Battery Charging with load

Discussion in 'General Electronics Chat' started by Nitrag, Aug 12, 2013.

  1. Nitrag

    Thread Starter New Member

    Sep 16, 2007
    I've got a magnetic lock that will be running 24/7 on DC (12v). In the event of a power failure I'm going to need a battery backup. The total draw of the system is less than 1 amp.

    I'm struggling to find a safe and simple setup. I need to both maintain the battery at 100% and also constantly draw about 500ma load.

    Will a battery maintainer just as the "Battery Tender 021-0123" work or will I need a custom circuit? I'm looking for cheap, safe, long-lasting, zero-maintenance solution.

  2. RodSTAR


    Jan 3, 2008
    Maybe using relays as UPS do. So, if mains power fails (... relay: off), then switch to battery. When mains power is back (... relay: on), then switch to 12v power supply to your magnetic lock, and battery charger starts charging the battery. That's a cheap, safe, long-lasting, zero-maintenance solution... i think...
    Maybe a cap between relay and load (your magnetic thing) to soften relay reaction time.
  3. ian field

    AAC Fanatic!

    Oct 27, 2012
    Over the years; a number of SLA battery maintainers have been published online - many based on the L200 linear regulator.

    For low maintenance; you may need 2 chargers in parallel - a high current charger for quick recharge, strictly limited to about 13.6V, add to that a current limited unit set about 1/10 - 1/20C

    A very convenient - if rather expensive possibility is the Optimate battery charger/conditioner, you can leave them connected to the battery indefinitely, there are a couple of gotchas; they're pretty slow recharging a dead flat battery, and the standing current of 500mA might cause the internal micro to indicate a fault - download the PDF user manual and see what it says about this. You might get away with some standing load - they can be left float charging a battery on a car with clocks, alarms etc drawing current.
  4. #12


    Nov 30, 2010
    I like the RodSTAR method. A cheap float charger on the battery, which only gets called into service if the power line fails.