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long lasting battery

Discussion in 'Electronic Design' started by RHRRC, Feb 26, 2007.

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  1. RHRRC

    RHRRC Guest

    I have a few remote sensors that needs 'embedding' in inaccessible
    positions but which have to last for years (ideally 10 years).
    The problem is that the mains supply will be cut off for 8 to 14 hours
    every day and completely for 3 days or so every 4 to 6 weeks.
    I thus need a battery that will spasmodically (4-6 weekly) be
    discharged down to (say) 30% of capacity (or whatever is prudent) and
    daily be discharged a few percent and subsequently recharged.

    What battery chemistry am I looking at here and how must it be
    electronically handled.
  2. linnix

    linnix Guest

    You might need to handle multiple banks of backups.
    Just monitor the discharged level and recharge when necessary.
  3. John Barrett

    John Barrett Guest

    you will need:
    AGM (absorbed glass mat) sealed lead acid gel cells
    a 4 stage automatic charger (bulk, boost, top, and float stages)
    a load controller
    a voltage stabilizer with low voltage cut-off.

    given the current draw for your equipment, you need a battery bank that will
    delivery (draw * 200) amp/hours of capacity... that is approx 72 hours * 3
    so you never take the batteries below 1/3 discharge except in extreme

    the voltage stabilizer is a 13.8 volt boost converter that will run on 10-14
    volts in... as your batteries discharge, their output voltage will drop..
    the stabilizer will make sure you have a precise output voltage no matter
    the condition of the batteries for equipment that is sensitive to input
    voltage fluctuations. The stabilizer you choose should have a low voltage
    cut off so that if the battery voltage drops to 10v, everything gets cut
    off -- this protects the battery from over-discharge which will cause damage
    and shorten the life of the battery. Stabilizers are readily available for
    up to 40 amps load.

    Lastly you will need a load controller to make sure that when mains power is
    up, the battery system is isolated from the load.. this should cut over when
    the voltage from the mains power supply drops below 11 volts. Depending on
    how criticaly your supply voltage must be regulated, you may want to put the
    stabilizer after the load controller.
  4. mpm

    mpm Guest

    Not much to go on, but could "inaccessible" translate into solar?
    If outdoors, maybe you could just float a battery with solar charging.
  5. John Barrett

    John Barrett Guest

    that might be a good idea for carrying some of the load during those
    planned 3 day outages -- but I wouldnt count on it as part of the load
    handling capacity, and it just adds complexity to a system that already has
    a "reliable" means of recharging the batteries.
  6. John Barrett

    John Barrett Guest

    I forgot to ask ?? is your equipment line powered or does it run off of 12V
    ?? if its line powered -- there is an easier solution

    The Xantrex Freedom series of charger/inverters handle up to 3000 watts load
    of AC load, include the 4 stage smart charger for your batteries, and will
    automatically cut over from charger mode to inverter mode when the AC mains
    are lost. Then all you need is enough batteries to meet your total load
    requirement for 9-10 days.
  7. RHRRC

    RHRRC Guest

    I am quite familiar with VRLA cells.
    I am not familiar with any Pb-acid cells that have a life approaching
    10years. Could you give further info on these.

  8. RHRRC

    RHRRC Guest

    I had a brief look at solar but could not find any life data.

    Do you know who offers such data?

  9. RHRRC

    RHRRC Guest

    The load is only 100 to 400mW
    I will design a switcher to handle the load so batt volts (largely)
  10. John Barrett

    John Barrett Guest

    The batteries I use for reserve power for my ham radio systems come from
    cell phone tower reserve power systems and are rated for 10 years life --
    the cell companies regulary replace them after 4 years, and they show up on
    the surplus market with plenty of life left in them.

    PowerSafe SBS C11

    with your slow discharge rates, and if you dont deep discharge them
    regularly, they would probably last a bit longer than that !!
  11. John Barrett

    John Barrett Guest

    Solar cells are usually rated for 10% degradation over 20 years life, but
    you still need a battery system to hold the power, and a charge controller
    to perform the 3 or 4 stage charging process required by SLA batteries
  12. PeterD

    PeterD Guest

    How many volts? How many amps?
  13. John Barrett

    John Barrett Guest

    ok -- since you didnt give a voltage, I cant compute power... so I'll assume
    12 volts at 400mw (1/2 amp close enough) * 200 hours reserve capacity is 100
    amp hours required, and you can get that from a single SLA... a 10 amp SLA
    smart-charger will restore full charge on a fully drained drained battery in
    10 hours or so... which should have no problem recharging the system in 3-4
    hours after your planned 3 day outages.

    There are some 3 panel 150 watt solar panel systems that include a charge
    controller on ebay reasonably priced (<$200) that would work very well for
    providing additional recharging when sunlight is available during the long
    outages. In good sunlight they will get you 10 amps, more than enough to
    power your load and top off the batteries after overnight discharge.... just
    remeber not to count on the solar, plan the capacity like its not there --
    or cloudy days will bite you HARD !!

    I would probably go ahead an add a 2nd 100AH gell cell as a "just in case",
    but thats mostly because I get them so cheap

    With currents that low -- you could probably get away with running your gear
    off the batteries 24/7, and let the charger carry the load when its active,
    so you can skip the load controller and stabilizer (I've been designing
    setups for off-grid applications that require 10 or more batteries with
    continuous draws in the 10-20 amp range and peak draws of 40-50 amps, with
    AC line, solar, and wind power inputs, and high current inverter outputs, so
    I tend to think big when I design :)

    You will still want a last-ditch cutoff in case the battery voltage drops
    below 10 volts to prevent damage to the SLAs (this is part of what the load
    controller does -- if you arent going to have a load controller, you still
    need the LV-cutoff !!)
  14. Hi RHRRC h.lewis
    Sounds like LiPo with a max voltage below 3.9 V. Sure, you don't have 100%
    of capacity then but no breakdown after 5 years.

  15. The choices are lithium, lithium, or lithium.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  16. Ian Stirling

    Ian Stirling Guest

    I think you want to reread that last line several times, and if you're
    still having problems, go and look up the meaning of the unit milliwatt.
  17. What power do your "remote sensors" draw?, and how much space do you

    Dave :)
  18. John Barrett

    John Barrett Guest

    your right -- my bad -- I saw it as milliamp :)
    Can the attitude -- everyone makes mistakes now again :)

    ok -- 400mw or 1/2 w and 200 hours = 100 watt hours -- at 12 volts you could
    cover that with 10 amp hours with some spare.. at 3v (lithium) need 33 amp
    hours (at about 2 amp hours per cell from googling various batteries -- call
    it 16 cells with some headroom)

    so a small gel cell or a triple handful of lithium AA size batteries

    The gel cell is still cheaper -- the battery charger is about equivalent in
    cost considering there are off the shelf charge controller chips for both
    types of cells
  19. Robert Baer

    Robert Baer Guest

    Many "emote" alarm sensors use a Lithium battery and there is no
    provision for charging; most claim a lifetime of 5 years or more.
    There are re-cheargeable Lithium batteries that might be worthwhile
    for comparison purposed during component evaluation and survey.
    You give no idea as to how much power drain there will be durint
    useage, you give no idea of the device will have "sleep" and/or "power
    down" modes, etc & etc.
  20. Robert Baer

    Robert Baer Guest

    Now where in the heck did you manufacture the voltage he needs as
    well as the power/current he needs?
    Maybe he needs 3V at a microamp (max); a Lithiumcoin cell will do for
    at least 5 years.
    Maybe he needs 440VAC three phase at 10,000 amps continuous load.
    There is no clue.
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