On Thursday morning I asked Enders Dickenson, Director of R&D for Axion Power International (AXPW) if I could get a copy of Axion's ELBC 13 presentation directly from him instead of waiting for the conference sponsor to send out the full proceedings "in a week or two." While I'm normally patient enough to wait for things to go through channels, the sponsor took a couple months to get the proceedings out in 2010 so I figured there was no harm in asking. My copy of the 37 slide presentation arrived last night and it's been uploaded to my Dropbox.
It's my understanding that much of the material in the ELBC 13 presentation was covered at the annual meeting, but slides like these frequently merit more study and thought than you can have in a live presentation.
While I don't want to drill down too deeply in my discussion of the technical issues because many readers know more about the subject matter than I do, I will highlight several slides that presented data and information I hadn't seen before and consider important.
Slide 5 shows a new emphasis on two key terms that Enders focused on heavily in his remarks. The first term, crystals, focuses on the sulfation problem and zeros in on the idea that small lead-sulfate crystals are normal and beneficial in a conventional lead-acid battery but that large insoluble crystals are the primary reason for loss of dynamic charge acceptance. The second term, concave down increasing or CDI, is the reason that strings of PbC batteries tend to self regulate because the weakest battery in the string is always charged first.
Slide 10 has an interesting graph that shows the up and down regulation performance from the PowerCube in New Castle.
Slide 15 is a copy of the DKE test I first saw in Istanbul. What makes it a little interesting is that Axion is finally taking some credit for doing the original development work on the testing protocol in conjunction with BMW. This ties in well with Eckhard Karden's description of the protocol as the "Axion-BMW" test protocol instead of the Ford-BMW protocol. In the 2010 Ford-BMW presentation at ELBC 12 in Istanbul, Axion only got a passing nod at the end of the presentation.
Slide 20 is very important because it shows what happens to a VRLA battery if you push the recharge delay after an engine off event from 10 seconds to two minutes. That kind of abuse drives the DCA down to minimal levels within a week. The reason the slide is important is that the most efficient way to run a micro-hybrid is to push the recharge timing out to the end of a drive interval when the car is decelerating and the engine is not being used to power the wheels. This is the heart and soul of so-called "regenerative braking" in stop-start and it's dreadfully hard on conventional VRLA.
Slide 26 shows what Axion is doing with the bench-top work under the SBIR grant. They'll be using a conventional flooded SLI battery for the cranking load only and a PbC for all the hotel loads. They'll also be increasing the system amperage from 100 to 150 amps. During the recharge intervals, 300 amp seconds of charge will be returned to the SLI battery (9%) and 3,000 amp seconds will be returned to the PbC (91%)
Slides 31 to 35 are dedicated to the difference between conventional lead-acid charging curves and PbC charging curves. Where lead-acid has a much lower voltage change from the beginning to the end of a charging cycle, the PbC has a wide voltage swing. More importantly, the voltage curve for conventional lead acid is slightly convex while the curve for the PbC is quite concave.
Slide 33 shows how concave charging curves tend to bring the batteries in a string into balance without active management of the individual batteries while Slide 34 shows how convex charging curves tend to leave the batteries out of balance.
Disclosure: I am long AXPW.