"whit3rd" wrote in message
...
On Tuesday, March 24, 2020 at 5:10:19 AM UTC-7, Jim Wilkins wrote:
"whit3rd" wrote in message
...
On Tuesday, March 17, 2020 at 11:06:10 AM UTC-7,
wrote:
On Sat, 14 Mar 2020 21:25:20 +0000 (UTC), Cydrome Leader
The alnico
magnets in old and/or inexpensive mag bases were/are magnetized
after
assembly.
Usually, metalworkers have access to high DC current sources from
Lincoln, Miller,
Hobart, etc. and that's what it'll take.
Arc welders inherently limit short circuit current by designed-in
self
inductance, core saturation, etc and can't easily be tweaked to
deliver higher current in a short pulse.
The current ought NOT to be delivered in a short pulse (it has to
penetrate the metal pole pieces as well as the magnet, which takes
some time)
which is why it has to be a DC welder. The induction is not just
'amps',
but is 'amp-turns', so a few turns of wire will multiply the effect
of the
welder current accordingly.
Also their rated current is
at 20-25V which doesn't allow for much wire resistance. At 20V the
0.1
Ohm resistance of a coil wound with 100' of 10AWG copper wire...
I'm thinking it's more on the order of five feet of wire, maybe 5 or
10 or so turns
around a circa 1.5" bar (it just has to be as thick as the pole
pieces it's being held
against). I'd consider using one of my auto jumper cables instead
of ten-gage.
You can obtain the maximum Amp-turns if the coil resistance is close
to the welder's output impedance. A short, thick jumper cable won't
allow as many turns and will still be limited to the welder's short
circuit (stuck electrode) current.
Then you have to figure or measure the temperature rise vs pulse
duration to avoid damaging the insulation of the expensive copper
wire.
The Overload Capacity chart, Figure A on page 4, gives an idea of time
vs current though it considers both wire and contact brush heating.
http://www.instrumentsgroup.co.za/in...stat_specs.pdf
It suggests that 10AWG wire could safely handle 200A for about 2.5
seconds, if it had their Powerkote insulation. Figure C shows 90C as
the temperature limit.
I picked 10AWG as the largest size that's useful elsewhere later, such
as in a solar system. I have up to 4 AWG in my system, connecting the
batteries, but it's short and I can't justify buying a lot more of it
for a one-time project. Perhaps the cheaper CCA (copper-clad aluminum)
that isn't legal for building wiring could be used and then resold to
car stereo installers. Pure copper wire is OFC, oxygen-free copper.
https://www.amazon.com/InstallGear-G.../dp/B01MXRVIPD