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Warning to fellows with fork trucks!!!! Welding!!

J

JD Seller

Well-known Member
I have had a fork truck at the shop for years. It is just hand all around. The latest one is 15 years old but has electric over hydraulic controls for the mast/forks.

So last week it would not lower the forks, only raise them. We looked at it some and figured it was a circuit board. There is a local fellow that used to be a full time fork lift mechanic. I get him for the deeper electrical stuff.

He came out yesterday and looked it over. Well we need a new harness. It was burnt in several places. HE said it was from welding on the fork truck. My son told him we did not weld anything on the fork truck. WRONG. HE was thinking of just the fork truck meaning like repairing it. That we have not done. Now stuff we have lifted with the fork truck we weld on all of the time. NEVER even though of it going back to the fork truck through the forks/mast.

I also got to thinking I weld things that are chained to the loader on the tractor too. That could easily go back to the tractor too. The JD 6400 has computers on it. They could get zapped too.

The repair guy told us to disconnect the battery if we were going to weld around the lift. I know that would never get done as the battery is very hard to get to on this lift. Then I got to thinking about just putting a disconnect switch in the ground cable to the battery.

A disconnect switch should protect the lifts electrical systems from the welder by breaking the ground when the disconnect is used????

P.S. the harness is going to be $700-900. OUCH
 
One of my contractors at work did that earlier this year.Rental 11K extend reach forklift. They were welding lifting eyes to a piece of 1 1/2" plate with it sitting on the forks using 1/4" 7014 jet rods and a lot of amps. Finished up and the forklift would not move. It would start but nothing else would work. Fried one of the onboard computers. The bill from the rental company was not pretty. We do not allow any burning or welding of any metal on the forks or hanging from them ( we have the factory lifting single point attachments for ours ) on any of our machines for that reason.
 
Those are what the electric fork trucks use to attach the main battery. They would work but you would have to route both cables through the plug. I think just disconnecting the ground would be all we need to do.
 
Floldford: You more then likely lift from above for most of your lifting??? We are usually lifting from below using just the forks. We have five foot forks on this propane powered lift. What we lift is different all of the time. So making isolated slings/forks would be problematic at the best. I think we will have to settle for just isolating the fork lift's electrical system when welding.
 
They do make protectors that just clamp on the batteries like a load tester but smaller, thats what we do with our new snow plow trucks when setting everything up. chris
 
Probably your best bet is like you said isolating the electrical system. We don't use our big lifts very often for loads below the forks as we have some smaller carry deck cranes for that. But we have a hard fast rule no welding on the machine or suspended loads. We learned that the hard way. Our new Tadano cranes have big signs on the battery boxes saying not to jump start as it will damage the electrical system. If the batteries go dead you have to disconnect them before charging.
 
We started removing battery connections from everything that touched a welding machine way back in the 70's after a few incidents of shorting because of poor grounds. We used an AC-DC welder a lot....James
 
jwal10: We removed the battery cables of things we were welding on to repair but did not think about lifts being used to hold things. We were not welding on the lift itself. We were welding on things the lifts had on the forks. No difference to the current just a different slant on things.
 
This may seem too easy, but how about having a couple 2 X 6 boards handy, that have been cut to length for the forks, and put them on the forks to electrically isolate the load from the lift. You could even put "sideboards" on the boards, and that would isolate a chain used to lift the load (and also keep the boards on the forks).
 
I had always heard about disconnecting a battery when welding on around a piece of equipment.
Just never could wrap my mind around the physical difference of the electrons path with or without the battery connected.

You break the ground at the battery; but isn't the computer you are trying to protect still grounded to the frame of the truck/forklift.
 
I guess I've been way too cavalier, because I've been lucky. I've never had an issue welding on anything like that. I figure if my ground is close to where I'm welding, why is there an issue? But everything is so, TOO sensitive now. Neighbor friend/custom operator lost a day, and a bunch of money for a service call, to find out his combine wouldn't work because some little electrical thing in header wasn't "recognizing" the combine!
 
We always disconnect batteries and physically ground equipment with a piece of pipe to prevent arcing through bearings and races, also a good idea to never drag welding leads over top of anything cast because an arc from a bad spot in the lead sheath can crack cast or heat treated housings, engine blocks etc.
 
I don't use a fork lift to hold anything while it's being welded. That also goes for a tractor loader.
While it happened about 30 years ago, it's still fresh in my mind.
An acquaintance was welding an item that was being held up by a tractor loader. Somehow, a spark from the arc burned through a hydraulic line that connected the lift cylinder and the hydraulic valve. He got a geyser of oil sprayed on him as the loader started to drop and the resulting fire sprayed him like a blow torch. It burned him pretty bad. He lived, but he had to have skin grafts and he still has scars.
 
John in LA: I think that there would not be a complete circuit. The computers and such could be grounded at different places but the positive side of the system would be isolated but the battery being out of the circuit. At least that is what I am thinking. Right or wrong????

The disconnect switch would be the same as unhooking the cable.
 
coshoo: I think why we have not had more trouble is many times we have wooden pallet under what we are welding on.
 
It seems strange that a wiring harness could be damaged from stray welding current. I could see if the harness itself became the ground for the weld current... Highly unlikely.

Or if the lift were being showered with hot weld splatter that could land on a harness, burn through, short something out... More likely.

But disconnecting the battery would have no bearing on either. Disconnecting the battery would prevent immediate damage to a circuit board if the harness were shorted, but as soon as the battery were reconnected, the damage would still occur.

Guess I've been lucky, never damaged any electrical components by welding near them. I did set a forklift on fire once, welding sparks went down inside where the nasty oily stuff was. I caught it before any damage though.
 
Somewhat related, about 30 years ago I was running a welding shop and a fellow came in with a small trencher on a small trailer. The operator had just greased his trencher and loaded it on the trailer lowering the front blade to secure it to the trailer. He wanted some welding done on the trailer and decided he needed a bit of work on the trencher also. My welder did not move the ground lead but just started welding on the trencher. Smoke started coming from under the machine. The current seeking a connection to the ground passed through the wire braid in the hydraulic hose rather than the pins to the blade because the pins had just been greased. lesson learned.
 
There's three or more different potential issues/scenarios here, depending upon if AC stick welding or using one of several DC welding processes.

With AC welding, there's a possibility for CONTINUOUS AC voltage to be INDUCED in wiring and electronics on the machine as long as welding current is flowing.

With DC welding, there would simply be a "spike" every time the arc is initiated or stopped.

Then there's another scenario, with either AC or DC welding where a ground is not connected properly and actual WELDING current (rather that INDUCED current) flows through the machine frame and mechanism and/or electrical system.


Several times over the years I have read instructions for various equipment that stated "If necessary to weld on this machine, disconnect battery cables and short/clamp them together".

This makes WAY more sense to me than disconnecting the (+) battery cable and simply allowing it to dangle. Doing that (to me) is worse than leaving it connected because there's NO limit on voltages that MAY be induced in that open circuit by AC welding.

With the battery still in the circuit, there's a BIG damping effect on stray voltages, as it takes AMPS to push around the battery's voltage, and not NEARLY so much current to fry electronics!

Comments???
 
I 'burned' up a brand new alternator by welding on a disk that was hooked to the tractor. 'grounded'right through the hitch pin.Heard about that type of thing happening,but never had it happen to me.......Lesson learned
 
Long time since the days when my Dad used to jump start his 1947 Chebby PU with electrode holder & ground clamp of his Lincoln SA200! Try that with today's 'puter intensive stuff!
 
Yup I try to remember to disconnect the battery but I've been lucky so far. I've welded thumbs on my eacavator and regularly hold up equipment with one of the forklifts. I was welding up the steel box on my old Louiville with an old AC Forney in the rain... Did get a few shocks from that repair but no electronics issue.

One of my neighbours just cooked the computer in his 15 year old Western Star dump truck. Ther were welding up some cracks in the trailer box. He said he'd done it before with no problem... Not so this time.

Guess it's a good lesson to remember.
Grant
 
Think that was in a GM service bulletin 35 or so years ago, no welding with battery connected.
 
Welding near any battery is a terrible idea. The sparks/slag alone will explode a battery, not to mention the voltage/grounding issues. Secondly, a fork truck or hand stacker or any other mobile material handling device is not a workbench. It is a terrible idea to work on items being supported by such device. How often do cylinders or hoses go bad? Too often to risk!! Be safe, all.
 
modern bull/chit computers will sideline everything with circuitry that was builtvin the last 30 yrs ,,.there will be good engines and trannys e verywhere with bad circuitry, .. in 50 yrs , the tractors and equipment built before 1980 or so will still be running along side junk with jumper cables hangin off the side of them that is only 10 yrs old,,.the old tractors will remain king for being dependable , and will bee the lifesaver for the small farmwr ,,. while those forced to go big will be forced to use the modern junk, that fails at the most critical time and ultimately will bankrupt the big time operators..
 
Disconnecting the battery may give you a sense of security, but I'm dubious it will prevent future wiring harness damage. This is not a case where electronics were fried by voltage spikes. To burn a wiring harness, it takes a lot of current over a significant period of time. ASSUMING the problem was caused by welding, somehow the weld current found a path through wiring harness. That would take a number of things happening; simply having the forks in contact with the work wouldn't have done it. I wouldn't be so quick to assume problem was caused by welding. Yes, that's what your repairman says, but you say you weld stuff sitting on the forks ALL THE TIME. How come it never happened before?

I would take a very careful look at the particular wires that were fried and figure out where they go. I'll bet you find another problem. It could be that if you install a new harness without determining the root cause you'll fry the replacement as well.
 
Uhm, with a normal AC/DC stick welder there is no way there is a significant current through components far away from the forks with ground clamp and rod both used on the workpiece unless you are getting inductive currents from the welder leads laying parallel to some of the forklift wiring. Unhooking a battery won't fix that. Did someone get lazy and clamp the counterweight?

Using a welder with fancy HF/HV arc starting circuitry while touching the forklift or near the wiring could/would cause problems but unhooking the batteries won't help you.
 
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