Quick Question about Alarm System Battery

Discussion in 'The Projects Forum' started by freemindbmx, Mar 11, 2014.

  1. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    So I was thinking of making a home security system with a couple of PUT's to make an oscillating circuit and have two 2n222 stacked to amp the signal from the two PUT's and have a Relay/2n222 set-up to keep the alarm circuit running when someone intrudes, and i'll also have a set-up that'll allow me to check to see if all the doors are closed and that the system will work when needed. This system requires 12v and less then 1A.

    My questions:

    It says that most people use a 12v battery and charger to run it, I was just wondering why. For emergencies I'm guessing, when the power goes out. And would it be ok to just use a AC-DC adapter? I'm guessing not, since it needs a uninterruptable charge from the source. But im not 100% on this one.

    And secondly, if I do get a battery. How would I set it up. I know the battery will hook-up to the circuit. But for the charger....Do I just run the battery for a couple days then unplug and charge and repeat???
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    Its usual to have the 12V battery powering an audible/xenon alarm as well as the system itself, thats why a battery rather than a simple wall wart being used to do both jobs.
    ie; if the mains failed so would your audible alarms or xenon flashers.

    For the battery , most use a SLA, sealed lead acid, these can be permanently be connected to the suitable charger which has been set to give a 'float charge' in order to keep the battery topped up.

    It is advisable to allow the battery to occasionally discharge down to say 11V and then fully recharge, this will tend to reduce the sulphation of the battery which may occur due to being left on float charge for long periods.

    E
     
  3. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    So I would connect the charger to the battery terminals and the security circuit to the battery terminals?
     
  4. #12

    Expert

    Nov 30, 2010
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    Yes.
    ......
     
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
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    You really need a battery in your alarm control panel and your outside alarm bell box. It's not beyond the realms of possibility for burglars to either cut the wire to the external bell box or even to remove it from the wall, either way you need the sounder to go off if this happens even though it may only be for seconds before it's disabled.
     
  6. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    I was just confused b/c I was worried that if I solder the Battery Charger Terminals to the Battery Terminals and then solder the Alarm Circuit to the Battery Terminals as well. It'd get fried b/c it'll have two kinds of power sources, powering it.
     
  7. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
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    I would recommend on any SLA battery powered system that a suitable fuse be fitted in the +V connection to the battery, close to the battery.

    Connecting the battery/charger and the system the way you have described is the usual way.
    However I would never solder terminals to a SLA, use the 0.25inch push on receptacle tags to connect to the SLA.

    E
     
  8. Hariharan Ayyasamy

    New Member

    Mar 7, 2014
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    better connect the charger terminal to the battery terminals and the alarm system parallelly and then connect the negative of the battery to the alarm system directly. connect the positive terminal of the battery to the system using a normally close(NC) relay. use the supply from the charger as trigger supply to the relay.now if the current fails then the battery power takes on...
    just a suggestion but probably will work out....
     
  9. #12

    Expert

    Nov 30, 2010
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    Just using a diode will probably "work out", too.
     
  10. freemindbmx

    Thread Starter Member

    Mar 5, 2014
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    Ive been looking up other ways to have more fail-safe methods but just to be clear about my original way of hooking it up I posted a picture of a semi-block diagram with polarity connections. And I like the idea of Hariharan's way. But in the mean-time while I try to make it I would like to hook it up this way.
     
  11. #12

    Expert

    Nov 30, 2010
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    That should work.
    The worst thing that might happen is that the battery tries to power the charger when the wall voltage fails. A simple diode between the charger and the battery will fix that, but it isn't likely that you will need a diode. Just measure and see if any current is running backwards into the charger when you unplug the charger.
     
  12. freemindbmx

    Thread Starter Member

    Mar 5, 2014
    72
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    Incase it is running backwards into the charger, just find a Diode that has values around with what im using and place it on positive lead of the charger and connect to positive of battery, correct.
     
  13. #12

    Expert

    Nov 30, 2010
    16,320
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    Right.

    There is still the concern that a diode will reduce the charger voltage too low to keep the battery healthy, but some chargers are just too high of a voltage. You're going to have to measure to find out.

    My electric start lawn mower came with a charger that would have ruined the battery in a few weeks. I just built a regulator for it. Now it works right.
     
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