Magnetic door holders question

[Adrian Tuddenham]

Michael A. Terrell <mike.terrell@earthlink.net> wrote:

Adrian Tuddenham wrote:

Michael A. Terrell wrote:


All I've seen in use, use AC to prevent this problem.

...except that A.C. doesn't prevent it. I've seen enough stuck
contactors with A.C. coils to be quite certain of that.


They are not contactors. Some hold the door open for years between
operations. Contactors get beat to death by repeatedly slamming the pole
piece into the metal on the moving contacts.


You're comparing apples to water melons.

These D.C. magnets with flat pole faces are getting stuck because of
residual magnetism - A.C. contactors with laminated pole faces which
have become hammered flat, get stuck in exactly the same way.

This is not because the contactors have had to do a lot of work in order
to develop flat pole faces, it is because the residual magnetism is the
same, regardless of whether it resulted from D.C. or the last half-cycle
of A.C.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

 

[Michael A. Terrell]

Adrian Tuddenham wrote:

Michael A. Terrell <mike.terrell@earthlink.net> wrote:

Adrian Tuddenham wrote:

Michael A. Terrell wrote:


All I've seen in use, use AC to prevent this problem.

...except that A.C. doesn't prevent it. I've seen enough stuck
contactors with A.C. coils to be quite certain of that.


They are not contactors. Some hold the door open for years between
operations. Contactors get beat to death by repeatedly slamming the pole
piece into the metal on the moving contacts.


You're comparing apples to water melons.

These D.C. magnets with flat pole faces are getting stuck because of
residual magnetism - A.C. contactors with laminated pole faces which
have become hammered flat, get stuck in exactly the same way.

This is not because the contactors have had to do a lot of work in order
to develop flat pole faces, it is because the residual magnetism is the
same, regardless of whether it resulted from D.C. or the last half-cycle
of A.C.

The old sliding fire doors on slanted rollers that used a rope and
weights were pretty much foolproof. They didn't need electricity, and
there was little you could do to screw them up. Once they were moving,
you couldn't hold them open.

Those laminated contactors take thousands and thousands of operations
to flatten into a solid face.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[Mick Nowell]

I work on commercial fire alarm systems mostly in apartment houses. Many of these buildings in the common hallways employ electromagnetic units mounted on the walls and an iron disk on the back corner of the doors. When the doors are opened and the disks are mated with the electromagnet the doors are held open in place. These doors all have pneumatic closers on them as well which are always applying a force in the opposite direction to try to close the door.

When the alarm is activated the 24VDC is removed from the coils and the doors are supposed to be automatically pulled closed by the force of the pneumatic unit. This doesn't always work because in spite of the opposing force applied by the pneumatic unit, in many cases the electromagnets seem to hold enough residual magnetism to keep disks from releasing and the doors from closing. It often becomes necessary to increase the opposing pneumatic force tremendously in order to overcome this.

I have discussed this with various manufacturers of these electromagnetic units and in all but one instance have received the same bullshit answer that they've "never heard of this".

The one exception was one tech who ventured that perhaps momentarily reversing polarity on alarm before DC drop out might work, however he had never tried it. Does anyone have any ideas about this? Thanks, Lenny

Disconnect the PU from the door. Get a scale and see how much force it
takes to open each unit.
Before any modification I suggest exercising them. Pop each one open
and "brillo" the oxidization/whatever on each surface. Repeat.

 

[ABLE1]

<captainvideo462009@gmail.com> wrote in message
news:70f7ee84-725c-48df-9486-f85ec7df2361@googlegroups.com...
Each coil draws .015A at 24VDC. Putting them in series would not be
practical especially in a large building. There are systems that use 120VAC
coils but the circuits have to have the correct cable, (Romex) pre wired for
them. Most buildings are wired using 18 or 16 AWG. FPLR low voltage cable
for initiation and indicating circuits. You would not want to run 120V
through these. Further, most fire alarm guys are certified in low voltage
and although I wired my own house and I could certainly wire a 120V circuit,
we are not electricians. For this reason all the door holders I've run into
are the 24VDC variety.

I do like Michael's idea of video taping the failure and sending it to the
manufacturer. Perhaps that will get them off their asses to come up with a
solution. Lenny

Sorry to dig this up but need to interject a bit of input.

First the problem you are having is unusual. Since this is a commercial
fire panel it needs to be worked on by the servicing alarm company to make
any adjustment or corrections to the system. This is required by NFPA as
well as the AHJ in your jurisdiction. There are procedure that can
determine the cause and correction of such issues.

Personally I would be checking residual voltage at the mag door holders when
power is removed. Also checking the door plates to see if they are somehow
magnetized and applying the extra holding force you describe. Depending on
the above results there are certain device applications that can correct the
problem.

Also knowing the mfg, model and the vintage of the Fire Alarm Panel itself
could go along way to solving the problem. Again, doing work on a
Commercial Fire Panel needs to done by trained professionals. If you are
not, don't touch it.

Les

 

[Tim R]

On Sunday, February 16, 2014 6:33:37 PM UTC-5, Mick Nowell wrote:

Disconnect the PU from the door. Get a scale and see how much force it

takes to open each unit.

Before any modification I suggest exercising them. Pop each one open

and "brillo" the oxidization/whatever on each surface. Repeat.

+1

All the speculation is based on the conclusion that residual magnetism is the problem, and that may be premature.

Turn the power off, take an ordinary piece of steel like a cover plate, and see if it sticks to the magnet. If it does (which I doubt) put a multimeter on it and confirm the power is really off. Then use the spring scale to see how hard the steel sticks.

Compare that to how hard it is to pull the door open.

 

[Tim R]

On Tuesday, March 25, 2014 3:44:44 PM UTC-4, Tim R wrote:

On Sunday, February 16, 2014 6:33:37 PM UTC-5, Mick Nowell wrote:

Disconnect the PU from the door. Get a scale and see how much force it



takes to open each unit.



Before any modification I suggest exercising them. Pop each one open



and "brillo" the oxidization/whatever on each surface. Repeat.



+1



All the speculation is based on the conclusion that residual magnetism is the problem, and that may be premature.



Turn the power off, take an ordinary piece of steel like a cover plate, and see if it sticks to the magnet. If it does (which I doubt) put a multimeter on it and confirm the power is really off. Then use the spring scale to see how hard the steel sticks.



Compare that to how hard it is to pull the door open.

Er, shut, I mean.

 

On Monday, February 10, 2014 at 11:02:26 PM UTC+5:30, captainvi...@gmail.com wrote:

I work on commercial fire alarm systems mostly in apartment houses. Many of these buildings in the common hallways employ electromagnetic units mounted on the walls and an iron disk on the back corner of the doors. When the doors are opened and the disks are mated with the electromagnet the doors are held open in place. These doors all have pneumatic closers on them as well which are always applying a force in the opposite direction to try to close the door.

When the alarm is activated the 24VDC is removed from the coils and the doors are supposed to be automatically pulled closed by the force of the pneumatic unit. This doesn't always work because in spite of the opposing force applied by the pneumatic unit, in many cases the electromagnets seem to hold enough residual magnetism to keep disks from releasing and the doors from closing. It often becomes necessary to increase the opposing pneumatic force tremendously in order to overcome this.

I have discussed this with various manufacturers of these electromagnetic units and in all but one instance have received the same bullshit answer that they've "never heard of this".

The one exception was one tech who ventured that perhaps momentarily reversing polarity on alarm before DC drop out might work, however he had never tried it. Does anyone have any ideas about this? Thanks, Lenny

 

[pfjw@aol.com]

It has been my experience that these beasts fail in three typical ways:

a) they are so seldom checked that dirt accumulates under the leaf and cements the door in place (!!).
b) the plate rusts to the magnet.
c) see a) above but insert carpet.

All due to systematic and systemic negligence. Under my watch, such devices are tested weekly, typically on Friday at office (or school) closing. I have never seen residual magnetism sufficient to hold the door. Neither plate nor magnet has enough mass for that.

Peter Wieck
Melrose Park, PA

 

Remember the power in these systems comes from a backup battery to make
it fail safe. It would involve major rebuild costs to do that.

Not true. Most of the systems that I have seen will automatically release the doors during a power fail. Since these are fire doors, the default is to close them in any "emergency". A power failure is considered an emergency and the doors are released.

As matter of fact, during a fire inspection we will trigger these doors in one of two ways: 1) Fire alarm trip and 2) power failure. In order for the facility to pass the inspection, both methods need to work.

Dan

 

[Pat]

On Thu, 7 Jul 2016 22:43:12 -0700 (PDT), adidevrk511@gmail.com wrote:

On Monday, February 10, 2014 at 11:02:26 PM UTC+5:30, captainvi...@gmail.com wrote:
I work on commercial fire alarm systems mostly in apartment houses. Many of these buildings in the common hallways employ electromagnetic units mounted on the walls and an iron disk on the back corner of the doors. When the doors are opened and the disks are mated with the electromagnet the doors are held open in place. These doors all have pneumatic closers on them as well which are always applying a force in the opposite direction to try to close the door.

When the alarm is activated the 24VDC is removed from the coils and the doors are supposed to be automatically pulled closed by the force of the pneumatic unit. This doesn't always work because in spite of the opposing force applied by the pneumatic unit, in many cases the electromagnets seem to hold enough residual magnetism to keep disks from releasing and the doors from closing. It often becomes necessary to increase the opposing pneumatic force tremendously in order to overcome this.

I have discussed this with various manufacturers of these electromagnetic units and in all but one instance have received the same bullshit answer that they've "never heard of this".

The one exception was one tech who ventured that perhaps momentarily reversing polarity on alarm before DC drop out might work, however he had never tried it. Does anyone have any ideas about this? Thanks, Lenny

I know this is an old post, but I find it interesting. Would using AC
on the electromagnets instead of DC solve the problem?

 

[Rheilly Phoull]

On 8/07/2016 8:01 PM, Pat wrote:

On Thu, 7 Jul 2016 22:43:12 -0700 (PDT), adidevrk511@gmail.com wrote:

On Monday, February 10, 2014 at 11:02:26 PM UTC+5:30, captainvi...@gmail.com wrote:
I work on commercial fire alarm systems mostly in apartment houses. Many of these buildings in the common hallways employ electromagnetic units mounted on the walls and an iron disk on the back corner of the doors. When the doors are opened and the disks are mated with the electromagnet the doors are held open in place. These doors all have pneumatic closers on them as well which are always applying a force in the opposite direction to try to close the door.

When the alarm is activated the 24VDC is removed from the coils and the doors are supposed to be automatically pulled closed by the force of the pneumatic unit. This doesn't always work because in spite of the opposing force applied by the pneumatic unit, in many cases the electromagnets seem to hold enough residual magnetism to keep disks from releasing and the doors from closing. It often becomes necessary to increase the opposing pneumatic force tremendously in order to overcome this.

I have discussed this with various manufacturers of these electromagnetic units and in all but one instance have received the same bullshit answer that they've "never heard of this".

The one exception was one tech who ventured that perhaps momentarily reversing polarity on alarm before DC drop out might work, however he had never tried it. Does anyone have any ideas about this? Thanks, Lenny

I know this is an old post, but I find it interesting. Would using AC
on the electromagnets instead of DC solve the problem?

Remember the power in these systems comes from a backup battery to make
it fail safe. It would involve major rebuild costs to do that.

 

[Pat]

On Fri, 8 Jul 2016 20:16:52 +0800, Rheilly Phoull
<rheilly@bigslong.com> wrote:

On 8/07/2016 8:01 PM, Pat wrote:
On Thu, 7 Jul 2016 22:43:12 -0700 (PDT), adidevrk511@gmail.com wrote:

On Monday, February 10, 2014 at 11:02:26 PM UTC+5:30, captainvi...@gmail.com wrote:
I work on commercial fire alarm systems mostly in apartment houses. Many of these buildings in the common hallways employ electromagnetic units mounted on the walls and an iron disk on the back corner of the doors. When the doors are opened and the disks are mated with the electromagnet the doors are held open in place. These doors all have pneumatic closers on them as well which are always applying a force in the opposite direction to try to close the door.

When the alarm is activated the 24VDC is removed from the coils and the doors are supposed to be automatically pulled closed by the force of the pneumatic unit. This doesn't always work because in spite of the opposing force applied by the pneumatic unit, in many cases the electromagnets seem to hold enough residual magnetism to keep disks from releasing and the doors from closing. It often becomes necessary to increase the opposing pneumatic force tremendously in order to overcome this.

I have discussed this with various manufacturers of these electromagnetic units and in all but one instance have received the same bullshit answer that they've "never heard of this".

The one exception was one tech who ventured that perhaps momentarily reversing polarity on alarm before DC drop out might work, however he had never tried it. Does anyone have any ideas about this? Thanks, Lenny

I know this is an old post, but I find it interesting. Would using AC
on the electromagnets instead of DC solve the problem?

Remember the power in these systems comes from a backup battery to make
it fail safe. It would involve major rebuild costs to do that.
Good point! Thank you for the reply.

 

[legg]

On Fri, 8 Jul 2016 20:16:52 +0800, Rheilly Phoull
<rheilly@bigslong.com> wrote:

<snip>

I know this is an old post, but I find it interesting. Would using AC
on the electromagnets instead of DC solve the problem?

Remember the power in these systems comes from a backup battery to make
it fail safe. It would involve major rebuild costs to do that.

For this service, loss of power would invoke the fail safe condition,
without a back-up battery. Fail safe is the de-energized state.

RL

 

[legg]

On Fri, 08 Jul 2016 08:01:14 -0400, Pat <pat@nospam.us> wrote:

On Thu, 7 Jul 2016 22:43:12 -0700 (PDT), adidevrk511@gmail.com wrote:

On Monday, February 10, 2014 at 11:02:26 PM UTC+5:30, captainvi...@gmail.com wrote:
I work on commercial fire alarm systems mostly in apartment houses. Many of these buildings in the common hallways employ electromagnetic units mounted on the walls and an iron disk on the back corner of the doors. When the doors are opened and the disks are mated with the electromagnet the doors are held open in place. These doors all have pneumatic closers on them as well which are always applying a force in the opposite direction to try to close the door.

When the alarm is activated the 24VDC is removed from the coils and the doors are supposed to be automatically pulled closed by the force of the pneumatic unit. This doesn't always work because in spite of the opposing force applied by the pneumatic unit, in many cases the electromagnets seem to hold enough residual magnetism to keep disks from releasing and the doors from closing. It often becomes necessary to increase the opposing pneumatic force tremendously in order to overcome this.

I have discussed this with various manufacturers of these electromagnetic units and in all but one instance have received the same bullshit answer that they've "never heard of this".

The one exception was one tech who ventured that perhaps momentarily reversing polarity on alarm before DC drop out might work, however he had never tried it. Does anyone have any ideas about this? Thanks, Lenny

I know this is an old post, but I find it interesting. Would using AC
on the electromagnets instead of DC solve the problem?

The OP already had multiple advice that the remanence was highly
unlikely to be the issue - so a different coil or drive method would
be unlikely to solve it, in an application where the installation has
been previously vetted. Fire doors have varying construction,
involving metalic or other heat resistant materials, but once
adjusted, performance should be repeatable.

It's much harder to get predictable performance from a pneumatic door
mechanism and the door it's controlling - without considering any
involvement from various external hold/release mechanisms. This is
complicated if staff are fiddling with the available adjustments at
their extremes, rather than examining other issues such a cleanliness,
lubrication or possible obstructions.

I understand his frustration, but safety critical features are best
addressed by those responsible for their installation and servicing.

This hardware operates on the principles of an electromagnet, as is
more commonly evident in solenoids and relays, so advice on their
operation is relevant.

RL

 

[Jon Elson]

adidevrk511@gmail.com wrote:

When the alarm is activated the 24VDC is removed from the coils and the
doors are supposed to be automatically pulled closed by the force of the
pneumatic unit. This doesn't always work

Try putting one layer of wide vinyl tape over either the electromagnet or
the door plate. (A couple parallel strips of ordinary electrician's tape
could also be used to test this idea.) If it now releases, remanent
magnetic field is certainly the problem. Possibly you could get a thin
durable material that could permanently replace the tape, which will
eventually wear down and cause the problem to recur.

Jon

 

Clean hinges with CRC Spray Silicone/\...use the spray as a cleaning hose..

then lube hinges with a drop or 2 of


http://www.3inone.com/images/3in1/product-lock-dry-lube.jpg

at HD

 

[Rheilly Phoull]

On 8/07/2016 9:25 PM, dansabrservices@yahoo.com wrote:

Remember the power in these systems comes from a backup battery to make
it fail safe. It would involve major rebuild costs to do that.

Not true. Most of the systems that I have seen will automatically release the doors during a power fail. Since these are fire doors, the default is to close them in any "emergency". A power failure is considered an emergency and the doors are released.

As matter of fact, during a fire inspection we will trigger these doors in one of two ways: 1) Fire alarm trip and 2) power failure. In order for the facility to pass the inspection, both methods need to work.

Dan

True, but we were discussing the mechanism's operating power.