Which Charge profile is ok for LifePo4?

[Deleted member 9967]

I think you sent me that same article when I asked about using an AGM charger on lifepo batteries. Or someone did. Anyhow, the argument was that an AGM charger would hurt lifepo batteries.
I can't seem to find that article now though dang it.
Oh well.
But I still say, you can't float lifepo like you can AGM's.
And that article in the spoiler appears to agree.
Thanks Dzl for the confirmation.

 

[Dzl]

I think you sent me that same article when I asked about using an AGM charger on lifepo batteries. Or someone did. Anyhow, the argument was that an AGM charger would [could] hurt lifepo batteries.

But I still say, you can't float lifepo like you can AGM's.
And that article in the spoiler appears to agree.
Thanks Dzl for the confirmation.

Emphasize the two parts I highlighted in green and we are mostly in agreement.

If your only takeaway is that the article confirms your statements, I think you are not appreciating the finer points, either look more closely at the article or at some of your past statements in this thread. Also please review the references to manufacturer recommendations I shared (this includes a reputable cell manufacturer, reputable battery manufacturer, reputable charger manufacturer, and two 3rd party resources). Specifically these recommendations from the article:

Standby Voltage – A voltage setting, usually programmed using the float voltage settings on a lead acid charger. This voltage should be one that results in the battery discharging to just below the full charge point of the battery or 90% SoC to 98% SoC, an being held there.

If you choose to use a standby (float) voltage be sure you are below 3.40VPC or 13.6V for a 12V nominal pack.

Here are the things (I think) we agree on (1) a non LFP profile could damage LFP cells and (2) you shouldn't use a non LFP profile if you aren't sure its safe (3) Float is not necessary (or even optimal) with LFP, and (4) Floating LFP in the same way as you float lead acid (above its resting voltage / at full SOC) can damage LFP cells.

Here are some of the statements I was referring to that I think express too much certainty & black/white:

You have lifepo batteries? NEVER use lead acid settings.
AGM is for AGM. Gel is for gel. Lifepo is for lifepo.

But hey, if you have money to throw away then go for it.

It is certainly possible to charge lithium cells with an AGM charger. It is also possible to survive a lightening strike.

As for floating though. I only ever did it the one time when top balancing them and then only for a few hours.

I don't want to argue or get more sidetracked on small points, much of what you are saying is right on, and it never hurts to err on the side of caution. My main point was just to avoid overly broad or overly definitive statements that don't apply to all contexts (I know this is something I fail at often too).

 

[BattMan]

Hi! 'Scuse me for jumping back on to someone-else's thread, but for starters, I would like to know how that worked-out.

Secondly, I am with you all in the conclusions generally reached here - that Bulk and Absorption Charging will be okay using the lead-acid profiles, even FLA will be okay, just don't float them. I have a Trojan FLA data sheet in front of me, and they recommend 14.75V, and that is 3.675V/cell, if that was applied to LiPO4s.

But, everywhere I call about replacing lead-acid with Lithium says you need a NEW CHARGER. What am I missing here??

Thanks.

 

[Mike Jordan]

The FLA chargers with LiFePO4 batts are a heated discussion in threads all over. And much like this thread, if there are 100 responses, there are 100 different answers. I'm always MORE confused after reading the thread, than before I started reading

Float was invented for all of the lead acid variants, because they self discharge. Leave a lead acid vasriant on the shelf for several months, not connected to anything, and it will be dead. So it needs to float the inactivity period.

LiFePO4 will be good as new at the end of the several months of non-use. No float required, and float might be detrimental, depending upon which of the 100 posts you believe. I side with detrimental

Does the 13.5 fixed profile from the OP, shut off at 13.5v? If so, would adding a SCC that has a proper LFP profile be a good answer to the whole scenario?

Why?
Why not?

 

[Dzl]

If you want simple guidelines for how to treat lifepo4 (generally) this article from Solacity is a good place to start.

In these discussion of small details, advanced/theoretical topics, and disagreements over wording or terms and people without solid understandings making overly broad or overly absolutist statements can obscure what is for the most part agreed upon and uncontroversial. We overthink a lot of things on this forum, me as much as anyone, but often we are just focusing on the finer points, and sometimes that get lost. I think most people would agree that:

1. The third stage of a 3 stage charge algorithm "float" is neither necessary nor ideal for LFP but it can be useful/convenient.
2. LFP does not want to be held or kept at a full state of charge for long periods of time
3. However so long as the float voltage is relatively low (less than or equal to ~3.4V per cell (<13.6V)) its not something to stress over.

Personally, I was confused and unsure about a lot this stuff at first too. I'm still not an expert by any means, but what I found is by focusing on what specifically LFP wants, and what the different charge phases mean, it became easier to understand the discussion. A lot of disagreement comes from people having different understandings of the term float.

As to the question of, can you use a lead acid charger or profile with Lifepo4, I think why you often here the answer "NO" is because its an easier answer to give (and also to understand) than "it depends, there are many variables to consider"

Some lead acid chargers or charge profiles could be fine, but generally speaking what lead acid wants and what LFP wants are different things so the charge profiles have different characteristics. Lead acid chargers often can't be customized by the user which is non-ideal in many cases.

Circling back to the article I mentioned: There is a learning curve with LFP for sure, and some things are not fully settled science yet or at least not common knowledge, but it doesn't need to be too complicated unless you like to nerd out on that sorta thing like many of us do, here are the cliff notes of how to be nice to LFP:

To sum up, for long and happy LFP battery life, in order of importance, you should be mindful of the following:

1. Keep the battery temperature under 45 Centigrade (under 30C if possible) – This is by far the most important!!
2. Keep charge and discharge currents under 0.5C (0.2C preferred)
3. Keep battery temperature above 0 Centigrade when discharging if possible – This, and everything below, is nowhere near as important as the first two
4. Do not cycle below 10% – 15% SOC unless you really need to
5. Do not float the battery at 100% SOC if possible
6. Do not charge to 100% SOC if you do not need it

 

[Gazoo]

The only thing I would add, which should be obvious to most, is do not attempt to charge/discharge any DIY pack with cells in series without a BMS. There will most likely be a runner at the top and a sleepy cell at the bottom.

 

[Mike Jordan]

If you want simple guidelines for how to treat lifepo4 (generally) this article from Solacity is a good place to start.

In these discussion of small details, advanced/theoretical topics, and disagreements over wording or terms and people without solid understandings making overly broad or overly absolutist statements can obscure what is for the most part agreed upon and uncontroversial. We overthink a lot of things on this forum, me as much as anyone, but often we are just focusing on the finer points, and sometimes that get lost. I think most people would agree that:

1. The third stage of a 3 stage charge algorithm "float" is neither necessary nor ideal for LFP but it can be useful/convenient.
2. LFP does not want to be held or kept at a full state of charge for long periods of time
3. However so long as the float voltage is relatively low (less than or equal to ~3.4V per cell (<13.6V)) its not something to stress over.

Personally, I was confused and unsure about a lot this stuff at first too. I'm still not an expert by any means, but what I found is by focusing on what specifically LFP wants, and what the different charge phases mean, it became easier to understand the discussion. A lot of disagreement comes from people having different understandings of the term float.

As to the question of, can you use a lead acid charger or profile with Lifepo4, I think why you often here the answer "NO" is because its an easier answer to give (and also to understand) than "it depends, there are many variables to consider"

Some lead acid chargers or charge profiles could be fine, but generally speaking what lead acid wants and what LFP wants are different things so the charge profiles have different characteristics. Lead acid chargers often can't be customized by the user which is non-ideal in many cases.

Circling back to the article I mentioned: There is a learning curve with LFP for sure, and some things are not fully settled science yet or at least not common knowledge, but it doesn't need to be too complicated unless you like to nerd out on that sorta thing like many of us do, here are the cliff notes of how to be nice to LFP:

Great article... mostly because it confirms exactly what I said about float charging LFP above.

But.... once again.... it says nothing... to answer the question of how to properly set an RV FLA charger, to best manage LFP batts

Does the 13.5 fixed profile from the OP, shut off at 13.5v? If so, would adding a SCC that has a proper LFP profile be a good answer to the whole scenario?

Why?
Why not?

 

[Download7]

Does the 13.5 fixed profile from the OP, shut off at 13.5v?

Correct me if I'm wrong but doesn't the charging effectively stop once both are battery and charger are at equal voltages at 13.5v?

 

[BattMan]

Thanks for continuing the discussion. I think the simplest answer to the question of why all of the golf cart shops recommend a new charger is that it is easier - there COULD be issues? I just can't SEE any issues. Leaving LiPO4s on float is like leaving an electric car plugged-in - the batteries are a little stressed at a full-charge, but the BMS sets the levels already so there are no serious consequences. I'd put myself into the nerd category, and knowing that a full charge all the time will reduce battery life by 5-10% if you leave it plugged-in all night every night for example is not ideal, but there are ways around that.

 

[Mike Jordan]

Correct me if I'm wrong but doesn't the charging effectively stop once both are battery and charger are at equal voltages at 13.5v?

I would "assume" but often that makes ass-u-me.

Thats why I have asked... twice, but no response.

But the bigger picture is the GENIUS... I think... method to use the FLA charger that folks got, on that 13.5v setting, with a SCC that has proper LFP settings, to give the LFP batt the happiest life, at the least amount of fuss and cost.

I STILL would REALLY like someone to critique that idea. But maybe the lack of responses indicates, that I am so far ahead of my time, I have to wait for everyone to catch up.

 

[Dzl]

Edit: just got done writing this comment and realized that I misinterpreted the 13.5V (which I mistook/misread for 3.5V per cell). 13.5V (3.375 Vpc) changes things a bit I'm currently editing my comment to reflect that.

Does the 13.5 fixed profile from the OP, shut off at 13.5v?

Not sure, but I would guess it doesn't. Sounds like a fixed simple CV or CC/CV mode, like a power supply. Which would target 13.5V and current would taper as it gets closer to the target voltage and then it would just hold at 13.5V indefinitely.
But that is just speculation, best bet is to look at the documentation.

edit 13.5V = 3.375V per cell, which is an acceptable float (actually this is the float voltage that Victron products use out of the box for LFP batteries). So even without any charge termination, this would be a safe voltage. Of course its still best not to hold LFP at a high state of charge indefinitely, but so long as its being cycled or disconnected during long periods of non-use its nothing to worry about.

If so, would adding a SCC that has a proper LFP profile be a good answer to the whole scenario?

What is the objective? In this thought experiment are we ruling out just buying a charger w/ a proper LFP profile? If so are we also ruling out the other charge profiles from the OP? I like thinking through things like this, but want to understand the goal.

An MPPT controller would not work but a PWM controller might, I'm not positive. Edit: With a fixed voltage of 13.5, I don't believe your idea would work.

Actually, I was looking at doing this in another context (using a PWM controller to give charge logic to a dumb power supply), there seemed to be differing opinions on whether it would work or not, I meant to look into the idea further but got distracted with other things. A PWM controller is cheap enough that the cost of buying one just to test it out is pretty low. Though one issue I found is that many of the cheap PWM controllers don't actually have a proper lithium profile. If I find that thread, I will give you a link

edit: a fixed voltage of 13.5 = 3.375V per cell. This would be too low an input for some downstream device (PWM controller) to add standard LFP charge logic. Since (I believe) it would never actually reach the end of the first stage, because it would never actually reach its target voltage.

Thanks for continuing the discussion. I think the simplest answer to the question of why all of the golf cart shops recommend a new charger is that it is easier - there COULD be [and often are] issues?

Their advice is a good default approach, if in doubt, get a charger made for your chemistry. If you are comfortable/confident you understand what you need in a charger, than you can be more creative and use any charger that has parameters that meet your needs.

Leaving LiPO4s on float is like leaving an electric car plugged-in - the batteries are a little stressed at a full-charge, but the BMS sets the levels already so there are no serious consequences.

So long as something disconnects the pack so its not just being held at elevated voltage levels all the time. This could be the charger or the BMS depending on your situation and goals and components. Usually its the charger but in some design-models its the BMS. But you need to be able to set the reconnect voltage low enough.

What BMS will you be using? Is it capable of functioning like you stated above (some are, some aren't, many/most people do not use the BMS for charge termination/charge control)

by 5-10%

5-10% wouldn't be a huge deal for some. But where did that number come from? Is it based on anything or just an assumption?

 

[Dzl]

Correct me if I'm wrong but doesn't the charging effectively stop once both are battery and charger are at equal voltages at 13.5v?

You are right in the sense that as the battery got closer to 13.5V (3.375Vpc) current would slow to a trickle and then effectively stop flowing into the battery.

BUT, the charger would still be active, so it would be holding the cells at that voltage. At a high voltage this would cause undesirable stress because the battery would be held at an unnaturally high voltage indefinitely. At a lower voltage like 13.5V, its probably not that big of a deal (as noted above 3.375Vpc is the voltage Victron uses as a float voltage for LFP so its probably pretty gentle). There may or may not still be some loss of cycle life, I'm not an expert when it comes to these things, but I am confident saying its not a huge deal at these lower voltages.

edit: changed 'state of charge' to 'voltage'

 

[John Frum]

Charging stops when there is not a enough difference in voltage between the battery and the charger to overcome resistance.
Even if 0 current flows its still a bit stressful on the battery to be exposed to voltage above its full resting voltage.
Pretty much what dzl just said.
Oops.

 

[Dzl]

Pretty much what dzl just said.
Oops.

Yes, but you said it in less words, which is a good thing.

 

[BattMan]

Hi Guyz.

Regarding the degradation entailed by leaving batteries plugged in all of the time, I used to own an EV car lot, so have seen a lot of EVs, and know a lot about Lithium (NMC, mostly). I also owned an EV conversion business, and so have dissected batteries (literally and figuratively) for years. I'm also an EE. So - my humble opinion, based upon years of learnings is that Lithium batteries prefer to be held at between 40 and 60% (and will of-course hold that charge for months). Here is a graph from the Battery University (THE AUTHORITY) as well. So long as they are only left plugged-in and so held at 100% for a few hours, the results will not be that bad, but you get the drift - the curves which correspond to fully charging the batteries are the lowest, but you have to get a long ways out before the difference between - say - the green and the black curves differ by 10%. Remember, charging every day is not necessary, and a few thousand charges corresponds to 5+ years. If you are using a lead-acid charger, I don't think leaving it plugged in would have any effect, until the cell voltage drops down to the float voltage (3.5V) - see next graph below this one.


I also just scooped this graph from a Charger supplier. I ordered two Chargers (8A and 15A), just in case. Blue is voltage, red is current. Too bad it doesn't indicate whether it ever shuts-off, so I assume not. I will test the ones I get when they arrive, but as someone stated above, if the voltage of the battery reaches the voltage of the charger, zero current will flow. In the OP's case, for a non-Lithium charger, the FLA profile goes to 14.4, or 3.6V/cell, so that is not 100%, is it? One could certainly choose one of the other profiles which are even less, but as the Lithium Profile goes to 14. 6 (higher), I'm going to keep telling my customers they can use their FLA-bases charger.

The BMS I'll be using will cut off at 58.8V, which is 3.675V/cell, so they will never go above that, regardless.



I feel like we are a Secret Society or something - we "know" the rest of the world is being fooled.

 

[Dzl]

if the voltage of the battery reaches the voltage of the charger, zero current will flow. In the OP's case, for a non-Lithium charger, the FLA profile goes to 14.4, or 3.6V/cell, so that is not 100%, is it?

Yes actually, 3.6V can be 100% SOC. Usually cell manufacturers define 0-100% as 2.5V-3.65V, BUT this is based on a high C (usually 1C) charge rate and disconnection as soon as current tapers to 0.05C. 3.65V is only considered 100% as a charge voltage, 100% SOC will have a noticeably lower resting voltage. Given a longer hold time / current taper, 100% will be reached at 3.6V, 3.55V, down to ~3.45V even. So holding a battery at 3.6V for long enough = >100%

The marinehowto article (see my signature) has a section explaining this is better detail.

Bear in mind, the stress does not come just from current flowing, it comes (I think) from being held at an elevated voltage and not being allowed to settle.

 

[BattMan]

Thanks, I'll follow-up on this. Important.

 

[Mike Jordan]

You are right in the sense that as the battery got closer to 13.5V (3.375Vpc) current would slow to a trickle and then effectively stop flowing into the battery.

BUT, the charger would still be active, so it would be holding the cells at that voltage. At a high voltage this would cause undesirable stress because the battery would be held at an unnaturally high voltage indefinitely. At a lower state of charge like 13.5V, its probably not that big of a deal (as noted above 3.375Vpc is the voltage Victron uses as a float voltage for LFP so its probably pretty gentle). There may or may not still be some loss of cycle life, I'm not an expert when it comes to these things, but I am confident saying its not a huge deal at these lower voltages.

How is 13.5 an unnaturally high voltage for LFP? Charge them to 14.4v, disconnect from everything, and they will settle at 13.6

 

[Dzl]

How is 13.5 an unnaturally high voltage for LFP?

Maybe I was not as clear as I could've been (often the case). Though I think if you reread my comment more slowly/carefully you will see I was not calling 13.5V unnaturally high, quite the opposite. From the comment you quoted:

At a high voltage this would cause undesirable stress because the battery would be held at an unnaturally high voltage indefinitely. At a lower voltage like 13.5V, its probably not that big of a deal (as noted above 3.375Vpc is the voltage Victron uses as a float voltage for LFP so its probably pretty gentle). There may or may not still be some loss of cycle life, I'm not an expert when it comes to these things, but I am confident saying its not a huge deal at these lower voltages.

And going back to the comment before that:

13.5V = 3.375V per cell, which is an acceptable float (actually this is the float voltage that Victron products use out of the box for LFP batteries). So even without any charge termination, this would be a safe voltage. Of course its still best not to hold LFP at a high state of charge indefinitely, but so long as its being cycled or disconnected during long periods of non-use its nothing to worry about.

 

[BattMan]

Hi. No more responses, and it seems we are only debating fine points. I will try a lead-acid charger, and also the Lithium ones I ordered. In the end, when I look at the prices, unless there is something wrong with the chargers I ordered, it is not necessary to buy a really expensive 50A Lithium Charger, so let's just see how they work. My EV charger is just 15A (220V), and works just fine, as it gets me an overnight charge (24kWh battery).

I admit that 3.6V may still be a bit higher than ideal, and it is my fault for not being more particular about that - I am used to NMC batteries from EVs, where 3.7 is nominal, and 4.2V is the "max." In that world, it is accepted 4V is a better maximum for long-life, and makes very little difference in terms of capacity.

I see a lot of posts where the "drop in" replacement is not seamless - it may be better to have a programmable charger, or at least a lead-acid one with AGM / SLA settings.