OT. Sparks

Ian Jackson wrote:
In message , Paul Ratcliffe
writes
On Sat, 31 Mar 2012 00:14:24 +0100,
wrote:

Afraid I don't know anything about arc welders. But a 'coil' doesn't
hold a
'charge'.

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.
Although presumably if the coil was part of a resonant circuit its
capacitance would have to be allowed for?

Bill

Steve Thackery wrote:
Frankly this is a massive mystery. An arc welder is just a transformer
- there is nothing that can store a charge. The probe and the earth
clamp are connected together internally by the coil secondary.

To get a flash from the electrodes implies it must have been plugged
in. are you *sure* it wasn't?

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.

Bill

On Sat, 31 Mar 2012 09:30:41 +0100, Jim Lesurf
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.

Yes.

There may also be some inter-winding capacitance between primary and
secondary. But again, that would be tiny, and it seems pretty unlikely to
be a way to store a high charge for any length of time. Particularly as it
would raise the question of how the charge got there in the first place.

OK, so what if there's a secondary component in there?
My point really was, whatever is holding the charge seemed to be doing
a good job of it, and for it not to have leaked away through the coils
and insulation speaks well of the condition of them.

Fwiw, I've come across this condition where a discharge happened where
one shouldn't exist - and I don't mean a girl on my knee.

In article ,
wrote:
There may also be some inter-winding capacitance between primary and
secondary. But again, that would be tiny, and it seems pretty unlikely
to be a way to store a high charge for any length of time. Particularly
as it would raise the question of how the charge got there in the first
place.

OK, so what if there's a secondary component in there?
My point really was, whatever is holding the charge seemed to be doing
a good job of it, and for it not to have leaked away through the coils
and insulation speaks well of the condition of them.

No capacitors in any arc welder I've ever seen - apart from in the timer
etc electronics of sophisticated ones.

Nor have I ever heard of a transformer storing energy.

--
*A fine is a tax for doing wrong. A tax is a fine for doing well*

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 31 Mar 2012 14:55:51 +0100, "Dave Plowman (News)"
wrote:

No capacitors in any arc welder I've ever seen - apart from in the timer
etc electronics of sophisticated ones.

Nor have I ever heard of a transformer storing energy.

Look, it's some redneck found what he thinks is an old arc welder in a
barn - who's to say what it is until he furnishes a photograph, signed
by two Justices of the Peace and a Federal Marshall.
Even then, I'd be leary - it could be snuck out the back gate of Area
51.

On 31/03/2012 11:50, Bill Wright wrote:
Steve Thackery wrote:
Frankly this is a massive mystery. An arc welder is just a transformer
- there is nothing that can store a charge. The probe and the earth
clamp are connected together internally by the coil secondary.

To get a flash from the electrodes implies it must have been plugged
in. are you *sure* it wasn't?

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...

--

Jeff

In article ,
wrote:
On Sat, 31 Mar 2012 09:30:41 +0100, Jim Lesurf
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.

Yes.

There may also be some inter-winding capacitance between primary and
secondary. But again, that would be tiny, and it seems pretty unlikely
to be a way to store a high charge for any length of time. Particularly
as it would raise the question of how the charge got there in the first
place.

OK, so what if there's a secondary component in there?

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. Otherwise we
could all dream up fantasy "so what if" ideas that may have zero to do with
what happened, amd tell us zip. Maybe its an interrositer in disguise...

For all I know the transformer was sitting where it was bathed in an
external a.c. H-field that induced the current. No idea. But given such
theoretical possibilities the thing would not have had to store any energy
for amazingly long times.

My point really was, whatever is holding the charge seemed to be doing a
good job of it, and for it not to have leaked away through the coils and
insulation speaks well of the condition of them.

For 15 years, not so much a "good job" as a truly amazing one. But all I
know about it is what has been claimed/described here. And that a 'coil'
doesn't hold any 'charge'. Hence my initial point.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Dave Plowman (News)
wrote:
In article ,
wrote:
There may also be some inter-winding capacitance between primary and
secondary. But again, that would be tiny, and it seems pretty
unlikely to be a way to store a high charge for any length of time.
Particularly as it would raise the question of how the charge got
there in the first place.

OK, so what if there's a secondary component in there? My point really
was, whatever is holding the charge seemed to be doing a good job of
it, and for it not to have leaked away through the coils and
insulation speaks well of the condition of them.

No capacitors in any arc welder I've ever seen - apart from in the timer
etc electronics of sophisticated ones.

Nor have I ever heard of a transformer storing energy.

Well, inductances do store energy. But due to having a non-zero current
though the inductance. Seems unlikely here if it has been open-circuit for
over a decade. :-)

You can, of course, get a spark from an inductive pick-up which is in a
suitable a.c. H-field. That is how Hertz and others did a lot of their
early experiments on what we know think of as radio waves. But that is
energy being picked up, not stored for many years.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

No the welder was not plugged in, It had got 15 amp round plug on it. My son
has now replaced it with a 13 amp plug ( first fuse blew )and since lowered
the voltage to weld a cast iron part of a pump successfully.
I have taken the top off it to take some photo's of it, but I have not yet
managed to up load them yet. I will send the URL when I have.
Thanks to you all for your comments and quips.
Keep smiling,

Bill


"Steve Thackery" wrote in message
...
Frankly this is a massive mystery. An arc welder is just a transformer -
there is nothing that can store a charge. The probe and the earth clamp
are connected together internally by the coil secondary.

To get a flash from the electrodes implies it must have been plugged in.
are you *sure* it wasn't?

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. :-)

--
SteveT



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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?