Would it be possible to make a timer for an electromagnetic door holder. so the door is kept open for a fixed period of time.
Any idea how to do that? possibly using 555 timer

 

Hello,

How would you detect that the door is pushed against the magnet?
Do you want the timer to start when this has happened?

Bertus

 

yeah thats what i thought. But im not sure if the "dot" in the middle of the primary part is a switch? maybe i can use that.. I dont have the e-magnet yet.

 

The 'Dot' could also be a way of ejecting it to release the residual magnetic effect, or just be a small spring plunger to achieve this.
Otherwise normally with this type of electromagnet, the polarity if briefly reversed in order the plate does not stay attracted.
More info on the unit is needed in order to suggest what may work.
Max.

 

If a magnet holds the door open, applying power to a coaxial electromagnet that counteracts and cancels the magnet, will release the door.

In other words, an electromagnet with a permanent magnet core will release a door by a brief activation of counteracting electromagnetism at the desired timing, consuming no power at other times, and able to hold open again at all times.

A better system may use a light beam interrupter timed when trough-traffic has ceased, as in elevator doors. Many ways to do it.

 

Do you have a 'cut sheet' for the door holder assembly?

Having been a fire alarm tech for 15 years, it looks to me that the 'red button' is probably a test switch to remove power from the coil in the 'wall mounted' part that serves to hold the door. (The 'door mounted' part).

The wall mounted part should contain the coil, and it needs to be provided continuous power, usually 12, 24 or 110v AC or DC at approx 20mA.

Door holders require a source of power and a means to control them. This is usually located in some central location such a FACP or fire alarm control panel.

Detecting when the door is engaged with the magnet, while not a common thing to do, is an interesting project.

 

possibly using 555 timer

Only if your timed period is shorter than a few seconds. For longer time periods a CD4060-based timer, or a MCU, would be better.
How long a period do you want?

 

I hope your not paying to much for that it looks really cheap. A good one is around $150 and have built in board that tells when the door is shut
And they use way more then 20 mA add a 0 to that and your about close.
I'm sure you all thinking what do I know I just install 1200 pounders on bank doors and such LOL.
Banks use motion detectors. on the inside to let the people out and a camera and remote button to see if you don't look like a robber to let you in.

 

The one im getting is a better quality than the one on the pic.

It needs to keep the door open for 1.30 - 3 min or so.

Ill get my hands on it tomorrow and write out some details here

 

This the type of door holder I was referring to.

 

CanaKit makes some interesting adjustable timers. I threw one together that holds a drain solenoid open for 5 min on my garden tub.

 

Which supply voltage option?

 

I've seen these door holders in use for a fire door. In that use, the door is held open for an indefinite period of time. An alarm cuts power and the door closes, requiring a manual reset.

How do you see operating the door? Is it always closed, manually opened and kept open only for 1.5-3 minutes?

As others have mentioned, detecting when the door is open and engaged is key. AFAIK, these devices do not do that. They are merely a passive electromagnet, driven by an alarm system.

 

That's not so they make them that tell if the door is open or closed plus they also have fast open which reverses the power so they open faster.
But those are used to hold the door closed and are a lot bigger.
The ones I put in banks have built in module that can make on break or make on closed.