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

[paradox]

Thank you for the information
I will have to read up on the Blue Seas ACR
What type of LFP batteries are you using?

[Delfin]

Originally Posted by paradox

Thank you for the information
I will have to read up on the Blue Seas ACR
What type of LFP batteries are you using?

The Blue Seas ACR has as an option an external switch that allows you to combine banks manually, not combine them, or have them combine automatically when the primary bank (usually the house bank) reaches a preset voltage that indicates that primary bank is nearly charged. When I am underway and the alternator is charging the LFP bank and it gets full, I will switch the ACR from Auto Combine to Manual Combine, joining the house and starter bank, but also disconnecting the BMS on the LFP bank so even though current could flow to both banks, it ends up only going to the starter bank. Since I am doing this manually, I can set the alternator and other charge sources (genset, Sterling chargers) to a profile suitable for the LA starter bank, since all the LFP bank sees is bulk voltage until I disconnect it from charge sources.

I bought assembled packs from Lithionics, 2 x 300 Ah@24vcd. Not cheap, but lacking the time and expertise to roll my own, that made sense for me. Lithionics matches the cells, installs cell level monitoring and shunting and offers their own BMS to handle low and high voltage protection as well as top balancing of the cells as long as you charge to 29.2+ volts, which I currently only intend to do annually or so.

[paradox]

did you go through bruce scwab for your lithionics batteries?

[Delfin]

Originally Posted by paradox

did you go through bruce scwab for your lithionics batteries?

I would recommend that you do. At that time, I didn't get from Bruce the availability of the 300 amp 24 vdc packs, so ordered them directly from Lithionics, who may, or may not still be willing to directly fulfill an order. But again, I would go through Bruce, as his expertise is worth a lot and you will have some learning to do. I haven't found direct support from Lithionics to be all that stellar. Some questions go unanswered.

[Delfin]

Originally Posted by john61ct

C'mon guys, he's promised to stop now.

Let's let it be maybe he'll honor that, no need to draw him back in.

And Delfin, I've never agreed with you more, great job there. . .

Thank you John...

[tanglewood]

Originally Posted by mat jam

I read the first few pages and the last ten or so pages so apologies if this has been covered, but what I gleaned was that there are too many unknowns with such a complex thing that has too many variables that requires a management system which is another thing that can go wrong.


LiFePO4 Battery 101


This guy worked at JPL on the Mars Rover.

I watched the video last night and it's quite good, but I think you are really misinterpreting a bunch of things. This discussion spun out of control, but I'll still take a crack at a hopefully objective response to your concerns.


I think the biggest disconnect between what's in the video and and your take-away is that the video is talking about the extremes of the technology. Things like discharge to 0V, charging to over 4V, freezing batteries then thawing them out and continuing to use them, operation at or above 60C, discharge rates of 20C (those "C"s are celsius and C-rate, respectively, just to be clear).


These operating parameters exist for many applications, like a mars rover that is baking in the sun then frozen solid based on the martian day/night cycle. Cars can be subject to such extremes as well. When you look at super high discharge rates (and charge rates), I think hand power tools might be the most strenuous. I have run power tools from full to empty in well under an hour, and then want it recharged as fast as possible.


A domestic power system, whether in a boat, an RV, or a stationary house, is a much more placid operating regime. This biggest difference is that these applications typically have discharge rates that center around 1 day. That's C/24, which is light years away from 20C. Some people size their batteries for longer time between recharge, and other accept shorter. I think a minimum to consider might be C/6 which is a discharge over 6hrs, then recharge. For a 600Ah bank, that's a continuous 100A load. That's huge.



Compare this to the discharge rates used in the video to illustrate some of the LFP pathological behavior. His lowest rate was C/2, and ran up to 20C. Our rates range from C/48 (2-days for full discharge) to C/6. So we operate at a trickle, and in the range where he described the electro-chemical reactions as near ideal.


In summary, he's talking about the equivalent of getting a car through the 24hr at LaMans, where we are talking about grandma's car. Now let's address you specific concerns.

Originally Posted by mat jam

Thickness of electrodes determines discharge efficiency rate. Thinner is much more effective and more expensive. Higher discharge rate creates heat which breaks down the electrolytes which ultimately affects life cycle. Short term heating is good, but it is specific to each cell structure and the required regimen to follow would be difficult for most cruisers to implement, especially without guidelines from the manufacturer.

This part was very interesting, but it's all about how to suck all the Li out of the cathode and jamb it into the anode as fast as you possible can, and what are the factors that limit it. If you want to run you boat bank at 20C, which is a full discharge is 3 minutes, then you need to be concerned about this. Maybe it's even a concern running at 5C, which is full discharge in 12 minutes. But that is so far away from the operating regime of a boat, it's silly to even talk about it other than philosophically.


Just to further add some sizing to this to help keep it in perspective, I would consider a 200ah banks to be on the small size for a boat, 500ah to be more common, and 1000ah to be pretty big. A 5C load on those banks would be a continuous, from full to empty, 1000A, 2500A, and 5000A respectively. Not gonna happen.

Originally Posted by mat jam

Long term heating is bad, period. And the higher the current discharge equals less and less energy available. So the bottom line is the battery manufacturers should be publishing the safe discharge load range for long term use efficiency. If you are pulling a constant rate of energy from the batteries within the range then your batteries will provide a longer life cycle. If you are putting high discharge loads on your batteries expect a shorter life cycle.

Agreed, and battery manufacturers do exactly what you suggest. Just go look at the spec sheets for a CALB or Winston cell. They provide operating ranges to get 2000 cycles. These ranges are way, way far away from the limits of the technology that was discussed in the video. If you operate even more gently that the spec sheets, as all boats do, even more cycles are expected. How many and what the factors are remains speculation to an extend because of the impracticality of testing.

Originally Posted by mat jam

If your use is on the higher SoC then you can expect thousands of cycles. If your use is on the lower SoC you can expect hundreds of cycles.

You have this all muddled up. He was indirectly saying that higher discharge rates leads to lower cycle life.


Principally he was talking about a Ragone plot which shows usable power vs discharge rate, and how LFP delivered power reduces at higher discharge rates. This is analogous to the Peukart effect in LA batteries. The bottom line is that stored energy is lost to heat, leaving less usable power. And the higher the discharge rate, the greater the loss.



Also related to discharge rate is cycle life, though that's not shown in a Regone plot. That's the comment he made about 1000s becoming 100s, or 10,000 becoming 1,000.


But to put this in perspective, here is a Regone plot of a few LFP cells. This has the axis reversed relative to the video, but it's the same. To keep it in perspective, there are discharge lines also drawn, and you can see that the cells performance doesn't start to reduce until you get into the 3C to 5C range. Our average discharge rate is C/24 which isn't even on the chart (C/5.5 is the lowest shown). So again, he's talking LaMans, and we are talking grandma.

Originally Posted by mat jam

Also says some interesting things about BMS and individual Cells.

Yes, and it's in the context of 18650 cylindrical cells - over 7000 in a tesla pack, for example. The economics are different for prismatics where the per-cell capacity is much higher.


And even with prismatics, more and more people are doing away with active cell management and doing exactly what he advocates; Do an initial top or bottom balance, then run and just monitor the cells watching for excursions. This is exactly how my "BMS" works.

Originally Posted by mat jam

And pulse charging regimen is better than a constant current. With a properly engineered cell (all cells equally balanced) potentially charge 40-50% faster with a pulse technique. And add about 10% life cycle. So the question is with so many charging methods being utilized on a boat – diesel, shore, solar, etc. how will this effect the life cycle?

I found this quite interesting too, but again, it's about working around the problems with very high charge and discharge rates. We don't have that problem. Now perhaps we could still gain some more cycle life with pulse charging. But I think everyone if first waiting to see what sort of live we get with our grandma operation. Some are anticipating 10,000 cycles which is 30 years of daily cycling. At that point, who cares about 10%.

Originally Posted by mat jam

I have read elsewhere stated that with Lithium batteries you can expect 7 years if you do not go below 50% SoC without proper battery management and 10 years if you do not go below 50% SoC with proper battery management.

That's too nebulous, too out of context, and too jumbled a comment to even understand, let along respond to. So I'll just pass on that.

Originally Posted by mat jam

Charge at 3.4 V.

Consistent with published spec sheets.

Originally Posted by mat jam

Above 4.3 V the electrolyte starts to break down.

Right. Don't do that. This is why chargers are regulated, and have been for all types of batteries for over a century.You will get similarly unpleasant results by grossly over charging a LA battery.

Originally Posted by mat jam

Do not let it go below 1.0 V.

Right. Don't do that. That's why low voltage cut out devices have been part of battery systems for decades. Same rules apply to LA.

Originally Posted by mat jam

Fast charging and fast venting can cause a spark and an explosion.

Yes, but again, bring it into context. We are not charging anywhere near these rates. If anyone can charge their boat system at 1C (empty to full in 1 hr) then they have a most bad-ass charging system. I bow to them.


Also, degree of venting, sparking, and fire risk vary greatly for different chemistries. The video talked about how much further below the decomposition voltage LFP operates, and how it makes it much safer in these respects. I think most of us feel that LFP is the only Li chemistry safe enough for use on a boat. I know I do.


And again, this is no different than LA, and probably safer. Over charged LA vents hydrogen which is about as explosive as anything on the planet. In fact, some LA types vent hydrogen during normal charge. How's that for a danger? But nobody bats and eye.

Originally Posted by mat jam

Stay under 50 C for longevity. Stay under 100 C for safety. They may fail or blow up.

Yup, true for pretty much any battery. And it's pretty easy to stay well away from these temps in a boat application.

Originally Posted by mat jam

The vents are potential areas where water can get in and contact with the electrolyte is not good (dangerous). And use of aluminum foil only makes this worse.

Manufacturers all say to keep the batteries dry, so just do that. It's not so hard. No harder that in a car, for example.


That said, it's not clear to me that it's dangerous vs damaging. I didn't get that from the video. Nor is it clear that the aluminum foil makes things worse. I didn't get that from the video either.

Originally Posted by mat jam

So essentially, if you thought you can take it down to 20% and put high loads on it and still get thousands of cycles...

Right, if you want to run continuous 2C (full to empty in 30min) or 5C (full to empty in 12 min), you are correct. But we operate an order of magnitude below that, so this simply isn't applicable.

Originally Posted by mat jam

Conditioning a battery (all cells equally balanced) and a starting regimen is very important. Management is very important. Seems like a lot of work for a cruising lifestyle.

It's actually easier than operating LA batteries. With LA, you have to stay above 50% SOC, keep track of how long it's been between full charges, then monitor very carefully every few days to be sure you do get a full charge. And if you think you have sulfation, you need to equalize and re-check, etc. If you are really careful, you can get 700-1000 cycles.



In my experience, LFP is MUCH easier to live with and requires MUCH less attention. Your BMS watches individual cells (assumes prismatics) and alerts you if one is starting to run astray. Active BMSes apply corrective charge, when passive BMSes leave it to you. So far experience suggests corrective action is less frequent than the need to equalize LA batteries. So with less effort, we can expect 2000+ cycles. Less work, and double the life. I like that.

Originally Posted by mat jam

He also mentions that LA with the proper regimen is really good and is amazing what you can do with it and that you can use a technique for removing the sulfation which I think most already know.

And for this reason many continue to use LA, and will for a long time. But like everything, the application has a huge influence on your battery choice. EV and portables are out of the question with LA because of weight. Weight is much less of a concern with boats unless you are a performance sail boat. And it's of no concern with trawlers and stationary applications.


But for off-grid domestic power, a C/2 recharge rate with no absorption tail is like a gift handed down from above. And no worries about partial state of charge operation, is like ANOTHER gift handed down from above. This makes LFP very compelling for such applications.

Originally Posted by mat jam

Some of this info may be outdated.

I think your reaction is just because you are overwhelmed by a bunch of new info. At first, LFP can seem like handling eggs with an excavator. But once you come to understand it, and put all the info and cautions in context, it's really not bad at all. It's just very different, which is what throws a lot of people for a loop. As more and more people become familiar with LFP, fewer and fewer people will shun it. Right now, most criticism comes from ignorance or fear.

[john61ct]

Haven't parsed the vdo nor your post yet for the details, but that is an admirable attempt to bring a rational engagement with mat's statements.

However, I think the consensus here is that your assumption he was acting in good faith may be misplaced.

But hopefully the net effect on furthering member's learning will be a positive one.

[tanglewood]

Originally Posted by john61ct

Haven't parsed the vdo nor your post yet for the details, but that is an admirable attempt to bring a rational engagement with mat's statements.

However, I think the consensus here is that your assumption he was acting in good faith may be misplaced.

But hopefully the net effect on furthering member's learning will be a positive one.

The video is excellent, and well worth watching. As best I can tell, some company using LFP brought him in to talk to them. The guy is very impressive. But the discussion really focused around what we would all consider to be extreme C rates, and rates that push the chemistry to it's breaking point. And then lots of very interesting discussion about what breaks and why, and interesting techniques to work around it. Like pulse loading the LFP, and using super caps to buffer the actual delivered load.

[john61ct]

Someone said it was a Lithionics group?

[greg_kulosa]

I actually thought it was a group doing Electric Vehicle work - but maybe I am thinking about a different video. As mentioned, this thread is long.

[john61ct]

I do not recall where I got this info:

Originally Posted by john61ct

In the first couple minutes he is talking about LFP in the video, and it is a talk to Thundersky (Winston) techs.

And no one responded directly to my Q, are there any links to the context, blog post, listserv etc, other than the video itself?

[Maine Sail]

That Whitacre video has been around since at least the 2009-2010 era...

[newhaul]

Here is a little video that just came out.
https://youtu.be/RAO5qARz6FA

https://www.amazon.com/LiFePO4-Lithi...language=en_US
He links to several other wise packs in the video .
It works out to be about 6 bucks per ah

[john61ct]

at 12V. Good pricing!

$520 per kWh, more universal measure.

I wonder who the manufacturer is?

And what's a wise pack?

[Delfin]

Originally Posted by newhaul

Here is a little video that just came out.
https://youtu.be/RAO5qARz6FA

https://www.amazon.com/LiFePO4-Lithi...language=en_US
He links to several other wise packs in the video .
It works out to be about 6 bucks per ah

Very interesting, thank you.