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  1. #1
    Join Date
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    Default can you weld on a vehicle while battery still connected

    Title says most of it .
    I recently purchased a 2005 ford transit cab chassis and need to weld some mounting plates on rear of tray and am wondering if I need to disconnect battery. I really dont want to as this will stop the stereo from working and I dont have code to restart it. I have received conflicting advice and am wondering if anyone here can advise
    Some people are like slinkies - not really good for anything, but they
    bring a smile to your face when pushed down the stairs .

  2. #2
    Join Date
    Aug 2009
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    Caversham WA
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    Default

    I would advise against it as it increases the chance of damaging any electronics in the vehicle if you leave it connected.
    You can however purchase a surge protection device that you connect across the battery terminals which may allow you to weld safely with the battey still connected.

  3. #3
    Join Date
    Dec 2005
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    Canberra
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    Default

    The correct answer depends on how lucky you feel....

    More often than not, everything is fine. But one fried EMU or triggered airbag and you're down $600. Check your local car stereo place, they may be able to get a code for your stereo.

    There are also little battery back up doodads (they plug into the lighter socket) that should keep power to the stereo while you disconnect the car battery.

    However, if it's an aluminium tray and you are tig welding, I'd place disconnecting the battery at a much higher priority than if you were mig welding steel.

  4. #4
    Join Date
    Mar 2008
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    Newcastle West Australia
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    Default

    Expoloding batteries, burt out computers, not often but all possible.

    www.solidwoodfurniture.com.au

    A good edge takes a little sweat!!

  5. #5
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    Default

    HI,
    The Really Correct Answer is NO as the Battery could Explode and not leaving out possible damage to the Vehicles Electronics. The Answer above is the same whether You are Arc, Mig or Tig Welding and probably even Plasma Cutting on the Vehicle. Think about it this way a car has a 12 volt Battery, some Batteries can take up to a 14.8 volt charge rate. For an example a Stick Arc Welder typically has a Voltage of 45 Volt and 70 Volts - Older Arc Welders were 50 volt and 80 volts. Imagine what that Voltage would do to the Car battery should it go through it for some reason.
    Off the Subject a bit, Years ago when I was about 5 I was holding some Timber for my Dad whilst He was Cutting it with a Circular Saw. The Car Battery that was on Charge nearby suddenly Exploded - We were both Okay.

    If You Contact Your Local Ford Dealer they should be able to Help You out with the Radio Code, providing it is the original Radio.
    PLEASE PLAY IT SAFE AND DISCONNECT THE BATTERY!.

    JUST A NOTE : For People thinking about the fact that You can Arc Weld with a Car Battery, Yes that is True. There is also a Danger there that if the Electrode sticks it will cause a Short Circuit and the Battery/s will Explode.
    Last edited by steran50; 20th Feb 2011 at 09:28 AM. Reason: JUST A NOTE
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  6. #6
    Join Date
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    Default

    Yes you can. But don't under any circumstances! On modern vehicles the computer would be the single item most at risk. Consider the measures we go to when jump starting. Special leads and allowing the charge to build up first amongst other things.

    The very first time I welded on a vehicle, which was an early model Dyna truck, I did not have the benefit of anybody advising me to disconnect the battery. I think I blew every single light in the vehicle. I was probably lucky I didn't burn out the points.

    Just disconnect the earth lead. Don't know what you can do about the code for the stereo.

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  7. #7
    Join Date
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    vic clayton
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    thanks guys I had only talked to 2 blokes one who said he had done it heaps of times with no problem the other who said similiar to you lot oh well really wanted to do the job today so now will wait till monday talk to ford re the code
    Some people are like slinkies - not really good for anything, but they
    bring a smile to your face when pushed down the stairs .

  8. #8
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    Murwillumbah Nthn NSW
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    Default

    Have welded heaps of times [arc ac and dc]on white a few different vehicles , never any problem .But all were pre 85 so no hi tec electronics.

  9. #9
    Join Date
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    Mackay North Qld
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    As per the warnings above.

    If there is no other choice place the earth return as close as possible to the area to be welded.

    Unless you are considering a moon orbit without the benefit of the space shuttle, also check out the fuel tank.

    How close is this to the welded area.?

    If you can smell fuel don't weld ,its highly dangerous as its a vapour exposion that will kill you.

    Does the fuel tank it or its ancillaries leak?

    ok its a pain in the bum to drop the fuel tank in a lot of cases ,but the alternative is much nastier.

    Check before you weld.!!

    Safety always
    Grahame
    Last edited by Grahame Collins; 20th Feb 2011 at 01:47 PM. Reason: proo fread,bloody proof read!

  10. #10
    Join Date
    May 2008
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    Sydney
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    Default A pic will explain

    Hi All,

    I have sketched a quick pic showing the relative current flows. If you can imagine the welding current shown in blue only flows in the chassis / frame / panels of the car. The actual car electrical equipment current shown in black uses the car chassis / frame / panels as a return path to the battery negative terminal.



    The car equipment current flows from high to low potential so from positive on the battery, via the fuse block, via the equipment (load) and via the return earth path (chassis, panels etc) back to the battery negative terminal.

    If you are welding on a car then you are doing the same except your welding current flows from electrode to earth clamp, the load is the chasis itself, more specifically the end of the welding electrode. The only way it is possible for you to damage the equipment in your car is if the current path for your welding is a much higher resistance than the electrical circuit in your car (impossible due to it all being steel). A poor earth connection will not do it as the poor earth connection is localised and common to both scenarios. In short you cannot destroy anything ELECTRICAL in the car by welding other than by blowing it up or setting it on fire as Graham has pointed out due to fuel or sparks.

    It is however a precaution often taken in case you put a hot (melts through plastic insulation) and live welding electrode onto a 12 Volt wire and inject a 70 volt open circuit voltage into a 12 volt system thus destroying many valuable car bits.

    Regards
    Pete (Tokentools)

  11. #11
    Join Date
    Dec 2005
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    South Australia
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    Default

    As Pete says above, if you diconect the battery make sure your plug a computer saver into the lighter/power socket to stop it losing its memory.
    Master Splinter whear can you get a air bag replaced for $600?

  12. #12
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    Think about this......you old style reluctance welder (iron core transformer type) may only have an open circuit terminal voltage of 50 - 70 volts... but because of the reluctance of the coil, on strike up or lift off or the very action of the arc, very much higher voltage pulses or surges may occur.

    Remember an arc has been the method of choice for producing big nasty voltage spikes since the beginning of electricity.

    Likewise modern electronic welders or old sytle tig, may also have a base voltage of 50 to 70 volts ish..... but there may be a high frequency high voltage component to assist striking arc and smooth arc flow.

    the above voltages may reach hundreds of volts, in the case of TIG lots more.

    Now the all one earth argument.......well the chasis earth does have a finite resistance.......large amount of current flows.....there will be voltages resulting between certain points in the chasis.
    Modern electronic cars have a multiplicity of sensors all grounded at different places on the chasis..many of these sensors may operate well below 12 volts.

    Combine that with the forgotten high voltages...um not good.

    Remember too that some car manufacturers are better at designing electronics to withstand the real world than others......some brands are known for their ECU's spitting the dummy without any provication at all.


    If it is a modern car.....no question, disconnect the battery.

    If I was tig welding on a modern car...I'd be realy thinking about yanking the ECU and anything else electronic too.

    cheers
    Any thing with sharp teeth eats meat.
    Most powertools have sharp teeth.
    People are made of meat.
    Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

  13. #13
    Join Date
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    Default

    if you diconect the battery make sure your plug a computer saver into the lighter/power socket to stop it losing its memory.
    This is the bit I don't quite get - won't disconnecting one battery and then plugging another battery back in, negate the effect.

    I can see that if the small battery explodes, it won't do as much damage as a big battery, but you are still not protecting all of the other electronics (if in fact they are in danger at all), by plugging in one of these devices.
    Cheers.

    Vernon.
    __________________________________________________
    Bite off more than you can chew and then chew like crazy.

  14. #14
    welding is offline Engineers are qualified to make claims
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    I think the hardest thing for people to wrap their head around is how current flows in a circuit. When welding on a car the only reason welding current would flow up the ground wire of a car's electrical device instead of directly back to the work clamp via the chasis is that the electrical device provided a lower resistance path than the chasis. For this to happen the current would flow via the device then via the battery and then to the work clamp. This is assuming the electrical device is turned on or permanently connected to the battery as in a clock / radio or ECU.

    It is not likely that this scenario will ever occur as the chasis is always the lowest resistance, the electrical device will always have a resistance greater than the chasis as it is a device that does work and in order to do work you must use power and in order to use power you must have resistance. Power = Volts x Current and to get current, Current = Volts divided by resistance.

    You can test the resistance of your chasis yourself. First touch your meter probes together and measure their own resistance, perhaps 0.2 to 0.3 ohms. Then measure the reistance across two points of your chasis within the reach of your meter probes. I bet you get the same reading that is because the resistance of your multimeter probes is higher than the chasis.

    Think about this for a moment, your battery at charge is 13.7V. A typical starter motor for a car would pull around 100 amps. On cranking the voltage would drop to aroun 10 volts. 3.7 volts is consumed by the internal resistance of the battery, 10 volts is consumed by the motor. The total resistance of the battery and motor and chasis combined is resistance = Volts divided by amps so 13.7 / 100 = 0.137 ohm. The reistance of the starter motor and chasis is 10 / 100 = 0.1 ohm. The way to determine chasis resistance is to measure the voltage between the starter motor case and the earth strap bolt on the chasis whilst cranking. You will find this value is extremely small hence a teeny weeny reistance can be calculated for the chasis.

    Right everyone, clear as mud? But for safety you should always disconnect the battery before welding, it stops people using your car whilst your pride and joy welder is tethered to it

    John

  15. #15
    Join Date
    Oct 2007
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    vic clayton
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    I use a kemppi 180 minarc so it would be real easy to drive away with it still attached of course the bottle is a bit bigger so maybe not
    thanks John for the explanation
    Some people are like slinkies - not really good for anything, but they
    bring a smile to your face when pushed down the stairs .

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