Mine was all backed by UPS. In this case, to ensure the safety for that 30s
even if building power goes out, I'd just do the same thing - separate power
supply for the maglock, backed by UPS, and then just use an ELK-960 time
delay board (sure, easy to build, but this thing is cheap and well-tested)
to do the 30s.

On Wed, Feb 18, 2009 at 1:56 PM, Robin D. Bussell <RobinB@excelerate.info>wrote:

> Wouldn't an electromagnetic lock be a problem as it's not "fail safe" in
> this application: if there is a need for the door to stay locked 30s
> after power down then a total power cut to would leave the door unlocked
> during this window, you might need some battery backup for the lock.
>
> Cheers,
>     Robin.
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Adam Field
> Sent: 18 February 2009 20:36
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Door safety interlock
>
> > These are about $400US, per the McMaster-Carr catalog.
> >
> > Some recommendations from a co-worker have me paging through Banner,
> > Schneider, Honeywell, and Jokab catalogs.  Maybe one of them will have
> > something, I don't know.
> >
> > This seems like a fairly common problem- I think this is yet another
> case
> > of not know what the right search term to put into Google is to find
> the
> > product I need.
>
> I googled  for electromagnet cabinet lock and found this page:
>
> http://www.basshome.com/industrial_cabinet_locks_806_ctg.htm
>
> They have a 24V DC electromagnet with 200 pounds of holding force. I'm
> not affiliated with the site, just an idea. You could easily integrate
> that with a 19" rack.
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist