[EVDL] Tesla Roadster Charging Efficiency...

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!
>
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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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