On Sep 29, 5:26*pm, Lew Hartswick wrote:
Spehro Pefhany wrote:
On Mon, 29 Sep 2008 13:42:11 -0700 (PDT), the renowned
wrote:

I have an old fleamarket growler for checking electric motor
armatures. *It warns not to be turned on without armature in V. *My
physics has faded over the years, what will happen with an incomplete
magnetic circuit? *Can this be modified to use as a de-magnetiser or
is it a piece of junk just worth the copper?

Thanks, John.

If the armature is not there then the inductance will be very low, and
thus the current will be very high, so the coil will likely burn out
unless it has been designed to handle the power dissipation.

I think you could limit the current through the coil (for example,
with a series electric heater element) and use it as a demagnetizer
(but it might not create a strong enough magnetic field to demagnetize
a strongly magnetized object). You could also try a series degaussing
PTC thermistor out of a CRT monitor or TV.

Best regards,
Spehro Pefhany

Or operate it from a "Variac" (reg TM). Lots of generic versions. :-)
* * ...lew...- Hide quoted text -

- Show quoted text -

What if I try increasing the inductance by placing something of
suitable size in the V, could there be sufficient field in the air to
be useful?

John.