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Old 10-12-2017, 21:45   #1
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[B]Best practice charging for LFP & LFMP bank?[/B]

Like many who are seriously contemplating moving to LFP or LFMP batteries for cruising, I have read about 2 somewhat contradictory viewpoints of the best voltage and charging practice for these batteries chemistries, in order to get the longest lifespan out of them, hence the best value. And yes, I have read every post on the loooong thread on LFP as house banks.

One school says drop-in LFP from vendors like Mastervolt and Valence are a no-no because the BMS/charging control is just not good enough, and the batteries will die a premature death. One main point of contention is the charging voltage, i.e. that LFP and LFMP (Lithium iron manganese phosphate) need to be charged at no higher than 13.85V, for a 12V battery. They say if you charge at 14.6V, your batteries will suffer damage.

The vendors of these "drop-in" batteries dispute this claim, and offer their batteries with guarantees, and lifespan claims of 10,000 charge-discharge cycles @ 70% DOD and still get 70% capacity after 10,000 cycles, while charging at 14.6V. They say you need 14.4 to 14.6V to get them "fully charged and balanced".

(see for example https://www.valence.com/solutions/marine/ )

I would like to get to the bottom of these contradictory positions re best charge voltage. It seems that both positions cannot be correct, so who's right? I'd like to see evidence for the claims of the anti drop in viewpoint, as well as from the vendors.

As they say, show me the data!

Has anyone else investigated this issue and reached a conclusion? If so, what data convinced you?
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Old 11-12-2017, 01:47   #2
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

There are several threads on here, multiple thousands of posts where this very topic is discussed, in depth.

The short answer is, they're both right.

If you carefully manage your batteries and never over discharge, never charge past about 13.8, never float etc, your life bank will outlive you and won't need all the fancy automatic balances etc - it is driving the voltages too high or too low that gets the cells out of step with each other, thus driving the need for the fancy balancing etc...

OTOH, if you buy the big brand name "drop in" system, and run it at ~14.4v, thief cells will still last a fair long while, but hen it needs active cell balancing..... And cell balancing costs $$$


End of the day simple answer, if you are happy with a DIY solution and technically capable, you will save a lot of $$$.... If you want to drop in a system and forget about it, get your platinum card out.....
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Old 11-12-2017, 01:52   #3
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

I use 3.45Vpc, at 4s 12V that's 13.8. I trust Maine Sail on that, not systems vendors.

Bare prismatic cells not packs from cylinders or pouches.

No cell-level electronics, looking only at bank-level LVD and OVD, maybe temps protection.

I plan to cycle right down to 8-12% SoC, figure I'm losing 5% AH capacity off the top for greater longevity.

My theory is that cell and systems vendors want to push the drop-in narrative, no need for special charge source regulation. And/or don't actually want the banks to last that many cycles.

I believe even though MS advocates for a "packaged systems" approach, he does not use the active balancing circuitry while cycling in use.
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Old 11-12-2017, 02:57   #4
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

Yes, I have read the posts. I do realise that there have been lots of declarative statements. I would just like references to the data that supports these statements.

Has anyone, anywhere, ever taken 2 identical batteries from the same batch, and put them through the 2 charging scenarios and measured the results? Has that been automated and run for thousands of cycles?

Does charging at 14.4V cause imbalance? Does charging at 13.8V prevent imbalance? Where is the data? Ditto on lifespan effects?


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Old 11-12-2017, 03:05   #5
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

Quote:
Originally Posted by BigBeakie View Post
I would just like references to the data that supports these statements.
I consider MS' extensive experience coupled with his evidence-based approach to be sufficient data for me.

Far more than just anecdotal reports from random members.

There certainly is no compelling reason AFAIC, to go to higher voltages.

But no, I don't know who you think would fund a long-term statistically valid study contradicting the mainstream industry narrative.

Would be nice if Consumer Reports poured resources into low-voltage off-grid electrics in general, but I won't be holding my breath.
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Old 11-12-2017, 03:15   #6
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

Note also I hadn't heard of Valence before, and perhaps their lithium chemistry has different characteristics, or their proprietary BMS does its own charge regulation / DC conversion internally, no idea.

What I'm referring to is vanilla prismatic LiFePO4 or close enough, as made by CALB, Sinopoly, A123, Winston Thundersky, GBS.
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Old 11-12-2017, 03:24   #7
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

> in order to get the longest lifespan out of them, hence the best value

> if you charge at 14.6V, your batteries will suffer damage.

These are not the same.

Just like going to a lower SoC, higher voltage charging pushed to a lower endAmps may results in a lower cycle lifetime. But this is not damage.

Most cell vendors rate around 2,000 and the main market EV usage is happy with that.

The lower voltage regime claims to get (maybe much) longer than that, not that standard charging reduces below rated.


> They say you need 14.4 to 14.6V to get them "fully charged and balanced".

That is just how their BMS is designed. They **define** Full by the higher voltage, and the balancing circuitry is kept dormant until a high V setpoint.
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Old 11-12-2017, 03:26   #8
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

Well there are some misleading information about all this topics.

The facts are:

- Lithium cells live long and prosper when kept between their bonds of charging / discharging voltages. In opposite to Lead Acid batteries they do not like to stay all the time at 100% SOC and they do not discharge themselves that fast either, depending on the Chemistry LiFePO4 vs. LiFeYPO4 vs. LiFeMnPO4 they are differently sensitive to ambient temperatures.

- Lithium Cells MUST be monitored cell-wise, because they do not auto-balance themselves like Lead Acid batteries, some believe they can save the money for the balancers and evangelize lower SOC to "prevent" cell-drift. This is BS. OVP / LVP MUST be implemented on cell voltage not on battery pack level and cells must be balanced for a long life expectancy.

- Manufacturer INSIST on charging the BMS supported battery pack to 14.4V and above to charge the Lithium battery because their balancer electronics kicks in earliest at 14V, charging with 13.8V alone will just circumvent the balancing and DAMAGE the Battery pack in the long run. This batteries have a smaller Ah (100..200Ah) and are very cost sensitive, therefore the manufacturer choose simpler balancer electronics, that work only in the upper range of charging voltage, they are not balanced on discharge at the bottom, instead when a single cell drops below the thresold, LVP is raised and the block is disconnected. Typically this balancer burn the excess energy into heat and not re-distribute it to the cells with lower SOC.

- More advanced BMS / balancer systems do active balancing on both top and bottom part of the cell or even monitor and balance the cells actively during all the time, not just when charging, but this systems are more expensive and therefore are used mostly in larger installations. The most part of the energy is conserved while balancing, usually a DC-DC step-up circuit takes the excess energy from a cell and transforms it to the block voltage to be used for charging the weaker cells, only a small amount of energy is lost by heat.

- Lithium batteries can safely be used within the bonds provided by the manufacturer (LiFeYPO4 e.g. between 2.8V-3,65V, what translates to block voltage 11.2V...14.6V in temperatures between -45C...85C) There is no need to keep the cells all the time below 3.45V. Preventing usage in extreme temperatures will extend the life too.

It is strongly recommended to use a BMS with balancing capabilities and LVP / OVP circuitry, you can keep the cells for a long time below 90% SOC, but they may drift if you have poor balancer, that work only on higher SOC.
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Old 11-12-2017, 03:42   #9
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

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Originally Posted by CatNewBee View Post
Well there are some misleading information about all this topics.
I completely disagree with virtually every statement there.

Petty I know, but to me a big red flag is your use of tge term "lithium" as if is anything more than a general category comprised of many chemistries with a huge variety of different charging needs.
IMO you basically buy into the worst aspects of all the different vendor myths.

Per-cell electronics are not just unnecessary in a lower-voltage regime, but add dangerous complexity, the active cause of many bank failures.
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Old 11-12-2017, 03:51   #10
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

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I completely disagree with virtually every statement there.

Petty I know, but to me a big red flag is your use of tge term "lithium" as if is anything more than a general category comprised of many chemistries with a huge variety of different charging needs.
IMO you basically buy into the worst aspects of all the different vendor myths.

Per-cell electronics are not just unnecessary in a lower-voltage regime, but add dangerous complexity, the active cause of many bank failures.
I agree to disagree.

Your recommended charging and usage regime is based on conspiracy theories and not on facts. This is dangerous and mis-leading. It even can shorten the life of a ready to use battery with built-in BMS like the ones from Victron or Mastervolt, it leads to un-balanced cells and due to missing cell-monitoring to a loss of the pack.

There are data sheets for each type of battery, and as long as you use the battery according to the specs, you will reach the stated life expectancy. By ignoring the facts and "inventing" your own charge and usage regimes you violate some time the bonds and destroy your cells.
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Old 11-12-2017, 04:32   #11
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

Quote:
Originally Posted by CatNewBee View Post
battery with built-in BMS like the ones from Victron or Mastervolt
just on terminology, to me "drop-in" and "built-in BMS" imply those 12V LFP batts like Battle Born.

LFP "systems with included BMS" I think makes the distinction clear for those unfamiliar with the different kinds.

Quote:
Originally Posted by CatNewBee View Post
There are data sheets for each type of battery, and as long as you use the battery according to the specs, you will reach the stated life expectancy.
Yes but that is setting the bar very low. The lower voltage is intended to get much longer than rated lifetimes, perhaps decades.

Hundreds of people are doing so, and very few have reported any capacity drop after several years, nor needing any balancing, just checking manually a few times a year.

If all you want is mfg rated lifespan I agree follow their higher specs.

Quote:
Originally Posted by CatNewBee View Post
you violate some time the bonds
Could you restate this another way? I don't understand that phrasing
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Old 11-12-2017, 05:21   #12
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

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Could you restate this another way? I don't understand that phrasing
Sure.

Assuming your statements: no cell modules, LVP / OVP done on block Voltage, charging with 13.6 / 13.8V only leads to unknown states of the cells.

Even if you have a sophisticated Battery Block wit built-in BMS like Victron / Mastervolt or whatever and this battery has cell-balancer, that operate during charging with trigger-Voltage of 14V, they never start balancing. You run the system without using the cell protection and instead decide the SOC based on a Coloumb counter (like Victron BC702 or Smartgauge or whatever)

Over the time one cell gets weaker, that means it is faster charged than the other. An out of balance block has then probably cell voltages of

3.2V + 3.2V + 3.5V + 3.9V way above the safe 3.65V and still 13.8V charging, the one cell gets way overcharged. On discharging you try to go down to 30%SOC before re-charging, but your battery is charged at 13.8V only to 60%, you will discharge one of the cell way below 2.8V

Monitoring the block voltage as done with lead acid batteries does not work for LiFePO4, they tend to drift. If you not monitor each cell separately you are on high risk losing one of the cells over time and you would probably even not notice it before it happens..

Un-balanced LiFe(x)PO4 batteries are dangerous. They can blew up and release poisonous gases.
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Old 11-12-2017, 05:35   #13
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

Yes I understand your beliefs about cell balance, I was just asking about the meaning of the actual phrase you used there.


To be sure, one should check cell V periodically and manually rebalance if the problem does arise.

But in gentle House usage, the bank never sees over 3.45V per cell

the balancing issue simply does not appear to be a problem in practice

as opposed to the industry-dominating EV use case

and there have been many reports of automated active cell balancing while in normal cycling use **causing** cell failures

to the point that expert professional installers of packaged systems go to the trouble of figuring out how to **disable** that part of the BMS circuitry in order to prevent such problems
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Old 11-12-2017, 09:15   #14
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

I made a small 4 digital voltmeter display under my companionway steps.
One meter per cell and it makes a nice nightlight/step illuminator which I can see from my V berth.
Now I am able to check cell levels 24/7.
Being that the meters were cheapies from eBay, I checked their calibration before installation.

Similar to these:

https://www.ebay.com/itm/3-10Pcs-0-2...6v7HzY1Y4rrWeA
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Old 11-12-2017, 09:23   #15
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Re: [B]Best practice charging for LFP & LFMP bank?[/B]

To BigBeakie's OP, I'm afraid there is no data on actual side by side charge cycle effects of 13.8v vs 14.4v. Only anecdotal and some non-controlled empirical evidence has been provided to date.

I do not subscribe to the syncophant philosophy that states if "x" person states this is the way to go it must be alpha and omega of battery science.

I have the exact same questions that you do about these drop in batteries and a few more.

I'm concerned about using them in a parallel installation to attain the AH target needed but maybe overly so.

I'm concerned about their rather low amperage discharge limits of anywhere from 40A to 150A depending on battery.

Hopefully we can get some answers.

And finally, at least for me, battery vendor bashing is not helpful especially when it's done on either second hand info or supposition.
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