Reasons for the battery being disconnected?

[Weldinator]

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

 

[Wozzaaah]

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.

 

[Iain Westland]

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

 

[pedrobedro]

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.

 

[roofman]

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

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

 

[ruston]

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.

Pete.

 

[stuvy]

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

 

[dannyp]

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

 

[Country Joe]

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

Yes, me!
It seems to have worked ok so far. It makes a kind of chirping noise when you connect it, and makes the same noise when it does it's thing.
All the Best,
CJ

 

[Weldinator]

The car thats being welded has carbs so no ecu, i was using MiG welding.

 

[keith19]

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.

 

[brightspark]

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.

allso charging the battery up without disconecting alternator knacks them sumtimes

 

[schnappi]

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?

 

[Iain Westland]

I just used a decent 'Anti-Zap' and never really had problems... and some ECU's seem to get odd when you disconnect them..

 

[keithski122]

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.

 

[Iain Westland]

I killed a vitara once, but it was a mercy killing as far as I am concerned

Never had a prob with ought else

 

[langy]

A surge protector and having the earth where your welding helps.

 

[s410man]

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

 

[the snooper]

ive never disconnected the battery and never had any problems what so ever, even on newer vehicles

 

[langy]

None !!!

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