What size LiFEPO4 bank

[ramblinrod]

Originally Posted by evm1024

Any scenario that >>requires<< that I run my engine or generator because of a few cloudy days is a failed system.

LiFePO4 allows freedom from running ICE.

But of course that is just my view on it. Some my have differing opinions. That is fine with me.

Say what?

Batteries don’t produce energy.

They only accept it, store it, and discharge it.

For primary solar charging, after so many days of no or low sun, regardless of battery technology, ICE (or some alternative charging source) IS required.

This is another fine example of exaggerated claims.

Actually LFP is a better technology for primarily ICE charging, because it can have a high charging rate (at the expense of LFP longevity if they charged slightly faster than FLA in early bulk mode).

FLA is an excellent technology for solar charging. If everything is sized properly, the diminishing afternoon solar output, matches the diminishing acceptance rate of the batteries quite well, and the FLA batteries will be charged to 100% most days, no bad sulfation, long life, low cost.

[newhaul]

Originally Posted by ramblinrod

????? Everything else equal, any battery system incorporating solar charging will need some form of alternate charging after a period of no sun. Batteries do not generator power. They only accept it, store it, and discharge it.

The high acceptance rate of LFP is virtually useless in a solar charging regime, doesn’t come into play, as the charge profile for solar is typically around 5 A / 100W around noon, and then slowly diminishes during the afternoon until sunset, similar to the diminishing acceptance rate of FLA. A pretty nice technological match. (The higher acceptance rate of LFP cannot be utilized unless the solar charging system is way oversized to actual charging needs, and the actual recommended acceptance rate to not hurt the longevity of LFP is not much higher than FLA (in the bulk charging stage, earlier in the day, when the solar output is there to use it.)

I have to throw the flag on this one. I have been running with 200watts of solar into my bank for over 2 years and have never had any issues or needs for running any other charging source. In times when I need the extra kick I have an additional 200 watts of flex panelist can deploy. ( have only needed to use them in the dead of winter.

With the acceptance rate that my Lfp bank has it can take the entire 25 amps output of the solar with "0" and by that I mean absolutely no issues right up to my " running " full point of 13.8 volts . That is a life stretching .25C charging rate. ( my cells are rated to be capable of charging at 5C with no issues. I am looking at installing the renogy 50 amp b2b/ mppt combined charger to allow me to comfortably use a 75amp alternator to charge the bank if I ever need it . ( doing this would allow me to sell my 200 watts worth of flex panels which will almost cover the cost of the charger/ mppt controller.

The hardest part about switching to Lfp for me was finding the manual to my solar controller i could change the stop point from 14.5 v to 13.8 v and unplugging the temperature compensation probe.

[newhaul]

Originally Posted by ramblinrod

Say what?

Batteries don’t produce energy.

They only accept it, store it, and discharge it.

For primary solar charging, after so many days of no or low sun, regardless of battery technology, ICE (or some alternative charging source) IS required.

This is another fine example of exaggerated claims.

Actually LFP is a better technology for primarily ICE charging, because it can have a high charging rate (at the expense of LFP longevity if they charged slightly faster than FLA in early bulk mode).

FLA is an excellent technology for solar charging. If everything is sized properly, the diminishing afternoon solar output, matches the diminishing acceptance rate of the batteries quite well, and the FLA batteries will be charged to 100% most days, no bad sulfation, long life, low cost.

you still don't get what the actual full charge cycle acceptance rate of Lfp is .
Lfp will take all that you throw at it right up to 99% of "full"
Fla on the other hand will reduce its acceptance rate considerably and logarithmicly reduce that further from approx 80% right up to the theoretically full.

Example 2 banks of 100ah capacity . Use 20ah and both are now at 80% the Lfp will be " fully " charged. In approx 2 hours with my 200 watts solar through an mppt controller .
The power being generated can then be directed to rerunning the watermaker , and or the holding plate refer.

For me ice is only a SHTF scenario possibility and nothing more.

Fla on the other hand will take " all day " to get hopefully fully charged. One good rain squall in the afternoon and it is now in a PSOC situation .

You can't run your watermaker or refer without using power from the Fla battery .

I have run both extensively in my lifetime of living on boats. Off grid. Now if I was a smudge pot that is a dock queen things would calculate differently . Then I would be looking at a single group 31 house battery and a good quality marine charger for it.

[ramblinrod]

Originally Posted by newhaul

I have to throw the flag on this one. I have been running with 200watts of solar into my bank for over 2 years and have never had any issues or needs for running any other charging source. In times when I need the extra kick I have an additional 200 watts of flex panelist can deploy. ( have only needed to use them in the dead of winter.

With the acceptance rate that my Lfp bank has it can take the entire 25 amps output of the solar with "0" and by that I mean absolutely no issues right up to my " running " full point of 13.8 volts . That is a life stretching .25C charging rate. ( my cells are rated to be capable of charging at 5C with no issues. I am looking at installing the renogy 50 amp b2b/ mppt combined charger to allow me to comfortably use a 75amp alternator to charge the bank if I ever need it . ( doing this would allow me to sell my 200 watts worth of flex panels which will almost cover the cost of the charger/ mppt controller.

The hardest part about switching to Lfp for me was finding the manual to my solar controller i could change the stop point from 14.5 v to 13.8 v and unplugging the temperature compensation probe.

The point is, if your solar charging system is sized well to work with FLA, switching to LFP will be little to know benefit.

With FLA, most days, the solar takes care of all charging needs.

In the rare occasions (cruising geographies where solar is effective) when the FLA bank is down to 40 or 50%) and there is no need to start ICE for other reasons (changing anchorages, going for services, water making, heating water, etc.,) then it may be necessary to use ICE charging for an hour or so. Depending on circumstances this may occur once per week to once per month.

In North America (not the only place in the world but what I’m familiar with) one buy FLA DC batteries for about $85/100 A-hr. To purchase a similar drop in solution in LFP, it is more like $1000/100 W.

That a lot more money for very little actual benefit.

(Yes I know if one wants to spend a lot of their time researching, sourcing, building, experimenting, and not consider the value of their time, there can be cheaper LFP solutions, but still way more than for FLA, again for very little if any benefit, over FLA.

[newhaul]

Originally Posted by ramblinrod

The point is, if your solar charging system is sized well to work with FLA, switching to LFP will be little to know benefit.

With FLA, most days, the solar takes care of all charging needs.

In the rare occasions (cruising geographies where solar is effective) when the FLA bank is down to 40 or 50%) and there is no need to start ICE for other reasons (changing anchorages, going for services, water making, heating water, etc.,) then it may be necessary to use ICE charging for an hour or so. Depending on circumstances this may occur once per week to once per month.

In North America (not the only place in the world but what I’m familiar with) one buy FLA DC batteries for about $85/100 A-hr. To purchase a similar drop in solution in LFP, it is more like $1000/100 W.

That a lot more money for very little actual benefit.

(Yes I know if one wants to spend a lot of their time researching, sourcing, building, experimenting, and not consider the value of their time, there can be cheaper LFP solutions, but still way more than for FLA, again for very little if any benefit, over FLA.

here is the reality for you see Lfp is better and and cheaper than Fla.

https://youtu.be/Rp8Hspi4BC4

and this is for drop in vs drop in .

Building my own saves about half the money.

[Q Xopa]

Originally Posted by ramblinrod

????? Everything else equal, any battery system incorporating solar charging will need some form of alternate charging after a period of no sun. Batteries do not generator power. They only accept it, store it, and discharge it.

The high acceptance rate of LFP is virtually useless in a solar charging regime, doesn’t come into play, as the charge profile for solar is typically around 5 A / 100W around noon, and then slowly diminishes during the afternoon until sunset, similar to the diminishing acceptance rate of FLA. A pretty nice technological match. (The higher acceptance rate of LFP cannot be utilized unless the solar charging system is way oversized to actual charging needs, and the actual recommended acceptance rate to not hurt the longevity of LFP is not much higher than FLA (in the bulk charging stage, earlier in the day, when the solar output is there to use it.)

Hmmm,

your opinion of Solar being imcompatable with LFP is flawed.

I hear where your coming from and agree that Solar hasnt generally got the output LFP is capable of accepting. So, something is better than nothing, and done cheaply and quietly is great IMO.

I think the reference to not having to run the Generator which you rebutted as a reference to LFPs 'generating' ( I assume you meant 'generating' instead of 'generator' as you wrote). I think you may have misunderstood the intent of that. Im pretty sure and took that as a reference to LFPs not caring about PSOC like FLAs. Which I agree is true.

But FLAs in Abosoption are pretty inefficient at accepting charge. The higher the SOC the less efficient they are.

So not only do LFPs accept charge from Solar or whatever source better.

It doesnt actually matter if they dont get completely charged. Do that with FLAs and they suffer.

Absorbtion Charge phase on FLAs IMO is inefficient and to me often inconvenient. Hours of generator or engine Alternator running to get the FLAs topped off is IMO noise, wasteful of fuel and engine time.

Even Solar getting inefficiently wasted trying to get your FLAs topped off to me seems wasteful.

Im not opposed to FLAs and if your on a budget then I agree they are great. They both have their cons.

[Q Xopa]

Originally Posted by ramblinrod

The point is, if your solar charging system is sized well to work with FLA, switching to LFP will be little to know benefit.

With FLA, most days, the solar takes care of all charging needs.

In the rare occasions (cruising geographies where solar is effective) when the FLA bank is down to 40 or 50%) and there is no need to start ICE for other reasons (changing anchorages, going for services, water making, heating water, etc.,) then it may be necessary to use ICE charging for an hour or so. Depending on circumstances this may occur once per week to once per month.

In North America (not the only place in the world but what I’m familiar with) one buy FLA DC batteries for about $85/100 A-hr. To purchase a similar drop in solution in LFP, it is more like $1000/100 W.

That a lot more money for very little actual benefit.

(Yes I know if one wants to spend a lot of their time researching, sourcing, building, experimenting, and not consider the value of their time, there can be cheaper LFP solutions, but still way more than for FLA, again for very little if any benefit, over FLA.

Hmm,

Do you want to try again with your price comparison units- "$85/100 A-hr. To purchase a similar drop in solution in LFP, it is more like $1000/100 W" ?

Can you atleast use the same units? Im assuming you mean- $1000/100 Ah for LFP? I thought an Industry professional should know the difference.

Speaking of knowing the difference. When you say "LFP are little to know benefit". KNOW and NO sound they same when we say them but dont mean the same.

[evm1024]

Originally Posted by Q Xopa

Hmmm,

your opinion of Solar being imcompatable with LFP is flawed.

I hear where your coming from and agree that Solar hasnt generally got the output LFP is capable of accepting. So, something is better than nothing, and done cheaply and quietly is great IMO.

I think the reference to not having to run the Generator which you rebutted as a reference to LFPs 'generating' ( I assume you meant 'generating' instead of 'generator' as you wrote). I think you may have misunderstood the intent of that. Im pretty sure and took that as a reference to LFPs not caring about PSOC like FLAs. Which I agree is true.

But FLAs in Abosoption are pretty inefficient at accepting charge. The higher the SOC the less efficient they are.

So not only do LFPs accept charge from Solar or whatever source better.

It doesnt actually matter if they dont get completely charged. Do that with FLAs and they suffer.

Absorbtion Charge phase on FLAs IMO is inefficient and to me often inconvenient. Hours of generator or engine Alternator running to get the FLAs topped off is IMO noise, wasteful of fuel and engine time.

Even Solar getting inefficiently wasted trying to get your FLAs topped off to me seems wasteful.

Im not opposed to FLAs and if your on a budget then I agree they are great. They both have their cons.

Very good post - thank you.

In regards to the statement underlined above - That statement is a red herring. It is easily understood by any reader that solar is supplying the charging current. Plus, that poster and I go way back. He is fully aware that I am an engineer and I can only assume that this is an attempt to cast aspersions on my opinion rather than deal with the facts.

I'll be out at the boat today (rebuilding the ice box, er fridge). Perhaps I'll run a 100 amp load for an hour or 2 to simulate a few cloudy days then turn on a charger at 25 amps to simulate 1000 watts of solar running at an average of about 1/3 full. Then record it all just to see what the graph looks like.

Of course LiFePO4 will be near 100% charge efficiency right up to near 100% SOC. And as we know LA charge efficiency decreases dramatically as the cells charge making it quite time consuming to reach 100% SOC and avoid chronic undercharge death.

Toss in some house loads and LiFePO4 just fine while LA steps closer to the grave.

[Dockhead]

Originally Posted by Q Xopa

Hmmm,

your opinion of Solar being imcompatable with LFP is flawed.

I hear where your coming from and agree that Solar hasnt generally got the output LFP is capable of accepting. So, something is better than nothing, and done cheaply and quietly is great IMO.

I think the reference to not having to run the Generator which you rebutted as a reference to LFPs 'generating' ( I assume you meant 'generating' instead of 'generator' as you wrote). I think you may have misunderstood the intent of that. Im pretty sure and took that as a reference to LFPs not caring about PSOC like FLAs. Which I agree is true.

But FLAs in Abosoption are pretty inefficient at accepting charge. The higher the SOC the less efficient they are.

So not only do LFPs accept charge from Solar or whatever source better.

It doesnt actually matter if they dont get completely charged. Do that with FLAs and they suffer.

Absorbtion Charge phase on FLAs IMO is inefficient and to me often inconvenient. Hours of generator or engine Alternator running to get the FLAs topped off is IMO noise, wasteful of fuel and engine time.

Even Solar getting inefficiently wasted trying to get your FLAs topped off to me seems wasteful.

Im not opposed to FLAs and if your on a budget then I agree they are great. They both have their cons.

Yes, that's the very thing. The main problem with FLA is two-fold -- (1) they HAVE the absorption phase; and (2) they NEED the absorption phase, during which charging is inefficient and time-consuming.


So whether you have solar or not, the lack of any absorption phase and lack of any need to keep charging is a huge advantage. Solar is a great complement to FLA but it is a logical fallacy to think that then solar is BETTER with FLA -- it's not. LiFePo is not better than FLA with solar ONLY in case you have so much solar power compared to your power needs that you can afford to waste power during absorption. Otherwise, LiFePo is better because it saves every watt you get out of the solar panels.


I agree with Rod that every use case is different, but LiFePo is so much superior to lead in almost every way, that there are only a few use cases where the advantages of LiFePo are not meaningful. As far as I can see:



1. Your boat is already configured for lead and you are on such a tight budget that you can't consider reconfiguring it.


2. You have a small cheap boat -- maybe a lake boat? -- with small power needs and don't spend much time off shore power.


3. You cycle your batteries so little (maybe because you are in Group 2, above) that you will never see the benefit from lithium's long cycle life.


4. You have a small boat with a huge solar installation and modest power needs, so always enough excess power to do the absorption charge on lead.



5. You are one of those who runs a generator all the time when off shorepower.





The case for lithium becomes really compelling with larger boats with large power demands used for long periods off-grid. Lead batteries on my boat, for example, are a huge faff -- 10 of them, needing water every few weeks when cruising off-grid, needing countless generator hours to give them their essential finishing charge once or twice a week, wearing out the expensive heavy-duty generator and ruining the pleasure of being away from civilization, and wasting tonnes of fuel, and still needing to be replaced every 3 or 4 years .



One mistake Rod makes is to extrapolate from the use case of small lake boats to large ocean-going ones. It's a different use case entirely, different economics.


Another mistake is to assume that the cost of conversion from a lead configuration if part of the inherent cost of lithium. On the contrary, this is just the cost of correcting a design mistake and should not be figured into the equation. If you build a boat from scratch, or order it, you will not incur this cost. Once the boat is already configured for lithium, the cells are cheaper than lead by far, when you consider cycle life. They further pay for themselves with less generator and/or main engine hours, less fuel burned, more efficient use of solar if you have solar, and less screwing around with it.


Lithium batteries are just like a fuel tank -- put power in as you like, take it out as you like, period. Nothing to it. Lead-acid batteries are like a 19th century Victorian Gothic science experiment -- boil and bubble, toil and trouble, acid, sulphur, lead -- sulfation, equalization, finishing charge, absorption -- argh!

[john61ct]

Originally Posted by newhaul

my cells are rated to be capable of charging at 5C with no issues

No, that is a "do not exceed" maximum rating, e.g. EV usage where fast charging is required by the use case.

Definite longevity issues even going near 1C charging. Reduced by preheating the cells.

In cold temps (far above freezing, say "sweater weather", that rate could do immediately measurable damage.

[john61ct]

Yes FLA is a better value **economically** than LFP for many use cases.

How important the cost factor is, is probably the biggest variable in the various factors involved.

But claiming lead's technical superiority in any way is simply not credible.

And being a fanboy, or just overly biased, in one direction or the other, seems often to be influenced by how you (would like to) make your living.

[Q Xopa]

Originally Posted by john61ct

Yes FLA is a better value **economically** than LFP for many use cases.

How important the cost factor is, is probably the biggest variable in the various factors involved.

But claiming lead's technical superiority in any way is simply not credible.

And being a fanboy, or just overly biased, in one direction or the other, seems often to be influenced by how you (would like to) make your living.

I think terms like 'cost' or 'economically' get bandied around way too loosely.

To me FLAs UPFRONT cost is less. But the story is changes depending on the amount you want to use them.

To me its like Printers. I remember seeing 'Sale- Printer $1'. Yes it was indeed true. We all know they get you with the ink. The cheaper they are to buy the more expensive they are to use.

Sure I know many of us struggle to find a big enough up front sum. We can get in the game cheaply, but we are going to keep paying more from then on.

[john61ct]

Of course **after** decades of worry free use, it will be easy to say, yes it was cheaper than lead.

But anything that requires a payback ROI timeline over a few years is inherently very risky to an economist.

Where fragile electronics are involved even more so.

A high level of knowledge and attention to detail helps improve the odds.

But for owners who don't care to spend the time required, the turnkey installed packaged systems are **lots** pricier than bare cells + DIY protections.

Personally I don't think money is that important, I'd rather have as much fun as possible.

And messing with DC power gear is lots of fun, but I am a bit odd that way.

[Dockhead]

Originally Posted by john61ct

Yes FLA is a better value **economically** than LFP for many use cases.. .

Only those cases, where the boat will rot and sink before the cycle life of lithium is half used.

[newhaul]

Originally Posted by john61ct

No, that is a "do not exceed" maximum rating, e.g. EV usage where fast charging is required by the use case.

Definite longevity issues even going near 1C charging. Reduced by preheating the cells.

In cold temps (far above freezing, say "sweater weather", that rate could do immediately measurable damage.

the 5C charge rate is yes the max safe rate that the manufacturer would honor the 10 year warranty. With a top end of 10C discharge. Standard rate is .5C for maximum longevity.

Now show me a 29 ft sailboat that is going to have the ability to charge at 500 amps
Not going to happen the top I will have is 50 amps or .5C
In testing I did run st 1C and monitoring temps . In the shop it was 60℉ the batteries were the same . There was no measurable change in temps of anything except the charging source.