What is a battery cycle ?

Plucka
Plucka Registered Users Posts: 130 ✭✭
edited November 2019 in Solar Beginners Corner #1
If i discharge my  lithium  battery from 13.8 volts down to 13.1 volts then recharge-is that a cycle or is a cycle fully charged down to fully discharged meaning that I'm doing only 1/2 a cycle roughly. 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    Every charge then subsequent discharge would be considered a cycle regardless of depth of discharge, the life expectancy in terms of cycles however would be dependent on depth, the deeper it is discharged the shorter the cycle expectancy and vice versa. This cycle expectancy is largely dependent on the how aggressively the batteries are charged and discharged as well, which can lead to internal damage.

    Most posted test results are those done in ideal laboratory conditions, in less than ideal conditions with limited charging windows such as off grid the results may differ significantly, particularly in some chemistries which don't tolerate partial states of charge well. This is compounded by operators who do not fully understand how their particular batteries function, which is why we hear the stories of premature failure all too often.



     


    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,170 ✭✭✭✭
    #3
    And then some batteries need to be charged aggressively in order to stay healthy. Always follow the manufacturer's recommendations.
    I always have more questions than answers. That's the nature of life.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,109 ✭✭✭✭✭
    edited November 2019 #4
    Wouldn't a battery at 13.1 volts still have some surface charge voltage from the float charge mode and thus , not actually be discharged at all?



    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    Without knowing the chemistry, cell config, and charging stage, a voltage range doesn't really tell the tale.

    Assuming FLA, a 13.x range could be no discharge at all, just the battery/charge source in the process of dropping from absorb to float voltage.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited November 2019 #6
    Not surprisingly, games are played with the definition of "cycle".   IMO, when it comes to battery life, it should always refer to "full cycles", ie it takes two 100->50% partial cycles to be a full cycle.

    +1 on the voltage - keep a 12V lead acid battery above ~12.7V and it will experience no cycles.  But that doesn't mean that it will last forever.

    I am available for custom hardware/firmware development

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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,170 ✭✭✭✭
    #7
    Generally, manufacturers publish their test results using BCI standard test methods - but there are several. The common tests are the 2 hour and 5 hour discharge from 100% to 0% - not exactly real world for off grid PV, but more typical of UPS systems. In fact they can be misleading if taken at face value without more explanation. Generally, 1.75v per cell is used as 0% remaining charge.
    Reputable manufacturers publish curves showing the numbers of cycles at various depth of discharge points,
    Remember that the definition of a "worn out" battery means different things to different people. A common value of 80% of original capacity has been heavily for many years, but I am seeing ratings based on 40%, 50% and 65% storage capacity is "end of life." 

    I always have more questions than answers. That's the nature of life.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #8
    Estragon said:
    Without knowing the chemistry, cell config, and charging stage, a voltage range doesn't really tell the tale.

    Assuming FLA, a 13.x range could be no discharge at all, just the battery/charge source in the process of dropping from absorb to float voltage.  
    The battery in question is LiFePo4 from recollection so 13.8-13.1V would represent somewhere in the mid to upper regon of state of charge depending if loads and size thereof are present at time of reading.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Plucka
    Plucka Registered Users Posts: 130 ✭✭
    edited November 2019 #9
    Sorry Forgot not everybody using lithium batteries..
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,905 ✭✭✭✭✭✭
    #10
    Definitely not everyone! Good and bad with all  battery chemistries. Tailor their attributes and live with their downsides.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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