Welding question ...

[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.