Good thesis on preserving the life of LiFePo4 lithium batteries

[Zhyachts]

I love the 80/20 charging regimen, long life and one less BM in my life. This is the way I would set up my system, if I had a year free to put it together.



My question is "why do we have to construct these systems ourselves?


When will a LiFePo master regulator be made that has wind, solar, SP charger and alternator inputs and out put controlled by three (3) buttons; MAX, for those into knees, 80/20, for those into long life, and "STORAGE" for self-discharge protection.


Am I asking too much?

[john61ct]

Yes, until volunteers in the open-hardware / FOSS arena make progress.

Those actually in the biz make tons of margin from proprietary closed systems.

Will happen though, just not soon.

[rajsach]

Please define longevity . Define long life.Let’s say I buy brand new LiFO4 batteries and have them professionally installed. 1200AH . If I come back from a trip and plug my boat up to shore power with charger on and walk away how much life in months, years etc. am I potentially giving up on my lithium battery bank.

[Cpt Pat]

I'm not an academic researcher. I don't have to defend a thesis. Check it out for yourself. The numbers I have seen show that storing a lithium (LiFePo4) battery at 100% SOC at 25 degrees C for one year (cumulatively) will decrease its capacity to 80% of original. 80% capacity is defined by some as "end of life", and by that definition, you killed your battery.

There's new data coming out all the time. Maybe you'll find something that contradicts. If so, I'd like to know. But for now, I'm storing my battery at 30% SOC. (Some studies say 50% SOC is optimal.) There's no downside to doing that, except the inconvenience of having to occasionally recharge a few amp/hours to compensate for self-discharge, and having to wait two hours while I recharge before going out.

I've eliminated the inconvenience of having to compensate for self-discharge by proving a "safety net" charge to prevent the terminal voltage from ever going below 11.7 volts (provided shore power doesn't have a prolonged failure).

Lithium batteries don't sulfate. They don't have to be stored in a fully-charged state. In fact, it's bad for them, according to the data I've seen.

[rajsach]

Originally Posted by Cpt Pat

I'm not an academic researcher. I don't have to defend a thesis. Check it out for yourself. The numbers I have seen show that storing a lithium (LiFePo4) battery at 100% SOC at 25 degrees C for one year (cumulatively) will decrease its capacity to 80% of original. 80% capacity is defined by some as "end of life", and by that definition, you killed your battery.

There's new data coming out all the time. Maybe you'll find something that contradicts. If so, I'd like to know. But for now, I'm storing my battery at 30% SOC. (Some studies say 50% SOC is optimal.) There's no downside to doing that, except the inconvenience of having to occasionally recharge a few amp/hours to compensate for self-discharge, and having to wait two hours while I recharge before going out.

I've eliminated the inconvenience of having to compensate for self-discharge by proving a "safety net" charge to prevent the terminal voltage from ever going below 11.7 volts (provided shore power doesn't have a prolonged failure).

Lithium batteries don't sulfate. They don't have to be stored in a fully-charged state. In fact, it's bad for them, according to the data I've seen.

Thank you for the reply. I apologize if the tone of my first post was off putting. It was unintended. Thanks for the information

[john61ct]

Originally Posted by rajsach

Please define longevity . Define long life.

Say a given batt is rated for 2500 cycles, if cared for according to vendor specs.

Say you care for them better than the vendor specs*, and can get 4000 cycles, or maybe 8000 cycles, we just don't yet know.

*For me that means charging **to** 13.8V only, not at their higher voltage. Also I prefer no Float, or very low voltage Float, but that is less critical.

Also of course storing at low SoC, and cooler temps make a huge difference.

______
> Let’s say I buy brand new LiFO4 batteries and have them professionally installed. 1200AH . If I come back from a trip and plug my boat up to shore power with charger on and walk away how much life in months, years etc. am I potentially giving up on my lithium battery bank

Depends, maybe none, if your charge regulator and other control gear is able to accommodate the regime you decide is optimum for longevity.

[hzcruiser]

Originally Posted by Zhyachts

[...]

When will a LiFePo master regulator be made that has wind, solar, SP charger and alternator inputs and out put controlled by three (3) buttons; MAX, for those into knees, 80/20, for those into long life, and "STORAGE" for self-discharge protection.


Am I asking too much?

Yes, you are, because there is no central point where all those charge sources come together and all the storage devices come out of. If we had such a point, it would be a pretty big device to handle them all.

[Cpt Pat]

Originally Posted by Zhyachts

I love the 80/20 charging regimen, long life and one less BM in my life. This is the way I would set up my system, if I had a year free to put it together.



My question is "why do we have to construct these systems ourselves?


When will a LiFePo master regulator be made that has wind, solar, SP charger and alternator inputs and out put controlled by three (3) buttons; MAX, for those into knees, 80/20, for those into long life, and "STORAGE" for self-discharge protection.


Am I asking too much?

No, you are not asking too much. The central charge/discharge control point is the LiFePO4 battery itself. From my research, it is becoming a common configuration to connect the lithium battery in parallel with a lead/acid (AGM, etc.) bank. When a lithium battery is fully charged, all charge current must CEASE. If the mechanism for stopping the charge current is to take the battery off the bus, there must be some other source of power to sustain the loads and absorb charge current if an alternator is involved. A lead/acid does that job just fine. My lead/acids do almost nothing on a short sail. The lithium does all the work.


When the charge/discharge reaches the user-set parameters (for me it's 12.7 volts discharge and 13.8 volts charge), the lithium battery is removed from the bank, and during charge the charging source can continue to charge the lead/acid batteries to their optimum absorption voltage limit (14.4 - 14.7 volts, depending on type). With my arrangement, I can continue to use my shore power charger that's designed for AGM batteries, and my solar and hydrogenerator sources underway without modification.

All you need is a good quality battery monitor that measures the voltage on the main bus, and monitors the SOC of the lithium battery using a shunt.

My set up is:

Discharging:

• Connect the lithium battery to the bus when the bus voltage drops to 13.2 volts. (Note: my lead/acid batteries float at 13.4 volts on the charger.)
• Disconnect the lithium battery from the bus when the bus voltage reaches 12.7 volts (after disconnecting, the lithium battery recovers to a terminal voltage of 12.95 volts -- about 20% SOC).

Safety Backup: if the battery monitor measures a SOC of 15% (by monitoring amp/hours in/out), disconnect the lithium battery (this has never happened - but could if there is a very low discharge current). It this backup disconnect ever occurs, I have to manually reconnect the battery for charging because it will never rise above the 15% SOC without recharge current. The battery monitor sounds an alarm if this condition ever occurs.

Charging:

• Connect the lithium battery to the bus when the bus voltage reaches 13.1 volts for more than 1 minute. (Note: lithium batteries don't draw a significant charge current until the terminal voltage reaches 13.4 volts.)
• Disconnect the lithium battery when the bus voltage reaches 13.8 volts. The charging sources can then take the lead/acids up to their optimal absorption voltage.

Safety Backup: disconnect the lithium battery when the SOC reaches 85%. This can occur before the battery terminal voltage reaches 13.8 volts with a very low charge current (such as from my solar panels). In fact, you can overcharge a lithium battery at very low charge current with a terminal voltage as low as 13.65 volts. This condition has never occurred.

I am accomplishing all that with a Victron Energy BVM-702 battery monitor, and a high current contactor that is energized by the Victorn monitor.

At the dock, I have a circuit breaker that disconnects the lithium that I open before I plug in the shore power charger. I store the lithium at whatever lower SOC it's at when I return. I leave it at less than full charge (typically 20% SOC) until I am ready to go out again.

So the my entire bill of materials: a BVM-702 battery monitor, a contactor, and a circuit breaker.

[hzcruiser]

Originally Posted by Cpt Pat

No, you are not asking too much. [...] My lead/acids do almost nothing on a short sail. The lithium does all the work.

Even though it's not quite doing what ZHYachts was asking (in terms of controlling all inputs and outputs), this is a fairly simple and reliable system similar to what I suggested not too long ago:

http://www.cruisersforum.com/forums/...en-206424.html

Which circuit breaker do you use? I'm wondering because I'm looking for a high current (say 150A) contactor, or, ideally, a latching relay since a standard relay can draw 200mA while on.

[ggray]

Originally Posted by Cpt Pat

I store my battery at 20% SOC. That is the SOC where my lithium battery is automatically taken off the bus and my AGMs take over. .

I'm still sitting on the sideline, but watching LFP with interest.

How do your AGMs fit into the system you have?

[hzcruiser]

Originally Posted by ggray

I'm still sitting on the sideline, but watching LFP with interest.

How do your AGMs fit into the system you have?

Hmmm, didn't he explain it in great detail in post #23 above?

[Delfin]

Originally Posted by StuM

Please, before advising others - learn the difference between amps and amp hours and use te correct units.

Other than spelling correction, was there anything the poster wrote that you have a reason to disagree with, based on your experience with LFP batteries?

[john61ct]

Cpt Pat knows his stuff.

Yes AH vs amps is "important" to help not confuse / educate noobs.

But his misuse of units is truly nit picking, and in no way undermines his credibility on this topic.

[john61ct]

Originally Posted by hzcruiser

Which circuit breaker do you use? I'm wondering because I'm looking for a high current (say 150A) contactor, or, ideally, a latching relay since a standard relay can draw 200mA while on.

Breakers that robust are crazy pricey, good ones anyway,

not designed to be used as switches and much more complex to select compared to fuses for CP.

Check out Blue Sea for ML switches that can be remote.

Their 9012 is great, NO, 0.13A draw while closed.

[travellerw]

Originally Posted by hzcruiser

Which circuit breaker do you use? I'm wondering because I'm looking for a high current (say 150A) contactor, or, ideally, a latching relay since a standard relay can draw 200mA while on.

BlueSea ML-RBS 7713. It can handle 500A continous, 700A for 5 minutes and only draws about 5ma when on (specs say 13ma but users report lower).

Of course the ML-RBS 7700 has the same specs but is a true "latching relay" and draws 0 current when sitting in a state. However, its not as safe as it will not switch to disconnected in the event of another failure (like the BMS dying).

Yes they are expensive devices (about $200USD), but are good quality and built like a brick dunny. I have paired mine with an EvPower (out of Australia) BMS. The total cost of the relay and BMS was under $350USD.