welding without isolating batteries!!!

[blackrose]

I just made the mistake of welding some annodes onto my hull thinking that my batteries were isolated when in fact they were not. We'd only put 3 on before I realised and everything seems ok - alternators at least. If my alternator light goes out at start up does this mean I have got away with it or could one of them be damaged (twin alternators)? What about batteries, or anything else? I have a voltage sensitive relay which also seems to be ok.

[NB Esk]

Hi blackrose, I'm a mechanic and have done a lot of vehicle welding. I do try to disconnect the batteries, but have also done a fair amount without. I have always "got away with it" but have heard of those that did'nt............hopefully you'll be ok.

[Cafnod]

Sounds like you have managed to be lucky, this time.

always disconnect batteries and alternators before welding, can be seriously expensive and dahgerous not to do so.

[Yamanx]

We weld onto vehicles every day.

 

Disconnecting the battery is to stop your alternator getting spiked, if it still works then its fine. The charge light goes out because the wire to it becomes live giving the light live live feed. Which means its working.

 

You wont damage your batteries and its not dangerous.

 

The most damage is done to engine management systems and they should always be disconnected.

 

Although some big welders are 300 amps or more they are only about 24volts.

[blackrose]

Thanks for your replies. It was only a small portable MIG welder (if that makes any difference). I don't have a battery management system or an alternator regulator, but I do have a Voltage Sensitive Relay between my start battery & bowthruster batteries. It sends the charge to the BT batteries when the start battery reaches a certain charge. The red indicator light is still on so I think it's ok.

 

By the way, I've heard some people say that you only have to switch off the battery isolators when welding, while others say you have to completely disconnect your batteries. Which is correct?

Edited July 21, 2006 by blackrose

[Yamanx]

Leave the batteries alone and pull out the conection to the alternator. Or fully disconnect your batteries as this will have the same effect. Switching off the isolator may not work anyhow if the charge doesnt go through it.

[james46]

You can get a tool you attach to the battery to stop this happening i weld trains we find if you have the earth near to where your welding we dont have to take the processor cards out 

[Alan de Enfield]

 

And, 17 years later we get an answer .............................

[ditchcrawler]

10 minutes ago, Alan de Enfield said:

 

And, 17 years later we get an answer .............................

Its just when the right person comes along

[Lily Rose]

 

Hopefully the person who asked the question hasn't been holding his/her breath waiting for an answer.

[james46]

41 minutes ago, Alan de Enfield said:

 

And, 17 years later we get an answer .............................

Haha i just saw that now it was posted in 2006 ive just joined 

[blackrose]

1 hour ago, Alan de Enfield said:

 

And, 17 years later we get an answer .............................

 

Since I asked that question I've learned a lot. The real answer is that isolating your batteries won't make any difference as long as the welder's earth clamp is properly connected and located near the welding because the current will always take the path of least resistance.

 

If on the other hand the earth clamp isn't connected properly near the work and the current chooses a different path to earth then isolating the batteries won't make much difference because your alternator will probably get fried anyway. You'd need to completely disconnect the alternators and a load of other electrical connections too if you really want to protect your system from welding currents, not just the batteries.

Edited August 21, 2023 by blackrose

[james46]

Yeah thats very true im welding on trains all the time as long you keep it close its fine 

[john.k]

I have always thought that leaving batteries connected would provide a better sink for any stray voltage spikes ..........anyway ,Ive never disconnected batteries ,but Ive never welded on cars either ........boats ,trucks or machinery.

[Peanut]

 

1 hour ago, john.k said:

I have always thought that leaving batteries connected would provide a better sink for any stray voltage spikes ..........anyway ,Ive never disconnected batteries ,but Ive never welded on cars either ........boats ,trucks or machinery.

The diode pack might provide a lower resistance between +ev and earth.

[Tony Brooks]

I think there is a very good chance that disconnecting things before electric welding may be an urban myth.

 

Firstly, even on a boat the positive current you are applying is to the hull/body which is normally at negative battery potential, so how does it get to the positive side of the diode pack. It could back flow via the negative wiring then backwards through the other equipment, and then backwards down the positive cable, but all that has resistance and in many cases the appliance switch will be off.

 

When the need to disconnect thing became "common knowledge" it was contemporaneously with the change from positive to negative earth cars. At that time, you could get both positive and negative earth alternators. The instructor on a Lucas course I attended at that time stated that after investigation they found that the body shop staff who claimed that the welding damaged the alternator actually caused it by connecting negative earth systems as positive earth.

 

It would be interesting if anyone has any definitive examples of welding damaging equipment, rather than human error.

[1st ade]

Not quite off topic. Many years ago, I nearly wrote off our Isuzu 3.1 TD Short Wheelbase. At the time, I subscribed to the disconnect battery "myth". We talked a local garage into fixing the (rear end shunt) damage for less than the insurance write off cost, and they did a wonderful job.

 

When I picked the car up, I thought "attention to detail" - they have set the clock after disconnecting the battery

 

On the way home, I turned the radio on - it wasn't locked; and was still on Radio 2. I checked - "no sir, we don't bother disconnecting the battery, if you do the job right it makes no difference".

[nicknorman]

I certainly fail to see how disconnecting the battery but leaving all the electronics connected could possibly help. In fact it could make it worse as probably the battery has some degree of ability to absorb voltage transients on the supply lines.