Quote:
Originally Posted by Kardax
Everything Fisker says is subject to change. They don't even have a driveable prototype yet.
All of your statements about firing up the ICE before battery depletion assume a low-power battery (commodity laptop cells in particular). These cannot survive the heavy cycling of a PHEV usage profile. They can't be used in WhiteStar. Tesla must use a high-power, high-durability design like A123 or AltairNano (although it may not come from either of those companies).
Since Tesla must go with such a battery design, there is no need to run the ICE except when the battery is critically low.
-Ryan
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For comparisons sake, in 100k miles (the proposed warranty on the battery) the Volt would fully charge 1750 times (since it lasts 40 miles until it reaches 30% charge). This would be true if the generator always went through the battery and you travelled the 40 miles in EV and the rest with the generator. This would also be true if you travelled exclusively on the battery regardless of the generator. So to allow the possibility of people who would travel exclusively on the battery, the battery will HAVE to last 1750 charges regardless if the generator bypassed the motor. So I guess you are right, Kardax, it doesn't really matter so much to the manufacturer whether the charge can go directly to the motor since the battery will need to last that long anyways.
However, if you were a person who travels more than 140 miles before you can charge, then the pack would only need to last 500 charges (typical commodity battery life) to last 100k miles, if the system can bypass the battery (an extension of this is that you can make an EV on commodity li-ion cells last 100k miles if the pack can travel 140 miles from full to completely drained). It is easy to see the implementation has a huge impact on battery life, but since the current cells supposedly last 7000 charges, it seems to make the argument moot.
I wonder what the advantages in performance each configuration will have. If the generator went directly to the motor with no battery assist, you would need a pretty strong generator to provide some decent performance, so I guess that would not be optimal. What I still don't know is if the performance will be better if the generator went exclusively through the battery (what you are proposing is the better solution) or if there was a mix (what TEG is proposing).
BTW the Volt was originally designed to fire the ICE up at 30% (don't know if they changed it though), so it's incorrect to say "there is no need to run the ICE except when the battery is critically low." I think if they want to keep decent performance and not just highway cruising, they will need to fire early and have a buffer regardless of how power dense the battery is (as you also can run into the problem of the charge depleting more quickly than you are charging the battery if there is no buffer). Though I'm not sure if the decision is based on preserving battery life (as it's bad to run li-ion fully down) or to preserve performance. I mean, since they have a generator on board anyway, it would be stupid to let the battery run down to critical levels and engage limp mode when you can fire it up early and prevent any negative effect on performance.