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[peter e]

Firstly hello to all
   I was reading a discussion on the forum as to whether you should disconnect your battery before welding. I was always taught to disconnect before welding, if the circuit is open then there is no way for the high welding amps going back through your sensitive electronics. But I have recently been using a surge protection device that clips across the battery. The company is sealey part No PROSAF/12 not cheap approx £70.00, but saves a lot of hassle

[Auto Addict]

Welcome to the forum

I'm moving your thread to the 'General Chat' section, as it's not Omega specific.

[Lazydocker]

I just err on the side of caution and disconnect the battery... Much safer that way!!

My best trick is setting fire to the stuck on sound deadening inside the car because I haven't cleared it back far enough!    

[Mike Collins]

I can see the reasoning behind disconnecting it for fire protection where a cable may be heat damaged.

What I question is that with the battery removed, the only path for spikes induced in the supply line is through whatever loads are connected. Surely the battery would act as a very good spike suppressor?

Is that the reason for the Sealey device?

[Lazydocker]

I can see the reasoning behind disconnecting it for fire protection where a cable may be heat damaged.

What I question is that with the battery removed, the only path for spikes induced in the supply line is through whatever loads are connected. Surely the battery would act as a very good spike suppressor?

Is that the reason for the Sealey device?

What loads... With the battery disconnected there is no complete circuit!! Anyway, it'll earth through the path of least resistance i.e. the fookin great earth lead you clamp the the car when mig welding!!!  :-? :-?

[Mike Collins]

Loads; any device connected between unswitched positive bus and ground, or switched bus if it's switched on. You could include any ECU in this range.

Earth cable may connect chassis to ground, but unless you short the disconnected battery positive lead to ground it will float within the limits of the connected loads.

High voltage spikes can behave very differently from DC.

[Kevin Wood]

Neither the battery nor any of the car's electrical systems are in the circuit you use for welding, which is established between the weld itself and the ground connection back to the welder, which should be as close as possible to the weld, of course.

What might be an issue are currents induced in the car's wiring loom and chassis by the currents used for welding. I can't really see that disconnecting the battery would help a lot here. Disconnecting every sensitive item (ECUs, Radio, etc) from the vehicle's loom would be my plan of attack. Disconnecting the battery might limit the damage done if, say a diode in the alternator got fried and went short circuit, but I can't really see how it helps to any greater degree, from a theoretical standpoint.

Anyone got any alternative theories?

Kevin

[Lazydocker]

Neither the battery nor any of the car's electrical systems are in the circuit you use for welding, which is established between the weld itself and the ground connection back to the welder, which should be as close as possible to the weld, of course.

Isn't that basically what I said here??

the fookin great earth lead you clamp the the car when mig welding!!!

Only in much clearer terms!!  

[peter e]

In the good old days you would disconnect the battery, because it is possible to damage the alternator, and you could also damage the battery if you did not (it might not happen but why take the risk).
 Nowadays you have the above risk plus very sensitive electronics. In some cases the car manufacturer would not recommend you jump leading your car without surge protection.
When welding yes you should put the earth lead as close as possible to the weld, but electrics does not always take the shortest route, but it does take the route of least resistance. It can be surprising how long that can be.
Don’t forget the shell of the car is also part of the electrical circuit. The reason I have now gone for the surge protection device is because after welding on my car and reconnecting the battery, I then tried to put in the radio code. I found out the code given to me by the previous owner was wrong and it cost me £26 to get it from the manufactures.
I have also spoken to people over the years that claim not to bother to do either, and get away with it. I personally will not be taking the risk.

[Lazydocker]

In the good old days you would disconnect the battery, because it is possible to damage the alternator, and you could also damage the battery if you did not (it might not happen but why take the risk).
 Nowadays you have the above risk plus very sensitive electronics. In some cases the car manufacturer would not recommend you jump leading your car without surge protection.
When welding yes you should put the earth lead as close as possible to the weld, but electrics does not always take the shortest route, but it does take the route of least resistance. It can be surprising how long that can be.
Don’t forget the shell of the car is also part of the electrical circuit. The reason I have now gone for the surge protection device is because after welding on my car and reconnecting the battery, I then tried to put in the radio code. I found out the code given to me by the previous owner was wrong and it cost me £26 to get it from the manufactures.
I have also spoken to people over the years that claim not to bother to do either, and get away with it. I personally will not be taking the risk.

I hope you got their Lottery numbers!!  

I'm never that lucky and would fry everything in sight!!  

[phil her up]

I've welded lots of cars/vans & have always disconnected the battery, but I spose with later cars & codes to remember the surge protector does the job. In fact I shall be welding my little sportraks chassis tomorrow getting it ready for the mot