Clare Snyder wrote:
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.

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.