18 months go by and my how the battery tech has improved! The price has come way down, the energy density has increased, and the capacity per cell has increased. Everything's coming up Milhouse!
A123 now sells a 20Ah LiFePO4 cell, which means I could use just 16 individual cells - instead of the 192 I use now - to achieve 80% of the nominal capacity of my pack on day one... as I've discussed previously, the pack no longer hits nominal due to some in-flight learning adjustments to the charge cycle over the last year.
The amazing thing is that these new 20Ah packs are not cylindrical, yet still push high current. Typically, blister pack cells don't get quite the discharge/charge performance, but A123 has pulled it off. The flat nature and lack of exoskeleton on each cell result in a huge volume reduction; I can fit 40Ah in 75% of the space that 25Ah fit in now! That works out to a 105 mile range using my pessimistic experience over the past 18 months (remember, this was my ideal range goal with the pack I have now; I've never hit it).
The price is fair, too. A single A123 20Ah cell costs ~$51, which works out to $816 to achieve 80% of my original capacity, or $1632 to achieve 160% of my original capacity (still fits in my existing PVC battery compartments). $816 is a couple hundred dollars less than I paid for the pack I have now, but remember, I only paid 33% of the retail price due to an interested $100 of $150 coupon that I was allowed to use multiple times (I asked).
So am I going to go out and replace all of my cells? In short, no, but it's good to see technology press on. Why 'No'? I originally planned on using the electric bike as a segway into designing an electric car. After selling my truck and going carless, I realized I didn't even need an electric bike, hence I use it very little. If at any point this changes, I'll swap the batteries in a heartbeat...
...but first, I've promised I will build a battery management system to completion. I've several times started a BMS design, but I've yet to focus 40 hours straight to follow through. At this point, I have at least 5 different half-baked plans, but nary a circuit to prove any thoughts.
I'm watching a guy convert his 2000 Honda Insight into an electric vehicle using 50 of the above A123 20Ah packs in place of the stock 8Ah cell... he's able to get 30 miles with this much juice, which is pretty good considering he's still got the engine and is using the stock (and highly confused) motor.
My room mate has a 2000 Honda Insight, too, and it's brand new battery pack (from Honda) is having numerous reset problems on a weekly basis... maybe I can convince him to drop $2500 on A123 cells and $1000 on various other junk to interface it to his car? :)
