Battery Management systems (BMS) for LiFePO4 batteries in real situations

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  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    inetdog wrote: »
    For the geometry of parallel batteries (there should be no "first" one) take a look at the diagrams on this site:
    http://smartgauge.co.uk/batt_con.html
    The rest of the site is also very helpful on a lot of off-grid subjects.
    So you say my friend, but you'll fine the first battery or batteries if in series on the positive side will show a lower voltage with a large load and will use more water that the others as they get the brunt of the charging with the path of least resistance. I use the diagonal method.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    So you say my friend, but you'll fine the first battery or batteries if in series on the positive side will show a lower voltage with a large load and will use more water that the others as they get the brunt of the charging with the path of least resistance. I use the diagonal method.

    In a series circuit all batteries get the same DC current. I can only think of two reasons why the first battery on the positive side should charge different from the rest: 1) That side of the battery box is at a different temperature than the other side, or 2) there is a high frequency component to the charging current that is dissipated by capacitance to ground as it propagates through the series circuit.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    vtmaps wrote: »
    In a series circuit all batteries get the same DC current. I can only think of two reasons why the first battery on the positive side should charge different from the rest: 1) That side of the battery box is at a different temperature than the other side, or 2) there is a high frequency component to the charging current that is dissipated by capacitance to ground as it propagates through the series circuit.

    --vtMaps
    I was not talking about a series circuit, I said Paralleled batteries I guess you'd have to service enough 8-10 battery GC-2 banks where you see the difference. It's very apparent. It may not be easy to explain, but it's real.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    So you say my friend, but you'll fine the first battery or batteries if in series on the positive side will show a lower voltage with a large load and will use more water that the others as they get the brunt of the charging with the path of least resistance. I use the diagonal method.
    Can I assume that when you measure the voltage of each of the parallel batteries you are going directly between the terminals of each battery in turn?
    When you use the diagonal method there is no common point to which you can connect the negative meter lead and get correct results for both batteries when there is current flowing.

    Of course the difference in water usage is a bit harder to explain. :)
    Maybe the effect of the conductive concrete on the outside of the battery cases, to resurrect an old wives tale?
    There may be an issue with pulsed current and the inductance of the charging leads that could be large enough to be significant.
    On the negative side the same effect might not be as pronounced because of distributed capacitance to ground.
    What happens on a positive ground battery bank? Is it the first battery on the negative side that works hardest?
    PS: Or while powering a load like an inverter, the load current might have some high frequency components, especially with an MSW inverter.

    The effect should show up on a DC clamp meter, and I would love to have the opportunity to actually look at the voltages on each battery with a scope.
    SMA SB 3000, old BP panels.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    inetdog wrote: »
    Can I assume that when you measure the voltage of each of the parallel batteries you are going directly between the terminals of each battery in turn?
    When you use the diagonal method there is no common point to which you can connect the negative meter lead and get correct results for both batteries when there is current flowing.
    Thats the way I do it, battery post to battery post. It's correct enough for me.

    Added : it's not just voltage, you take a DC clamp meter and put it on the positive lead and say it shows 100 amps. if you have 10 batteries in parallel if perfect they would they would all be contributing 10 amps to the draw. That won't happen, the first set will be contributing more and some others less as you move the meter down the line. If you one pair that is significantly less that set should be investigated. It takes a little addition and subtraction, but easy to find a problem pair. Then you can go to the interlink and find if it's just one battery. Whatever method you use if it works for you , I am happy for you.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    PNjunction wrote: »
    How about an example of simple conservatism with no external balancing:
    <snip>. Moral: just don't go beyond 80% and you'll keep things simple.
    I'm satisfied.
    PNjunction wrote: »
    By running conservatively, you can run without a cobbled up system, and use standard componentry. Just look for adjustments that mimic a lower voltage requirement, like those used with GEL.

    For example, the Samlex series of AC chargers <snip>
    From big to small, you just need to look around and by being conservative, can easily charge and maintain lifepo4 without a mess. For larger stuff, then BlueSea and other big name / big system stuff can be used. Just match the voltage to your application.

    We are talking about two very different situations, you are talking about monitoring and balancing while doing very interesting and useful bench testing where I am talking about battery monitoring over the hopefully ten year plus life of the battery.

    Aren't we getting a little off topic? All the equipment you are talking about has little to do with off-grid systems and Battery Monitoring

    I can't say that any off-grid LiFePO4 battery that you would make would be damaged during its lifespan if it doesn't have a Battery Management system of some sort, just as I don't believe you could guarantee that there might not be some situation where a Battery Management/Monitoring System could save the battery from damage.

    I can't see how a properly designed Battery Monitoring system could possibly damage a large battery bank that is being charged on a regular basis in an off-grid system. There is evidence and I agree that it is not a good idea to have battery balancing circuits across the cells by themselves. I think a well designed battery balance circuit that takes account of the failure modes that might occur in the circuit/software coupled with some sort of battery monitoring that would pick up that a balancing circuit had failed would be OK. Automatic battery balancing is probably unnecessary for a system that you or I might build and maintain, however I think it might be useful in cases like my friend's 48 volt system, I am still undecided about this.


    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
     

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    karrak wrote: »
    Aren't we getting a little off topic? All the equipment you are talking about has little to do with off-grid systems and Battery Monitoring

    Not really. I have a BMS. It includes two levels of LVD and two levels of HVD. (Powerwerx ITS-12 for my small system). But no balancing (other than the initial first one). Monitoring consists of regular, but not obsessive checks of cell balance with my Flukes. I think it is exactly on topic.

    The reason I can run with such as simple bms, that emulates what one would do with lead, is that we are in a sub-c type of application, where once you initially set the balance, it stays that way. Run conservatively, at say no more than 3.5v per cell, and you have a little bit of additional headroom. This is even achievable at 48 volts.

    But nevermind that, many of the advanced EV'ers do the same, at much higher voltages and cell counts! Usually after something tacked onto the top of the cells croaks on the previous battery setup. They run conservatively, and of course do coulomb counting. Of course, they are also using a complicated wiring infrastructure, which could take out a cell, but in our case, our cell count is very small comparatively. I took the hint.

    Take monitoring to any level one wishes. So what are you going to do about it when one cell fails 3 years down the road? Marry a new one in? Keep a lot of spares on hand? Not the greatest idea unless you are out at sea and need to do that to get back to shore.

    So yes, if I have a cell failure, I'll be replacing all 4 cells most likely and raising hell with the manufacturer / dealer. Maybe get a 5th one as a spare, and marry into a "frankenstein" battery of old and new cells for less critical needs. And again, this is crucial - unless one is buying complete crap, at the mundane rates we charge / discharge at, it puts nearly zero stress on the cells, nevermind that we don't really want to take them to 80% regularly in a typical solar application. So in addition to low charge / discharge rates, we are also not deep cycling them, even though they can take it if necessary.

    I keep stressing the point that if you take into account our application, where the demands are miniscule compared to what the cells were designed for in the first place, (EV), then one who is willing to do just a little bit of sanity monitoring can achieve a lead-like status of simplicity.

    What you typically find is that all the BMS players come FROM the EV-application market, but we aren't in that category.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    PNjunction wrote: »
    Take monitoring to any level one wishes. So what are you going to do about it when one cell fails 3 years down the road? Marry a new one in? Keep a lot of spares on hand? Not the greatest idea unless you are out at sea and need to do that to get back to shore.

    Hmm. Replying to myself again - not good. :) But I think it needs mentioning now that I think about it.

    With our relatively mundane usage, it *may* be good to keep a spare cell on hand, say charged at 50% SOC or so in storage. Because we are NOT hammering these batteries, we just might get away with "marrying" a new cell into an old pack, provided we still run conservatively (and of course balance it initially). Up to you I guess.

    But consider that with a lead-based 48v system using a string of 12v batteries, if one cell fails, you'll be replacing 6 of them, not just one. I could see the hand-waving about this issue beforehand. :)

    Ok, back to topic ...

    Lets say your BMS monitoring system is reporting a cell going bad. First thing you'd do is grab the Fluke. Then you'd disassemble all that exterior wiring to make sure the bms itself isn't the cause or reporting bad values. If you are using an rc-modeling hobbiest-type Junsi cell logger, you'll be calibrating that against the Fluke. If the cell is going low, and you don't know if the bms is a contributing factor, you'll be charging the cell up individually, and testing the battery / cells balancing naked anyway. So back to square one.

    If running cells naked, you'll know real fast that either 1) Yes, the cell is bad or 2) the wiring infrastructure may be bad. With an external bms / monitoring across the cells, those 2 possibilities multiply exponentially. One spec I don't see much of is that of RFI-suppression, actually RFI-ingress from outside sources, which could be the neighbor kid's UHF FRS walkie-talkie to NOAA weather transmitters, broadcasters, you name it.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    But consider that with a lead-based 48v system using a string of 12v batteries, if one cell fails, you'll be replacing 6 of them, not just one. I could see the hand-waving about this issue beforehand. :)
    This shouldn't be a detractor for either Battery types. One has to consider the economics of replacing a cell that will degrade to the level of the older cells. A new FLA cell won't be noticed, but I don't know how much different a LiFeP04 cell would charge and discharge in the relationship to the older cells. Something to test, since you wouldn't be taking it to a extreme on either end, probably a non issue.
  • cosmicraycosmicray Registered Users Posts: 24 ✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    It could, if they would come up with a reliable Specific Gravity probe with a remote readout, it'd be about all you need. It'd make me a happy guy.

    I've looked for anything that would give me the ability to measure SG in a FLA cell, but I've not found it yet. My take is that may end up being something that a battery manufacturer would have to build into the physical case (if for no other reason, than to give them a product differentiation edge). Sell me a GC-2 with a small jack to connect an active monitor to.
  • cosmicraycosmicray Registered Users Posts: 24 ✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    PNjunction wrote: »
    Single cell monitoring may be ideal, although from a practical standpoint, perhaps monitoring 12v "modules" for a 48v battery might be in order, and manual checks once in awhile for individual cell voltage could be performed for sanity. It all depends on your trust level. Note that your cell-monitoring or coulomb-counting gear should NOT be powered by the cells under test, but from another power source.
    There are some small micro-controllers that will operate as low as 0.7V, so single cell monitoring might not be out of the question.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations

    I guess my position is near PNs.

    0. conservative setpoints
    1. Cell level monitoring , loud beeper on first low cell.
    2. No balance baords
    3. The only kind of LVD that i think is practical is a signal that depowers the inverter. Most permanent wire inverters have such aux ports. All a big contactor is going to do (other than fail when you least expect it), is upset the charge controller, which might do unpredictable things. You could put the contactor in the inverter line, and leave the controller conencted. But nah...

    This would work on any chemistry.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations

    Earlier was asked if could trip a RCD/GFCI -- Yes--You would only need to pull a 10-100 mAmps (0.01 to 0.10 amps) to trip a typical RCD/GFCI on the AC output of an inverter. 10 mAmps may be "iffy"--100 mAmps should trip.

    And, yes, I am (was?) a electronic/systems design engineer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    zoneblue wrote: »
    I guess my position is near PNs.

    0. conservative setpoints
    We all agree about this
    1. Cell level monitoring , loud beeper on first low cell.
    Unless I have misinterpreted what PNjunction has been saying, this is the main point of disagreement between us. I understand that he does not think it is worth doing automatic individual cell monitoring and thinks it is more trouble than it is worth.
    2. No balance baords
    I agree here with maybe the exception of systems where you can't expect the user to be doing much if any monitoring and can't expect them to manually balance the cells if it ever becomes necessary.
    3. The only kind of LVD that i think is practical is a signal that depowers the inverter. Most permanent wire inverters have such aux ports. All a big contactor is going to do (other than fail when you least expect it), is upset the charge controller, which might do unpredictable things. You could put the contactor in the inverter line, and leave the controller conencted. But nah...
    I agree with you here. If my memory serves me correctly when I was looking for Inverters some years ago I couldn't find one with a simple shutdown at a reasonable price. When the warranty runs out on my inverter, which should be any day now I will look at modifying it by either jamming the Reset or shutting down the power to the controlling Microprocessor. Will have to be very careful about unintended consequences of this but the manufacturer was the one that suggested killing the power, my other thought was to simulate a LVD fault within the inverter.

    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
     

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    karrak wrote: »
    Unless I have misinterpreted what PNjunction has been saying, this is the main point of disagreement between us. I understand that he does not think it is worth doing automatic individual cell monitoring and thinks it is more trouble than it is worth.

    In regards to individual cell monitoring, I only think it is more trouble than it is worth simply due to our application only pulling about no more than 0.15C or so. With conservative setpoints, and at this relatively low level current discharge, no cell is going to do a fast dive to the bottom like you may experience with EV's pulling hundreds of amps upon accelleration. A pack-level lvd, even with a small imbalance, will prevent the weakest cell from doing the deep dive in our application. EV's are a different story.

    But, if you want to do individual cell monitoring, by all means do so.
    I agree here with maybe the exception of systems where you can't expect the user to be doing much if any monitoring and can't expect them to manually balance the cells if it ever becomes necessary.

    Yep, that is the "drop in" mentality for the average consumer who won't be taking the time to run conservatively, adjust setpoints properly etc. It is one of the reasons Gel cells were so (and still are) widely abused, typically dropping them into a charging system that takes them to 14.4v or higher, which fries them and not knowing the reason why. Even MK makes a point not to charge above 14.1v, but plenty are abused after being dropped in. So this is kind of the same consumer problem with lifepo4 too - you can fake it by shoe-horning drop-in setups based on lead, and compensating on each and every charge cycle with a balance that is not generally needed after it has been performed once - but again, in our low-current application as compared to EV.

    Instead of relying on an inverter for the lvd, why not use an external programmable LVD from the likes of Blue-Seas Systems, Victron etc - typically at the max or default of 12.2v (check to be sure). 24 and 48v lvd's should be similar. Then again, this is only pack-level lvd. Good for me, but might not be for others.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations

    With the advent of midnites disconencting combiners, Carling now make their 125-250A breaker range with a trip circuit. Someone on the midnite forum ordered one by mistake and, posted a photo of it. Iit was identical to the usual carling, but had a third small terminal, that you can use to trip the breaker. Dunno how much current it takes, but id guess not much.

    If i was going to trust anything to relaibly break 250 amps, itd be carling.

    Outback at least, has an aux switch port. Im gona use it for a remote on off switch, but you could just as easily series in a tiny shut down relay.
    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: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    PNjunction wrote: »
    In regards to individual cell monitoring, I only think it is more trouble than it is worth simply due to our application only pulling about no more than 0.15C or so. With conservative setpoints, and at this relatively low level current discharge, no cell is going to do a fast dive to the bottom like you may experience with EV's pulling hundreds of amps upon accelleration. A pack-level lvd, even with a small imbalance, will prevent the weakest cell from doing the deep dive in our application. EV's are a different story.

    You are right that the speed that things can go wrong with an off grid system is much slower than with an EV, but with an EV there is a driver who would hopefully see that things were going wrong and stop the car fairly quickly. An off-grid system like ours has small loads that are running all the time even when we are asleep or away, which over time can use as much power as the EV does over a small period of time. If the cells are balanced at the top end, i don't think you can assume they will be balanced at the low end especially as the cells age. A single LVD might be OK for a twelve volt system, but i don't think is adequate for a 24 volt or 48 volt system.
    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
     

  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    karrak wrote: »
    A single LVD might be OK for a twelve volt system, but i don't think is adequate for a 24 volt or 48 volt system.

    That has always been my concern... Even for Lead Acid batteries... 2 volts "missing" on a 12 volt bank--10 volts and nothing works (10.5 volt cutoff).

    2 volts missing on a 48 volt bank, 46 volts and things still work OK (assuming 42 VDC is "cutoff").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations

    I agree that in general terms, that for RE use, there is nothing materially different, in terms of cell balance, between say 3v lithium cells and 2V AGM cells. Under lead you typically operate your system with comfortable reserve margins. You have to. LVDs in inverters not withstanding, the potential of reverse polarising the individual low cell(s) is what drives this. High IR, means LVDs are set too low.

    However, i look at this the other way around, lithium brings us the technology to monitor at the cell level and with any chemistry, thats something that would help me sleep, to be able to go away for a few days, a week, whatever and leave the SO, {friend, random house sitter, whatever} in charge.

    If anything, lead needs low cell detection even more than lithium, because its my impression that cell capacity and IR are much more consistantly controlled / binned in the Li manufacturing system. Has to be for EV and other high C applications.
    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: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    zoneblue wrote: »
    However, i look at this the other way around, lithium brings us the technology to monitor at the cell level and with any chemistry, thats something that would help me sleep, to be able to go away for a few days, a week, whatever and leave the SO, {friend, random house sitter, whatever} in charge.

    Understandable. I think we're meeting half-way. Now that I have demonstrated to myself that I can maintain a bank without it, IF I did want to use one for my own DIY setup, I'd probably go with the home power bms here:

    http://www.cleanpowerauto.com/
    If anything, lead needs low cell detection even more than lithium, because its my impression that cell capacity and IR are much more consistantly controlled / binned in the Li manufacturing system. Has to be for EV and other high C applications.

    You would think so, and for now, CALB seems to be the most consistent from word on the street, but I'm plenty happy with my GBS cells.

    In that EV application, even if you did have some capacity and Ri differences, the usual way to treat that is to bottom-balance all the cells, which of course leaves the top balance a bit ragged. Cells can be individually monitored to stop the charge upon the very first cell meeting the upper voltage limit. OR, they can run conservatively, sacrifice a quarter mile, and do it from an upper-limit pack-level voltage. But here we go again. :)

    On the whole, we're on the same page - I'm just more extreme than most.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations

    In other words, bottom balance gives the inverters LVD the best possible chance of success?

    PN, im like you, my pack never goes anywhere near critical low levels and so its not something in actual fact i lose any real sleep over, ie the chances of it ever happening are low. That wasnt always so, especially in the beginning. I imagined the mrs leaving her iron on in the afternoon, and then forgetting about it.

    But she actually only irons in the morning ;-) (And irons while they might draw a bit, cycle on and off, so the average draw isnt quite as bad as youd think.) And theyre hot and you pay attention...bla bla bla bla. Read general off grid acclimatisation.

    However when i do migrate to lithium i foresee some things happening:

    1. The bank will be smaller (has to be to make the costs stack up).
    2. With the sulphation bogey vanquished, means less fear of low SOC.

    Both things imply lower average SOCs, and hence an elevated risk of low voltage events.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    zoneblue wrote: »
    Both things imply lower average SOCs, and hence an elevated risk of low voltage events.

    I when expressed concern about this very issue I was told that these batteries don't go down in Voltage as SOC decreases.

    Must be some form of magic, because it sure ain't physics.

    Now if someone would like to put up a chart equating Voltage to SOC for all to see then maybe we poor engineers can understand what is going on.

    The promotion of this technology is still woefully short on established facts.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    I when expressed concern about this very issue I was told that these batteries don't go down in Voltage as SOC decreases.

    Actually, they do according to physics, it is just that the range is VERY small from about 3.1v to 3.6v per cell. Here is what I use when i don't want to break out the Fluke. Like all batteries, this voltage should be measured after a long rest period:

    http://www.amazon.com/TecMate-TS-127-OptiMate-Charge-Battery/dp/B00DRPRZ9E

    Notice too the "tick" marks between 25 and 75% SOC, and the relative flatness. There are other charts. Shorai has one that some tape up in room. Nearly all lifepo4 manufacturers provide similar charts in their documentation.

    Here is a primer from the guy who has some batteries on Mars:
    http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387

    These are the facts, and have been for well over a decade now. If you don't want to use them, that's fine. What I'm presenting here is NOT some slick BS. When I see unfounded cheerleading, I'm all over that.

    Like I mentioned, once you actually get some in your hands, it tells all.
  • creekycreeky Banned Posts: 31
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    PNjunction wrote: »
    Actually, they do according to physics, it is just that the range is VERY small from about 3.1v to 3.6v per cell. Here is what I use when i don't want to break out the Fluke. Like all batteries, this voltage should be measured after a long rest period:

    http://www.amazon.com/TecMate-TS-127-OptiMate-Charge-Battery/dp/B00DRPRZ9E

    Notice too the "tick" marks between 25 and 75% SOC, and the relative flatness. There are other charts. Shorai has one that some tape up in room. Nearly all lifepo4 manufacturers provide similar charts in their documentation.

    Here is a primer from the guy who has some batteries on Mars:
    http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387

    These are the facts, and have been for well over a decade now. If you don't want to use them, that's fine. What I'm presenting here is NOT some slick BS. When I see unfounded cheerleading, I'm all over that.

    Like I mentioned, once you actually get some in your hands, it tells all.

    thanks for this pn. et tu zoneblue. reed. karak. informative discussion.
    I have yet to see any unfounded cheerleading. Seen some leading is all.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations

    If you find anyone cheerleading, and promoting lifepo4 as the answer to all battery needs, then steer very very clear!

    The aim there is either for your wallet, your votes, or investments, and has nothing to do with the batteries at all. :)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Management systems (BMS) for LiFePO4 batteries in real situations
    PNjunction wrote: »
    If you find anyone cheerleading, and promoting lifepo4 as the answer to all battery needs, then steer very very clear!

    The aim there is either for your wallet, your votes, or investments, and has nothing to do with the batteries at all. :)

    Personally I would like to experiment with these myself, but it just is not financially possible. There is not only the capital investment to consider (things are even more expensive up here unless you do buy the cheap junk which is just a waste of money) but there is not much chance of there being any reasonable payback for me.

    So far I see two viable advantages to LiFePo: variable SOC tolerance and high energy density.

    Neither of these are advantageous to me, but may well be to someone else. If the characteristic demand is obvious in a particular system design they should be considered.
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