LifePo4.. Yes AGAIN!

[john61ct]

I think BMS can just mean the minimum protection.

"Premium" and "true" descriptors are arbitrary, best to just spell out functionality desired / offered.

I wouldn't go without temperature-based shutdown, at both extremes for example. Full setpoint adjustability is a must. And ability to disable active balancing.

DIY done right can be better than a packaged solution, in both cases "quality" depends on many factors.

[john61ct]

Originally Posted by travellerw

At this point, we are kinda picking nits.... but.. The SOC I have seen suggested most for storage is 40-60%. Mainsail's article suggests no higher than %50-60.

Yes but since then I've seen many statements from people I trust that, lower the better for maximizing longevity.

Balanced against **never** taking chances of going dead flat.

For me that means 8-12% long as cool and 100% isolated, checking monthly.

Increase to 20% if hot or only checking every couple months.

But it's a judgment call, no hard rule.

And obviously if stored for many months then calendar-based aging kicks in, another largely unknowable topic, depends so much on temperature.

[alctel]

Originally Posted by travellerw

I'm a little confused.. Maybe it was how I worded it (we live by our power every damn day).

I won't be relying on checking every day. I'm relying on the chargers to actually follow the settings I'm inputing. "If" they somehow don't follow the settings I input and try to overcharge the battery, then the BMS should catch that (at the cell level) and disconnect the 7700 (isolating the bank and leaving the boat still powered by the controllers). The BMS is only the insurance policy and is not controlling the charging in any way whatsoever.

As to the 7700 vs the 7713. The 7700 works much easier with my BMS as my BMS code is designed to send that "blip" of power. If I was to switch to a 7713, then I would need to modify the code to make the 7713 function correctly. With the 7700, I do nothing but hook the wires up to my BMS and its done.

The physical switch on the 7700 (or 7713) is an integral part of my design. It allows me to disconnect my bank and "lock it off" in the event we actually ever go to a marina. Then we just run the boat on the charger/power supply and don't worry that the batteries might "accidentally" get reattached.

However, your post has made me think a little more on the charger/power supply and the wind generator. I think I may add a relay to those devices as a second level of protection. That way, both of those devices will require 2 switches and can't be "accidentally" switched on.

Ah I see. That makes sense to use a 7700 then if the BMS is already set up that way!

However, I'd still be tempted to put a separate HVC/LVC relays on the charge/discharge bus - as (correct me if I'm wrong here) if the BMS power fails or something breaks then the 7700 could be stuck closed? On mine if the BMS loses power or breaks then all the contractors opens and the whole circuit shuts down. Another consideration is that if you are in a HVC situation it'd be nice to still have the discharge bus connected, and likewise in a LVC situation with the charge bus.

HAVING said that, Lipo design is all about choices and yours will work just fine I think! It also has the big advantage of being relatively simple and it sounds like you've done your homework!

[john61ct]

Just to be clear, LiPo is completely different from LFP / LiFePO4 .

Everything in this thread is about LFP.

Right?

[DeepFrz]

This guy has some informative videos on LFP and equipment settings. He also has posted his 12 volt wiring diagrams that may be of interest to some of our members.

https://www.youtube.com/watch?v=wuEE3JlxGAM

[travellerw]

Originally Posted by DeepFrz

This guy has some informative videos on LFP and equipment settings. He also has posted his 12 volt wiring diagrams that may be of interest to some of our members.

I appreciate the video, since I like "all things batteries" these days.. However, he is running a Victron system. Loads different than the DIY prismatic LFP environments we are talking about.

We have a good friend buddy boat with that system. Good stuff, but different from prismatic cells. If you have the budget, then I think the Victron gear is a good buy.

[john61ct]

I think the packaged systems are in fact stock prismatics, just wrapped up in their added-value proprietary BM$

[travellerw]

Originally Posted by john61ct

I think the packaged systems are in fact stock prismatics, just wrapped up in their added-value proprietary BM$

Yup absolutely... An unnamed Victron dealer shared with me that the inside of those batteries are CALB cells..

However.. Due to that proprietary BMS, they are completely different animals now. If you are going to buy Victron lithium batts, you are really buying into the whole system!

Its a good system... but not for me. After 2 years of cruising, I realize I don't want to rely bullcrap bluetooth apps to manage my system. Just more complexity and things to go wrong. I want real guages I can look at multiple times per day.

[john61ct]

I'm expecting open source designs projects to mature in the next few years that will work with OTS sensors & relay etc components compatible with a variety of mfg cells and sizes.

Only then will "packaged" systems be priced competitively.

[travellerw]

Ok.. I want to bring this thread back more on topic.. So I decided to wade into the top balance vs bottom balance debate and provide my reasons for currently choosing a bottom balance. First.. Please understand that this is only my opinion, based on ZERO actual experince with a pack yet. However, my opinion is based on the work and information published by many others. Its my wallet, my pack that I'm putting on the line!

First, lets really break down balancing to the basics. The basic purpose of balancing is to bring the cells into balance at a certain SOC (top, bottom, or for crazy people middle). The primary reason we do this is because not all cells are equal. Manufacturing tolerances introduce a variation in cell capacity, even for cells produced one after another. Of course any pack you build from those variable cells will only be as "strong" as its weakest cell. Example, if you buy 4 x 100AH cells, you may recieve cells ranging in capacity from 95ah to 110ah. That means any pack you build from those cells in series can only be a 95ah pack. By balancing the cells, we are trying to ensure we don't push that one weak cell outside of its safe voltage range (or even into a range where we damage it over time and reduce capacity). Hopefully this is clear and not too simplified. Now to the balancing methodologies, again simplified.

A top balance - All cells are brought to their absolute top safe charging voltage (either as a parallel pack or one by one). They are then connected in parallel and left to equalize for a period of time. After that the pack is put into service. Since we now know that all cells were in balance at that high state of charge, we know that we should be able to safely charge them to a slightly lower voltage without risk of pushing a single cell (the weak one) into a danger zone. This should hold true as long as the cells remain in balance. The cells in the pack are relatively protected from overcharge!

A bottom balance - In this scenario, all cells are brought to their absolute bottom safe discharge voltage. We essentially take the cells to what the manufacturer says is 0 SOC. The cells are then allowed to equalize for a period of time. After that the pack is USUALLY charged to a lower cutoff voltage (and amperage) than a top balanced pack. At a point where the end user is happy, we call that value %100 SOC and charging is terminated (%90 rated capacity is usally a common number that is chose for this). Of course we know how close we are to the rated capacity as we just took the pack from 0 SOC and recorded the AH we put back in. In this scenario we have essentially equilized the capacity of all the cells (yes we are throwing some capacity away). However, we now know the absolute 0 SOC value for each cell. As long as we never discharge anywhere near that value, we can be pretty sure we won't destroy a cell with an over discharge.

Unfortunately, with chinese LFP cells we just can't have our cake and eat it too. It would be super rare to order 4 cells and have them match closely enough to be %100 balanced at both the top and bottom. That leaves us in a position where we need to choose one type of balance over another. Top balance technically provides a better protection from over charging. However, bottom balancing provides better protection for an over discharge.

So for me... I'm leaning to bottom balance my cells for the following reasons (in no particular order).
1. Bottom balancing is easier and can be done without special equipment (danger danger though)
2. Bottom balancing doesn't hold the cells at a high voltage for a long time (proven to be damaging)
3. I get to initially know both my 0 SOC and 100 SOC without the extra step of a capacity test.
4. My top charge voltage is essentially a constant. My solar controllers will only put in the voltage I tell them too. This limits my risk of pushing to a high voltage. However, as a liveaboard my bottom voltage is a constantly changing metric. Depending on how much charge we have, and how much we draw, there is a bigger possibility we could get to the bottom. Thus I want to protect the cells more at the bottom.
5. Cells are a little more tolerant to an overchange than an overdischarge.

OK... So first.. Change my mind.. Am I crazy to lean towards a bottom balance?

Second... Once we are done debating the above, then you can try and change my mind that a begal is very much a donut.

P.S. Yes I completely understand that if I follow sane charging routines and stay out of the "knees", either balance methodology is fine. However, I like to stack as many odds into my corner as I can. If one methodology provides just that extra little bit in the event of a no holds bared turd fan catastophe, I want to be on that side.

[arsenelupiga]

Originally Posted by john61ct

I think BMS can just mean the minimum protection.

"Premium" and "true" descriptors are arbitrary, best to just spell out functionality desired / offered.

I wouldn't go without temperature-based shutdown, at both extremes for example. Full setpoint adjustability is a must. And ability to disable active balancing.

DIY done right can be better than a packaged solution, in both cases "quality" depends on many factors.

that sums up how i see it ^^

BMS needs to be able to monitor only as well. My pack will not be full every day, but most time will wander somewhere around 40-80% soc. I can for example commit to get full once per week. So, AH counter may get out of whack as well during these periods and cant be relied on, completely.

At 400 AH battery, powering BMS from one battery should be minor issue, i think, especially if monitor only.

I want to run system manually initially (balance via manual charger, and use battery monitor system) , just to see what is going on and familiarize with the thing.

[BigBeakie]

Originally Posted by john61ct

Here's my "boilerplate" LFP summary, mostly from marine electrics discussion forums involving long-term users and professionals, with special thanks to Maine Sail (see below).

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/f14/...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.

Best of luck, and do please report back here!

Thanks john61 for such a comprehensive summary. I have read all those resources, and I have re read then again to make sure I was not missing what I was looking for. I was not missing it. It is not there. Again, I would like to know WHY Mainesail states that it is harmful to charge above 13.8 volts. I'm not trying to be contrarian, or pedantically skeptical, I just want to see the data. And let's not de-reail this thread with this point, maybe it's for another thread on LFP.

But to cut to the chase, someone, somewhere, sometime would have had to have 2 identical LFP test banks and run them through thousands of charge-discharge cycles at say 14.2V and 13.8V, to arrive at the conclusion that one regimen was better than the other. I have been unable to find this data or test result summary. It would not be an easy thing to accomplish, time wise, so maybe that's the reason it hasn't been done.

It is looking like nobody has actually ever done this, including by the way, the battery manufacturers. I also asked Victron to show me data that supports their charge recommendations and lifespan statements, and they could not, but he challenged me to show him that 13.8V was better than 14.2V ( which is what they use to trigger their BMS top balancing), and I could not send him anything that supports the 13.8V-13.85V charge regimen, other than a bunch of declarative statements.

I hope it's not one of those "the world is flat" beliefs. Meaning, I hope we all are VERY sure that Mainesail is right. Personally, I would be more comforted by seeing the data.

[BigBeakie]

Sorry, a typo in my last post, replace Victron with Valence.

[john61ct]

Originally Posted by travellerw

top balance vs bottom balance

The bottom is too dangerous for me, there be monsters.

I don't **ever** want to get that close to cell death.

My day to day cycling top point is 3.41-3.49 Vpc "then stop".

The "danger" of getting closer to mfg spec top point is simply losing some cycles off the EOL hopefully decades away.

And that will only be rarely, for maintenance routines.

My day to day cycling **low** point is 11.95, multiple alarms higher than that plus several hard cutoffs, there and 11.85.

And I feel much better knowing I will never go lower than that.

Most regular usage will stay above 30% SoC via AH counting.

[alctel]

Originally Posted by john61ct

The bottom is too dangerous for me, there be monsters.

I don't **ever** want to get that close to cell death.

My thoughts as well.