LFP or LifePo4: questions about using

124

Comments

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using
    zoneblue wrote: »
    Its my understanding that currently the primary hazzard with Lithium ion cells is the electrolyte carrier, which is a flamable organic solvent (read "petrol" like). They are working on replacements for the carrier. See http://chargedevs.com/newswire/researchers-find-new-non-flammable-electrolyte-for-li-ion-batteries/

    Overall that is good info.

    But, yet another research lab without a product on the market. The solution here is to not take your batteries to 100-200C, or more than 200F. Most tech reviews (not just singling this one out), are merely parroting back what the marketing department tells them to. The actual reviewer may not have ANY experience with batteries at all. I'd love to put 3 sealed batteries on a table, like a maintenance-free flooded, a gel, and an agm, and have them tell me what the difference is. :)

    They also may not be able to tell me the difference between a carbon-additive and a graphite additive (Deka vs Exide) to lead-acid batteries, and that their main claim for psoc operations is targeted primarily at the "micro-hybrid" vehicle (not a true hybrid, but just one that stops and starts the engine at stoplights for example), but often shoe-horned into other applications - primarily trying to attract the grid-stabilization market.

    Many like to include lifepo4 with other chemistries of li-ion, or non-related applications with a broad brush-stroke, simply out of ignorance, or for fear-based marketing purposes. I read right through most of it and laugh.

    They never do their homework to discover that Winstons are actually LiFeYPo4 (a dash of Yttrium is added for better lower temp specs), GBS are actually LiFeMnPo4 (a little manganese added to the phosphate), or that in the case of GBS, don't even use "PVDF" in their electrolyte, common for others - each technique achieving a slightly different result. Supposedly using an alternative to PVDF in the electrolyte is nicer to the environment. I chose GBS based on availability, and not necessarily for the lack of PVDF. Or CALB who uses very fine powdering techniques to get the utmost in high charge/discharge rates. ALL of these guys have steadily improved their manufacturing process to be more precise than when first starting out in 2008 or so.

    The biggest difference is that they are not in the lab relying on "any day now" vaporware, but actually have things that small-fry like myself can get my hands on relatively easy without NDA agreements, single-vendor point of sales and the like.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using

    OK, I'll try to keep the ranting down. :)

    One thing often overlooked about lifepo4 chemistry vs other li-ion chemistries, is that like our lead-based brethren, there IS an absorb period. That is, if you charge faster than about C/20, you will observe a point where the battery itself is regulating current in an absorb stage - but once absorb is finished, continued application of voltage merely causes a heating of the electrolyte, and voltage rises again - albeit with no appreciable current flowing. So you aren't directly overheating the anodes / cathodes with current.

    With LiCo02, they will continue to accept current beyond 100% SOC, and is part of the reason for the very, very critical voltage cutoff specs. Yes, if your charger is voltage limited, the difference between the charge source and the battery will be the one limiting current. BUT, raise that voltage just a little beyond normal with a LiCo02, and more current flows into an already fully charged battery - which eventually goes thermal very fast. Lifepo4 on the other hand, if you raise the voltage on an already charged battery will only serve to raise the voltage from the heated electrolyte, even though no major current flows. Note that I am not saying this means lifepo4's can be abused - just pointing out a difference not often known.

    Those coming from RC-modeling or other applications not using lifepo4, may be of the obsessive mindset - and should be! - but with lifepo4 you do have a little bit of reasonable headroom one way of the other. Obsessing about minute differences in cell voltage is just not called for unless you are an EV'er taking these things down to the dregs - which you shouldn't be doing anyway since you have a conservative LVD like 3.15v or so per cell.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: LFP or LifePo4: questions about using

    PN, what seems like a bit of a pity is that running lifepo4 at high average SOCs reduces there life. Off grid users tend to be protective of pack capacity, which leads to high average SOCs, and that is particularly acute in systems without gensets. By designing systems to work year round, leads to higher SOCs in summer.

    Can you manage this by dialing down the absorb setpoint in summer, so the bank is only say 75% charged? And how much lower than 100% do you have to go to protect the bank?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using
    zoneblue wrote: »
    PN, what seems like a bit of a pity is that running lifepo4 at high average SOCs reduces there life.
    The main concern is storing them like that. Regular cycling not so much. However, I have not been able to dig up any specific numbers - all we know is that it is a "best practice" to run at a lower SOC. I'm not going to let my lifepo4's sit around fully charged for more than about 2 days - if so, then I'll start thinking about discharging them a bit to get them off the top.

    This is part of what I got from the Jay Whitacre video class, where he just states that running up to 90% SOC is better than 100%. Running up to 80% is better than running up to 90%, and so on. But at what point does one stop from a practical standpoint? - especially without any numbers to back anything up. What I want to avoid is running my cells to the very high-soc levels just to satisfy the needs of a balancer on each and every cycle.

    So while it doesn't actually kill them right off, TIME spent at those higher voltages is also key. If I were running with balancers, I'd want to hit those cells hard, to reduce the time spent at those high soc's. It is just a matter of not giving the parasitic reactions time enough to cause damage long term. Still, nobody has supplied numbers. This is kind of opposite the fallacy of doing repetitive cycle-testing, without taking into account that one is merely beating the clock from a parasitic reaction standpoint - so the cycle count can be skewed. That kind of prediction comes from Dalhousie Uni's lab.

    From a practical standpoint, I just plan to not actually do any absorb and call it a day, and let the soc land where it lands. This is ok, since I have oversized my battery to give me some headroom. I'm planning on somewhere around 90-95% SOC that way.
    Can you manage this by dialing down the absorb setpoint in summer, so the bank is only say 75% charged? And how much lower than 100% do you have to go to protect the bank?

    Sure - as long as you have the capacity to operate with. While most of the members in the "non active-balancers club" shoot for about 13.8 to 14.0v max, some have been known to take it lower to 13.6v. Or, one may simply just be able to discharge deeper - since you don't have to worry about sulfation, you can "walk" your way back up over the course of a few days - provided your loads are reduced or you have better solar insolation.

    Just know that you will finish absorb at 13.8 as much as you will at 14.4. Absorb just takes longer at 13.8, that's all. Absorb is still miniscule compared to lead. The SOC when finished is about the same - IF you are talking about the kinds of current that a solar housebank user can provide. Running more than >1C may be a slightly different story. But that means you haven't sized your battery properly. :)

    This is the problem - with no sulfation to deal with, it opens the doors to using the battery in many different ways depending upon need / desire. That can actually be frustrating for the pocket-protector geek in me, that wants to just be told very specific voltages, capacity, balancing rules and the like. It is uncomfortable at first to operate with this new found freedom - surely something must be wrong. You get used to it after awhile. :)
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: LFP or LifePo4: questions about using
    zoneblue wrote: »
    PN, what seems like a bit of a pity is that running lifepo4 at high average SOCs reduces there life. Off grid users tend to be protective of pack capacity, which leads to high average SOCs, and that is particularly acute in systems without gensets. By designing systems to work year round, leads to higher SOCs in summer.

    Can you manage this by dialing down the absorb setpoint in summer, so the bank is only say 75% charged? And how much lower than 100% do you have to go to protect the bank?

    I have set my system up to try and keep the SOC and associated charge voltages as low as practicable while still storing as much as possible for that rainy day. On Monday my controller sets the 'absorb' voltage to 27.6 volts (3.45 V/cell) and stays there until the batteries reach this voltage with a charge current of C/20 or less, then until the following Monday the controller sets the voltage to 27 volts (3.375 v/cell) which equates to an SOC of around 80%. The float voltage of our system is 26.4 volts (3.3 V/cell). I have been using this regime for over a year now and it works very well. In cloudy weather it is a struggle for the batteries to reach the 3.45 V/cell so the system tends to spend days if not weeks trying to get to the higher SOC which is just what one wants. In sunny weather, especially in summer the battery gets to the 3.45 V/cell on the Monday so doesn't spend much time at this higher voltage. The higher voltage is also used to reset my SOC counter.

    I Think it maybe possible with some commercial charge controllers to do something like this using the 'Equalise' charge cycle.

    The attainable long term power produced by our solar panels is fairly close to our consumption. In winter with the power production being more erratic the battery works as a long term buffer. A few months ago we had a period of over five weeks between the battery being full, with the average SOC around 50%, going as low as 15%. In summer we use the extra power produced by the panels to run an electric oven. When we do use the oven we would be taking the SOC of the batteries down to about 40-50%.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • ReedReed Solar Expert Posts: 55 ✭✭
    Re: LFP or LifePo4: questions about using

    PNJunction

    Had similar worries about SOC before reading your posts and talking with son Cary. The BMS (and we disagree on requirement for such) does set charging voltage to 3.6 V/cell and adjusts individual CALB cells (4 per battery) until they are at 3.4 V float. The four batteries have individual BMS and each battery box has a fan to regulate temperature. Having suffered for LAS (lead acid syndatrome) for years and obsessing with unattainable full SOC, we formerly would turn off inverter etc at night to awaken with highest possible SOC. Now we just leave inverter on and, if we know we shall have a full solar day, leave the Dometic refrigerator on and start the day at -3000 W-hr deficit (about 65% SOC). This is up to 3.4 V/cell by noon or early afternoon.

    Son requested Manzanita if they could adapt BMS to more fully satisfy the lower C requirements of solar users. They e-mailed him recently that they were working on this.

    Been following the Aussie fora that you pointed me to. They are a divisive crew. Quite a bit of snarky slagging going one. Your friend T1 does get a bit of abuse. Wrote him a PM and shall see if he repliess.

    Reed and Elaine
  • westbranchwestbranch Solar Expert Posts: 5,180 ✭✭✭✭
    Re: LFP or LifePo4: questions about using

    PN, Reed Karrak, this opens up an entirely new line of discussion, that is how to do/manage a LiFePO4 battery use to do what we have been calling an OPPORTUNITY LOAD. In some ways I think that an LFP battery, especially an over-panelled one, would allow constant Op loads as Reed stated...

    Should this be a new thread?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • ReedReed Solar Expert Posts: 55 ✭✭
    Re: LFP or LifePo4: questions about using

    Attachment not found.
    Westbranch. Concept is good since the last several posts have been considering how to maintain proper voltages. PNJunction and other extremely qualified folks believe that a BMS is not required and might be a detriment. Others feel that since a BMS will adjust the cells individually to the proper level and may provide a fan for cooling to lower the temperature and prevent over-heating, that they do provide an added convenience and safety factor. It might be well to find out how many work each way and what their results have been.

    At least one manufacturer (fabricator) is now looking a modifying BMS to be more useful for low power consumption of solar users, as opposed to high C of their normal electrical vehicle users. Have noted as of today that AM-Solar is now discussing LFP with a vendor/fabricator for possible future use. AM-Solar has an extremely good reputation and is quite conservative. Shall be interested in where they go

    The attachment is meant as humor for the lurkers of which I am one. I generally read everything in a thread before I think of responding and generally try to follow every similar thread on that and other fora. There is a lot to learn on a lot of threads. Unfortunately, many turn into ego trips between individuals and "schools of thought" and their gurus and disciples. Right now, the vast majority on this thread have had things of use to say.
    Reed
  • Mountain DonMountain Don Solar Expert Posts: 494 ✭✭✭
    Re: LFP or LifePo4: questions about using

    link broken or something
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using
    Reed wrote: »
    At least one manufacturer (fabricator) is now looking a modifying BMS to be more useful for low power consumption of solar users, as opposed to high C of their normal electrical vehicle users.

    That is OUTSTANDING! Finally, some are getting the hint that our actual application matters, and differs from EV, Ebike, RC modeling, and powersports SLI duties. The closest are the marine solar-housebanks, where one also has to watch out for burning up alternators, bad switching infrastructure and the like.

    Generally, to stay conservative, all one has to do is stay out of the extreme charge / discharge knees. Start with a *reasonable* balance, but it doesn't have to be hobbiest-obsessive to meet an 80% DOD goal at the most.
  • ReedReed Solar Expert Posts: 55 ✭✭
    Re: LFP or LifePo4: questions about using

    Found two more posters at IRV2 "Boondocking thread with reasonably large solar arrays (2 kW) and reasonably large LFP banks (1.2 kA at 12 V) on RVs who are quite happy with their choices. Another one is planning to go LFP as current battery bank goes down that long lonesome road. Will be sending them PMs to get more information.
    Reed and Elaine
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: LFP or LifePo4: questions about using

    If they carry on persisting with 12v at that sort of power level theyll need some of these:

    Attachment not found.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • ReedReed Solar Expert Posts: 55 ✭✭
    Re: LFP or LifePo4: questions about using

    Zoneblue

    A lot of folks stay at 12 V since the smaller panels are nominally 12 V and their battery banks are 12 V.

    As noted ad nauseum in earlier posts, our system is six 235W (30 V) panels ganged in two series of three (90 V) and then parallel to MPPT-45 (14 amps at 1300 W) and then 4 batteries (4 cells each) in series to 48 V nominal.

    Someone could have a 48 V nominal system at say 200 amp-hr but call it an 800 amp-hr system as far as the 12 V DC system of the coach.

    Reed and Elaine
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: LFP or LifePo4: questions about using

    It's also because if you bootleg a non compliant UL 458 Inverter and system it's does not meet code for a Mobile system. 30 amps is the maximum with Automatic neutral / ground switching is mandatory in a mobile system. There a lot of 12v Inverters and a few 24v and a couple 48v inverters that would qualify. Most Boaters are shaky about using 48V on the water. I guess RV people do whatever they can get away with.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: LFP or LifePo4: questions about using

    What can you say except that if anything can do 12v its lithium.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: LFP or LifePo4: questions about using
    zoneblue wrote: »
    What can you say except that if anything can do 12v its lithium.
    Not proven yet to me, I have to much faith in 6, 2v FLA cells on longevity and price. LiFep04 does seem to fit some uses. One issue I have is how my customers existing equipment will adapt to charge them in the 800 - 1,200 amp hr range banks. A lot of existing equipment can't meet the specs necessary.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: LFP or LifePo4: questions about using

    All i was saying is that the internal resistance is very low, and like AGM, ought to be able to support inverters above its general WH rating.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: LFP or LifePo4: questions about using
    One issue I have is how my customers existing equipment will adapt to charge them in the 800 - 1,200 amp hr range banks. A lot of existing equipment can't meet the specs necessary.
    What specs are a problem?
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: LFP or LifePo4: questions about using
    karrak wrote: »
    What specs are a problem?
    FIXED Battery charging algorithms. Most all the Inverter / Chargers made in the last year or two have custom charging settings (+ / - .5 % may be as good as it gets ), if they can be adjusted to the LIFep04 charging perimeters and the small voltage changes. All the older Inverter / Chargers your out of luck. Your not only talking about expensive Batteries, but buying new equipment to use them. We're not talking about these batteries you guys are testing and a 5 amp battery charger. A $2,000 inverter charger in not considered cheap.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using
    All the older Inverter / Chargers your out of luck. Your not only talking about expensive Batteries, but buying new equipment to use them.

    Can your existing charger voltage be set to anywhere from 13.8 - 14.2v? Multiply by 2 or 4 for 24v or 48v nominal systems. CC/CV is all you need. Running conservatively and with reasonable balance allows one to do this. Check upon the first charge that no cell goes above 3.6v, if it does, you can employ a simple temporary discharge from a bulb to bring it down a little. Keeps it simple. Due to their very very low internal resistance, some may need to beef up their alternator.

    Likewise with a solar controller. Can you set your voltages as above? Worst case if you have fixed presets, can you set them to "Gel"? Disable temperature-compensation. Add an lvd of your choice. Spice it up with individual cell monitoring, complicated chargers and other infrastructure if you like. I have proven to myself that it is not necessary when running conservatively.

    No, I'm not running an 800ah battery, but the techniques I use with the smaller setup scales to the larger systems. If one wants proof of that bad enough, visit sites like Cruisersforum where they do, or better yet, get a pair (or two of large capacity cells) and prove me wrong. Envision the Monty-Python skit where you have just been fish-slapped. :)

    I think we are getting sidetracked here worrying about others and their issues as if we were some sort of retail dealership for lifepo4 systems.

    While the readership here is general purpose, the questions and answers are intended to provide some information to see if YOU the reader, can handle it, and not worry about things from a universal industry level pro or con. Those with no intention of ever running lifepo4 from budgetary or other concerns don't need to worry about it so much.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using

    ANOTHER REASON TO RUN CONSERVATIVELY, 13.8 TO 14.0V (3.45 TO 3.5V per cell)

    Much of the discussion about running conservatively is to give the DIY'er who balances manually a bit of headroom at the top so that no cell goes above 3.6v. But there is another major reason for doing so.

    The problem is that we are not taking into account solar, where charge current can vary, and this can prove to be a problem with high upper-limit voltages.

    Ideally, 0.1C is a minimum recommended to charge with (Winston mentions this), although you can get by with 0.05 (C/20), but with a precaution - and that has to do with TIME. Add to the fact that we are running batteries with enough capacity to get us through the night, and charge capabilities that are probably no more than 0.1 to 0.2C at best. But what happens when it gets cloudy, or is in the early or late solar-insolation hours, and your battery is already fully charged?

    The time problem is not so much taking too long to charge, but staying at a high voltage too long - to the point where you may already have a fully charged cell, BUT now all you are doing is heating the electrolyte.

    You can fully charge a lifepo4 cell with less than 0.1C, and just stop at 3.4 to 3.45v. There is no absorb, since basically this is already the absorb current territory. You will achieve about 99% SOC this way (as opposed to a higher current with absorb at 90-95% or so).

    IF you were to set your upper charge voltage high, say to 3.6v per cell, and charge current at say 0.05C, the cells will never get there! Actually, they will, BUT the cell is already fully charged, and with basically no current flowing into a fully charged cell, the voltage increase you eventually see is coming from the electrolyte heating. You can prove this to yourself with your own charger, voltmeter, and ammeter.

    The same situation exists with the variables of solar. For instance, early on I set my charge controller to 3.6v per cell (14.4 on the CC for 12v nominal setup). Problem was that my panel and the solar conditions were typically at 0.05C or even lower at times. While I watched the ammeter eventually drop to nothing, the voltage of the cells never reached 3.6, and just hung in there at around 3.45v. BUT, when I waited long enough, yes, that voltage started to rise due to electrolyte heating.

    (Note that one never really wants to take cells to zero current during absorb or other charge - anything less than C/20 is the region where it transitions from finishing absorb to starting to heat the electrolyte - and it's subsequent voltage rise with no current.)

    The solution of course would be to ensure that I had more than 0.1C charge to actually reach the 3.6v upper absorb setpoint, but Mr. Sun had other plans.

    What I'm trying to emphasize is that in a solar application where one might face the possibility of charging with a very low current, even if their panel is capable of much more, you could end up easily overcharging the cells with too high a set point - and never actually reaching it as far as finishing a charge is concerned. Kind of a catch-22.

    So, instead of the possibility of having a fully charged battery go into electrolyte heating trying to reach 3.6v all day, set a CONSERVATIVE value that is possible to actually reach under these conditions, like anywhere from 3.45 to 3.5 volts. Personally, I have dropped mine back to 3.48v per cell, (13.9v for my 12v nominal setup) splitting the difference.

    AC charging 0.1C and over is one thing - but with solar where you have no major control (unless you go totally bananas with excess panel power or insanely small batteries), running conservatively provides you not only some slight imbalance headroom, but also limits the electrolyte heating that may occur under very weak solar conditions on already fully charged cells.

    Whew - hard to explain, but that's the best way I can express it so far.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: LFP or LifePo4: questions about using

    Here is some data from a test I did awhile ago that I think backs up the case for not charging to 3.6 volts/cell with low charge currents.
    Attachment not found.
    The test was mainly done to see the difference in the amount of charge stored in a LiFePO4 battery versus end charging voltage. The charge current came from my solar array with a charge current of around 0.09C. Results were taken from when the battery voltage reached 27.2V (3.4 V/cell) until the total battery voltage reached 28.8V (3.6 V/cell). The voltage was then kept at around 28.8V until the current dropped to 5A

    Simon
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: LFP or LifePo4: questions about using
    PNjunction wrote: »
    ANOTHER REASON TO RUN CONSERVATIVELY, 13.8 TO 14.0V (3.45 TO 3.5V per cell)

    Which is in fact the normal "top Voltage" for a 12 Volt system using lead-acid, save maybe half a Volt. This also aides with the old problem of screaming 12 Volt inverters which do not like being part of a system that equalizes at 15+ Volts.

    But since one of the supposed benefits of LiFePo is lower SOC then obviously you start running into the problems at the opposite end: before you reach your desired low SOC the inverter can scream and shut down from LVD. To say nothing of the fact you can not get around the physics of V goes down I goes up in order to get W; the system becomes less efficient the lower you go.

    I'm mentioning this (again) to point out that as yet the technology for both charging and usage is not entirely suitable for LiFePo and you have to adapt and compromise. This reduces the benefits.

    Clearly still not ready for the average Joe's system.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: LFP or LifePo4: questions about using
    But since one of the supposed benefits of LiFePo is lower SOC then obviously you start running into the problems at the opposite end: before you reach your desired low SOC the inverter can scream and shut down from LVD. To say nothing of the fact you can not get around the physics of V goes down I goes up in order to get W; the system becomes less efficient the lower you go.

    As the discharge profile of LiFePO4 cells is so flat this is not a problem. The 100% SOC voltage of a four cell (nominal 12 volt) LiFePO4 battery is around 13.2 volts, the 10% SOC voltage is around 12.8 volts. If anything the problem is that the inverter LVD cannot be set high enough to protect the battery.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using
    But since one of the supposed benefits of LiFePo is lower SOC then obviously you start running into the problems at the opposite end: before you reach your desired low SOC the inverter can scream and shut down from LVD.

    With lifepo4, you don't depend upon an inverter using a lead-acid based lvd voltage - if you do, then you have gone too far. One must use an external lvd programmed to the right voltage, and ideally watch their coulombic consumption so they don't bang into the lvd as a normal practice.
    To say nothing of the fact you can not get around the physics of V goes down I goes up in order to get W; the system becomes less efficient the lower you go.

    Yes, but not at anything practical to notice, especially in our application. Consider Peukert gone from a practical user standpoint. In fact, this is what can get people into trouble - nearly FULL performance right down to 90% DOD, with a high voltage as compared to lead. Be smart. Don't go there without an lvd. Oh yes, EV'ers pulling HUNDREDS of amps will notice a "voltage sag", but that sag follows an extremely flat profile, and not anything like the curve of a lead-based system battling with Peukert. Keep in mind we are not EV'ers or RC modelers, so our application is different.
    I'm mentioning this (again) to point out that as yet the technology for both charging and usage is not entirely suitable for LiFePo and you have to adapt and compromise. This reduces the benefits.

    Adapt and compromise? Just buy the infrastructure that supports the right voltage. It isn't as hard as it sounds.
    Clearly still not ready for the average Joe's system.
    The problem here is that the average Joe will happily run with a 45-watt HF panel attached to a 100ah SLI flooded battery - and then wonder why it doesn't work with a deficit-charge situation. You (and others) go to great lengths to educate them beyond the "average Joe" status, and that is part of the reasoning behind our discussions of lifepo4 here. And quite frankly the raison d'etre for the board here itself right?

    Practical suggestions and viewpoints from those who don't actually have any hands-on experience with these cells only goes so far, and in many cases is filled with spin. I emplore you to get a small explorer set of your own (see the GBS 20 and 40ah battery review), and contribute to the knowledge base from a first-hand standpoint. It will sweep away a lot of the cobwebs of FUD that come from those outside our application, or from those who have no intention of running lifepo4 in the first place, but seem to have the most to say about it.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: LFP or LifePo4: questions about using
    PNjunction wrote: »

    Practical suggestions and viewpoints from those who don't actually have any hands-on experience with these cells only goes so far, and in many cases is filled with spin. I emplore you to get a small explorer set of your own (see the GBS 20 and 40ah battery review), and contribute to the knowledge base from a first-hand standpoint. It will sweep away a lot of the cobwebs of FUD that come from those outside our application, or from those who have no intention of running lifepo4 in the first place, but seem to have the most to say about it.
    Does my 3 LiFep04 Vacuum Cleaner batteries qualify as a member of the talking class ?? When the Batteries and Equipment to use them becomes Plug and Play, only then will they become main stream for the " Average Joe " until then it's just experimental.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: LFP or LifePo4: questions about using
    Does my 3 LiFep04 Vacuum Cleaner batteries qualify as a member of the talking class ?? When the Batteries and Equipment to use them becomes Plug and Play, only then will they become main stream for the " Average Joe " until then it's just experimental.

    This is correct.
    But it seems the proponents of the chemistry will not admit to any short comings no matter how clearly and accurately expressed.
  • creekycreeky Banned Posts: 31
    Re: LFP or LifePo4: questions about using

    Thank you PNJunction and Karrak ... factual replies to my request for answers to questions about using. It is very much appreciated. I apologize that I have not been able to get to the forum recently due to a massive workload. Why oh why do I consistently underestimate jobs???

    I would point out that the battery system I initially proposed includes a bms with automatic low voltage disconnect, cell voltage management etc. It even has a fuse. Indeed all you do is plug it in and play. And it works with any good quality mppt controller. Certainly my TBS inverter will have no trouble with it. Would that be, (pinky finger raised) perfect for the "average Joe?" (! Myers fans)

    So, in fact, quite unlike lead acid packs which require a special room, heating, watering, cooling etc. Cables and connectors ... And don't forget getting the little device out to measure cell charge while siphoning and discharging a highly toxic acid... but I'll bet that's right within "average joe" users idea of a good time. Hey kids, don't drink daddy's battery koolaid.

    Whatever. Please tho. If you are not answering my question about using. Stop posting to this thread.
    (although I was intrigued, 6 pages (last chance to visit) to 12... wow.)
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: LFP or LifePo4: questions about using
    Whatever. Please tho. If you are not answering my question about using. Stop posting to this thread.
    (although I was intrigued, 6 pages (last chance to visit) to 12... wow.)

    It seemed to me that most of the posting was about using and using with re. I have a feeling these 12 pages are handy for forum users like me who come to this site to try and learn. Great forum for all.
    Cheers
    gww
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: LFP or LifePo4: questions about using

    Please guys - let's not go there with the "us and them". The shortcomings of course could all be turned on their head with us denigrating lead-acid too. Hydrogen? Acid? Massive Peukert effect? Are you nuts? All batteries have shortcomings - none are perfect as witnessed by the hundreds of threads bashing lead-acid manufacturers and their problems. But, in this instance, people willingly go to help. Come lifepo4, and all you get is misguided drama.

    What I constantly hope for and recommend is that we stick to the technical side of things, and let the user / owner decide. All I am saying is that without ownership, it is far too easy to just parrot back what you hear in the media or from other misinformed sources - frequently NOT in our application or using our specific chemistry.

    Thing is, I could guide a newcomer about the generics of flooded batteries, but you would NEVER find me trying to act as an authoritative guide for a Rolls-Surrette without ever having owned one.

    In the end, all we are seeking is fair-play.
This discussion has been closed.