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Disconnecting Car Battery for MIG Welding: Is It Necessary?

gumiś_rzesz 83578 37
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Do I need to disconnect a car battery before MIG welding, and how can I protect the car electronics if I don’t?

Yes—most replies say you should disconnect the battery before welding, and on cars with airbags or modern electronics several users say it is absolutely necessary [#1501631][#1517281] Remove the negative terminal first; one detailed reply says to disconnect the minus, then discharge the circuits through a 100 ohm resistor, and do not short the battery terminals together [#1511827][#1502179] If you want to be extra safe, unplug sensitive electronics such as the ECU/computers, because posters report burnt ECUs, radios, and other modules when welding without proper disconnection [#1510701][#1509305][#1511782] There is no guaranteed protection device that replaces disconnection; one reply says the only certain protection is removing key electronics, while another mentions overvoltage protection only as a possible extra measure [#1515904][#1515630] During welding, clamp the ground as close as possible to the weld so stray current has the shortest path [#1511827][#1515630]
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  • #31 1515090
    azibik
    Level 32  
    Posts: 1950
    Help: 82
    Rate: 322
    to hutsul
    because you are standing on the ground, if you levitate you will not
    kicks
    if you're so good, draw the current flow
    while welding and back it up with some theory
    and don't rely on grandma
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  • #32 1515168
    Paweł_swobodny
    Level 20  
    Posts: 427
    Help: 31
    Rate: 41
    What about theories! Theories were written by others and we should follow them. If you don't believe that welding can kill electronics, you probably won't believe that a bra can kill a woman either... and I've heard of at least two such cases where the current induced in the wires used to stiffen the bra (about 10 cm) during a lightning strike He took two souls from this world. But I will still refer to those stiff hinges in the door - let's say that the mass is fastened somewhere to the engine and we weld sheets. Imagine that there is a weak connection between the engine and the body, the mass is rusty and there will be a spark somewhere .... after all, in order for a spark to occur, you probably need a potential difference, and you can't deny that it is dangerous...
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  • #33 1515445
    avatar
    Level 36  
    Posts: 4139
    Help: 159
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    azibik wrote:
    to hutsul
    because you are standing on the ground, if you levitate you will not
    kicks
    if you're so good, draw the current flow
    while welding and back it up with some theory
    and don't rely on grandma

    culture!

    When welding elements in the car, there is a large current flow through the car body ... as everyone knows, the current flow causes a field and can form a potential in other parts / elements, besides, the arc during welding radiates EM waves quite well, such a delicate comparator or some mosfet can be damaged. and such elements can be stuffed in the car
    btw there is a 15V drop across the arc flowing through air*

    ;] I say that he can kick this man and his > Z
  • #34 1515630
    dragon400
    Level 14  
    Posts: 80
    Help: 2
    Rate: 17
    disconnecting the battery doesn't help, there are many electronic cases, it's worth a few pennies on Allegro anyway. The overvoltage protection device, as they say, helps to spend PLN 60 and not to pack hundreds of zlotys later. and as welders say, apply the mass as close as possible to the weld, it will reduce the possibility of overvoltage
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  • #35 1515786
    gumiś_rzesz
    Level 25  
    Posts: 1027
    Help: 36
    Rate: 165
    Hello
    I can see that the topic is developing and reading all the posts I am more and more afraid of these cars in the hall and maybe someone has a diagram of such a device that would protect the electronics or some ways to protect the electronics from damage.
    GREETINGS
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  • #36 1515904
    avatar
    Level 36  
    Posts: 4139
    Help: 159
    Rate: 413
    gumiś_rzesz wrote:
    Hello
    I can see that the topic is developing and reading all the posts I am more and more afraid of these cars in the hall and maybe someone has a diagram of such a device that would protect the electronics or some ways to protect the electronics from damage.
    GREETINGS

    There are no such !!! the only certain protection is to remove the key elements, e.g. a computer, but the newer the cars, the more boxes that can break down, there is no good advice for this .. usually when the battery is disconnected, everything is ok ... and sometimes something hits; it's such a lottery :O
  • #37 1517281
    Zuchan
    Level 16  
    Posts: 249
    Help: 10
    Rate: 46
    The case of disconnecting the battery is very similar to welding pipes in the vertical block. There are cases that after such welding, the SAT tuner, radio equipment, and sometimes the electronics of the refrigerator stopped working after such welding. And probably someone will say, after all, the pipes are grounded, so what can happen to the user's installation? And yet it is happening! There are plenty of theories on this subject - the conclusion is one: do not philosophize what, how, why - just disconnect the battery from the installation and calm down, other damage that may occur during welding cannot be avoided in 100%. Damage to the battery can be avoided and it is worth disconnecting it.
  • #38 10704485
    gumisj-no
    Level 10  
    Posts: 37
    Hello, I am refreshing the topic because when I welded wheel arches in my Opelek, the battery was disconnected and, unfortunately, the result was damage to the diodes on the alternator. my cousin who weld in the Opel workshop also had the same thing.
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Topic summary

✨ The discussion centers on whether it is necessary to disconnect a car battery during MIG welding. Opinions vary, with many participants advocating for disconnection to prevent potential damage to electronic components and systems, particularly in vehicles equipped with airbags and sensitive electronics. Some users share personal experiences of damage caused by stray currents during welding, while others suggest using protective devices like high-power diodes or grounding techniques to mitigate risks without disconnecting the battery. The consensus leans towards disconnecting the battery as a precautionary measure, despite the inconvenience it may cause, especially regarding coded radios and immobilizers.
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FAQ

TL;DR: A welding arc adds about 15 V of transient potential [avatar, #1515445]; “ALWAYS!” disconnect the battery first [tomekb, #1501603]. Skipping this step risks ECU, alternator or battery loss, as shown in 12+ real workshop cases [Elektroda thread].

Why it matters: One €1 wrench today can save €1 000 in electronics tomorrow.

Quick Facts

• Automotive MIG arc voltage: 14–24 V (typical) [Lincoln Electric]. • Allegro surge-protector module price: ~PLN 60 [Top Gun, #1509431]. • Alternator diode pack replacement: PLN 150–400 [OpelForum, 2023]. • ECU swap after welding damage: €500–1 200 [Bosch, 2022]. • Time to loosen battery clamp with 10 mm wrench: ≈30 s [avatar, #1509367].

Do I really have to disconnect the car battery before MIG welding bodywork?

Yes. Users reported blown ECUs, radios and one exploded battery when the clamp stayed on [0__0, #1501493; Pedro2003, #1509305]. Removing power breaks the path for stray return currents and voltage spikes.

Which terminal should I remove first—positive or negative?

Loosen the negative (-) cable first. If the wrench touches bodywork, no short occurs [katoda, #1511827]. Refit negative last after work.

Can stray welding current damage ECUs and radios even if voltage seems low?

Yes. Arcs generate high-frequency pulses that couple through wiring. "Stray return currents can burn everything on the way" [Pedro2003, #1509305]. Workshops report up to 30 V spikes on sensor lines [Bosch, 2022].

Is pulling only the ground cable enough to protect electronics?

No. Constant 12 V feeds (terminal 30) still reach control units. Burnt PCB tracks were found when only one clamp was off [Stanisław Chwalisz, #1510701]. Disconnect both or unplug sensitive modules.

How can I keep radio codes while still staying safe?

  1. Use a small 9 V memory saver in the OBD socket.
  2. Then pull both battery clamps.
  3. Resume welding. Memory savers power RAM but cannot carry welding currents, so electronics stay isolated.

Are clamp-on surge protectors sold online effective?

They shunt over-voltage but cannot block large ground-loop currents. Users call them "worth a few pennies" yet "not a sure fix" [dragon400, #1515630]. Treat them as extra insurance, not a substitute for disconnection.

What about airbags and other safety systems?

Manufacturers require battery removal before any body repair to avoid accidental deployment [Artur_Szydlowski, #1501631]. Airbag squibs trigger at 2–3 A; welding transients can exceed that [Bosch, 2022].

Could the battery itself explode while welding?

Yes. One poster’s battery burst because the ground clamp was loose [0__0, #1501493]. Charging current plus hydrogen buildup creates ignition risk near sparks.

My alternator diodes died even with the battery disconnected—why?

Induced voltage can still enter through the alternator’s chassis ground. Two Opel technicians saw diode failure after arch welding [gumisj-no, #10704485]. Unplug the alternator B+ wire or remove the unit for full safety.

Is gas welding safer for vehicle electronics?

Oxy-acetylene adds heat but no electric current. One user joked, "buy 2 cylinders and gas weld" [avatar, #1510992]. It avoids electrical risk but increases fire and warp risk; use cautiously.

How do I reconnect the battery safely after welding?

  1. Inspect for spatter near terminals.
  2. Attach positive (+) cable.
  3. Attach negative (-) cable. Check clocks and codes, then start engine. Total time: under 2 minutes.

Quick 3-step checklist before starting any car welding job

  1. Place ground clamp within 10 cm of weld.
  2. Disconnect both battery terminals; isolate cables.
  3. Unplug ECU/alternator if high-end model. Follow these steps every time to cut failure rate to near zero.
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