From: mike brown <mike@n5qmg.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 19 Jan 2020 15:24:14 -0800
Subject: Re: [EE] Magnetic lock
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Mine were DC as well.  No idea why they'd generate more heat unattached,
unless the strike plate was acting as a heatsink and thermal radiator.

On Sun, Jan 19, 2020, 15:07 Sean Breheny <shb7@cornell.edu> wrote:

> I definitely have seen some that are AC (they have an audible 120Hz buzz =
-
> 120Hz because they attract more strongly on both positive and negative
> peaks)
>
> On Sun, Jan 19, 2020 at 12:36 PM David C Brown <dcb.home@gmail.com> wrote=
:
>
> > They are DC
> > __________________________________________
> > David C Brown
> > 43 Bings Road
> > Whaley Bridge
> > High Peak                           Phone: 01663 733236
> > Derbyshire                eMail: dcb.home@gmail.com
> > SK23 7ND          web: www.bings-knowle.co.uk/dcb
> > <http://www.jb.man.ac.uk/~dcb>
> >
> >
> >
> > *Sent from my etch-a-sketch*
> >
> >
> > On Sun, 19 Jan 2020 at 16:25, Sean Breheny <shb7@cornell.edu> wrote:
> >
> > > If the electromagnet uses AC then it will indeed draw less current wh=
en
> > it
> > > is closed against the piece of metal it attracts. This is because the=
re
> > is
> > > no longer an air gap in the magnetic circuit so the inductance is
> higher.
> > >
> > > On Sat, Jan 18, 2020, 8:43 PM mike brown <mike@n5qmg.com wrote:
> > >
> > > > In my experience, the electromagnet appears to draw less current wh=
en
> > > > latched to the metal plate.  This is an unscientific observation
> based
> > > upon
> > > > the temperature of the magnet increasing when not latched to the
> steel
> > > > plate.  Amazing that they can generate such a strong holding force
> > using
> > > > three watts of power as long as the two parts perfectly mate to eac=
h
> > > other.
> > > >
> > > > On Sat, Jan 18, 2020, 19:07 Bob Blick <bobblick@outlook.com> wrote:
> > > >
> > > > > Admin message to Allen, since his email address seems to reject
> > direct
> > > > > email.
> > > > >
> > > > > Hi Allen,
> > > > > Please, when you reply to a piclist post, insure that the subject
> > line
> > > > > topic tag is not preceded by your own email system's bracketing
> > system,
> > > > > because it does not conform to the piclist topic tag definitions
> and
> > > > > interferes with our archiving system, and also with users that re=
ly
> > on
> > > > the
> > > > > topic tag to sort their piclist emails.
> > > > > Thanks.
> > > > > Bob
> > > > >
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