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Thread: LifePO4 Cells

  1. #11
    Senior Member John_Koorn's Avatar
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    Solavei
    Quote Originally Posted by BobZilla View Post
    Thanks John.

    Hey I know you are working on similar builds with the 18650's, if you have the funds you might consider getting some of these and testing them out for yourself too. I have both cheap 18650's and some actual name brands (efest) which live up to their rating but since I got these lifePO4 cells I cannot see investing any more in the 18650's, these are just SO much better. Anyway I know you are on your own path and I respect that but I'm just saying these cells are winners for sure.
    That's good news Bob. Will definitely look to get some LiFePO4's when I get some cash together.

    John K.

  2. #12
    I found this nice little study a guy did on charge voltages for lifePO4 cells and thought it worth pointing out here.

    Link:
    http://www.powerstream.com/lithium-p...ge-voltage.htm

    I have been studying a bit on my own about this chemistry and how to work with it. The number one NO-NO is to go to a higher voltage. They love current but voltage above 4+ per cell will damage them. It has to do with the anode forming dendrites and causing shorts. There is a lot of conflicting information on this topic but if you read enough you start to get the picture, basically heat and voltages above 4 (per cell) cause failure.

    Here is another paper to gleen from:
    http://ecst.ecsdl.org/content/41/39/1.full.pdf

    I know it has been said that charging with bedini tech will destroy lifepo4 chemistry but I wonder if it was the voltage that has done it? Mr. Bedini said not to do it and Tom has said it too but I wonder if we could make a limiting circuit to keep from crossing that over voltage zone.

    I normally charge my lifepo4 packs with a charger that is made for them but supply that from my larger LA batteries that soak up the sun ( with an inverter). It works great but it is really inefficient this way. I am thinking about experimenting with setting a cap-dump to ramp up to 14v and dump, never going higher than the safe voltage zone for a 4S configuration. It seems to me that the pulse of the cap is not a problem and if the voltage is controlled it shouldn't hurt cells.

    Has anyone played with this type of arrangement for lifepo4? I have a 20AH prismatic 4S pack that I have had for a few years now that I may subject to this treatment in the name of science ;-)

  3. #13
    My understanding of what John Bedini and Tom have said it's not the tech so much as the uncontrolled tech, either charging too high or with too high of a voltage spike, that can damage a battery or possibly start a fire. I do not have any lithium batteries or I would probably try it too. (well that and I had a fire in my greenhouse and will be dealing with that mess for a while) My biggest caution would be sure you were present during the charging, such as don't leave them charging overnight. It would be nice if Tom could chime in here but he might not be able to, do to liability with his charger business.

  4. #14
    Senior Member John_Koorn's Avatar
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    Hi Bob, I think the cap dumper is a good idea and a neat way to limit the voltage so you don't damage the cells. I'd expect the dump rate to increase as the cell voltage increases, but the current pulses to decrease at the same time.

    Another thought that comes to mind is a Bedini SG into a Bedini Linear Regulator Amp, however you may need to fiddle with the upper voltage limiter to dial it into your terminating voltage.

    John K.

  5. #15
    Quote Originally Posted by John_Koorn View Post
    - snip -

    Another thought that comes to mind is a Bedini SG into a Bedini Linear Regulator Amp, however you may need to fiddle with the upper voltage limiter to dial it into your terminating voltage.

    John K.
    Yup, this was the whole reason John B. came up with the Linear Current Amplifier...


    I've found the LifeP04's love to feed on solar panels also...

    - Patrick A.

  6. #16
    Thanks for the feedback guys. I am going to try my simple cap dump idea since I have everything at hand to do that.

    Did Mr. Bedini ever release details on building the regulator? I see teslagenx sells them but man I cannot see spending that much on one. What I don't get is what does he do with the surplus of energy once the backside has reached the 15v or wherever he sets it? The wheel is feeding in gen mode which is pretty strong to begin with so when the back is no longer taking it what the heck is he doing with it? Maybe he just has a heavy ceramic resistor to bleed it off? I'm not familiar with the circuit so any clarification would be appreciated.

    I will start fiddling around with the cap dump method and report back if it's worth mentioning.

  7. #17
    Posting a short video of what I have found out so far. In short I do think the low voltage cap dump will work. I will have to continue testing and especially to see if the battery still performs well after many cycles but I think it will.

    Video:
    https://1drv.ms/v/s!AmzmftzD-V0miGZfnsik0HUJYgdA

  8. #18
    Hi Bob nice video. In my cap dump runs with LiFePo4, they always charged ok, and performed ok when discharged. I didn't have the problem you have because my lifepo4s are single cell small batteries. Now days I am running tests with common ground without diode and solid state without cap dump. My batteries are in bad shape, they are giving me like 70% of the rated amps hours. Will see if lifepo4s also gets rejuvenated...

  9. #19
    Hey guys,
    I went ahead and did a full test run using the low voltage cap approach, same thing as the last short video but a full run to see if it would truly work.

    It did work pretty good but took a long time. I'm not sure I could tolerate doing this on a regular basis. This was just a small 20AH pack and I have much larger to consider. It as a good experiment though. I can charge the same pack with the lifepo4 charger and an inverter in about 3 hours because it is a 10A charger.

    Here is a chart:
    LifePO4_lowPower_capDump.JPG

    And a video of the run:
    https://1drv.ms/v/s!AmzmftzD-V0miGesUAd2Y-c_ZnTh

  10. #20
    Senior Member John_Koorn's Avatar
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    Solavei
    Hey Bob, that was a pretty good run. Even though it did take a while. You'll see a lot better charging if you fatten up and shorten the wires between the caps and the charge battery.

    I know it was an experimental test run, but I also would've run the SS SG a bit harder - around about 1A draw.

    Thanks for sharing.

    John K.

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