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Thread: float (maintenance) charge without a charge controller

  1. #1

    Default float (maintenance) charge without a charge controller

    Hey guys,

    I have recently acquired 24 used 2V 500Ah batteries reading 2.09V each which I plan to use for my future install. Now if i am correct, they will loose thier charge over time and possibly become useless/damaged. I have not purchased a charge controller neither solar panels as yet, but i do have a couple 60W panels that i experiment with laying around.

    Now i was doing some research and came across this quote in the Battery FAQ section of the Forum.

    When using a small solar panel to keep a float (maintenance) charge on a battery (without using a charge controller), choose a panel that will give a maximum output of about 1/300th to 1/1000th of the amp-hour capacity. For a pair of golf cart batteries, that would be about a 1 to 5 watt panel - the smaller panel if you get 5 or more hours of sun per day, the larger one for those long cloudy winter days in the Northeast.
    Now, does this mean that if i configure my batteries into two parralell banks of 24V each totalling 1000Ah, that i can safely connect a panel outputting 1.6A to maintain a float charge?

    Can anyone elaborate on this, as it apears to be an economical way to save my battery investment, until I decide on my panels and charge controler.

    Thanks in advance.

  2. #2
    Join Date
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    SF Bay Area (California)
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    Default Re: float (maintenance) charge without a charge controller

    Yes, you can. I would install a "blocking diode" and a ~5 amp fuse for safety.

    Is this an AGM bank or a Flooded Cell battery bank?

    You should monitor the bank for state of charge. Flooded Cell batteries tend to have higher self discharge and as they age, the self discharge rate goes up...

    You may find you will need closer to 240-1,000 watts of solar panels to properly keep the bank charged due to self discharge (depending on brand/model/age/current state of the batteries).

    At that power level, you may as well look at a "real charge controller" (PWM or MPPT type) to insure that you do not over charge them either (AGM's do not take well to overcharging).

    If the batteries have been sitting for awhile--You should check their current state of charge and get them on an AC charge controller if they are below 80% stage of charge.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  3. #3
    Join Date
    May 2006
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    Florida, USA
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    Default Re: float (maintenance) charge without a charge controller

    At full state of charge, the cells should read 2.12 vdc after a idle, no load, no charge, period of rest of a few hours. At 2.09 vdc the batteries are slightly discharged.

    You can get a small PWM charge controller for $20-$30 that will ensure they are not overcharged.

    In the evenings, make sure they have achieved at least 2.10 vdc rest voltage to ensure they are getting enough charging.

  4. Default Re: float (maintenance) charge without a charge controller

    you might want to look at something to inhibit or reduce sulfation. See http://leadacidbatterydesulfation.yuku.com/ for discussion and links. BatteryMINDer also makes an 8 amp solar controller that uses this technique that seems to work fairly well. That one costs under $100.

  5. #5
    Join Date
    Jun 2003
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    Default Re: float (maintenance) charge without a charge controller

    are you the same wagoneer that used to be on here way back when that sold his solar house? i don't advocate desulfators, but rather proper care for the batteries in the first place to prevent it.
    NIEL

  6. #6

    Default Re: float (maintenance) charge without a charge controller

    Is this an AGM bank or a Flooded Cell battery bank?
    This is a Flooded Cell Battery Bank aprox 3 yrs old. The make is Enersys Hawker(model unknown) I think they are submarine batteries.

    Now the panels are rated at 60W 3.3Amps but output aprox 2.5Amps each. Would 2.5Amps current be to much for the bank?
    Does it matter if i increase the voltage from the panels by placing them in parallel (ie 24V @ 2.5Amps) ?


    You may find you will need closer to 240-1,000 watts of solar panels to properly keep the bank charged due to self discharge
    Is this to fully charge the bank under load or just to keep them at float charge without load?

    Sorry neil I'm not that guy from way back when.

  7. #7
    Join Date
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    Default Re: float (maintenance) charge without a charge controller

    ok on not the same guy.

    it would seem odd to me that they would put flooded type batteries on a sub as they gas regularly. a sealed battery makes more sense to me for a sub, but who knows?
    NIEL

  8. #8
    Join Date
    Oct 2003
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    Default Re: float (maintenance) charge without a charge controller

    Quote Originally Posted by niel View Post
    it would seem odd to me that they would put flooded type batteries on a sub as they gas regularly. a sealed battery makes more sense to me for a sub, but who knows?
    Sealed would seem the preferred choice and maybe newer subs have them.

    I spent almost 3 years underwater in the early seventies (6 years on the boat, 1/2 the time under, 1/2 the time at home). Our battery bank was FLA.

    One of the most concerning things about that was if there was a saltwater leak, and IF that leaking seawater migrated to the battery room, I wouldn't be here now. Sealed batteries would help with that situation.

    Phil
    Happily off-grid since 1977

  9. #9
    Join Date
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    Default Re: float (maintenance) charge without a charge controller

    Well NIEL...

    I asked about the batteries at a sub sailor forum and learned that the first lithium ion batteries for subs are supposed to start shipping in 2011.

    http://www.defenseworld.net/go/defensenews.jsp?id=4893

    It was also mentioned that the reason they've stuck with FLA for so long was the "forgivability" of them.

    Phil
    Happily off-grid since 1977

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