Please Define a Battery Cycle

[AgroVenturesPeru]

Let's say I have a LiFePO4 battery bank connected to a charge controller and a solar panel array and an off-grid inverter, and I turn on an electric oven that uses 4000w but my mppt is only outputing 3000w from the solar panel array, resulting in a net draw from the battery bank of 1000w. I leave the oven on for a few minutes and it discharges the battery bank by 10%. Then I turn the oven off and the battery bank recovers this 10% with the 3000w of solar power. Is that considered a Cycle?

 

[SeaGal]

No

 

[SeaGal]

.... it will depend on the algorithm implemented by your specific BMS, but safe to say it will usually be a cycle from a high-ish SOC down to a low SOC and back up again. Mine is showing 125 cycles in just over 200 days usage when most days we use a significant % of the battery capacity.

But if it starts at 100% and goes down to say 60% then back up again, that doesn't increment the cycle counter.

 

[Farm Boy]

.... it will depend on the algorithm implemented by your specific BMS, but safe to say it will usually be a cycle from a high-ish SOC down to a low SOC and back up again. Mine is showing 125 cycles in just over 200 days usage when most days we use a significant % of the battery capacity.

But if it starts at 100% and goes down to say 60% then back up again, that doesn't increment the cycle counter.

I'm using eg4 life power batteries, how would I tell how many cycles it's had?

 

[629658]

My system installed in Sept. lowest draw down 42% so far. My BMS still registers zero cycles. I usually work in the 60-95% SOC range.

 

[SignatureSolarPeyton]

I'm using eg4 life power batteries, how would I tell how many cycles it's had?

You can use the BMS Interface Software to see cycles, I'll attach a video that explains how to set it all up.

 

[Farm Boy]

You can use the BMS Interface Software to see cycles, I'll attach a video that explains how to set it all up.

Thanks!

 

[Ampster]

My inverter tracks the total kWh my battery was charged each month. In February my 42 kWh battery was charged 448kWh. In my mind that was 10.3 cycles or an average of 16kWhs per day. I am sure there is some overhead but my winter usage is greater than spring, summer and fall so I would guess I do less than 100 full cycles per year. That is how I define a cycle.

 

[sunshine_eggo]

Let's say I have a LiFePO4 battery bank connected to a charge controller and a solar panel array and an off-grid inverter, and I turn on an electric oven that uses 4000w but my mppt is only outputing 3000w from the solar panel array, resulting in a net draw from the battery bank of 1000w. I leave the oven on for a few minutes and it discharges the battery bank by 10%. Then I turn the oven off and the battery bank recovers this 10% with the 3000w of solar power. Is that considered a Cycle?

Yes and no. Some might call that a micro-cycle or mini-cycle.

A cycle is any time the battery is charged and discharged or vice versa.

How does that relate to the cycle life of the batteries? That's where it comes down to the BMS algorithm as has been mentioned above.

If you only cycle between 80% and 20% at 0.2C and mild temperatures, you should experience more than the stated cycle life. How much more? Nobody but the cell manufacturer knows.

Different BMS and battery monitors count cycles in different ways. Mentally, I just think of it linearly. If it says I'll get 4000 cycles at 80% DoD, then I'll get 40,000 cycles at 8% DoD. This is conservative as it will likely be even more than that.

If you're worried about consuming cycles with shallower discharges, that's not a thing, i.e., that 10% cycle you describe does not consume one of the rated cycles.

Like @Ampster my Victron BMV reports total extracted energy. I can divide that by capacity and get an equivalent cycle value, e.g., if my 5kWh battery has delivered 500kWh of energy, that's 100 cycles.

 

[mountkay]

Ill link a post i made about different Depth of Discharge amounts and the effects they can have on a battery. For instance a DoD of 10% from 100% to 90% is worse for the battery than a 10% DoD from 75% to 65%. Basically there is a lot to what helps keep a battery healthy and its complicated when you are doing small amounts of discharge and charging in a solar system. This is why most manufactures will give a certain statement like 7000 cycles at 80% DoD.

Hopefully this post and the one im linking can help you understand how battery cell chemistry is a very dynamic thing, and there many ways you can measure it, each one only giving a snapshot of the truth. I like to just think of the batteries as living things because of how complicated they are. How could you determine the health of a plant or a person? There are many ways you can measure it per-say, but the absolute truth will be difficult to know. But the more you understand about how health works, the better you can grasp whats really going on.

You could consider your 10% DoD a cycle, but you can do 10s of thousands of those cycles as opposed to just 7000 80% DoD cycles

what should be the state of charge change so as not to damage battery

I have a Growatt with 48V pack, LFP, using a Neey active balancer and Solar Assistant to provide data. Solar assistant will allow me to turn on/off Utility vs Solar/Battery/Utility based on the calculated state of charge of the battery. How low should the state of charge be allowed to go...

diysolarforum.com

 

[629658]

Ill link a post i made about different Depth of Discharge amounts and the effects they can have on a battery. For instance a DoD of 10% from 100% to 90% is worse for the battery than a 10% DoD from 75% to 65%. Basically there is a lot to what helps keep a battery healthy and its complicated when you are doing small amounts of discharge and charging in a solar system. This is why most manufactures will give a certain statement like 7000 cycles at 80% DoD.

Hopefully this post and the one im linking can help you understand how battery cell chemistry is a very dynamic thing, and there many ways you can measure it, each one only giving a snapshot of the truth. I like to just think of the batteries as living things because of how complicated they are. How could you determine the health of a plant or a person? There are many ways you can measure it per-say, but the absolute truth will be difficult to know. But the more you understand about how health works, the better you can grasp whats really going on.

You could consider your 10% DoD a cycle, but you can do 10s of thousands of those cycles as opposed to just 7000 80% DoD cycles

what should be the state of charge change so as not to damage battery

I have a Growatt with 48V pack, LFP, using a Neey active balancer and Solar Assistant to provide data. Solar assistant will allow me to turn on/off Utility vs Solar/Battery/Utility based on the calculated state of charge of the battery. How low should the state of charge be allowed to go...

diysolarforum.com

At the end of the day you bought the batteries to use them. Like everything they have a life and will need replacement at some point. My batteries have a 10 year warranty (if they are in business). In 10 years we will not be using what we are now.