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Old March 17th 20, 06:06 PM posted to rec.crafts.metalworking
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Default mag base remagnetizing

On Sat, 14 Mar 2020 21:25:20 +0000 (UTC), Cydrome Leader
wrote:

Has anybody remagnetized a rotary on-off mag base before? I was thinking
about a large capacitor and some turns of wire on EI transformer core
with the Is removed and the indicator base across the center and one side
leg.

How are these magnetized at the factory?

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.
Eric

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Old March 18th 20, 11:31 AM posted to rec.crafts.metalworking
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Default mag base remagnetizing

"Richard Smith" wrote in message
...
writes:

On Sat, 14 Mar 2020 21:25:20 +0000 (UTC), Cydrome Leader
wrote:

Has anybody remagnetized a rotary on-off mag base before? I was
thinking
about a large capacitor and some turns of wire on EI transformer
core
with the Is removed and the indicator base across the center and
one side
leg.

How are these magnetized at the factory?

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.
Eric


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
resulted.
Rich S


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
https://www.amazon.com/AMMETER-SHUNT.../dp/B005BHPG6K
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.


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Old March 18th 20, 12:07 PM posted to rec.crafts.metalworking
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Default mag base remagnetizing

On Wed, 18 Mar 2020 07:31:34 -0400, "Jim Wilkins"
wrote:

"Richard Smith" wrote in message
...
writes:

On Sat, 14 Mar 2020 21:25:20 +0000 (UTC), Cydrome Leader
wrote:

Has anybody remagnetized a rotary on-off mag base before? I was
thinking
about a large capacitor and some turns of wire on EI transformer
core
with the Is removed and the indicator base across the center and
one side
leg.

How are these magnetized at the factory?
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.
Eric


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
resulted.
Rich S


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
https://www.amazon.com/AMMETER-SHUNT.../dp/B005BHPG6K
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.


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Old March 18th 20, 02:43 PM posted to rec.crafts.metalworking
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Default mag base remagnetizing

On 3/18/2020 8:07 AM, Pete Keillor wrote:
Reminds me of the old mag cells. A building was a row of pots up one
side and down the other ...


What's a mag cell/building?
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Old March 19th 20, 01:50 AM posted to rec.crafts.metalworking
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Default mag base remagnetizing

On Wed, 18 Mar 2020 09:11:53 +0000, Richard Smith
wrote:

writes:

On Sat, 14 Mar 2020 21:25:20 +0000 (UTC), Cydrome Leader
wrote:

Has anybody remagnetized a rotary on-off mag base before? I was thinking
about a large capacitor and some turns of wire on EI transformer core
with the Is removed and the indicator base across the center and one side
leg.

How are these magnetized at the factory?

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.
Eric


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
resulted.
Rich S

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.
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Old March 19th 20, 11:32 AM posted to rec.crafts.metalworking
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Posts: 5,571
Default mag base remagnetizing

"Clare Snyder" wrote in message
...
...
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
part.

http://www.cooperindustries.com/cont...ing_Rating.pdf


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Old March 19th 20, 11:42 AM posted to rec.crafts.metalworking
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Default mag base remagnetizing

On Wed, 18 Mar 2020 10:43:08 -0400, Bob Engelhardt
wrote:

On 3/18/2020 8:07 AM, Pete Keillor wrote:
Reminds me of the old mag cells. A building was a row of pots up one
side and down the other ...


What's a mag cell/building?


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
easier.

Pete Keillor
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