Solve The Problem: Sticky Maglock

Here's a common maglock problem that leaves many access control techs scratching their heads.

Your customer asks you to fix a problem with this door:

Everything works great, except one side of the maglock seems to hold the door closed a split second longer than it should - it almost seems 'sticky' - a user has to push on it hard to open it, with noticeable 'pop' and maybe even some door vibration. Over time, the door could bend and not lock correctly, or someone might even injure themselves trying to force it open.

After you inspect the maglock, power supplies, and access settings, everything seems correct. The lock wiring is in good shape, there is even an MOV/diode installed at the lock, and the controller is opening the lock contacts as it should. At a glance, everything looks the same as another door nearby, except that door works perfectly.

The customer thinks the $1800 maglock must be bad. Your company installed the lock 11 months ago, so the customer is asking for a warranty replacement.

What do you think?

Have you ever experienced this problem in the field?

What should you do first?


Have you checked the relays inside the maglock to verify that they both release cleanly? These relays have been know to stick and the replacement cost for the relay boards is minimal.

That is a good (cheap!) troubleshooting step to take. Over time, lock contacts could oxidize or 'get burnt' and cause malfunction. Bond sensors seem to be especially bad at failing over time, and may need the be swapped out.

However, let's say you check the lock's contacts and everything is in good working order. What's next?

I do not know what I am talking about :)

never done maglocks

but how about demagnetize lock/plates

Yes, I agree with Alex K. that magnetic hysteresis is possible here.

Suggestions:

  1. Switch plates, if the problem follows the plate, get a new plate (or deguass), if it stays on the same side then
  2. Remove plates and place a ladder(s) underneath the door jam, with something soft to catch the falling plates.
  3. 'Lock' both plates to magnet
  4. Disengage lock by cutting power at the supply if possible.
  5. See if they fall at the same rate
  6. If they do, then try to disengage thru the normal button

@Brian, are there two independently controlled magnets or one? If there are two then maybe one of them is sticking the one side a bit. Also when you say that the "maglock seems to hold on a spllt second more than it should", do you mean that if you wait a second before trying to exit then its ok?

Degaussing coil may help

If the maglock already has a built-in MOV installed, adding a second can have this effect.

Also, if you are switching ground instead of positive voltage, this can also have this effect.

ps. That REX motion is mounted backward.

ps. That REX motion is mounted backward.

+1 bonus point! lol.

Is there only a single MOV/Diode? It sounds like the collapsing magnetic field of one coil may be inducing a burst of current into the other coil.

There is a potential ground issue as well. When a power supply isn't properly grounded, the maglocks become "sticky". As in, it takes a brief moment to drain off the residual voltage.

We sometimes "dimple" the lock. Using a linemans pliers hit the mag lock sharply with the edge of the pliers to raise a tiny dimple in several places on the magnet. Overall it lessens the holding force of the lock but depending on the lock and it's application this works.

Besides damaging the lock and voiding the warranty, what is the point of marring the face of the magnet?

I think it is a new way to be efficient. You can decrease the holding force of your expensive magnetic lock, possibly damage your linemans pliers and potentially send metal fragments into your eyes or skin, all at the same time! Imagine the added benfit if your customer sees you forcefilly beating your tools into that equipment.

I am reminded of the old Samsonite commercial filmed in the baggage sorting area of an airport with the Gorillas beating the hell out of the luggage!

"Jus git a bigger hammer Earl, and womp it good! That'll teach that stupid lock who's boss." Doh!

Besides damaging the lock and voiding the warranty, what is the point of marring the face of the magnet?

Dimpling...

1. disrupts the formerly even and formerly parallel electromagnetic lines of force traveling between poles, because of introduced surface irregularities, thereby reducing holding force,

2. creates random protruding surface aggregations which occlude the ideal mating of magnet and plate, effectively increasing distance between the same, thereby reducing holding force,

which may have the intended effect of eliminating the "stickiness". However the resultant reduction is hard to estimate and, (in addition to the voiding warranty), will likely have the unintended effect of reducing the max. holding force for the maglock by as least as much.

Troubleshooting the sticky side of the maglock.

1. As mentioned previously, check to see if there is a separate feed for each of the electromagnets. If so switch the feeds and observe if the stickiness follows the feed. If there are two feeds and the stickiness follows the change in feeds then check the lock power relays (Altronix or equal) to see if they are sticky.

2. If there is only only one feed, switch the internal maglock circuit boards to see if the stickiness follows the change.

3. If there is no change in step 2, change the order that the internal maglock circuit boards are feed (which is first in the parallel circuit).

4. If none of this makes a difference remove any MOV/diodes and check again.

5. Last, but not least, if none of this makes a difference switch (assuming the posulated good maglock is the same as the sticky one) and see if there is a change in behavior.

I would be suprised if at this point you have not isolated the problem with the lock, the lock relays or the lock power supply.

Incidentally, testing the lock does not require removing the plates from the door- a screwdriver or any ferro-magnetic object will fall to the floor just as surely when the field collapses.

Incidentally, testing the lock does not require removing the plates from the door- a screwdriver or any ferro-magnetic object will fall to the floor just as surely when the field collapses.

That's true of course, and the simplest course.

The thought behind detaching the plates was just to rule out the possibility that the steel had become partially magnetized somehow or was especially prone to a lingering hysteresis, as well to reduce the number of troubleshooting steps.

Thanks for the responses everyone.

In most situations, maglock 'stickiness' is attributable to power. In the situation described above, the 'MOV (metal oxide varistor)' or diode is a good place to start.

First, it is important to verify whether or not the lock actually needs an external MOV/diode. Many installers simply get into the habit of including them and add them without thinking if they potentially can cause issues.

Many new types of maglocks include internal MOVs and do not need a separate unit installed. See this RCI installation clip with the emphasis underlined:

Also note the importance polarity can play in wiring maglock RTEs for best performance. In this RCI example, connecting the RTE interupt (pushbutton or PIR) on the wrong leg may cause the bond to collapse more slowly than expected.

Secondly, confirm the MOV/diode is connected properly. Catch this Securitron instruction below:

In this case, an external MOV is recommended, but installing it backwards changes the behavior of the component and can cause 'sticky' locks.

Ignoring the role of these small components is no answer either. MOVs/Diodes are commonly specified or included with electronic locks to prevent long term damage to supply sources when the lock's electromagnetic field collapses. The field collapse causes an effect similar to 'backfeeding' into the power conductors. Over many thousands of cycles, this can damage power supplies or connected controllers.

In any case, residual magnetism is related to the presence of electricity (ie: capacitance) in the lock circuit. Degaussing the armature or 'dimpling the lock' are unnecessary and likely would have unintended negative consequences!

Props to Tyler Graham, Timothy Mc Pheron, and Bryan Kirkland.

Stay tuned for the next access problem: "Why did my proximity cards stop working?"

Good lesson learned about not doubling diodes!

But, I'm confused though, are there two armatures at the top of the door or just one? I thought there was a working side and non-working side, but now I don't know...

...except one side of the maglock seems to hold the door closed a split second longer than it should...

We can't make these too easy. :) Like many with experience will attest, troubleshooting in the field often throws wrinkles into properly diagnosing root causes.

Even if a double maglock is installed with a single MOV (there are dual magnets with discrete leads in the market for specialty applications), the ill effects of capacitance may only be seen in one coil pack. However, the MOV/diode is not performing it's proper function in either.

In this case, an external MOV is recommended, but installing it backwards changes the behavior of the component and can cause 'sticky' locks.

Since a diode and a resistor are cheap yet vital, what is the reason that ANY maglock would not have them built in?

Degaussing the armature... [is] unnecessary and likely would have unintended negative consequences!

Unecessary yes, but what negative consequences are 'likely'?

We can't make these too easy.

LOL! I missed that fact that you made them at all... I thought it was a real customer and a picture of a real sticky glass door (like that other glass door question, written in a similar tone). In retrospect, its pathetic to see me taking pains not to 'dimple' the hypothetical, non-specific plate(s).

...underneath the door jam, with something soft to catch the falling plates.

$1800 Maglock??? Is it gold plated?

Reminds me of an anekdote I once had.

I recieved a support call from a customer saying that their door wouldn't open.
I went over there and they had a maglock holding the door shut. I tried to get it to open, and indeed, it wouldnt budge. So I started to measure and noticed that the maglock wasn't getting powered. Which was weird, cause the door was still shut. I was starting to question the law of physics and started to unscrew the wires in case my meter was broken.

Yet to no avail. The damn door wouldn't open.

So I did what every technician would do. Use brute force. I slammed my large screwdriver between the maglock and the plate and excerting force. Finally I got the damn thing lose. And to my suprise, the plate was fully covered in sticky residue.

So what happened ? Well, apparently, the local lads thought the door falling shut would make quite a noise. So they stuck a few strips of isolation tape on the plate on the door. They then quickly found out that the door wouldn't lock, cause yeah, the plate isn't connecting anymore with the maglock. So they tried to remove the tape. But as we all prolly know, isolation tape doesn't remove so easy. So they only pulled off the foam, but the sticky stuff was still there.
THis then 'glued' the door shut.

After some chemicals I managed to get the damn stuff off. But it really made me question my sanity for a second there that a powerless maglock could still keep a door closed.