LifePo4.. Yes AGAIN!

[travellerw]

Alright, 2 years after refitting our boat and cruising full time, I have decided to upgrade my battery bank to LFP. Our 6 X 6V GC battery bank has served us admirably for the last 25 months and still has life left, but I want to replace it before a complete failure. It has over 600 cycles on it at this point (albeit NEVER under 12.2V). Since we are in an area where I can replace it fairly easily, I have decided to do it before thats no longer the case.

Of course, I have spent a large amount of time in the last 25 months reading and studying the mountain of information available all over the Internet. However, I'm really struggling with some of the information as most of it is posted by people with strong personalities. In some cases the discussions actually break down into name calling, or rooster pecking, with no clear information coming forward. In other cases people that have zero experience (in the lab, or real life) are posting as "experts" because they have done some research. Yes I have read all the most often suggested items (Mainsail's article, the 398 page thread here on CF, solar forums and RV forums).

So I would like to use this post as a sounding board of sorts. I'm hoping that this post will illicit some responses from people without arguing, name calling, or uselessly saying to go and read the information already out there. I'm hoping this will not only help me, but maybe provide a shorter roadmap for DIYers using 2018 information and numbers. I'm also hoping we can get more data from people using them in a full time liveaboard scenarios as lots of the experienced information I have seen comes from "weekend warrior" type coastal cruisers. Nothing against that type of cruising, but I think a full time liveaboard is a little different use case.

So without further adue, gilding the lilly or fanfare, here is the details of our boat and systems.

Batterries
We currently have 6 X 6V Costco golf cart batteries equalling about 600AH(ish) of capacity . These will be replaced with 4 X 400AH CALB cells.

Load Side
1 refrigerator, 1 freezer, lights, fans, small 14" LED TV, 2 laptops, 2 tablets, 3 Kindles, 3 Game Boys, WIFI, washing machine (run on inverter), water pump, shower sump.

The above loads average about 175AH/day averaged over a 1 week period. I find averaging over a 1 week gives me a better number as all these devices are not continually in use (e.g. we only run the washer every 3 days or so for one 6kg load). Of course this is at anchor, if we are sailing, the instruments add about a 5-7A draw (usually for 5-6 hours between anchorages here in the Caribbean).

On top of this, we also have the ability to run the hot water heater off our inverter when we have excess solar. This takes about 50AH (yes, 50A for 1 hour at 13.8V) to heat enough water for 2 warm showers.

Charge Side
- 900W of solar separated to 4 banks with an MPPT solar controller on each bank. 3 of the banks have Victron MPPT controllers and the final bank has an EPEVER controller. All controllers are fully user adjustable.
- 400W wind Chinese off brand wind generator
- 60A SBC 700FR house battery charger (Quick brand name)

The alternators are completely disconnected from the house banks and only charge their own LA starting batteries. The alternators will remain disconnected from the house bank for a multitude of reasons (costs, complexity, not required). However, there are 2 relays controlled by momentary switches at the helm that can be used to boost the motors from the house bank. In theory, the relays could be used in an emergency to connect the alternators to the house bank.

The Plan
As stated above, the current LA batteries will be replaced with 4 X 400AH CALB cells (already ordered). I have thought carefully on this number and strongly believe that 400AH is the right number for us. It strikes a good balance between capacity, cost and hauling "dead lithium"! It also means that I can use just 4 cells to build the bank, in theory reducing the points of failure.

We will be using an EV-Power BMS controlling a BlueSea 7700 for HVC/LVC/temperature cutoff. I'm not super keen on the 3.9v high and 2.6V low cutoff voltage on this BMS, but the design engineer is another one of those "strong" personalities and swears that it has been installed on tons of banks with no problems. Unfortunately, these values are hard coded in the cell modules and cannot be modified by the end user. I picked this BMS as its very close to the old Housepower BMS that has had lots of sucessful installs. The design is simple, robust and based on open source protocols. The source code for the main control board is available and easily modifyable as its written in basic. Best of all its very affordable (the whole system for a 4 cell bank is about $100 USD).

Our Victtron BMV-700 will then be configured with a high voltage alarm at 14.0V and a low voltage alarm at 12.8V (an external loud buzzer will be connected to the relay port).

Our solar controllers will be configured with the following settings.
- 13.8V absorbtion
- 2.0 hour absorbtion time (may need more)
- No temp compensation
- 13.2V float
- NO EQUILIZATION

Our 400W wind generator will be manually controlled as I cannot find an LFP friendly wind controller. Even now, we rarely turn the thing on as its noisy and we just don't need the power. It will remain off most of the time and only be on under supervision on cloudy days.

Finally, the house charger. This is one of my biggest worries. Its quite old (about 8 years) and only has 2 settings. Gel and LA. However, in LA mode it has an absorbtion voltage of 14.1V and a float of 13.5V (I know, strange voltages for lead acid. I have confirmed it with the manufacturer). I have also confirmed that this charger can be used as a power supply without a battery connected (its actually right in the manual). So the plan for this charger is to wire it through 2 switches (one on the main electrical panel, the other hidden to prevent accidental activation... Sigh, kids!) and only use it under supervision. While running it will be closely monitored and when the voltage gets to 13.8V, we will turn it off IMMEDIATELY. This will only be done on extended cloudy periods to dump some AH back into the bank to carry us until the sun shines again. This charger will also be used in the event we do actually go into a marina (not very often as we spent zero nights on a dock in the last 14 months). If that does happen, we will use the manual switch on the 7700 relay to disconnect the LFP bank and lock it off, then run the boat %100 off the charger as a power supply.

[travellerw]

Ok.. Now that I have laid out the details and the plan, I still have some questions. I'm sure there are just some things and I'm failing to grasp from my lead acid brain programming. I'm hoping some will chime in here and help set my thinking straight.

My first issue is about the excess power that we generate. With our current lead acid system, its easy to see when we are generating excess energy. Once the controllers switch to float, we know our batts are %100 and we can start burning the excess energy to second tier uses (laptops, tablets, game boys, external battery banks, hot water, laundry, ect). The controllers continue to float the batts and cover our excess draw easily. This usually happens twice a week or more with our current setup.
Now with LFP, we won't be floating the batteries (or 13.2V which is really no float). So, I can't really wrap my head around how to best utilize our excess energy. My latest line of thinking is I need to burn that excess energy from the actual batteries themselves. Do the big energy things either the night before, or early in the morning. Leaving more of an "empty tank" for the solar controllers to pour the AHs into? Is this the correct line of thinking? If this is correct, then I really need to adjust my other behaviors. I will need to keep a closer eye on the weather and be more proactive than reactive (since a cloudy day could mean more generator running if I get I wrong and pull a bunch of energy that the solar controllers can't replace).

My second issue is about wire voltage loss. Due to the logistics of boat wiring, there is a some voltage loss between my solar controllers and the batteries (even though they are like 6 inches apart). Once you add the cabling to the buss bar, the buss bar, the current shunt and the cabling back to the batteries, there is about a 0.12V difference in voltage when measured at the controllers and the battery terminals (at 14.8V). For our LA bank, I have taken this loss into consideration and bumped the voltages on the controllers to compensate (when our controllers show 15V, we are really seeing 14.8 and change at the batts). Should I do the same for the LFP settings. That would mean setting the absorbtion voltage to 13.9V instead of 13.8 . Would this be correct (maybe it seems trivial, but I'm trying to cover all bases here)?

I have a couple of other questions I'm mulling, but I think this post is MORE than long enough. Lets stop here. Thanks for reading and I look forward to the responses!

[alctel]

Are you just using one relay for everything? (the bluesea 7700) How does that work, diodes? I had to use a blue sea 9012, a 7713 and then 2 70amp relays to cover everything (9012 as the 'oh ****' relay in case the other ones fail, the 7713 as the LVC, a 70amp as the HVC for charger/solar and the other 70amp as a cutoff for the alt to avoid blowing diodes)

Also, why the 7700 over the 7713? iirc the 7700 can remain open even with a power failure while the 7713 will latch shut if power is lost to the BMS, which is a bit safer.

With LFP you really want to avoid holding it at close to 100% if you can avoid it in answer to your first question. Maybe leave the water heater on overnight or something.

As for voltage loss, I guess I'd try with the lower value first in the controllers and see how it goes. Bump it up after a few months if it's not doing the job.

[evm1024]

Just thought to toss in a pet peeve of mine and not to detract from your questions too much.

LiFePO4 is a chemical formula

Li - Lithium
Fe - Iron
PO4 - Phosphate

P - Phosphorus
O - Oxygen (times 4 in this case)

Regards

[travellerw]

Originally Posted by alctel

Are you just using one relay for everything? (the bluesea 7700) How does that work, diodes? I had to use a blue sea 9012, a 7700 and then 2 70amp relays to cover everything (9012 as the 'oh ****' relay in case the other ones fail, the 7700 as the LVC, a 70amp as the HVC for charger/solar and the other 70amp as a cutoff for the alt to avoid blowing diodes)

Also, why the 7700 over the 7713? iirc the 7700 can remain open even with a power failure while the 7713 will latch shut if power is lost to the BMS, which is a bit safer.

With LFP you really want to avoid holding it at close to 100% if you can avoid it in answer to your first question. Maybe leave the water heater on overnight or something.

As for voltage loss, I guess I'd try with the lower value first in the controllers and see how it goes. Bump it up after a few months if it's not doing the job.

I was hoping you would chime in as I have been reading some of you posts..

I choose the 7700 as it draws no power when not being pulsed. The BMS I choose actually sits on the battery side of the relay (drawing just ma). So as long as the battery has power, it should be able to activate the relay. I actually plan to use 2 control boards (they can be used in parrallel) to mitigate the risk of a failure.

As to only having 1 relay. Yup, only one "OH CRAP" relay. It sits between EVERYTHING and the batteries. The only thing on the battery side is the BMS and sensor boards. The control board mosfets should have the power to pulse the relay. Its really our "insurance policy", that I hope to never need. I do NOT plan on having any relays for the charging devices. I have justified this because I really only have 1 full time charging source. Solar. These will be the only charge devices %99 of the time. I'm relying on the fact that they are %100 configurable and will be monitored every day (we live by our power, every damn day). I will also be installing a physical switch for each solar controller, allowing me to switch off the charging by flipping a toggle switch. In practice I'm hoping to never need those switches and rely %100 on the controller software "doing the right thing". Maybe this is mistake that I will be quickly correcting after a month or so, we will see (I would love some feedback, am I being an idiot).

However I do agree that the 7713 would have been a little more safe by adding a second "failsafe".

[travellerw]

Originally Posted by evm1024

Just thought to toss in a pet peeve of mine and not to detract from your questions too much.

LiFePO4 is a chemical formula

Li - Lithium
Fe - Iron
PO4 - Phosphate

P - Phosphorus
O - Oxygen (times 4 in this case)

Regards

How about we agree to call it LFP from here on in

[senormechanico]

If you find the lithium bank is charged and you want to take advantage of the solar, just turn on the inverter and hot water tank element.
That's what we do.

I made a simple circuit to audibly tell me when the tank temp hits the limit.
The heating element is in series with the thermostat contacts and is hooked to the AC supply in the normal fashion.
Additionally, I wired a simple AC power brick (wall wart) supply with a 12 volt DC output to a car's ignition chime.
The AC side of the power brick is wired across the thermostat contacts.
When the thermostat opens, the power brick is in series with the hot water tank's element.
99.9% of the voltage gets applied to the little power brick as the tank's element is a relatively low resistance.
The chime goes off to tell us we have a tank of hot water, so we turn off the inverter.
In practice, we don't usually run the inverter that long because we usually just need some water for dishes or a shower.
However, if we should forget, it would serve as, "Hey dummy, turn off the inverter !!"

[BigBeakie]

In your research before committing to the LFP, where did you find any real data/evidence for the "charge LFP at no more than 13.8 volts otherwise you'll damage the battery (or at least lessen the LFP lifespan)" school of thought?

Any references you can point me to?


Sent from my iPad using Cruisers Sailing Forum

[elaak]

These guys seem to make it real easy. Not too pricy either (although maybe not compared to CALB cells). Seems to work with most chargers/solar controllers etc.

https://battlebornbatteries.com

[john61ct]

The "drop-in" variety of LFP is a completely different beast from 4S sets of 3.2V prismatic cells.

Built-in BMS for a start, no way to bypass.

Same guidelines apply for longevity, unless you only need it to last a few years.

[john61ct]

Originally Posted by BigBeakie

In your research before committing to the LFP, where did you find any real data/evidence for the "charge LFP at no more than 13.8 volts otherwise you'll damage the battery (or at least lessen the LFP lifespan)" school of thought?

Any references you can point me to?

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!

[alctel]

Originally Posted by travellerw

I was hoping you would chime in as I have been reading some of you posts..

I choose the 7700 as it draws no power when not being pulsed. The BMS I choose actually sits on the battery side of the relay (drawing just ma). So as long as the battery has power, it should be able to activate the relay. I actually plan to use 2 control boards (they can be used in parrallel) to mitigate the risk of a failure.

As to only having 1 relay. Yup, only one "OH CRAP" relay. It sits between EVERYTHING and the batteries. The only thing on the battery side is the BMS and sensor boards. The control board mosfets should have the power to pulse the relay. Its really our "insurance policy", that I hope to never need. I do NOT plan on having any relays for the charging devices. I have justified this because I really only have 1 full time charging source. Solar. These will be the only charge devices %99 of the time. I'm relying on the fact that they are %100 configurable and will be monitored every day (we live by our power, every damn day). I will also be installing a physical switch for each solar controller, allowing me to switch off the charging by flipping a toggle switch. In practice I'm hoping to never need those switches and rely %100 on the controller software "doing the right thing". Maybe this is mistake that I will be quickly correcting after a month or so, we will see (I would love some feedback, am I being an idiot).

However I do agree that the 7713 would have been a little more safe by adding a second "failsafe".

Sorry - I went back and edited my post as I actually have a 7713 not a 7700.

The parasitic draw from a 7713 is only 0.13a, it's way easier to wire up (the 7700 requires a 'blip' of power to change state) and is safer as regards a failsafe device. Like everything in boating however, it's a compromise. I'd probably replace my 7713 with another 9012 if I did it again - physically smaller and easier to wire up and I don't think I'll actually ever use the physical switch on it.

Honestly, I'd maybe add at least a relay for the solar - you could get by with a cheap one (my 70amp ones cost 20 bucks each) - relying on physically checking every day makes me nervous

[travellerw]

Originally Posted by alctel

Sorry - I went back and edited my post as I actually have a 7713 not a 7700.

The parasitic draw from a 7713 is only 0.13a, it's way easier to wire up (the 7700 requires a 'blip' of power to change state) and is safer as regards a failsafe device. Like everything in boating however, it's a compromise. I'd probably replace my 7713 with another 9012 if I did it again - physically smaller and easier to wire up and I don't think I'll actually ever use the physical switch on it.

Honestly, I'd maybe add at least a relay for the solar - you could get by with a cheap one (my 70amp ones cost 20 bucks each) - relying on physically checking every day makes me nervous

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.

[travellerw]

Originally Posted by BigBeakie

In your research before committing to the LFP, where did you find any real data/evidence for the "charge LFP at no more than 13.8 volts otherwise you'll damage the battery (or at least lessen the LFP lifespan)" school of thought?

Any references you can point me to?


Sent from my iPad using Cruisers Sailing Forum

Hhmm, I think you infered something from my original post. I don't remember saying "charge LFP at no more than 13.8 volts otherwise you'll damage the battery (or at least lessen the LFP lifespan)".

However that is the voltage I have chosen for my cutoff. I chose this for a few of reasons. First I'm trying to stay away from %100 SOC. We have tons of solar and I don't need to push my batteries to %100 everyday as they only need to carry me overnight and the rare cloudy days (down here). LFP batteries spending extended time at %100 IS damaging. You can find data on that (I suggest you read Mainsail's article as he tested this).

The second reason I chose that voltage is because we are based in the tropics. High heat environments has been proven to shorten the life of LFP cells. I'm hoping that being more conservative on my charge voltage will help offset that damage (maybe I'm dreaming).

Finally, based on my research I believe that bottom balancing and charging to more conservative top voltages is a safer methodology. I believe it massively reduces the risk of a low voltage cell polarity reversal. I personally feel a low voltage event is much more likely on a liveaboard boat with solar as its primary charge source. For weekend warrior types, this may not be the case.

Now I will encourage you to not just use cruisers forum or Mainsail as gospal. There are tons of other very smart people out there that also have great information (and in some cases, completely different opinions). Contrary to the impression that CF gives you, there are quite a few cruisers here in the Caribbean with LFP cell banks (in just our close buddy boats, there are 5 I count). About %50 are using prismatic cells. The other %50 are using the various big manufacturers (Victron, Lithionics, ect).

Here is another forum I suggest you do some reading on. However, I will warn you that there are some "strong" personalities like I spoke about earlier.
https://www.solarpaneltalk.com

Finally.. I choose to not ignore the EV guys completely. Yes they are a completely different use case, but, that doesn't mean their data is invalid. There are nuggets of gold in some of those forums.

[arsenelupiga]

i have pretty similar solution to you in mind, including 400 AH. However my motivation is to have energy for cloudy days, as we are modest users. Still throw away around 50% of energy on sunny day via solar, and we have sun plenty here.

Relying on 360 W panels to fill the whole thing. My charging voltage will be slightly lower, however definitely will have monitor for each battery, if not even BMS. So I wont have to worry about what to do with free energy.

Also will purchase LFP charger, to be able to correct voltages manually for each battery - running on generator.

From what i gathered so far, your solution looks robust and simple although for my taste too many powerful chargers.