Best LifePo4 charge controller settings known to man for Maximum Service life and Minimum battery stress!!! 5,000-10,000+ cycles?

[Go2Guy]

I

see PM, we have hijacked this too much already.

My apologies to the readers for the Hijack, was not intentional. Back to your Regular Programming.

I dont mind I just want the ability to add any points that are brought up to the main post, any it becomes difficult when its to much data, BUT with discussion comes great knowledge which i am grateful for, I just want a way to cliff note this data to add to the main post. .

 

[Horsefly]

I

I dont mind I just want the ability to add any points that are brought up to the main post, any it becomes difficult when its to much data, BUT with discussion comes great knowledge which i am grateful for, I just want a way to cliff note this data to add to the main post. .

@Go2Guy - I hate to speak for @Steve_S (he does it pretty well himself) but I think the three main points he made - if I were to reduce them to bullet points - are:

1. Temperature matters, because colder cells will accept current (absorb energy) slower than warmer ones. This can be important when you have more than one parallel battery being charged.
2. With this chemistry, millivolts matter. In the case of AGMs or any other lead acid, you can get things to the nearest 1/10th of a volt and it's probably OK. Not so much with LiFePO4.
3. Recognize that there are voltage drops throughout your system, even with large wires. Because of #2 (millivolts matter), you need to know and account for those drops from your SCC and Inverter/Charger to your battery at different charge currents and as the charge cycle finishes.

I'm sure if I didn't get that right Steve will correct me.

 

[curiouscarbon]

(you can actually watch the resistance push back against the charge input)

neat!

SERVER/TELECOM Rack-mounted batteries, or Battery Packs on shelves.
Again, remember heat rises and the bottom will always be cooler than the top and while not a Huge Difference it does make a difference.

Now if you are in an area where it is always between 20-30 Celsius year-round then no worries EH !

But if you live in an area with -30C to +40C temps, you're in the thick of it.

?️

IR in the cold. During my Thrash Testing last spring which pushed Max Amps at pack limits, one of those cycles was with the Batteries at 0C/32F. The IR was definitely higher as they resisted and would not accept full charge at them but as they warmed during charge the amount of Amps taken went up. @ 0C/32F they took 40A at the start ut within an hour they were up to 100A and another 1/2 or so the 280 was taking 140A but then it started to drop as it filled up. I did that with 2x280's and 2x175's each independently. With the reconfig, I will have to do another Thrash Test Run and may document that whole process on here for everyone to see but it is very time-consuming to do (worse now because the bank grew) and there is a lot in between, fortunately it is not too physically demanding so it should not be a problem to do for the last time. I want to Doc it anyways to go with the Solar System Docs I am doing to go with the house when it gets sold, along with the House design & build documentation that started with the 1st tree being cleared off the land.

thank you, taking notes, i'm in a warmer area and few naturally occurring opportunities to discover these finer points of LiFePO4 operation in cold temperatures.

 

[Mr-Sandman]

This is a very educational thread.

In my setup I have a Schneider MPPT and XW Pro and sell to the grid. I have (3) EG4 batteries that are there as a buffer and for power outages. They pretty much stay at 100% SOC all the time. Overnight they might get pulled down to 96% SOC, but easily charge back up in the morning with low amperage and then the system starts selling.

My application doesn't cycle the batteries on a normal basis, they are essentially held near 100% SOC waiting on a power failure. Would that be consider storing them at 100% SOC which is not recommend? They are in climate controlled room and should never be over 80F.

Thoughts on the battery life of batteries used for emergency backup with constant 100% SOC?

 

[Steve_S]

This is a very educational thread.

In my setup I have a Schneider MPPT and XW Pro and sell to the grid. I have (3) EG4 batteries that are there as a buffer and for power outages. They pretty much stay at 100% SOC all the time. Overnight they might get pulled down to 96% SOC, but easily charge back up in the morning with low amperage and then the system starts selling.

My application doesn't cycle the batteries on a normal basis, they are essentially help near 100% SOC waiting on a power failure. Would that be consider storing them at 100% SOC which is not recommend? They are in climate controlled room and should never be over 80F.

Thoughts on my application and the battery life of batteries used for emergency backup with constant 100% SOC?

Just about every Spec Sheet for cells of any format LFP clearly state that keeping them @ High SOC its not healthy. They do need to work & cycle at least partially and should remain below 3.450Vpc and not in the knees. If stored static over time it's best at 50% @ 25C temp average.

SOC is relative & subjective and that is where most get muddled. Working Range (3.000-3.400) vs Full Range (2.500-3.650) and what do "you" designate as your 0% and 100% ? MY 100% = 3.425Vpc, 0% = 2.900Vpc which takes in the full "Working Range". ALSO LFP will always settle post charge which on average is about 1.0V within an hour, even when saturated.

 

[Horsefly]

Thoughts on the battery life of batteries used for emergency backup with constant 100% SOC?

A little bit of a variation on what @Steve_S said: It seems like your SoC may remain at or near 100%, but you clearly should try and stay away from the 3.65V/cell 100% charge voltage except as a part of regular cycling. Rather your cells should remain at a float level most of the time, e.g. 3.35V or 3.4V (as captured by @Go2Guy in the first post)

If you think of it that way, it may be that your charge profile is really no different than those of us that cycle frequently: Set your bulk / absorption to 3.45V or 3.5V (again, per the first post), but yours will not be at that voltage long, since the cells are at almost 100% already. So the current should drop quickly (0.02C - 0.05C), and the charge profile should then drop down into float. You'll stay there until you use some energy overnight and the charge source (PV, mostly) is not there. In the morning, your SCC will initiate back in Bulk / Absorption and you go again.

In this way, your charge profile may be just exactly the same as mine, but you may be in bulk and absorption for 15 minutes out of each day, and float the rest of the day.

 

[sshibly]

deleted wrong thread, sorry

 

[Mr-Sandman]

Right, so my current mode of operation is to Bulk/Absorb to 3.4 volts when the sun comes up which takes them to about 98%/99% SOC on the batteries BMS at less than 10 amps of current in less than 30 mins. Then it immediately goes to float at 3.35 for remainder of day.

Even though the BMS's show 98% to 100%, the batteries are not charged into the "heals" at all. I figured I would do a higher charge occasionally to engage cell balancing in the BMS.

I don't have to have 100% SOC I would be fine for emergency use at 90% or even 80%. I would consider this if it helped extend their life.

 

[Steve_S]

Right, so my current mode of operation is to Bulk/Absorb to 3.4 volts when the sun comes up which takes them to about 98%/99% SOC on the batteries BMS at less than 10 amps of current in less than 30 mins. Then it immediately goes to float at 3.35 for remainder of day.

Even though the BMS's show 98% to 100%, the batteries are not charged into the "heals" at all. I figured I would do a higher charge occasionally to engage cell balancing in the BMS.

I don't have to have 100% SOC I would be fine for emergency use at 90% or even 80%. I would consider this if it helped extend their life.

That's right on there. You just showed the GOTCHA with BMS', they have to go through "your cycle" and learn. Many assume they are preset but the defaults for SOC change as the cells get charged & discharged. Yes they read the collective cell voltages but the coulomb counting takes it from there. It does work differently with different BMS' but basically the same effect. Some you have to take up to "your" 100% and then set the AH/kWh values and then ned a full cycle down to where you mark the 0%. Others just need to run through a full cycle and just held at your 100% and they auto set from there. Even the most common, JBD, JK, Chargery, Daly even have their own peculiarities and some are annoying to boot.

 

[Horsefly]

Right, so my current mode of operation is to Bulk/Absorb to 3.4 volts when the sun comes up which takes them to about 98%/99% SOC on the batteries BMS at less than 10 amps of current in less than 30 mins. Then it immediately goes to float at 3.35 for remainder of day.

Even though the BMS's show 98% to 100%, the batteries are not charged into the "heals" at all. I figured I would do a higher charge occasionally to engage cell balancing in the BMS.

I don't have to have 100% SOC I would be fine for emergency use at 90% or even 80%. I would consider this if it helped extend their life.

Yeah, I'll admit I feel better if I charge to a high enough voltage that both my BMS and SmarthShunt re-sync themselves to 100% SoC. Otherwise, I don't know that you can trust the SoC that is being reported. I don't know what BMS you have, but on the JBD / Overkill you can set the "Single Full" voltage (I think that is the one) to whatever your bulk / absorption voltage is. When it gets to that level, the BMS will reset the SoC to 100% and you will be good to go. I personally like 3.45V better and actually use 3.5V myself, but I know others that I respect say 3.4V, so I think that is valid too.

 

[Mr-Sandman]

I have (3) 48V EG4 LL batteries "ones with LCD screen", so I don't know for sure what BMS that is either. I'm not sure when the balancing engages or the SOC resets. That would be good info to have for an occasional balance and SOC reset, to make sure I go high enough, but not stress the battery too much.

 

[Horsefly]

I have (3) 48V EG4 LL batteries "ones with LCD screen", so I don't know for sure what BMS that is either. I'm not sure when the balancing engages or the SOC resets. That would be good info to have for an occasional balance and SOC reset, to make sure I go high enough, but not stress the battery too much.

I assume the EG4 battery doesn't provide any Bluetooth or other access to the settings of the BMS? Ugh.

 

[Mr-Sandman]

I assume the EG4 battery doesn't provide any Bluetooth or other access to the settings of the BMS? Ugh.

They have access to the BMS via USB and RS-485 port. I hooked the laptop up and looked at it once.. Those parameters might be in there, but nothing can be changed, read only

 

[Dzl]

This is a very educational thread.

In my setup I have a Schneider MPPT and XW Pro and sell to the grid. I have (3) EG4 batteries that are there as a buffer and for power outages. They pretty much stay at 100% SOC all the time. Overnight they might get pulled down to 96% SOC, but easily charge back up in the morning with low amperage and then the system starts selling.

My application doesn't cycle the batteries on a normal basis, they are essentially held near 100% SOC waiting on a power failure. Would that be consider storing them at 100% SOC which is not recommend? They are in climate controlled room and should never be over 80F.

Thoughts on the battery life of batteries used for emergency backup with constant 100% SOC?

From recollection--and with the caveat that my understanding comes primarily from a single study on calendar aging + bits and pieces I've picked up here and there--the data I've seen on storage SOC and lifepo4 health/degradation, shows that:

1. The most basic/simple/10,000ft view explanation = the higher the storage SOC the faster the capacity loss/degradation. But the simplest explanation is also the least nuanced.

2. Adding a little more nuance, while the generalization that higher storage SOC = more capacity loss is true, its not linear.
One study on storage and calendar aging shows the rate of capacity loss is pretty stable between 40-70% SOC, but increases somewhat sharply above 70%. If at all possible storing at or below 70% SOC and at a reasonably cool mild temperature might make the biggest difference in terms of longevity (see the chart below)

The 70% steep increase is only based on data from a single study, its probably smart not to overstate its significance/broad relevance (it may or may not be representative). That said multiple studies show the same general trend (1) higher temperatures, and (2) higher storage SOC lead to accelerated capacity loss. Of these two factors temperature is the bigger factor from what I've read.

 

[Mr-Sandman]

I suppose I could do some light load shaving after sunset and pull the SOC down to below 70% then recharge and repeat the next day.

It makes me wonder if LifePO4 is the best choice for emergency backup power where the batteries stay fully charged, never cycle, waiting on a power outage.

 

[Dzl]

It makes me wonder if LifePO4 is the best choice for emergency backup power where the batteries stay fully charged, never cycle, waiting on a power outage.

I'm not an expert by any stretch of the imagination, but emergency backup and/or UPS applications seems like a use-case where lead acid retains a competitive advantage and still makes a lot of sense unless you are space constrained. There may well be limitations/downsides I'm not considering or don't understand.

 

[Mr-Sandman]

Doesn't this chart show a sharp INCREASE in life expectancy of the batteries at 80% plus SOC @ 25c?



It can be seen that the SOC levels at both ends (smaller than 20% SOC or larger than 80% SOC) and cooler temperatures preserved the Li-ion battery when not in use, which followed the analysis results based on the capacity fade model.

 

[offgridfarmgineer]

This is a great thread. It would also be helpful to add the absorption time as a parameter as I have read that very short absorb times are better for LFP cells, especially relative to FLAs. Folks care to chime in on absorb times?

So it looks like Will recommends a bit more aggressive values relative to this summary and Signature Solar recommends a higher bulk/absorb and a MUCH higher float than either, which seems out of place. @signaturesolarrichard do you have any comments on the your settings versus the settings listed in the first edited post?

 

[Solar Guy Richard]

This is a great thread. It would also be helpful to add the absorption time as a parameter as I have read that very short absorb times are better for LFP cells, especially relative to FLAs. Folks care to chime in on absorb times?

So it looks like Will recommends a bit more aggressive values relative to this summary and Signature Solar recommends a higher bulk/absorb and a MUCH higher float than either, which seems out of place. @signaturesolarrichard do you have any comments on the your settings versus the settings listed in the first edited post?

I will see what I can find on testing for our parameters - that being said it is possible a longer lifespan may be achieved with different settings. Our goal is to provide correct information - so I know that the testing was done with the specs as outlined in the manuals and that's where we get our # of charge cycles and DOD numbers from. So, it is probably possible to extend the life with more conservative numbers - but after 15 years of charging/discharging fully daily and still only being at 80%DOD I think I'll just leave well enough alone.

 

[Solar Guy Richard]

This is a great thread. It would also be helpful to add the absorption time as a parameter as I have read that very short absorb times are better for LFP cells, especially relative to FLAs. Folks care to chime in on absorb times?

So it looks like Will recommends a bit more aggressive values relative to this summary and Signature Solar recommends a higher bulk/absorb and a MUCH higher float than either, which seems out of place. @signaturesolarrichard do you have any comments on the your settings versus the settings listed in the first edited post?

I will see what I can find on testing for our parameters - that being said it is possible a longer lifespan may be achieved with different settings. Our goal is to provide correct information - so I know that the testing was done with the specs as outlined in the manuals and that's where we get our # of charge cycles and DOD numbers from. So, it is probably possible to extend the life with more conservative numbers - but after 15 years of charging/discharging fully daily and still only being at 80%DOD I think I'll just leave well enough alone.