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Discussion Starter #1
In case you didn't know, the official EPA range estimates of the Tesla
Roadster are in....BA, BUM, BA, DADA.....245 miles! And they have
confirmed, themselves, that 0-60 is still under 4 seconds! Yay!

Now...the bad news. 1. It's delivery to customer will be delayed
another 3 months. (But 6 months total delay isn't that bad for a new
car, from a new car company, isn't it?)
All this info above, however, is aside from my point.

Bad News 2. is that on the Tesla Motors blog they answered one of the
questions presented in the comments. In the answer, they said it takes
73 AC KWH in all to CHARGE the Tesla Roadster. The battery pack only
holds 53 kwh!!! This is a mere 70% efficiency; that sounds just awful
compared to their other specs.

These 73 AC Kwh of course include the amount of energy to cool the
battery pack while it is charging, but does cooling a battery pack
really require that much energy to be cooled? And wouldn't just
charging the battery pack slower reduce the need of cooling, and
therefore dramatically decrease the amount of energy wasted?

I always heard, and thought, that lithium-ion batteries were so
efficient with charging, but now I'm not so sure.

And one last question, you can see from the specs (~30kwh/100miles)
that they took the total energy used for the car (73 AC Kwh) and not
the energy in the battery pack. 73/245 is about 0.3kwh a mile i.e.
30kwh/100 mile.

Is this how they rated older EVs, such as the ratings for the Rav4 EV
found on fueleconomy.gov?

Woah...this is a long post for just asking questions!

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Discussion Starter #2
Supposedly one of the things that they did to give the pack long-life is to
very tightly control temperature while charging. I suspect they cool and
maybe even heat it in cold environments.

It could also be their balancing system eating up the extra power.

Anyway, 20kwh a charge is not all that much to pay for much longer cycle
life (if their claim is true).

-Phil
----- Original Message -----
From: "Joseph T. " <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 26, 2007 8:41 PM
Subject: [EVDL] Tesla Roadster Charging Efficiency...


> In case you didn't know, the official EPA range estimates of the Tesla
> Roadster are in....BA, BUM, BA, DADA.....245 miles! And they have
> confirmed, themselves, that 0-60 is still under 4 seconds! Yay!
>
> Now...the bad news. 1. It's delivery to customer will be delayed
> another 3 months. (But 6 months total delay isn't that bad for a new
> car, from a new car company, isn't it?)
> All this info above, however, is aside from my point.
>
> Bad News 2. is that on the Tesla Motors blog they answered one of the
> questions presented in the comments. In the answer, they said it takes
> 73 AC KWH in all to CHARGE the Tesla Roadster. The battery pack only
> holds 53 kwh!!! This is a mere 70% efficiency; that sounds just awful
> compared to their other specs.
>
> These 73 AC Kwh of course include the amount of energy to cool the
> battery pack while it is charging, but does cooling a battery pack
> really require that much energy to be cooled? And wouldn't just
> charging the battery pack slower reduce the need of cooling, and
> therefore dramatically decrease the amount of energy wasted?
>
> I always heard, and thought, that lithium-ion batteries were so
> efficient with charging, but now I'm not so sure.
>
> And one last question, you can see from the specs (~30kwh/100miles)
> that they took the total energy used for the car (73 AC Kwh) and not
> the energy in the battery pack. 73/245 is about 0.3kwh a mile i.e.
> 30kwh/100 mile.
>
> Is this how they rated older EVs, such as the ratings for the Rav4 EV
> found on fueleconomy.gov?
>
> Woah...this is a long post for just asking questions!
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Discussion Starter #3
hmm a 70% charging efficiency is in stark contrast to previous claims
that the entire charge-discharge cycle is 85% efficient

Dan

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Discussion Starter #5
Hi Joseph,

I found it interesting to translate their numbers into Watt-hrs per mile.

So 73 kWh to charge a 53 kWh pack. 53/73 = 72.6%

City cycle: Recharge energy kWh per 100 miles = 30 * 72.6% = 21.78 / 100 =
.218 * 1000 = 218 Whrs per mile

Highway cycle: Recharge energy kWh per 100 miles = 32 * 72.6% = 23.23 / 100
= .232 * 1000 = 232 Whrs per mile

Combined: Recharge energy kWh per 100 miles = 31 * 72.6% = 22.51 / 100 =
.225 * 1000 = 225 Whrs per mile

Checking the results by going 53 kWh pack / 232 Whrs = 243 miles, close to
their 245 mile result.

By comparison, The Electric Imp uses about 225-250 Whrs per mile highway @
60 MPH as long as I do not get too lead footed.

Cliff
www.ProEV.com



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Discussion Starter #8
Joseph wrote:

< How efficient is the charge-discharge cycle for the ProEV?>

I don't know. We have never checked. We have a Fluke clamp on meter so it
would not be hard to check.

Cliff
www.ProEV.com




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