Battery backup for home project

Discussion in 'The Projects Forum' started by chrisrpriceuk, Apr 30, 2013.

  1. chrisrpriceuk

    Thread Starter New Member

    Apr 30, 2013
    2
    0
    Hi all,

    I've got a bit of a home project on the go that is being supplied power from a 12v 7ah Lead acid battery.

    The project itself runs at 5v 3a so I have a UBEC connected to the battery first switching the power down for me. It can handle an input voltage of up to 23v input. Apparently it draws around .5Ah

    There is one other device connected directly to the battery that can accept 7.8v > 16v drawing 10Ma.

    What I want to do is to keep the battery charged all the time whist it's still powering the project so that if the mains power were cut it keeps running - like a UPS.

    Can anyone advise me on what I need to do / get in order to do this?

    Your help is much appreciated!!!
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Sounds like you need a power supply that can supply about 15W minimum into about 14V. You need that peak voltage to keep the battery fully charged. You'll need a bit more voltage if you're going to use a regulator with some amount of dropout voltage.

    An old laptop power supply brick would be a handy starting point. It'll be putting out 18-20V and would have plenty of capacity for your project. Maybe just use an LM317 regulator to supply a trickle to the battery. If you want to be able to rapidly charge a depleted battery, you'll need a more powerful charger.
     
  3. #12

    Expert

    Nov 30, 2010
    16,346
    6,835
    Something like this?
     
  4. chrisrpriceuk

    Thread Starter New Member

    Apr 30, 2013
    2
    0
    #12, just want to make sure I fully understand this (i don't so far)...

    Can you explain it, specifically I'm not sure I understand the purpose of the diode and resistor.

    Sorry for my ignorance, I'm fairly new to all of this:(
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    That's a low cost, low current voltage regulator to achieve your 9v, 10mA supply.

    What #12's diagram doesn't show is any detail on what the charger is. If that's a subtle way to recommend buying one instead of building one, I agree.
     
  6. #12

    Expert

    Nov 30, 2010
    16,346
    6,835
    I wasn't suggesting anything. I was checking to see if I understood the request.
    12+V 3A isn't all that hard to build, but, as usual, if you can get it retail, you can't build it any cheaper.
     
Loading...