Reasons for the battery being disconnected?

  1. Weldinator

    Weldinator Astalavista baby....

    Posts: 771
    Why does it have to be disconnected before welding, would it blow up or kill its cells ?

    I had forgot to do this one time, started the car and it was fine :ashamed:
  2. Wozzaaah

    Wozzaaah The wizard of woz Staff Member

    I was always led to believe it was to protect the diodes in the alternator.
    With the myriad of electronics in today's cars I suppose it's erring on the side of caution.
  3. autocare

    autocare Forum Supporter

    Posts: 1,054
    Bolton UK
    When welding you firing electricity at the point of weld, if everything is good then you only use the exact amount of electricity you need but that will not happen on cheap welders so at points your gonna have surplus floating about...

    I used an anti zap, it caught all of the surplus in its capacitors and when the welder went below max would trickle it back in to be caught by the weld again (simplistic explanation).

    If you disconnect the battery then the cars electronics are not in the circuit so welding wont affect them... got to watch for ECU's these days as well
  4. pedrobedro

    pedrobedro Man at Matalan

    Many years ago a lad I worked with was arc welding his Mini without disconnecting the battery, no alternators or fancy electronics it had a dynamo and points and condenser ignition. He got a sticker, the rod was in contact with the metal and wouldn't pull off and the battery actually split in the boot of the car.
  5. roofman

    roofman Charles Darwin fan club

    Posts: 2,181
    North West
    yep my E46 beemer being an example,the final stage resistor on the heater motor has a permanent live feed even when the ignition is off and the heating system has its own ECU so very easy to get caught out on this type of car if you dont disconect the batt;)
  6. ruston Member

    Posts: 11
    I used to own a VW Passat and had to MIG a crack on the door hinge, I disconnected the battery and even uncoupled the alternator BUT I didn't disconnect the ignition control module which was situated under the bulkhead! Yes, you guessed, it burnt out internally and of course the thing wouldn't start! Of course it was a Sunday....................:( lesson learned the hard way.

  7. stuvy Member

    iv always disconnected the battery, does anyone use the battery savers that have the crocodile clips attached. Are they any good?

    On long way round with ewan and charlie one of there pannier racks cracked and they had someone do an emergency weld repair and it cooked the brake ABS
  8. dannyp Member

    don't go near a modern car with a TIG welder, the HF will kill various controll units around the car.

    stick welders kill alternators due to the relativly high volts compared to mig and tig. mig is about the safest wy to weld on a car but disconecting ecu's and controll units is a good idea
  9. Country Joe Argoshield Dark

    Posts: 970
    Somerset - United Kingdom
  10. Weldinator

    Weldinator Astalavista baby....

    Posts: 771
    The car thats being welded has carbs so no ecu, i was using MiG welding.
  11. keith19 Forum Supporter

    One job I had years back, I worked on repairing/rebuilding car alternators most every day. Half our work came from garages, where welding had been done without disconnecting the battery and/or alternator.

    The odds against welding doing any harm are quite high, about 1 in seven in those days. But not worth taking the chance, because alternators are costly, and ECUs are worse.
    With lots more electronics on modern cars, read up the manuals on what to disconnect before welding. Some can cost a fortune to reprogram alone, without replacing anything.
  12. brightspark

    brightspark Member

    Posts: 13,304
    yarm teeside
    allso charging the battery up without disconecting alternator knacks them sumtimes :(
  13. schnappi Member

    Posts: 111
    So far all my welding has been on older vehicles and I've always got by with just disconnecting the battery. Sooner or later I'm going to have to deal with newer vehicles built in the mid to late 90's as they're starting to corrode nicely now.

    To be honest, this prospect terrifies me as they've got ECUs, EDCs, Airbags, Immobilisers, etc..

    To anyone familiar with welding newer vehicles, to what extent do you have to go around the car disconnecting the electronic gadgetry before MIG welding?

    Without access to manufacturer specific guidelines, what would a modern bodyshop be looking to disconnect?
  14. autocare

    autocare Forum Supporter

    Posts: 1,054
    Bolton UK
    I just used a decent 'Anti-Zap' and never really had problems... and some ECU's seem to get odd when you disconnect them..
  15. keithski122 Member

    Posts: 326
    I sometimes use a surge protector, mainly if I'm welding something modern(not very offten now).Never had any problems with zapping ecu's,batteries or alternators with or without protector.
  16. autocare

    autocare Forum Supporter

    Posts: 1,054
    Bolton UK
    I killed a vitara once, but it was a mercy killing as far as I am concerned :)

    Never had a prob with ought else
  17. langy

    langy langys rodshop

    Posts: 4,991
    A surge protector and having the earth where your welding helps.
  18. s410man trainee dogsbody

    Posts: 808
    i heard(off here i think) that you only needed to disconnect the battery if the current had to go across it

    eg earth on one side and welding the other side of it

    any truth in this
  19. the snooper

    the snooper getting older by the day

    Posts: 11,605
    Hull UK
    ive never disconnected the battery and never had any problems what so ever, even on newer vehicles
  20. langy

    langy langys rodshop

    Posts: 4,991
    None !!!

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