What size LiFEPO4 bank

[john61ct]

Chemistry is chemistry.

Of course manufacturer specs will vary, but it would be foolish to just take them at their word.

Of course some use cases, like an electric vehicle's highway stops, the huge hit to longevity by fast charging at rates higher than 1C is just a cost of doing business.

In 100° weather, a much smaller hit than at 40°.

Below freezing, might render the bank instantly worthless scrap.

Context is important.

[Rorzech]

That world that Jack Handey described did exist in Peru. No crime No coveting No war No stealing. The Spanish leader that squashed their system regretted doing so immensely.

[AndyEss]

Originally Posted by Rorzech

That world that Jack Handey described did exist in Peru. No crime No coveting No war No stealing. The Spanish leader that squashed their system regretted doing so immensely.

Must have been a different species than homo sapiens in Peru. Maybe gerbils.

[newhaul]

Originally Posted by AndyEss

Must have been a different species than homo sapiens in Peru. Maybe gerbils.

sounds about right
What I'm still trying to figure out is what his post has to do with sizing of a lifepo4 bank

I assume he ment to post to a different thread

[AndyEss]

Nah, it was just a side comment to Delfin’s signature text. I’d size the LFP bank for 2 days usage. I wouldn’t even think of lead acid batteries anymore just over weight concerns. Not boat displacement, but my health. My battery bank sits in a pretty awkward place - the size and light weight of LFP (and superior performance) is a total winner for me.

[jbinbi]

Originally Posted by Delfin

Is that what the manufacturer of your LFP bank says? Oh right, you don't have one, nor a boat, but do like to pretend. We all need a hobby, I suppose.

Whoa. Why the need for a personal attack? John has provided this forum a ton of excellent advice. I don't know the guy, in fact just assuming his name is John, but I appreciate his comments. When you attack people personally, then they might not post anymore.

If you think his comments are wrong, then say so, and back it up if you can.

Let's keep this civil.

[ramblinrod]

Originally Posted by jbinbi

I currently have 420ah bank, with 580 W of solar and 2 80A Hitachi alt. On sunny days, with a hour of motoring I can put 100-200As back into the battery bank, though I am conservative and try to keep to using 120A a day. Refrig, navs. All LED lighting.

I would like to up these numbers, knowing I can use 150 to 200A a day, and be able to put that back in. Would be ok if maybe have to run the engine an extra hour.

Was looking at getting 600 Ah of Trojans, but now thinking of Li.

What size bank Li should I be looking at if I want to be able to use 200A a day.

Assuming the 2 80A alternators, how much can I put back in to a Li bank in what time? Can I get 150 A in in an hour or so?

The way to decide capacity need is to consider the average daily consumption, plus a reserve capacity for higher than normal consumption, times the number of days of no sun (very rare to have zero solar input but...) that you wish to be able to span without any other charge source.

The latter varies by use case. Some want A/C and run a generator all day. So they may only need a few hours of capacity. Others may loathe ICE power generation and wish to have 3 days of storage capacity.

For a sailboat, (not motor sailing) if your avg daily consumption is 120 A-hrs, and is highly variable (as many are underway with radar and autohelm running) your max consumption could be 240 A-hrs. If you wish to go 2 days with no sun before ICE charging, you need 480 A-hrs, add 20% so you don’t go below 80% DOD and now you are talking ~ 600 Ahrs.

For charge capacity, you need to size your array, to avoid ICE power generation, you need 240 A-hrs per day, which is about 1kW of panels. For ICE power generation you will want about .5C, or 480 A-hrs /2 = 240 A charge capacity to recharge from empty (80% DOD) to full (0% DOD) in a little over 2 hours. If you can tolerate running the ICE longer, you can reduce the charge capacity to suit.

[Delfin]

Originally Posted by jbinbi

Whoa. Why the need for a personal attack? John has provided this forum a ton of excellent advice. I don't know the guy, in fact just assuming his name is John, but I appreciate his comments. When you attack people personally, then they might not post anymore.

If you think his comments are wrong, then say so, and back it up if you can.

Let's keep this civil.

Happy to. John's comments are wrong, as they frequently are even when stated authoritatively. Other times, as you point out, he offers accurate statements of what he has read from others with experience, and that can be valuable. It's just sorting out the chaff from the wheat on any Internet forum that is the trick if you are actually interested in becoming better, rather than less informed.

But as John says, chemistry is chemistry. If you wish to believe John's understanding of that chemistry, that is just fine with me. If you wish to listen to those with actual practical experience with these batteries, or better yet, the manufacturers that do the kind of testing the U.S. military requires, like Lithionics, then you can do that as well.

Best of luck with your project.

[jbinbi]

Originally Posted by ramblinrod

The way to decide capacity need is to consider the average daily consumption, plus a reserve capacity for higher than normal consumption, times the number of days of no sun (very rare to have zero solar input but...) that you wish to be able to span without any other charge source.

The latter varies by use case. Some want A/C and run a generator all day. So they may only need a few hours of capacity. Others may loathe ICE power generation and wish to have 3 days of storage capacity.

For a sailboat, (not motor sailing) if your avg daily consumption is 120 A-hrs, and is highly variable (as many are underway with radar and autohelm running) your max consumption could be 240 A-hrs. If you wish to go 2 days with no sun before ICE charging, you need 480 A-hrs, add 20% so you don’t go below 80% DOD and now you are talking ~ 600 Ahrs.

For charge capacity, you need to size your array, to avoid ICE power generation, you need 240 A-hrs per day, which is about 1kW of panels. For ICE power generation you will want about .5C, or 480 A-hrs /2 = 240 A charge capacity to recharge from empty (80% DOD) to full (0% DOD) in a little over 2 hours. If you can tolerate running the ICE longer, you can reduce the charge capacity to suit.

Thanks. For me doing coastal cruising, I pretty much need to motor 30-120 min per day to get in and out of the harbor (With 2 stock 80A Hitachi alts, at 0.5C that would put in 80A in a hour of motoring). I usually count on 60-100 A of solar as well. I think I really only need 1 day reserve, and if it wasn't sunny for a day, I could always turn on the engine. So I think 400 Ah bank with 300 useable would cover my needs and then some. If I am doing this project, getting 400Ah vs. 300Ah is not a significant part of the cost considering all the other components I need plus labor, and would rather have this now than not.

[ramblinrod]

Originally Posted by jbinbi

Thanks. For me doing coastal cruising, I pretty much need to motor 30-120 min per day to get in and out of the harbor (With 2 stock 80A Hitachi alts, at 0.5C that would put in 80A in a hour of motoring). I usually count on 60-100 A of solar as well. I think I really only need 1 day reserve, and if it wasn't sunny for a day, I could always turn on the engine. So I think 400 Ah bank with 300 useable would cover my needs and then some. If I am doing this project, getting 400Ah vs. 300Ah is not a significant part of the cost considering all the other components I need plus labor, and would rather have this now than not.

Yeah, use case has a huge bearing on everything.

If one marina hops, off shore power 8 hrs per day max, their needs are far less than someone who swings on hook for days or weeks on end.

For anchoring out, my general rule of thumb for FLA batteries is as follows:

For every 100 A-hr avg. daily electrical consumption:
Battery capacity: 300 A-hrs
Shore power charger: 30 A
Alternator: 75A
Solar: 400 W
If desired, to reduced ICE generation on cloudy days...
Wind: 400 W (and cut solar in half).

When one switches to LiFeP04, they really can't reduce capacity as much as some first believe.

[roland stockham]

My formula for min battery bank capacity is 2-3x normal daily ah used when sailing. This is a safety factor and the chemistry is irrelevent. If you run for 24hrs and then find you can't charge the bank for whatever reason it means you will have enough power for about a week on emergency running. That means turn off all non- essentials including the autopilot. Hopefully this will get you safely to habour. Don't count on solar as electrical problems are most likely in bad weather when solar output is low.
So if you want 200ah/day your min bank size shoud be 600 for a cruising boat or 400 for purly coastal (within 100m of a safe harbour).

Does not matter what chemistry as anything can be run flat in an emergency.This also means your normal dod will be 60% wich any chemistry can take. I normally take it a bit higher to give 75% dod for fla's to increase longevity but don't go lower as power availability is pretty critical for the safe handling of most boats these days.

The exception may be that you have multiple fully independent charging systems. That must be fully independent though. A generator running of the same fuel tank as the main engine is not independent as fuel contamination will nock out both.

[newhaul]

Originally Posted by ramblinrod

Yeah, use case has a huge bearing on everything.

If one marina hops, off shore power 8 hrs per day max, their needs are far less than someone who swings on hook for days or weeks on end.

For anchoring out, my general rule of thumb for FLA batteries is as follows:

For every 100 A-hr avg. daily electrical consumption:
Battery capacity: 300 A-hrs
Shore power charger: 30 A
Alternator: 75A
Solar: 400 W
If desired, to reduced ICE generation on cloudy days...
Wind: 400 W (and cut solar in half).

When one switches to LiFeP04, they really can't reduce capacity as much as some first believe.

rod we are talking specifically Lfp so your numbers for the most part don't apply due to the charging profile for them . With 300ah Lfp I would want no less than 100amp shore charger.
He is on a lagoon 380 so personallyI i would keep one alternator stock and bump the other to at least a 200amp unit with external regulator so it can be derated to 150amp or so for longevity of the alternator itself.
As to solar he already has over 500 watts just run that through mppt controllers .
If wind is not already installed then don't do it . The sharing caused by it will overshadow any advantages ( wrt the solar output. ) . Dock/ anchorage mates will thank you .

[newhaul]

Originally Posted by roland stockham

The exception may be that you have multiple fully independent charging systems. That must be fully independent though. A generator running of the same fuel tank as the main engine is not independent as fuel contamination will nock out both.

he is on a lagoon 380 so each engine has its own dedicated fuel source . If he has the diesel genset option it also has its own fuel tank .
But you are correct in mentioning that for those of us on mono hulls.
That is the reason I carry a 6 gallon outboard tank full of diesel just in case and to run the portable generator when I need to. ( yanmar air cooled unit) .

[mikedefieslife]

Originally Posted by jbinbi

I currently have 420ah bank, with 580 W of solar and 2 80A Hitachi alt. On sunny days, with a hour of motoring I can put 100-200As back into the battery bank, though I am conservative and try to keep to using 120A a day. Refrig, navs. All LED lighting.

I would like to up these numbers, knowing I can use 150 to 200A a day, and be able to put that back in. Would be ok if maybe have to run the engine an extra hour.

Was looking at getting 600 Ah of Trojans, but now thinking of Li.

What size bank Li should I be looking at if I want to be able to use 200A a day.

Assuming the 2 80A alternators, how much can I put back in to a Li bank in what time? Can I get 150 A in in an hour or so?

You are in the same boat I was. Well not literally, though both are catamarans. I had 675ah of Trojan T105s. Waaay to heavy, and they were getting on in years. I reduced the bank to 4 giving 450ah capacity, and a usable figure of around 200ah.

Still 4 T105 batteries weigh 120kg and I wanted a more constant voltage when dealing with heavy loads, so I went with a DIY 271ah LiFePO4 bank (30kg). This should allow me to use over 216ah. Plus when you go for an LFP bank your solar charging instantly becomes 10-20% more effective. Added to that I stuck on another 230w giving me 850w in total.

I have an 80a internally regulated alternator, so bought an AGM started battery as a load dump for it, and a 60amp Sterling B2B Charger. Even 60amps is probably too much for an 80amp alternator to cope with over a long period, but the Sterling has a half load load option if needed. That being said my solar on a good day will put out 2.5kw

It's early days I've only recently completed the install, but very happy with everything so far. I will treat is as a modular system and will be adding and upgrading devices as I go along. Probably the next step is to upgrade my cheap BMS to something with more functionality. Then perhaps an externally regulated alternator.

It's going to be a lot of fun over the coming months, years.

What you will need to watch out for with your setup and usage is how to handle alternator charging, and shore power. You don't want the batteries sitting their at 100% full for days on end whilst at the dock.

[ramblinrod]

Originally Posted by newhaul

rod we are talking specifically Lfp so your numbers for the most part don't apply due to the charging profile for them . With 300ah Lfp I would want no less than 100amp shore charger.
He is on a lagoon 380 so personallyI i would keep one alternator stock and bump the other to at least a 200amp unit with external regulator so it can be derated to 150amp or so for longevity of the alternator itself.
As to solar he already has over 500 watts just run that through mppt controllers .
If wind is not already installed then don't do it . The sharing caused by it will overshadow any advantages ( wrt the solar output. ) . Dock/ anchorage mates will thank you .

New Haul,

Everything I posted applies to FLA (what he currently has), exactly as I posted.

I then posted that the "storage" capacity requirements to change to LFP don't really change. (Some believe they can cut "storage" capacity substantially, but for the same use case, this will rarely work well, unless they had too much FLA "storage" capacity in the first place.)

As for the other "capacity" parameters mentioned...

Shore power charger: 30 A. No change.

Shore power chargers are not generally sized to the house bank acceptance rate. Connection to shore power is generally for 18 hours min, so there would be no advantage to changing the capacity.

Exception: If one has a generator AND if they do not run it enough for purposes other than charging (e.g. AC electrical appliances, air conditioning, water making), then they may choose to increase the shore power charger capacity to suit the acceptance rate of the house bank, whatever the technology.

For standard FLA, this would be .25C, for AGM .4C, for LFP .5C (always check manufacturers recommendations).

Alternator: 75A. No change.

Exception: If one does not run the engine enough for purposes other than charging (e.g. propulsion, water heating, or water making) then they may choose to increase the alternator charging capacity to the acceptance rate of the house bank, whatever the technology (as described above).

Solar: 400 W - No change.

Solar charging systems are rarely sized to the house bank acceptance rate, whatever technology.

If desired, to reduced ICE generation on cloudy days...
Wind: 400 W (and cut solar in half). - No change.

Same reason as solar.

Not related to this thread regarding "capacities", some changes that would definitely be required are the charge profiles of all charge sources (some may be just a matter of programming, others may require device replacement) and a method to protect the engine alternator(s) from an LFP BMS disconnect, (such as a BMS alternator field wire disconnect, separate alternator protector, or an FLA battery in parallel with the LFP bank).