mag base remagnetizing

On Tuesday, March 17, 2020 at 11:06:10 AM UTC-7, snipped-for-privacy@whidbey.com wrote:


There's a two-part magnetization process for alnico, you have to observe the built-in (at ceramic-firing time) polarity when you apply current. It WILL magnetize one direction, not the other.
Usually, metalworkers have access to high DC current sources from Lincoln, Miller, Hobart, etc. and that's what it'll take.
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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. 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 would limit the current to around 200A. Unless you can reuse the wire in a solar system it's cheaper to replace the magnetic base.
Perhaps a motor shop can repolarize it.
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On 24/3/20 11:10 pm, Jim Wilkins wrote:

What about a spot welder, hooked up to a fat coil of copper tube on a magnetic core?
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I've used a pedestal spot welder on sheet steel and don't remember the metal being pulled into the current loop or otherwise disturbed when I stepped on the pedal.
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On 24/03/2020 23:31, Jim Wilkins wrote:

I thought about a spot welder as mine is about 6000A hand held unit but it's AC so wouldn't be any good. Mine does exhibit a bit of buzz and can cause near items to buzz a bit but the magnetic field definitely upset my Swatch watch, not permanently but I had to read the instructions to reset the time, I took it off after doing that a few times.
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On 25/3/20 11:19 am, David Billington wrote:



I have a small spot welder for welding s/s dental wires and it uses a contacter to dump a capacitor into a chonky transformer - so it's mostly a big DC current pulse. If that was fed through a suitable winding it would work, to some extent.
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On 25/03/2020 00:41, Clifford Heath wrote:



OK a different sort to mine which is basically a heavy high current output mains transformer intended for welding sheet metal upto 2mm + 2mm with about a 5 - 6mm spot.
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On Tuesday, March 24, 2020 at 3:58:09 PM UTC-7, Clifford Heath wrote:

The spot welders I'm familiar with are all AC, so they'll only magnetize as deeply as the field-penetration-distance after one half cycle (if you can time it so a full half-cycle is the end of the conduction). That won't usually be enough for magnetization of a sizeable lump.
If you could spin the lump, so that the lump turns 180 degrees WITH the AC reversal, it'd be a possibility.
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On Tuesday, March 24, 2020 at 5:10:19 AM UTC-7, Jim Wilkins wrote:

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.

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.
Other than using the magnet holder completely assembled, it'd be a nuisance to orient the magnetic field appropriately. Thinking about it, some of my bench vises are just about the right shape to take windings and hold against the mag base for this task.
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On 25/3/20 12:12 pm, whit3rd wrote:

Flattened copper water pipe is better. Tightly packed square section is better still (approximately square winding cross-section, too).
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wrote:

For the price of a harbor fright mag base you really can't affoed to re-magnetize one - I know , it HURTS to throw something away that you might be able to repair, but even I have been known to "cut my losses" on occaision.
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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/index_files/Superior/powerstat/powerstat_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. (Amazon.com product link shortened)
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wrote:

My 300 amp Miller would not provide enough current for decent magnetization. Not even close. Eric
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On Tue, 24 Mar 2020 09:14:40 -0700, snipped-for-privacy@whidbey.com wrote:

Might work to charge the capacitor bank, but definitely won't do the magnetizing unless you have a lot of turns - it's ampere turns that make the feild strength - and too many turns increase the inductance/reluctance and slow down both the build-up and collapse of the feild.
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On 3/24/20 3:10 PM, Clare Snyder wrote:

The setups from some of the experimenters that use high-current pulses to shrink coins might be a good place to start.
<https://www.google.com/search?as_q=shrink+coin
Delivering 100,000 Amperes from capacitors charged to 12,000 Volts is a bit of a challenge, though.
--
Bob Nichols AT comcast.net I am "RNichols42"

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in message wrote:

12KV arcing across contacts is enough to generate X-rays.
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Not really. I've successfully done coin crushing and the setup doesn't need to be overly complex like all the junk on google. The hype about specially crafted parts, bullet proof chambers etc. is pure puffery and marketing bullshit.
There probably isn't a need for a one-use solenoid for remagnetizing a mag base though, or the energy levels needed to crush a coin.
I sold my can crushing capacitor bank, but have some other large can electrolytics. They're not really special low ESR versions but might be coaxed into limited pulse use. The required amp-turns remains a mystery though.
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On 15/3/20 8:25 am, Cydrome Leader wrote:

Is this a mag base to mount an antenna on a car roof?
Why not get a bunch of old hard drive (rare earth) magnets, and just epoxy them onto the bottom of the existing mag base, and cover with some thin felt for protection?
Clifford Heath
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On Wed, 25 Mar 2020 17:47:35 +1100, Clifford Heath

I was thinking he was talking about a mag base for a dial indicator.
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wrote:

(Amazon.com product link shortened)
The rotary switch that turns the magnetic pull on or off is essential for many machinist uses.
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