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Posted by Curt Welch on August 4, 2008, 2:42 pm
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> "Curt Welch" wrote: (clip) It seems to me that keeping the battery
> connected is more likely to protect
> > all the electronics in the car than harm them while welding. It acts
> > as a voltage regulator so in case there are any currents induced in any
> > of the wires, it's more likely to clamp the voltage levels to 12V
> > instead of allowing them to rise to higher levels that could do some
> > harm.
> ^^^^^^^^^^^^^^^^^^^^^
> Actually, following that logic, you should turn everything on--radio,
> ignition, lights, global navigator, etc. Otherwise, the 12v clamp isn't
> there.
> ^^^^^^^^^^^^^^^^^^^^
Yeah, I was thinking the same thing.
> The only thing I would expect to be protected by disconnecting the
> battery is the battery.
> ^^^^^^^^^^^^^^^^^^^^
> And it will carry more current without harm than most welders will put
> out.
--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/
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Posted by Joe Pfeiffer on August 4, 2008, 3:27 pm
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> "Curt Welch" wrote: (clip) It seems to me that keeping the battery
> connected is more likely to protect
>> all the electronics in the car than harm them while welding. It acts as a
>> voltage regulator so in case there are any currents induced in any of the
>> wires, it's more likely to clamp the voltage levels to 12V instead of
>> allowing them to rise to higher levels that could do some harm.
> Actually, following that logic, you should turn everything on--radio,
> ignition, lights, global navigator, etc. Otherwise, the 12v clamp isn't
> there.
>
Just about anything somebody would regard as "modern" electronics that
might be damaged by the welder is actually still powered-up (albeit in
a standby mode) even when the ignition is turned off -- that certainly
includes the engine controller and radio. Haven't checked, but I'd be
pretty surprised if that wasn't also true of the transmission
controller, GPS, etc etc.
>> The only thing I would expect to be protected by disconnecting the battery
>> is the battery.
>
> And it will carry more current without harm than most welders will put out.
Right.
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Posted by Kelly Jones on August 4, 2008, 11:33 pm
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>
>> "Curt Welch" wrote: (clip) It seems to me that keeping the battery
>> connected is more likely to protect
>>> all the electronics in the car than harm them while welding. It acts as
>>> a
>>> voltage regulator so in case there are any currents induced in any of
>>> the
>>> wires, it's more likely to clamp the voltage levels to 12V instead of
>>> allowing them to rise to higher levels that could do some harm.
>> Actually, following that logic, you should turn everything on--radio,
>> ignition, lights, global navigator, etc. Otherwise, the 12v clamp isn't
>> there.
>>
>
> Just about anything somebody would regard as "modern" electronics that
> might be damaged by the welder is actually still powered-up (albeit in
> a standby mode) even when the ignition is turned off -- that certainly
> includes the engine controller and radio. Haven't checked, but I'd be
> pretty surprised if that wasn't also true of the transmission
> controller, GPS, etc etc.
>
>>> The only thing I would expect to be protected by disconnecting the
>>> battery
>>> is the battery.
>>
>> And it will carry more current without harm than most welders will put
>> out.
>
> Right.
I wouldn't worry too much about the battery for the reasons stated above.
The point of disconnecting the battery is to protect the electronics. Most
electronics are not designed for reverse polarity. The possibility exists
when welding for forcing current back through the "wrong" side of the
battery - not normally a problem as that's how battery chargers work. The
issue is the potential for allowing the current through the electronics
first.
We could argue for ever about it and only the auto electronics designer
knows for sure. Given the cost of replacing the electronics it seems like
cheap insurance to break the electrical path through the electronics (i.e.
remove the battery cable). I think that everyone would agree that if the
conductive path through the electronics is removed then the likelihood of
damage is significantly reduced.
hope this helps
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Posted by Leo Lichtman on August 5, 2008, 12:37 am
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"Kelly Jones" wrote: I wouldn't worry too much about the battery for the
reasons stated above.
> The point of disconnecting the battery is to protect the electronics.
> Most electronics are not designed for reverse polarity. The possibility
> exists when welding for forcing current back through the "wrong" side of
> the battery - not normally a problem as that's how battery chargers work.
> The issue is the potential for allowing the current through the
> electronics first. (clip)
^^^^^^^^^^^^^^^^^^^^^^^^
Do you disconnect the battery before attaching a charger? Try to visualize
a path that would send current backwards through an electronic component.
Say your radio is turned off, but receiving 12v standby current. You start
welding. Because you have not properly routed your ground return cable, a
surge reaches the battery ground through the frame and pushes current
BACKWARDS through the battery and out to the radio. Your current surge
would have to be more than 12v for this to happen. That's probably more
than half your arc voltage being spent in the return circuit. You wouldn't
be welding--you would be scratching your head.
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Posted by Randy on August 5, 2008, 9:23 am
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>My SIL is a good guy and treats my daughter good. He can't back a trailer
>for crap, though. He put two nice dings in my truck so far, and I've had to
>repair two trailers.
>
>He comes to me with his Yukon Denali. It has a small 4" x 4" plate where
>the plug plugs in that has somehow (?) been ripped off the bumper right
>along the original MIG welds.
>
>No problem, sez I. Sez he, "Aren't you going to disconnect the battery so
>it doesn't foul up the computer?" I really don't think it's going to put
>any electricity into the system, and it's not welding near any computer type
>component, so I sez no. But, I tell him I'll check with the pros.
>
>I've heard to disconnect the battery, and not to disconnect. When is it (is
>it) appropriate to disconnect?
>
>Steve
I've done it both ways, main thing is to ground to what you're
welding, if you're welding exhaust ground to the exhaust. If you're
welding on the bumper ground to the bumper. If you're welding on the
exhaust and you ground to the frame, you never know what's rusty and
what path the current will take. If a nice path by way of the o2
sensor through the ECM and back to the frame is the way the current
travels then you just smoked the ECM.
Wire brush or grind a clean spot for the ground clamp.
Last car I welded on (mine) had an air bag, I disconnected the
battery and shorted the battery cables together. I don't know if this
was the best thing to do but I wanted no chance of the air bag circuit
to get power.
Anyone shows up or calls me to weld on a car I send them to a body
shop.
Thank You,
Randy
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> connected is more likely to protect