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  1. #1
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    Default When is a charge regarded as a cycle?

    I am not educated enough to understand everything...

    I have 2 banks of 48V (4x200Ah per bank) driving my 10 year old 6kW UPS as backup system. Actually not anymore.

    With solar on the roof the system is charged daily when Eskom is switched off at 9am and on at 4pm. During these times our complete household, the shop, koi pond (with aquaponics) and diesel depot is served perfectly. At times when overcast the system switches back to Eskom at 49V to save the batteries. This switch was designed by Richard Mackay (on the forum) and works well.

    My question, as in the heading. Switching at 49V, being 12.25V per battery can this switch regarded as a 'cycle'? As every battery has limited cycles I would like to know how long the batteries will last.

    Thanks for your replies.
    Johan Maree
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  3. #2
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    Default Re: When is a charge regarded as a cycle?

    Good question.
    Me too.
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  4. #3
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    Default Re: When is a charge regarded as a cycle?

    With lithium batteries a cycle counts as fully charging an empty battery.
    If you charge a partially discharged battery, e.g. the battery is down to 50% and you charge it to 100%, that would count as half a cycle. In other words, if you do the above twice, it's one cycle.
    You can essentially add up the percentages that you recharge, even if you don't charge the batteries up to 100% and once the sum reaches 100% it's a cycle. E.g. your battery is at 30% and you charge it to 80% (charging up 50%) is again half a cycle. Do it twice, it's a full cycle.
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  6. #4
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    Default Re: When is a charge regarded as a cycle?

    From the Victron BMV manual. How monitor sees it.

    A charge cycle is counted every time the SOC drops below 65%, then rises above 90%
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  8. #5
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    Default Re: When is a charge regarded as a cycle?

    Quote Originally Posted by HugoNotte View Post
    You can essentially add up the percentages that you recharge, even if you don't charge the batteries up to 100% and once the sum reaches 100% it's a cycle. E.g. your battery is at 30% and you charge it to 80% (charging up 50%) is again half a cycle. Do it twice, it's a full cycle.
    +1 but one can add more cycles at lower DOD.
    IF the battery has 100 full charge/discharge cycles and you discharge only to 50% then one can expect 240+ partial cycles.
    Last edited by ekkekan; 2021/06/20 at 06:58 PM.

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  10. #6
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    Default Re: When is a charge regarded as a cycle?

    The way I have always understood it, If you are using wet lead acid batteries then at 12.25v your batteries are approx at 65% State of Charge or seen the other way round they are approx 35% discharged (DoD). This is a very safe level of DoD as 50% DoD is seen as the lowest you should go for long term health of your batteries (and you are 15% above that).
    If your batteries are rated at 1000cycles at 50% DoD it means they should be able to handle 1000 times going from 0%DoD(100% charged) to 50%DoD (12.06v) before going below 80% health (only able to deliver 80% of its capacity) , if you only go down to 35%DoD (65% charge left over) then you will probably get more than 1000 cycles out of them (maybe 1150 cycles) but temperature plays a big role in this.
    So 1000 cycles/365days=2.7 years if you go down to 50%DoD each day @20degrees.
    Neil

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  12. #7
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    Default Re: When is a charge regarded as a cycle?

    So, as per the above I can expect 3 years from my gel batteries?

    Not very good but they are so convenient during load shedding and as bonus save on daily Eskom use.

    Thank you guys.
    Johan Maree
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  13. #8
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    Default Re: When is a charge regarded as a cycle?

    Quote Originally Posted by JohanMaree View Post
    So, as per the above I can expect 3 years from my gel batteries?

    Not very good but they are so convenient during load shedding and as bonus save on daily Eskom use.

    Thank you guys.
    I have 8 x 150Ah AGM batteries going into their sixth year. Still above 50.4V in the morning at start of day. I am anal about it not dropping below 70% SOC
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  15. #9
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    Default Re: When is a charge regarded as a cycle?

    Quote Originally Posted by Prof View Post
    From the Victron BMV manual. How monitor sees it.
    This. ^^^^
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  16. #10
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    Default Re: When is a charge regarded as a cycle?

    I would say there is no straight answer to your question. Every battery I have seen of any type will list the number of cycles graph with the depth of discharge. SO you may get 10000 cycles with 5% discharge and 2 cycles at 100% depth of discharge.

    Ultimately no battery will last forever, but as a general rule, the deeper you discharge the batteries, the shorter the life span. The lesss they discharge the longer the lifespan.

    I was always careful to run around switching off lights. I gave my old system to my beancounter. I installed around 2013, with 4 x 150AmpHr batteries. I added 4 x 200AmpHr a few years back and he is still running all those batteries today and it is working well. (They were all gel batteries)

    If you google Depth of Discharge vs Cycle life graphs you will get loads of images of the typical pattern.

  17. #11
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    Default Re: When is a charge regarded as a cycle?

    Every single discharge and recharge is regarded as a cycle.

    If you discharge by 2% and then recharge, that is a 2% cycle.

    So even if you charge and discharge daily, "that" daily cycle can consist of a few 10% cycles, a few more 5% cycles and a few dozen 2% cycles, if you system is set to using own power incl batteries.

    Lets say you switch the kettle on. There isn't enough PV energy so it sucks from the battery. When the kettle stops the PV takes over and refills the battery. That's a cycle, albeit only a small one.

    Every time you do this you use up the battery life. You can look at the charts for the effect on battery life, but good luck to you summing up all the different mini cycles and finding a meaningful answer.
    Cheers

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  19. #12
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    Default Re: When is a charge regarded as a cycle?

    Presies soos Fluffy skryf.
    Dit is nou helder soos troebelwater.

    Soms is te veel kennis nie genoeg nie. Live and let live.
    Last edited by JohanMaree; 2021/06/21 at 09:24 PM.
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  21. #13
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    Default Re: When is a charge regarded as a cycle?

    Nie wat ek uit my duim suig maar wat op Bat Varsity geskryf is.
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