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Thread: LiFePO4 Batteries - Lithium Iron Phosphate

  1. #11
    Senior Member Branch Gordon's Avatar
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    Thanks for sharing all this info Bob. I am looking forward to reading about your personal experience with the ones you purchased.

  2. #12
    Networking Architect Aaron Murakami's Avatar
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    I just want to repeat what Peter told me yesterday about the LiFePO4's.

    The equalization circuits is important.

    With lead acids, to equalize, all are charge up to push up the lower ones.

    With the LiFePO4s it's the opposite. The equalization circuits avail on some of them bring the highest ones down to the lower ones.

    I don't recall seeing this equalization circuit on the LiFePO4s at John's unless they're internally built into the batteries.
    Aaron Murakami





    You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete. ― Richard Buckminster Fuller

  3. #13
    Aaron I don't think you understood what I said. Let me try again because not that it matters a great deal but the point shouldn't be lost.

    We push cells to their upper limit in the first place because of sulphation right. These cells have no such issue so taking them all the way up is not necessary.

    I agree you would NEED the equalization IF you insist on trying to get each cell to 3.6v /3.8v but there is no reason to do that, in fact by prolonging the charge and holding upper voltages with it is detrimental to the negative electrode because of the positive/electrolyte reaction that deposits gunk on the negative electrode.

    As I said before if you have 4 cells in series and each one has slightly different charge then if you never take the string up to maximum there will not be an issue. (just don't bring any cell to 3.8 which is MAX) Ideally we would want to balance them all even and they would rise and fall exactly the same but perhaps one has more or less impedance or some manufacturing difference which makes it impossible to have them perfectly matched. So if one is 3.5 and another 3.4 and 3.6, 3.2 , it really doesn't matter because we do not have to push them to FULL to reverse any sulphation. From what I have read on other forums you do not find that much variation between cells, in the real world it is more like a few hundredths or at least all are within a tenth of each other. I just use those numbers to illiterate my point.

    The notion of charging them up fully is carried over from dealing with LA chemistry for so many years, these cells do not need the upper limit and actually prefer to stay away from it.

    I would say a better target range would be 14v for a 12v pack. If all cells were even that would be 3.5 each but if some tend to go higher or lower then it allows the margin for no cell going over 3.8 which is the stated max value per single cell.

    My intention is not to stir up any trouble with anyone. i am just pointing out what I have understood about these cells from various sources.

    They are exactly opposite in the respect that they destroy themselves quicker when pushed to higher voltages where we are all used to intentionally pushing high for LA to desulphate.

    Anyway I do have some on the way which I will be experimenting with and I will post what I am up too with them. I admit that so far I am only going from information which I have read and not first hand experience.
    Last edited by BobZilla; 09-15-2014 at 05:07 PM.

  4. #14
    Networking Architect Aaron Murakami's Avatar
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    14.8 is the max they should be charged to, which is 3.7 volts per cell - that is why the solar charge controllers max the LiFePO4's at that voltage - happens to be same max voltage for sealed lead acids.

    14.8 is considered the top from the tests done at Bedini's and over that can seems to have no benefit from what I can tell.
    Aaron Murakami





    You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete. ― Richard Buckminster Fuller

  5. #15
    Thanks for pointing this out bobzilla, i belive the only reason to bring them up high would be to make use of there potential storage capacity, if you need to charge these cells on something designed for Lead acid you could always drop a Diode in series with the charger either a 0.2v schottky a 0.5 - 0.7v silicon would do the trick easily although slightly wasteful.
    if manufacturers insist upon set voltages which seems a bit silly considering its likely to be a single resistor value and that it means that if you want to run a different chemistry you have to get a new charger, well silly for the customer it probably makes the manufacturers quite alot of exta cash.

  6. #16
    Hello everyone,

    So I have received my LifePO4 batteries and I can now make some observations rather then speculation. I do intent to make my own post and shw some charge curves but I wanted to follow up once on this thread in case people don't follow to the other one.

    I want to speak to the balancing circuits again. I have tried charging up below the ceiling as I described and that method will work BUT you will not get the capacity out. When I did some charges to 14v I was only getting about 10AH out of a 20AH pack at a 5A rate down to 10.5v. That is done with a CBA. When I push all the way up I have pulled 19AH,, and 21AH a few times so it is important to push all the way up IF you need the full capacity. What I mean is you could under run them if you had enough cells to ensure you could meet your requirements but given the price of these cells it doesn't make sense to do that in my opinion. The thing that makes these cells special is that you can get more energy usage out of them safely, you can run them 80 percent or even more Dod making them stronger than their LA counterparts which really should only be brought down 50 percent or so. To put it another way you would need many more LA AH in your bank to get the same usage as with these.

    Another observation is that the cells I am testing do not rise and fall so equally as I thought. One of them was reaching 3.8v well before the rest although standing they were all within a few hundredths of a volt. This presents another problem. once these cells reach saturation they do not pass current so imagine a middle cell reaching capacity before the rest, it will sit there and damage itself while simultaneously starving it's partner cell down the string because it passes little to no current. LA will just gas off but these shut off basically.

    I am going to order some of the balance boards and see how that effects the charging, not sure if bedini tech will play nicely with them since these things are really meant to regulate high current and I am hitting them with spikes. If they are compatible I would say it is probably best to use them. As I have said you can run without them if your careful not to go to close to the top of the charge but personally I want the most capacity I can get out of these expensive cells and with the balancing circuits you probably don't have to babysit. For me it now hinges on whether or not feeding spikes through them is compatible.

    Of course this is all experimental stuff, I'm sure it all works wonderfully with the new trackers. I am just experimenting with spike charging as a curiosity.

  7. #17
    Hello to all, I bought some lifepo4 small AA cells, 3,6 volts each rated at 700 mAh.

    I have them in series, 4 AA, to make 12 volts batteries.

    I am charging them with a comparator cap dump but I have a doubt.

    In all places they say charge until 14,4 volts, but the cap dump don't raise the voltage that much as spikes or direct current. So for cap dump is a lower voltage?

    I charge 1 pack with cap dump until 13,34 volts, and then it rested at 13,2 volts.

    Should I try to push them higher even with cap dump?

    best,

    Alvaro

  8. #18
    Senior Member Tom C's Avatar
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    Quote Originally Posted by BobZilla View Post
    Hello everyone,

    So I have received my LifePO4 batteries and I can now make some observations rather then speculation. I do intent to make my own post and shw some charge curves but I wanted to follow up once on this thread in case people don't follow to the other one.

    I want to speak to the balancing circuits again. I have tried charging up below the ceiling as I described and that method will work BUT you will not get the capacity out. When I did some charges to 14v I was only getting about 10AH out of a 20AH pack at a 5A rate down to 10.5v. That is done with a CBA. When I push all the way up I have pulled 19AH,, and 21AH a few times so it is important to push all the way up IF you need the full capacity. What I mean is you could under run them if you had enough cells to ensure you could meet your requirements but given the price of these cells it doesn't make sense to do that in my opinion. The thing that makes these cells special is that you can get more energy usage out of them safely, you can run them 80 percent or even more Dod making them stronger than their LA counterparts which really should only be brought down 50 percent or so. To put it another way you would need many more LA AH in your bank to get the same usage as with these.

    Another observation is that the cells I am testing do not rise and fall so equally as I thought. One of them was reaching 3.8v well before the rest although standing they were all within a few hundredths of a volt. This presents another problem. once these cells reach saturation they do not pass current so imagine a middle cell reaching capacity before the rest, it will sit there and damage itself while simultaneously starving it's partner cell down the string because it passes little to no current. LA will just gas off but these shut off basically.

    I am going to order some of the balance boards and see how that effects the charging, not sure if bedini tech will play nicely with them since these things are really meant to regulate high current and I am hitting them with spikes. If they are compatible I would say it is probably best to use them. As I have said you can run without them if your careful not to go to close to the top of the charge but personally I want the most capacity I can get out of these expensive cells and with the balancing circuits you probably don't have to babysit. For me it now hinges on whether or not feeding spikes through them is compatible.

    Of course this is all experimental stuff, I'm sure it all works wonderfully with the new trackers. I am just experimenting with spike charging as a curiosity.
    Bob,

    lifepo4 batts like current, its the nature of the battery. they like to be equalized thru discharge not charge. 14.8 is the finish voltage the trackers are set for with lifepo4. in the long term I am not sure they will play nice with the spike. they do like the linear regulator though....

    Tom C


    experimental Kits, chargers and solar trackers

  9. #19
    Bob,

    lifepo4 batts like current, its the nature of the battery. they like to be equalized thru discharge not charge. 14.8 is the finish voltage the trackers are set for with lifepo4. in the long term I am not sure they will play nice with the spike. they do like the linear regulator though....

    Tom C
    Thanks for the advice Tom. Now that I have had some time to play with these I agree that current seems to work the best. Second I would say a cap dump which is also current but not the same. I also tried just straight generator mode and mode one. All will charge them but i'm with you that over the long haul the spikes might cause issues or even the beating they take on a dumper. As far as just charging them the quickest with the least waste on an SG circuit i would say dumper, gen, and mode 1 in that order. Without question the most preferable way I have found is with my little tracker 3A, I have the regular LA model and it works great but I also have the boards Aaron recommends installed on each cell. In that setup you still don't want to let it keep going once they go red so it is not as noce as having the tracker with the correct calibration but as long as I keep an eye out it works very well.


    Hello to all, I bought some lifepo4 small AA cells, 3,6 volts each rated at 700 mAh.

    I have them in series, 4 AA, to make 12 volts batteries.

    I am charging them with a comparator cap dump but I have a doubt.

    In all places they say charge until 14,4 volts, but the cap dump don't raise the voltage that much as spikes or direct current. So for cap dump is a lower voltage?

    I charge 1 pack with cap dump until 13,34 volts, and then it rested at 13,2 volts.

    Should I try to push them higher even with cap dump?

    best,

    Alvaro
    Alvaro I cannot say much about the small AA's your working with but I have the 20AH packs and I can cap dump them to full charge so perhaps you just need to let them go a bit longer. Just as they discharge in more of a flat line pattern, they also flat line a bit on a charge so even if your not gaining voltage you may still be building capacity but I am only guessing since I do not have the AA's. Good luck ----Bob
    Last edited by BobZilla; 01-06-2015 at 02:31 AM.

  10. #20
    Quote Originally Posted by BobZilla View Post
    Alvaro I cannot say much about the small AA's your working with but I have the 20AH packs and I can cap dump them to full charge so perhaps you just need to let them go a bit longer. Just as they discharge in more of a flat line pattern, they also flat line a bit on a charge so even if your not gaining voltage you may still be building capacity but I am only guessing since I do not have the AA's. Good luck ----Bob
    Tnx Bob, I will try to push them higher.

    best

    Alvaro

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