Magnetic door holders question

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

 

[Cydrome Leader]

captainvideo462009@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

feed them less than 24 volts, or maybe put a layer of packing tape over
the plate to add some space, or get somebody to "accidentally" paint over
the mating surfaces, although this is likely to make them stick as well.

 

[hrhofmann@sbcglobal.net]

On Monday, February 10, 2014 11:32:26 AM UTC-6, 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

Ken and Cydrome's idea to put a thin spacer on the disc to make it easier to release sounds like a good idea. My experience has always been that the magnetism was not strong enough to hold the door open, not that it would not release.

 

[Tim R]

On Monday, February 10, 2014 2:06:37 PM UTC-5, hrho...@sbcglobal.net wrote:
> Ken and Cydrome's idea to put a thin spacer on the disc to make it easier to >release sounds like a good idea. My experience has always been that the >magnetism was not strong enough to hold the door open, not that it would not >release.

I've never seen this and I have a fair amount of experience with these doors in hospitals.

It is more commonly hard to get them to stay open.

I would suspect a door closer problem first.

 

[Ken]

captainvideo462009@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

Couldn't you place something over the metal disks to reduce the magnetic
coupling with the magnet? I would think you could find a point where it
would still hold the door when needed, and release it when 24v is removed.

 

[RobertMacy]

On Mon, 10 Feb 2014 10:32:26 -0700, <captainvideo462009@gmail.com> wrote:

...snip...
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've always found that having ferrous metal in a DC field touching each
other is not a good idea. Add a 3 mil layer of kapton tape between the
two. the extra distance will prevent the 'residual' magnetism from having
enough strength to hold and keep the doors open. More likely difficulty
keeping them open.

 

[Adrian Tuddenham]

<captainvideo462009@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

That last idea is an elegant one which would probably work quite well;
however, it has one very big drawback:

The safety of the whole system depends on the doors closing if anything
goes wrong. If the wires were burned through, the control box would
lose contact with the magnets and could not demagnetise them. The
fail-safe aspect of the system would be lost.


The usual method is to insert a non-magnetic shim of some kind, but this
can wear down and fail after a few years. A more subtle way is to
abrade or machine down one of the pole faces so that it is not quite in
the same plane as the other. If these are 'pot' magnets, you could skim
a thou or so off the centre pole if you have access to a lathe.
Unfortunately this would destroy any anti-corrosion plating on the
metal, but that might not matter if the buildings are dry.

An alternative would be to 'dish' the armature plate so that the concave
side was towards the magnet. To do this you would need to take it off
the door and stand it outside on a solid foundation (or an anvil, if you
have one). A supporting ring to back up the outer edge can be
improvised from a piece of hard wood with a hole in it or a short offcut
of steel pipe. To dish it slightly you will need a steel bar or other
hard object with one end slightly rounded - and a sledge hammer to hit
it with. Try to do it in one hit, so as to avoid peening the surface.


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

 

[Cydrome Leader]

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:

captainvideo462009@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

That last idea is an elegant one which would probably work quite well;
however, it has one very big drawback:

The safety of the whole system depends on the doors closing if anything
goes wrong. If the wires were burned through, the control box would
lose contact with the magnets and could not demagnetise them. The
fail-safe aspect of the system would be lost.


The usual method is to insert a non-magnetic shim of some kind, but this
can wear down and fail after a few years. A more subtle way is to
abrade or machine down one of the pole faces so that it is not quite in
the same plane as the other. If these are 'pot' magnets, you could skim
a thou or so off the centre pole if you have access to a lathe.
Unfortunately this would destroy any anti-corrosion plating on the
metal, but that might not matter if the buildings are dry.

An alternative would be to 'dish' the armature plate so that the concave
side was towards the magnet. To do this you would need to take it off
the door and stand it outside on a solid foundation (or an anvil, if you
have one). A supporting ring to back up the outer edge can be
improvised from a piece of hard wood with a hole in it or a short offcut
of steel pipe. To dish it slightly you will need a steel bar or other
hard object with one end slightly rounded - and a sledge hammer to hit
it with. Try to do it in one hit, so as to avoid peening the surface.

The problem with the heavy handed methods is you're then deliberately
altering a safety device. A little tape here and there could have been
done by anybody who just didn't know better.

Granted, it's unlikely to cause the building to catch on fire, with the
doors stuck open killing everybody inside, but these are not really
devices to mess with. The door might just slam into somebody's face- you
never know.

While I may have done electrical work before, if it's conduit painted red
(at least here in Chicago this is common) or marked Life/Safety or L/S or
something similar, the rule is don't open it, don't touch it.

 

[Michael A. Terrell]

captainvideo462009@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

Shoot video of the failure, and send it to them. Tell them if they
can't fix the problem that you will post the video and details online,
in case of a fire. Put it some place like Youtube or Vimeo, where it is
sure to be seen by people and asked the OEM what it will do to their
reputation and their insurance costs.


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

 

[Adrian Tuddenham]

Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
captainvideo462009@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

That last idea is an elegant one which would probably work quite well;
however, it has one very big drawback:

The safety of the whole system depends on the doors closing if anything
goes wrong. If the wires were burned through, the control box would
lose contact with the magnets and could not demagnetise them. The
fail-safe aspect of the system would be lost.


The usual method is to insert a non-magnetic shim of some kind, but this
can wear down and fail after a few years. A more subtle way is to
abrade or machine down one of the pole faces so that it is not quite in
the same plane as the other. If these are 'pot' magnets, you could skim
a thou or so off the centre pole if you have access to a lathe.
Unfortunately this would destroy any anti-corrosion plating on the
metal, but that might not matter if the buildings are dry.

An alternative would be to 'dish' the armature plate so that the concave
side was towards the magnet. To do this you would need to take it off
the door and stand it outside on a solid foundation (or an anvil, if you
have one). A supporting ring to back up the outer edge can be
improvised from a piece of hard wood with a hole in it or a short offcut
of steel pipe. To dish it slightly you will need a steel bar or other
hard object with one end slightly rounded - and a sledge hammer to hit
it with. Try to do it in one hit, so as to avoid peening the surface.

The problem with the heavy handed methods is you're then deliberately
altering a safety device. A little tape here and there could have been
done by anybody who just didn't know better.

Granted, it's unlikely to cause the building to catch on fire, with the
doors stuck open killing everybody inside, but these are not really
devices to mess with. The door might just slam into somebody's face- you
never know.

While I may have done electrical work before, if it's conduit painted red
(at least here in Chicago this is common) or marked Life/Safety or L/S or
something similar, the rule is don't open it, don't touch it.

It is a sad situation where a safety device could be made more reliable
by a simple modification but this is prevented by the legislation which
is there to make things safer.

My biggest worry would be how such a badly-designed "safety" system with
an easily-recognised fault came to be made by a manufacturer who
presumably specialises in that field. Add to that, the inspection and
checking processes which must all have failed to pick up the problem.
It isn't as though D.C. electromagnetism is a new and unknown field full
of unsuspected effects - this problem has been well-understood for over
100 years.

Perhaps the O/P should contact the manufacturer and suggest they stamp
their armatures slightly concave in future.

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

 

[Leif Neland]

captainvideo462009@gmail.com:

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.

Would it be possible to feed the electromagnets with 24V AC?

That should prevent the doors to get permanently magnetized.
I don't know if that'll make the doors/magnets hum though.

Leif

--
Husk křrelys bagpĺ, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

 

[Cydrome Leader]

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:

Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
captainvideo462009@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

That last idea is an elegant one which would probably work quite well;
however, it has one very big drawback:

The safety of the whole system depends on the doors closing if anything
goes wrong. If the wires were burned through, the control box would
lose contact with the magnets and could not demagnetise them. The
fail-safe aspect of the system would be lost.


The usual method is to insert a non-magnetic shim of some kind, but this
can wear down and fail after a few years. A more subtle way is to
abrade or machine down one of the pole faces so that it is not quite in
the same plane as the other. If these are 'pot' magnets, you could skim
a thou or so off the centre pole if you have access to a lathe.
Unfortunately this would destroy any anti-corrosion plating on the
metal, but that might not matter if the buildings are dry.

An alternative would be to 'dish' the armature plate so that the concave
side was towards the magnet. To do this you would need to take it off
the door and stand it outside on a solid foundation (or an anvil, if you
have one). A supporting ring to back up the outer edge can be
improvised from a piece of hard wood with a hole in it or a short offcut
of steel pipe. To dish it slightly you will need a steel bar or other
hard object with one end slightly rounded - and a sledge hammer to hit
it with. Try to do it in one hit, so as to avoid peening the surface.

The problem with the heavy handed methods is you're then deliberately
altering a safety device. A little tape here and there could have been
done by anybody who just didn't know better.

Granted, it's unlikely to cause the building to catch on fire, with the
doors stuck open killing everybody inside, but these are not really
devices to mess with. The door might just slam into somebody's face- you
never know.

While I may have done electrical work before, if it's conduit painted red
(at least here in Chicago this is common) or marked Life/Safety or L/S or
something similar, the rule is don't open it, don't touch it.

It is a sad situation where a safety device could be made more reliable
by a simple modification but this is prevented by the legislation which
is there to make things safer.

My biggest worry would be how such a badly-designed "safety" system with
an easily-recognised fault came to be made by a manufacturer who
presumably specialises in that field. Add to that, the inspection and
checking processes which must all have failed to pick up the problem.
It isn't as though D.C. electromagnetism is a new and unknown field full
of unsuspected effects - this problem has been well-understood for over
100 years.

Perhaps the O/P should contact the manufacturer and suggest they stamp
their armatures slightly concave in future.

It might be worth looking into the power source for those devices. Too
much voltage will likely cause them to be too strong.

 

[Adrian Tuddenham]

Leif Neland <leif@neland.dk> wrote:

captainvideo462009@gmail.com:
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.

Would it be possible to feed the electromagnets with 24V AC?

That should prevent the doors to get permanently magnetized.
[...]

A.C. magnets can also get stuck because of residual magnetism, depending
on whereabouts in the cycle the current is broken.

I occasionally have to file down areas of the pole faces of A.C.
contactors that have become polished through frequent use and have
started randomly sticking in the "on" position (highly embarrassing if
they control motors).

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

 

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

 

[John-Del]

Any chance the door closer arms can be relocated to have a better angle to act on the door? Maybe when the door is fully open, they're pulling "across" the door too much.


On Tuesday, February 11, 2014 5:08:58 PM UTC-5, captainvi...@gmail.com wrote:

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

 

[Adrian Tuddenham]

Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
captainvideo462009@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

That last idea is an elegant one which would probably work quite
well; however, it has one very big drawback:

The safety of the whole system depends on the doors closing if
anything goes wrong. If the wires were burned through, the control
box would lose contact with the magnets and could not demagnetise
them. The fail-safe aspect of the system would be lost.


The usual method is to insert a non-magnetic shim of some kind, but this
can wear down and fail after a few years. A more subtle way is to
abrade or machine down one of the pole faces so that it is not quite in
the same plane as the other. If these are 'pot' magnets, you could skim
a thou or so off the centre pole if you have access to a lathe.
Unfortunately this would destroy any anti-corrosion plating on the
metal, but that might not matter if the buildings are dry.

An alternative would be to 'dish' the armature plate so that the concave
side was towards the magnet. To do this you would need to take it off
the door and stand it outside on a solid foundation (or an anvil, if you
have one). A supporting ring to back up the outer edge can be
improvised from a piece of hard wood with a hole in it or a short offcut
of steel pipe. To dish it slightly you will need a steel bar or other
hard object with one end slightly rounded - and a sledge hammer to hit
it with. Try to do it in one hit, so as to avoid peening the surface.

The problem with the heavy handed methods is you're then deliberately
altering a safety device. A little tape here and there could have been
done by anybody who just didn't know better.

Granted, it's unlikely to cause the building to catch on fire, with the
doors stuck open killing everybody inside, but these are not really
devices to mess with. The door might just slam into somebody's face- you
never know.

While I may have done electrical work before, if it's conduit painted red
(at least here in Chicago this is common) or marked Life/Safety or L/S or
something similar, the rule is don't open it, don't touch it.

It is a sad situation where a safety device could be made more reliable
by a simple modification but this is prevented by the legislation which
is there to make things safer.

My biggest worry would be how such a badly-designed "safety" system with
an easily-recognised fault came to be made by a manufacturer who
presumably specialises in that field. Add to that, the inspection and
checking processes which must all have failed to pick up the problem.
It isn't as though D.C. electromagnetism is a new and unknown field full
of unsuspected effects - this problem has been well-understood for over
100 years.

Perhaps the O/P should contact the manufacturer and suggest they stamp
their armatures slightly concave in future.

It might be worth looking into the power source for those devices. Too
much voltage will likely cause them to be too strong.

It's the residual magnetism that is causing the problem; if the main
magnetisation is above a certain minimum level, the residual is not much
affected by any extra energisation. The limit to the power source is
more likely to be the temperature rise of the energising coils.

I don't know how the O/P's system is arranged, but I think the UK ones
have the magnets in series around the building, so that the circuit can
be broken near any doorway and all the doors on that circuit will shut.
In that case the PSU would either be constant-current or would have a
transformer with adjustable tappings which can be set according to how
many magnets are in circuit.


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

 

[bud--]

On 2/11/2014 4:08 PM, captainvideo462009@gmail.com wrote:

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

The panel and other components are likely UL listed. I would set a video
to UL. May not help your immediate problem but could prevent similar
problems elsewhere in new installs.

 

[Michael A. Terrell]

Adrian Tuddenham wrote:

Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
captainvideo462009@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

That last idea is an elegant one which would probably work quite
well; however, it has one very big drawback:

The safety of the whole system depends on the doors closing if
anything goes wrong. If the wires were burned through, the control
box would lose contact with the magnets and could not demagnetise
them. The fail-safe aspect of the system would be lost.


The usual method is to insert a non-magnetic shim of some kind, but this
can wear down and fail after a few years. A more subtle way is to
abrade or machine down one of the pole faces so that it is not quite in
the same plane as the other. If these are 'pot' magnets, you could skim
a thou or so off the centre pole if you have access to a lathe.
Unfortunately this would destroy any anti-corrosion plating on the
metal, but that might not matter if the buildings are dry.

An alternative would be to 'dish' the armature plate so that the concave
side was towards the magnet. To do this you would need to take it off
the door and stand it outside on a solid foundation (or an anvil, if you
have one). A supporting ring to back up the outer edge can be
improvised from a piece of hard wood with a hole in it or a short offcut
of steel pipe. To dish it slightly you will need a steel bar or other
hard object with one end slightly rounded - and a sledge hammer to hit
it with. Try to do it in one hit, so as to avoid peening the surface.

The problem with the heavy handed methods is you're then deliberately
altering a safety device. A little tape here and there could have been
done by anybody who just didn't know better.

Granted, it's unlikely to cause the building to catch on fire, with the
doors stuck open killing everybody inside, but these are not really
devices to mess with. The door might just slam into somebody's face- you
never know.

While I may have done electrical work before, if it's conduit painted red
(at least here in Chicago this is common) or marked Life/Safety or L/S or
something similar, the rule is don't open it, don't touch it.

It is a sad situation where a safety device could be made more reliable
by a simple modification but this is prevented by the legislation which
is there to make things safer.

My biggest worry would be how such a badly-designed "safety" system with
an easily-recognised fault came to be made by a manufacturer who
presumably specialises in that field. Add to that, the inspection and
checking processes which must all have failed to pick up the problem.
It isn't as though D.C. electromagnetism is a new and unknown field full
of unsuspected effects - this problem has been well-understood for over
100 years.

Perhaps the O/P should contact the manufacturer and suggest they stamp
their armatures slightly concave in future.

It might be worth looking into the power source for those devices. Too
much voltage will likely cause them to be too strong.

It's the residual magnetism that is causing the problem; if the main
magnetisation is above a certain minimum level, the residual is not much
affected by any extra energisation. The limit to the power source is
more likely to be the temperature rise of the energising coils.

I don't know how the O/P's system is arranged, but I think the UK ones
have the magnets in series around the building, so that the circuit can
be broken near any doorway and all the doors on that circuit will shut.
In that case the PSU would either be constant-current or would have a
transformer with adjustable tappings which can be set according to how
many magnets are in circuit.

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

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

 

[Adrian Tuddenham]

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

Adrian Tuddenham wrote:

Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
Cydrome Leader <presence@MUNGEpanix.com> wrote:

Adrian Tuddenham <adrian@poppyrecords.invalid.invalid> wrote:
captainvideo462009@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

That last idea is an elegant one which would probably work quite
well; however, it has one very big drawback:

The safety of the whole system depends on the doors closing if
anything goes wrong. If the wires were burned through, the
control box would lose contact with the magnets and could not
demagnetise them. The fail-safe aspect of the system would be
lost.


The usual method is to insert a non-magnetic shim of some kind,
but this can wear down and fail after a few years. A more subtle
way is to abrade or machine down one of the pole faces so that it
is not quite in the same plane as the other. If these are 'pot'
magnets, you could skim a thou or so off the centre pole if you
have access to a lathe. Unfortunately this would destroy any
anti-corrosion plating on the metal, but that might not matter if
the buildings are dry.

An alternative would be to 'dish' the armature plate so that the
concave side was towards the magnet. To do this you would need
to take it off the door and stand it outside on a solid
foundation (or an anvil, if you have one). A supporting ring to
back up the outer edge can be improvised from a piece of hard
wood with a hole in it or a short offcut of steel pipe. To dish
it slightly you will need a steel bar or other hard object with
one end slightly rounded - and a sledge hammer to hit it with.
Try to do it in one hit, so as to avoid peening the surface.

The problem with the heavy handed methods is you're then
deliberately altering a safety device. A little tape here and there
could have been done by anybody who just didn't know better.

Granted, it's unlikely to cause the building to catch on fire, with
the doors stuck open killing everybody inside, but these are not
really devices to mess with. The door might just slam into
somebody's face- you never know.

While I may have done electrical work before, if it's conduit
painted red (at least here in Chicago this is common) or marked
Life/Safety or L/S or something similar, the rule is don't open it,
don't touch it.

It is a sad situation where a safety device could be made more
reliable by a simple modification but this is prevented by the
legislation which is there to make things safer.

My biggest worry would be how such a badly-designed "safety" system
with an easily-recognised fault came to be made by a manufacturer
who presumably specialises in that field. Add to that, the
inspection and checking processes which must all have failed to pick
up the problem. It isn't as though D.C. electromagnetism is a new
and unknown field full of unsuspected effects - this problem has
been well-understood for over 100 years.

Perhaps the O/P should contact the manufacturer and suggest they
stamp their armatures slightly concave in future.

It might be worth looking into the power source for those devices. Too
much voltage will likely cause them to be too strong.

It's the residual magnetism that is causing the problem; if the main
magnetisation is above a certain minimum level, the residual is not much
affected by any extra energisation. The limit to the power source is
more likely to be the temperature rise of the energising coils.

I don't know how the O/P's system is arranged, but I think the UK ones
have the magnets in series around the building, so that the circuit can
be broken near any doorway and all the doors on that circuit will shut.
In that case the PSU would either be constant-current or would have a
transformer with adjustable tappings which can be set according to how
many magnets are in circuit.


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.


--
~ 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 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.

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