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

[OceanSeaSpray]

Originally Posted by tsmwebb

I thought they were using LiNiCoAl02 in 18650 size cells (eg. Panasonic NCR18650A), no?

Indeed. Different chemistry and different properties, lithium cobalt dioxide alone is just too much of a liability.

I think I can remember reading last year that Tesla was considering nickel manganese cobalt (NMC) for its off-grid storage solution.
This would mean getting setup for manufacturing both types of chemistry.

There is a very interesting paper here about the differences in thermal behaviour of a few lithium chemistries. Basically, they gradually baked charged cells until the heat alone set them off. LFP has an ignition temperature close to 200degC / 390degF, quite a bit higher than the others, but it also burns quite smoothly afterwards. NMC appears to have exploded in a ball of fire, looking at the graphs they recorded, and I believe NCA is more energetic again.

[exMaggieDrum]

Originally Posted by Highland Fling

YES then you could have a long hard look at my simple system.

MY FREE FOR NOTHING ADVICE to YOU - IS

Purchase four CALB 180AH or four WTS 200AH LIFePO4 cells and the EV-Power BMS and Cell Boards that fit whatever cells you purchase.

Purchase the cheap and cheerful battery cell monitor.

Adjust your charging souces to suit AND learn on the job, it is so easy really.

Then you can come back and tell everyone here how easy it really was once you 'decided' to actually do this.

I've been off a couple of days because of some login bug on CF that has affected CF. But good to go now, for better or worse.

I've pretty much decided to go ahead but lots of general and specific details to nail down, including competing advice from different posters. That's okay, I'll just put together based on all the sources what makes me feel good. Good stuff here.

I would not in any case say that any of this is easy. There doesn't seem anything cut and dried about it. Every vendor has a different take on things as does every poster. There are some common "threads" though - enough to give me enough comfort I can pull it off.

I got a reply back from Winston in China. They do not have a US distributor and don't seem to have any plans for one. They will sell me 100Ah cells at US$130 on EXW terms. I had to look that up. It means that they will sell them to me if I pick them up at their warehouse dock. They will not ship them - I would have to hire a freight forwarder. I have done that before with other things and it was always a bit of a nightmare with hidden costs and erratic information. I can get Sinoply cells and CALB cells in the US for the same price and just have to pay shipping from Utah to Washington. So Winston cells are out of the picture.

RE: EV-Power in Oz - is it this site: http://www.evpower.com.au/-Thundersky-Battery-Balancing-System-.html

The BMS's on here are all out of stock.

Regarding how easy it is - installation looks straightforward. Design does not.

[exMaggieDrum]

I'm going to go into "lurk" mode for a bit to digest as much as I can. I'm sure some of you will appreciate not getting my stupid questions for a while.

[mcarling]

Originally Posted by exMaggieDrum

I'm going to go into "lurk" mode for a bit to digest as much as I can. I'm sure some of you will appreciate not getting my stupid questions for a while.

There are no stupid questions. Please feel free to ask whatever you want to ask.

[Highland Fling]

Originally Posted by mcarling

There are no stupid questions. Please feel free to ask whatever you want to ask.

Only stupid answers ......and when your opponent sinks to the level of the asinine, it tells you they have already lost the argument.

[exMaggieDrum]

Originally Posted by Highland Fling

Only stupid answers ......and when your opponent sinks to the level of the asinine, it tells you they have already lost the argument.

Couldn't agree more! That's part of the reason I'm laying low for a bit.

[exMaggieDrum]

Ok, Ok. I couldn't stay off completely. I am committing enough to going with LiFePO4 to start getting some equipment. I'm going to incorporate the special bits in my, already started, battery rewire. If I don't need some of this I will resell it.

I just ordered two Gigavac GX200BA contactors. They are low wattage after initial trip. Gigavac claims they exceed the specs of the EV200 contactor used by many. I think these will work as well in any case from what I can see. I got them for $69 each on eBay yesterday. See attached.

They will be the LVC and HVC contactors to connect/disconnect the Load and Charge circuits from the battery. They are NO SPST. They do not have auxiliary contacts. For the price I'm OK with that as I wasn't sure I needed it anyway.

[OceanSeaSpray]

Originally Posted by Highland Fling

Only stupid answers ......and when your opponent sinks to the level of the asinine, it tells you they have already lost the argument.

Ohh, what an angry, abusive, little crowd of KISSers!

Sinking?? Like sinking to the level of throwing insults into the thread, Asinine Fling? And what argument?

There is no argument. See, I have a little piece of news for you: anybody can make lithium cells work on a boat: just charge them in parallel and put them in!! Yes, it is that simple. Everybody knows that. We know that too. Now, isn't that KISS?? Hardly a brilliant accomplishment! This is why we get a range of one-installation overnight experts coming back here to tell everyone how brilliantly successful they have been six months later, also boasting that none of all those bad things that could supposedly happen have, so basically since they are not happening, DON'T WORRY about any of them and FOLLOW ME! It is a "just do" (and all risks are yours anyway, what the hell).

See, it is the principle of social proof. If enough are doing it and saying it is great, no need to think about it further: you just follow the others.
Problem is that people don't come back to tell when it turned pear-shape (it goes against the flow and certainly wouldn't meet with approval) and many people are just reading the stuff as guests without participating, before, during or after.
I tend to hear the other, more interesting, side of the story however, after some acclaimed KISS principles threw a (usually expensive) wobbly, or system engineering was just bad. Something suddenly needs to be done about it, if the whole LFP contraption is going to stay on board at all. Back to the lead is actually something that takes place now and then - in the real world.
Meanwhile, what happens when I mention one of those odd real-life "incidents" here? Silence, or an angry little crowd of KISSers gather up, suddenly feeling threatened by the prospect that they might have inadvertently (or rather not) followed the other closely adjoint principle Keep It Stupendously Stupid.

So, no, it doesn't particularly worry me that we have a growing crowd of KISSers on the thread trying to harness the principle of social proof to justify to themselves what they have done, together with minor prof. electrochemist mcarling stating with authority that SLAs are in fact "more dangerous" together with other random bits of "information". Risk = probability x consequences, and short of something completely extreme combined with very bad luck, the dumb old lead-acids just sit around almost no matter what happens around them. They have done so for 150 years and there are at least hundreds of millions of them around.

It is just that bad things do occasionally happen around batteries - in fact they seem to happen quite a bit. They cause much more grief to those with dodgy LFP systems and give the technology a bad name.
Lastly, when I hear about some LFP fiasco, people often have genuinely tried to do the best they could, the extent of which varies a lot. Recurring issues are that:

• They were misinformed by others
• They browsed, copied and averaged across various sources of information before knocking something together -> it left significant gaps
• They didn't really understand what they were building -> more gaps
• They couldn't identify/get their hands on decent gear to build a system -> more gaps
• Some of their earlier arrangements caused special complications they couldn't foresee or were unable to deal with

The bottom line is always that it worked great until something silly happened. One lost all his cells and came very, very close to burning the boat down, one fried the boat's electrical systems almost from end to end, others damaged cells, destroyed various bits of equipment etc.



My interest has always been to see whether we could come up with a simple, but fully engineered, almost "just add cells" DIY solution (at which point KISSers start yelling that it is completely superfluous of course, and I couldn't care less really). Dealing with battery risks is easy, doing so without risking collateral damage can be a bit more interesting. Dealing with on-board integration in a uniform way is more challenging: some of the stuff we find on yachts these days was designed with the express assumptions that there is always a battery, that fully charged is always best, etc.

Still, it is steadily progressing in the right direction and one of these days I will have something built just for that: 4-cell LFP marine house bank applications (and maybe 8 cells too).

[evm1024]

All, (and I mean all of you!) can we toss the barbs out and focus on the batteries? This thread is too informative to sink low. We all have egos and our own way to do it and there is little need to pit KISS against a fully engineered solution.

Originally Posted by OceanSeaSpray

SNIP >%

My interest has always been to see whether we could come up with a simple, but fully engineered, almost "just add cells" DIY solution (at which point KISSers start yelling that it is completely superfluous of course, and I couldn't care less really). Dealing with battery risks is easy, doing so without risking collateral damage can be a bit more interesting. Dealing with on-board integration in a uniform way is more challenging: some of the stuff we find on yachts these days was designed with the express assumptions that there is always a battery, that fully charged is always best, etc.

Still, it is steadily progressing in the right direction and one of these days I will have something built just for that: 4-cell LFP marine house bank applications (and maybe 8 cells too).

This is a very desirable goal and I for one would welcome such a fully engineered BMS. And I want to point out that such a solution becomes a black box that is KISS. Technology at a high level appears to be magic er KISS. Let's get there sooner rather than later.

[T1 Terry]

My oh my, we do get a little testy about our idea being right and everyone else being wrong here sometimes :lol: At least it's better than the attacks I received 4 yrs ago when I first mentioned replacing lead acid with Li, but that was mostly on the RV forums back in Aust.
Now for me to add a my way.... but it's just a suggestion based on experience, I won't get all hot and excited if no one agrees

Originally Posted by mbartosch

After reading all of this thread, digesting a lot of insight and information and doing my own research and design I have finished most of the installation on our boat Entropy just recently.

In order to give something back to this great community I have documented my design on our cruising blog in the Engineering section. It's not yet finished, I would like to add posts about the physical installation of the system, but the schematics are all there already.

Find the overview on the Engineering Articles here:
Engineering - Entropy

Direct link to the design documents:
Designing a LiFePO4 Battery System Part 3 - System Design - Entropy
Designing a LiFePO4 Battery System Part 2 - Battery Management System Module - Entropy

I hope this helps other cruisers with their design.

Cheers

Martin

What a great build, congratulations. The only thing I would recommend you do differently is the cell links.... but I would also recommend compressing and strapping the cells to stop the cases bulging as this results in capacity loss. No matter how you treat them, they will bulge, they will even bulge sitting on a shelf not connected to anything.


As far as the cell links goes. The very low internal resistance in these cells along with the flat voltage curve will result in the 4 cells in series between the positive and negative doing the majority of the work as the links connected the way they are in the photo makes this the shortest possible path through the pack.
To get the cells to work together you need to pass the current over all the cells, not just offer it to them. If you remove all but one of the link straps in the series connections and move the positive cable to one end and the negative cable to the other end you will spread the load and charging evenly. The idea is to have the 4 parallel linked cells joined to the next group of paralleled cells at the opposite ends forcing the current to flow over all 4 cells in each group.


Cell voltage monitoring? there is no other way you will know if a cell runs away at the top end of the charge, no board type cell balancers can shuffle enough current to stop that run away as it happens so quick. Under charging the cells works for a while, but you will progressively loose pack capacity, but that is another item too deep to go into here at the moment.


T1 Terry

[exMaggieDrum]

T1Terry,

Is the attached what you meant?

[mbartosch]

Originally Posted by T1 Terry

My oh my, we do get a little testy about our idea being right and everyone else being wrong here sometimes

I must admit was a bit surprised by the heat of argument which ensued after I posted my design.
Maybe we can just all agree that there often are multiple ways to solve an engineering problem, and all of them have their advantages and disadvantages.

In the end this thread should help people make their own decisions about the technology they use in their boats. This thread has become a fantastic resource with a number of excellent contributions, and it would be a pity if it ended like many other Internet discussions.

What a great build, congratulations. The only thing I would recommend you do differently is the cell links.... but I would also recommend compressing and strapping the cells to stop the cases bulging as this results in capacity loss. No matter how you treat them, they will bulge, they will even bulge sitting on a shelf not connected to anything.

Thanks a lot! The images on my blog were taken in my home lab in a test installation, long before I set things up on the boat.
I will publish a blog post later with the actual installation on the boat.

Please have a look at the attached image (yes, need to clean up the thin wire mess, it's not 100 % done yet...), it shows how I installed things physically.

In order to connect the cells I chose tinned copper ground straps (36 of them, each sized 35 mm^2).
Four of them per serial link to even out current and in order to dimension cable sizing according to max. design current. (The main bus connection uses 120 mm^2 cables and is fused 355 A).
Your comment about connecting pack + and - "diagonally" is interesting, as you see I chose a symmetric approach. Good point, will probably rewire accordingly.

Regarding bulging and strapping: on the attached image it's not very easy to see, but I chose perforated metal plate, bent 90 ° (think of two bookends with the cell block sitting between them) and attached them to the wooden bottom of the box with wood screws.
I then tightened the parallel edges against each other using six threaded rods, then used the blue straps to prevent the cells from falling out in the hopefully unlikely case of capsizing.

And now, folks, for the geeky part. Those who have considered my solution already to be severely overengineered may consider me completely insane now

In a situation where the cells are really bulging I would expect an internal pressure of 100 - 200 kPa (100 - 200 kN/cm^2) before the emergency pressure vents open. When using 3 mm slotted stainless steel plates and 6 threaded rods, screws and bolts tightened with about 5 Nm, resulting in an estimated normal force of about 3 - 5 kN pressing against the cells.

My nephew is studying mechanical engineering, and I asked him for an opinion on the mounting option I planned. I gave him some parameters of the battery pack and my idea of the perforated metal plate and asked if he could give me an estimate on the expected bulging in an extreme situation.

I kid you not, he simulated this and gave me the rendered results. See attachments. This shows the simulated deformation of the pack (note how the metal bends near the threaded rods).
He computed the maximum bulging in the middle of the pack would be around 20 mm (see last rendering) - which is quite a lot, but I accepted it for my case.

[OceanSeaSpray]

Thanks evm1024. The thread has been free-falling for a while in the sense that the KISS moniker has become the blanket behind which there is not a design, concept or any consistency, but anything and everything that involves cutting corners and the justification is always "don't waste time thinking about it, it works great".

Now I read some who would like to peg this as a difference in "opinion", "different ways" etc. Sure. Does this look like an opinion to you: thousands of dollars in damage, still not repaired after weeks and accumulating berthing fees for the owner in the most recent instance here. Lithium battery KISS-job in Fiji.
When you are the promoter, you fully deserve that kind of result. When you are the guy who was taking his advice from a forum, you don't.

Still want to build KISS-crap? Can't design anything or even be bothered following Martin's "too complicated" diagrams? Sure, go for it. Knock yourself out. Just don't go and tell everyone else to do the same afterwards because it worked when you turned it on, please.

Systems can be both simple and well-engineered. I got interested in solution engineering because the designs were convoluted, didn't address all the issues and the hardware not suitable or any good at all.

I want to push out some hardware and information to support good marine systems built from bare cells (and not EVs, off-grids, everyone else and their cats too), but I do care a great deal about the outcome for others and this is why I haven't rushed it.
It takes time and a number of pilots systems to get feedback and validate these things.

A few things I would like to know are, of all the people out there with wind generators (and even hydro-generators):

• Does your model have a "kill" input (which is different than shorting it out) and if so, what signal does it require to activate? +12V or go to ground instead? Does it keep working if the battery has been disconnected?
• If it must instead be shorted out with a switch, relay etc, any idea of the current it pumps out through the short-circuit, in high winds etc?
• If you free-wheel it (open-circuit), what kind of voltage does it get up to in a given wind speed? Be careful not to get a shock while measuring.
• How much current can it put out while charging?

I am not fond of bloody wind generators myself, so unless some adepts help me out, I am not going to get there easily. I have 2-3 boats that should allow me testing, but that will just be those models only.

[T1 Terry]

Originally Posted by exMaggieDrum

T1Terry,

Is the attached what you meant?

That is what I was trying to say, yes. As far as the 20mm bulge, is that per cell? 5mm rod is the biggest that will fit between the cells side by side with the narrow edges meeting, in the early days we constructed a pack this way and the pressure stripped the thread out of the stainless nut and distorted the thread on the rod so much a nut could no longer be wound past the damaged area. 4 cells will bend 50mm x 3mm steel strap, so we now use 3mm aluminium plates and stainless band strapping folded over each end cap and screwed through the end plate, 3 up each side. This will hold a pack in normal use but will not stop them from bulging if overcharged or completely drain and heat causes gassing to occurs. Once the cells have bulged a 10 tonne press would not flatten them until the vent cap was released..... that much pressure. I have seen them fitted in a confined space where the owner determined strapping was not required as there wasn't enough room for it and the confined space would act as the case for holding them together. In this case the owner was quite correct, they fitted into the space quite nicely and each swelled to the room available. The down side was he could not remove a cell from the group when he attempted to remove them to swap them to his new RV, they are there for life.

T1 Terry

[scaredycat]

Originally Posted by OceanSeaSpray

Thanks evm1024. The thread has been free-falling for a while in the sense that the KISS moniker has become the blanket behind which there is not a design, concept or any consistency, but anything and everything that involves cutting corners and the justification is always "don't waste time thinking about it, it works great".

Now I read some who would like to peg this as a difference in "opinion", "different ways" etc. Sure. Does this look like an opinion to you: thousands of dollars in damage, still not repaired after weeks and accumulating berthing fees for the owner in the most recent instance here. Lithium battery KISS-job in Fiji.
When you are the promoter, you fully deserve that kind of result. When you are the guy who was taking his advice from a forum, you don't.

Still want to build KISS-crap? Can't design anything or even be bothered following Martin's "too complicated" diagrams? Sure, go for it. Knock yourself out. Just don't go and tell everyone else to do the same afterwards because it worked when you turned it on, please.

Systems can be both simple and well-engineered. I got interested in solution engineering because the designs were convoluted, didn't address all the issues and the hardware not suitable or any good at all.

I want to push out some hardware and information to support good marine systems built from bare cells (and not EVs, off-grids, everyone else and their cats too), but I do care a great deal about the outcome for others and this is why I haven't rushed it.
It takes time and a number of pilots systems to get feedback and validate these things.

A few things I would like to know are, of all the people out there with wind generators (and even hydro-generators):

• Does your model have a "kill" input (which is different than shorting it out) and if so, what signal does it require to activate? +12V or go to ground instead? Does it keep working if the battery has been disconnected?
• If it must instead be shorted out with a switch, relay etc, any idea of the current it pumps out through the short-circuit, in high winds etc?
• If you free-wheel it (open-circuit), what kind of voltage does it get up to in a given wind speed? Be careful not to get a shock while measuring.
• How much current can it put out while charging?

I am not fond of bloody wind generators myself, so unless some adepts help me out, I am not going to get there easily. I have 2-3 boats that should allow me testing, but that will just be those models only.

This is quite different from most of the other, and more expensive, 400W generators. The typical marine wind generator's charge controller uses 50 year-old technology, which is simply a load-diverter switch, which, upon reaching a set-point, diverts 100% of the energy to a set of resitive elements (essentially heater coils). There are two reason why this is bad and inefficient. The first reason is that when the battery reaches its set-point it isn't actually fully-charged, and this type of Partial State of Charge (POSC) cycling damages the battery by reducing its capacity and sulphating the battery plates. They can't fully-charge the battery because they have no way to dump just the excess power. They can only dump all of it. The best scenario would be to have a way to progressively dump power so the batteries could be fed with only the power that they need at this final stage of the charging process. The second reason that old-fashioned load diverter controls are bad is that even though the set-point has been reached, the wind generator will keep turning, and it does so at full load and at a 100% duty-cycle. So, the wind generator continues to spin with a large load, but is at this point just heating up resistive piles down below..........etc. Read more on their website:
https://store.marinebeam.com/marinek...ind-generator/
It looks like the ducks guts, but not specifically mentioning LiFePO4 chemistry.