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

[Anjin]

Proud that my first post here is #5071 in this thread.

And yes, I've read them all. What an incredibly valuable resource!

I've recently purchased a 2011 Lagoon 450 and am planning for a Lithium upgrade. I've been doing all the detail design based on the wisdom of the "crowd" that posts here and I'll post my plans soon. But right now I have a small dilemma.

My wife and I plan to cruise and stay in remote areas and want to be able to enjoy some luxuries while at anchor for days at a time. My plans had been to replace the 840AH AGM bank with a 1600AH LiFePo4 bank using 400AH cells in a 4P4S configuration. I had checked availability of these cells in advance and found a US based source (Electric Car Parts Company in Utah) that had them in stock. Now that I'm ready to order what I've found is that they have the older model SE400 CALB cells available but not the newer CA400 cells. The SE400s have a recent manufacture date so they're not leftovers; I've been told that there is still some demand for the older style ribbed case. The supplier also has lots of CA180's available - and he says that they generally test at above 200AHs making them a bit of a bargain.

So, at this point I can go ahead with the SE400s in a 4P4S or switch to the CA180s in an 8P4S or even 9P4S and save a little money, a little weight and a little space but have more connections.

Several places in the thread there have been assertions that using larger than 200AH cells in a marine environment is not recommended because the larger cells don't have adequate mechanical strength in their internal design. That seems to be contradicted by the experience of at least some users (Maine Sail among them) but there are certainly examples of larger cells experiencing earlier than expected loss of capacity.

I'm leaning toward the smaller cells despite the extra connections but would really appreciate the thinking from this group.

Thanks in advance!

- Art

[toddedger]

I'very read them all too. I think the size limit advice was quoted from a battery manufacturer. I don't Rember who originally posted it ,or who the quote came from.

1600Ah is a lot of connections either way. If I were going to double the size of my 4p4s 400 Ah battery, I personally would be considering dividing it up into two separate and redundant batteries.

[poiu]

Originally Posted by Anjin

Several places in the thread there have been assertions that using larger than 200AH cells in a marine environment is not recommended because the larger cells don't have adequate mechanical strength in their internal design. That seems to be contradicted by the experience of at least some users (Maine Sail among them) but there are certainly examples of larger cells experiencing earlier than expected loss of capacity.

I'm leaning toward the smaller cells despite the extra connections but would really appreciate the thinking from this group.

Thanks in advance!

- Art

I have the 700Ah cells, so am concerned to read they might not be suitable for use in a boat. I've had them about 3 years now. Once cell is a bit lower than the others, but I have more capacity than I need, so I just live with it. Otherwise, no problem and no sign of damage.

I can't see why they might not be suitable in my boat as the motion is never anything than very gentle in the centre of the boat, where the batteries are located. They were previously used in yard trucks, where I expect there was the odd pot hole with much worse vibration than in most boats.

[Anjin]

Originally Posted by toddedger

If I were going to double the size of my 4p4s 400 Ah battery, I personally would be considering dividing it up into two separate and redundant batteries.

There are some good arguments (and some good schematics) posted on this thread for a dual bank system, but I'm trying to focus on which cell size to choose and I think the pros and cons of dual banks apply equally regardless of individual cell size.

Originally Posted by poiu

I have the 700Ah cells, so am concerned to read they might not be suitable for use in a boat.

Several contributors on this thread have made that assertion - I don't know if it's a manufacturer's recommendation or just an opinion, but others are successfully using the 700AH and 1000AH cells in their installations.

[transmitterdan]

To run a boat on DC requires more net power generation than consumption over some time period (say 24-48 hours). A battery bank that cannot be fully charged in the same time period (or at least twice that) is mostly a waste of money. So the amount of energy you can get from your bank has to be matched by a little more generation capacity. A bigger bank doesn't change that equation. It just makes it possible to last longer without recharging. But the generation capacity must be there else the bank will always be discharged.

If you have a fossil fuel generator then a super size bank isn't cost effective as energy density is greater in the fuel. If you have renewable generation then the cost/space for generation becomes a limiting factor making huge banks not very practical. Do the math before investing in a huge bank that cannot be kept charged.

[exMaggieDrum]

Originally Posted by Anjin

Proud that my first post here is #5071 in this thread.

And yes, I've read them all. What an incredibly valuable resource!

I've recently purchased a 2011 Lagoon 450 and am planning for a Lithium upgrade. I've been doing all the detail design based on the wisdom of the "crowd" that posts here and I'll post my plans soon. But right now I have a small dilemma.

My wife and I plan to cruise and stay in remote areas and want to be able to enjoy some luxuries while at anchor for days at a time. My plans had been to replace the 840AH AGM bank with a 1600AH LiFePo4 bank using 400AH cells in a 4P4S configuration. I had checked availability of these cells in advance and found a US based source (Electric Car Parts Company in Utah) that had them in stock. Now that I'm ready to order what I've found is that they have the older model SE400 CALB cells available but not the newer CA400 cells. The SE400s have a recent manufacture date so they're not leftovers; I've been told that there is still some demand for the older style ribbed case. The supplier also has lots of CA180's available - and he says that they generally test at above 200AHs making them a bit of a bargain.

So, at this point I can go ahead with the SE400s in a 4P4S or switch to the CA180s in an 8P4S or even 9P4S and save a little money, a little weight and a little space but have more connections.

Several places in the thread there have been assertions that using larger than 200AH cells in a marine environment is not recommended because the larger cells don't have adequate mechanical strength in their internal design. That seems to be contradicted by the experience of at least some users (Maine Sail among them) but there are certainly examples of larger cells experiencing earlier than expected loss of capacity.

I'm leaning toward the smaller cells despite the extra connections but would really appreciate the thinking from this group.

Thanks in advance!

- Art

I'm basically doing what you are doing. Right now I am just trying to source the cells I want to use. I have everything else ready to start once I find those.

One of the very first, and one of the most important, decisions is how big a bank you need. Going from a 840Ah LA bank to a 1600Ah LFP is definitely going on a different path than most on here as the general consensus (right or wrong) is that you usually go with a much smaller total Ah bank to provide the same usable energy as your previous bank. Could you share how you came up with the size of the bank you are planning to install, and perhaps also give what charging sources you have to recharge such a relatively massive bank? Sizing the bank is the starting point for me. 1600Ah just seems massive to me. Of course that depends on what your energy needs are on your boat and may be just what you need.
Thanks, Joe

[greg_kulosa]

Originally Posted by transmitterdan

To run a boat on DC requires more net power generation than consumption over some time period (say 24-48 hours). A battery bank that cannot be fully charged in the same time period (or at least twice that) is mostly a waste of money. So the amount of energy you can get from your bank has to be matched by a little more generation capacity. A bigger bank doesn't change that equation. It just makes it possible to last longer without recharging. But the generation capacity must be there else the bank will always be discharged.

Some of this is based on old thinking from LA batteries. They want to be kept fully charged, but lifepo4 batteries do not care. In fact, lifepo4 seem to have longer life if kept in the middle part of their SOC range.

I do agree that you still want the ability to recharge more in a day than your daily use, otherwise you will slowly discharge until you have nothing left. But you don't have to worry about getting back to full charge with lifepo4. They would be happy bouncing back and forth between (say) 40% - 60% SOC (if your daily usage and recharge ability was 20% of the total capacity of the bank).

[transmitterdan]

Yes, LiFePo is happy to run between 20-50% but it makes no sense economically. My comments were strictly based on math and efficient use of money, not "old thinking".

[evm1024]

LiFePO4 cells make large capacity banks possible and as we have seen they do not need to be fully charged. Both facts are at odds with LA cells.

The basic equation that Transmitterdan spoke of holds true. That for some given time frame the energy used must be replaced. With the replacement being less than 100% efficient thus if you consumed 100 watt hours you would need to replace it with (oh say) 105 watt hours.

Due to weight and size constraints I suspect that the typical LA house bank was sized so that a days consumption was equal to about 25% to 40% of the bank capacity.

Watt hours do not equal amp hours but for this discussion let's pretend there is no voltage sag....

So a boat that uses 150 AH daily would need a bank that was 600 AH (150/0.25) to 375 AH (150/0.40) in size. (Roughly 6 or 4 T105)

And of course due to LA physics charging that LA bank to 100% daily was highly desirable.

Enter LiFePO4 - with its desired SOC range of 80% to 20% (LA SOC range is 100% to 50%) yo end up with more usable capacity. Take our 150 AH usage and we find that a LiFePO4 bank of 250 AH would be able to stay within the SOC range while using 150 AH daily.

A 400 AH LiFePO4 bank that goes 2 days without any charging would range between 87.5% SOC and 12.5% SOC which LiFePO4 could handle (with decreased cycle counts). And with some charging during that 2 day period could stay within a 80%-20% SOC range which is desirable.

Some will say that 400 AH is optimal but that presupposes that the conditions and goals are the same for all....

Sliding Windows

Imagine a wall where the height of the wall represents your total house bank capacity. The bottom of the wall is 0% SOC and the top is 100% SOC. Now place a window on that wall centered right in the middle. The window represents your power usage. The top of the window represents your SOC when you are done charging for the day and the bottom of the window represents the SOC when you are done consuming for the day. Of course it is more complicated than this but go with it.

If you use lots of power and put it all back each day you will have a very tall window. If you only use a little power and put it all back you will have a smaller window.

(now the fun begins)

Some days you use more power than you can replace. lower edge of the window goes down and the upper edge of the window goes down also. thus the window slides downward. Or other days your usage may be smaller or your charging may be greater (or both) so the window slides upward. Thus Sliding Windows.

In any given time period the window changes size and slided up and down on the wall. The key is to keep the window fully within the desired region of the wall (less than 80% SOC and greater than 20% SOC).

With a small(ish) bank (er, wall) of 400 AH the range for the window to slide is small(ish) but with a larger bank your window has a much greater range of freedom.

A week of cloudy weather (assuming solar as your main charge source) where your run your espresso machine off the inverter will trend the window to the bottom part of the wall (lower SOC). On Sunny days where you are out doing things all day the window will slide up higher and higher.

With a 1600 AH bank that window can be quite large and/or never get to the upper or lower portions of the SOC wall. Lot's of freedom (as in not a slave to charging).

Of course this all needs a charging source that keeps your SOC above 20% (you pick your number) and shuts off before exceeding 80% SOC.

Regards

[evm1024]

Originally Posted by transmitterdan

Yes, LiFePo is happy to run between 20-50% but it makes no sense economically. My comments were strictly based on math and efficient use of money, not "old thinking".

When I think of "Efficient use of money" and Boats at the same time I experience severe
Cognitive dissonancece

[svrodeorm]

Originally Posted by evm1024

When I think of "Efficient use of money" and Boats at the same time I experience severe
Cognitive dissonancece

Year, it's a love affair, nothing ro do with logics for sure!

[SV THIRD DAY]

Originally Posted by Anjin

My plans had been to replace the 840AH AGM bank with a 1600AH LiFePo4 bank using 400AH cells in a 4P4S configuration.

Welcome Art....
Can you walk us through the thought process of needing a 1600AH LiFePO4 battery bank?

I have a 400AH, and have friends cruising with 800AH banks that we can run our hot water heater, AC water makers, washing machines and espresso machines with ease. So are you doing the more is better (which isn't always the case) or do you "really" need a 1600AH LiFePO4 bank?

I had a 900AH Lead Acid and went down to a 400AH LiFePO4 bank and am happy as a clam in the mud.

[ColdEH]

Originally Posted by SV THIRD DAY

Welcome Art....
Can you walk us through the thought process of needing a 1600AH LiFePO4 battery bank?

I have a 400AH, and have friends cruising with 800AH banks that we can run our hot water heater, AC water makers, washing machines and espresso machines with ease. So are you doing the more is better (which isn't always the case) or do you "really" need a 1600AH LiFePO4 bank?

I had a 900AH Lead Acid and went down to a 400AH LiFePO4 bank and am happy as a clam in the mud.

Same here, I have 600 ah bank of Lifepo4 batteries and have never needed more , I run my washing machine, microwave , furnace , also have a headhunter 110v domestic water pressure pump . Never needed a bigger bank . 1200 AH is really a lot! Are you going to not run a charging source for a month at anchor ?

Regards

[Anjin]

Wow, what a great response. Thanks for all the interest.

Why 1600AH? My daily usage is (conservatively) 300 - 350AH (if we live with the luxuries we'd like) and every third or fourth day I use an additional 100-150 AH making water. I will have 1500 or so watts of solar and I expect that to make us largely self sufficient - as long as there is a decent amount of sun. But I plan for 3-4 days of minimal solar input which would put me right up at 1200AH. LiFePO4 should allow for a 75% "usage window" of capacity so that's 1600.

If we have continuously good weather I'd also like to be able to try occasionally using a single cabin A/C unit on an inverter for 4-6 hours. I've sized my inverters for the startup current and, in theory, I should have the capacity. But ultimately I may have to replace the compressor motors with DC ones to make it work well.

There is a much more detailed discussion I could have (and will at some point) but right now I'm really looking for some input on the cell size:

400AH in 4P4S vs 180AH in 9P4S

Any thoughts?

My thoughts were that the 180s are lighter and easier to "stack" in place and a failed or failing cell is less expensive to replace. The 400s have half the number of connections - and the connections are, according to this thread, often the source of problems. Then there's the assertion on this thread that anything larger than 200AH may not have adequate internal mechanical strength.

Thanks in advance -

- Art

[toddedger]

I bet the 400 Ah have more internal connections. And with what's been said about the larger sizes on boats I would rather have more connections where I can see them.