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mwalsh
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Re: Quick Charging

Fri Jul 22, 2011 3:38 pm

GaslessInSeattle wrote:I'm no physicist or EE but I think it's a pretty big stretch to assume that quick charging for 300 miles of range would still only take 30 minutes.


I doubt anyone is realistically expecting that. I would imagine you'd be looking at something like 2.5-3 hours. But then, honestly, after 250-300 miles I'm ready to stop for at least a couple of hours and eat/rest. Actually, I don't like to drive more than 300 miles, period, so I'm probably good for L2 charging overnight (assuming 6.6kW or better on the charger).
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DaveEV
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Re: Quick Charging

Fri Jul 22, 2011 4:39 pm

wsbca wrote:
GaslessInSeattle wrote:cars like the Tesla S coming soon with a 300 mile range, stopping to charge for a half an hour every 4-5 hours will not be such a big deal and the wisdom of frequent stations to charge will become very apparent, IMHO.

I'm no physicist or EE but I think it's a pretty big stretch to assume that quick charging for 300 miles of range would still only take 30 minutes. Improvements in the energy density of batteries don't necessarily imply equally impressive improvements in charging speed, in fact I would not be surprised if the opposite turned out to be true (eg higher temps in the smaller/denser packaging) - you're still talking about transferring the same "amount of electricity" per mile of range - the laws of physics the motor and mass/shape of the car have to respect relative to gravity, friction and air resistance aren't going to change.

Let's say the Tesla S was using LEAF batteries - but had 3x the batteries - 72 kWh instead of 24 kWh.

There's nothing there that would keep the bigger pack from taking a 1.6C charge - charging from empty to 80% in 30 minutes. A 1.6C charge rate is absolutely minimal in the battery world.

Of course - supply the battery with 150 kW instead of 50 kW is a big difference - you're going to need a lot of copper to push 150 kW for 30 minutes. Let's assume that the battery pack voltage stays around 500V - you need wire big enough to handle 300A - serious stuff. With bigger packs we'll likely start seeing battery pack voltages approach 1kV to avoid having to use such large diameter wire.

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