OT. Sparks

On Sat, 31 Mar 2012 16:01:03 +0100, Jeff Layman
wrote:

The only explanation that tentatively comes to mind is if it's a DC
welder (as used for cast iron). I assume they have some kind of
rectification. If there were a capacitor across the DC output, then I
guess it could store a charge, although fifteen years is impressive.

Bill, we need you to take the case off and investigate. :-)

The best thing would be to poke the innards with a length of steel bar.

May offer a slight improvement on that? The best thing would be to get
someone else to poke the innards with a length of steel bar...

I hear there's a woman in York who might volunteer. I believe she's
temporarily (or perhaps permanently) indisposed though.

In message , Paul Ratcliffe
writes
On Sat, 31 Mar 2012 08:25:29 +0100, Ian Jackson
wrote:

So a coil has no capacitance whatsoever?

No, it has inductance.

The coil - like any coil - will have capacitance - 'self capacitance'.
However, self-capacitance cannot hold a charge as any charge is acquires
will be almost immediately shorted out by the DC connectivity of the
winding. In this situation, any reference to it is absolutely and
totally irrelevant.

So my statement was right and your additional comment was, by your own
words, totally irrelevant. So why bother mentioning it?

I was just pointing out that it's not strictly correct to say that a
coil has "no capacitance whatsoever" - or to agree with such a
statement. It has some (self) capacitance - but that doesn't come into
it at all when we are discussing storing charge long-term.
--
Ian

Jim Lesurf wrote:

My first comment was that I know nothing about the innards of an 'arc
welder'. So you or someone else would have to look inside it and tell us
what components, connected in what arrangement, it may have.

Well, I know all about the innards of my arc welder, because I've had
it in bits more than once.

Mine was a SIP 140 - popular 25 years ago, and cheap - and it really is
just a transformer with an adjustable tap on the secondary and
aluminium windings (yes, really - not copper).

It was so utterly useless as a welder that I fitted a high-current
bridge rectifier (with cooling fan) and used it to fast-charge my boat
batteries. By God, it could cook those batteries, and they were
seriously big.

--
SteveT

Sorry to have been so slow uploading these photo's

http://dl.dropbox.com/u/70318740/P1010056.JPG

http://dl.dropbox.com/u/70318740/P1010057.JPG

http://dl.dropbox.com/u/70318740/P1010058.JPG

http://dl.dropbox.com/u/70318740/P1010059.JPG

http://dl.dropbox.com/u/70318740/P1010060.JPG

Bill


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