Can you get the magnet out of the base?
If so, find a really powerful magnet and let it clamp to the base
magnet. Then lightly tap the base magnet with a hammer. May need to tap
several times. Must be very old mag base or very cheap magnet.
On Sat, 14 Mar 2020 21:25:20 +0000 (UTC), Cydrome Leader
Probably your best bet is to replace the old alnico magnet with a new
rare earth magnet. This is because if the alnico magnet is removed
from the magnetic circuit it loses a lot of its magnetism. The alnico
magnets in old and/or inexpensive mag bases were/are magnetized after
assembly. This takes a LOT of current. I have seen the setups for
doing this and they are not trivial.
On 17/03/2020 18:06, firstname.lastname@example.org wrote:
The magnets in my cheap magnetic bases are black ceramic magnets. I did
once re-magnetise a screwdriver by putting it into a coil of wire and
connecting it a DC power supply as I didn't have any permanent magnets
I save the magnetising assembly at a magnet factory in Sheffield, UK,
a long time ago.
Which leads me to voice agreement with Eric.
It fitted on top of a pallet, took some huge current, dust was
flying and their were major creaking sounds as enormous forces
I've built 1000A test stations for devices such as electric locomotive
controllers. The construction is considerably different from normal
electronics, requiring copper buss bars, crimpers for 4/0 welding
cable lugs, mechanically strong and heat resistant insulators etc. All
conductors must be well supported to resist the magnetic attraction
between them and to the steel chassis. Common test equipment won't
measure the high currents or microOhm resistances involved.
My personal test gear collection includes second-hand lab grade and
new import hobby grade shunts like this
(Amazon.com product link shortened)
to measure AC and DC current and a 1000V hipot tester to find
accidental shorts or leakage, mainly keep shocks or exploding wires
fom putting me in the hospital.
Reminds me of the old mag cells. A building was a row of pots up one
side and down the other electrically in series, running at about
30,000 amps. The workers commonly stored their tools by just slapping
them on a buss bar above a cell. There was a massive tool drop every
time they took a cell building down.
On Wed, 18 Mar 2020 10:43:08 -0400, Bob Engelhardt
Electolytic production of magnesium metal from magnesium chloride,
which was extracted from seawater. There were about 30 pots in one
building. Each pot was a heavy steel pot, refractory lined, with
about 10 10" diameter graphite anodes descending through the insulated
lid into the bath within an inch or so of conical steel cathodes.
Voltage drop was a couple volts, liquid magnesium metal and chlorine
gas were produced.
It took a special breed to work in the cell buildings, but they did
get a lot of breaks to avoid heat exhaustion. My cousins that grew up
like I did in the rice fields worked there during a strike, said it
wasn't much hotter than shoveling levees in a rice field, and a lot
I have some axial field servo motors. They have a magnetizing loop
(#14 wire)-that they sharge with a capacitoe to top up the feild after
they are assembled because without the small gap the magnets cannot
hold a full field (apparently they quite quickly drop to about half
strength if you dissassemble the motor) They hit that coil with close
to 1000 amps for a millisecond or so to do the deed.
How do they keep the LC circuit from oscillating? If it's a clamp
diode I'm curious which one they chose to handle 1000A. The energy it
converts to heat is 0.5CV^2.
Some components such as diodes and breakers have a one-time surge
rating tht's far above their normal operating current but AFAIK they
aren't normlly tested for it in production, as it may degrade the
Do you know what sort of magnets these motors had? From what I've seen,
Alnico magnets are the ones that lose their fields the easiest. This is
why even the decent ones ships with keeper plates.
I suspect it's usually Alnico in these mag bases, had to send one back to
Mitutoyo once, it just lost it's field and wasn't stored in the on
position. They just swapped it for a new one.
There's little chance I'll locate the same sized rare earth to retrofit
into the base itself. I don't want to mangle the faceplate to tear into
this one either. I have a supply of large electrolytic caps and some mega
SCRs. Don't mind trying something out if the magnetizing currents and
times aren't something too insane.
On 3/23/2020 12:47 AM, Cydrome Leader wrote:
... I have a supply of large electrolytic caps and some mega
I once tried to re-magnetize an indicator base & don't remember any
details, just that it involved really large current and didn't work very
I do remember what I thought was a neat trick for switching. The switch
was 2 copper leafs, separated by an air gap. To turn it on you hit it
with a hammer! Very fast and very low resistance as the oxide is
displaced and you have a large area bare copper-copper contact.
An SCR switch blocks the LC oscillation that would immediately
demagnetize the magnet. You still need a flyback diode to suppress the
reverse voltage spike.
"As a side note, please be advised that proper (mechanical) 'clamping'
is essential to device operation and integrity and not merely for
heat-sink efficiency! It seems the construction 'expects' a precise
compressive force (should be found in the Specs) --- Indeed many such
units will test (electrically) open while 'uncompressed'..."
The actual SCR is a thin silicon wafer slice between the anode and
cathode contact disks. The specified clamping pressure ensures that
enough of the area of the wafer disk will be in electrical contact to
distribute the current and the heat it produces across the wafer
rather than allowing it to concentrate in a few spots and burn out the
SCR. Driving the gate harder than the minimum helps rapidly spread the
initial area(s) of conduction and even out the instantaneous heating.
The clamps GE sent us for our test stations consisted of two U
channels connected by bolts. The dimples accept alignment pins that
center the anode and cathode contact disks while you are assembling
the awkward sandwich of SCR, contacts, insulation and clamps. We used
a simple sheetmetal gauge that aligned two points when the channels
had bent far enough to produce the specified clamping pressure.
We didn't need heatsinks to test the SCRs with one or a few
full-current pulses. The heat generation can be estimated as 1 Watt
per Amp continuously, or 1 Joule per Coulomb for a capacitive
I had some blade magnets made for a guitar pickup, cut with a diamond
from neutral (but permanent) ferrite into slabs 120x22x4mm and
magnetised across the 22mm dimension in one of these machines.
It was a small machine, about 1.6m long, 1.2m high, with a C-shaped
armature (gap upwards) about 40cm broad with a massive winding like a
small oil drum across the bottom. The ferrites were spaced up with soft
magnetic spacer blocks and clamped in to remove most of the air gaps.
The operator hit the switch and the lights dimmed, the concrete slab
floor noticably thrummed, for about 30-40 seconds, and the magnets were
cooked. I believe it was being fed from a rectified three-phase feed,
which is 50Hz here.
Does that give you some idea?
Only vaguely. I get that there are giant magnetizers, but in the grand
scheme of things, there isnt that much iron in the circuit of a mag base
and it will saturate at field strengths that don't require a 50 ton
machine warehouse and three phase power.
Anybody got some dead-ish bases for sale for the price of shipping and a
On Sunday, March 22, 2020 at 6:02:38 PM UTC-4, Cydrome Leader wrote:
I knew an old man (25+ years ago) in Mt. Dora Florida who restored 'Huff
and Puff' engines. His prize possessions were a photo of him selling an en
gine to 'Grandpaw Jones' (and an uncashed check) who was part of the Grand
He also rebuild Magnetos and sold magnet rechargers that he built in a 10'
x 20' rental warehouse. He used a large electric hacksaw to cut a large bun
dle of soft iron rods into the cores, and wound the coils on his lathe. The
re are businesses that recharge magnetos that may be able to do what the OP
On Sun, 22 Mar 2020 22:02:36 +0000 (UTC), Cydrome Leader
See below from the link above.
5. Pulse Analysis
All of the capacit
discharge magnetizer circuits shown may be modeled as a series
combination of a capacitor, a resistor, and an inductance. The
electrical resistance must include the
resistance of the source as well as that of the fixture (especially
including the ESR,
resistance, of the capacitors), and also includes components from
current conduction in surrounding
conductors, etc. In addition, the resistance may
increase during the
period of the pulse (by perhaps 30%) due to heating in the fixture
(the resistance of
copper and most other metals increases with temperature). The
inductance of a fixture containing steel
pole material is dramatically affected by whether the fixture is
below or above magnetic saturation (the
inductance dropping greatly at currents above saturation). Other
effects may be of importance too, such as
the retention of energy by the electrolyte of the capacitors, the
absorption of energy by the magnet, and
other nonlinearities. Nonetheless, in many cases the overall system
behavior of the magnetizer and fixture
is modeled to sufficient accuracy by assuming constant values for the
resistance, inductance, and
capacitance. Even where the assumption of const
ant values of these parameters is not justified for final
design, the linear analysis may provide a good first approximation and
a check on the calculations. Where
the linear approach using fixed values is not accurate enough,
however, a computer simulat
ion including all
nonlinear effects may be used. The method is described in detail in
the bound notes (reference 7).
6. Design of Fixtures
There are five types of conditions which must be met in the
design of a magn
(1) The fixture, in combination with the magnetizer,
must provide a magnetic field of sufficient
strength and in the proper direction to saturate the magnet. The
directional requirement is usually not much
of a problem in m
agnetizing anisotropic materials, which can only be magnetized along a
directional line (although with either sense, i. e. from right to
left, or from left to right, along that line).
This is because the field component in the required directio
n varies as the cosine of the angle between the
two, which does not change much for angles up to ten degrees of arc or
so. If the material is isotropic,
however, meaning that it can be magnetized in any direction, the
direction of field may be of much gre
The magnet domains themselves align in a very short time (on the
order of 10
field may have to be maintained for a significantly longer time,
however, in order to overcome electrical
eddy currents, which may oc
cur in the fixture, the magnet itself, or in associated structure.
(2) The part must be held in the fixture in the proper
orientation, accurately but without imposing
stresses on the part during magnetizing (and possible thermal cycling
ll) without breaking it. The part
must also not be damaged, chipped, or broken as it is being removed
from the fixture, or as it is loaded.
(3) The windings must be strong enough, or must be
reinforced to be strong enough, to withstand
echanical forces on them during the magnetizing pulse, either to fail
due to ultimate stress limits or, at
a much lower level, in fatigue (after a number of cycles). Fields
high enough to magnetize high
magnets often cause forces which could pull
apart copper conductors in a single pulse, if they are not
strengthened by other means. These forces are also more than strong
enough to bend, crush, or extrude out
epoxy potting plastics.
(4) The thermal requirements must be met. the near
nstantaneous temperature rise in the windings
during the pulse occurs too quickly for much of the heat to escape
across even a single thin layer of
electrical insulation. If this rise is too great, the insulation will
fail, on a single pulse. A thermal t
constant exists for this effect, and a thermal mass, which is often
significantly different from that of the
fixture as a whole (that is, the time constant is shorter than that of
the fixture, and the mass is less). Both
must be taken into account. A
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