Convert AC oil cooled to DC source.

[bigegg]

I'm thinking of getting a cheap Tig welder and someone has suggested a viper HF unit powred by a DC stick welder.

I only have an AC welder.

But...
I notice there are some 1600v 200a bridge rectifiers on the bay for about £15 - from china.

https://m.ebay.co.uk/itm/MDQ-200A-2...983270?hash=item3d500c38a6:g:NCMAAOSw9hdaE8on

For example...

Would this work on an oil cooled Oxford - 100a 50v ocv (75a 80v)

I only want to Tig up to 3mm mild steel.

 

[Hood]

Not and electrical or electronics expert but I think you would also need some big capacitors to smooth things out.
I was once going to use an oil cooled for a DC power supply, fitted rectifier and a big bank of caps and it scoped OK but in the end I went with AC servo drives which took mains input.

 

[Hood]

Found some pics of the setup and the scoped output I was getting.

 

[dannyp]

it'll sort of work badly and function as a tig even worse

 

[MattF]

it'll sort of work badly and function as a tig even worse

Why?

 

[merryman]

Sorry to hijack the thread, but my Clarke 100E MIG has blown it's rectifier, could the eBay ones be used as a replacement?

 

[Bladevane]

I can't help thinking that if Oxford designed a rectifier to look like this

then a £15 pocket sized unit might not cut the mustard. Just saying.

 

[dannyp]

Why?

tryed it before, worked ok as a DC stick welder but seemed a to want to run flat out regardless of setting, for tig way more volts than needed, for 3mm its just going to burn up tunstens and melt holes

 

[Bladevane]

The voltage creates the arc. It's the current that blows holes. MMA and TIG are both constant current processes which is why many DC welding machines can be converted to scratch TIG use. I would have thought even a basic buzzbox, run through a decent bridge rectifier and heat sink with smoothing capacitors, could be used as a TIG source. Happy to be told otherwise by a proper sparky though.

 

[dannyp]

every transformer DC machene ive had apart has had a choke in it

 

[Seadog]

Capacitors will not provide a steady current. You need a choke.

 

[dannyp]

The TIG add on boxes that you stick on old oil cooleds have quite a bit in them they arn't just a near empty box with a set of dioeds and caps in there.

big issue with useing an oil cooled is the current selection, they generaly have a movable link so you have to choose between. not much, some, some more, all of it.
thats not really compatable with tig and most people

 

[bigegg]

How much of the conversion work will be done by the viper HF unit ?
Does it *need* to have a perfect DC input or will it do it's own cleaning of the input?

If the oil cooled is no good, I also have a 180a clarke buzzbox that I could use.

 

[Turbo]

Why are you going to the bother when you can buy a half decent dc inverter at reasonable money? There was a decent one just sold in the for sale section for £75 and the parkside units pop up regularly in Lidl.

 

[Morris]

My first tig welder was done like this. I used a BOC transformer, some massive 150A diodes (I still have them) and a choke out of a wrecked migatronic set. Worked a treat. Looked crap.