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

--
"...the man who really counts in the world is the doer, not the mere
critic-the man who actually does the work, even if roughly and imperfectly,
not the man who only talks or writes about how it ought to be done."
Theodore Roosevelt 1891

In article , "SteveB" wrote:
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?

Why take a chance?

"SteveB" toquerville@zionvistas writes:

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?

I've heard anecdotal stories from people claiming that somehow welding
on a vehicle without disconnecting the battery caused computer
problems. If somebody would come up with a plausible explanation for
how this is possible (even if only for a particular process, like
TIG), when the ignition system doesn't do it, I'd love to hear it.

Joe Pfeiffer wrote:
"SteveB" toquerville@zionvistas writes:

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?

I've heard anecdotal stories from people claiming that somehow welding
on a vehicle without disconnecting the battery caused computer
problems. If somebody would come up with a plausible explanation for
how this is possible (even if only for a particular process, like
TIG), when the ignition system doesn't do it, I'd love to hear it.

I've seen that as well and can't figure out why that would be true.

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. The only
thing I would expect to be protected by disconnecting the battery is the
battery.

--
Curt Welch http://CurtWelch.Com/
http://NewsReader.Com/

"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.
^^^^^^^^^^^^^^^^^^^^
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.

"Leo Lichtman" wrote:
"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/
http://NewsReader.Com/

"Leo Lichtman" writes:

"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.

"Joe Pfeiffer" wrote in message
...
"Leo Lichtman" writes:

"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

Sun, 3 Aug 2008 22:12:21 -0800, "SteveB" toquerville@zionvistas
wrote:

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

Remove 333 from email address to reply.

Randy writes:

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.

Finally, an explanation for how welding can damage electronics that
makes sense! Note that the way to avoid it has nothing to do with the
battery.

Joe Pfeiffer wrote:
Randy writes:

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.

Finally, an explanation for how welding can damage electronics that
makes sense! Note that the way to avoid it has nothing to do with the
battery.

Yeah, that makes a lot of sense. If you weld the exhaust, which will
likely have a very good electrical connection to the engine, but might have
a poor connection to the frame because of rusty brackets and rubber engine
mounts, and you ground to the frame instead of to what you are welding, the
path the current finds from the exhaust to the frame might well be through
many places you didn't want it to go including your drive train and
bearings as well as through sensitive electronics. I could see how that
could be a common error people could make which could lead to bad issues if
the engine wasn't well grounded to the frame.

--
Curt Welch http://CurtWelch.Com/
http://NewsReader.Com/

Aside from all the issues about damaging the electronics, there is an
overriding reason to make a good ground connection near the weld. You'll
get a better weld. Welding currents are high, and arc voltage is low.
Voltage drop in the return path is going to have a bad effect.