Comments on: External Filter Capacitor for Cisco Physical Access Gateway

By: Keith Neufeld

Keith Neufeld — Sun, 06 Dec 2009 01:20:24 +0000

John, my experimentation with external capacitors was never intended to be the production solution, but a test to see whether I could identify a means of keeping the gateways up.

For our building, we’re ending up using Cisco-recommended non-standards-based ethernet power injector / splitter sets, which have passed all tests on the bench and on real doors with nothing but installer-provided catch diodes. We’re using ethernet power because our generator only powers the computer room and the wiring closets, and we want the IT department to have full card access and logging even if utility power is out.

For other buildings on campus, we’ve already unanimously agreed that local, external power will be our preferred method.

By: John Edwards

John Edwards — Sun, 06 Dec 2009 01:03:39 +0000

What you’ve ended up with is a Rube Goldberg contraption that only you can support. An external power supply with 16 individually fused channels, battery backup, fire alarm disconnect, capable of supporting maglocks or any other lock hardware is about $200. POE is fine for indoor cameras, gateways and readers but to rely on it for lock power is asking for trouble. Running the extra wire is well worth it for a reliable system. Put an 18/4 along with the UTP and you will have the option of bailing out on the POE completely if need be.

By: Mike

Mike — Mon, 09 Nov 2009 11:51:36 +0000

Have you considered other options?
E.G.
http://www.hidglobal.com/prod_detail.php?prod_id=125

By: Keith Neufeld

Keith Neufeld — Sun, 08 Nov 2009 22:14:52 +0000

Mike, we’re ending up using a lower-power strike, pre-market non-standards power injectors, lots of firmware updates from Cisco, and some compromises on our part to achieve a system that we think we’ll be pretty happy with. So far we’ve only accepted one working test door, but we seem to be back on track and should have a complete system by mid December.

By: Mike

Mike — Tue, 03 Nov 2009 20:24:57 +0000

I’d be interested in the end result of this, since we’re going down the door access route, and Cisco’s product has already attracted attention from higher levels.

By: John Laur

John Laur — Tue, 04 Aug 2009 17:26:23 +0000

Of course the simplest solution is probably just to put cisco power injectors into the wiring closet on the door’s ports. A benefit here is cisco won’t be blaming you for problems when things go wrong.

By: Kevin

Kevin — Tue, 04 Aug 2009 17:06:25 +0000

Do you have two data jacks at each door? You could use one drop just for power, charge the battery and power the strike off of that one.

By: Kevin

Kevin — Tue, 04 Aug 2009 16:55:09 +0000

I have a Sprint USB “Aircard” that has a small lithium battery in the little dongle itself. It seems to charge most of the time then draw from the battery for transmit. Newer Sprint devices dont seem to need this.

Anyway, if your duty cycle is low you could charge a battery pack for fifty minutes out of each hour then draw quite a bit of current for the strike. That would put your average power real close to the minimum draw.

By: Keith Neufeld

Keith Neufeld — Tue, 04 Aug 2009 16:29:15 +0000

Tomaž, thanks for the clarification, and that’s a good observation. I’m not concerned about cutting off the forward flow if the capacitor falls below the forward drop of D2, so as far as I can tell you’re absolutely right. If we end up using this, I’ll definitely try it your way, since it looks equivalent and saves an unnecessary component.

Thanks!

By: Tomaž

Tomaž — Tue, 04 Aug 2009 16:18:15 +0000

Keith, I was asking about the significance of the diode D1, not the resistor. I understand you need the resistor to limit the peak current, but I believe your circuit will work identically without the diode D1.