LiFePO4 vs FLA - The Real Deal

[Simi 60]

Feeling happy about our agm batts after reading these posts.

They have never been lower than 78% so 22% DOD and always at 100% by midday.
Guessing they should have a long and happy life.

[CatNewBee]

Originally Posted by Paul L

What is magic about the temperature water freezes at for LiPo batteries. I assume there is very little if any pure water in them. So does the charging at cold temperature problem start at around 0C and continue to get worse as it gets colder or is it some hard transition point?

LiFeYPO4 are chargeable down to -40°C according to the manufacturer data sheet. They have a broad temp range, Reduced charge current is a non-event so, nobody is usually abel to charge a LFP at 1C, there is simply no such charger around, so with 0.2..0.3C what you normally use you are mre than safe in let's say down to -20°C, I guess you will freeze before the battery does.

[downunder]

Originally Posted by Simi 60

Feeling happy about our agm batts after reading these posts.

They have never been lower than 78% so 22% DOD and always at 100% by midday.
Guessing they should have a long and happy life.

Your situation is similar to mine on a smaller vessel.

Large solar capacity(1800watt Sunpowers) 780 ah AGM's means bank rarely gets down to 80% and is always recharged daily to 100% so should last.

With lithiums I recon however i could easily run a 240V water maker.

[CatNewBee]

Originally Posted by downunder

Your situation is similar to mine on a smaller vessel.

Large solar capacity(1800watt Sunpowers) 780 ah AGM's means bank rarely gets down to 80% and is always recharged daily to 100% so should last.

With lithiums I recon however i could easily run a 240V water maker.

You can run your Watermaker on solar without draining your AGM too, with that huge solar array.

[mbartosch]

Originally Posted by downunder

Large solar capacity(1800watt Sunpowers) 780 ah AGM's means bank rarely gets down to 80% and is always recharged daily to 100% so should last.

With lithiums I recon however i could easily run a 240V water maker.

This is very likely true.

For me the main advantage of LiFePO4 is not energy density or weight. IMO, the main advantage of LiFePO4 is that you can make practical use of almost the entire potential energy production (short of a few %) of your charging sources, provided the bank is not 100 % full. More than 95 % of the Joules put into the bank can be extracted later again for consumption.

Hence, sizing the bank can solely be done on the calculation how long the averaging period should be for evening out fluctuations of energy consumption and usage. The larger the bank, the longer time frames you have for averaging energy input and output. That way, the bank size has almost nothing to do with your daily energy budget.
And as long as the bank is less than 100 % charged, potential charging does not go unused, it's stored in the bank.

In other words:
The daily energy budget only impacts choice and size of the charging sources. Over time your energy budget must be even, provided your SoC stays between about 20 % (for safety reasons) and 100 %. When charging with engine alternator or generator, tactically it makes sense to stop at about 80 % to leave room should more charging capacity come available. (It's also beneficial for the bank to stay below 80 %, but I don't care about that on ocean crossings.)


In contrast, with LA banks you actually need an over dimensioned charging system, otherwise your LA bank won't go near 100 %. The higher LA SoC gets, the more of the available charging sources power is wasted (unless it is used immediately on the spot).

With a LiFePO4 bank you have almost the total energy harvest at your disposal for actual usage, in contrast to LA where you need the charging sources to work against increasing internal battery resistance and Peukert effect to get close to 100 %. Which you need to achieve frequently, otherwise the bank gets damaged over time.

Finally, I don't know how others decide on equipment. I don't decide on cost alone. There are numerous decisions we took on our boat where we chose the more costly but engineering-wise better and longer lasting solution.
I don't see a difference with batteries. Yes, LiFePO4 is more expensive but they last longer, require little care and feeding once properly setup and do their main task extraordinarily well.

And I think this concludes my engagement with this thread.

[john61ct]

Originally Posted by a64pilot

Reference the lead / Lithium hybrid.
I supposed the idea is use the Lithium’s better charge abilities and then discharge them into the lead so as to maintain a safety buffer if you will?
So do you charge them both when charging? If so then you only need enough lithium to cover both house loads and 15% of the leads capacity so that when discharged to a comfortable level the lead is 100%?
Run off of the lead until 50%, then crank the generator and charge both lead and Lithium?
I don’t see what that won’t work?

This is the thread discussing that idea

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

But many don't like the complexity and inefficiencies, on principle.

[john61ct]

Originally Posted by thinwater

Obviously. It gets far colder than that.

Battery University is not a great source, but in general yes true, can turn the bank into instant scrap.

Those who allow their batteries to approach freezing temps will need automated protection systems to stop charging, and perhaps insulated boxes with a heat source like warming pads.

[ramblinrod]

Originally Posted by newhaul

wrong

Here is Maine sails reply to this 50% reserve bs

Routinely dipping to 80% DOD on lead acid, other than GEL (they actually handle this marginally well), in the real world is just not good for the batteries. I see this repeatedly in actual capacity testing of used marine batteries.

This is not to say never dip to 80% DOD. The occasional dip to 80% DOD is fine, and can even be somewhat healthy, provided you recharge ASAP to 100% SOC immediately there after.

Or in other words, I am correct.

Mainsail appears to be in complete agreement that the region of 50% to 20% SOC for FLA batteries can be used as reserve capacity, that one may dip into on occasion, as long as they recharge fully shortly thereafter.

This is consistent with my experience.

Thank you for supplying a reference that corroborates my position on this.

So if one has an average daily consumption of 100 A-hrs, and occasional peak daily consumption of 150 A-hrs, a 200 A-hr capacity FLA would be a good choice to be able to sustain operation for 24 hours without wind or sun.

This would dip down to 33% SOC if the battery was previously fully charged.

If the sun comes out or wind comes up after that 24 hours and the battery is fully charged, no harm, no foul.

In the case of LiFePO4, to achieve the same results, one would need 188 A-hr capacity to ensure on the peak demand day, with no wind or sun, they did not dip below 20% (from fully charged) and damage their very expensive LiFePO4s they just installed 2 months ago, that they were planning on getting a lifetime of sailing out of to justify the cost.

In contrast, if one selected a LiFePO4 battery of capacity equal to their average daily consumption (100 A-hrs), as suggested, and they had a peak demand day of 150 A-hrs, they would be firing up the ICE charging system in about 13 hours.

So the LifePO4 supposed benefit, that one can cut the bank capacity in half when switching, IS FALSE.

FWIW, for those cruisers who prefer not to operate ICE solely for house bank charging, I normally recommend 36 hours storage capacity.

For a 100 A-hr daily discharge this would be 300 A-hrs of battery capacity, and it makes no difference what the battery chemistry is.

Anyone who selects a LiFePO4 bank = their average daily capacity is going to be doing a lot of ICE charging.

If that's how one intends to recharge, that's fine.

If one intends to recharge with solar and wind, so they don't heat up the cabin, and burn up all their diesel or gasoline charging, then whether LifePO4 or FLA, they need reserve capacity.

The sun don't shine every day.

Oh, and LiFePO4 reserve capacity, that one needs only on occasion, may cost up to 9 times FLA reserve capacity.

[CatNewBee]

For me with LFP it is just capacity and in no meaning waste of money.
The system runs on solar only and I have always the power I need, maintenance free
and no fossile fuel burning, nor propane - and this for everything on board, water, cooking, washing, navigation, entertainment, heating and cooling, coffee and ice cubes.

This is about comfort and lifestyle, money well spent.

[thinwater]

Originally Posted by john61ct

... but in general yes true, can turn the bank into instant scrap.

Those who allow their batteries to approach freezing temps will need automated protection systems to stop charging, and perhaps insulated boxes with a heat source like warming pads.

If this is true--and no one has mentioned installing heat--then this is a major question. I'd bet half the boats see subfreezing temps for months and most probably leave the batteries on solar chargers in the off season, which will charge automatically whenever they see fit.


Not sayin' it isn't solveable, just that it is a serious consideration in design and operation.

[ramblinrod]

Originally Posted by mbartosch

This is very likely true.

For me the main advantage of LiFePO4 is not energy density or weight. IMO, the main advantage of LiFePO4 is that you can make practical use of almost the entire potential energy production (short of a few %) of your charging sources, provided the bank is not 100 % full. More than 95 % of the Joules put into the bank can be extracted later again for consumption.

Hence, sizing the bank can solely be done on the calculation how long the averaging period should be for evening out fluctuations of energy consumption and usage. The larger the bank, the longer time frames you have for averaging energy input and output. That way, the bank size has almost nothing to do with your daily energy budget.
And as long as the bank is less than 100 % charged, potential charging does not go unused, it's stored in the bank.

In other words:
The daily energy budget only impacts choice and size of the charging sources. Over time your energy budget must be even, provided your SoC stays between about 20 % (for safety reasons) and 100 %. When charging with engine alternator or generator, tactically it makes sense to stop at about 80 % to leave room should more charging capacity come available. (It's also beneficial for the bank to stay below 80 %, but I don't care about that on ocean crossings.)


In contrast, with LA banks you actually need an over dimensioned charging system, otherwise your LA bank won't go near 100 %. The higher LA SoC gets, the more of the available charging sources power is wasted (unless it is used immediately on the spot).

With a LiFePO4 bank you have almost the total energy harvest at your disposal for actual usage, in contrast to LA where you need the charging sources to work against increasing internal battery resistance and Peukert effect to get close to 100 %. Which you need to achieve frequently, otherwise the bank gets damaged over time.

Finally, I don't know how others decide on equipment. I don't decide on cost alone. There are numerous decisions we took on our boat where we chose the more costly but engineering-wise better and longer lasting solution.
I don't see a difference with batteries. Yes, LiFePO4 is more expensive but they last longer, require little care and feeding once properly setup and do their main task extraordinarily well.

And I think this concludes my engagement with this thread.

Nope.

For LiFePO4, to take advantage of the faster charge rate "feature", one would need over-sized charging systems, compared to FLA.

If we look at the recommended charging system ratios I posted previously for a FLA system of 100-Ahr average daily energy consumption, we see that the alternator is only 80 A.

Why?

That is all the current the 300 A-hr FLA bank can accept below 75% SOC (the region where charging by alternator may be required if little wind or sun forecast that day).

If one wishes to realize the "benefit" of the higher acceptance rate "feature", of LiFePo4, they would need a larger alternator, for there to be any practical difference in alternator charge time to that same level.

Same goes for wind and sun recommendations.

On a day of ample sun and wind (most common when using the ratios I posted), the FLA system will be fully charged by the end of the day, fully utilizing the maximum capacity of the bank.

Once the bank is charged, any additional charge capacity is waste or extraneous to design need.

In either case, if one is generating more electrical energy than needed, they may dump it to an extraneous load, like water heating or AC.

This is not exclusive to LiFePO4 banks, it can be done regardless of battery tech.

[ramblinrod]

Originally Posted by 44'cruisingcat

Yeah you're probably right. But it'sdifficult to say nothing when something as completely ridiculous as the OP is presented as fact.

Because a battery CAN be charged in one hour you MUST buy a genset big enough to do so.

Really?

My point exactly.

Thank You!

If a FLA bank has a max acceptance rate of 80 A, then any more than an 80 A alternator or generator is a waste.

If considering two alternators, an 80 A and a 160 A. The 160 A would be a poor choice.

The higher charge capacity "feature" is of little or no practical "benefit" to the user.

Alternatively, for the higher acceptance rate "feature" of LiFePO4 to be realized as a "benefit", one would need to choose the 160 amp alternator.

This is pretty simple stuff.

In the latter case, the bank would be charged faster.

However, if the design intent was to primarily charge by sun and/or wind, and those systems provided all of the charging capacity needed 95% of the time, then the benefit of the larger capacity alternator would only be realized 5% of the time.

That's only 18 days out of an entire year that the alternator will be run for the purpose of charging.

If on 50% of those days, one would be travelling a couple hours or more under engine power, the wind and/or solar deficiency may be compensated by the 80 A charger on the FLA system.

So the larger alternator is only a "benefit" on 50% of the 5% or 2.5% - 9 days per year.

That's very difficult to justify 9 times the cost for the LiFEPO4 bank over FLA, and the extra $1-2K of the higher capacity alternator.

[Paul L]

Originally Posted by CatNewBee

LiFeYPO4 are chargeable down to -40°C according to the manufacturer data sheet. They have a broad temp range, Reduced charge current is a non-event so, nobody is usually abel to charge a LFP at 1C, there is simply no such charger around, so with 0.2..0.3C what you normally use you are mre than safe in let's say down to -20°C, I guess you will freeze before the battery does.

But that isn't the lithium battery chemistry that most people are using.

[newhaul]

Originally Posted by ramblinrod

Nope.

For LiFePO4, to take advantage of the faster charge rate "feature", one would need over-sized charging systems, compared to FLA.

If we look at the recommended charging system ratios I posted previously for a FLA system of 100-Ahr average daily energy consumption, we see that the alternator is only 80 A.

Why?

That is all the current the 300 A-hr FLA bank can accept below 75% SOC (the region where charging by alternator may be required if little wind or sun forecast that day).

If one wishes to realize the "benefit" of the higher acceptance rate "feature", of LiFePo4, they would need a larger alternator, for there to be any practical difference in alternator charge time to that same level.

Same goes for wind and sun recommendations.

On a day of ample sun and wind (most common when using the ratios I posted), the FLA system will be fully charged by the end of the day, fully utilizing the maximum capacity of the bank.

Once the bank is charged, any additional charge capacity is waste or extraneous to design need.

In either case, if one is generating more electrical energy than needed, they may dump it to an extraneous load, like water heating or AC.

This is not exclusive to LiFePO4 banks, it can be done regardless of battery tech.

ok do the math how are you going to recharge that 300ah Fla battery from your hypothetical
70% DOD in one day on 300watts solar.
(Please show your work on this math problem)
That will only provide about 100ah. You say no problem start the engine and charge with your 80 amp alternator .run how long?
With my Lfp I can just run a couple lighter power consumption days . The bank don't care .in fact it is happier if not fully charged after every discharge. Best for me is no dino juice used.

The facts are in the real world with my Lfp I don't need an engine. With your Fla well you do. Or you need to double the solar for charging without killing your Fla battery bank prematurely.

You seem to like the its so much more expensive well in the real world its not . And no its not the solution for everyone but it is best for this cruiser on this boat.

[senormechanico]

Originally Posted by ramblinrod

My point exactly.

Thank You!

If a FLA bank has a max acceptance rate of 80 A, then any more than an 80 A alternator or generator is a waste.


This is pretty simple stuff..

So nobody ever runs the holding plate refrigeration, freezer, instruments, 12 or 24 volt watermaker etc, while running the engine?


That's pretty simple stuff too.