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'[EE] Door safety interlock'
2009\02\18@142819 by Mike Hord

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Hi everybody-

I'm trying to find a way to hold an enclosure (19" rack bay, really) shut
while the equipment inside is energized, and for about 30 seconds after
it gets powered down.

This is a tester for bare PCBs, which have some high voltage going on,
and I basically don't want people to be able to grab the boards until
I'm fairly sure they won't get blasted.

Cheap is the real issue- most electronic locking mechanisms I'm finding
are designed to keep a dedicated intruder from gaining entry to a room.
I just want to keep an absent-minded employee from getting to the
parts before they are de-energized.

I'm not really looking for a DIY type solution, here- more a product
recommendation in the $50US range.  I don't mind working something
up to provide the 30-second hold period, but I don't want to kludge up
the locking mechanism.

Mike H.

2009\02\18@145044 by Jon Chandler

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An idea that comes to mind instantly is the solenoid lock used on clothes
washing machines to prevent opening the lid during the spin cycle.  They
usually latch through a hole in a sheet metal tab.  Doesn't seem like this
would be too difficult to rig up depending on how the solenoid is mounted.

Jon


On Wed, 18 Feb 2009 13:27:38 -0600, Mike Hord wrote
{Quote hidden}

> --

2009\02\18@145757 by Alan B. Pearce

face picon face
>I'm not really looking for a DIY type solution, here- more a
>product recommendation in the $50US range.  I don't mind
>working something up to provide the 30-second hold period, but
>I don't want to kludge up the locking mechanism.

How about one of those magnetic latches used for card entry door systems,
where there is a steel plate on the door, and a whacking great electromagnet
mounted on the frame? Done right the magnet could latch onto the back of the
rack unit (if you used a steel back panel rather than aluminium) to stop it
being pulled out.

2009\02\18@151421 by KPL

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On Wed, Feb 18, 2009 at 9:49 PM, Jon Chandler <spam_OUTchandlerTakeThisOuTspamseanet.com> wrote:
> An idea that comes to mind instantly is the solenoid lock used on clothes
> washing machines to prevent opening the lid during the spin cycle.  They
> usually latch through a hole in a sheet metal tab.  Doesn't seem like this
> would be too difficult to rig up depending on how the solenoid is mounted.
>
> Jon
>

Or may be the motor from car door locking system?

--
KPL

2009\02\18@152808 by Mike Hord

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On Wed, Feb 18, 2009 at 1:58 PM, Alan B. Pearce <.....Alan.B.PearceKILLspamspam@spam@stfc.ac.uk>wrote:

> >I'm not really looking for a DIY type solution, here- more a
> >product recommendation in the $50US range.  I don't mind
> >working something up to provide the 30-second hold period, but
> >I don't want to kludge up the locking mechanism.
>
> How about one of those magnetic latches used for card entry door systems,
> where there is a steel plate on the door, and a whacking great
> electromagnet
> mounted on the frame? Done right the magnet could latch onto the back of
> the
> rack unit (if you used a steel back panel rather than aluminium) to stop it
> being pulled out.
>

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.

Mike H.

2009\02\18@153222 by Thomas Coyle

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I've done both solenoid locks (such as car door locks) and maglocks for
racks previously in a high-security environment. The maglocks are more
expensive but cleaner and last forever (no moving parts). Check out
Ebay 110353048779 - $50.

On Wed, Feb 18, 2009 at 11:58 AM, Alan B. Pearce
<Alan.B.PearcespamKILLspamstfc.ac.uk>wrote:

{Quote hidden}

> -

2009\02\18@153626 by Adam Field

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face
> 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.

2009\02\18@165743 by Robin D. Bussell

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face
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 removed}

2009\02\18@170903 by Tamas Rudnai

face picon face
On Wed, Feb 18, 2009 at 8:32 PM, Thomas Coyle <.....zxcasdKILLspamspam.....gmail.com> wrote:

> I've done both solenoid locks (such as car door locks) and maglocks for
> racks previously in a high-security environment. The maglocks are more
> expensive but cleaner and last forever (no moving parts).
>

It's  bit off, but just happened yesterday that the openig system failed on
the entrance door in the building of my apartment. Practically noone could
go in or out of te building. After an hour or so the management company
still failed to show up and as it was in a busy hours there were like 15-20
people waiting to either enter or leave... so one of the magnet had been
removed by someone leaving only one remaining magnet lock. The door was
openable by just a quick and strong force with one hand.

What I was wondering how secure is such a system with two magnets
functioning properly? One magnet by one hand, two magnets by two? Or is
there something else that I missed?

Thanks,
Tamas


--
Rudonix DoubleSaver
http://www.rudonix.com

2009\02\18@171224 by Thomas Coyle

picon face
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 <EraseMERobinBspam_OUTspamTakeThisOuTexcelerate.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 removed}

2009\02\18@171614 by cdb

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face


:: 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.

The circuit could be wired with a double set of relay contacts so that
in the event of a power failure the power will not automatically be
re-applied on power restore. Then it doesn't  matter if the solenoid
unlocks.

I mus investigate how my Asko washing machine achieves the timed
doorlock as that still works with no power attached - must have a
mighty big capacitor as a power source perhaps.  very annoying  that
the anti door opening mechanism is still active once the machine has
finished - I mean the drum is motionless - I want to get into the
machine!

Colin
--
cdb, colinspamspam_OUTbtech-online.co.uk on 19/02/2009

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359






2009\02\18@172210 by Thomas Coyle

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Depends on the force of the magnet. You can get multi-thousand-pound force
units. It's surprising that something so small, with so (relatively) little
current, could be that powerful, but it's true. The little one on Ebay that
I linked earlier would probably be defeated with a good shoulder and the
right leverage, but you'd probably break the door frame before opening the
magnet on the bigger units.
That is, of course, assuming that it's mounted properly. If the two parts
aren't mounted perfectly flush, you won't have the force.

As far as your situation is concerned - I'm surprised that could happen.
>From what I've seen, building code requires a physical power disconnect
button on maglocks - you hit the button and it physically breaks the power
so that it has to open - since it's a severe hazard if people get trapped.

On Wed, Feb 18, 2009 at 2:09 PM, Tamas Rudnai <@spam@tamas.rudnaiKILLspamspamgmail.com>wrote:

{Quote hidden}

> -

2009\02\18@173128 by Michael Algernon

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face
Get some NEODYMIUM ring magnets from SuperMagnetMan.
 http://www.supermagnetman.net/
You can add magnets to get 1000s of newtons of force. They fail-safe  
lock the cabinet together.  Use a motor driven cam to separate the  
magnets so the door can be opened.
MA



> 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.
>

2009\02\18@174605 by Tamas Rudnai

face picon face
On Wed, Feb 18, 2009 at 10:22 PM, Thomas Coyle <RemoveMEzxcasdTakeThisOuTspamgmail.com> wrote:

> As far as your situation is concerned - I'm surprised that could happen.
> >From what I've seen, building code requires a physical power disconnect
> button on maglocks - you hit the button and it physically breaks the power
> so that it has to open - since it's a severe hazard if people get trapped.
>

Exactly! People inside should have been able to unlock the door by pressing
the button, but it did not work eventually. I guess in case of fire there
would have been a disaster. The good thing is that the door is 90% glass so
I gusess one can brake it if anything like that happens. But of course there
is no axe next to it... Anyway, here in Ireland I do not surprise on things
like this anymore...

Tamas
--
Rudonix DoubleSaver
http://www.rudonix.com

2009\02\18@190601 by Richard Prosser

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2009/2/19 Tamas Rudnai <spamBeGonetamas.rudnaispamBeGonespamgmail.com>:
{Quote hidden}

Did they just remove a magnet, or did they add a spacer (eg cardboard)
"air gap" to the remaining magnet. Any air gap will significantly
reduce the force required.

RP

2009\02\18@202821 by Tamas Rudnai

face picon face
On Thu, Feb 19, 2009 at 12:05 AM, Richard Prosser <RemoveMErhprosserspamTakeThisOuTgmail.com>wrote:

> Did they just remove a magnet, or did they add a spacer (eg cardboard)
>  "air gap" to the remaining magnet. Any air gap will significantly
> reduce the force required.
>

They removed one of the magnet, and did not put any spacer to the other one.
However, I would not be surprised if it was not properly installed or used a
cheap / not-so-strong one. Here in Ireland the locksmith does not really
know how to install a mechanical lock anyway. When they broke into my apt
just few month ago, one of the best locksmith company here in Dublin put a
new lock but it is still not in level to the door so it can be broken off
again. I guess they just do not care - sorry about my bitter, but I am just
sad every time I am thinking about this.

Tamas
--
Rudonix DoubleSaver
http://www.rudonix.com

2009\02\18@222457 by Jake Anderson

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face
Tamas Rudnai wrote:
> On Thu, Feb 19, 2009 at 12:05 AM, Richard Prosser <rhprosserEraseMEspam.....gmail.com>wrote:
>
>  
>> Did they just remove a magnet, or did they add a spacer (eg cardboard)
>>  "air gap" to the remaining magnet. Any air gap will significantly
>> reduce the force required.
>>
>>    
>
> They removed one of the magnet, and did not put any spacer to the other one.
> However, I would not be surprised if it was not properly installed or used a
> cheap / not-so-strong one. Here in Ireland the locksmith does not really
> know how to install a mechanical lock anyway. When they broke into my apt
> just few month ago, one of the best locksmith company here in Dublin put a
> new lock but it is still not in level to the door so it can be broken off
> again. I guess they just do not care - sorry about my bitter, but I am just
> sad every time I am thinking about this.
>
> Tamas
>  
Without a steel door jamb a "lock" isn't going to do much against a
decent foot/shoulder.
If its subject to being "opened" by force that is, generally the
deterrent is that is somewhat noisy.

With a steel door jamb then you need at least a solid timber door, that
raises the bar to a police style "key" (bigass battering ram) or a
sledge hammer.
Its probably easiest for them to just smash the hinges off in that case.

Step up from that is a steel door, which always spells classy ;->.

(and the baddies would just knock a hole in the wall)

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