Howdy Roughbert,

It would be a pity to throw it away. Indeed, it would be a crime
against the great 'Gods of Weldness'.

Ok, I have to admit to a good degree of ignorance on mains powered
welders, as I don't have mains power here, or a mains welder.

Could I safely assume that your welder is little more than a heavy
transformer in an oil filled container?

If so, perhaps you may try these tests:

Measure the resistance of the output windings.
This will be very low, so low that it will appear as zero ohms.

Measure the resistance of the mains input windings.
This will be higher, but still quite low.

Heat the old girl up, until she goes lame.

Repeat the ohmic measurements.

This ought to tell us a lot more about the fault.


Another test, if the ohmic tests on the secondary side are impossibly
low:

Unplug the welder from the mains,

Connect a 12V, 50W headlamp in series with a 12V battery to the
welder's secondary side,
The lamp should slowly light up.

Keep a mental image of its final brightness.

Disconnect the lamp and battery circuit.

Heat the old girl up until she starts limping again,

Repeat the lamp and battery test,

Is the lamp's brilliance level the same?

If so, this suggest a possible problem with a part called the 'sliding
choke'.
This part is used in some welders as a current controller.
Perhaps this part moves in response to temperature?

I honestly don't know just how these are used, but they certainly can
cause the problem you are seeing.


Do you have any pics of the welder?
Can it be taken apart?


In the meantime, perhaps you could use it to build an AmpTramp :) .

Now there's a good project for the old girl ;) .



Best wishes,

Steve.





--- In Amptramp@yahoogroups.com, "roughbert" <roughbert@y...> wrote:
> Hello Group.
> My recently-acquired but ancient oil-filled BOC welder works a treat
> when cold, but after a couple of hours work it becomes dreadfully
> feeble (now what does that remind me of?). I assumed that somewhere
> some resistance is creeping in - or out. Is there anything practical
> which one can do about this, or should it be consigned to the heavy
> scrap pile?
> R