battery backup question

Discussion in 'General Electronics Chat' started by Macabra, Dec 7, 2008.

  1. Macabra

    Thread Starter Active Member

    May 31, 2008
    49
    0
    Hi,

    I have set up a simple battery backup system which includes using just two diodes. Can I expect this to work with a lot of load in it? The output of these diodes are connected to regulator which feeds to different things. I'm just seeking a general answer, because I'm concerned about my design.

    Thank you.
     
  2. mentaaal

    Senior Member

    Oct 17, 2005
    451
    0
    The best thing to do would be to find out how much is "alot of load" and see if the diodes can support the current demand. As is the usual case with questions like this, a schematic speaks a thousand words :)
     
  3. Macabra

    Thread Starter Active Member

    May 31, 2008
    49
    0
    The circuit would be quite big, so the best I can do for now is list the stuff that goes into actual source from wall and stuff that goes into battery. These is how I have it:

    From wall source:
    3 sensors and associated circuitry
    LCD
    microcontroller
    encoder for keypad
    GMS wireless module

    Battery:
    microcontroller (same as above)
    encoder w/keypad (same as above)
    GMS wireless module (same as above)
    comparator LM339
    LT1440 which is a low battery indicator chip

    ----The rest of the stuff simply doesn't work when there is no power from wall outlet. I don't have the GMS wireless module connected yet to the board, but the microcontroller already stops working when I switch to battery source or when the original wall outlet source is gone :(

    For diodes that does this battery backup thing, I got it so one diode is supplied with 12V regulator which comes from wall outlet and the other diode connected with 9V battery. These diodes are in parallel and connect to regulator that feeds to the stuff they have to power (uC, encoder/keypad,and GMS).

    I'm using these for diodes.
    http://www.vishay.com/docs/88711/s1.pdf
     
    Last edited: Dec 7, 2008
  4. Macabra

    Thread Starter Active Member

    May 31, 2008
    49
    0
    I take it the diodes can't hold the current that the load demands like you stated? How do I determine this?

    Thanks a lot for your help :). I really need lots of help with this :(
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    How much current does the load draw? Is that value more or less than what the diodes are rated for?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    One can use MOSFETs as "ideal diodes" if efficiency is important. P-channel MOSFETs are sometimes used for this function.

    Standard diodes (such as the 1N400x, 1N540x series) have a significant voltage drop across themselves when current is flowing through them. MOSFETs can have an extremely small voltage drop across themselves. Your challenge would be to implement an efficient design using such a scheme.
     
  7. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Battery:
    microcontroller (same as above)
    encoder w/keypad (same as above)
    GMS wireless module (same as above)
    comparator LM339
    LT1440 which is a low battery indicator chip

    Your stated items above powered by battery backup through your diode is probably close to the diodes maximum specification. The pdf data sheet shows the diode has a 1 amp continuous rating. While I have idea what the items above actually consume in current, a 1 amp diode seems marginal at best. A three amp diode would probable to a much better choice.

    Lefty
     
  8. Macabra

    Thread Starter Active Member

    May 31, 2008
    49
    0
    Much thanks to all of you, my problem got resolved =).
     
Loading...