybe, but for a few minutes work, it's a little insurance.
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Old 12-19-2017, 02:05 PM   #7
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Originally Posted by TitanMike View Post
My first question is why?

Unless you're willing to go to every single electronic device and disconnect the grounds from them (almost all ground to the chassis or grounded part of body) you really aren't accomplishing anything.

When welding any current flow is localized between the area being welded and the welder's ground clamp. Welding on the rear of the frame won't bother anything at all. I spent some time in the Paccar research facility and we welded all the time on the truck chassis under development and never disconnected batteries. (Paccar builds Kenworth and other large trucks, all of which today are loaded with computers and "electronics".

This "disconnect the battery" business is a holdover from the days when people though computers were magic boxes and were afraid of even touching them.
This statement surprises me. I have been a diesel tech my whole career, have seen 1 instance of the current actually welding the bearings to the crankshaft, and 1 time it fried the ECM, which controls all engine functions. I have always disconnected the ground, and you put the ground as close to the part your welding as possible.
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Old 12-19-2017, 02:09 PM   #8
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I'm with TitanMike, clamp the ground to the frame where your welding and you won't have an issue, Done it hundreds of time with no problems
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Old 12-19-2017, 02:52 PM   #9
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Should not be an issue at all. Disconnect if you want. Definitely not an issue with MIG and with TIG it would only be the autostart that could possibly be a problem. As mentioned, all voltages and currents are local.
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Old 12-19-2017, 03:43 PM   #10
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I agree, I have degrees in Welding and Electronics, current takes the path of least resistance. If you clamp close to what your welding you won't have a problem. Done it hundreds of times but if you feel better and like resetting radios and clocks go for it.
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Old 12-19-2017, 06:18 PM   #11
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Can't comment on the trailer welding but if you read the Allison transmission owners manual states to disconnect the trans plug before welding because of the computer
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Old 12-19-2017, 06:41 PM   #12
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IMO, if AC welding, induced currents might be a problem for low voltage electronics. The voltage spike when striking an arc could certainly be significant when the ground connection is less than solid. DC welding, probably not so much.

When frame welding an RV, remember that wiring running along the floor inside the house can be within an inch or two of the current flow and has no shielding through the plywood deck. Full metal bodies, as with automobiles, provide very good shielding in this circumstance.
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Old 12-19-2017, 07:04 PM   #13
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The main thing is to have ground right next to the work like others have said, the most important thing is the welders ground is clean and tight, or while welding voltage spikes can be sent through the frame with unknown consequences. I am surprised the guy that works for Paccar didnít mention Peterbilt which is their number one line.
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Old 12-19-2017, 07:29 PM   #14
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Not disconnecting the batteries, pos. and neg., is just plain asking for it.

You may get away with it may be 95% of the time but if that high current ever flows through expensive electronics you don't fix it you throw it away. Be aware of other ground wires connected to the frame also, the path the current takes is not always predictable. Even then, the ground clamp should be as close as possible to the spot being welded on on blank metal, not on paint or rust.

That's what's right and that's how it's being taught, at least back in the day before there were tens of thousands worth of electronics on every piece of equipment and the risk of frying electrics wasn't high. I've seen it more than once where I was welding and 20' away there was something smoldering.
How long does it take to get that 9/16 out and pull the cables of - a minute?
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Old 12-19-2017, 08:07 PM   #15
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Stray Currents BAD.

As a long time Machinist, we were taught to never weld on working machinery.
Someone mentioned welding roller bearings, O Yea. It happens. Expensive machinery like Motorhomes etc. need all the protection they can get. Grind a clean spot on the frame, use a very strong clamp to same. I would also do another ground close by for added safety. Cost, 5 minutes vs thousands.
Again, if in doubt don't do it. Use 9 line, case harden bolts and skip welding altogether on such toys. Just my 2 cents and short circuts.
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Old 12-19-2017, 10:34 PM   #16
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Welding with computer on board

I always disconnect the battery even though theoretically it may not be necessary, like was said before itís only a couple minutes, many times automotive components can be damaged just by the load of a test light or an old analog meter, and of course when working on those components one should wear a grounded wrist band. That type of sensitivity is what you are dealing with.
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Old 12-20-2017, 10:31 AM   #17
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Always Disconnect the Battery

Learned my lesson a long time a go, when I welded on my Car with a MSD 7AL Ignition and it killed one of the Output Transistors, expensive lesson.

I was at the Welding Shop last week to get something Welded on my Jeep and just before He started, I asked if he way going to Disconnect the Battery and He looked puzzled and then the Owned told him to disconnect the Negative Battery Cable.

Bottom line, the amount of time it takes to remove the Negative Cable is not that long, alway Disconnect the Battery.

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Old 12-26-2017, 08:49 PM   #18
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I had rollers welded to the back of mine and didnít disconnect anything. Iíve used it several times since and everything is good. It sure saves the back if it drags.
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