Frequency of getting LFP batteries fully charged

[sailorboy1]

I love how after all this time there isn't any agreement really on how to operate a LFP bank :-) . There are just "camps" of position groups.

[PaulCrawhorn]

The average depth of discharge per cycle is EXTREMELY influential on cycle lifespan.

Sitting at high SoC less so but still a strong factor.

There no "opinion" involved in these causative relationships.

But it is true that many owners are not interested in the complications of varying from "normal usage" patterns (lead thinking) in order to extend longevity.

And that is a valid choice if course, their boat.

15 years and still at 95% capacity is for me just past break in stage, others can't imagine it...


> Attempting to balance lower might actually unbalance them.

There is no such thing as a "balanced" battery without stating what SoC/voltage point.

By definition a set in balance at the top will be unbalanced at the bottom, and vice versa

Originally Posted by wholybee

Also, an active balancer will not balance cells at a lower voltage. You can only balance cells at a higher voltage, in the upper knee. Period.

Absolute rubbish, but yes for 99.99% based on the industry, standard practice.

If your cells are of good quality and always cycle between (at most) 3.05V and 3.40 you may not need to re-balance for years at a time.

If your LVC is per-cell based but HVC is pack-voltage, then top balancing is best.

If your HVC is per-cell based but LVC is pack-voltage then you should use bottom balancing.

Most balancer devices cannot do the latter at all.

The term "active balancer" is often misused, and in general they are rarely used at all but most of them can indeed balance at any chosen SoC/voltage point selected.

Now you may be saying "I believe top balancing is best" or even "top balancing is the only way" but that is a completely different statement from the last bit there.

[sailorboy1]

sorry but I didn' really understand a lot of that and I don't plan to figure it out, did it answer the topic queestion?

[Fuss]

Originally Posted by PaulCrawhorn

The average depth of discharge per cycle is EXTREMELY influential on cycle lifespan.

Sitting at high SoC less so but still a strong factor.

There no "opinion" involved in these causative relationships.

But it is true that many owners are not interested in the complications of varying from "normal usage" patterns (lead thinking) in order to extend longevity.

And that is a valid choice if course, their boat.

15 years and still at 95% capacity is for me just past break in stage, others can't imagine it...


> Attempting to balance lower might actually unbalance them.

There is no such thing as a "balanced" battery without stating what SoC/voltage point.

By definition a set in balance at the top will be unbalanced at the bottom, and vice versa


Absolute rubbish, but yes for 99.99% based on the industry, standard practice.

If your cells are of good quality and always cycle between (at most) 3.05V and 3.40 you may not need to re-balance for years at a time.

If your LVC is per-cell based but HVC is pack-voltage, then top balancing is best.

If your HVC is per-cell based but LVC is pack-voltage then you should use bottom balancing.

Most balancer devices cannot do the latter at all.

The term "active balancer" is often misused, and in general they are rarely used at all but most of them can indeed balance at any chosen SoC/voltage point selected.

Now you may be saying "I believe top balancing is best" or even "top balancing is the only way" but that is a completely different statement from the last bit there.

Thanks for this post.
Is it possible to give some information on your charging regime on your boat. For example, the main BMS settings and when the BMS does it’s balancing.

How do you handle the battery being almost fully charged and now you start motoring for 8 hours, do you switch off the alternator or just ignore as the alternator is only charging to a lower voltage like 13.6 for example.

I imagine that 15 years is only possible if the day to day unplanned boat activities like motoring and solar and big discharges like electric cooking are working in a style that does not significantly degrade the batteries.

This would be interesting to those of us who don’t want to damage our batteries but also don’t want to be a slave to them either.

[wholybee]

Originally Posted by Fuss

Thanks for this post.
Is it possible to give some information on your charging regime on your boat. For example, the main BMS settings and when the BMS does it’s balancing.

How do you handle the battery being almost fully charged and now you start motoring for 8 hours, do you switch off the alternator or just ignore as the alternator is only charging to a lower voltage like 13.6 for example.

I imagine that 15 years is only possible if the day to day unplanned boat activities like motoring and solar and big discharges like electric cooking are working in a style that does not significantly degrade the batteries.

This would be interesting to those of us who don’t want to damage our batteries but also don’t want to be a slave to them either.

15 years is almost a given if you start with high quality cells, do not overcharge, and do not completely discharge.

I have seen nothing to indicate that deep discharging an LFP battery shortens its life. In fact, Rod Collins, who has perhaps done more testing than anyone else in this application, claims to only charge every few days when his batteries are deeply discharged, and thus less time near 100%. He does not charge to 3.65Vpc, but still very close to 100%(IIR 3.55Vpc). He is also well over 15 years, and tests his batteries at 100% of original advertised capacity.

The information posed about balancing at lower SOC is plain wrong. It is impossible to balance except at nearly 100% or nearly 0%. The voltage curve of LFP between 10% and 90% is very flat. So you can match cells to the same voltage, but they can still be 10%,20%, or even 30% different in SOC(not balanced). But if you charge them to 100%, where the voltage curve is steep, you know they are all 100% SOC, and balanced. The reason to balance is so that when you charge to 100%, all cells reach 100% at the same time. There is no other reason to balance. So any balance at less than 100%, where the SOC might vary by as much as 30%, is pointless and doesn't actually balance them.

The most damaging thing to LFP cells, show by many studies and testing, is heat. Don't put them in the engine bay. And you will probably have to live with a slightly reduced life in the tropics unless you have A/C. High SOC also reduces life, but mostly when combined with high heat. In cooler climates, the damage by high SOC is minimal, but still there.

[Sailingcal21]

I couldn't vote as requested, because "fully", IMHO, is kinda subjective.

I've set my 100% SOC at 14.0 vdc. During the sailing months I charge to 14.0 vdc and 13.6 vdc during the off season. My LFPs rarely go below 13.2 vdc before the PV/MPPT kicks in and charges them back. Only 24/7 load is refrigeration and a small fan for ventilation.

[patja]

Victron used to state that their LFP batteries needed to be fully charged monthly in order to balance the cells. They've made a firmware update and now require that their LFP batteries spend at least two hours per month in absorption in order to balance cells. This is what has kept me from adjusting an "off season/storage" charging profile to keep them at say 70% to 90% rather than "floating" at 100% -- I can't see myself going to the boat each month just to change the profile and balance cells and then running them down to store at 70 - 90% until the next month. I'll be a test case for whether keeping them at 100%/float will kill them.

[IolantheSF]

LiFePO4 batteries last longest when kept near 50% SOC. Cycling between 20% / 80% is fairly optimal. Charging to 100% or discharging to 0% will dramatically shorten their life. Using a lead-acid charging profile on them is very sub-optimal. Get a quality programmable BMS and let it do its job.

[wholybee]

Originally Posted by IolantheSF

LiFePO4 batteries last longest when kept near 50% SOC. Cycling between 20% / 80% is fairly optimal. Charging to 100% or discharging to 0% will dramatically shorten their life. Using a lead-acid charging profile on them is very sub-optimal. Get a quality programmable BMS and let it do its job.

This is people trying to apply lead acid rules to LFP. For some reasons people have a hard time believing that similar rules don't apply to LFP.

Perhaps you missed the recent comment by Mainsail / Rod Collins, a foremost expert on the topic. His personal battery he uses as much capacity as he can, and has taken it all the way to 0% about 100 times. His battery is 15 years old and still has 100% of its original capacity. Don't overcharge, don't charge to 3.65Vpc, but a bit lower, 3.5Vpc. You can still get very close to 100% SOC, and the battery will outlast your boat.

https://www.cruisersforum.com/forums...ml#post3738110

[Sailingcal21]

Originally Posted by patja

Victron used to state that their LFP batteries needed to be fully charged monthly in order to balance the cells. They've made a firmware update and now require that their LFP batteries spend at least two hours per month in absorption in order to balance cells. This is what has kept me from adjusting an "off season/storage" charging profile to keep them at say 70% to 90% rather than "floating" at 100% -- I can't see myself going to the boat each month just to change the profile and balance cells and then running them down to store at 70 - 90% until the next month. I'll be a test case for whether keeping them at 100%/float will kill them.

Definitely the manufacturer knows best for their product. However not sure how'd you accomplish that protocol without a monthly visit. Perhaps Renogy sells a charger specifically for their batteries that will do the job for you.

I'm one of those wildcats who have built their LFP battery and used an Overkill BMS which allows its passive balancer to be programmed in terms of when its active/inactive. I also use an active balancer which I can control if necessary. In practice, I periodically check the cell balance and have never found one of them to be grossly far from the pack that would require rebalancing.