LFP FLA hybrid

[john61ct]

Originally Posted by rgleason

* How often would the LFP batteries have to be brought up to 100%?

No need at all for batt's sake.

But if you do, don't hold it there, actually bad for longevity.


> How long would that take for a small LFP?

Putting 200AH into a 400AH bank

with a 200A source takes 1 hr. At 400A only 30min, at 100A takes 2hrs.

.5C, 1C and .25C respectively

or 250AH or 800AH bank, same time but different C rates.

> What is the LFP typical:

- Max Discharge level C
2-4C maybe but that's EV not House usage

Cycles vs DoD not known for maybe 10+ years

Vendor ratings are low underestimates if avoiding shoulders, maybe accurate if pushing to their (too high) charge specs

I think 3-5x their ratings will be possible, maybe. Depends if EoL defined at 70% SoH, higher or lower.

- Bulk level C -max absorption amps & voltage level. (14.2-14.4v quite high 500a )

13.8V for longevity. Those following vendors reco, maybe 14.6?

- Absorption level C -CV? amp ranges, trailing amps?

No absorb necessary in daily use, I use .03C endAmps, only when calibrating precision required.

Dunno what vendors spec, irrelevant IMO.

> Float level C & voltage?

Best to just stop, never float.

Some say under 13.2V is OK because no current, below resting.

[rgleason]

Originally Posted by rgleason

John:




2C = 2 x C? I do not understand. Incomprehensible.

Is this value actually supposed to be 0.2C?

Now I've got it. LithiumFePo allows unheard of discharge rates compared to FLA, just as it has unheard of charge rates.


But after reading your recent post, it may be better not to push those charge and discharge rates too much.
Thank you for taking the time to respond. Much appreciated!


Regarding the transients being discussed with regard to LFP, isn't there some other way to stop those with an electrical device?

I understand FLA would help, but wouldn't some size of capacitor help, or maybe something else?

[john61ct]

Here's my "boilerplate" LFP summary yet again.

Any and all feedback is welcome, especially if more "canonical" information from the links cited conflict with my summary.

______
Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

Best to size your cells for two parallel strings for redundancy, unless you have a separate reserve/backup bank. Don't go past three, or you may see balancing issues that affect long-term longevity, maybe four in a pinch.

Note nearly **every** vendor, also those of ancillary hardware touted as "LFP ready", gives charging voltages **way too high** for longevity.

My (conspiracy) theory is that manufacturers would prefer their cells get burned out in under 10 years.

EV usage is very different from much gentler House bank cycling. Most EV people talking "lithium-ion" mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

My charge settings for LFP: 3.45Vpc, which = 13.8V max for 4S "12V".

The point is to look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve.

Either "just stop" charging when voltage is hit, or if you want another couple % SoC capacity, stop when trailing amps **at your spec'd voltage** hits endAmps of .02C, or 2A per 100AH.*

Note even at the "low" max charge voltage, letting the charge source continue to "push" even low currents long past the endAmps point is **over-charging, and will** greatly reduce lifecycles.

So if you can't then "just stop", set Float well below resting Full voltage, at say 13.1V, but that is a compromise, and *may* shorten life cycles.

With LFP, you don't need to fill up all the way at all, as far as the cells are concerned. In fact, it is bad for them to sit there more than a few minutes. Therefore only "fill up" if consumer loads are present, ready to start discharging, ideally right away.

Many sources claim there is a "memory effect" from keeping charge voltage and ending point exactly the same every time lower than manufacturer specs, that can apparently over time lead to apparent lower capacity. The recommended fix is to "go higher, into the shoulder" every so often, similar to "conditioning" a FLA bank monthly. To prevent the issue, vary your setpoints a bit, sometimes go a point or two higher or lower, vary Absorb time a bit etc. There is no consensus just how serious the problem is.

Store the bank as cool as possible and at 10-20% SoC, or maybe higher to compensate for self-discharge, if not getting topped up regularly (I would at least monthly).*

Letting the batts go "dead flat" = instant **permanent unrecoverable** damage.

Same with charging in below 32°F / 0°C freezing temps.

Persistent high temps also drastically shortens life.

Charging at 1C or even higher is no problem, as long as your wiring is that robust, vendors may spec lower out of legal caution.

Again, going above 14V won't add much AH capacity, but will shorten life cycles dramatically.

And of course, we're talking about gentle "partial C" House bank discharge rates, size appropriately and be careful feeding heavy loads like a winch or windlass.

Following these tips, letting the BMS do active balancing is unnecessary and potentially harmful, just look for LVD / OVD and temp protection. Multiple layers of protection are advised if it is a very expensive bank, so you don't rely on any one device to keep working.

Check cell-level voltage balance say monthly to start, then quarterly, finally every six months if there are no imbalance issues, but only if that seems safe to you.

This thread is long but informative
http://www.cruisersforum.com/forums/...nks-65069.html

, make sure to give both Maine Sail and Ocean Planet your close attention.

Also MS' summary notes here
https://marinehowto.com/lifepo4-batteries-on-boats/

**Everything** at that site is worth reading, very valuable. He also has great articles in Practical Sailor. His new site under development transitioning the pbase content is here

https://marinehowto.com/support, feel free to make a donation to help with those expenses.

[Dockhead]

Originally Posted by ramblinrod

Well there is certainly "disconnect" somewhere, because Mainsail won't even consult remote customers on LFP anymore because too many were zapping their electronics and trashing their LFP banks.

That is not at all what MaineSail said.

[Delfin]

Originally Posted by john61ct

Store the bank as cool as possible and at 10-20% SoC, or maybe higher to compensate for self-discharge, if not getting topped up regularly (I would at least monthly).*

Once again, and for at least the third time, could you provide the data that supports the idea that storing a LFP bank at 10% SoC is rational? You keep posting this recommendation, and I and others keep asking you for the basis for the recommendation, yet you ignore those requests. Can you not supply that data? Or will you once again ignore this simple, and reasonable request? You might be right, but it doesn't comport with anything anyone I know of has suggested but I am open to learning the wisdom of your advice, as I am storing my LFP bank at the 50% or so that folks like Maine Sail have recommended.

While you are at it, you have also stated that "minutes count" in starting to discharge an LFP bank once it is charged to avoid a reduction of capacity, so could you provide the data source that supports this conclusion? Really John, if you can't back up your recommendations with empirical data, should you feel comfortable making definitive statements to people trying to learn about this technology?

[ramblinrod]

Originally Posted by Dockhead

Exactly. If the fear is that a LVC event may occur because of operating heavy loads when the bank is at a low SOC -- lithium has almost no voltage sag and won't trigger a LVC unless the battery is really empty.

Cut-off is cut-off.

Not having some voltage sag and things slow down to warn diminishing capacity, probably makes an under load cut-off event more inevitable.

[Delfin]

Originally Posted by Dockhead

That is not at all what MaineSail said.

No, it is not. My impression, from what he has written, is that he does not want to take responsibility for people's systems who don't bother to pay attention to his clear, and empirically derived recommendations.

The beauty of the Internet is that it provides a forum for the wisdom of experts. The problem with the Internet is that is also provides a forum for frauds, nut cases, or well meaning people who need to feel they are experts in something, even if they lack practical experience or knowledge other than what they gain from using Google. As consumers of Internet data, we have to sort out the frauds, self-promoters and expert wannabes from those who actually know what the heck they are talking about. Not always easy.

[Delfin]

Originally Posted by ramblinrod

Cut-off is cut-off.

Not having some voltage sag and things slow down to warn diminishing capacity, probably makes an under load cut-off event more inevitable.

With LFP, when the voltage drops below 13 v with a .1C discharge rate, you are approaching the lower knee. Why on earth would you want to hear motors slowing down, exposing PCBs to damage, as the indicator that you need to recharge?

Are you saying that voltage sag is a virtue?

[ramblinrod]

Originally Posted by evm1024

A quick look at Mainesails website shows:


Beyond all that we’ve had a LFP bank on our own boat since 2011. I am a huge fan of LFP banks, for many reasons, but I will not act as a “fan boy“, that would be unfair to you the reader… I will give you both sides of the story, not just the pluses.

And

I no longer do any long distance consulting or design work for LFP batteries or systems. If the boat is not readily accessible here in Maine, Casco Bay to be specific, I can no longer do LFP consults. Why? Far too many owners insisting on cutting corners and multiple situations where end user implementation was not done to the design or design criteria have forced my hand. If you happen to glean something from this article, that’s great, but please don’t email me with further consulting questions on LFP.

So the disconnect is in understanding why mainesail does not do long distance consulting.

The disconnect is when someone uses what they know about FLA to make choices with LiFePO4. Simple things like assuming that the LiFePO4 voltage will sag at low SOC (what is low SOC? 20%?).

But nobody assumed voltage sag from LFP.

?????????????????????????

[evm1024]

Originally Posted by ramblinrod

But nobody assumed voltage sag from LFP.

?????????????????????????

Nobody assumed it. You postulated it.

Originally Posted by ramblinrod

Question: When is this disconnect most likely to occur?

Answer: When the bank is low, someone is not paying attention, and operates one of the high current loads.

You really should take some time to come up to speed with current technology. A number of your assertions assume that LiFePO4 will act like FLA. This leads to errors in logic and assumptions that are false.

[evm1024]

Originally Posted by ramblinrod

But nobody assumed voltage sag from LFP.

?????????????????????????

Oh and by the way. Perhaps you could address the point of my post i.e. Mailesails reasons for not consulting remotely rather than offering up the voltage sag strawman.

[CatNewBee]

Originally Posted by evm1024

Oh and by the way. Perhaps you could address the point of my post i.e. Mailesails reasons for not consulting remotely rather than offering up the voltage sag strawman.

I would also not do remote consulting PROFESSIONALY because of liability issues, espesialy in the USA. AFAIK Mainsail provides professional services in boating installations, so this could jeopardize his businesses if it comes to legal claims. Its like the disclaimers, that you should not dry your pets in the microwave nor wash them in your washing machine to not be sued when someone tries this.

So what I am doing with my system can be re-used or not - on own risk.

[john61ct]

The reduction of longevity of LFP vs length of time sitting at Full is Unknown.

I am not asking you for evidence that "days" sitting at Full is harmless, but I am very sure that is not the case, in fact strongly believe it is silly to even consider it.

The rule is, less time at Full the better. Especially if your definition of Full is charging higher than 14V and holding Absorb well into the top shoulder.

There is no black and white here, just like "don't discharge too low too often" is correct for lead, 50% is an arbitrary guideline.

I'm just being more conservative than you.

I am sure that this is true:

You should not charge to Full unless you know loads are "imminently" online ready to start pulling it back down,

**if** maximizing bank lifetime is a priority for you.

I concede those operating off mostly-solar must gather energy when they can, and if it is necessary for your setup to sit near full (no need to be all the way Full) for a few hours, then fine, we do the best we can.

If you disagree, note also without hard evidence,

feel free to state what you believe to be true, and one day maybe a Higher Authority will make a case that changes one of our minds.

[john61ct]

Storage SoC

There is no black and white here, just like "don't discharge too low too often" is correct for lead, 50% as the common wisdom is an arbitrary guideline.

However, in the last 3-4 months I came across statements

from sources I consider authoritative

that in fact lower SoC is better for longevity, even 10-20% being better than 30-40%.

I do not have the links in my KB, if I come across them I will post them.

The risk for **long term** storage is letting the bank drop too low, possible permanent fatal damage.

Especially where cells may not be 100% isolated, have vampire loads from the BMS.

50% is "safer" in that sense, perhaps better to give to noobs.

However, as long as the owner knows the self-discharge rate

which varies greatly by temperature, colder is better, and

is regularly checking in on the bank to ensure it does not drop below say 3.1Vpc / 12.4 for 4S, **and**

the cells are isolated from **all** loads, including BMS or other monitoring circuitry,

then **if** longevity of the bank is a top priority

lower SoC is better than the mainstream arbitrary 50%.

Obviously just leaving your boat for a while is not long-term storage, and

if the cells have any load at all, then a completely different protocol is required.

I am not asking you for evidence that 50%, or 40-60% is the right number.

Again, perhaps I'm just being more conservative wrt prioritizing longevity than you.

If you disagree, feel free to state what you believe to be true, give hard evidence if you have it, I am certainly open to that.

Otherwise we can wait and one day maybe a Higher Authority will make a case that changes one of our minds.

[ramblinrod]

Originally Posted by evm1024

Nobody assumed it. You postulated it.

False.

No where, did I assume or postulate, there was any FLA like sag associated with LFP.

Knock off the insults.

You are the one in error here.