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Discussion in 'General Electronics Discussion' started by shumifan50, Feb 17, 2015.

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  1. shumifan50

    shumifan50

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    Jan 16, 2014
    I am now sort of settled in in South Africa, but have some issues that are power/security related. I hope to get some answers here. (My electronics projects are on the back burner for the moment until the more basic issues are sorted out.)

    I have a 12V electric gate motor, a 12V energiser electric fence(4 Joule), and a 12V gate intercom system. Each one of these have their own battery backup, but they typically use 7ah batteries that will last for about 4 hours if the power fails. They do a thing here, called 'load shedding', where power is interrupted for certain areas. These power cuts typically last about 4 hours, but rumors are that they are planning power cuts of up to 10 hours, in which case these little batteries will be of little use. Also note that the electric fence energiser has a radio connection to the alarm system and will alert armed response if triggered.
    I have bought myself a 6kva generator and this will see me through any power cuts provided I am at home to start the gennie. However, if I am away it could leave the property unprotected and as these power cuts are advertised, the thieves know which areas to target.
    So after that ramble, finally the problem:

    I would like to use a large car battery as backup to all the systems at the gate(say 70 or 90ah) connecting all the devices to this battery instead of the little battery in each unit.
    1. Will it be OK to use a normal charger/conditioner charger to charge the battery? I have an Optimate charger that I use for keeping motorcycle batteries optimally charged.
    2. Do I have to do anything special to make these connections work?

    I have a similar situation with the alarm system in the house and would like to put a larger battery on there as well. The alarm system is connected to a radio that alerts an armed response service if the alarm is triggered. Again the alarm and radio have individual batteries and I would like to replace them with a large car battery. In all cases space is not an issue and security will not be compromised with the batteries where I intend to install them.

    Any advice appreciated.
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hello and welcome back :)

    Larger battery should be fine. I would also have a separate fuse for each unit, the car battery has a lot more available current behind it if a fault was to occur. The only issue I have had with using a battery conditioner is that it's doesn't always come out of absorption mode and onto float mode if it has a load connected other than the battery.

    This killed our batteries within 6 months. What we did was get a large SMPS set to 13.8 V+ diode drop, put a diode in series to stop back feed and they have been out their over 5 years now. I know it's not the best thing for a battery to be charged from flat at 13.8 volts but for you it might just do the trick.

    Adam
     
  3. Gryd3

    Gryd3

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    Jun 25, 2014
    Perhaps a different approach should be made... This would require 12V low voltage wiring to be ran to the various components. Perhaps an AC inverter with 2 or 3 car batteries in the basement or other discrete location would be preferred. The inverter would run until it's battery dies, then the individual smaller batteries would continue from there... or if an AC line was severed.
    The larger batteries could charge back up again when mains power is restored.
    (This could also hold up other electronics in the house while the generator powers up.)
     
  4. shumifan50

    shumifan50

    548
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    Jan 16, 2014
    I had a look at going the inverter route, but that is very expensive compared to just using my simple proposition and there is more to go wrong, which is exactly what I am trying to avoid.

    How about using a battery charger from a car spares shop?
     
  5. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    As long as the equipment you are running can cope with the voltage the charger puts out yeah I guess this would work. You have to keep an eye on it and take it off charge when ready.

    Cheers
    Adam
     
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