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Need electronic experts pointers...

Discussion in 'General Electronics' started by Seraphina Lee, Sep 26, 2004.

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  1. Dear all,

    I am an electronic hobbyist... beginner :) ... and have mainly
    theoratical knowledge of electronics. I've decided to design and
    build, what i call, a BBU. I'm not sure if this is going to tedious
    but i'm willing to give it a try. I've found so far 1 schematic
    diagram and the reason i'm posting here is because i would like to
    gather more pointers regarding the BBU or perhaps links to any other
    'royalty free' schematic diagrams which fulfils the following;-

    Design Philosophy
    The purpose of this Battery Back-up Unit (BBU) is for the back-up of
    equipment such as (aquarium... maybe fridges at a later stage)
    especially motor loads during power outage. During normal conditions,
    the battery will be charged through a 13A switch socket outlet. The
    equipment will be attached in series with this BBU unit. When a power
    disruption occurs, this unit will cut out the charging unit and will
    deliver power to the load via a Lead Acid Battery which is on stand-by
    mode. There will be an interruption during this switch over. When the
    power supply is available, the BBU will switch the load supply from
    Battery to main power supply. Then the battery charger will charge the
    battery that has been consumed. When the battery is fully charged,
    trickle charging mode will be selected automatically to ensure a
    healthy battery for next power outage.

    Tech Details
    Battery Charger input source: 240VAC 50Hz 13A Plug-Top*
    Battery Charger Output Current: 5A
    Charging Algorithm: 1. Trickle Charge 2. Bulk Charge 3. Over-Charge
    4. Float Charge
    Battery: Lead Acid 12VDC (Maintenance Free Battery)

    Inverter
    DC Input: 12VDC**
    Rated Continuous Power Output: 500W
    Max Surge Power Output: 1000W
    AC Output Waveform: Square Wave
    AC Output source: 240VAC 50Hz 13A Switch Socket Outlet*
    Frequency Output: 50Hz

    Options
    *Variable input 220 - 240VAC 50Hz
    *Variable input 110 - 120VAC 60Hz
    **24VDC

    Would appreciate it if some kind soul out there could point to me to a
    site (which either sells or gives out free schematic diagrams) which
    does the above. Other pointers / tips before start of work would also
    be appreciated even though many have told me that it's extremely
    simple to create :) It's always the case of 'easier said than done' to
    me..

    Many Thanks,
    Seraphina L.
     
  2. Rich Grise

    Rich Grise Guest

    You're joking, right?
     
  3. Generally for heavy loads such as a frig a generator would be called for.
    For a battery back up schematic I'd suggest looking for a UPS, assuming
    you're not just a troll.

    Charles
     
  4. N. Thornton

    N. Thornton Guest


    This is no beginners project. But if its what you want it could be
    turned into one.

    Forget fancy 4 stage charging, use a basic charger circuit, just
    transformer, rectifier, capacitor. Or else buy a ready made multistage
    charger.

    The trick here is to use a self oscillating relay and mains
    transformer for the invertor section: that way it can indeed be done
    by beginner. But only a beginner who knows a lethal transformer
    kickback when they see one, and knows how to not end up a statistic.

    The downside of such a simple invertor is no regulation or stability.
    Your lead acid has a working range of smoething like 14 to 10.4 volts,
    and the transformer has resistance too, so your output V is going to
    be all over the shop. OK for lighting or computers, but not for
    fridges.

    Wind a few extra turns on the TF and you can do tap changing to
    improve your Vout hugely, but it will never be especially stable.

    Still interested?


    NT
     
  5. Suraj Singh

    Suraj Singh Guest

    Here is a simple circuit for an DC-AC Inverter for begineer.
    http://www.aaroncake.net/circuits/inverter.htm

    I have two comments based on your description:
    1. For a 500 Watt output you need to draw 500/12 = ~ 40A from a 12 v
    battery which is quite high for a transister/MOSFET switch to handle
    without too much power wastage. So think of using 48V battery.
    2. Square wave is not recommended for inductive loads such as motor,
    fridge.
     
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