coil whine on electrified lockset and other questions


Active Member
So I do not like the currently trending electronic locks with any technology/protocol and I hate it with passion if they are cloud based. I bit the bullet and went ahead with electrified cylindrical locksets from SDC to retrofit my front and rear doors.
They are Grade 1, very nice finish, very solidly built. I had no difficulty installing them, I have foam-filled metal doors, and was easy to drill through. I got the fail-secure version, and these are egress compliant, always open from the inside. Perhaps I will write up all the detail in a blog if there is interest.

​I wired them as 12 VDC, and connected it with my Elk M1. All works as expected, except the locks came supplied with a "power regulator" which according to the manual reduces power consumption. It does do so, but also causes an audible whine from the coil inside the lock. My ears have had their fair share of abuse, but I can hear this from rooms over. The metal door likely also amplify it and it is a very high pitched, pulsating whine that is hard to ignore. I reached out the SDC, but not getting through or got any response.

​If any of you has experience with this brand, make: SDC Z7252   is this normal?

​The PR7200 power rectifier seems to be a small PCB with few components in heatshrink tube, likely acting as a pulse width modulator (PWM), turning off and on the power very quickly and thus saving power, but also causing the whine.
​Without the PR7200 the lockset is silent and works fine, it does however become warm to touch, not hot, but warm enough that when you touch it, your brain senses that it is not cold metal. According to its datasheet, the lockset pulls about 600mA at 12 VDC and half of that at 24 VDC. With the power rectifier this is much reduced, to about 0.15-0.20 A at 12 VDC, not sure how accurately measured it.
Another question I have is that the lockset comes standard with a Request-To-Exit (REX) output, with Common. and N.O. and N.C. wires. I do not completely understand the function of these, especially on a egress compliant, fail-secure lock, but it seems that the NC connection is broken and the NO shorted when the lever is depressed.
Thanks for sharing your thoughts.

The coil shouldn't be making noise on a fail secure lock in standby period. It also shouldn't be warming up unless you're running it unlocked for a period of time (schedule).
I'd ask SDC if it were me. Basically, you should hear a small click when the solenoid pulls in and the same when it releases.
Since you've got the M1, I don't know if you're running a KAM or straight through a relay and controlled via another means. The programming should be (not verbatim) output fires for 3-5 seconds max and relocks on door open. That's it.
The REX is for connection to an ACS that would be used to shunt the DSM for alarm purposes.


Active Member
Thanks Del, I had hoped you would chime in. I have no KAM, hooked it up through a relay output at the panel. Both doors have a keypad next them and simply configured a function key to toggle the output. You said something that caught my attention: is the solenoid not designed for sustained opening? Like keep the lock open for few hours depending on situation?
I will setup keyfobs to open it from the outside, but needing to unlock at every entry will kill my WAF
You can drive them to be unlocked, however you're going to shorten the lifespan and the lock will heat up, period. Anything that is running on continuous duty is going to wear faster than something that is momentarily unlocked.
I can't comment about the SDC and hold voltage on the solenoid, but you might want to look at a HES Smartpak and see if that'll work in your application. We really don't use SDC hardware too often. The whine doesn't sound normal to me.
If you have a KP in the vicinity, I'd put in a prox reader off of that and call it a day. No maintenance and easy to use, unless the WAF doesn't like prox fobs.
The only other item to consider is where you're getting the power from for the lock....?


Active Member
Thanks a lot, this was helpful. Just to be clear, the noise is in the unlocked state of the fail-secure lock. When locked or fail-secure, it is silent. It is also silent when unlocked if I do not use the supplied power rectifier to reduce power use and decrease temperature, but then it warms slightly up. Will try the SmartPak, maybe uses other technique to reduce voltage as is described in its cut-sheet.

​The reason I am going this extra effort with the electrified lockset is that the most I can hope when my family leaves home is that they will press a keyfob button and this would lock the doors, and arm the security system. Hopefully will not jinx my luck but we live in a low security threat area. My neighbor has not locked his door for the last 25 years. Our rear door is also left unlocked a lot of times.
​Recetly there were a number of burglaries in the neighborhood, mostly described as tief entered through open door or window. Could be a bored teeneger or something more serious. The way we live, when we get home, all doors will get open (in the lucky case they were locked) and they are so unlocked until we go to bed. That is about 5 hours/weekday, more like double on weekends. Hence I chose a fail-secure lock.
​Should have I chosen the fail-safe locksets, assuming that those are designed to be energized continuously to be locked?

​I used 22 gauge wire for the power to the lock, distance being about 25 feet of wire. I can measure 12.3 volts or more at the door, so voltage drop seems not to be an issue. the specified gauge however is 18 gauge.
​I have tried one of the locks with 16 gauge wire about 5 feet from the panel, and still got the whine when used the power rectifier.

​These power rectifiers, like the SmartPak need to be installed at door side or panel side?  Will have problem at the door side as the space to tuck away wires and this is very limited.
​The fact that I have two locks both showing this symptom is suggesting something is wrong with my install...

​One more question: could not find any info on the expected life of these locksets, in comparison strikes and maglocks have number of entries stated, but this does not have any like that. Sure running it a lower power will extend the life, but from what to what?


Senior Member
I don't see any reason you couldn't install the voltage regulators in your panel rather than at (or in) the door.   They are most likely switching voltage regulators, which run at high frequencies, resulting the noise you hear. 
The SDC installation instructions contain a comment that says the regulator reduces the voltage, which reduces the operating temperature.  That makes it sound like the lock can be used in a continuous duty mode.  If the solenoid were being activated for just a few seconds, it would have no effect on the operating temperature.  It's strange that they don't mention continuous duty at all, though.
It's hard to say how much the life is shortened by higher temperatures.  In general, heat is the enemy of electronics, and components like a solenoid need to be designed for continuous duty to have a reasonable service life.  Otherwise, they will fail sooner rather than later.
A good question to ask SDC is whether these locks are meant for continuous duty or not.
Electrified hardware can be used in continuous duty, the only difference is the overall lifespan of the device. A lock that only is unlocked for 1-5 seconds at a time is going to last longer than a lock held unlocked for 4-12 hours at a time. From dealing with handsets all the time, the solenoid coil either burns out or the return spring on the plunger fails and ends up causing the solenoid to fail.
Normally you would install any regulator (different from a straight rectifier) at the door as close to the lock as possible to help negate the effect of voltage drop. The "smart pack" devices reduce the voltage from the initial full voltage to a "hold" voltage that keeps the solenoid pulled but at a lesser voltage (no inrush). What you would not want to do is install a device that drops the voltage down first thing in the circuit, then pass the lesser voltage through a length of cable to a device that needs a certain voltage to function properly (inrush). This is why on larger locking hardware (VonDuprin crash bars for example) the supply is located as close as possible to the door and heavy AWG cable is specified. The devices need to be installed at the door/hardware themselves.
600 mA on a 22 AWG is pretty light.
You should be able to make enough of a pocket in the door, assuming steel/foam core, around the butt side of the rosette. Basically there should be enough room to drive a truck through once you get past the wood edge of the door.


Senior Member
@DEL - I agree with you in general - much better to locate the regulator close to the load it is driving.  But in this particular case, the OP has only 25' of wire between the panel and the lock.  If he were to replace the 22 ga wire with the recommended 18 ga, that's only 0.32 ohms, and with the inrush current of 600 mA, would result in a voltage drop of 0.2V.  In this situation, if he located the regulator at the panel, I think he could make it work.


Curious if the power supply itself is the cause of the noise. I wonder if a quick test where you power the lock just with a large 12 volt DC battery would have any merit (assuming it's DC powered solenoid)


Active Member
Thank you Both! I immensely appreciate your thoughts and suggestions. Will get a SmartPak to see if it will make a difference and will report back.
​While re-reading the thread realized that I did not address a question/suggestion from DEL: I got power for the locks from a brick 4A 12VDC switching power supply, and later I added an ELK-P212S that I had lying around, thinking that it needed cleaner supply. I believe the P212S is a filtered and regulated supply, Got the same result for both.



Active Member
This is scary... in a funny way...
​So I started drafting my post probably few hours ago, and now when I pressed post, noted the the conversation on this...


Active Member
And I did not think to try it this way, but it was easy to try, BSR, I used my spare ELK battery to get the same effect, I guess it is official that it is a noise generated by the supplied power rectifier.


Active Member
Just speculating... if the rectifier really is a PWM device that saves power by rapidly switching the coil on and off, the coil itself could be singing. If that is the case, where you mount the rectifier will not affect the sound much. Might even reduce it some with the capacitance of the cable. I'm not sure I'm entirely following the conversation though- did you say that the lock is silent with any supply unless the regulator is in?


Active Member
Yes, the lock is silent with any supply if the rectifier is absent, and yes the noise is from the solenoid in the lock not the rectifier.