On Thu, 20 Jan 2005 17:29:04 -0600, "Tim Williams"
wrote:

For the welder rectifier I'm assembling, I need some filtering (so I hear).
Since I have some #0 AWG aluminum wire on hand I'm going to wind it around
some MOT cores. I already made one (barely managing to squeeze ten turns on
it, there's space for two more but the wire is too tough!), with about 1/16"
cardboard shim and welding the core back together (MOTs are normally welded,
I don't see anything wrong here).

My question is, what's the best way to hook up the wire to the rest of the
system? The welder's power transformer is wound with aluminum wire and just
clamped on the output terminals, so I'm guessing a washer and bolt will do.
But this is 7 strand, not solid... I might be able to do it, or it might
squish apart. I suppose I could drill a hole in a block and use a clamp
screw to hold it in place.

Tim

Not too sure what sort of welder you're building. If it's for
MIG welding you need a near constant voltage source with a filter
inductance after the rectifier. This needs a large airgap to prevent
saturation by the DC component of the welding current. Commercial
inductors are multi layer wound on a long rectangular stack of
laminations with no attempt at a closed iron circuit - typical
inductance is 300 uH - about 40T If you're using a uwave oven
transformer core 1/16 gap is not enough. Just discard one limb and
wind on the remaining "E" stack - this shape should be fairly close to
optimum.

If it's an add-on rectifier to a stick welding transformer,
the same design is OK but it's much less critical as it only makes a
small improvement in the striking and smooth running of the arc.

I just use bolt and washer termination for aluminium wire but
always include a beefy spring washer (a belville washer would be even
better) to look after the differential expansion.

Jim