Elk M1: Need small 250ma door strike power source

[Casher]

Greetings!  I'm trying to add a single 12v electronic door strike to a small M1 system.  Existing power draw is limited to three keypads, three Optex motion sensors, an an 8-relay board with only one relay firing at a time.  As a result, I would think I could "steal" the 250ma max I need for the door strike from somewhere.  One thought is the smoke alarm power circuit since I'm not integrating smoke alarms. 
 
I know the 'right' way to do this would probably be to install a stand-alone power supply for the door strike, but I'd prefer not to.  Any help would be appreciated!  I did search and review topics under "ELK power" prior to starting a new thread so I apologize if this has already been covered.

 

[BraveSirRobbin]

From the Elk M1 Installation Manual:
 

UL Commercial Burg requires 4 hours of standby power. Limit combined continuous current draw from terminals +SAUX, +VAUX, +VKP, and connector J16 to 450 mA max. and use one (1) 8 Ah battery. A supplementary UL Listed, Battery Backed-up Power Supply must be connected to power additional Keypads and Expanders if the combined continuous current draw from terminals +SAUX, +VAUX, +VKP, and connector J16 exceeds 450 mA.

 
So that would leave only 200mA to operate your keypads, Optex motion sensors, and 8-relay board.  The operating currents of each of those devices should be available via their specific manuals.  I think a good practice would be to leave around a 15% overhead as well.

 

[gatchel]

I would not recommend running a door strike off ht e M1 main power. Anything is better than that, even a 12vdc wall wart.

 

[BraveSirRobbin]

I would not recommend running a door strike off ht e M1 main power. Anything is better than that, even a 12vdc wall wart.

Not knowing all the specifics of the particular door strike in mind, some merit should be given to emergency/backup power during the need for a quick egress.

 

[gatchel]

Not knowing all the specifics of the particular door strike in mind, some merit should be given to emergency/backup power during the need for a quick egress.

Door strikes should never require anything more than turning the lever set / knob set to egress regardless of fail safe or fail secure strike configuration. For ingress, yes a backup power system would be nice but a key also would work in the rare event of a power failure.

To add to my original thought above...

Assuming the strike is fail secure (power to unlock) the OP could probably get away with 250mA for a short duration depending )5 seconds) on the total current draw of the system even if it equaled 100% of the system capacity. While it' is not recommended it would work. Don't forget to take in to consideration that you should size your power supply for the maximum load of the system. All KP's, Motions, all aux relays turned on, siren sounding, etc... should be taken into consideration.

I was more concerned with a electrically noisy door strike on the same power bus as the panel devices. Some strikes are electrically "cleaner" than others.

As a side note, there should also be a suppression diode installed across the strike wiring (assuming DC power)at the door regardless of where the power comes from.

 

[Casher]

Thank you all for the prompt responses.  I'll heed the advice and just go with a 'wall wart' 12v stand-alone power supply.
 
Gatchel - you mentioned the supression diode and I understand why such is needed.  I'm going to trigger the fail-secure door latch with an Elk-M1RB and the manual says it has diode protection across the relay coil.  Do I still need another diode at the latch if I'm using an M1RB?

 

[Del91574]

Gatchel has it correct. Strikes and door hardware should be free egress, otherwise a lot more needs to be considered, such as panic hardware, buttons to break power to the strike, fire alarm interface, etc. etc. When considering access control, you need to take all thought of an end user out of the equation in an emergency situation otherwise you're just creating a fire trap.
 
As for suppressors, honestly,  it depends on the strike and if it's a quality unit or not, whether or not a supressor is needed or recommended. Most of the more modern, quality units work fine without a supressor installed. In many cases, the diode (which is all they reallty are) is installed to help collapse the magnetic flux that is generated by the solenoid of the strike (or maglock). I can't think of the last system or manufacturer (besides Northern) that specifies they should be installed, and that includes Amag, Advantor, Cardkey, Casi, Software House and Linel. ACS panel hardware now is far more sensitive than most alarm panels, IMHO....they have NIC's and are basically small computers now. Can a strike be noisy and generate EMI...sure, have I seen it recently, can't say so, and this is on sites with upwards of 3000+ access controlled doors, various hardware, maglocks, strikes, electrified handsets, electrified crashbars, automatic opener doors with sequenced locks, etc.
 
In the case of power considerations, usually in the case of a strike, I like to oversize the supply by at least 20% vs the listed current draw and plan for the inrush current headroom on the supply for when the solenoid first fires.

 

[gatchel]

I am old school when it comes to a simple diode on a strike or relay. I was trained by someone who had 20 years experiance 15 years ago and was very meticulous. Here is the thought, a 1N4001 diode cost a few pennies in 1000 qtys and they take no time to install since you are already connecting the wires at the strike anyway. I have had boards that had lock up problems stop locking up after installing doides across the strike. It only takes 1 warranty service call to cover the cost of a ton of diodes.
 
Casher- A coils is a coil. The relay coil  has a diode across it for this exact reason. It's also good engineering which I have also been told by my HAM buddies and electrinocs guru's.
 
The strike is also a coil. I would install a diode across it at the strike location splice point.

 

[Casher]

I appreciate all of the experience on this forum.  The strike is a Seco-Larm SD-995C.  I'm happy to install a diode across the strike contacts at the strike for safety's sake.  I'll have to grab a diode from Radio Shack.  If anybody could please point me in the right direction of which diode - I've been told both a 1N4001 and a 1N4004 (by Seco-Larm) and it would also be appreciated for a 'diode newbie' to know which way to wire the diode, I'd appreciate it.

 

[gatchel]

The higher the last number in the diode relates to the PIV of the diode the higher the number the better in so many words. If they recommend a 4004 use it. The diode would get wired like this. Twist the positive supply and the positive strike wires together. Add the stripe side of the diode to this connection under a wire nut or other connector. Twist the negative power supply wire and the negative strike wire together, then add in the opposite side of the diode to the negative connection. It will look like a sideways "H" with the stripe on the diode going to the red (positive) wires.