LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[gscriba]

Hi John,
Yes, I've done my research. Saw all that. Thanks. Looking for more hands on practical experience from those here who have set up and are using their LiFePO4 and BMS system.

[CatNewBee]

I saw the Simarine at the boat show, nice display, small and clean, lots of accessories. Downside was the shunts ratings are far away for what I needed. You can measure single branches for power consumption and the like, but it requires a complete rewiring of those through the shunts, so you may mess up your installation and build new power distributions to leverage the functionality. Also somewhat expensive if you want all the features.

My personal verdict is, it is a nice toy, but needs effort. If I would like to re-wire my vessel, I would probably go a different path, similar to the installation of the eXquisite x5, a rigid bus system containing thick wires from the batteries along both hulls and inside of the salon with lokal break out units, all fuses automatic resetable and all circuits remote switcheable with manual override and all circut currents measurable, all switch panels programmable.

You can program scenes for lighting and control everithing from any point. Expensive, but very clean and easy to manage, no clutter. I don't know the manufacturer of the distributions, but was very impressed of the installation.

[JmanC]

Why exactly is Floating at correct voltages bad? For example if your on shore power and floating at around 50% soc all the time. Have not found anything anywhere as to why it's bad. Just the same old "you better not its probably not good for it"

From my tests the battery will cycle slowly from say 60-40% at 13.2V depending on loads. C/5 loads will bring it right down way too low due to no dedicated voltage sensing. So is this kind of small cycling with typical loads bad in the long run? My guess is if so it will be negligible.

[Maine Sail]

Originally Posted by JmanC

Why exactly is Floating at correct voltages bad? For example if your on shore power and floating at around 50% soc all the time. Have not found anything anywhere as to why it's bad. Just the same old "you better not its probably not good for it"

From my tests the battery will cycle slowly from say 60-40% at 13.2V depending on loads. C/5 loads will bring it right down way too low due to no dedicated voltage sensing. So is this kind of small cycling with typical loads bad in the long run? My guess is if so it will be negligible.

I think the term itself, "float", is confusing at best when applied to LFP. In a lead acid sense "floating" is;

Float Charging – A continual charge applied to the battery with a voltage that is in excess of it’s natural resting 100% SoC voltage. Eg: Full 12V lead acid battery = 12.72V - 13.0V and float would be 13.2V to 13.8V or above the natural 100% SoC open circuit voltage.

LFP batteries are not lead acid batteries and they were not designed nor intended to be “float charged“ (continually over charged), in the typical lead acid sense (see above).

There is scant data on "float charging" LFP cells. We have two years of testing "float" (actually storage and standby voltages see below) conditions on LFP and unfortunately the data collected is all over the map.

While we have a few premium branded LFP cylindrical 18650 cells that suffered zero capacity changes, after being held at 3.400V (13.6V for a 12V nominal bank) 24/7, for six months continuously, we also have capacity losses holding the same voltage on counterfeit cells and no-name LFP cylindrical cells exceeding 16%. We also have an 11% Capacity loss on some CALB SE prismatic cells from leaving them at 100% SOC and letting them sit for 12 months. In other-words the data is confusing at best and our "float" life testing, though no higher than 3.40VPC, is still on-going.

Unfortunately there is no real definition for a voltage setting that is not holding an LFP battery at a voltage above the natural resting 100% SoC point, as we do with lead acid batteries. I would suggest there are really actually two types of voltages that can be used for LFP;

Storage Voltage – A voltage setting, usually programmed using the float voltage setting on a lead-acid based charger, that results in the battery discharging to approximately 40-60% SoC then being held there by the charger. A storage voltage would ideally be used anytime the batteries will not be used for any more than a week or (owners discretion) such as dockside storage. This still leaves open the possibility if a system malfunction while the owner is not there.

Standby Voltage – A voltage setting, usually programmed using the float voltage setting on a lead acid charger, that results in the battery discharging to just below the full charge point of the battery or 90% SoC to 98% SoC, and being held there.

As long as you are below the 100% voltage point of an LFP cell you're not technically "floating" the batteries by continually charging them, at voltages above the 100% SoC point, when they are already at 100% SoC.

When discussing "float" & LFP I think it is a good idea to accompany that term with the voltage you are considering. I don't see anyway the term "float" is disappearing, as applied to LFP, but we should try to define whether we are considering "floating" above or below the 100% SoC point.

[mikedefieslife]

Originally Posted by Maine Sail

snip

Don't most just set 13.2v as their "float" voltage and be done with it.

[CatNewBee]

I do use 13.5V as float setting for solar, it translates to 3.375V cell voltage during the day. So the solar array does provide power for regular loads while the battery is resting at 95% or so, but she is cycled during the night by the fridges, freezer and other gear and recharges in the morning.

When leaving the boat, I would set it to a lower value to keep the battery at 80% and have power if a bilge pump needs it or what ever.

While cruising, absorption is set to 14.4V, we do use a lot of power for the water maker, induction cooking, power winches, hydraulic autopilot, radar... Even with 1650Wp solar we get to absorbtion only a few days of the month due to shading by the boom and rig while sailing, but needed the generator only for 3 hours during the whole sailing season 2019.

I guess, it is a quite healthy set up, regular discharge is about 40.. 50%, deepest was around 65%.

We completed now the second year of usage and we like it.

[Maine Sail]

Originally Posted by mikedefieslife

Don't most just set 13.2v as their "float" voltage and be done with it.

I am sure some do, but this places you at a mid SoC and some don't like that for daily use. Other systems I have seen, mostly DIY configured drop-ins, have been set as high as 13.8V or 3.45VPC.

On my own boat, when I leave it, the BMS is physically turned off and there are no charge sources or loads connected. This is just how I designed the system to operate. For our particular design use I don't really need a float setting. When we are done charging charging is simply off. We don't even consider recharging unless we are below 40% SoC, and have an opportunity to charge, otherwise we don't turn on charge sources until we've dropped to about 20% SoC.

Everyone's usage will be different, and some don't want to set a "float" or storage voltage at 13.2V because it will mean a bank at about mid point capacity. In that case a voltage of 3.38V - 3.40V would leave you nearer or at 100% SoC.

[Delfin]

Originally Posted by Maine Sail

I am sure some do, but this places you at a mid SoC and some don't like that for daily use. Other systems I have seen, mostly DIY configured drop-ins, have been set as high as 13.8V or 3.45VPC.

On my own boat, when I leave it, the BMS is physically turned off and there are no charge sources or loads connected. This is just how I designed the system to operate. For our particular design use I don't really need a float setting. When we are done charging charging is simply off. We don't even consider recharging unless we are below 40% SoC, and have an opportunity to charge, otherwise we don't turn on charge sources until we've dropped to about 20% SoC.

Everyone's usage will be different, and some don't want to set a "float" or storage voltage at 13.2V because it will mean a bank at about mid point capacity. In that case a voltage of 3.38V - 3.40V would leave you nearer or at 100% SoC.

Exactly how I manage my bank when at the dock. BMS disconnected, watch the voltage, which never seems to get below 13.15v, but charge for an hour or so to get resting, disconnected voltage above 13.3v if the bank drops below 13.15v. Simple.

[rgleason]

Mainesail seems to manage their battery discharge and charging manually.

"..For our particular design use I don't really need a float setting. When we are done charging, charging is simply off. ... otherwise we don't turn on charge sources until we've dropped to about 20% SoC.

Catnewbee:

"I do use 13.5V as float setting for solar, it translates to 3.375V cell voltage during the day."

"While cruising, absorption is set to 14.4V, we do use a lot of power for the water maker, induction cooking, ...etc ...... Even with 1650Wp solar we get to absorption only a few days of the month.."

Catnewbee is this basically while you are on board using power?

[mikedefieslife]

Originally Posted by rgleason

Mainesail seems to manage their battery discharge and charging manually.

"..For our particular design use I don't really need a float setting. When we are done charging, charging is simply off. ... otherwise we don't turn on charge sources until we've dropped to about 20% SoC.

Catnewbee:

"I do use 13.5V as float setting for solar, it translates to 3.375V cell voltage during the day."

"While cruising, absorption is set to 14.4V, we do use a lot of power for the water maker, induction cooking, ...etc ...... Even with 1650Wp solar we get to absorption only a few days of the month.."

Catnewbee is this basically while you are on board using power?

I thought that you don't use absorption at all for LFP? Pretty sure most things I've seen say set the absorption time to 0 on Victron products.

[HeinSdL]

Originally Posted by gscriba

John, are you using the Simarine Pico? I'm looking for more details from someone who has installed one and is using it.

I installed the Simarine system in my boat. Reason to replace the old system was that the old system was a rather old fashioned 'knob' with which you could select a small number of sensors: water tank, diesel tank, current draw from house batteries. Even though the measurement capabilities were therefore limited, the amount of wiring and mechanical contacts inside the panel was quite extensive (over time, more and more failure prone), and ultimately the actual monitor broke. So I took out the knob + monitor (actually 2 of them) and a lot of wiring, and replaced with an aluminium sheet, spray painted black as per the overall panel, with Simarine Pico fitted in this panel. Looks great.

And then it's a matter of running a daisy chain lead along the various Simarine units you might want to incorporate and you're done. So now I have measurements of house battery voltage + current (and hence a SOC which I think is quite OK but some say is a bit inaccurate, no opinion on that), engine battery voltage + current & SOC as well as current measurement of anything else that's interesting: alternator, solar panels, shore power. All tanks are also monitored (and calibrated properly) and for good measure I have the occasional temperature sensor here and there to keep me informed of anything happening 'out of the ordinary'. And they gave me the barometer functionality for free (hurray!) which I actually quite like, not sure if it is completely accurate, but the trend is very clear and in line with changing weather conditions.

Can monitor on an App via WIFI, though don't really use that functionality, am not that obsessed. And I understand NMEA comms are in the pipeline.

[JmanC]

Originally Posted by Maine Sail

I think the term itself, "float", is confusing at best when applied to LFP. In a lead acid sense "floating" is;

Float Charging – A continual charge applied to the battery with a voltage that is in excess of it’s natural resting 100% SoC voltage. Eg: Full 12V lead acid battery = 12.72V - 13.0V and float would be 13.2V to 13.8V or above the natural 100% SoC open circuit voltage.

LFP batteries are not lead acid batteries and they were not designed nor intended to be “float charged“ (continually over charged), in the typical lead acid sense (see above).

There is scant data on "float charging" LFP cells. We have two years of testing "float" (actually storage and standby voltages see below) conditions on LFP and unfortunately the data collected is all over the map.

While we have a few premium branded LFP cylindrical 18650 cells that suffered zero capacity changes, after being held at 3.400V (13.6V for a 12V nominal bank) 24/7, for six months continuously, we also have capacity losses holding the same voltage on counterfeit cells and no-name LFP cylindrical cells exceeding 16%. We also have an 11% Capacity loss on some CALB SE prismatic cells from leaving them at 100% SOC and letting them sit for 12 months. In other-words the data is confusing at best and our "float" life testing, though no higher than 3.40VPC, is still on-going.

Unfortunately there is no real definition for a voltage setting that is not holding an LFP battery at a voltage above the natural resting 100% SoC point, as we do with lead acid batteries. I would suggest there are really actually two types of voltages that can be used for LFP;

Storage Voltage – A voltage setting, usually programmed using the float voltage setting on a lead-acid based charger, that results in the battery discharging to approximately 40-60% SoC then being held there by the charger. A storage voltage would ideally be used anytime the batteries will not be used for any more than a week or (owners discretion) such as dockside storage. This still leaves open the possibility if a system malfunction while the owner is not there.

Standby Voltage – A voltage setting, usually programmed using the float voltage setting on a lead acid charger, that results in the battery discharging to just below the full charge point of the battery or 90% SoC to 98% SoC, and being held there.

As long as you are below the 100% voltage point of an LFP cell you're not technically "floating" the batteries by continually charging them, at voltages above the 100% SoC point, when they are already at 100% SoC.

When discussing "float" & LFP I think it is a good idea to accompany that term with the voltage you are considering. I don't see anyway the term "float" is disappearing, as applied to LFP, but we should try to define whether we are considering "floating" above or below the 100% SoC point.

Thanks for that. Much clearer than I was just using the term Floating.

[john61ct]

Originally Posted by mikedefieslife

I thought that you don't use absorption at all for LFP? Pretty sure most things I've seen say set the absorption time to 0 on Victron products.

Three uses for the term.

Absorption **voltage** is the mfg spec setpoint, toward which the source is "striving" to reach during the initial Bulk / CC stage, voltage climbing, as much current as the bank can accept / demand from source.

Soon as the setpoint is reached, you are in Absorb **stage**, aka CV, source is holding voltage down to that setpoint, current starts falling as SoC continues to rise.

If you are (for whatever reason) choosing to get to a higher SoC, 100% Full by your definition, or even higher, up to the stressful maximum limit spec'd by the maker,

then some AHT, Absorb **Hold Time**, is required.

With lead, at a high C-rate, might take several hours of AHT to get to Full. With LFP, especially at a low C-rate, might be just a few minutes.

Often a minimum AHT is required by the charge source.

If you manage to cut off charging at exactly the point the battery post reaches your setpoint voltage, that is a CC-only charge profile.

With LFP, if the C-rate was high and setpoint low, you may be well under 90% SoC. At a high setpoint and low enough C-rate, you may be at the 100% mark, or even stressfully higher.

Hope that helps.

[JmanC]

Originally Posted by mikedefieslife

Don't most just set 13.2v as their "float" voltage and be done with it.

That's what I would do, when I get to shore just spend about 10secs at the sterling panel to quickly set both absorb/float to 13.2V and walk away. Dropins are getting cheaper & cheaper & the hope for me is they will at least last as long as golf cart 6V, but being alot lighter & no sulfation problem (EQ & getting back to 100%). They are only about 50% more cost than trojan t105 in my area and for a 200-300AH that to me is not a problem. By the looks 13.1V is better as it keeps it in the 30-40% region which I hear is better than 50-60.

[JmanC]

Originally Posted by mikedefieslife

I thought that you don't use absorption at all for LFP? Pretty sure most things I've seen say set the absorption time to 0 on Victron products.

From all my testing with my dropins:

No absorb duration required for hard constant power sources with at least 13.8-14V at terminals, just straight to float after setpoint is reached. This is what I do as chargers like sterling don't have a good absorb timer at all for LFP, and some use a tail current value to float which isn't reliable with these conservative voltages and goes to float early. Longterm AC charging ( & maybe even genny use) obviously doesn't need absorb because it will absorb it's way to full (good enough) with as little as 13.4V. You don't need the last 5% capacity.
Charge from 20%SoC to 100% at 13.8V 0.3C and the absorb duration will only need to be about 30-45mins if that. But this doesn't mean the absorb stage is slow like lead acid, it is pretty quick overall. Unless you want to get to 2% tail current.
But charge at lower 0.1C and the battery will be dead full by the time 13.8V is reached. I avoid higher voltages and try to make sure charge rate is at least .3C so even at 13.8V you can charge very quickly.
Charging to 14V with no absorb with a descent current rate will probably land you in the 90% range and so good enough to turn off genny.
14V looks to be the minimum you should use as there is a nasty volt drop inside my chargers and with all the wiring (fuse, shunt, busbars etc).

With solar it will be based on environment. Solar alone is usually always never even remotely enough to fully charge and the days are always inconsistent with long cloud periods so no chance of over absorbing in long run. But I hear higher voltages like 14V+ mixed with constant low & partial charging mean possible damage overtime?
But if the motor or genny is ran early in morning and you let solar finish as long as you got a decent wattage I would keep absorb time to about 30mins max or just 0. You should ideally land in the 90-95% soc unless there are clouds.