I understand that my battery has an estimated charge cycle life of 2000-6000 (maybe more dependent on depths of use/charge levels) charge cycles before becoming roughly 80% of original capacity. What I'm wondering is what defines a charge cycle when my battery is hooked up to one or two 100W solar panels while installed in my RV? For instance, let's say it's 2pm and my battery has been charging from 40% capacity since the sun came up. Now a storm rolls in and the sun is obscured and charging drops to zero or near zero. 30 minutes later, the storm blows over, the sun is out in full force again and my battery is charging until sundown in a few hours. Did my battery bms interpret this as TWO charge cycles? Thanks in advance for any replies!
What constitutes a "charge cycle" on a Lifepo4 100ah battery?
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timselectric
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Yup
Two cycles
Two cycles
timselectric
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If not needed, probably so.
Koldsimer
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That just doesn't seem right to me. If that were the case, the battery could reach 2000 cycles in just 20 days.
GXMnow
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I really don't think short cycles and charging and stopping, then charging more, at reduced current etc. due to clouds or whatever, is not that much of an issue. If you charged just 5%, then stopped, and it discharged 5%, then you charged it 5% back again, that is not going to do the wear of 2 cycles.
In my JK-BMS, the "Cycle Count" is not like that at all. It counts a cycle when you have cycled the full capacity of the battery. Mine is set to 360 amp hours, this is only 1 half of my total battery capacity now though. I have another matching bank of cells, but they are on a dumb Daly BMS. When I discharge and recharge just 120 amp hours out of that bank with the JK BMS, it takes 3 cycles before it adds one to the cycle count. If I cycle 180 amp hours out of the 360 capacity, then it will add one cycle count after 2 cycles.
So if your 100 amp hour battery was discharge from 100% down to 50%, then charged back up 30% to 80% capacity, but then clouds come in and it discharged again, down to only 40% capacity, and charged back up another 50% when the sun came back out, your battery is now back at 90% charged, and you cycled 80% of the capacity, but in two shorter cycles. My JK BMS would see that as still less than 1 cycle. My JK BMS has been up and running for 1 year and 277 days, or 365 + 277 = 642 days. It cycles up to 35% capacity some days, but most days are less. The BMS cycle count is only at 123 cycles. 123 / 642 = 19.16% of the days. I know it missed cycling a few days, and some days it does not run all the way down, so I guess only 19% per day is a possible average.
Now the real question is... Is this realistic? I don't know. My gut thinks this is a bit too optimistic. I have read in several places that the shorter the cycle the more cycles you will get, but do you really get twice as many cycles of 50% vs 100%? I can't say for sure. At the rate my JK BMS is counting cycles, my battery is going to last a really long time. LG claims the cells should be good for over 2,000 cycles. It took over a year (360+ short cycles) to hit 100 cycles on the JK BMS. If it was truly a cycle per day, I would only get 5 years out of the cells, I am hoping for 7 years, and 10 would be a bonus.
I really don't care what the cycle count number says. I will judge the cells performance based on how many watt hours I can use in the voltage range I am running. Right now, I can cycle 14 KWH's a day with my now 720 amps hours of cells (about 36 KWH's of total capacity) with the voltage going from 57 volts on the high side down to 51 volts on the low side. In a few years, I expect the same voltage swing will only be giving me 11 KWH's instead of 14. That's how I will know the cells have degraded to 80% capacity. Yesterday's cycle was quite a bit shorter because the sun was intense and we had cool wind keeping the solar panels efficient. So my house only used 10 KWH's from battery overnight. But that is still almost 27% of the battery capacity cycled out and back. Even doing that short cycle each day, I should be closer to 180 cycles, not just 123. So I think that count number is too low to be realistic for battery life. Something in between the two makes the most sense.
In my JK-BMS, the "Cycle Count" is not like that at all. It counts a cycle when you have cycled the full capacity of the battery. Mine is set to 360 amp hours, this is only 1 half of my total battery capacity now though. I have another matching bank of cells, but they are on a dumb Daly BMS. When I discharge and recharge just 120 amp hours out of that bank with the JK BMS, it takes 3 cycles before it adds one to the cycle count. If I cycle 180 amp hours out of the 360 capacity, then it will add one cycle count after 2 cycles.
So if your 100 amp hour battery was discharge from 100% down to 50%, then charged back up 30% to 80% capacity, but then clouds come in and it discharged again, down to only 40% capacity, and charged back up another 50% when the sun came back out, your battery is now back at 90% charged, and you cycled 80% of the capacity, but in two shorter cycles. My JK BMS would see that as still less than 1 cycle. My JK BMS has been up and running for 1 year and 277 days, or 365 + 277 = 642 days. It cycles up to 35% capacity some days, but most days are less. The BMS cycle count is only at 123 cycles. 123 / 642 = 19.16% of the days. I know it missed cycling a few days, and some days it does not run all the way down, so I guess only 19% per day is a possible average.
Now the real question is... Is this realistic? I don't know. My gut thinks this is a bit too optimistic. I have read in several places that the shorter the cycle the more cycles you will get, but do you really get twice as many cycles of 50% vs 100%? I can't say for sure. At the rate my JK BMS is counting cycles, my battery is going to last a really long time. LG claims the cells should be good for over 2,000 cycles. It took over a year (360+ short cycles) to hit 100 cycles on the JK BMS. If it was truly a cycle per day, I would only get 5 years out of the cells, I am hoping for 7 years, and 10 would be a bonus.
I really don't care what the cycle count number says. I will judge the cells performance based on how many watt hours I can use in the voltage range I am running. Right now, I can cycle 14 KWH's a day with my now 720 amps hours of cells (about 36 KWH's of total capacity) with the voltage going from 57 volts on the high side down to 51 volts on the low side. In a few years, I expect the same voltage swing will only be giving me 11 KWH's instead of 14. That's how I will know the cells have degraded to 80% capacity. Yesterday's cycle was quite a bit shorter because the sun was intense and we had cool wind keeping the solar panels efficient. So my house only used 10 KWH's from battery overnight. But that is still almost 27% of the battery capacity cycled out and back. Even doing that short cycle each day, I should be closer to 180 cycles, not just 123. So I think that count number is too low to be realistic for battery life. Something in between the two makes the most sense.
timselectric
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I think that 100 cycles, was sarcasm. lol
timselectric
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They said discharged to nearly zero.
And previously charged up from 40%, since daybreak.
Not sure if it made it to 100%, before the storm. But if it got anywhere close, that's a cycle.
No, I said battery was at 40% at sunrise, it charged full sun until 2pm when a storm rolled over and CHARGING dropped to zero. I'd assume around this time using one or two 100W panels that my battery capacity (SOC) would be roughly 60-80% depending on how many panels I used.
Then the storm blew away and the sun was unobscured until sunset, so it received full charge from the panel(s) during this end of day, 4-5 hour period.
Then the storm blew away and the sun was unobscured until sunset, so it received full charge from the panel(s) during this end of day, 4-5 hour period.
timselectric
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Ok,
40% to 60% would not constitute a full cycle.
TomC4306
Solar Obsessive
So bear with me here, I'm just trying to understand "cycling". I appreciate your time and help!
Let's say my RV sits unused in the sun for a week. The 100ah battery begins at 100% SOC. It it's using some power from the battery but minimal, like 10-20ah/day because the radio and fridge are on. During the course of the day (24 hours) the battery never drops below 80% SOC. So thanks to the solar panel it stays between 80-100% SOC all week. Does this constitute a "cycle" every day of the week (7 cycles) or none at all because it was never discharged below 20% or 50% or whatever defines a "cycle"??
Let's say my RV sits unused in the sun for a week. The 100ah battery begins at 100% SOC. It it's using some power from the battery but minimal, like 10-20ah/day because the radio and fridge are on. During the course of the day (24 hours) the battery never drops below 80% SOC. So thanks to the solar panel it stays between 80-100% SOC all week. Does this constitute a "cycle" every day of the week (7 cycles) or none at all because it was never discharged below 20% or 50% or whatever defines a "cycle"??
timselectric
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I completely misread your original post. lol
My mistake.
timselectric
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That would equal out to about 2 cycles, for the week.
Maybe 3, at best.
Maybe 3, at best.
timselectric
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I wouldn't leave it unattended, in a hot RV.
But other than that, not a problem.
But other than that, not a problem.
timselectric
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Or cold
robby
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As defined by Fortress Power and Confirmed by looking at my BMS Cycle counter.
One full cycle is from 100% SOC to 0% SOC
Even going from 100% to 20% at night does not increment my counter. I have to use another 20% to get an increment.
I often wonder if all companies are using the same method? That could explain the 8000 and 10K cycles I have seen some companies claiming.
One full cycle is from 100% SOC to 0% SOC
Even going from 100% to 20% at night does not increment my counter. I have to use another 20% to get an increment.
I often wonder if all companies are using the same method? That could explain the 8000 and 10K cycles I have seen some companies claiming.
