LiFePO4 and absorption charging

[CaptainRivet]

Originally Posted by newhaul

Your boat your choice and all that
Now why every 3 months and please be concise. Shorter the answer the better for my mind.

The small balancer in these no communication dropins has not much power so it's key to get an imbalance as soon as possible and from 20 years Experience all 3 month is the best compromise timeframe to check in a well(!) adjusted system if everything OK.
If not OK the deviation won't be too big so you can change settings and the small passive balancer in these no communication dropins can still get it back to balance in normal(!) operations without loosing lifespan.
If a dropin like this is heavily out of balance it's a painful time consuming emergency process with also long time at very high SOC to get it back to balance which then costs lifespan. And that is what you wanna avoid by checking at least all 3 month, earlier checks won't harm, later checks rise the chance exponentially that it's already heavly out of balance if someting is wrong before you discover it.
That's as short as possible.

Sure your boat your choice, an as low as possible absorption voltage and time brings you the longest lifespan, how to do that without communication I described above. Follow it or not, I just help and give you advise how to do it right.

[HeinSdL]

So I further learned here: even with these no communication 'surprise' boxes (which includes Litime which so far has surprised only to the upside for me and others) it IS possible to get an indication of how well the cells are balanced by occasionally going to 14.6. If no cut off occurs or in any case doesn't occur much below 14.6 that would mean that the cells are in balance, any cell beyond 3.65 would cause the BMS to trip so getting to near to 14.6 is a good result.

A battery experiencing a high voltage cutoff doesn't damage the battery? It's kind of designed to do that in a clean and controlled way? Of course I would not at the same time be doing something energy critical so no load on the battery.

[CaptainRivet]

Originally Posted by HeinSdL

So I further learned here: even with these no communication 'surprise' boxes (which includes Litime which so far has surprised only to the upside for me and others) it IS possible to get an indication of how well the cells are balanced by occasionally going to 14.6. If no cut off occurs or in any case doesn't occur much below 14.6 that would mean that the cells are in balance, any cell beyond 3.65 would cause the BMS to trip so getting to near to 14.6 is a good result.

A battery experiencing a high voltage cutoff doesn't damage the battery? It's kind of designed to do that in a clean and controlled way? Of course I would not at the same time be doing something energy critical so no load on the battery.

Not near 14.6V, you want the battery to cut off every time you do this test (that's why 14.6V with a high absorption time, i use an MPPT and just set with the app the values higher for the test)and remember/note down that voltage always from the same source eg your bat monitor.
If that cutoff voltage get lower and lower from your reference voltage the surprise box gets out of balance and you need to countersteer by raising absorption voltage and time.
Key for all that is a proper top balanced battery which you achieve simplest by running the dropin for 1 month with 14.4V and 30min absorption per 100AH. That makes 100% sure it's top balanced as good as it can be, if cuts off then it was not top balanced at all or you have bad quality cells with high deviation, then go down to 14.2V first and when not cutting off raise step by step to 14.4V during that month. If you know how to properly do this another way eg power supply or the manufacturer describes it in the manual go ahead, important is its 100% top balanced. Then charge till cutoff and note down the cutoff voltage. That's your reference value/voltage.

No cutoff doesn't harm the battery at all and you also test it still works properly in case you really need it it works.
What harms is keep it at that high state of charge, so put a load on it and discharge it afterwards.

If your drop in has parallel cells inside (to find out search for a teardown of your make/exact model or homepage) you always need a longer absorption time as the parallel cells only even themselves out in the upper knee AND the balance current is half as its 2 cells in parallel!!!
If you buy new avoid that, if you have them already my advice would be not to go below 14.4V absorption voltage and 15min per 100AH based on 20 years experience. Better keep them on this higher voltage longer as long before that little reduction in lifespan will come into affect that battery will be heavly out of balance which causes much more harm. That's only for surprise box dropin!!!

[newhaul]

Originally Posted by CaptainRivet

The small balancer in these no communication dropins has not much power so it's key to get an imbalance as soon as possible and from 20 years Experience all 3 month is the best compromise timeframe to check in a well(!) adjusted system if everything OK.
If not OK the deviation won't be too big so you can change settings and the small passive balancer in these no communication dropins can still get it back to balance in normal(!) operations without loosing lifespan.
If a dropin like this is heavily out of balance it's a painful time consuming emergency process with also long time at very high SOC to get it back to balance which then costs lifespan. And that is what you wanna avoid by checking at least all 3 month, earlier checks won't harm, later checks rise the chance exponentially that it's already heavly out of balance if someting is wrong before you discover it.
That's as short as possible.

Sure your boat your choice, an as low as possible absorption voltage and time brings you the longest lifespan, how to do that without communication I described above. Follow it or not, I just help and give you advise how to do it right.

To un muddy it your saying that the bms in a dropin is crappy so you need to check the battery every 3 months .

If something like your scenario happens that's what the warranty is for .

That is the same but much shorter.

I bet you are the guy that used a hydrometer every month on your old GC2 batteries to make sure all was good.

[CaptainRivet]

Originally Posted by newhaul

To un muddy it your saying that the bms in a dropin is crappy so you need to check the battery every 3 months .

If something like your scenario happens that's what the warranty is for .

That is the same but much shorter.

I bet you are the guy that used a hydrometer every month on your old GC2 batteries to make sure all was good.

The BMS is not by default crappy, it's balancer has just not enough power in normal operation to correct if you f.. with absorption or you have bad quality cells inside.
Mostly troubles with surprise dropin occur because people who buy them new read or get advice to put absorption at 13.8V. But these are not top balanced properly when you received them and with this low absorption voltage and the passive balancer the battery has no chance to correct that so after 3 till 6 month it cuts off at 14.0V or even below. Congrats in best case you reduced it's lifespan by min 10% as the emergency process to get that back in balance involves keep it constantly at a very high state of charge for weeks...

No I am definitely not that guy, that's why my lead always died before a typical lifespan....
I also don't buy surprise boxes without communication, I built the batteries myself now preffered with the EEL kits.

That process you have to do once and roughly every 3 month just set one MPPT to 14.7V and wait at what voltage the BMS cuts off the chargebus.
I don't need to do this as I get warning if mine runs out of balance and a powerfull 5A active balancer makes sure that also at 13.8V with 15min absorption my 1088AH 4P4S bank stays in balance.

[Chotu]

this is interesting. Really liking where the thread has gone. I’m going to try the top cutout test out a bit later.

is it harmful to the solar charge controllers to have the load just pulled away like that while they are in the middle of charging? Is that abusive to them at all?

my BMS cuts out only for a second, literally, and then is back on, then cuts out for a second, then back on and repeats. This is the default cut out for over voltage.

Overcurrent is a 20 min cutout, returning if the short is fixed. it behaves differently for different situations


Was thinking of doing this on the generator with AC->DC charger that i care less about and never use

[newhaul]

Originally Posted by Chotu

this is interesting. Really liking where the thread has gone. I’m going to try the top cutout test out a bit later.

is it harmful to the solar charge controllers to have the load just pulled away like that while they are in the middle of charging? Is that abusive to them at all?

my BMS cuts out only for a second, literally, and then is back on, then cuts out for a second, then back on and repeats. This is the default cut out for over voltage.

Overcurrent is a 20 min cutout, returning if the short is fixed. it behaves differently for different situations


Was thinking of doing this on the generator with AC->DC charger that i care less about and never use

Your solar panels and controllers don't care at all

[newhaul]

Originally Posted by CaptainRivet

The BMS is not by default crappy, it's balancer has just not enough power in normal operation to correct if you f.. with absorption or you have bad quality cells inside.
Mostly troubles with surprise dropin occur because people who buy them new read or get advice to put absorption at 13.8V. But these are not top balanced properly when you received them and with this low absorption voltage and the passive balancer the battery has no chance to correct that so after 3 till 6 month it cuts off at 14.0V or even below. Congrats in best case you reduced it's lifespan by min 10% as the emergency process to get that back in balance involves keep it constantly at a very high state of charge for weeks...

No I am definitely not that guy, that's why my lead always died before a typical lifespan....
I also don't buy surprise boxes without communication, I built the batteries myself now preffered with the EEL kits.

That process you have to do once and roughly every 3 month just set one MPPT to 14.7V and wait at what voltage the BMS cuts off the chargebus.
I don't need to do this as I get warning if mine runs out of balance and a powerfull 5A active balancer makes sure that also at 13.8V with 15min absorption my 1088AH 4P4S bank stays in balance.

I build my banks unless customer specifically asks for ' drop ins" and I use dumb BMS units .top balance 1 time on the bench then verify balance once a year with a fluke meter to .001v
Never have had any out of balance more than .005v in a 5 year time-frame. So don't see the need to micro manage the bank like you seem to feel should he done .
Just run the bank from 20% to 90% and stay off the knees .
Do you have technical reports from manufacturers to support your opinions?
I do.

[sailorboy1]

Originally Posted by newhaul

Do you have technical reports from manufacturers to support your opinions?
I do.

did you not read earlier how manufacturers are stupid and forums are smart

[newhaul]

Originally Posted by sailorboy1

did you not read earlier how manufacturers are stupid and forums are smart

Yes I saw that fart in the wind.
After all these years on here you know I'm not that guy I have the technical papers to back up my statements . I'm just asking if there is new data that I don't have as I do wish to expand my technical knowledge.

[barcoMeCasa]

Originally Posted by newhaul

Just run the bank from 20% to 90% and stay off the knees .

Why stay off the top knee?

How can you know what the SOC is without hitting the top knee?
(ignoring the paranoia of needing to balance constantly)

It seems the only repeatable accurate piece of data available.

[newhaul]

Originally Posted by barcoMeCasa

Why stay off the top knee?

How can you know what the SOC is without hitting the top knee?
(ignoring the paranoia of needing to balance constantly)

It seems the only repeatable accurate piece of data available.

99% of my charging is to 13.8v
One time a year I charge to 14.6v to reset my meter
I have never even gone below 50% except when doing my annual capacity check.

[barcoMeCasa]

Originally Posted by newhaul

99% of my charging is to 13.8v
One time a year I charge to 14.6v to reset my meter
I have never even gone below 50% except when doing my annual capacity check.

Same here, 13.8V.

Which is well into the top knee.

I set the smartshunt capacity manually to 95% SOC when the solar regulators go to float if/when it starts to drift either way.

Easy to see with a Pi logging everything, even when the fridge runs can make a difference to SOC if it kicks in very near the knee as it pulls down the voltage just enough to keep the it charging for a little longer.

[newhaul]

Originally Posted by barcoMeCasa

Same here, 13.8V.

Which is well into the top knee.

I set the smartshunt capacity manually to 95% SOC when the solar regulators go to float if/when it starts to drift either way.

Easy to see with a Pi logging everything, even when the fridge runs can make a difference to SOC if it kicks in very near the knee as it pulls down the voltage just enough to keep the it charging for a little longer.

My boat is my escape from technology as much as possible while still having information available.
My mppt is Bluetooth and that's how I check everything .
I hate micro management. I did enough of that when on the Dungeness crab boats in summer season .
My refrigeration runs most after my bank is full.
Holding plate system .
When my battery monitor says full I turn on the watermaker. Or cook some rice.

[sailorboy1]

Originally Posted by newhaul

Yes I saw that fart in the wind.
After all these years on here you know I'm not that guy I have the technical papers to back up my statements . I'm just asking if there is new data that I don't have as I do wish to expand my technical knowledge.

doesn't matter what I think, I am just a forum member trying to live in a practical world

I had a thread once about charging LFP batteries to 100% charged all the time and that is pretty much the same as this thread. I searched and read tech papers for days and the closest to this I could find was about leaving them fully charged at storage. In that it looked that the capacity loss was 3-5%. That in a practical boat world is meaningless plus we weren't really talking about leaving them there. I got crucified by the "experts" who "knew" the right answer.

In all these threads it seems people have lost sight that we are talking about boat battery use. Batteries are there to serve us, we aren't there to serve them. We lived in past with acid batteries and now we are concerned about a few % of LFP capacity, which is still WAY better than the acid batteries were. And the LFP batteries are now cheap in the big picture. My cheap drop in LFP batteries cost what my current house electrical cost is for 7 months and have been operating for 2 years. If they only last 4 years it works out to $27/mo. What a GREAT deal!