LFP battery chatter ( AKA LiFePo4, Lithium Iron Phosphate )

[Living Large]

{snip}

FWIW I would not buy Balqun. Just too many ifs for my comfort. CALB is best bang for the buck and has a good track record. I cannot answer about Balqun as I or anybody I know has any experience with them. My first choice is GBS followed by Calb. GBS is a little higher in cost, but offers slightly better performance, and a better mechanical package.

Hope that helps.

After looking around for a bit of time, I've arrived at a few solutions. The first thing that became apparent, is there doesn't appear to be a large selection for my use. I was looking at a 700Ah+/- need with FLA. I found 400Ah and 500Ah LFP cells. CALB for the 400Ah (and another manufacturer I can't remember the name of) and Sinopoly for the 500Ah. The Sinopoly discharge curve was not as flat as all the other curves I have seen, but worse I don't believe there is a US distributor. There are reports of people having some shipped, but I didn't see an order of the size I am looking at, and I guess I am a bit uncomfortable making such a large purchase so remotely, and what if there is a problem. My guess is many people do buy direct, but I'm not sure I want to with this purchase.

CALB looks like a fine product, and they have a US distributor. It's about $500-550 depending on which of two varieties you choose. I didn't find a GBS battery over 200Ah.

While the 400Ah is a little smaller than I was thinking, it may be sufficient. Unless I am missing something, with this reduced capacity, I can charge faster, and maybe run the generator only 4 hours. This is a plus - I wasn't looking forward to it running 6-8 hours with the FLA bank. Plus while charging with the gen, I can bathe and run the pump to replenish a large holding tank - taking a good part of my usage off the batteries for that first day. So I may make 3 day intervals when cloudy. The pump consumption is included in my planned daily usage.

EditThe CALB battery "standard" charge current is 0.3C. I would be a little lower than this - around 100A+/- each, from the PV or generator.

[Sunking]

My apologies for hijacking the thread this discussion was in.

Don't worry about it, it was a dead end thread going no where

I was not specific enough. I had seen that you should initially balance them before use (and I have seen multiple methods of doing that), but my question has to do with ongoing operations. What I meant was, how will I know things have become unbalanced, and what role do "Balance Boards" play in either detection (monitoring) and/or manually correcting an imbalance that develops? Seems like at the extreme, one could disassemble the entire bank, and start over with the initial procedure. But who wants to do that. Can you give me an idea of what the balance boards actually do dynamically.

The Balance boards will give you a clue, and your volt meter will confirm it. You will start noticing one, two, or three Balance Boards will light up long before any of the others. When ther light comes on the cell is full and the Balance Board is in Bypass. Unlike Pb LFP cannot be equalized as they stop passing current when fully charged up so they have to be Bypassed. Understand?

To balance the cells, you use the Balance Boards by applying a low current charge until all Balance Boards light up. That is one of the Big differences between Active and Passive BMS. An Active BMS actually takes energy from higher cells and gives it to lower cells continuously. A Passive system is a Bleeder aka Shunt that bypasses the full cells. Active systems takes Smarts and Communications with all other cells and the charger. Passive is just an inexpensive dumb circuit board unitasker taking care of it one lonely cell and knows nothing else.

Think of it this way. The Balance Boards make LFP behave like Pb when being EQ'd. A Pb cell still passes current when fully charged to allow lower cells to keep charging. A LFP cell quits passing current when fully charged.

[Sunking]

Thanks for all the info on LFP's Sunking! Fortunately, I don't need replacement batteries for a while. Definitely will consider these in the future.

Sure about that? From you rother thread sounds like you already need a replacement.

[Living Large]

{snip}
A4. No the LVD is not part of the of the CC, charger, or inverter. It is a stand alone system. This is one of those things you have to work around because there are no CC or inverters that I know designed to work with lithium. All Inverters and charge controllers are designed to interface with Pb.{snip}

Don't freak out, it can be dealt with in one of two ways.

1. Purchase a LVD from who ever you buy the batteries from. The LVD gets installed between the batteries and inverter or load. They are nothing more than a high current relay switch with a voltage sense circuit to operate the relay at the voltage set point.

2. This one I am unsure of but know it can be done. Use the Inverters built in LVD by making your own sense circuit to replace the Inverters circuit, or modify the inverters internal LVD circuit. This would void the Inverter warranty. What I would do if I were you is contact the Inverter manufacture and ask them if they can do it for you at an added cost.
{snip}

OK, what I am hearing is that the LVD is built into many inverter/chargers, however here we have one of the current incompatibilities in technologies - that the voltage threshold is fixed, and designed for Pb. Being an EE, I would lean towards modifying the built in detection circuit. Why add complexity, and another device in series with the power source? And I do see this wouldn't be part of the CC.

Excellent suggestion to contact manufacturers before backwards engineering, breaking out the soldering iron, and voiding the warranty. Sounds like LVD is done on the entire bank voltage, and not the individual cells. Seems like potentially one cell may dip below the death threshold, and not trip the LVD. But the assumption is someone (me) is monitoring regularly to detect a trend, and the cells will generally track together. Thanks again. Very useful info!

[Living Large]

My apologies for hijacking the thread this discussion was in.

{snip}
A3. Very first thing you do when you receive the cells is to fully charge each cell individually. One of those PIA things with Lithium. Best way to do that is with a hobby RC charger. Or you can use a standard 48 volt battery charger and the Balance Boards, after you see the first Balance board turn on, you gotta reduce current to match the Balance Board current capacity, then it goes slow from there.
{snip}

I was not specific enough. I had seen that you should initially balance them before use (and I have seen multiple methods of doing that), but my question has to do with ongoing operations. What I meant was, how will I know things have become unbalanced, and what role do "Balance Boards" play in either detection (monitoring) and/or manually correcting an imbalance that develops? Seems like at the extreme, one could disassemble the entire bank, and start over with the initial procedure. But who wants to do that. Can you give me an idea of what the balance boards actually do dynamically - I assume they are principally for ongoing use, not initial setup.

I will look at the LVD comments separately, and I'm sure I'll have a question or two. Thanks for this info!

[northerner]

Thanks for all the info on LFP's Sunking! Fortunately, I don't need replacement batteries for a while. Definitely will consider these in the future.

[Sunking]

1. Choose a CC (and I assume inverter/charger) with software programmable thresholds
2. Passive BMS is all that is needed, but optional if I monitor the operation (charging V, I assume) regularly. The cost you mentioned is about what I was hoping it would be - small premium over battery cost - I would probably opt for this. But sounds like if I regularly monitor the cells, I will see when one or more is getting out whack - and at this point I would rebalance to bring things back to a par.
3. Balancing occasionally is needed, and Battery Balance Boards are cheap "insurance".
4. A LVD is a must.

Looks like Mike moved the thread. Thanks Mike.

Yes to all 4 summaries.

Questions:
#3 - I have no clue, sitting here right now, what "balancing" will entail. What I *know* is I plan for 16 cells in series (48V), and I *believe* some of them may charge faster than others which I an guessing is when I may want to balance. My question is, would "Battery Balance Boards" help *identify* the imbalance and/or assist in the balancing procedure, and in what manner would they provide "insurance"?
#4 - I saw someone somewhere say that the LVD might be a function of the CC and/or charger/inverter. Not so under most cases? (recall I am looking at Schneider MPPT 60 or 80 and XW). How would a LVD be added as an option if it is a separate box, and whose command would cause it to open?

A3. Very first thing you do when you receive the cells is to fully charge each cell individually. One of those PIA things with Lithium. Best way to do that is with a hobby RC charger. Or you can use a standard 48 volt battery charger and the Balance Boards, after you see the first Balance board turn on, you gotta reduce current to match the Balance Board current capacity, then it goes slow from there.

A4. No the LVD is not part of the of the CC, charger, or inverter. It is a stand alone system. This is one of those things you have to work around because there are no CC or inverters that I know designed to work with lithium. All Inverters and charge controllers are designed to interface with Pb. Example most all inverters, any worth having anyway, have a LVD built in. However on a 48 volt inverter the trigger voltage is 42 voltswn. You can only take a 48 volt lithium down to 48 volts. Go below that and you would turn it into a brick. Remember lithium discharge curve is very flat unlike Pb. Technically the cut-off voltage for lithium is 2.5 volts but from 3 volts to 2.5 volts is on the edge of the cliff with only 5% remaining. You do not want to flirt with that last 5% of capacity. Take a look at the chart below and note that knee curve that happens at 3 volts. It is a sharp knee and the slope of death. So don't cross that line.

Don't freak out, it can be dealt with in one of two ways.

1. Purchase a LVD from who ever you buy the batteries from. The LVD gets installed between the batteries and inverter or load. They are nothing more than a high current relay switch with a voltage sense circuit to operate the relay at the voltage set point.

2. This one I am unsrue of but know it can be done. Use the Inverters built in LVD by making your own sense circuit to replace the Inverters circuit, or modify the inverters internal LVD circuit. This would void the Inverter warranty. What I would do if I were you is contact the Inverter manufacture and ask them if they can do it for you at an added cost.

EDIT NOTE: Go read this short article on LFP charging. It will put you at ease

So it can be done and is fairly easy.

[Sunking]

Tell you what. We hijacked this tread. I think a lot of folks would like to hear more about LFP but would be lost in this thread. So copy and paste your last reply and start a new thread OK? I will answer in the new thread OK? I bet if you asked Dave, Mike, or Russ they might cut out the LFP stuff from here and move to your new thread. Drop them a PM if you want. I would do it but cannot.

[Sunking]

Tell you what. We hijacked the thread. Info I am sharing would be useful to others and lost in this thread. So copy and paste your last reply into a new thread and I will answer there OK?

---Mod note: for some reason this post was held for moderation.

[Living Large]

{large snip}

Only thing you have to worry about is over discharging. Like all Lithium you can turn them into a brick with just one over discharge. Easy fix, use a LVD problem solved.

{snip}

Thank you for this extensive reply. A lot of what you have offered is along the lines of what I was seeing, but you have pointed out places where I was seeing something that pertains to EV, and not a PV system. Not surprising, given these LFP's primary application. And as you can see, I am in the process of pushing past HomePower's article as we speak.

Your comments agree with what I saw elsewhere - stay away from the extremes of the discharge curve to avoid problems (creating imbalance). The balance will be retained over long periods of time if operated this way. As for temperature, I had seen a comment somewhere, possibly CC specific, that said the user might get away with choosing from one of 3 temperature "settings" based on season.

So you are recommending specific things for my app, which is exactly what I was hoping for (thanks again). I have a few questions about them, but before I go there, let me say I have no problem at all taking my Fluke and checking each cell regularly. Easier than checking SG, and hey I'll need something to do where I can keep my hands clean. Yes, I am looking at prismatic. Also, this will be in a basement at 50 deg or more, and I did look at the curves and noticed the behavior at colder temperatures which won't be an issue. OK. Let's see if I have your suggestions right:

1. Choose a CC (and I assume inverter/charger) with software programmable thresholds
2. Passive BMS is all that is needed, but optional if I monitor the operation (charging V, I assume) regularly. The cost you mentioned is about what I was hoping it would be - small premium over battery cost - I would probably opt for this. But sounds like if I regularly monitor the cells, I will see when one or more is getting out whack - and at this point I would rebalance to bring things back to a par.
3. Balancing occasionally is needed, and Battery Balance Boards are cheap "insurance".
4. A LVD is a must.

Questions:
#3 - I have no clue, sitting here right now, what "balancing" will entail. What I *know* is I plan for 16 cells in series (48V), and I *believe* some of them may charge faster than others which I an guessing is when I may want to balance. My question is, would "Battery Balance Boards" help *identify* the imbalance and/or assist in the balancing procedure, and in what manner would they provide "insurance"?
#4 - I saw someone somewhere say that the LVD might be a function of the CC and/or charger/inverter. Not so under most cases? (recall I am looking at Schneider MPPT 60 or 80 and XW). How would a LVD be added as an option if it is a separate box, and whose command would cause it to open?

Thanks again! I'm kinda psyched about this battery until someone pulls out a wet washcloth.

[Sunking]

I had seen a March 2013 article (http://www.homepower.com/articles/so...s-grid-systems) that I scanned, and rejected LFP after reading. Note on the third page there is this statement: "At present, the lack of BMS integration in residential RE power conversion equipment is the biggest hurdle" [to adoption of LFP in off grid RE applications]. To me, this is the only negative for my application, unless I have missed something. So far, the cost I have estimated to be the same or less than a quality FLA solution. (400Ah vs 700Ah)




There seems to be continued debate whether the MPPT and/or inverter/charger need to either have a BMS integrated, or be capable of receiving status from the BMS for disconnecting under abnormal conditions detected at the individual cell level. Some believe the MPPT and inverter/charger can be totally independent, and others like the author of the 1-1/2 year old article believe the opposite. There are articles from 2014 that continue to say BMS must be integrated into the charging device. The question appears to not be one of what happens in normal operation, but in cases of operating outside each individual battery's safe envelope - LVD and HVD for example. I have seen mention of a very small selection of charge controllers and inverter/chargers that may incorporate LFP-friendly features.

OK LivingLarge my comments are directed at Home Power Magazine, not you so don't take offense.

Ignore most of the articles you read on Home Power Magazine. Most of the articles are written by users who really do not know what they are talking about. Most of there so called experts only know enough to be dangerous, and this article is one of them and I am going to tear it apart.

To start the author of the article does not know a lot about lithium batteries. The reason I say this is because he/she lumps all lithium batteries into a single basket, well I guess three baskets by stating the 3 types are Pouch, Prismatic, and Cylindrical. That is just plain ole everyday ignorance. Those are not types, those a cases used to contain the battery. I have lost count on how many types there are, but the type has to do with the chemistry not the case that contains it. There are dozens of types and the most notable are Lithium Cobalt, Lithium Manganese, and Lithium Iron Phosphate. EV manufactures use the higher energy density types like Lithium Cobalt and Lithium Manganese. Lithium Cobalt and to some extent Lithium Manganese are the bad boys that get all the negative press of catching fire and do require Active BMS with Thermal Management. Enough of that and lets stick with Lithium Iron Phosphate aka LFP.

LFP comes primarily in two package types of Prismatic and Cylindrical. Prismatic are the Chi-Coms, the ones that look like Building Blocks in an assortment of colors. The Cylindrical are the Cadillac of the bunch made by A123 Systems which there is no point for me to discuss at this time because of the expense. All I will say about them is they are the have very high charge/discharge rate units that is not needed in most applications except power tools thus justifying their $2/wh cost. We want to use the $0.40/wh prismatic cells with a lower discharge rate of 2 to 3C which is still overkill for Solar. We don't need 10C rates of LFP Cylindrical cells and the high price tag. With me so far?

OK the Prismatic Chi-Com LFP units have some great advantages over all the other Lithium chemistry:

• Compatible cell voltage of 3.2 vpc nominal. A 4S configuration yields 12.8 voltage compared to Lead Acid 12.6 volts. Note what Home Power said they were incompatible. That comes from lumping all Lithium into a single basket as nominal voltage of all other Lithium is 3.7 vpc which would be a problem. Home Power missed that point. LFP is completely compatible with Lead Acid (Pb) applications along with identical charging algorithm of Constant Voltage with one minor change I will talk about shortly.
• Very Stable and Forgiving crystalline structure of Iron Phosphate. It is impossible for LFP to go into Thermal Runaway thus eliminating the need for any Thermal Management. Having Thermal Management would be a complete waste of money. Only thing you need to do thermally is try to install them where they can stay warm. Home Power really showed their ignorance when they stated LFP has better cold tolerance than Pb. Exact opposite is true. LFP and all Lithium batteries loose significant capacity when the get cold below freezing. Is it a problem? Not IMO because it is about the same with Pb so nothing lost or gained. Warm them up with a good load or charge current and they fix themselves.
• Longest Cycle Life of all the Lithium chemistry. 2000 cycles typical to 100% DOD. Limit to 90% SOC, and 90% DOD and you can double the cycle life to 4000 cycles. That is real easy to accomplish which I will talk about later.
• Very flat discharge curve. At 100% SOC voltage = 3.33 volts (4S = 13.32) and at 100% DOD = 3.0 volts (4S = 12.0). Compare that to Pb 100% SOC = 2.2 (12.6 volts) to 100% DOD = 1.75 (10.5 volts).
• Least expensive of Lithium @ 40-cents per watt hour. Compare to 18 to 22-cents of Pb

Can you use Lithium on solar today? Yes you can if you understand the differences and what to look for in charge controllers and add one or two pieces of equipment available from all LFP distributors. One is a must a LVD (low voltage disconnect). The other is optional of a PASSIVE BMS. The other caveat is the expense. Are you willing to pay for it?

How to make it work. Select a CC that has programmable voltage set points. Not selector switches. You want to set the FLOAT either at or just below 100% SOC. Preferable just below 100% to extend battery life, and eliminate the need for BMS. Catch that? You do not need BMS if you understand what is going on. There are two types of BMS. Passive and Active. Active is expensive, complicated and requires communication with the charger and each cell. Active is what EV’s need to pump every Amp Hour into every cell to get maximum range out of each charge. Active systems take energy from higher cells and transfer it to lower cells. Complete waste of money in a solar system.

If you are going to use BMS on solar it will be Passive. All Passive is just a dumb circuit board that is attached to each cell and Bleeds or Shunts Current around a fully charged cell to pass the current to lower cells. They do not talk to each other or the charger. They are either On or Off. When you charge and a cell reaches a voltage set point they turn on and bypass the cell. When the charging stops they turn off. They cost anywhere from $5 to $20 depending on the AH capacity of the cell. On a 48 volt battery requires 16 of them.

LFP is very forgiving to over charge and go to as high as 4.0 vpc without significant stress. Recommended charging voltage is 3.6 vpc so you got a lot of room for error. So if you set the charging voltage to 3.6 vpc no BMS is needed period. If you do not run a BMS wil require some manual monitoring and PM on your part. After many cycles the cells will become unbalanced requiring you to manually monitor them and balance periodically. No big deal if you know what to look for. Personally I recommend the Passive Balance Boards as cheap insurance.

Only thing you have to worry about is over discharging. Like all Lithium you can turn them into a brick with just one over discharge. Easy fix, use a LVD problem solved.

So once again Home Power Magazine if full of chit again. Only thing they got right is there is not many Solar Charge Controllers for LFP batteries. I only know of one made by GenSun for a small 12 volt marine battery. Any charger can be used when you use Passive BMS Balance Boards or do not push the 100% SOC line. So if you want to go Lithium you can once you understand what has to be done and can afford it. OK?

Quit reading Home Power Magazine, they are idiots most of the time.

[Living Large]

Not silly at all. For FLA you design for 5 day reserve capacity with roughly 3 days usable down tho the 50/60% DOD. With lithium we can do that with 3 day capacity to be apples to apples. So lets say you want 1 Kwh per day using a 48 volt battery system.

To do that with FLA requires [5 days x 1 Kwh] / 48 volts = 104 AH, or 100 AH is close enough.
For LFP requires requires [3 days x 1 Kwh] / 48 volts = 62.5 AH or call it 60 AH.

I need to add a caveat here. FLA is significantly effected by Peukert Law and this example assumes no more than C/20 discharge rate over a 24 hour period. Usually no problem. LFP is not effected by Peukert Law to any extent so it can be ignored. Where this example falls apart is if you have an application that requires a continuous high discharge current all at one time. For example lets say after dark at 10:00pm you run a irrigation pump for 2 hours at 500 watts. That turns your 100 AH FLA into a 50 AH battery and would be fully discharged in 1 day of use. It would require a 200 AH FLA to equal a 60 AH LFP.

Thanks again. One apparent result is I am thinking this will make the cost somewhat equivalent, unless I am missing something. By "equivalent" I am including a fudge factor to include all the advantages I see in LFP - so I would pay 30%, 40%, even 50% more. I was planning for 16 x L16REB earlier, which was $5600. Helpful folks here enlightened me to a single string of batteries, and I was then looking at an 800Ah FLA bank that was around $11,000 and might last 8 years. A 400Ah bank of LFP (which may be undersized, but it is the closest I have seen so far), would be about $8000 not including a BMS, and last maybe 6 years.

[Living Large]

Mike - yes, I absolutely plan a generator as has been discussed here. I simply haven't mentioned it recently. I'd prefer not running it 8 or more hours every other day. I still have on my to-do list to assess the size needed, relative to storage chemistry and capacity, and planned loads. I haven't looked into this yet, but I've seen where LFP can take a high current charge, which may or may not be an advantage in reducing gen run time, based on the inverter/charger capability. That whole topic is a bit murky yet, but choice of chemistry I'd like to hammer out first. By the way, there is a stream/river on this property, with 400' of frontage. I don't believe there is sufficient head, so I am not currently planning for micro-hydro. But I digress.

I didn't want to hijack this thread away from AHI, but I have succeeded. While sorry for that, I am excited about what I see in LFP so far. Very. And this remains a discussion about comparing chemistries so that is good. There are several things I like about LFP - weight, energy density, internal resistance, permitted DOD, # cycles, maintenance, ventilation requirements, hazard.

I had seen a March 2013 article (http://www.homepower.com/articles/so...s-grid-systems) that I scanned, and rejected LFP after reading. Note on the third page there is this statement: "At present, the lack of BMS integration in residential RE power conversion equipment is the biggest hurdle" [to adoption of LFP in off grid RE applications]. To me, this is the only negative for my application, unless I have missed something. So far, the cost I have estimated to be the same or less than a quality FLA solution. (400Ah vs 700Ah)

There seems to be continued debate whether the MPPT and/or inverter/charger need to either have a BMS integrated, or be capable of receiving status from the BMS for disconnecting under abnormal conditions detected at the individual cell level. Some believe the MPPT and inverter/charger can be totally independent, and others like the author of the 1-1/2 year old article believe the opposite. There are articles from 2014 that continue to say BMS must be integrated into the charging device. The question appears to not be one of what happens in normal operation, but in cases of operating outside each individual battery's safe envelope - LVD and HVD for example. I have seen mention of a very small selection of charge controllers and inverter/chargers that may incorporate LFP-friendly features.

As far as balancing, some seem to believe that by staying in the 10% to 80% region and avoiding the knees on each end, the batteries will stay well balanced. Also, they believe that the protection in the BMS is a last resort, and the programmable limits in the MPPT and charger will take care of normal operation.

I haven't found anything definitive on whether some MPPTs and inverter/chargers would be more compatible than others with a LFP battery bank with a standalone dedicated BMS. I guess one question would be what happens if the BMS detects a problem, and the load to the charging device changes abruptly. Someone reported that when they asked MS if their MPPT was compatible, the reply was that as long as the battery bank/BMS could both source and sink current it would be ok. I guess that has to do with the MPPT sensing the state of the bank.

[inetdog]

I appreciate very much appreciate these further thoughts on that system, including alternatives and suppliers.

Just curious and this is probably a silly question - what explains going from a 700Ah FLA to 430Ah LFP? Is this assuming close to a 80% DOD for the LFP? ....

With FLA, you usually target a 20% DOD over the course of a day, not 50%. But a normal range from top charge (not full charge!) on the LFP to bottom SOC for one day's use will be more like 35%. Right in the ball park for the AH numbers you mentioned.

[northerner]

Winston aka as the Yellow LFP is a spin-off from bankrupt Thundersky. Thundersky split between three companies Sinoploy the black LFP and Winston the Yellow LFP battery, Balqon the other Yellow battery. Calb is the Gray LFP and GBS is the blue LFP battery. I do know a few EV folks that use Black LFP batteries and no real complaints. Take away here is all of the Chi-Com primatice large format batteries are copies of the original Thundersky batteries. Balqon schtick is the very large format cells of 200 AH plus intened for large EV's

.

I was actually just reading up on this. There is a short write up here but is in dutch (can click on translate): http://de.wikipedia.org/wiki/Winston_Battery

Also, I found a university that did some testing on a Winston cell. They did repeated charge and discharge cycles and posted the results. They only took the cell up/down 10% each time though:

http://www.auto88.cz/_info/Tests/GWL-Power-Performance-Test.pdf

Like I said that is not unique. Any of the authorized distributors from any manufacture sell packed systems for E-Bikes, vehicles, or energy storage. All do custom Turn Key packages to any specification. For example I bought my 48 volt package deal (16 cells) 100 AH battery from Elite. That same package can be used for solar. They came fabricated in a 4 x 4 block with BMS ready to drop right in place with all hardware and handles You can use any charger. Can be a plain ole 48 volt golf cart charger or a solar mppt controller. Makes no difference as the BMS is the interface. All the charger needs to do is operate at the correct voltage, and for LFP is the exact same as Lead Acid.

Thanks for that!