From: Sean Breheny <shb7@cornell.edu>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 19 Jan 2020 12:58:00 -0800
Subject: Re: [EE] Magnetic lock
Thread-Topic: [EE] Magnetic lock
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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 when
> it
> > is closed against the piece of metal it attracts. This is because there
> is
> > no longer an air gap in the magnetic circuit so the inductance is highe=
r.
> >
> > On Sat, Jan 18, 2020, 8:43 PM mike brown <mike@n5qmg.com wrote:
> >
> > > In my experience, the electromagnet appears to draw less current when
> > > latched to the metal plate.  This is an unscientific observation base=
d
> > upon
> > > the temperature of the magnet increasing when not latched to the stee=
l
> > > 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 each
> > 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,
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