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John Petersen is the executive vice president and chief financial officer of ePower Engine Systems, Inc., a Kentucky-based enterprise that has developed, built and demonstrated an engine-dominant diesel-electric hybrid drivetrain for long-haul heavy trucks that promises fuel savings of 30 to 40... More
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  • University Of Sheffield Ultrabattery Modeling 9 comments
    Nov 27, 2012 2:57 AM | about stocks: AXPW, MXWL

    One of the more intriguing presentations at ELBC 13 was an evaluation of the Ultrabattery by the University of Sheffield. In their study, the researchers compared four device configurations including:

    • A conventional AGM battery;
    • An AGM battery in parallel with a 200 Farad supercapacitor;
    • An AGM battery in parallel with a 2400 Farad supercapacitor;
    • A Furukawa Ultrabattery.

    By the time they adjusted for voltage differences between the battery and the supercapacitors, the 200 Farad supercapacitor pack resulted in a 33 Farad system and the 2400 Farad supercapacitor pack resulted in a 416 Farad system.

    Since the researchers used a BoostCap from Maxwell Technologies (MXWL) for their 2400 Farad parallel string, the following impedence chart compares the Ultrabattery with the technical equivalent of the Maxwell-Continental system.

    (click to enlarge)

    As I understand the impedence chart, the Ultrabattery performed better than the AGM battery or the AGM battery in parallel with a small supercapacitor module, but worse than the AGM battery in parallel with a large supercapacitor module.

    I was surprised because I always assumed that the Ultrabattery would have more capacitance than the Continental-Maxwell system and that doesn't seem to be the case.

    While Axion Power International (OTCQB:AXPW) doesn't typically talk about the capacitance of the PbC, the unsuccessful DOE grant application it filed jointly with GM in February 2011 did note, "The large capacitance of the PbC battery (13,000F) means that it can support typical vehicle loads for up to 600s above 12V without the need for charging."

    I'm sure there's more in the University of Sheffield presentation than I've been able to glean for myself, but it should give some of our more knowledgeable friends something to chew on.

    Disclosure: I am long OTCQB:AXPW.

    Stocks: AXPW, MXWL
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Comments (9)
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  • John, I think your interpretation of the capacitance of Ultrabattery probably right.
    However, PbC is not a true capacitor. It is regretfully not a true supercapacitor either( Therefore the 13,000F mentioned may only be used as a equivalent number (as PbC discharge curve is just like a capacitor) to support the following declaration
    "The large capacitance of the PbC battery (13,000F) means that it can support typical vehicle loads for up to 600s above 12V without the need for charging."
    27 Nov 2012, 05:39 AM Reply Like
  • Author’s reply » The technical classification of the PbC is an "asymmetric lead carbon capacitor." The positive electrodes undergo the same chemical changes as the positive electrodes in any lead-acid battery. The negative electrode assemblies provide electrostatic storage. There's a lot of discussion about the PbC's sloping discharge curve and I think most people assume that the device has a linear decline from 12 Volts to zero volts – sort of like a big right triangle.


    That's not really the case. Energy storage in the positive electrodes has a typically blocky discharge curve. Energy storage in the negative electrode has a typical sloping discharge curve.


    When you put the two electrodes together in a PbC cell you get a rectangular base with a sloping triangle perched on top of the base.
    27 Nov 2012, 08:35 AM Reply Like
  • Sorry Mr John:


    "When you put the two electrodes together in a PbC cell you get a rectangular base with a sloping triangle perched on top of the base".


    Very interesting explanation, but would need a drawing to understand.


    27 Nov 2012, 08:44 AM Reply Like
  • Author’s reply » Carlos, to see what I'm talking about draw a 1" square on a piece of paper. Now extend the left hand border upward by 1" and draw a downward sloping diagonal line from the top of the left hand border to the top of the right hand border. The scale won't be right, but the general shape will.
    27 Nov 2012, 08:58 AM Reply Like
  • Gracias, now I understand perfectly.
    Have a good day.
    27 Nov 2012, 09:10 AM Reply Like
  • Sorry, I did not make my point clear in the first post.
    My point is I do believe PbC 13,000F claim in regard to energy stored in the battery. However, because of structure difference, PbC may not be a drop-in substitute for a capacitor though PbC power profile is very high among battery rivals.
    27 Nov 2012, 09:41 AM Reply Like
  • Author’s reply » I don't think I've ever heard somebody suggest that the PbC would work as a replacement for supercapacitors because those darned things charge and discharge in seconds, which is way beyond the performance of the PbC. As a hybrid device the PbC can handle charge and discharge rates that are fairly comparable to most lithium-ion chemistries (other than titanates) and an order of magnitude better than lead-acid, but it can't even come close to a supercapacitor in terms of raw cycling speed.
    27 Nov 2012, 09:53 AM Reply Like
  • 416 F capacitor at 12V could theoretically hold 29952 joule energy, or 7.1 kilocalorie( or Cal used by food industry), less than a mouthful of soda drink I think. The capacitor is useful for cranking only.
    27 Nov 2012, 05:50 AM Reply Like
  • Sure wish we had more independent studies where the PbC goes head-to-head with these competitor chemistries.


    27 Nov 2012, 11:22 AM Reply Like
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