LFP battery chatter ( AKA LiFePo4, Lithium Iron Phosphate )

[Living Large]

Just pointing out how to go large. Honestly I forgot what AH you thinking about with LFP


Parallel LFP is no problem unlike FLA. Only difference is you use a Ladder Type configuration. In addition it cuts down on Cell Balance Boards. All commercial EV's parallel Lithium batteries.

I only have a few minutes, but I am checking in to click a few replies off the list and show I'm still following along. I still need to get back to your earlier long reply.

I had an idea you forgot my Ah needs. Doubling the Ah is a major change for multiple reasons, so the suggestion blew my mind. You may have mentioned a ladder configuration previously, and I forgot. I can look into it, if I decide I need to gain Ah by paralleling. Seems to me that things would get complicated as far as both balancing and shunting; the individual battery can't be assessed for measurement or accessed for balancing. But for the moment, I'm going to be satisfied with knowing that LFPs are commonly paralleled.

[Living Large]

Great and it should work out great. Commercial 48 volt LFP LVD operate at 2.9 vpc, so a set point of 46.4 volt is in that range. They also have switch selectable delay times just for that purpose. but unless you are discharging in excess of 1C, Ri of LFP is so low voltage sag is not much of an issue in a solar application. Not so with EV's high current demands of 5 to 10C



Great as that gives you another LVD option using an external BMS.



Options and more options to work with. All this means is you can do LVD externally, or internally on your Inverter. You gotta figure out which way is best for you. All I can do is consult and call out the Pro's and Cons allowing you to make an informed decision. I am not making a penny off you and unlike a salesman I am not going to push the more expensive options influenced by a commission. However I would never turn down a check for helping.

OK, super. Since you earlier suggested that inverters may have a fixed threshold for Pb (you suggested a manufacturer might alter it if it is fixed), I wanted to bounce this off of you. Sounds like there is more than one way this particular inverter can implement LVD to work with LFP - great! I don't expect people to be familiar with all the models out there, but I didn't know if this "LCBO" was the same level of disconnect as what I need (I have seen standalone disconnects). It sounds like it is, and whatever power the XW draws is negligible enough to not kill the batteries before I respond to the emergency low V situation. Super - no wet washcloth yet on this plan. I'd just go with #1, set the settings, and done.

[Living Large]

The XW's internal, programmable LVD should work fine. The logic circuits DO stay alive, that's how it knows how to count time to attempt a restart. But the logic circuits don't pull much power. If you get the ComBox with the XW, you have some AUX commands & outputs you can trigger an audio alarm or a generator start module. With the XW, you need either a dumb SCP or smart ComBox. I strongly recommend the combox

Thanks Mike. I suppose the amount of power for the XW with inverter off is negligible compared to a 200 or 300W load. Point is, I shouldn't be off on a vacation when this condition occurs, so I should be able to respond to a LV event before the parasitic load (in the case of a LVD event) of the logic circuits causes damage. I'm seeing "no-load" current of 26W, which seems like the inverter might be on, and "Search" power of <8W. Don't know if either of these would apply after the LCBO is triggered. In any event, both you and Sunking say the LCBO of the XW will satisfy the need for the LVD, and that's good enough for me.

Yup, you've mentioned the ComBox multiple times now, and I jotted it down your strong recommendation. The first time you mentioned it, I had already read about it and the other options and wasn't sure which I would want for me needs. I may have some questions about it versus other options - and I'll ask you here if I do. It involves imagining what monitoring and control capabilities will be required. I know it has the gen controller, and the display interface as one option. Currently, my configuration is two XW MPPT 60 150 and a XW 5448, about 4900W of PV, 400 Ah LFP, and I am still leaning towards the Ecogen. I think I am pretty close to done, without giving this to a consultant to refine and/or bless. Actually, I may turn next back to the interface (ComBox, etc) now that these other matters are coming to fruition.

[Living Large]

OK we still have a little Tweaking to do.

1. It is a MUST HAVE a CC that you can use a laptop, PC, inertnet or someway of programming set point voltages to at least 1/10 a volt like 58.4 volts for all stages. No switches to to select Gel, FLA or AGM. You are going to need to fine tune.

2. IMO Balance Boards are not optional as they are too important. PNJunction will disagree with me, but I stand my ground. They will do two very important functions for you. One is give you visual indication when the cells are getting out of Balance. Otherwise you are going to have to get a DMM out constantly and check. More so then with Balance Boards. Second and this is a big one. Without them to balance the cells is going to require you to take the string apart and balance each cell individually and that will takes many days.

Look if you go with LFP you are talking what in terms of money? $10,000? Balance boards are around $15 each and you need 16 of them for a total of around $250. That is a deal of the century for the insurance and convenience your are going to get and will allow you to sleep at night. Ever watch Shark Tank. I am like Kevin and do not want to go to bed at night worrying about my investments. I am out. Let PNJunction loose sleep.

3. Correct a MUST HAVE hardware.

I understood about the CC needing to be programmable - I am planning for two (2) XW MPPT 60 150, and it will do what you say. I haven't kept mentioning it, because I know I plan to use it. But I do understand I need the fine level of programmability. I'm on board!

I am not leaning against balance boards. I only mentioned optional because you stated they are optional, but good insurance. I heard you - and as I have stated, I plan to use them. I may not carry collision insurance on my cars, but I do carry comprehensive. I don't mind taking some risk, but I'm not foolhardy. I'm on board!

I am going to answer all three question in one reply because they are all related.

Initially when you receive the batteries you are going to fully charge each cell. It is a PIA to do and takes a few day or a week. Example a hobby charger set up to charge four at a time. The hobby chargers have built in BMS but you will need a interface cable which is just a simple plug with 5 wires that connect to each cell. So a 1000 watt hobby charger set up for 4S will deliver 60 amps. Do the math on a 800 AH battery. Fortunately they come from the factory at Storage Voltage of roughly 60% SOC. Once you get them all charged up life is easy.

A cell Balance Board is roughly a .5 to .7 amp shunt. Sounds low I know. Once you do the initial Balance, the cells will unbalance so dang slowly the shunt will be plenty fast to keep them balanced even when you are charging at full current. As long as you don't have a cell with an internal short, it shouldn't get far enough out of balance to ever get beyond the shunt's ability. If your pack can't regularly maintain close enough balance so that the shunt can keep up with it, you have bigger problems than just choice of BMS.

Now for some other news. One of my Australian friend I know from another EV forum told me another route you might be interested in. We were discussing your situation. I only have about 4 months experience with a real LFP system in my golf cart, and he has years as a manufacture of BMS systems. He has suggested a true BMS system he sells and makes. In addition to the cell Balance Boards is a BMU. Total cost of around $550 USD. Listen up because it is a good idea and a streamlined BMS without the FuFu.

It is a single BOX with 16 Cell Balance Boards, and a real Fuel Gauge. The Balance boards do communicate over a single pair serial cable so no rats nest. Here is the beauty of it. It interfaces with any Solar Charge Controller and LFP battery up to 80 amps with built in LVD. It has 3 DC Power Ports. One for the CC, Battery, and Load. The port for the CC can be any charger type, makes no difference as long as it is a 3-stage charger which any good Solar CC is. It will used the Bulk and Absorption stages.

Check this out. Here is the company website.

I understand initial setup (balancing) will be its own special animal, but since I have your time and advice, I'd like to focus on ongoing operations. What happens when the batteries do get out of balance - even though it happens slowly, we know it will happen. The BMS will shunt to take care of small imbalances, but what happens and is done to correct larger imbalances that develop slowly?

I had no idea the shunt we are speaking of is only 0.5 to 0.7 amps. I believe that means is a very small percentage, maybe less than 1%, of the the current is being shunted around an individual battery - and this is enough to do what is needed. Interesting!

A real fuel gauge is something I have seen mention of - that would be great. The 80 amps catches my eye, because I am hoping to be able to push 100 from the PV or generator - but let's not get hung up on that right now. I note that these boards evidently talk to each other, which I thought you said doesn't normally happen with a passive system.

I still don't understand how I will do the balancing that will take place every month or two, or however long it takes for a significant imbalance to develop. Am I going to have to take the system down, and do something with each individual battery? What equipment will be needed? Thanks!

EDITOK, I looked at the links. The system in the first link is 12/24V, maybe they do 48V. Now, the company website appears to advertise the product does exactly what I am asking about - the longer term balance. Whether it does it gradually, or when it decides it is needed. If this is true, I guess I'd like you to assume I don't have this particular system in case I can't use it. I saw a video where in a series string that got out of balance, a device connected to a car battery was used to discharge individual cells one by one so they all had the same resting voltage. Something like that. In the absence of a smart device like the one you mentioned above, does this sound like what I might need for this periodic rebalance?

[Sunking]

I understand initial setup (balancing) will be its own special animal, but since I have your time and advice, I'd like to focus on ongoing operations. What happens when the batteries do get out of balance - even though it happens slowly, we know it will happen. The BMS will shunt to take care of small imbalances, but what happens and is done to correct larger imbalances that develop slowly?

I had no idea the shunt we are speaking of is only 0.5 to 0.7 amps. I believe that means is a very small percentage, maybe less than 1%, of the the current is being shunted around an individual battery - and this is enough to do what is needed. Interesting!

Did you catch this part back in post 35?

Once you do the initial Balance, the cells will unbalance so dang slowly the shunt will be plenty fast to keep them balanced even when you are charging at full current. As long as you don't have a cell with an internal short, it shouldn't get far enough out of balance to ever get beyond the shunt's ability. If your pack can't regularly maintain close enough balance so that the shunt can keep up with it, you have bigger problems than just choice of BMS.

Here is the deal. When you go to buy say a 48 volt 400 AH LFP, they are going to come with BMS as the manufactures require them for warranty. If you go to one of the site, make a dry run on ordering. You should get a lot of drop down boxes for number of cells, balance board types, upgrade, BMU, blah,blah... You want a LVD with that burger Sir? How about a 40 amp charger vs the 20 amp one the batteries come with? You get the idea.

[Sunking]

Dmm

One thing I think I should point out. Since you are a Train Driver you might already have a good DMM, but if not include that into your budget. I am not talking about a $20 special at Harbor Fright. I am talking about a good 4-1/2 digit Fluke or like quality meter. With Pb the discharge curve is steep from 2.2 vpc @ 100% SOC down to 1.75 vpc @ 0% SOC. LFP is very very flat from 3.3 to 3.0. Example at rest 100% SOC = 3.345, 80% = 3.339, 50% = 3.305. Very few meters can read those voltages. 10 mv for Pb is few percentage point. 10 mv for LFP is up around 10 to 20% difference depending on where you are at on the curve. Good thing with being so flat it becomes fairly linear from 90% down to 20% where 1 mv = 1%

[Mike90250]

Currently, my configuration is two XW MPPT 60 150 and a XW 5448, about 4900W of PV,

2 things. 1) why the XW5448 , is the XW6048 no longer being made ? 2) The Combox is remote controllable via password and web interface, I just have it plugged into a wireless router ($30) and view it via wifi. The combox should let you set all the charge settings on the MPPT's to whatever you need. And it has a great graphic display of what is happening with everything, and many options for custom logging for daily .CSV logs

The SCP you have to stand in front of, and push buttons many many times. Enter. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. 49.2V Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. 51.3V Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. get it ? Combox, well worth the extra bux.

The SCP is a dumb box. BUT you don't NEED a computer to control it. The Combox will do firmware updates.

[Living Large]

Did you catch this part back in post 35?

"Once you do the initial Balance, the cells will unbalance so dang slowly the shunt will be plenty fast to keep them balanced even when you are charging at full current. As long as you don't have a cell with an internal short, it shouldn't get far enough out of balance to ever get beyond the shunt's ability. If your pack can't regularly maintain close enough balance so that the shunt can keep up with it, you have bigger problems than just choice of BMS."

[/FONT][/COLOR]Here is the deal. When you go to buy say a 48 volt 400 AH LFP, they are going to come with BMS as the manufactures require them for warranty. If you go to one of the site, make a dry run on ordering. You should get a lot of drop down boxes for number of cells, balance board types, upgrade, BMU, blah,blah... You want a LVD with that burger Sir? How about a 40 amp charger vs the 20 amp one the batteries come with? You get the idea.

I did NOT understand that a passive shorting BMS will keep the batteries in balance (assuming one or more isn't defective), as long as the important initial balance is done. That appears to be what you are saying. I missed that. My thought would have been there is a chance that in cycling, there wouldn't be enough "rebalanciing" (as a result of shunting) during the charge cycles and cells could slowly wander.

It turns out the video I watched is an example of bottom balancing of an EV bank, not top balancing, which is what the initial balancing you describe appears to be.

There seems to be a debate out there about passive vs active BMS, and choice of BMS depending on energy storage application.

I didn't realize that resellers will force me to buy a BMS, but it isn't surprising because they say you have to have one. The only ones I went through the initial steps on were overseas, so the process stops abruptly when they ask you to send for a quote. I'll check out some domestic resellers, and see what options there are. I saw on one that the BMS appeared be made up of an insane number of components - there was picture with like 12 different items.

[Living Large]

One thing I think I should point out. Since you are a Train Driver you might already have a good DMM, but if not include that into your budget. I am not talking about a $20 special at Harbor Fright. I am talking about a good 4-1/2 digit Fluke or like quality meter. With Pb the discharge curve is steep from 2.2 vpc @ 100% SOC down to 1.75 vpc @ 0% SOC. LFP is very very flat from 3.3 to 3.0. Example at rest 100% SOC = 3.345, 80% = 3.339, 50% = 3.305. Very few meters can read those voltages. 10 mv for Pb is few percentage point. 10 mv for LFP is up around 10 to 20% difference depending on where you are at on the curve. Good thing with being so flat it becomes fairly linear from 90% down to 20% where 1 mv = 1%

Yeah, I won't be able to use dad's Triplett from the 1950's. I have a Fluke 26III, which I think will work.

This is a great warning. In the video I mentioned, where 60 CALB 180Ah batteries are in series in an EV, the guy pointed this out. He compared the reading on the PowerLab8 charge/discharge device he was using with a cheapo DMM. They differed by .05V. He pointed out that in the heart of the curve, you might be able to use either for balancing, as long as you used the same one for all your readings.

[Living Large]

2 things. 1) why the XW5448 , is the XW6048 no longer being made ? 2) The Combox is remote controllable via password and web interface, I just have it plugged into a wireless router ($30) and view it via wifi. The combox should let you set all the charge settings on the MPPT's to whatever you need. And it has a great graphic display of what is happening with everything, and many options for custom logging for daily .CSV logs

The SCP you have to stand in front of, and push buttons many many times. Enter. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. 49.2V Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. 51.3V Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. Up arrow. get it ? Combox, well worth the extra bux.

The SCP is a dumb box. BUT you don't NEED a computer to control it. The Combox will do firmware updates.

Ok Mike I get it - get the ComBox! I'll add it to the budget. One question - doesn't the SCP (which I won't be buying ) allow you to set the charge settings? I believe Schneider told me those are synched on the bus between the XW and MPPT. Maybe that is just thresholds, and not modes.

Can you tell me why I would choose the 6048 over the 5548 (I misspoke it isn't "5448")? Future expansion? I believe both are current - they dropped the 4548. As you know, I'm a newbie - the 6048 looked like overkill to me, though I believe one of the installers I spoke with recommended this upgrade also.

[Sunking]

I have a Fluke 26III, which I think will work.

Yep that will work on the 4 volt range. Perfect.

[Living Large]

Bms

OK, I think I have enough to pursue BMS further, Sunking. I need to stop bothering you, and do some research. I found one good thread, which appears to be people primarily using small banks of LFP for sailing.

http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

There is something like 217 pages to this one thread, and on the first there are already several posts that are informative (eg "I bought 4 400Ah batteries, did an initial balance using this technique, here are the voltages, what does this mean and what should I do now?") I need to wade through threads like this to get more of an understanding.

I really appreciate the advice you have given me, and who knows, perhaps some members/lurkers here will consider becoming converts in the future. I feel good about the possibility of using LFP in a solar system. Thanks!

[Sunking]

OK, I think I have enough to pursue BMS further, Sunking. I need to stop bothering you, and do some research.

No bother at all. I am happy to help those willing to help themselves and know what they are getting themselves into. Normally I would not even touch LFP for solar because as you have discovered it is very expensive and just one ignorant mistake you have a very expensive boat anchor. Lithium is just not ready for solar as evident by no equipment made for lithium on the solar side. Today lithium is for power tools, laptops, and EV's. Solar is down the road a ways for John Doe consumer. You had better know WTF you are doing to go solar with lithium and know how to work around the equipment issues. You got that now and I am happy to assist you in your journey. I am even learning something I can take and put into application.

Just keep researching and asking questions until you are comfortable before making the investment.

[Living Large]

No bother at all. I am happy to help those willing to help themselves and know what they are getting themselves into. Normally I would not even touch LFP for solar because as you have discovered it is very expensive and just one ignorant mistake you have a very expensive boat anchor. Lithium is just not ready for solar as evident by no equipment made for lithium on the solar side. Today lithium is for power tools, laptops, and EV's. Solar is down the road a ways for John Doe consumer. You had better know WTF you are doing to go solar with lithium and know how to work around the equipment issues. You got that now and I am happy to assist you in your journey. I am even learning something I can take and put into application.

Just keep researching and asking questions until you are comfortable before making the investment.

I'm curious - what obstacles do you see? Is it just a case of economics at this point - too high a cost of the storage system to justify adapting charge equipment to accommodate it? The chemistry appears to be proven.

It appears LVD is not a big issue, as it can be handled with some current equipment and easily added to others. It seems like the obvious missing piece is integral BMS. Are there any hurdles like requiring the MPPT and inverter/charger to talk to each other? I haven't found any yet that do. Xantrex shares parameters, but that is about it. Making the battery status available on the user interface would obviously be a big improvement. I assume if I look hard enough, I may find a current standalone solution for that. Would you want the charger/inverter together with the MPPT controlling shunting? That is probably a yes.

PV power appears to be pretty much hands-on. The current gold standard appears to be FLA, unless I have that wrong. There is quite a bit of work involved in that. It seems like the principal hurdle for LFP is cost. I'm now babbling. Interested in any thoughts.

[Sunking]

I'm curious - what obstacles do you see? Is it just a case of economics at this point - too high a cost of the storage system to justify adapting charge equipment to accommodate it? The chemistry appears to be proven.

You got it all right except for the proven part. Lithium batteries are still early in the developing stages and have a long way to go. Exxon in the mid 70's and were extremely dangerous and self ignite in the presence of oxygen and water. It took until 1991 for scientist worked out a formula that was safe enough for consumer use and the first commercial release. If you remember correctly it did not go well as many fires were reported. It almost bankrupt Micheal Dell.

In 1996 Lithium Iron Phosphate was discovered by Akshaya Padhi. Soon after Yet-Ming Chiang of MIT refined the process and first commercial release of LFP soon after in 2003 from A123 Systems. So LFP is still very young and has not lived up to its promises. Every one of the first LFP manufactures has gone bankrupt as a result of the product not meeting the claims of cycle life of 2000 to 3000 cycles. All the ones you see are 2nd and 3rd attempts from defunct bankruptcies. One example Thundersky went bankrupt, sold off to two other companies called Winston and Sinopoly. Calb the most trusted of the bunch was fulsomely Sky Energy. Calb in 9 short years is now on its 4th generation. As of now none of the LFP's have been on the market long enough to prove themselves with the test of time. Just ask Nissan Leaf owners about problems they are having and Nissan's troubles.

From equipment POV, it is just the market at work. Technically making chargers, BMS, Inverters, and all the other equipment we have already have mature technology to make lithium work. There is just no demand for it yet until Lithium cost become competitive and lithium proves itself from pioneers like you giving it a chance. It is the exact same reason EV's are not mainstream because Lithium technology is not ready. DIY EV's use LFP because they are the most safe, easiest to deal with, and most importantly th eleast expensive with longest cycle life. But LFP is not used in commercial pure EV's because its energy density is too low. Unfortunately today to get the required density for commercial EV's means using unstable formulations requiring a high degree of management and short cycle life.

Rumors are running wild that Panasonic has developed a LiPo that is cheap to manufacture, high power density, stable, and long cycle life and those rights have been sold to Tesla Motors and is building a factory to build them in NV. Have to wait and see. Exon Mobile is also suppose to have one getting ready to release for commercial production.

What I do know is is the first company that can manufacture a battery that has:

300+ wh/Kg
5C min Charge/Discharge rates
4000 cycles at 90% DOD to 80% capacity
Operating temps from -20 to 150 F
30to 50-cents/wh retail

Will become the largest company in the world and can afford to buy their own country of their choice including the good ole USA. No one could stop them.