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

[JmanC]

Lab cycle life is typically claimed 1600-2000 for cycling from 20%dod back up to 100%. And many 1000's for shallow 20-30%dod. But how many can be expected from cycling between 20-85 all the time? Never getting back to 100%. Is it alot more cycles than 20-100? If so roughly how much.

[newhaul]

Originally Posted by JmanC

Lab cycle life is typically claimed 1600-2000 for cycling from 20%dod back up to 100%. And many 1000's for shallow 20-30%dod. But how many can be expected from cycling between 20-85 all the time? Never getting back to 100%. Is it alot more cycles than 20-100? If so roughly how much.

the 2 biggest killers of Lfp are being under charged ( discharge below a specific set point significantly reduced service life.
The other is over charge . Hence the bms has both HVD and LVD
It has been estimated using real world conditions that when kept between 20% and85%
The extrapolation shows a likelihood of well over 5k to 7k ( or more) cycles in service .

[newhaul]

Originally Posted by Oceanride007

Would like to put a smallish pack together say 180AHrs, Intend having largish AGM battery in parallel but isolated, have read 165 pages here, takes forever. Intend to charge LFP with MPPT mostly, maybe a DC2DC charger as standby.
Aware that any MPPT charge voltage can overcharge. Suppose Float voltage can be wound down to safe "No charge" voltage, (don't know?).
Is that done is it possible, how do you avoid mini charge cycles, if vessel layed up. Have thought of applying Logic with timers, relays etc (yuck?). And keeping safe margins, but capacity is being lost.
How is this done without baby sitting, esp those without cell level BMS? Thks.

simple answer is during extended periods of layup discharge the Lfp bank to approx 50% and disconnect it from everything.

[rgleason]

Originally Posted by newhaul

the 2 biggest killers of Lfp are being under charged ( discharge below a specific set point significantly reduced service life.
The other is over charge . Hence the bms has both HVD and LVD
It has been estimated using real world conditions that when kept between 20% and85%
The extrapolation shows a likelihood of well over 5k to 7k ( or more) cycles in service .

So the real key is not to abuse them, ie: overcharge above 95% or undercharge below 15%? I think I would also want an alert of some sort when I am aboard, particularly when charging by alternator, as well as the HVD and LVD (disconnects). The alerts would be before HVD and LVD. I think the alternator would also disconnect from LiFePo and continue charging the reserve FLA battery, then shut down, controlled by the LiFePo ready regulator.



How much of a factor do you think occasional charging at 35%C would have on cycles and capacity?

[newhaul]

Originally Posted by rgleason

So the real key is not to abuse them, ie: overcharge above 95% or undercharge below 15%? I think I would also want an alert of some sort when I am aboard, particularly when charging by alternator, as well as the HVD and LVD (disconnects). The alerts would be before HVD and LVD. I think the alternator would also disconnect from LiFePo and continue charging the reserve FLA battery, then shut down, controlled by the LiFePo ready regulator.



How much of a factor do you think occasional charging at 35%C would have on cycles and capacity?

you do realise that charging at .35C ie well within the specifications for every brand , make and model of Lfp battery.
My bank is regularly charged at .5C
I guess I don't understand your question . Are you asking about charging at a slower rate ?

Now more than occasional charging at much over the maximum C charge rate specified for your particular make of cells would IMO be detrimental to the life expectancy.
But by the same metric I don't see to many boats that have that kind of charging capability onboard.

[sparrowhawk1]

All the charge controllers I've ever used have said not to disconnect from the battery when the solar panels are connected. So it seems to me drop-ins would be harmful to my controller. I would think the easiest way around this is to have a sensor on the battery and have a disconnect where the panels go into the charge controller. Recommendations appreciated.

[newhaul]

Originally Posted by sparrowhawk1

All the charge controllers I've ever used have said not to disconnect from the battery when the solar panels are connected. So it seems to me drop-ins would be harmful to my controller. I would think the easiest way around this is to have a sensor on the battery and have a disconnect where panels go into the charge controller. Recommendations appreciated.

easiest would simply be to set your charge controller to stop charging at a set point below the HVD.
As to the disconnect of the panels that is easily accomplished with a simple switch ( most commonly a dc breaker ) in the positive line coming from the panels .
This should always be installed for maintenance disconnect purposes anyway.

[KTP]

I know LiFePO4 batteries are one of the safest lithium chemistries but how are your thoughts on the dangers of hydrogen flouride gas if the batteries start going up in smoke (unlikely that they would cause a fire but I was reading a paper that seemed to indicate a large bank could produce grams or possibly even kilograms of hydrogen flouride)?

You see some of the puncture testing and volumes of some sort of smoke coming out of the battery but most of the videos are really focused on the fire danger or in LFP case, the lack of fire. They don't seem concerned with what is in all of that smoke.

If you were on a crossing, out 2000 miles in the Pacific and the battery pack started emitting this much smoke, would it be a situation where you could just sit on the bow for a few hours and wait for everything to burn down or would you need to keep some sort of 3M filter mask on board so you could go down below and turn things off? Hydrogen flouride I think can cause blindness too, so maybe a full face mask?

Or is this just not a concern with LFP? Since it doesn't usually or ever really catch on fire?

[sparrowhawk1]

Originally Posted by newhaul

easiest would simply be to set your charge controller to stop charging at a set point below the HVD.
As to the disconnect of the panels that is easily accomplished with a simple switch ( most commonly a dc breaker ) in the positive line coming from the panels .
This should always be installed for maintenance disconnect purposes anyway.

My controller is only adjustable for sealed, gel and flooded. I understand getting a controller for lithium would be the best answer but not cost-wise.
Besides it would seem a good idea to have a redundancy backup set at a slightly different voltage

[newhaul]

Originally Posted by sparrowhawk1

My controller is only adjustable for sealed, gel and flooded. I understand getting a controller for lithium would be the best answer but not cost-wise.
Besides it would seem a good idea to have a redundancy backup set at a slightly different voltage

if your solar charge controller has so little user settability . Then you would be miles ahead to replace it with something more user adjustable regardless of battery chemestry.
My current one while just PWM it is adjustable to within a hundredth of a volt and cost under $50.

[newhaul]

Originally Posted by KTP

I know LiFePO4 batteries are one of the safest lithium chemistries but how are your thoughts on the dangers of hydrogen flouride gas if the batteries start going up in smoke (unlikely that they would cause a fire but I was reading a paper that seemed to indicate a large bank could produce grams or possibly even kilograms of hydrogen flouride)?

You see some of the puncture testing and volumes of some sort of smoke coming out of the battery but most of the videos are really focused on the fire danger or in LFP case, the lack of fire. They don't seem concerned with what is in all of that smoke.

If you were on a crossing, out 2000 miles in the Pacific and the battery pack started emitting this much smoke, would it be a situation where you could just sit on the bow for a few hours and wait for everything to burn down or would you need to keep some sort of 3M filter mask on board so you could go down below and turn things off? Hydrogen flouride I think can cause blindness too, so maybe a full face mask?

Or is this just not a concern with LFP? Since it doesn't usually or ever really catch on fire?

no more of a concern than with lead acid batteries and in some ways la is more dangerous .
It off gasses hydrogen while being charged . Contact between the acid and sea water will produce chlorine gas as well.

[sparrowhawk1]

Originally Posted by newhaul

if your solar charge controller has so little user settability . Then you would be miles ahead to replace it with something more user adjustable regardless of battery chemestry.
My current one while just PWM it is adjustable to within a hundredth of a volt and cost under $50.

Mine is a 40amp mppt which might not make as much difference with lithium but it made a huge difference with lead. If I recall correctly the lowest setting is 14.4 with an unadjustable absorption of 2 hours. What is a drawback to having a voltage adjustable disconnect before the controller? And can anyone recommend one?

[newhaul]

Originally Posted by sparrowhawk1

Mine is a 40amp mppt which might not make as much difference with lithium but it made a huge difference with lead. If I recall correctly the lowest setting is 14.4 with an unadjustable absorption of 2 hours. What is a drawback to having a disconnect before the controller?

with my bank I have not noticed due to charge profile of Lfp the need or desire to switch from PWM to mppt as of yet I still have real estate for panels.

As to a disconnect between the panels and the controller there is no downside that I know of.

[KTP]

Originally Posted by newhaul

no more of a concern than with lead acid batteries and in some ways la is more dangerous .
It off gasses hydrogen while being charged . Contact between the acid and sea water will produce chlorine gas as well.

I use Lifeline AGM at the moment and they pretty much don't off gas anything. Maybe when you are equalizing them at 16 volts or something.

I am not too concerned about the hydrogen flouride although it sounds like a very nasty gas but was just wondering if anyone gives it a thought.

Reason for my concern is I eventually plan on a huge LFP bank of 40 to 50kWh so there would be significant volume of batteries if something goes really sideways.

[sparrowhawk1]

Equivalent programmable replacementAttachment 194001