Battery Bank

Discussion in 'General Electronics Chat' started by pilko, Jan 10, 2012.

  1. pilko

    Thread Starter Active Member

    Dec 8, 2008
    213
    20
    Hi everyone,
    I have aquired 3 heavy duty truck batteries and would like to use them in parallel to supply some lights and a computer via an inverter.
    I will only connect the load during power outages.

    - Does the settup look OK regards the charging and the diode isolation?
    - Do I need to charge the batteries individually (one switch closed)?
    - Can I float charge all at the same time (all switches closed)

    Regards
    pilko
     
  2. colinb

    Active Member

    Jun 15, 2011
    351
    35
    Be aware that these batteries aren't designed for deep-cycle discharge use, so they will not last long. But if you rarely use the battery supply, you might not care that you'll only get a few cycles from it. Better batteries would be deep-cycle marine batteries.
     
  3. pilko

    Thread Starter Active Member

    Dec 8, 2008
    213
    20
    @ colinb,
    Thanks for the response.
    I'm using them because they were free and they hold a good charge.

    pilko
     
  4. colinb

    Active Member

    Jun 15, 2011
    351
    35
    Sure, you might as well make use of them. Anyway they should last a long time as long as the float charge doesn't overcharge them.
     
  5. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,229
    You may be able to charge them in parallel. This company claims their charger will do just that. But you don't want diodes in series with the charger as the diode voltage drop will not allow the batteries to fully charge.
     
  6. pilko

    Thread Starter Active Member

    Dec 8, 2008
    213
    20
    @ crutschow,

    Thanks for the info.

    pilko
     
  7. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Even deep cycle batteries have limited life if discharged below 50% repeatedly and /or left discharged for periods of time.

    So keep this in mind: For longest life, avoid deep cycling any lead-acid battery more than what is necessary.
     
  8. pilko

    Thread Starter Active Member

    Dec 8, 2008
    213
    20
    @ crutschow,
    I just noticed your comment about the diodes in series with the charger.

    "But you don't want diodes in series with the charger as the diode voltage drop will not allow the batteries to fully charge".

    If I ommit the diodes, then when more than one charge switch is closed, The batteries will attempt to voltage equalize and high currents will flow through the switches.

    pilko
     
  9. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,229
    If the batteries had significantly different charge levels, that could happen. But if the batteries are discharged in parallel then they should all be at essentially the same (dis)charge level already.
     
  10. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    It looks a little more complicated than it needs to be, you have one load (inverter) and one charger, you can have one, two or three batteries in parallel. When batteries are in parallel the only thing that changes is the capacity (run time).

    I suggest you connect the batteries in parallel without diodes, they will be happy as long as they are about the same age and capacity. In fact the diodes will hurt you in the long run because the load will draw current from the battery with the highest state charge instead of all batteries equally.

    Look at how solar powered people connect there systems to the inverter.
     
  11. pilko

    Thread Starter Active Member

    Dec 8, 2008
    213
    20
    Thanks Smoke Maker,
    I'm still a little unsure/nervous ---while researching on this forum I came accross these comments by wookie.

    "Connecting discharged batteries of the same voltage directly in parallel with each other is not a good idea as one battery my never get fully charged. An excepting to this is if the batteries were the same date code and originally put is parallel for service.[/QUOTE]
    Connecting batteries in parallel can result in very high current flow, overheating and
    fires/explosions if one battery is fully charged and another deeply discharged.
    Even if they start off being the same voltage, if one battery develops a shorted cell
    (a very common failure mode) it will prevent the other battery or batteries in parallel
    with it from becoming fully charged, leading the remaining to early failure. This can
    get expensive in a big hurry."

    "There ARE situations where several or dozens or even hundreds of lead-acid batteries are connected in parallel or series-parallel arrays, such as when being float-charged in
    storage, in UPS banks, even in large trucks. However, in these situations the batteries
    are installed when fully charged, and are maintained all at the same charge levels.
    In our OP's situation, his children have a number of battery-powered toys, and although it's pretty likely that the batteries will be exhausted when the kids finally connect them to be charged, the same voltage is not guaranteed by any way, shape or form.
    Connecting two batteries of same labeled voltage but different charge levels will
    result in high current flow until the charges are equalized; with resulting power
    loss and increased internal temperatures, which shortens battery life. Using resistors
    will limit the current flow externally, but will waste power when charging.
    Additionally, if any one battery develops a shorted cell (a very common failure mode)
    it will prevent any cells in parallel with it from becoming fully charged, leading to
    their early failure. This can and does happen, all too frequently".

    pilko
     
  12. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    Being cautious is good. When you jump start a car you connect two 12 volt batteries in parallel and the longer you leave them connected together the more energy is moved from the good battery to the discharged battery and the two batteries will become equal in state of charge if left connected long enough, this is done thousands of times every day all over the world with vehicles and VERY routine and I do not see any news reports of fire or problems.

    Use caution, use proper size wire when you make your battery bank, fuse your battery bank, and do it like the pro's do it, Home power has a wealth of information on what your doing.


    http://homepower.com/view/?file=HP114_pg54_Dankoff

    To start, go ahead and connect two batteries in parallel (use jumper cables ) and charge them with a battery charger, connect your inverter and power something.
     
    evilclem likes this.
  13. evilclem

    Member

    Dec 20, 2011
    118
    16
    I agree that there is no need for diodes from the charger. If large currents are a concern then charge each battery individually prior to connecting all three into the system (or measure their voltages to check how different they are).

    You can connect batteries in parallel fine for charge and discharge, we did it with 8 x 120 Ah batteries, just make sure you fuse each battery individually so that the fuse blows in the event that a battery loses a cell (unlikely). We used 50A fuses on each battery.
     
  14. pilko

    Thread Starter Active Member

    Dec 8, 2008
    213
    20
    Thanks everyone, you've all been a great help.

    pilko
     
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