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

[john61ct]

Originally Posted by Delfin

Different chemistry than the LiFePO4 batteries discussed in this thread.

What makes you think so?

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

Originally Posted by mat jam

This guy worked at JPL on the Mars Rover.

Who is he? Any links other than the video itself?

[Delfin]

Originally Posted by john61ct

What makes you think so?

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

Who is he? Any links other than the video itself?

See CatNewBee's post, and mine. The summary of the information provided by the poster doesn't describe LiFePO4 batteries. The information in the video may be correct, but not the summary.

[senormechanico]

Originally Posted by mat jam

This guy worked at JPL on the Mars Rover.

Some of this info may be outdated.

https://youtu.be/QlDd3jkcxoQ?t=3000




At 50:00 he makes a very interesting statement about overcharging !
You can do it all day long.

[mat jam]

Originally Posted by Delfin

See CatNewBee's post, and mine. The summary of the information provided by the poster doesn't describe LiFePO4 batteries. The information in the video may be correct, but not the summary.

Your first reply appears to be an attempt at subterfuge. And now you are talking semantics. I concede the BMS does what it is supposed to do in varying degrees dependent on the supplier, but my summary IS that LifePO4 requires a lot of physical management in that if you want a long life cycle you should be careful how you use it which requires you doing a lot of managing in terms of the loads you put on it, how low you allow it to be discharged, etc.

Catnewbee,

You have misread or misunderstood the meaning of the word "at" for "to" in reference to 3.4v. I am only stating the info in the video and adding my thoughts.

john,

He mentions it in the video. I believe he is also a prof now and his name may be in the comments below the video.

[Delfin]

Originally Posted by mat jam

Your first reply appears to be an attempt at subterfuge. And now you are talking semantics. I concede the BMS does what it is supposed to do in varying degrees dependent on the supplier, but my summary IS that LifePO4 requires a lot of physical management in that if you want a long life cycle you should be careful how you use it which requires you doing a lot of managing in terms of the loads you put on it, how low you allow it to be discharged, etc.

No subterfuge, just pointing out that your summary is flawed and doesn't correspond to reality. And why would I bother to try to be sneaky?

I gather you don't have a lithium setup. I do, as do others. It is easier to manage in many ways than Lead Acid, not more difficult. Charge, use, recharge, and repeat a few thousand times. Simple. No water, no sulfation, much less weight, higher and stable voltage for 80% of the capacity of the battery, flat charge and discharge curves so minimal recharge time, etc. Suggesting that one should worry about what loads you put on a LIPO pack on a boat is largely irrelevant, since the danger zone is north of 2 C, which in my case would be 1200 amp draw on a 600 Ah pack. My typical draw is 15 Ah and I have no idea how to draw 1200 Ah without installing an array of Klieg lights. Perhaps review the information provided here for real world testing that describes how to kill/charge/maintain a lithium pack, and what their actual life cycle should be given routine usage.

The only folks who make the argument you seem to be making about the difficulty, complexity, danger, etc. of LIPO are those who have no experience with them.

[evm1024]

With 6171 posts in the thread I think that we have hashed out the basics. This is not to say that nothing new will come about but rather there is a lot of material to review if yo are just joining the thread.

[evm1024]

Darn, I must be getting old. I just do not remember if I posted this before. I know that I was thinking about posting it but please forgive me if I am repeating myself, forgive me if I am repeating myself....

So how much Lithium are we talking about moving from the anode to the cathode and back again in a charge or discharge cycle?

I have 700 AH cells and I'll use them in this example. I will also assume that there is 700 AH per cell capacity.

First off we need to convert amp-hours to coulombs. A coulomb is 1 amp for 1 second so we will need to convert from amp hours to amp seconds so we multiply by 3600.

700 AH = 2,520,000 amp seconds (or coulombs)

We know that there are 6.24 * 10^18 electrons per coulomb so we get:

2.52^6 * 6.24^18 = 1.57^25 electrons in 700 AH.

We know that on charge or discharge we are only stripping 1 electron in or out of each Lithium atom so we have a 1 to 1 ratio of Lithium to electrons so we have 1.57^25 Lithium atoms to move between the anode and cathode.

Avogadro's number (6.02^23) is the number of atoms per mol so if we divide the number of Lithium atoms by Avogadro's number we get the number of mols of Lithium. Thus:

1.57^25 / 6.02^23 = 26.13 mols of Lithium

The mol weight of Lithium is 6.94 grams per mol and thus we get:

26.13 * 6.94 = 181.32 grams of Lithium moved between the electrodes in a 700 AH cell

With 4 cells for a "12 volt" battery we get a total of 725.29 grams of Lithium moving between the electrodes.

1.6 pounds for us US folks for the 4 cell battery or 6.4 ounces per cell.

Not much....

[john61ct]

Originally Posted by Delfin

See CatNewBee's post, and mine. The summary of the information provided by the poster doesn't describe LiFePO4 batteries. The information in the video may be correct, but not the summary.

Sorry thought you meant

He is not talking about LFP.

That is different from saying

I disagree with what he's saying about LFP.

I imagine JPL's priorities in supplying power to equipment that is never coming back would be different enough from the usual high-C-rate use cases addressed by industry, and both different enough from House bank usage on a boat, that may account for at least some of the discrepancies.

Then again, he might be an idiot, or talking about other LI chemistries mixed in with LFP, or the whole video is not credible, I dunno.

[john61ct]

Originally Posted by Delfin

your summary is flawed and doesn't correspond to reality

Do you mean he misrepresented the contents of the video?

Or that the views stated in the video do not agrre with your beliefs about properly caring for LFP?

> difficulty, complexity, danger, etc. of LIPO

I don't think anyone was talking about LiPo? Completely different beast from LFP.

And just the fact that many say you really need a BMS makes LFP much more difficult for a DIYer to purchase and install their own cells.

Remember the comparison for prospective noobs is,

how risky / expensive that process is compared to buying and installing a lead bank.

[john61ct]

Originally Posted by evm1024

Avogadro's number (6.02^23) is the number of atoms per mol so if we divide the number of Lithium atoms by Avogadro's number we get the number of mols of Lithium. Thus:

1.57^25 / 6.02^23 = 26.13 mols of Lithium

The mol weight of Lithium is 6.94 grams per mol and thus we get:

26.13 * 6.94 = 181.32 grams of Lithium moved between the electrodes in a 700 AH cell

With 4 cells for a "12 volt" battery we get a total of 725.29 grams of Lithium moving between the electrodes.

1.6 pounds for us US folks for the 4 cell battery or 6.4 ounces per cell.

Not much....

Interesting!

But how does all that relate to decisions faced by a noob end-user who just wants to get maximum functionality at a reasonable price?

[newhaul]

Originally Posted by john61ct

And just the fact that many say you really need a BMS makes LFP much more difficult for a DIYer to purchase and install their own cells.

.

why is adding a bms considered so difficult to your thinking ?

Here is the wiring schematic for mine .
Nothing difficult here

[Delfin]

Originally Posted by john61ct

Do you mean he misrepresented the contents of the video?

Or that the views stated in the video do not agrre with your beliefs about properly caring for LFP?

> difficulty, complexity, danger, etc. of LIPO

I don't think anyone was talking about LiPo? Completely different beast from LFP.

And just the fact that many say you really need a BMS makes LFP much more difficult for a DIYer to purchase and install their own cells.

Remember the comparison for prospective noobs is,

how risky / expensive that process is compared to buying and installing a lead bank.

Typo, brain fart, whatever. Meant to type LIFO, but that is also incorrect, so I should use LFP, which is a better abbreviation for LiFePO4 - thanks. And no, I don't think he misrepresented the video content, but I also don't think he understood it well enough to represent it helpfully in the marine context.

The video does underscore that LFP technology has numerous applications and that what is a reasonable statement in one use case, like the video guy's comment that individual cell monitoring is economically infeasible, so not done, is wrong in the boater context where individual cell monitoring is pretty standard. He's correct that with thousands of cells in a Tesla, individual monitoring isn't done. But that's because you can lose a few of thousands and have little impact on battery performance, but if you have 4 of them, it is a different story.

The main point is that IMO, and that of others with actual experience with these batteries, to say that they require more manual management than other chemistries is simply wrong. There is no downside other than cost, and the upside for many of us is more than worth that cost.

[john61ct]

Well if you go bareback (no BMS) then more manual monitoring regulation and maintenance is required.

And I'm not saying hooking stuff up is a challenge when you know what you're doing.

However, if you want to assemble your own system, require reasonable pricing, adjustability of setpoints, compatibility with a wide range of cells, decent documentation and helpful support,

just identifying and sourcing the "right" BMS is certainly a challenge, and not just for noobs.

[newhaul]

Originally Posted by john61ct

Well if you go bareback (no BMS) then more manual monitoring regulation and maintenance is required.

And I'm not saying hooking stuff up is a challenge when you know what you're doing.

However, if you want to assemble your own system, require reasonable pricing, adjustability of setpoints, compatibility with a wide range of cells, decent documentation and helpful support,

just identifying and sourcing the "right" BMS is certainly a challenge, and not just for noobs.

not hard at all you find the manufacturer and specify what you want they will tell you what they have that will meet your specs or they can recommend specs that would be beneficial for your particular install. For mine all I needed was hvd and lvd at my specified values .
Max charge and discharge current . Cost under 20 USD. For the one I posted the wiring diagram for.

[CatNewBee]

It is not rocket science, there are ready to use BMS kits on the market in different flavors and price ranges, also cell sizes from 20Ah to 1000Ah, and for submarines even 15000Ah.

Regarding the price, LFP is not more expensive than GEL or AGM, in the long run it is cheaper.