Re: [EVDL] Press release on Firefly "Oasis" battery
----- Original Message ----
> From: Jeff Shanab <[email protected]
> To: [email protected]
> Sent: Thursday, November 1, 2007 10:54:00 PM
> Subject: Re: [EVDL] Press release on Firefly "Oasis" battery
> But lets not forget peukert
> The 50ah rating of an orbital is the 20hr number.
> we need the 1hr
number or about 24ah. :-(
That's one reason why I derated to 50% in my post, giving 25 Ahr for the Orbitals.
> The second part is that you can use 80% of the lithium ion without as
> much derating of power. Ie the discharge curve is flatter so volts x
> amps stays higher longer.
You have a Lithium pack that costs around $40k -- are you really going to push it to 80%? Also, don't forget you have around 2000 A123 cells vs. about 30 Firefly batteries. It is going to be tricky to push 2000 A123 cells reliably to 80%. It is also going to take a sophisticated BMS that can shunt power around that one cell that hits 80% well before the rest. At this point, since I'm not aware of anyone that has independently done depth of discharge and cycle life tests with A123, a 50% design point is alot safer.
> While I think there is room for improvement. as Lee said 2x, the
> intrinsic capability at the molecular level to hold electrons can't be
Agreed -- but also don't forget carbon is alot lighter than metal, too. The best way to figure this is with real life tests -- let's see how real life Firefly batteries do compared to real life lithiums.
> Then lets throw in the cycle life difference and I think it becomes
Actually not so obvious to me -- Firefly is claiming much better cycle life compared to regular lead acid batteries. If the energy density is higher, you'll tend to have more weight budget for batteries and discharge them less deeply (good for both Lithium and Firefly). If they are cheaper, you'll tend to buy more and discharge them less deeply (big Firefly benefit over Lithium). Even if lithium has more cycles, it is going to be hard to overcome the price difference in terms of battery cost per mile. Even if Lithium had infinite life cycles, $40k upfront is going to be a problem compared to $5k or $10k.
> One last piece of info, the A123 cells give up some energy density to
> get very high power density, That same size cell restricted to 1C can
> built to give 3.3ah, nearly 30% more. When larger format cells are
> the energy density will increase.(more egg, less shell)
Understood, and it was stacking the deck a bit to compare to the current A123 batteries that are good on power and not as good on energy density. Even so, my analysis showed that Firefly batteries could have (time will see if it is true) energy density comparable to A123, and about 1/2 that of energy dense Lithium batteries.
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