My Lithium Upgrade

[markopolo]

It's mostly well explained in the manual:

05 set to b-0 = User Defined
94 set to ALb = Lithium Battery
26 t0C = Maximum charging voltage for Lithium battery
27 |-C = I'm not 100% sure what that is now that I've read it again. I had assumed it was the voltage at which one wanted charging to be maintained at. I now think 27 FLu is the better choice.
27 FLu = Float voltage. 13.4V should basically keep the LFP battery in stasis.

You could ask them what 27 |-C is used for.

There seems to be consensus out there that very little happens with LiFePO4 if charging below 13.6V - that's why I think 13.4V would keep the batteries at a good state of readiness without harming them.

[booster]

Originally Posted by markopolo

It's mostly well explained in the manual:

05 set to b-0 = User Defined
94 set to ALb = Lithium Battery
26 t0C = Maximum charging voltage for Lithium battery
27 |-C = I'm not 100% sure what that is now that I've read it again. I had assumed it was the voltage at which one wanted charging to be maintained at. I now think 27 FLu is the better choice.
27 FLu = Float voltage. 13.4V should basically keep the LFP battery in stasis.

I think Marko is on the right path, and it points to the confusion of all the lithium charging specs we have seen over time and continue to show up.


Currently most appear to say change to a less than 100% condition and shut off until down to some lower SOC and repeat. They also say not to store totally full. They also say not to continuously charge the batteries as in float, but are very squishy if that means at full voltage or at a lower float voltage. I certainly makes sense that if they want lower than full for storage as it will be better for the batteries, and that picking up any use by floating at that voltage would be a good idea. However, I have never been able to get an answer on that when I contact the battery and charger manufacturers to get a resolution. They dance around it like a ballet troupe, which seem strange because it is such a basic question.

[markopolo]

I've been considering LFP batteries for use in a standby backup power scenario. You'd have to oversize the bank if going with charge then drop-off then charge again so that there's adequate capacity when needed.

13.4V float would eliminate the need to oversize the bank and keep the batteries above 80% (my guess). It would also take care of parasitic losses.

The advice here: https://www.solacity.com/how-to-keep...tteries-happy/ seems accurate.

Float Voltage

LFP batteries do not need to be floated. Charge controllers have this because lead-acid batteries have such a high rate of self-discharge that it makes sense to keep trickling in more charge to keep them happy. For lithium-ion batteries it is not great if the battery constantly sits at a high State-Of-Charge, so if your charge controller cannot disable float, just set it to a low enough Voltage that no actual charging will happen. Any Voltage of 13.6 Volt or less will do.

and

Charge Voltage Needed

So what Voltage is enough to get those ions moving? A little experimenting shows that 13.6 Volt (3.4V per cell) is the cut-off point; below that very little happens, while above that the battery will get at least 95% full given enough time. At 14.0 Volt (3.5V per cell) the battery easily charges up to 95+ percent with a few hours absorb time and for all intents and purposes there is little difference in charging between 14.0 or higher Voltages, things just happen a little faster at 14.2 Volt and above.

[booster]

Originally Posted by markopolo

I've been considering LFP batteries for use in a standby backup power scenario. You'd have to oversize the bank if going with charge then drop-off then charge again so that there's adequate capacity when needed.

13.4V float would eliminate the need to oversize the bank and keep the batteries above 80% (my guess). It would also take care of parasitic losses.

The advice here: https://www.solacity.com/how-to-keep...tteries-happy/ seems accurate.

and

That is the first I have seen where anyone actually was willing to say something like that, and it certainly makes sense as mentioned earlier. This simple clarification would certainly be a huge benefit those who don't want to severely oversize the bank just to cover the charge/recharge cycle. When on shore power it just makes sense to use it the for current power requirements rather than charging and discharging the battery and having the possibility of leaving the site at less than adequate on charge.


Good find,

[markopolo]

For RV use, keeping the LFP batteries at a near full, but safe SOC would be easier on the alternator when it's time to hit the road.

[booster]

Originally Posted by markopolo

For RV use, keeping the LFP batteries at a near full, but safe SOC would be easier on the alternator when it's time to hit the road.

Absolutely.

[markopolo]

The 45A in at 13.6V with charging terminating soon after that Rowie reported would be a big concern for me. The charger was set to 45A so that's still bulk stage IMO so still very early in the charging process.

[booster]

Originally Posted by markopolo

The 45A in at 13.6V with charging terminating soon after that Rowie reported would be a big concern for me. The charger was set to 45A so that's still bulk stage IMO so still very early in the charging process.

IIRC the charging curves we saw for lithium showed very similar characteristics in that they would show max charger CC output until they hit the knee of the charge curve at 13.8/13.9v or so, unless they were huge chargers. The high acceptance rate of lithium can really mess up lead acid comparisons that way, I think. The current drop off at the knee is nearly vertical, so really hard to tell exactly what to expect, I think. If the current didn't start to drop by 14v, I do think I would start to get concerned.

[markopolo]

Absorption time with Renogy inv/charger is determined by an algorithm according to the manual. That imposed timeout could explain an early exit.

However, the manual says bulk continues until 0.3V less than the Boost (absorption) setpoint. It should be able to get to 14V+ in the earlier bulk stage.

[booster]

Originally Posted by markopolo

Absorption time with Renogy inv/charger is determined by an algorithm according to the manual. That imposed timeout could explain an early exit.

However, the manual says bulk continues until 0.3V less than the Boost (absorption) setpoint. It should be able to get to 14V+ in the earlier bulk stage.

Since the charger is a constant current device, if the acceptance of the batteries is high, it is very well be not able to provide enough current to hold the voltage up very high. I seem to recall charge curves that only got near the full charger (bulk, absorption, whatever called in lithium setting) voltage at the very end of the charge cycle and were almost a flat line for current until nearly at the knee due to the high acceptance of lithium batteries. Voltage rose at an even taper through that same time. If you were putting lead acid charging terms on them, they were in bulk for nearly the whole charge cycle, absorption for a tiny amount of time, and no float due to full cut off charging.


Most chargers don't have a timer on the bulk stage as such, AFAIK, but will have fixed or algorithm timer on the absorption and/or total cycle time, so while unlikely an absorption timer would max out, a full cycle timer might.


This may be a case that would indicate that using a threshold voltage and amperage of charge to the batteries would be a better indicator for accurate end of charge, as it is for lead acid batteries.

[markopolo]

To illustrate Booster's excellent points I circled in yellow where 100% charged occurs on Renogy's Charging Characteristics chart:

136v.jpg

I also added a black line at approx where 13.6V would be. It's not precise but indicates to me that 13.6V during recharge wouldn't get the battery higher than 80%.

The User Guide from Renogy ( https://www.renogy.com/content/files...anual_V1.0.pdf ) describes the charging procedure as follows:

Standard Charge shall consist of charging at 0.2C constant current rate until the battery reaches 14.6V. The battery shall then be charged at a constant voltage of 14.6V while tapering the charge current. Charging will terminate when the charging current has tapered to a 0.02CA.

That would be amps in having dropped to 2A at 14.6V on a 100Ah battery.

Choosing to go with say 14.2V with amps in having dropped to 10A would presumably result in longer life of the battery. We don't know enough about the BMS and Balancing specifically to disregard Renogy's instructions though.

Edit: I'll just add that if you Google "4S30P 0.02c 26650 14.6" https://www.google.com/search?q=4s30p+0.02c+26650+14.6 you see that other manufacturers of these 120 cell batteries (26650 cell type) have the same charging instructions as Renogy.

[booster]

It is interesting that other "brands" of batteries have the same charging instructions for the same style of cell. That probably would indicate that the cell manufacturer is same and it is there callout.



Over time, we have seen the charging recommendations change quite a bit as they learn more and more about what helps preserve life, and it would be possible/maybe likely that this charging spec is a bit outdated in relation to stopping the charging early to improve battery life. Current trends seem to be running closer to 14v, I think.



The folks with the very large battery banks usually have more extra capacity than those that are just using normal bank sizes in lithium (200ah?) so stopping early isn't as much of a loss of needed capacity but the small amount of loss be as important.



If the charge cycle followed the curve Marko showed with good consistency, you could pretty much just control it by amps to the batteries as there is very little hold time at full charger output.


It is also likely that the hold time it gets at full charger voltage would vary with the charger size, with a higher amp charger having a longer full voltage time. It might be best for anyone trying to tweak the the charging cycle to optimum to watch the charging and note how long it stays at full voltage before the current starts to drop to assure the best settings. Of course this also is based on having a charger that can do amp controlled charging, which are rare and expensive, so I am sure most will have the ability to select termination voltage, at most.


It is also very interesting they call out .2C charge rate, as that is more like what normally used for AGM charging and even on the low end for them. We do seem to see the charging rate recommendations dropping a lot for the more mainstream lithium systems, which is pretty interesting considering many of the advantages that were touted for lithium were very fast charging rates from day one.

[markopolo]

I suspect that the care instructions for this type of LFP battery is intended to primarily get maximum performance and capacity out of them.

Samlex offers some cost effective lead acid battery chargers that could take pretty good care of those batteries automatically for use in a standby power setup. They'd always be at a high state of readiness at near full capacity.

SEC-1230UL for 1 battery: selectable 14V or 14.4V transitioning to 13.5V when absorption current drops to 2.5 to 3A.
SEC-1250UL for 2 batteries: selectable 14V or 14.4V transitioning to 13.5V when absorption current drops to 5A.

[booster]

Originally Posted by markopolo

I suspect that the care instructions for this type of LFP battery is intended to primarily get maximum performance and capacity out of them.

Samlex offers some cost effective lead acid battery chargers that could take pretty good care of those batteries automatically for use in a standby power setup. They'd always be at a high state of readiness at near full capacity.

SEC-1230UL for 1 battery: selectable 14V or 14.4V transitioning to 13.5V when absorption current drops to 2.5 to 3A.
SEC-1250UL for 2 batteries: selectable 14V or 14.4V transitioning to 13.5V when absorption current drops to 5A.

Yes, totally agree that the recommendations are biased toward max capacity at the possible cost of some life.



The Samlex chargers are an interesting choice, and it is unfortunate that they would have the same problem with lithium that they have with the lead acid applications, which is the internal amp measurement getting messed up because of van loads being seen as battery charging amps.


Perhaps the slope of the amp drop is steep enough with lithium to minimize the issue, but a lot would probably depend on just how many amps you might be using and how much the varied.



I wish someone like Samlex would make a slightly modified version of the above chargers. It would be so easy, and relatively inexpensive, to have a separate output on the charger to power the van loads that is tapped off before the controlling amp measuring device. A simple relay to connect the two outputs when not on shore power is the only other thing needed. We know that such a setup would work well from the very similar add on circuit I used on our internally measured Blue Sea charger. The Blue Sea already had multiple outputs so it could be done externally. The Blue Sea would work for the lithium application well, I think, and is less expensive than the other options like Magnum but still more than Samlex I think. The switching setup was well under $50 and probably could be done for a lot less. If you were a very large power user like with AC it would be more as you would be switching many more amps. The largest Blue Sea is 40 amps.

[markopolo]

Good points. Loads will affect charging with the Samlex chargers, no way around it other than to reduce loads when charging (and other than reduced voltage power supply mode).

After transitioning to Float, the SEC-1250UL is forced out of Float when 10A is seen. That would comfortably allow for fan use and some LED lights for example with the charger remaining at 13.5V. They do have a "Battery With Load" option aka Power Supply Mode with voltage held at 13.5V.

----------------------------------------------
Rowie might have to use the load trick he discovered to force his inverter charger back into bulk to keep charging his LFP batteries and see the amps in taper at 14V+. Unplugging / replugging the RV often restarts the charge process. That is brand/model dependent though.

[rowiebowie]

All this is interesting reading and a bit disconcerting at the same time. I was hoping that parameters for charging lithium battery cells was settled science that "smart" chargers could hit consistently and precisely regardless of application. That batteries would be so accurately maintained by these chargers that observations on a SOC meter would be consistent with both what is optimal for the battery and within the parameters of the charge manufacturer's manual. We may be talking only within 5-10-% of maximum charge and battery life (everything is a compromise), but even that is a bit bigger range than I expected.

First things first. To satisfy myself that my anecdotal observations (like never seeing more than 13.6 volts) aren't missing something, I need to do the following:

> Spend some time in the driveway man-cave observing several charging cycles on shore power from various levels of discharge and accurately log what happens. Time, amps, voltage with loads and without.

> Do the same as above while charging from the engine alternator. I just realized that the SOC meter came with a rather lengthy connection cable and the monitor itself is mounted with velco. I might have just enough cable length to bring it up to the cab for an extended testing period.

I cannot say when I will get around to doing this, but I will report back.

[booster]

Originally Posted by rowiebowie

All this is interesting reading and a bit disconcerting at the same time. I was hoping that parameters for charging lithium battery cells was settled science that "smart" chargers could hit consistently and precisely regardless of application. That batteries would be so accurately maintained by these chargers that observations on a SOC meter would be consistent with both what is optimal for the battery and within the parameters of the charge manufacturer's manual. We may be talking only within 5-10-% of maximum charge and battery life (everything is a compromise), but even that is a bit bigger range than I expected.

First things first. To satisfy myself that my anecdotal observations (like never seeing more than 13.6 volts) aren't missing something, I need to do the following:

> Spend some time in the driveway man-cave observing several charging cycles on shore power from various levels of discharge and accurately log what happens. Time, amps, voltage with loads and without.

> Do the same as above while charging from the engine alternator. I just realized that the SOC meter came with a rather lengthy connection cable and the monitor itself is mounted with velco. I might have just enough cable length to bring it up to the cab for an extended testing period.

I cannot say when I will get around to doing this, but I will report back.

That sounds like a reasonable plan to me. it will be interesting to see what you find out.


The manufacturers of chargers seem to be famous for claims they don't achieve in real life. We have seen the exact same thing in the lead acid charging with smart chargers that claim "perfect" charging. Essentially none of them do that unless the end charging is base on amps, and there are only a couple that do that. No real reason to believe that lithium chargers and claims would be much different, I think.


They can get away with the claims because battery life is usually spanning years and can be influenced by lots of things. If folks are getting earlier than best case failures, there is essentially no way to prove it for sure.

[Winston]

There are a few ‘Rules of Lithium’ for which we’d love to see justification.

The first: Lithium batteries should not be maintained at 100% charge for long-term storage.

This may well be, but we’ve never discovered any studies to document this. And without a ‘study’, we are left with the question: If 100% is not good, what percentage is good? 90%? 80? Less?

Turns out, for us, between time actually ‘on-the-road’ and periods where we’re ‘piddling’ with the van - - we keep the ProMaster ‘on’ most of the time. Normal use is long-term in our case. It would appear that whatever the ‘magical’ long-term storage SoC is - - we should adopt it for our normal in-use target.

Then there’s the oft-repeated “Rule” that Markopolo quoted: “LFP batteries do not need to be floated.” Or, worse, they “should not be” floated. Again, we have found no data to support this Rule and question, as noted below, its logic.

This Rule has caused several of our compatriots to shut-off their charging sources even during periods of actual 12 volt use. They do this - - thereby cycling their batteries - - even at SoC levels well below 100%, in the belief that to do otherwise would be to improperly Float their lithium packs.

Discharging and recharging our batteries is normal while dry camping - - it is, in fact, why we have batteries. But why cycle our battery packs when alternate sources of energy are available? Unless, of course, Floating is evil.

Our position is that leaving ones ‘charger’ on is not really Floating the batteries. First, let’s not call it a charger. Why not call it a power supply? What’s wrong with having a 12 volt power supply to provide the necessary 12 volt energy?

And how do we justify that leaving the power supply on is not Floating?

At Post 78 of this thread we offered a table of Resting Lithium Voltage vs SoC. As we don’t know what a good long-term SoC should be, we’ll just arbitrarily pick one - - say 90%? Our data establishes that 90% SoC equates to 13.36 volts. Unfortunately, none of our charging sources (power supplies) allows us to program them with 1/100 volt precision (and, even if we could, the manufacturers have told us that their equipment can only hit a programmed number +/- 0.1 volts anyway). So we have to choose either 13.3 or 13.4 - - we’ve erred on the high side: 13.4 volts.

In support of our assertion that maintaining our 13.4 volt power supply isn’t “Floating” the battery, we note the following. If we start with the battery ‘resting’ at 13.4 volts (90% SoC), attaching a power supply of exactly the same voltage . . . causes no change. The battery pack continues to ‘rest’ - - it is neither being charged, nor discharged. Some will call this “Floating” . . . but if it is Floating, the battery doesn’t know it’s floating and the connection of that power supply cannot in any manner cause damage to the battery.

The advantage to this arrangement occurs when loads are applied - - the normal situation when camping. The 12 volt current required by any load is, effectively, being supplied by the power supply, not the battery - - thereby avoiding what we contend to be the needless discharge/recharge cycles (that our noted comrades are imposing on their lithium systems in fear of Floating them).

The point of this somewhat lengthy addition to the present thread is this: You can probably set all your charging sources to 13.4 volts and be assured that, at some point in time, your lithium reservoir will be at 90% SoC. This is what we (mostly) do. The only time we take our chargers to 14 volts and higher is when we want to quickly restore depleted batteries or, on rare occasions, to implement our systems ‘shunt resistor’ cell balancing system.

[booster]

Originally Posted by Winston

There are a few ‘Rules of Lithium’ for which we’d love to see justification.

The first: Lithium batteries should not be maintained at 100% charge for long-term storage.

This may well be, but we’ve never discovered any studies to document this. And without a ‘study’, we are left with the question: If 100% is not good, what percentage is good? 90%? 80? Less?

Turns out, for us, between time actually ‘on-the-road’ and periods where we’re ‘piddling’ with the van - - we keep the ProMaster ‘on’ most of the time. Normal use is long-term in our case. It would appear that whatever the ‘magical’ long-term storage SoC is - - we should adopt it for our normal in-use target.

Then there’s the oft-repeated “Rule” that Markopolo quoted: “LFP batteries do not need to be floated.” Or, worse, they “should not be” floated. Again, we have found no data to support this Rule and question, as noted below, its logic.

This Rule has caused several of our compatriots to shut-off their charging sources even during periods of actual 12 volt use. They do this - - thereby cycling their batteries - - even at SoC levels well below 100%, in the belief that to do otherwise would be to improperly Float their lithium packs.

Discharging and recharging our batteries is normal while dry camping - - it is, in fact, why we have batteries. But why cycle our battery packs when alternate sources of energy are available? Unless, of course, Floating is evil.

Our position is that leaving ones ‘charger’ on is not really Floating the batteries. First, let’s not call it a charger. Why not call it a power supply? What’s wrong with having a 12 volt power supply to provide the necessary 12 volt energy?

And how do we justify that leaving the power supply on is not Floating?

At Post 78 of this thread we offered a table of Resting Lithium Voltage vs SoC. As we don’t know what a good long-term SoC should be, we’ll just arbitrarily pick one - - say 90%? Our data establishes that 90% SoC equates to 13.36 volts. Unfortunately, none of our charging sources (power supplies) allows us to program them with 1/100 volt precision (and, even if we could, the manufacturers have told us that their equipment can only hit a programmed number +/- 0.1 volts anyway). So we have to choose either 13.3 or 13.4 - - we’ve erred on the high side: 13.4 volts.

In support of our assertion that maintaining our 13.4 volt power supply isn’t “Floating” the battery, we note the following. If we start with the battery ‘resting’ at 13.4 volts (90% SoC), attaching a power supply of exactly the same voltage . . . causes no change. The battery pack continues to ‘rest’ - - it is neither being charged, nor discharged. Some will call this “Floating” . . . but if it is Floating, the battery doesn’t know it’s floating and the connection of that power supply cannot in any manner cause damage to the battery.

The advantage to this arrangement occurs when loads are applied - - the normal situation when camping. The 12 volt current required by any load is, effectively, being supplied by the power supply, not the battery - - thereby avoiding what we contend to be the needless discharge/recharge cycles (that our noted comrades are imposing on their lithium systems in fear of Floating them).

The point of this somewhat lengthy addition to the present thread is this: You can probably set all your charging sources to 13.4 volts and be assured that, at some point in time, your lithium reservoir will be at 90% SoC. This is what we (mostly) do. The only time we take our chargers to 14 volts and higher is when we want to quickly restore depleted batteries or, on rare occasions, to implement our systems ‘shunt resistor’ cell balancing system.

Great post, thank you!



I totally agree with the lack of data to back up the current claims to proper lithium battery care. Of course there is also a lack of similar for AGM after all these years, so not surprising, I guess. Many of us remember what the original recommendations for lithium care were, and how much they have changed already. No reason to believe there won't be more changes in the future.



I also totally agree with you on the lack of logical explanation for not "floating" the lithium at a moderate volt that is less the 100%, especially when on shore power and using the van. It just makes sense to me to not cycle the batteries when it is not needed. I certainly could understand totally disconnecting the loads and letting lithiums sit while in non use, as the self drain is so low it probably would not be an issue even for extended times.


The real test will be if we start seeing failures of some the types or lithium batteries with the various controls and protections over the long term. Until then, it is pretty much conjecture unless you can get access to the research data that we know is around but not visible to the masses.

[booster]

Expanding on Winston's comment a bit further concerning float/no float.


If it is really not horrible to "float", or really maintain, lithium at a less than full state, especially during use, it also would give a big benefit to those who have solar. AFAIK, solar controllers nearly all will float and not do full cutoff and rebulk. Many will rebulk if the voltage drops below float setting or and arbitrary other voltage. For those trying to stay offgrid for extended times, doing a full cutoff and running of the batteries instead of using the solar for the power as used, will certainly limit offgrid time as you are throwing away energy the solar could be providing. That make no sense to me from an energy standpoint, unless there is compelling evidence to show it is necessary for battery life.