LiFePO4 - How are you controlling your SoC?

[CaptainRivet]

Originally Posted by fxykty

Because not everyone has a system like yours. It works for you, so stick with it.

I have 8 charge sources and not all of them can be controlled precisely and not all those that can do I trust. Plus, I don’t believe that everyday charging to 100% SOC is suitable for best longevity. I thinks it’s also worthwhile to see what is happening and to control things like charging and discharging based on cell measurements.

Regarding monitoring absolutely agree.
Charging everyday to 100%SOC is a absolute standard in 99.9% of BMS and eg all Victron gear.
And that doesn't harm if you just hit the 100%SOC and then discharge it right away. It equals the cells so less stress in the weakest one. Calender aging has a much higher effect.
What effects lifespan is keeping it at this high voltage/95-100%SOC.

[sailorboy1]

Originally Posted by CaptainRivet

Till your cells bloat because you floated them to death...if you would read Eric Bertschers article then you would know that...

what a load of ***p

I wonder where in you head you get stuff. I charge my batteries per the manufacturers specs.

[pbiJim]

Originally Posted by CaptainRivet

Till your cells bloat because you floated them to death...if you would read Eric Bertschers article then you would know that...

Can you please post a link to that article?

[GreenWave]

Originally Posted by CaptainRivet

Regarding monitoring absolutely agree.
Charging everyday to 100%SOC is a absolute standard in 99.9% of BMS and eg all Victron gear.
And that doesn't harm if you just hit the 100%SOC and then discharge it right away. It equals the cells so less stress in the weakest one. Calender aging has a much higher effect.
What effects lifespan is keeping it at this high voltage/95-100%SOC.

Victron has ways to not charge all the time to 100%. SUSTAIN setting is one such method when you have solar or other non-shore power charging.

[SOLAR SUPPORT]

Originally Posted by Iron E

From what I'm reading controlling charge/discharge voltage may be a better way to avoid LiFePO4 battery degradation than % of charge/discharge (ex: 80/20DoD 70/30DoD, etc).

So long as charging doesn't rise above 3.4v (per cell) or discharging doesn't fall below 3.1v the battery remains healthy and cycles aren't degraded.

If this is true and you are following this idea, how are you achieving this SoC?
For example, how do you keep batteries stored at 95-97% I can see that the Victron smart shunt can prevent batteries from falling below x%

I'm interested in hearing about the plan you're implementing... Smart Shunt? Advanced BMS? Coulomb Counting?

Simple Coloumb Meter.

I passed the main power cable of the service battery bank through the round type current transformer. I also passed the solar energy main power cable through the same current transformer. In this state, the Coloumb Meter to which the current transformer is connected calculates the instantaneous capacity of my batteries quite consistently.

It measures the consumption current passing through the main power cable of the service batteries as a "+" value. It measures the energy sent by solar energy to the batteries as a "-" value. When there is simultaneous energy consumption and production, I instantly monitor the difference in flow. For example, if solar energy produces 30A and consumption is 10A, the Coloumb Meter shows - 20A.

[wholybee]

Originally Posted by Iron E

From what I'm reading controlling charge/discharge voltage may be a better way to avoid LiFePO4 battery degradation than % of charge/discharge (ex: 80/20DoD 70/30DoD, etc).

So long as charging doesn't rise above 3.4v (per cell) or discharging doesn't fall below 3.1v the battery remains healthy and cycles aren't degraded.

If this is true and you are following this idea, how are you achieving this SoC?
For example, how do you keep batteries stored at 95-97% I can see that the Victron smart shunt can prevent batteries from falling below x%

I'm interested in hearing about the plan you're implementing... Smart Shunt? Advanced BMS? Coulomb Counting?

You are over worried about nothing. Don't overcharge LFP. That is a voltage setting in your charge device. That's the main thing. You will reduce the life _a_little_ if you charge it to 100% and then leave it there for months at a time. But, normal charging to 100% is fine, because it isn't there for very long, maybe 1% of its life if you are cycling it daily. And discharging to 0% once in a while is fine to. But I expect you will never do that because you want to keep the power on. So that is a non issue.

Whether or not you are using voltage or SOC to determine if the battery is in the 80/20 range is splitting hairs. You don't need to stay in the 80/20 range. Use it, don't baby it like you are used to with lead. Like, is the battery going to last 20 years, or 19 years? Who cares, you are going to replace it by then for something bigger.

The most amazing thing about LFP is being able to forget about your batteries. Despite people here posting about complex systems that let them monitor every detail and stress over the smallest thing, with LFP, you can forget it. Get a victron SOC meter, set an alarm at 10% SOC so you can start a generator or something before the power goes out and you lose the food in your freezer. That is pretty much all you need to worry about if the system is setup correctly.

[Iron E]

Originally Posted by wholybee

You are over worried about nothing.

I'm not worried - certainly not over worried, I simply asked a question regarding ideas and options regarding SoC and asked how people are accomplishing the build.

While a basic approach works for some, others might feel it's best to build a self-managed system optimal for performance and longevity.

Also yes, there will be times when we leave the country for a month. I would like a system that cycles appropriately.

Originally Posted by wholybee

Get a victron SOC meter, set an alarm at 10% SOC so you can start a generator or something before the power goes out and you lose the food in your freezer.

Thanks for the suggestion. Yes, The Victron Monitor and/or smart shunt is def in the works, also like the BMS Rivet suggested.

[Iron E]

Originally Posted by SOLAR SUPPORT

Simple Coloumb Meter.

I passed the main power cable of the service battery bank through the round type current transformer. I also passed the solar energy main power cable through the same current transformer. In this state, the Coloumb Meter to which the current transformer is connected calculates the instantaneous capacity of my batteries quite consistently.

It measures the consumption current passing through the main power cable of the service batteries as a "+" value. It measures the energy sent by solar energy to the batteries as a "-" value. When there is simultaneous energy consumption and production, I instantly monitor the difference in flow. For example, if solar energy produces 30A and consumption is 10A, the Coloumb Meter shows - 20A.

Thanks SP

[Iron E]

Originally Posted by sailorboy1

what a load of ***p

I wonder where in you head you get stuff. I charge my batteries per the manufacturers specs.

I read his comment as "Maintaining 100% SOC". That would also be considered Storing at 100%. I don't believe there are huge problems with doing this for several days. Still, there's not an LFP battery manufacturer I'm aware of that would recommend maintaining 100% (or 0%) SoC for an extended period.

[wholybee]

Originally Posted by Iron E

While a basic approach works for some, others might feel it's best to build a self-managed system optimal for performance and longevity.

There isn't any evidence that a complex system provides any better performance or longevity though. A simple system with a FET BMS, and basic chargers with an LFP profile will provide the exact same performance and longevity as the most complicated systems with a REC BMS or Electrodocus or whatever.

I am away form my boat often right now. I simply changed the full charged voltage (absorption or bulk depending on the charger implementation) to 13.8V (or 13.5V or whatever, as long as it is lower than fully charged) With everything except my freezer turned off, my battery cycles a little bit, and never hits 100%.

[s/v Jedi]

Originally Posted by Iron E

I read his comment as "Maintaining 100% SOC". That would also be considered Storing at 100%. I don't believe there are huge problems with doing this for several days. Still, there's not an LFP battery manufacturer I'm aware of that would recommend maintaining 100% (or 0%) SoC for an extended period.

He claims they (the manufacturers except the one who makes his batteries of course) just parrot some info from the Internet and no serious testing has been done to prove that.

Except when I post serious testing showing he’s wrong, then he already knows that and 4.7% degradation per 6 months is peanuts

[sailorboy1]

Originally Posted by s/v Jedi

Except when I post serious testing showing he’s wrong, then he already knows that and 4.7% degradation per 6 months is peanuts

you have such a reading trouble

[Wandering1]

Or Rod Collins Marine How To site on lithium. A good explanation of why not to float lithium

[CaptainRivet]

Originally Posted by wholybee

There isn't any evidence that a complex system provides any better performance or longevity though. A simple system with a FET BMS, and basic chargers with an LFP profile will provide the exact same performance and longevity as the most complicated systems with a REC BMS or Electrodocus or whatever.

I am away form my boat often right now. I simply changed the full charged voltage (absorption or bulk depending on the charger implementation) to 13.8V (or 13.5V or whatever, as long as it is lower than fully charged) With everything except my freezer turned off, my battery cycles a little bit, and never hits 100%.

Or make it even simpler, pull the main fuse at any SOC below 80% and keep it like this, even unplug BMS. Lifepo4 has no self discharge....
No cycle, no risk of deep discharge,nothing can fail or need to be managed nor monitored.
just flip a switch and bilge pumps run off the lead starter/soon LTO.

ElectrodacusBMS is very simple and steers all.source means you can use eg a lead charger

[wholybee]

Originally Posted by CaptainRivet

Or make it even simpler, pull the main fuse at any SOC below 80% and keep it like this, even unplug BMS. Lifepo4 has no self discharge....
No cycle, no risk of deep discharge,nothing can fail or need to be managed nor monitored.
just flip a switch and bilge pumps run off the lead starter/soon LTO.

ElectrodacusBMS is very simple and steers all.source means you can use eg a lead charger

That works, unless you have a bilge pump, freezer, etc. I leave my boat for a few weeks at a time, and leave those things on.

For those that haul their boat and winterize it, I recommend just disconnecting it like you say.