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  1. #11

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    How long does it take to remove the battery cables, couple of minutes? If there's the slightest possibility of screwing something up why take a chance.
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  2. #12
    Join Date
    Dec 2011
    Posts
    419

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    Quote Originally Posted by gnforge View Post
    Never thought of double ground. That is good idea. Maybe double ground both sides of weld area in high risk cases??
    I'm not so sure it always is a good idea. By adding more grounds you could increase the possible paths for current that otherwise wouldn't exist. As in from anywhere on the vehicle to ground. If you were welding with an engine powered weld that is not connected to earth ground the only path to complete the circuit is via the work cable. If you were to add more grounds and are using a grounded welder like one plugged into your shop power you will have created multiple paths. No? It might be an idea for person safety but not for electronic safety.---Meltedmetal

  3. #13
    Join Date
    Dec 2011
    Posts
    419

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    Quote Originally Posted by dandeman View Post
    I have the factory service and body collision repair manuals for several Toyota vehicles... Their guidance for on vehicle welding, in addition to the clamp as close to work and to know the welding current path, is also concerned about inadvertent firing of the air bags and seat belt tensioners..

    Toyota air bag systems (unlike certain GM models as we have learned) have an auxiliary energy storage system that can fire the airbags for up to 90 seconds after battery power has been lost and independent of ignition switch setting.. This function is there as in the early phase of a collision, or 2 strike collision, the battery/wiring can be destroyed, yet the air bags still have power to fire.

    Therefore their guidance is to disconnect the battery and wait 90 seconds before performing any on vehicle welding.
    That's a good point I hadn't thought about the air bags. I would guess even disconnected if you were to burn though a wire on the air bag system you could fire the air bags too.---Meltedmetal

  4. #14
    Join Date
    Apr 2013
    Location
    metro Detroit
    Posts
    91

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    I started off my working career as a tow truck driver. I have blown a few abs computers by hooking the ground cable to the master cylinder. But now I weld on semis and never hurt the ecm.

  5. #15

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    dandeman, do you have an autobody repair shop? Tell 'em what a typical repair bill is for damage done by an airbag going off. In my ignorance, I supposed that the airbag just blew out and protected the driver, with no other consequence. That was before my dad's idiot second-wife ran their three-year-old Focus into a pole at low speed, discharging the airbag. Minimal damage from the pole, but the insurer "totaled" the car due mostly to the effects of the airbag.

    A 1/2" end-wrench, possibly a screwdriver, and two minutes time or less disconnects the battery clamp . . . (all my own vehicles get the quick-disconnect battery clamp with the big knob on top).

  6. #16

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    Quote Originally Posted by old jupiter View Post
    dandeman, do you have an autobody repair shop? Tell 'em what a typical repair bill is for damage done by an airbag going off. .
    No do not run an autobody repair shop but have learned quite a bit doing modifcations to older and newer airbag equipped vehicles for serious off road activity and as moderator on an 4x4 off road forum.

    You point is valid about the damage done by the airbags firing... the cost of air bag replacement, instrument panel component replacement (ripped up from firing airbag), windshield replacement (broken by instrument panel air bag firing) can end up totaling the vehicle.

    Some states have vehicle registration laws that if the airbags have ever been fired on a vehicle, the vehicle has to carry a savage title.

    The low speed pole strike is similar to another slow speed situation that can fire the air bags on an off road vehicle.. a frame strike down on a boulder with some forward speed.

    From reading of several automotive engineering journals about the current GM problem there is a lot of variability on airbag / sensor design as indicated by my earlier post on the Toyota energy storage design and the GM cars in question loosing the ability of fire after 150ms loss of power. Federal standards for airbags do not dictate this level of design performance and the GM ignition switch issue has brought up the question of whether they need to be updated. You typically won't even find this level of discussion in the more general news sources. The message here is we can't assume all vehicles would behave the same with regard to inadvertant firing.

    From a purely g force triggering, some systems (and, my knowledge is dated) use g force mechanical sensors on each side of forward radiator bulkhead that goes across the front of the vehicle (these being a steel ball in a cylinder held in place with a magnet, calibrated to release into gold contacts) beyond a certain g force level. This signal closure goes to the airbag controller typically mounted on the transmission console (well protected area) underneath the center console.. That unit has the energy storage and accelerometers to further analyze the g force, direction and other things like passenger seat occupant and makes the final decision whether to fire or not. Given injuries to children in the passenger seat, I believe all manufacturers have adopted variable rate airbags for the passenger seat, which are essentially gas inflated bags to fire at a rate consist with the weight of the person in passenger seat (yes there is a sensor in the passenger seat to guestimate the weight of the passenger.) I think most driver side air bags still use sodium azide (think a small amount of slow burning explosive) to fire at a fixed rate.

    I guess the point I'm trying to make here is these are quite complex systems.. Manufacturers documentation for a specific vehicle would be the only reliable answer to the original question.
    Last edited by dandeman; 08-30-2014 at 03:41 PM.
    Hobby Welder for about 32 years
    Hobart 190 MIG with SpoolGun
    Hobart AirForce 700i Plasma Cutter
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    295A AC Buzzbox (what I learned on)
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  7. #17
    Join Date
    Mar 2011
    Location
    st-eustache qc.canada
    Posts
    239

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    For the guys that use a f-250 to f-550 2005 and later as a welding rig or used one, because according to ford fleet it should be fried by now

    https://www.fleet.ford.com/truckbbas...tml/Q123R1.pdf
    Last edited by snowbird; 08-30-2014 at 05:56 PM. Reason: ponctuation

  8. #18

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    Quote Originally Posted by snowbird View Post
    For the guys that use a f-250 to f-550 2005 and later as a welding rig or used one, because according to ford fleet it should be fried by now

    https://www.fleet.ford.com/truckbbas...tml/Q123R1.pdf
    wow! these systems sound awfully fragile..and surprised at such a fragile design.

    My career was in digital system product development for a major computer company (or should I say was when we actually designed and manufactured in this country.)

    The really dense technologies, CMOS for example are very sensitive to transients and stray voltages, but the normal design practice was to surround that technology off chip/off circuit board drivers and receivers that were much more robust in handling the treacheries of the outside world.. Hard to believe Ford would put a system into production that fragile.

    One weakness in most body on frame vehicles which I know many of you are already aware of from past posts I've read, is the relatively weak electrical bonding between drive train, body and frame.. On modern vehicles with the liberal use of rubber mounting systems dam near for every thing, the engine and drive train are electrically insulated from the frame by engine mounts, suspension bushings, and the body sitting on the frame is of course sitting on rubber bushings, all of these with no direct metal to metal contact to minimize NVH (noise, vibration and harshness) as they like to call it. Of course they add ground straps to bond all this together, but they can be pretty chincy.. Welding currents through these straps would smoke them.

    A common failure that has happened to off road (serious rock crawling type off road vehicles) is when someone doesn't really lock down tight the battery hold down bracket, during really violent manuevers, the heavy battery shifts and the positive terminal makes contact with the bracket, shorting positive to ground.

    Another scenario was vehicle roll over with the hood crushing down on top of the battery making battery positve terminal contact (In the 4x4 world many consider sheet metal highly overrated and optional, that rollover tin damage will buff right out! )

    With that short circuit, the most weak thing completing the short is going to be burned up until it opens.. The negative grounding is done in different ways but a rather common method is for the heavy negative battery terminal cable to go only to engine block to handle the starter current, then much smaller straps to ground the engine, frame and body together as the negative return for much lighter return currents of every thing else on the vehicle.

    Rather common for the ground straps in the above short circuit to first burn open, then the real damage starts... then the instruments, sensors, anything else crosses the body to frame to drivetrain that have their own ground wiring to minimize noise in the sensor circuits gets burned up. It really can make a mess of the vehicle electrical system..

    The battery short I can understand, passing welding currents through rather fragile vehicle ground wiring I can understand, but the above service bulletin is over the top..
    Last edited by dandeman; 08-30-2014 at 07:17 PM.
    Hobby Welder for about 32 years
    Hobart 190 MIG with SpoolGun
    Hobart AirForce 700i Plasma Cutter
    Hornell Speedglas 9000X Helmet
    295A AC Buzzbox (what I learned on)
    Miller Bobcat 225, factory propane option, also serves as my emergency power generator
    Dandeman's Toy Page

  9. #19
    Join Date
    Dec 2010
    Posts
    355

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    been welding for years on just about everything they got down here in louisiana. when i pull up to a boat i connect my ground to the hull and start working. the electronics that these boats have these days are out of this world yet they never disconnect any of them when we are welding. the only time we use a second ground is when i'm installing a new crane or welding on the old one to repair it.and i also run a striaght ground to the jacking system of the lift boats they way no curent flow through the gears same with the crane pedistals we will run a direct ground from the machine and if we don't have enough ground wire we will use flatbar to jump from the deck to the crane to bypass the ball ring on the pedistal.if anyone thinks that they don't need a direct ground they are crazy one time i was called out to cut out and replace 2' for gear track on a leg for a lift boatwhen i got there i checked the grounds and they had a flatbar going from the deck and welded to the leg so i started to cut out and change the track section out. after i had the new section in and tacked off they wanted to do a test run to check for spacing in between the gears on the gear box and the track. everything checked out or so they told me to weld it up well the spot i changed was now 20' higher than it was before so they lifted me in a basket the foreman gave me the thumbs up to start welding after two hours of welding they lowered me down and fired up the engines as soon as they pressured up the hydraulic lines oil went flying out the crankcase vent. turnes out they forgot to reconnect the ground and after two hours of welding the heat inside the gearbox where the curent was grounding through had melted the o rings. costly mistake. so now i always carry flatbar and an extra 100' of ground wire and i hook up my own grounds and never rely on others to say it's ok go ahead and weld. i didn't have to pay for repairs because it was the captain who removed the ground and it was the foreman who gave the all clear.

    but in all the years of workin on boats i have never heard of any elctronics being fried by not disconnecting them.

  10. #20
    Join Date
    Mar 2011
    Location
    st-eustache qc.canada
    Posts
    239

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    source ford fleet :

    Code:
     Aftermarket Plasma Cutting/ Welding Operations on F250-550 Trucks
    
    
    Warranty Statement: Before electric welding or plasma cutting on the frame or body of F250-550 units, disconnect the 
    battery, instrument cluster, ABS module and the PCM. Just disconnecting a battery cable is not 
    enough to prevent damage to these components. Damage seen in newly-constructed trucks has been 
    traced back to welding. Electronic module damage due to this customer or vehicle modifier action is 
    not covered in vehicle warranty. 
    If you have any questions, please contact the Ford Truck Body Builders Advisory Service as shown in the header of this bulletin.
    Wether they exagerate or they made it cheap and want welders to be responsible for it.

    Have you fried a ford lately ?

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