Welding question ...

[WantedWolf]

Well I guess like most said its cheap insurance to dissconect. so why risk it.
But as was also mentioned most devices are still connected to ground through the truck. So in witchcraft situations At least your battery will be safe

 

[greenmule]

Yeah,its a good question for sure,once you think about it a little.
But I'm sure there is somebody out there who can tell us so us dummys can understand why,what,etc.

I been around welding for many years,can't tell you why?

I know computors have come into play here,but don't forget the battery charger thing I mentioned.And most things like the rear light I just put on,is grounded to tractor.

Maybe it kinda caught in the seams here,mechanic not a welder,welder not a mecanic,computor guy,don't know what a welder is,etc.

 

[BrentD]

Having quite a bit of electronics experience and lots of experience troubleshooting electrical interference gremlins, I think the reason the portable welders might not cause a problem when welding on the vehicle it's mounted to is because the portable welder shares a primary ground plane with the vehicle. I'm not just talking about the ground clamp either. Welders are generally going to have a transformer in them. Feeding power through a transformer can do weird things if measures aren't taken to equalize the ground planes on both sides. If you connect your ground clamp to a vehicle that has an internal power supply, then electrically speaking, your welder's ground may actually be at a lower potential than the vehicle's ground. If that is the case, then power can feed back through the vehicle into the welder's ground, particularly if you're using an A/C welder. Reversing the current flow will do all sorts of bad stuff to electronics.

Now, the portable welders, on the other hand, even if they're driven by a separate engine, they are usually bolted to the bed of the truck. That creates an electrical ground connection. As long as both sides of the transformer share the same ground then your generator/welder's ground will always be at the same potential as the vehicle's ground.

Now, none of that takes EMI into account. Electromagnetic interference can also wreak havoc with a vehicle's electrical system. I drive a Pontiac Aztek, and absolutely love it, but I have to be very careful when disconnecting the battery that I don't make a spark. Azteks are very sensitive to EMI and voltage fluctuations and their body control module and gauge cluster in particular are know to die suddenly after a battery connection has sparked. I belong to an Aztek owners group and it's really surprising to hear how many of them have had electrical problems after a simple battery change.

 

[Skyco]

Curious- how do you disconnect the battery making sure you don't get a spark?

 

[Inkomodius]

Make sure all electrical accesories are turned off then disconnect your ground, if your still gettin a spark there could be an open or a short still creating a circuit.

As far as most portable welders the case is isolated and isnt grounded to the ground terminal of the welder. IE you cant strike and arc off the case without throwing your ground clamp on it.

I was talking with my welding supply guy today and his explanation was " Vehicle alternators have a voltage regulator for a reason, if your alternator spikes then you fry electronics. Welders are giant alternators (Kind of) and if your creating an electrical circuit through a vehicle with an electrical device that is higher then what the electronics are designed for so things start frying."

I also think of it like, when lightning hits your house, it frys stuff inside. Its a larger scale picture then whats happening but similar principle i believe.

 

[BrentD]

Curious- how do you disconnect the battery making sure you don't get a spark?

We're still trying to figure that out. What I generally do is try to move as quickly as I can to get the terminal against the post. I've been considering putting a main switch on my main battery feed to try to permanently solve this problem.

 

[Cap-n-Cray]

Years ago when I was a youth, I had a job loading large and small sail boat on to trailers for shipment back east. Occasionally the boat's cradle need to be welded to the flat bed trailer with the truck still attacked. The driver always had me ground the trailer and truck to the earth with a bar of metal. I never knew why, but always did it. Of course this was before all the new computer controls.

Cary

 

[WantedWolf]

Curious- how do you disconnect the battery making sure you don't get a spark?

All loads or accessories off helps the most, but would one of those RV type battery disconects be good enough to skip the sparks?

Like this about $10 at P.A.

 

[BrentD]

All loads or accessories off helps the most, but would one of those RV type battery disconects be good enough to skip the sparks?

Like this about $10 at P.A.

That would probably be sufficient. If you want to be 100% certain, a contactor with magnetic blowouts would probably be best. For those that don't know what I'm talking about, there are switches out there for high voltage or high current uses that have a pair of relatively high-power permanent magnets with like poles positioned on either side of the switch contact so that their magnetic field lines intersect the gap between the contacts. Since electrons are deflected by magnetic fields they can't arc between the switch contacts without a lot of power driving them.

 

[WantedWolf]

That would probably be sufficient. If you want to be 100% certain, a contactor with magnetic blowouts would probably be best. For those that don't know what I'm talking about, there are switches out there for high voltage or high current uses that have a pair of relatively high-power permanent magnets with like poles positioned on either side of the switch contact so that their magnetic field lines intersect the gap between the contacts. Since electrons are deflected by magnetic fields they can't arc between the switch contacts without a lot of power driving them.

Just for the sake of it, Whats the price on a contactor with magnetic blowouts these days?

 

[MikeD74T]

I'm seeing a lot of opinion, and I'm not disputing any of it, but how does disconnecting the battery protect anything but the battery??? MikeD74T

 

[Iplayfarmer]

I'm seeing a lot of opinion, and I'm not disputing any of it, but how does disconnecting the battery protect anything but the battery??? MikeD74T

Here's my layman's attempt to answer...

With the negative battery cable disconnected it effectively opens every circuit (with few exceptions) turning your complex electronic circuitry into a bunch of metal and silicone.

This is a strech here, but it's the same reason that a bird can sit on a thousand volt power line without getting fried. As long as the bird doesn't complete some circuit, no juice flows through the bird. If the bird stepped between the right two wires; poof! You can put 250 amps or so to your vehicle with the circuits open, but as long as that 250 amps is not running through some circuit, it has little effect on the electronics.

Now we just need a volunteer to remove their battery and connect the positive and negative cables (closing the circuits); and then weld on their vehicle to proove the theory.

 

[MikeD74T]

Here's my layman's attempt to answer...

With the negative battery cable disconnected it effectively opens every circuit (with few exceptions) turning your complex electronic circuitry into a bunch of metal and silicone.

This is a strech here, but it's the same reason that a bird can sit on a thousand volt power line without getting fried. As long as the bird doesn't complete some circuit, no juice flows through the bird. If the bird stepped between the right two wires; poof! You can put 250 amps or so to your vehicle with the circuits open, but as long as that 250 amps is not running through some circuit, it has little effect on the electronics.

Now we just need a volunteer to remove their battery and connect the positive and negative cables (closing the circuits); and then weld on their vehicle to proove the theory.

So I want to weld on my truck frame! I disconnect my battery ground. Everything else is still connected to power & grounded to the body, block, frame, etc. How is anything but my battery disconnected MikeD74T

 

[Redneck in training]

Here's my layman's attempt to answer...

With the negative battery cable disconnected it effectively opens every circuit (with few exceptions) turning your complex electronic circuitry into a bunch of metal and silicone.

This is a strech here, but it's the same reason that a bird can sit on a thousand volt power line without getting fried. As long as the bird doesn't complete some circuit, no juice flows through the bird. If the bird stepped between the right two wires; poof! You can put 250 amps or so to your vehicle with the circuits open, but as long as that 250 amps is not running through some circuit, it has little effect on the electronics.

Now we just need a volunteer to remove their battery and connect the positive and negative cables (closing the circuits); and then weld on their vehicle to proove the theory.

You still can fry your electronics even when the battery is disconnected. It all depends on how the current flows trough your vehicle. To decrease the chance of frying anything always put the ground on the same part you are welding on.
Here is the physics behind that: It is called Ohm's law. Let say you put ground on the front bumper and then weld on the rear bumper. You need 100 Amps to weld. The resistance between front and rear bumper is low but it isn't zero. If it is mere 0.1 ohm the voltage between front and rear bumper will be 100 Amps x 0.1 ohm=10V. If the resistance increases to 1 ohm the voltage will be 100V and so on.
The current loop can close trough the light bulbs, relays, switches, solenoids etc. so only defense is not to pass any current trough the vehicle but only the shortest distance between welding ground and the electrode.
If you disconnect ground and plus from the battery connect ground and plus wires together. It will short all electronics (without power applied to it) improving the protection.

 

[Iplayfarmer]

So I want to weld on my truck frame! I disconnect my battery ground. Everything else is still connected to power & grounded to the body, block, frame, etc. How is anything but my battery disconnected MikeD74T

I'm just going on the assumption that disconnecting the battery breaks the circuits. Maybe this is an erroneous assumption. I figure everything is wired to get power from the battery, run it through the components (bulbs, relays, etc.), and return it back to the battery. If every circuit involves the battery somehow, then disconnecting the battery would open the circuits.

What am I missing?

You still can fry your electronics even when the battery is disconnected. It all depends on how the current flows trough your vehicle. To decrease the chance of frying anything always put the ground on the same part you are welding on.
Here is the physics behind that: It is called Ohm's law. Let say you put ground on the front bumper and then weld on the rear bumper. You need 100 Amps to weld. The resistance between front and rear bumper is low but it isn't zero. If it is mere 0.1 ohm the voltage between front and rear bumper will be 100 Amps x 0.1 ohm=10V. If the resistance increases to 1 ohm the voltage will be 100V and so on.
The current loop can close trough the light bulbs, relays, switches, solenoids etc. so only defense is not to pass any current trough the vehicle but only the shortest distance between welding ground and the electrode.
If you disconnect ground and plus from the battery connect ground and plus wires together. It will short all electronics (without power applied to it) improving the protection.

I would have to agree that the best defense is putting the welding ground as close to the arc as possible. That just makes sense on all levels IMO.

 

[PILOON]

My welding and electrical 'logic' tells me that it is all a matter of grounding paths.

SO, when I weld on a vehicle, I ground to the part that I am welding or that I will attach to.

Stands to reason that if you weld to the frame but ground to the axel housing that you are inviting arking at the bearings and entire drive train.
Just look at where you clamp your ground next time you weld and you will always see a small ark mark or two.
Electricity will always take the shortest and path of lowest resistance.