Wiring Door Phone Card and Strike

[htr]

I have an installation that requires me to wire-into an exiting door strike that resides on a access control system. I am looking for a second option on the wiring, the first opinion is mine *smile.
My thoughts:
Use a DPST relay that will act as an isolation relay as wel as a device to through the strike. I believe the existing strike is 24vdc. My biggest concern is running power through the door phone card contact. I am not sure of the power rating on the card termination points. If the strike is DC, I can use the door phone contact to break the ground, providing an incomplete circuit.

Does this make sense to anybody? This is my first shot at doing this, I prefer not to let the smoke out of any boards, if you know what I mean.

Thanks,
Chris

 

[mrpeabody]

Take the door opener unit apart and look at the rating on the relay inside.

 

[Phoneguy65]

The safest way to integrate with the door strike would be through an external relay. The internal one will pass about 100ma at 24vDC without difficulty (this is a close guess, but my manuals are at the office) but it's always a good idea to put a reverse biased diode across the coil to prevent back EMF when the field collapses.

The contacts are N.O. and the KSU will strobe the requested contact closed for 5 seconds when triggered.

Unless I am installing the strike, I use an intermediate relay to protect the KSU card. (if the strike type changes later, you risk the possibility of a non compatible one being out into service.) So use an external DPDT relay, a diode, and a small 12vDC wall wort PSU to power the circuit. That way you get the best possible scenario: N.O. and N.C. contacts if needed, or you could parallel the contacts to provide a bifricated contact system that will likely last a heck of a long time. Plus, if something ever causes high current on the strike circuit, $5 at radio shack and a few minutes later and you're back in business.

Good luck,


Pat MacKinnon
Omni telecommunications Inc.,
London, Ontario, Canada
omnitel-ca

 

[htr]

Phoneguy65,

Thanks for replying. I actually completed the door integration with the phone system last week. My design matched yours exactly (except the diode). Since I used a between the lock and the door card, I didn't thinkg I needed the diode, though now that you mention it, it is not a bad idea to have as a saftey. I figured it was best to install an isolated relay powered by a "wall wort p/s".

Thanks again for the input.

Chris

 

[Phoneguy65]

Exactly, but a back-EMF proection diode is always a good idea when the coild are being powered by DC. Just remember, you can't employ them across AC powered coils.



Pat MacKinnon
Omni telecommunications Inc.,
London, Ontario, Canada
omnitel-ca

 

[BTBZ]

The door phone Mod can handle AC or DC Volts careful amp rating.