The Classic Machinery Network

Whenever welding on a vehicle or machine with batteries / electrical system I've always disconnected the battery as habit. More recently it's been suggested to me that...

1, You don't have to disconnect when using MIG.

2, You don't have to disconnect when using TIG.

3, You don't have to disconnect when using stick/rod if the earth clamp is on the same component you're welding.

To me this is risky nonsense especially considering modern electronic systems, I'll still disconnect regardless. That said I can't MIG or TIG to save my life and my rod welding can be abysmal.
Any advice / opinions please!!!

My 2 bobs worth

You dont have to disconnect the battery to weld but you have to disconnect the the alternator and to do that you have to disconnect the battery
The alternator has a rectifier in it to convert AC to DC and the back EMF or if you want the collapsing magnetic field of the welder choke each time you take the electrode off creates a momentary spike in voltage like the points on a petrol motor does on the coil for the spark plug
And being as a welder has a lot bigger choke (coil) than the coil on a petrol motor it is easy to see how this can damage the alternator rectifier if it is still connected
The reason you can damage it the rectifier is because even with key off the the rectifier is still connected unlike the rest of the vehicle
As a general rule the battery positive goes straight to the starter motor and then a large wire goes to the the back of the alternator and another large wire goes to the key switch
The large one to the alternator needs to be disconnected as thats were the circuit connection is if this alone was disconnected the wire would be live so battery is disconnected first on the grounded side then the positive side then the alternator other wise someone only has to bump that wire off the alternator and you have sparks

hope I havent bored you

Paul

As a uninteresting side note a older type vehicle with a generator you dont have to disconnect anything just hook in and weld no electronics all big simple plane wires nothing to go bang except the fuel tank LOL

Thanks for that explanation Paul. Always tell people to disconnect the battery but always had to blag the reason lol.. On another note, I've just replaced my old buzz box with a new inverter stick welder from weldequip. Well!!! what the f#uk is the wizardry behind this???? It weighs all of 2.5kg and comes with a shoulder strap?? min of 5amp for thin work but goes up to 180amp and takes 4mm rods... Theres no trying to get an arc, it just happens. The best way I can describe it is a mastic gun with liquid metal. I'm probably behind the times but if anyone is still using a buzz box, don't, get one of these. At £180ish it is worth every penny.

Deleted copy post...

Don't forget on anything with an ECM that disconnecting the battery protects the ECM. It's always good practise to keep the earth as close to where you're welding as possible, and not on the opposite side of alternators, ecm's etc. Applies for mig, tig, stick, AC or DC.

Thanks for the advice, disconnect is still the way to go!
My local supplier has tried to sell me an inverter on several occasions but I just don't do enough these days to warrant the cost. In fact It's probably been a year or more since I last welded anything. I learned using an oil cooled Oxford RT300 in prehistoric times, and have now inherited it, I love it but at probably close to 200kg it didn't come with a shoulder strap! As long as I don't have to move it...

I bought my first Inverter welder about 7 years ago "CIG WELD" what a piece of junk it worked well when it was working but nobody even fixes them not even CIG WELD so in the bin with it then I bought a Lincoln Inverter TIG welder well the difference is huge can weld all day never gets hot put it down 30 amps with a small rod and I can weld almost tin I reckon and they make parts and will fix them
I can weld hard face rods on farm equipment all day long on full power never gets hot

Paul

Lets dredge up an old thread...
At a huge investment of £65 I decided to upgrade and got a Rohr S-Mini. It comes in a case little bigger than a shoebox and still has room for the cables! Not got around to trying it yet but reading the manual (I know, I know...) it says you can get different results dependent on the polarity. New one on me. If I'd not read the book I would have put + to the rod and - to the earth and thought no more about it.
According to the book, rod negative is straight and gives a faster deposition rate, while rod positive is reversed and results it deeper work penetration.
Does this sound right or has it been lost in translation?

Theyre known generally known as DCEP (electrode positive) or DCEN (electrode negative).
DCEP is as per your book better for good penentration, but tends to blow away thinner materials, and DCEN the opposite.

Ive never experimented much with DCEN in practice because usually I use my mig or the tig on thinner stuff anyway.

Thanks, we'll have to wait and see if the machine is as good as the book.