Magnetic door holders question

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.

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.

All the speculation is based on the conclusion that residual magnetism is t he 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 multimet er 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.

the problem, and that may be premature.

nd see if it sticks to the magnet. If it does (which I doubt) put a multim eter on it and confirm the power is really off. Then use the spring scale to see how hard the steel sticks.

Er, shut, I mean.

of these buildings in the common hallways employ electromagnetic units moun ted 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 w ell which are always applying a force in the opposite direction to try to c lose the door.

oors are supposed to be automatically pulled closed by the force of the pne umatic unit. This doesn't always work because in spite of the opposing forc e applied by the pneumatic unit, in many cases the electromagnets seem to h old enough residual magnetism to keep disks from releasing and the doors fr om closing. It often becomes necessary to increase the opposing pneumatic f orce tremendously in order to overcome this.

units and in all but one instance have received the same bullshit answer t hat they've "never heard of this".

rsing 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.

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 cem ents 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 ha ve never seen residual magnetism sufficient to hold the door. Neither plate nor magnet has enough mass for that.

Peter Wieck Melrose Park, PA

Good point! Thank you for the reply.

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

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

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

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

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

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

then lube hinges with a drop or 2 of

at HD