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Should I be "exercising" my battery regularly?


MdF
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2 hours ago, Tariq said:

i have a 4.8 kWh battery, which I run down to 20-25 % every night, "usually"load shedding is announced, so IF the SOC is low and there is no pv, i charge the batteries from the grid, the only time I got caught flat footed was on a stormy morning, with batteries at 20 % SOC and then we had a power outage, so had to shut down the inverter, so, yes, I don't cater for EVERY situation, but I am getting the most bang for the buck from my batteries.

I have a 6.4 kWp array and run all my major loads during the day, only have 250-450 watt loads at night.

Hi Tariq

How long have you been doing this and what is your observations on the SOH of the batteries?

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1 hour ago, Vani said:

2. (During the day) When the battery charges up to maybe 80% then allowed to discharge to perhaps 65% and then charge up again, is this not using up a charging cycle of the battery??? If this is true, then does it mean that multiple charge cycles are used up each day, and therefore reducing the lifespan of the battery???

I do the same thing and I'm sure it increases the number of cycles. Whether its significant enough to drastically reduce the lifespan of the battery , i'm not sure.

I have asked a similar question on this forum and the answer I got is that the BMS calculates the cycles based on the cumulative energy into and out of the battery, so if you discharge to 50%  and charge back up to 100% it will be 0.5 cycles.

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With Tariq's 98% SOH after 14 months, its not that bad. But i am also pretty sure that the deterioration will not be linear with time.

I think Pylontech talk about having at least 60% capacity (SOH) after 10 years. So Tariq's deterioration does not seem that bad at all

My system is only a month old on the batteries so it will be interesting to see the rate of deterioration based on my "ONE cycle per day" theory.

The idea that a full cycle is accumulated based on percentage discharge and charge reaching a certain point seems to concur with the logic from manufacturers that claim you get more cycles if the DOD is not too low.

Theoretically there could be many small discharge and charge cycles depending on the settings, amount of sun and load demand on any given day. While lithium is resilient, i still "think" the chemistry has certain thresholds that will affect stamina long term. To what extent, only somebody with some long term data can support.

My gut feel is based on the anecdotal evidence of my experience with smartphones.

 

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I found this info on prolonging battery life. It seems to suggest that multiple small discharges and charges are not bad for a lithium battery and if anything can aid longevity.

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

and this one with a snippet below:

https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

image.png.d29de067549a433fcf1861d8f1a09bcc.png

 

 

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19 minutes ago, Vani said:

I found this info on prolonging battery life. It seems to suggest that multiple small discharges and charges are not bad for a lithium battery and if anything can aid longevity.

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

and this one with a snippet below:

https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

 

 

Thank for this information.

MdF

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From battery university; Ideally, you should never fully charge (100% is a no-no) or discharge your battery, charge to 95% and then discharge to max 90% (DoD). High heat and fully charging/discharging a battery is what kills it. The additional 5% from 95 to 100% charge is what stresses the battery. Keeping it at 100% for extended periods is also not good.

The only device I have found that allows me to prevent a battery from fully charging is my Dell laptop, I set it to charge to a max of 95%.

The Goodwe / Pylontech setup charges the battery to 100% but then insists on discharging to 90% every day, at a minimum, if you are running in general mode.

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21 hours ago, Tariq said:

i have a 4.8 kWh battery, which I run down to 20-25 % every night, "usually"load shedding is announced, so IF the SOC is low and there is no pv, i charge the batteries from the grid, the only time I got caught flat footed was on a stormy morning, with batteries at 20 % SOC and then we had a power outage, so had to shut down the inverter, so, yes, I don't cater for EVERY situation, but I am getting the most bang for the buck from my batteries.

I have a 6.4 kWp array and run all my major loads during the day, only have 250-450 watt loads at night.

I have similar base load and run mine down to between 60% and 50% during the evenings. I also allow the battery to be used in preference to the grid during the day, where this is necessary.  Been doing so for about 10-11 months, and battery health is at 99%.

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14 minutes ago, FixAMess said:

From battery university; Ideally, you should never fully charge (100% is a no-no) or discharge your battery, charge to 95% and then discharge to max 90% (DoD). High heat and fully charging/discharging a battery is what kills it. The additional 5% from 95 to 100% charge is what stresses the battery. Keeping it at 100% for extended periods is also not good.

So then, based on this, I should change the table below for the two instances of 100% fully charged to say 98% or even 95%?

Battery_%Charge-01.png

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I'm not sure how much difference the extra 5% makes on reducing battery life over a 10 year period, go to battery view and read all the info, its really good. Their view is probably based on a purely scientific basis, so it might not be practical to only charge to 95%. Your BMS should prevent stressing etc but who knows, the battery and BMS technology changes so quickly maybe the newer BMS's don't stress the batteries.

My BMS takes the battery to 100% but then discharges it to 90% every day so its never kept at 100% for an extended period. 

If you feel it will make a difference then make it 98% for e.g, just not 100%.

 

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I have just set my minimum charge level to 95% from 16:00

So typically it would charge to 100% during the day but won't be there for more than 3 to 4 hours and then start discharging down to 95%.

My SOH also dropped to 99% this week and have been in use since Feb this year (8 months)- I have 3 x 3000C batteries.

Run them down to 40% every night

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  • 2 weeks later...

Morning All,

Just an update on what has happened over the past few weeks since I started exercising my battery on a daily basis.

Here is what I have managed over the past 30 days.

MdF

SA_Overall_29Sep2021-01.PNG

Edited by MdF
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Another interesting question if anyone is in the know. Also related to "exercising". We all can agree that excessive heat hinders battery longevity.

I was noticing that battery temps were higher the more amps I used for charging, albeit anecdotal evidence.

My two 3.5KW batteries can be charged at a max of 74A. Even though CAN is enabled on my Sunsynk 5KW and the BMS is in charge, it still obeys when i set a max charge and discharge below the 74A maximums. So i set it to 50A charge and 50A discharge. It does not breach these user settings even when solar is in excess. Excess solar simply supplies the load or is lost. It does take longer to charge the batteries and there is no downside on a very dull day because solar does not produce 50A on such a day.

Are there any benefits to charging at a lower than max charging amperage? Specifically with regard to heat generation from charging??

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1 hour ago, Vani said:

Another interesting question if anyone is in the know. Also related to "exercising". We all can agree that excessive heat hinders battery longevity.

I was noticing that battery temps were higher the more amps I used for charging, albeit anecdotal evidence.

My two 3.5KW batteries can be charged at a max of 74A. Even though CAN is enabled on my Sunsynk 5KW and the BMS is in charge, it still obeys when i set a max charge and discharge below the 74A maximums. So i set it to 50A charge and 50A discharge. It does not breach these user settings even when solar is in excess. Excess solar simply supplies the load or is lost. It does take longer to charge the batteries and there is no downside on a very dull day because solar does not produce 50A on such a day.

Are there any benefits to charging at a lower than max charging amperage? Specifically with regard to heat generation from charging??

If they are Pylontechs then I expect that the max 74A charge rate will never be allowed by the BMS. I have 4X pylontechs, I've never seen more than 70A charge...Its not a 1C battery, the inverter allows max 100A charge.

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1 hour ago, Vani said:

Are there any benefits to charging at a lower than max charging amperage? Specifically with regard to heat generation from charging??

As long as you keep it at 0,5 c there shouldnt be any excessive degradation from heating up. People baby their LiFePo4 batteries way too much . 

US3000C will do 74 amps for 5+- mins  and 90 amps for a few seconds . Not that i would recommend anyone to do that lol. Everything you do with the battery gets logged by the bms, so if you are pulling 90 amps regularly and the battery breaks they will definitely know about it if you return it and probably not give you a replacement. 

Edited by Nexuss
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This post from another topic which I found useful. It says edzachery what we need to do - use your system as that is what it was designed for 😀

Quote

 

Don't worry about the cycles, as soon the battery hits 80% it counts a cycle, charge a little bit and drop again to 80%, another cycle.
That's why we don't base our warranty on cycles but years.

The cells rating is 7000 cycles full discharge and charge at 0.5c so don't stress to much, utilize the battery or else your not saving on your power bill.
Also another thing that will make the cycles stupid is working of voltage as it keep discharging that bit and charging a bit.

The 56v is a conservative value, only 3.5v per cell.

If you use 4kwh per day from the battery over the life of the battery you will be saving well over 100k on power if calculated at 3.5 bucks per Kwh and the battery won't even be at end of life.

So USE the battery and save on your bill, that's why you got the system in the first place I believe?

So set your bulk and float to 56 if not running with CAN coms 

My suggestion, do coms, set back to AC at 15%, low SOC cutoff to 5% and back to battery at 30%.

 

 

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So, with the cold and rainy weather hitting Gauteng last night, I have had to turn off my usage of the battery at night to allow for the possible Eskom issues during the day that they have predicted for the weekend.

I just do not have enough battery capacity to get us through on that alone when the PV is low.

The piggy bank is starting to be used again to save up for a second battery 🤑

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