Ascension of Lithium

[CMS]

Well just like the CC-CV transition, it's the bank chemistry causing the amps dropping, not the charger, right?

Let's remember that a all a voltage regulator does, once in constant voltage mode, is limit voltage. I say this over and over, but try to think not in terms of a voltage regulator but rather a voltage limiter.

Once you attain the pre-set "voltage limit", let's call that 13.8V, the battery will only accept X current for so long without over-shooting the voltage limit. The VR simply begins PWMing the chargers power supply or field of an alt etc. to match supplied current to the battery voltage limit to avoid over-shooting the voltage limit. As SOC rises, with all batteries, in CV mode, the current has to go down or the limit will be over-shot.

The battery is essentially telling the VR "Whoa, if you send me 30A, at this SOC, I am going above the 13.8V limit." The VR simply holds voltage constant by PWMing the source, to decrease current, in order to not over-shoot the voltage limit.

The taper is very rapid with LFP, especially when compared with LA when holding voltage steady to avoid voltage over-shoot. The current taper to what I consider full on my 400Ah bank at an approx .34C charge rate is about 30 minutes or so. If I boosted the charge voltage to 14.4V the taper is essentially non-existent at a .34C charge rate so any absorption duration is technically now over-charging the cells..

With our solar array at 13.8V the taper is zero because the array is only capable of 10A +/- so when it gets to 13.8V my bank is, for all intents and purposes, "full". Holding 13.8V beyond this point with my solar array is over-charging... Charge rate, voltage limit and CV duration all play a role.

Yes, with lead, you need to ensure the charger doesn't **end** Absorb too early, while with LFP that's not a problem, you want to ensure it doesn't go on **too long**.

Bingo! One of the biggest problems we face with LA is "premature floatulation" or ending absorption too soon. It is a MAJOR chronic issue and millions upon millions of $$$$ in LA batteries are destroyed each year due to sulfation from chronic under charging/under absorbing..

Conversely, one of the biggest problems we face with LFP is over absorbing or holding CV too long......

If a charge source doesn't give good options there perhaps could work around with a good shunt Battery Monitor with a relay, set to disconnect/divert the charge source at X SoC, say 95%?

When you find an Ah counting battery monitor that can remain accurate for SOC, even with LFP, please let me know. For now Ah counting LPF or LA SOC, with any level of accuracy, is simply a pipe dream. I have many, many hundreds of hours of testing SOC devices for LFP and suffice it to say there are currently NONE that work beyond a few cycles.

You could not pay me enough to trust my LFP bank to an Ah counting shunt based device set to 95% because eventually it is going to get itself out of whack. I use one, a Link-Pro, but it is an at a glance guide only and I DO NOT trust it for SOC at all. I can say this because I have tested it, and numerous others, against lab grade equipment.

Keep it simple with LFP and purchase charge sources that can be programmed correctly for the shortest CV duration with the right voltage parameters. Attempting to shortcut LFP & charging/using with an LA mentality destroys cells.

 

[CMS]

Lithionics explained that the reason they recommended 29 vdc for bulk charging was that this was the point at which the BMS would balance the cells. At that voltage they recommend 18 minutes absorption. I explained that I would prefer not to exceed 28 vdc per your recommendations and they said that was fine, but just run them up to 29 v "once a month" to trigger balancing. Fair enough, and easy to do with my charging sources, but my question is what would you recommend for duration of absorption at 28 v, which I can set at any value? I guess I can discover that myself by seeing how long at CV it takes for the current to drop to 15 amps or so (600 amp bank), but I would greatly appreciate your thoughts.

I think you'll find that balancing every month is entirely unnecessary if duration is kept short and voltages are kept at or below 14.0V/28.0V.

Lithionics is used to selling these batteries to folks who insist on adapting them to LA mentality and LA voltages. Why people do this and why Lithionics goes along with it is beyond me. I can say their charge voltage guidance has dropped over the years as has Mastervolt's. I suspect they have both learned along the way.. Charging LFP to high voltages creates a need for balancing, why create this need...... If you charge LFP at a lower voltage and short duration's the need for continual balancing is almost nil unless you have poor cell matching to begin with. Poor cell matching should not be an issue with Lithionics...

The duration issue is easy, keep it short. You're talking a difference of couple of Ah's at most vs. a bank that costs thousands. Pushing the bank to full regularly is a cycle life shortening LA mentality.. That mentality needs to be thrown out with the garbage.. I beat the LA mentality issue with a dead horse but it really is the hardest part of an LFP conversion.... 18 minutes is more than enough at 14.0V. Zero minutes would be fine too.

Remember you don't need nor actually want to drive these cells to 14.0V and 15A each cycle. You can, but there is no need to do this. If your bank has been sized so that those few Ah's matter to you, it has been sized too small.. If you want to use 14.0V @ 15A to manually reset an Ah counter to full, every few cycles, that's fine but feel free to stop at 40A+ too.

 

[Xsbank]

So, how do you determine if your boat has "premature flotulation?" I just bought a solar array which gets hooked up today and the mppt controller, Outback 60, is supposed to be smart - will it solve the length of absorption issue? If I have to program it manually, how long is adequate? 4 LA golf carts.

Good information, thank you for sharing it. I am a candidate for new batteries soon but likely not until the charging systems become bulletproof. As nice as lithium is I will have a hard time convincing SWMBO that it is better for us at its current cost.

As I am just getting the nuances of LA technology, I will be slow to absorb Li and reject the LA information but older age is your friend in the forgetting process!

 

[mike66]

So if someone came up with a system that used an ac source for charging, coupled with a specific battery pack, then many of the problems could be addressed. All charging sources could be inverted to ac. There would be some power inefficiency, but the system could then possibly be more of a drop in solution. But, as mentioned, not cheap because it would be proprietary.

 

[Delfin]

I think you'll find that balancing every month is entirely unnecessary if duration is kept short and voltages are kept at or below 14.0V/28.0V.

Lithionics is used to selling these batteries to folks who insist on adapting them to LA mentality and LA voltages. Why people do this and why Lithionics goes along with it is beyond me. I can say their charge voltage guidance has dropped over the years as has Mastervolt's. I suspect they have both learned along the way.. Charging LFP to high voltages creates a need for balancing, why create this need...... If you charge LFP at a lower voltage and short duration's the need for continual balancing is almost nil unless you have poor cell matching to begin with. Poor cell matching should not be an issue with Lithionics...

The duration issue is easy, keep it short. You're talking a difference of couple of Ah's at most vs. a bank that costs thousands. Pushing the bank to full regularly is a cycle life shortening LA mentality.. That mentality needs to be thrown out with the garbage.. I beat the LA mentality issue with a dead horse but it really is the hardest part of an LFP conversion.... 18 minutes is more than enough at 14.0V. Zero minutes would be fine too.

Remember you don't need nor actually want to drive these cells to 14.0V and 15A each cycle. You can, but there is no need to do this. If your bank has been sized so that those few Ah's matter to you, it has been sized too small.. If you want to use 14.0V @ 15A to manually reset an Ah counter to full, every few cycles, that's fine but feel free to stop at 40A+ too.

Very helpful, thank you. Your comment on Lithionics makes sense. I couldn't figure out why they were recommending such high voltage and when I pressed them, the "need" for 29 vdc ceased being a battery issue and became a BMS requirement. If the cells don't need balancing often, then why cook the battery?

It looks like I can adjust charge sources (alternators/Balmar 624) and genset (Trace 4000) to 6 minutes minimum "Bulk Time" (duration of Bulk after Bulk voltage is reached, which would be a maximum of 28 v) and 6 minutes minimum "Absorption Time". I guess that means that 12 minutes is as low as I can make it go, since zero time isn't an option on the Balmar. I was planning on setting Float at 26.2 vdc. Sound right to you?

 

[john61ct]

When you find an Ah counting battery monitor that can remain accurate for SOC, even with LFP, please let me know. For now Ah counting LPF or LA SOC, with any level of accuracy, is simply a pipe dream. I have many, many hundreds of hours of testing SOC devices for LFP and suffice it to say there are currently NONE that work beyond a few cycles.

I wasn't planning on relying on more than one cycle, having the monitor reset to Full every time it trips the relay.

Many sources can be set to stop based on endAmps, like solar controllers and DCDC chargers, and that would be the "proper" Full mark for the BM to get max AH capacity (not important).

My idea is for the dumber charge sources let the BM overestimate the AH in vs out efficiency, maybe use 1.05. To the extent that source is used every time, the Full marker would drop lower and lower a little every time, NBD.

If it's convenient and I think about it, I could do a manual top up based on endAmps and reset the BM full.

Letting the BM do it as a protective measure is also just belt and suspenders, the dumb source would be set to stop well before 95% best as it can, say minimum Absorb time at 13.8V

 

[Art]

I've learned quite e bit from this thread and am thankful for being able to read much knowledgeable input form several persons.


Must say though... although I'm [overall and in general] more informed than before... I am also more confused than before regarding what the correct path for battery placement/power are as well as coinciding charging apparatus/applications/conditions that will work best inside a boat.


Although I'm "treading water" [pun intended] waiting to more clearly understand a really good procedure for maybe altering my boat's battery bank types and charger items... I can probably keep on treading for at least a year or two before my LA batt bank's cell conditions reach a point of no return...


Then I may throw a couple boat bucks into a whole new type of DC power system!