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Thread: Lead-acid battery

  1. #1 Lead-acid battery 
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    When we say 100 ampere hour for a battery what we exactly mean? I mean what is the energy stored in coulomb or kWh? Can any one give me some idea?


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  3. #2  
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    It means that if you multiply the battery current by the time until it is discharged, you will get 100 amp-hours. For example if the current is 10 amps it will last 10 hours. To get the stored energy, multiply by the battery voltage to get volt-amp hours, i.e., watt-hours. If the battery is rated for 100 amp-hours and is a 12 volt battery the energy is 1200 watt-hours, or 1.2 kilowatt hours.


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  4. #3  
    sak
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    Thanks for the reply. In fact I was trying to decide requirements of a back up storage facility.

    As the discharge is in progress the voltage reduce. To maintain the required rate of energy we may increase the consumption of ampere.

    Next point - as far as I know we don’t discharge the battery full. Then what shall be an optimum level of voltage we can discharge the battery?

    Considering the above case how we determine an actual storage capacity of a 100Ah battery? Pl.
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  5. #4  
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    You shouldn't really discharge a lead acid storage battery completely. Typically a battery might be considered fully charged at 2.15 volts per cell and fully discharged at 1.9 volts per cell. So, you really can determine the capacity pretty closely by multiplying the amp-hour rating by the voltage, as I have stated above.
    http://xtronics.com/reference/batterap.htm
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    dont let it go below 10.8 volts otherwise youll shag it, like harold says but it is not exact. the higher the current the less you will get in amp hours so at 100 amps you might only get 30 minutes but at 1 amp you might get 120 hours. ask the manufacturer for the data sheet
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  7. #6  
    sak
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    That was quiet informative.
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  8. #7  
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    I have ruined a few batteries by discharging them too much.

    The effective Ah is somwhat less that the stated Ah as has been said.
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  9. #8 Lead acid batteries and excessive charge voltage 
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    Here is a scenario that seems to be happening more frequently lately:

    You have a"high voltage" solar panel designed for grid tie use, but it is used for battery charging instead. A pulse width modulator controller is connected between the solar panel and battery, and it switches 25 volts at 6.3 amps into a bank of 12 volt batteries. Although the panels are rated at 170 watts each, only about 90 watts are actually going into the battery. During bulk charging the 25 volts are connected continuously to the 12 volt battery until the battery reaches 14 volts, and the pwm controller then starts to modulate the pulse width to maintain absorb or float voltage.

    The question I have is, where are the extra watts going? Are the watts lost in the batteries through heat or gassing, or are the panels simply not generating 157 watts at 25 volts, or is something else is happening? Could the higher than normal voltage damage the batteries?

    A similar situation exists with small unregulated wind turbines where voltage is a function of rotational speed, and batteries of much lower voltage are connected directly to the generator.
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  10. #9  
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    Peukert's law explains the actual capacity due to the current draw, and in turn, it explains the actual battery discharge time as a function of the current and Peukert's number. This is important because, to some extent, you will always have less actual discharge time than the theoretical time (h) = capacity (Ah) / current (A).
    Grief is the price we pay for love. (CM Parkes) Our postillion has been struck by lightning. (Unknown) War is always the choice of the chosen who will not have to fight. (Bono) The years tell much what the days never knew. (RW Emerson) Reality is not always probable, or likely. (JL Borges)
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  11. #10  
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    I bought a deep cycle sealed lead acid battery (AGM) recently. As I am new to lead acid batteries, I am probably missing something, and would appreciate any insight into my current problem:

    Simply put, every time I recharge my battery, it takes a half hour longer. As part of my initial test runs, I'm powering a simple fan through an inverter off the battery for 40 minutes, and promptly recharging it. I've done this three times now, and each time I recharge it, it takes 30 minutes more than it did the last time, before my "Battery Tender" charger gives me the green light telling me it's fully charged. My battery is a 12-volt, 35Ah. I should mention that I have no actual battery-testing instruments whatsoever, so I'm flying a bit blind here. Still, I've read extensively about lead acid batteries, and I'm staying well away from all the things I read I shouldn't do, like draining the battery completely, letting it sit around and become permanenly dead, etc.

    The obvious problem with not having any meters is, I don't know how much current is being drawn out of the battery when in use. Still, I'm fairly sure that the recharge time shouldn't be increasing relative to the exactly-duplicated discharge scenario I'm using.

    I have read that a brand new lead acid battery takes a few cycles ("up to 50") before it reaches its rated capacity, and that their capacity starts at around 90 percent when new. The "plates aren't fully formed" at first, and the discharge/recharge process accomplishes that over several cycles, I read. So, at first I thought this was the reason for the mysteriously ever-increasing recharge times: the battery was simply being gradually brought to its full capacity, and that capacity "ceiling" was being raised with each recharge. But then I realized, "Even if that is happening, shouldn't the recharge time STILL be a constant number each time?"

    I've researched these batteries for probably a good ten hours or more all over the internet, carefully comparing what I read with other sources to see if they agree, so as not to become misinformed. Yet, still, I am confused, and need help cracking this puzzle.

    I've used rechargeable batteries extensively in hobby r/c applications for over 20 years, from Ni-Cd, to Ni-Mh, to Li-Po, and I've never run into a battery so apparently difficult to understand as the lead acid. Therefore, any help would be greatly appreciated!

    Extra info: the fan says it draws 0.46 Amps, and the inverter uses a modified sine wave.
    Last edited by Ragtime; July 19th, 2011 at 01:28 PM.
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  12. #11  
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    There are probably few lead acid batteries that will suffice also. Don't use car batteries. Anymore, they put the plates too close to the bottom. It only takes a few short years before one or more cells die.
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  13. #12  
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    Try this site for additional informatio: batteryuniversity.com very good
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