Automatic fire door release troubleshooting

Status
Not open for further replies.
ultramegabob

ultramegabob

Senior Member
Location
Indiana
I have a customer that has a magnetic door release on a fire door on his building, It has 120 a.c. to the device (it is designed to work off of 120v.), but does not hold the door open, I checked for continuity on the coil of the device, it appears to be open, I am assuming that it is defective. normally I would have thought this would have been a low voltage d.c. circuit, How does the electromagnet in this work? does it have a built in diode that converts it to direct current to make the magnet work? Is doing a continuity test the proper way to troubleshoot this device? thanks....
 
Bob, I'd say that, if it's rated fror 120v, and it's receiving 120v, and it won't hold the door, it's defective.

Unless the problem is mechanical, like the plate not being free enough to meet the magnet squarely.
 
ultramegabob said:
Larry, I guess I am trying to understand exactly how a 120v a.c. magnet works.
Click to expand...

its like this:

when you put the power on, the magnet sticks to metal. and when you put the power off, it doesn't.

yours doesn't when the powers on, so its broken.


:grin:
 
nakulak said:
its like this:

when you put the power on, the magnet sticks to metal. and when you put the power off, it doesn't.

yours doesn't when the powers on, so its broken.


:grin:
Click to expand...

I use a similair theory on lamps :D

but Don's answer was a bit more enlightening
 
At the bare minimum, I would assume it needs a diode to change the AC to DC. I guess it could even have a more complex AC to DC power supply.

If it does have a diode, you should try checking continuity twice- once with the meter leads reversed. That way, the diode won't trick you into thinking its just an open circuit.
 
It probably does not have a diode, all the ones I've seen are AC coils. More likely is that the door plate doesn't sit flat on the magnet. If the plate is not completely flat on the magnet it will not stick.
 
may I inquire as to the system brand name and some more pertenant info. lets look at in a lighter sense..think of it as a piece of iron with a winding on it and when energized it is a magnet, denergized it is piece of iron with copper around it.
 
Last edited:
whillis said:
It probably does not have a diode, all the ones I've seen are AC coils. More likely is that the door plate doesn't sit flat on the magnet. If the plate is not completely flat on the magnet it will not stick.
Click to expand...

I'm not really familiar with these. I guess I was thinking about a motor, and assuming the same principles apply. A magnetic field in one direction causes attraction, and when the field reverses, it repels.

But on second thought, I guess that's only true because the motors rotor also has a magnetic field. A door doesn't have any magnetic field, its just a chunck of metal. So it doesn't matter which way the magnetic field runs, and it doesn't matter if AC is applied.

Either direction of current flow still pulls the door in to complete the magnetic circuit.

Does that sound right?
 
Steve,
Yes, that covers most of it, except the fact that when the voltage is at zero (at each zero crossing of the sine wave)the magnetic force is also at zero.
 
Status
Not open for further replies.
Top