LiFePO4 cycles

[xcentric]

What is meant by a battery cycle? (let's ignore odd percentages here and take full as 100% and empty as 0%)
full - empty to full again is one, 1 get that.
but what about 100 - 50 - 100 - one cycle, or half a cycle? And 100-80-100 - ⅕ cycle, or one? just trying to optimise battery charging and discharging options and wondering about battery wear/lifetime.....

 

[chrisski]

Noone will have a good answer for that. Just use the data to realize the lithium batteries will last a long time.

I have serious doubts that each manufacturer comes up with their own cycle data based off their cells and just uses an industry standard chart modified a little.

FWIW, my BMS took two and a half years to get enough cycles to read SOC correctly. Until then one BMS was reading 100% the other 72% when both batteries were full.

 

[FilterGuy]

What is meant by a battery cycle? (let's ignore odd percentages here and take full as 100% and empty as 0%)
full - empty to full again is one, 1 get that.
but what about 100 - 50 - 100 - one cycle, or half a cycle? And 100-80-100 - ⅕ cycle, or one? just trying to optimise battery charging and discharging options and wondering about battery wear/lifetime.....

Different people have different definitions, but most people have some formula around counting a partial discharge-charge a partial cycle.

However, Does it matter? With cycle counts in the 6000+ range even a full 100% -> 0% -> 100% cycle per day will take 16 years, and even then the batteries are supposed to be at 80% of the original Whr capacity.

What people don't talk about (and there is little data about) is Calendar Life. I suspect Callendar Life may be a bigger issue than Cycle life for LiFePO4 batteries in solar setups.

 

[timselectric]

That, 100%.

 

[Steve_S]

There is also a new twist in a way because of the prices dropping. If you build a Lead Acid Bank using Real Solar lead batteries like Trojan or Rolls, the equivalent (8x 6V) 48V/100AH it actually costs you more now. And with exceptional care & maintenance, you may get 7/8 years +/-. LFP really does rule the roost for ESS systems now.

 

[Mattb4]

.. just trying to optimise battery charging and discharging options and wondering about battery wear/lifetime.....

I have only a couple years experience with LiFePO4 so far so my advice may not be the best practice, but it is what I do. I choose Conservative charge and discharge. I limit my max charge voltage to 3.55vDC (often only 3.5 during initial break-in of a new battery) and I do not discharge below 3.00vDC. Typical capacity use for my over night needs results in 25-30% discharge before solar begins to restore. Seems to avoid issues.

I am really curious of how long these dirt cheap LiFePO4 batteries I have last. I figure anything over 3 years is a great deal. My oldest one is now just 2 months shy of 2 years.

But as to cycles counts I really don't care all that much as I do total longevity.

 

[xcentric]

helpful, all - thanks. Was wondering if using agile pricing and optimising feed-in @15p/kWh from solar and battery, whilst avoiding using peak power on agile and topping up battery etc would cause too many changes and lead to increased battery wear, but I've got the point that it'll be a good dozen years and even then the batteries should be at 80% - so not to worry about it.