LFP battery chatter ( AKA LiFePo4, Lithium Iron Phosphate )

[Living Large]

Ok, Dereck, What is the SOC at 2.9 volts per cell? how long does it take to go down to 2.5 volts assume the load is between C/10 to C/20 rate? Some Inverter took a minute or two to cut off the power after it reach the preset voltage to cut off. They don't want to cut off the power prematurely.

Thank you.

The XW inverters have a programmable delay from 0 to 600 seconds to prevent premature cut off.

[peakbagger]

I noticed an ad in Home Power that Iron Edison, a nickel iron battery supplier now sells assembled LiPo batteries complete with all the battery protection circuits included. I am not in the battery market but it may be of interest to those considering LiPo batteries that don't want to DIY a system.

[Sunking]

I noticed an ad in Home Power that Iron Edison, a nickel iron battery supplier now sells assembled LiPo batteries complete with all the battery protection circuits included.

Name 3 pronouns that have a nasty reputation.

LiPo? Is that a typo by chance?

LiPo has a few different meanings, but would be the last choice anyone would make to power anything with a price tag of $2/wh and a 300 to 500 cycle life. Only thing they are used for is Drag Racing as they can supply up to 50 to 100C rate. Not to mention a nasty habit of bursting into flames.

[peakbagger]

Lithium Iron Phosphate , I thought the normal abbreviation was LiPo.

As usual, you are shooting the messenger. All I did was make folks aware of an option of a prepackaged lithium battery as the title and direction of the thread was "LFP battery chatter. Many of the concepts being discussed in the thread appear "home brew" by buying a bunch of cells of the internet with an unknown pedigree and then sourcing the various battery protection systems and hoping the assemblage will work and not kill anyone. I have no skin in the game either way as I pay my utility to be my battery. Here is the link, feel free to cut out the middleman and technically tear it apart. http://ironedison.com/12-volt-lithium-battery-for-solar.

[Living Large]

Lithium Iron Phosphate , I thought the normal abbreviation was LiPo.

As usual, you are shooting the messenger. All I did was make folks aware of an option of a prepackaged lithium battery as the title and direction of the thread was "LFP battery chatter. Many of the concepts being discussed in the thread appear "home brew" by buying a bunch of cells of the internet with an unknown pedigree and then sourcing the various battery protection systems and hoping the assemblage will work and not kill anyone. I have no skin in the game either way as I pay my utility to be my battery. Here is the link, feel free to cut out the middleman and technically tear it apart. http://ironedison.com/12-volt-lithium-battery-for-solar.

I had come across this site, and these prepackaged units. I viewed them from exactly the lens that you suggest (cobbling together vs all-in-one), and I believe Dereck was possibly going to research prepacked unit resellers at one point.

Personally, I felt they were on the expensive side, and I don't think they had a size I needed. I got to the point (with the help here) of deciding to use the built in features of the inverter for LVD, and was last considering the MiniBMS system for BMS. But then I wasn't sure again about the capacity I could build being what I wanted. LFP selection isn't what it is with FLA.

Then a few really cold days and snow and ice hit, and made me reconsider moving to the Adirondacks...

[Sunking]

Lithium Iron Phosphate , I thought the normal abbreviation was LiPo.

No Sir, it is LFP, thus the title of the thread

As usual, you are shooting the messenger.

No Sir, you are just paranoid. Put your big boy pants on and grow thicker skin. It is not about you.

All I did was make folks aware of an option of a prepackaged lithium battery as the title and direction of the thread was "LFP battery chatter. Many of the concepts being discussed in the thread appear "home brew" by buying a bunch of cells of the internet with an unknown pedigree and then sourcing the various battery protection systems and hoping the assemblage will work and not kill anyone. I have no skin in the game either way as I pay my utility to be my battery. Here is the link, feel free to cut out the middleman and technically tear it apart. http://ironedison.com/12-volt-lithium-battery-for-solar.

Iron Edison is the point.. They ave a horrible reputation as does Home Power Magazine. Again it is not about you.

[Sunking]

Personally, I felt they were on the expensive side, and I don't think they had a size I needed. I got to the point (with the help here) of deciding to use the built in features of the inverter for LVD, and was last considering the MiniBMS system for BMS. But then I wasn't sure again about the capacity I could build being what I wanted. LFP selection isn't what it is with FLA.

Getting the size you need in LFP is not different than FLA, just requires more ingenuity and close enough for hand grenades. LFP come in a variety of sizes. Unlike FLA can be paralleled without any real issues. LFP common sizes are 10, 20, 30, 40, 60, 80, 100, 125, 140, 160, 200, and 300 AH. So say you need 500 AH. You have a few options. If you want exactly 500 use 4 of the 125 AH in parallel. Most likely 3 of the 160's are close enough.

Like I said Lithium is not ready for mainstream solar applications. Only those who know what is going on can take the challenge. It will be at least another 10 or more years for lithium to go main stream.

[Living Large]

Getting the size you need in LFP is not different than FLA, just requires more ingenuity and close enough for hand grenades. LFP come in a variety of sizes. Unlike FLA can be paralleled without any real issues. LFP common sizes are 10, 20, 30, 40, 60, 80, 100, 125, 140, 160, 200, and 300 AH. So say you need 500 AH. You have a few options. If you want exactly 500 use 4 of the 125 AH in parallel. Most likely 3 of the 160's are close enough.

Like I said Lithium is not ready for mainstream solar applications. Only those who know what is going on can take the challenge. It will be at least another 10 or more years for lithium to go main stream.

I attempted to get comments on paralleling LFP batteries several days ago, and my memory is I really didn't get responses. I specifically asked about creating 500 Ah and 600 Ah. I had only found one supplier of 300 Ah, and I wasn't sure about it. May have been Energex.

I also asked about paralleling, hoping to get comments that compare paralleling LFP to FLA. The recommendation previously here when I was considering them was generally not to parallel FLA. I was (and still am) wondering if paralleling LFP is any better, and avoids possible pitfalls of paralleling FLA. There was a comment here I believe where someone advised against paralleling LFP, I believe, but no discussion of negatives. Now you are suggesting paralleling as many as 4 batteries - so I'd ask again, is there less of a concern with LFP? If I could parallel three 200 Ah CALB batteries (whereas no more than two is advised with FLA), I'd be happier than a pig in slop.

[Sunking]

I attempted to get comments on paralleling LFP batteries several days ago, and my memory is I really didn't get responses. I specifically asked about creating 500 Ah and 600 Ah. I had only found one supplier of 300 Ah, and I wasn't sure about it. May have been Energex.

I also asked about paralleling, hoping to get comments that compare paralleling LFP to FLA. The recommendation previously here when I was considering them was generally not to parallel FLA. I was (and still am) wondering if paralleling LFP is any better, and avoids possible pitfalls of paralleling FLA. There was a comment here I believe where someone advised against paralleling LFP, I believe, but no discussion of negatives. Now you are suggesting paralleling as many as 4 batteries - so I'd ask again, is there less of a concern with LFP? If I could parallel three 200 Ah CALB batteries (whereas no more than two is advised with FLA), I'd be happier than a pig in slop.

You must be like me getting old and forgetful. I have answered you every time in many post.

Paralleling lithium batteries is done as a matter of fact. You will not find a single EV manufacture that does not do this which I told you in great detail about Tesla putting 69 cells in parallel. Two requirements:

1. All cells shall be the same size like 20, 50 or whatever. Not a 100 in parallel with a 200.
2. Cells are in parallel in LADDER FASHION rather than stings in parallel.

[Living Large]

You must be like me getting old and forgetful. I have answered you every time in many post.

Paralleling lithium batteries is done as a matter of fact. You will not find a single EV manufacture that does not do this which I told you in great detail about Tesla putting 69 cells in parallel. Two requirements:

1. All cells shall be the same size like 20, 50 or whatever. Not a 100 in parallel with a 200.
2. Cells are in parallel in LADDER FASHION rather than stings in parallel.

I am getting old - guilty as charged. But I did understand they would be connected as you describe - like sizes and what you call ladder. We went over that a few days back.

What I am not understanding is the basis for the difference between paralleling LFP and FLA. My memory is I was advised to double capacity using parallel strings of FLA - say 8 cells of 6 V in parallel with another string of 8 cells of 6 V. But not more than 2 strings. I don't believe I came across the ladder until LFP.

Is there a reason for the difference (paralleling individual batteries in sets, and connecting the sets in series) ? Seems like it may possibly be rooted in full LFP cells not passing current.

[Sunking]

Is there a reason for the difference (paralleling individual batteries in sets, and connecting the sets in series) ? Seems like it may possibly be rooted in full LFP cells not passing current.

No not the current, Economics and Form Factor to the best of my knowledge.

Lithium requires BMS, and BMS gets costly. Example say a 48 volt battery requires 16 cells in series, and 16 control boards. If you used 2 series string and parallel them together would require 32 control boards.

Form Factor is just a matter of putting 10 pounds of chit in a 5 pound box. Example if you needed say 300 AH, they do make 300 AH cells, but you have very few options for the shaped of the box. By using smaller cell give you more option on the final shape to fit the application. No treal important in solar, but real important in EV's. That is why Tesla uses 6080 1 AH cells. It gave them the ability to make a rather odd shaped box to contain them.

EDIT NOTE:

I remember going to a Battery Conference about 3 years ago and attended a Lecture given by a peer who went over this very subject with respect to Lithium cells. As I stated above economics and form factor are two of the reasons. Anyway It took me a while but I found his slide presentation which will go over all the points. Don't forget to say Thank You, it took me an hour to find it. HERE YOU GO

[Living Large]

No not the current, Economics and Form Factor to the best of my knowledge.

Lithium requires BMS, and BMS gets costly. Example say a 48 volt battery requires 16 cells in series, and 16 control boards. If you used 2 series string and parallel them together would require 32 control boards.

Form Factor is just a matter of putting 10 pounds of chit in a 5 pound box. Example if you needed say 300 AH, they do make 300 AH cells, but you have very few options for the shaped of the box. By using smaller cell give you more option on the final shape to fit the application. No treal important in solar, but real important in EV's. That is why Tesla uses 6080 1 AH cells. It gave them the ability to make a rather odd shaped box to contain them.

EDIT NOTE:

I remember going to a Battery Conference about 3 years ago and attended a Lecture given by a peer who went over this very subject with respect to Lithium cells. As I stated above economics and form factor are two of the reasons. Anyway It took me a while but I found his slide presentation which will go over all the points. Don't forget to say Thank You, it took me an hour to find it. HERE YOU GO

Heh heh. THANK YOU. I haven't looked at it yet, but obviously you felt it is valuable. I'll check it out.

EDIT Interesting document, and analysis of what happens when a weak or bad cell is present. What is the significance of the short discharge times of LFP being the longest? Is this only relevant to the initial paralleling of the cells, and not a penalty one will pay on an ongoing basis? It looks like the author calculates the energy that will be lost when cells are initially connected. Is the point that the batteries are desired to be close to the same voltage, so as to not have a long period of current and heating that could damage the cells?

Good stuff - thanks again.

[Sunking]

What is the significance of the short discharge times of LFP being the longest?

I was hoping you would notice and ask that question. Remember the wirty dord Internal Resistance?

In theory if you were to short out a fully charged cell is how many seconds it would take to fully discharge the cell. The time is the result of the Ri.

Not something you have to worry about with Solar. Keep in mind that slide is for the EV industry. A EV engineer wants that line as SHORT as possible. It tells the Engineer the C-Rate capability of one battery up against another. The cheap Chi-Com batteries can only be discharge around 2 to 3 C continuously (5 to 10C pulse for 15 seconds) without significant voltage sag and over heating. Some of the higher end cells can deliver 10 to 20C continuously. For an EV you need those high discharge rates for acceleration. Example my golf cart is 100 AH with a 650 amp controller. I can pull up to 650 amps for 4 seconds from going from full stop to 50 mph. I cruise at 50 mph with 40 to 50 amps. Solar does not need the high C-Rates.

Drag Racers actually use the same LiPo batteries for RC planes, boats, cars, and trucks. You know expensive toys. Some of those can supply 100C discharge rate. You put 4 wheels,a seat, on a 250 KW 3-phase Induction Motor with a 1000 amp controller, 50 pound 400 volt 10 AH LiPo battery, and a switch. Throw the switch, hang on for dear life, hope you live through it for the 8 second ride, and the chute opens.

[Living Large]

I was hoping you would notice and ask that question. Remember the wirty dord Internal Resistance?

In theory if you were to short out a fully charged cell is how many seconds it would take to fully discharge the cell. The time is the result of the Ri.

Not something you have to worry about with Solar. Keep in mind that slide is for the EV industry. A EV engineer wants that line as SHORT as possible. It tells the Engineer the C-Rate capability of one battery up against another. The cheap Chi-Com batteries can only be discharge around 2 to 3 C continuously (5 to 10C pulse for 15 seconds) without significant voltage sag and over heating. Some of the higher end cells can deliver 10 to 20C continuously. For an EV you need those high discharge rates for acceleration. Example my golf cart is 100 AH with a 650 amp controller. I can pull up to 650 amps for 4 seconds from going from full stop to 50 mph. I cruise at 50 mph with 40 to 50 amps. Solar does not need the high C-Rates.

Drag Racers actually use the same LiPo batteries for RC planes, boats, cars, and trucks. You know expensive toys. Some of those can supply 100C discharge rate. You put 4 wheels,a seat, on a 250 KW 3-phase Induction Motor with a 1000 amp controller, 50 pound 400 volt 10 AH LiPo battery, and a switch. Throw the switch, hang on for dear life, hope you live through it for the 8 second ride, and the chute opens.

Ah-ha! That makes perfect sense. No, I did not remember this was tailored towards EV uses. Thanks!

[inetdog]

1.

Lithium Iron Phosphate , I thought the normal abbreviation was LiPo.

Lithium Iron Phosphate is most unambiguously abbreviated LiFePo4, shorter either LiFe (rare) or LFP (as in this thread title.)

LiPo stands for Lithium Polymer and refers more to the cell packaging than to the basic cell chemistry.

Lithium Phosphorus (which would just be LiP, not LiPo) is not a valid cell chemistry.

2. One reason that paralleling LiFePO₄ cells directly (ladder or not) is less problematic than doing same with FLA is the flatness of their voltage versus SOC curve in the useful region. The current moving between two batteries with a different SOC is directly proportional to the voltage difference and inversely proportional to 2 x Ri, the internal resistance of each battery.
So even though the LiFePO₄ may have a low Ri, the lower voltage difference helps keep the parallel batteries from sharing damaging current when first connected.