Bad practice or not?

Discussion in 'Homesafe & Security Access & Control' started by zx9, Apr 26, 2012.

  1. zx9

    zx9

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    Wire a door strike using the alarm backup battery as the power source?

    Recently during a power outage I was able to disarm my ness alarm via the reader yet unable to enter as the door strike was wired up using a separate 12v power supply. As I only have one strike that draws 12v150mA I was wondering would it be wrong to wire it to use the 12v ness backup battery (right next to the relay) as a powersource instead so that it would always work. I assume I could isolate the circuit using a diode or something if needed.

    can anyone tell me if this is a bad idea and why?
     
    zx9, Apr 26, 2012
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  2. zx9

    mdooher

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    Normally I power the strike from the alarm panel anyway..so then the backup part is automatic..

    normally the strike has a flywheel diode built in, if it doesn't the instructions should tell you to add one anyway

    As for powering the strike straight from the battery.. I run various things from my backup battery (small sine wave inverter for my gas fire and gas califont, and a couple of random 12V devices). I just made sure that the battery and the charging circuit are sized accordingly
     
    mdooher, Apr 30, 2012
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  3. zx9

    tobex

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    You need to decide if you want failure to open the door or close the door.

    For example. In the event of a fire, some clients will have the garage door open so that the fire brigade will use the internal door and not smash the very expensive front door. So the roller door opens to let people have access to a more conventional door they can unlock with a key or axe through. The damage would be much less.

    As a rule, if you need access in the event of a failure, you need to provide

    a) A path of less resistance

    b) Opens on fail

    c) Key operated if the failure makes it closed.


    A battery is only good for DC door strikes. Some are actually AC. So it can get complicated.

    As a guide, I would isolate the door strikes with a cheap but extremely effective UPS. The powerboard that plugs into the DC adaptor can be driven by a 500Va UPS for quite some time. The onboard panel batteries are very small. So having a UPS externally also gives you one more level of surge protection.The wholesale price of a UPS from such brands as APC / Merlin is about $120. This then stops your alarm panel from having too much power drain.
     
    Last edited by a moderator: Apr 30, 2012
    tobex, Apr 30, 2012
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  4. zx9

    zx9

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    thanks

    thanks for your feedback...

    I went ahead and did it and don't have any problems as yet.

    Ness installation manual recommends using a separate power source for anything above 12v100mA - the strike is 12v150mA which is why it had a seperate power source. I couldn't see a diode on the strike but I imagine it is inside. The strike is DC.

    The only reasons for my hesitations was any current drain by creating a circuit between the ness relay which has very low power and the ness battery.

    Also as a x firefighter I never deadlock my doors when home. The strike is only used on entry. Normal door handle is used for exiting.
     
    zx9, May 1, 2012
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