[ClaBerCla]

The Energy density in the battery will be 16kwh. GM said recharging the batteries will take 6 hours at 110V and 15 amperes. But 110V * 15A *6H= 9.9kwh
So it should take 16000/(110*15) = 9.7 hours to recharge the batteries instead of 6 hours.
Could somebody explain this difference?

 

[Jason M. Hendler]

From Wiki, under the heading AC conversions:

Link

V(avg) = 0.637 * V(peak)

Depending on whether you use 110 or 120, and divide your result by 0.637, you end up on either side of 16 kWH. I am not sure which way is the right way to do it, as I am tired, but it seems your calculation should be correct, because V(avg) is intended for quick DC like calcs, but I could be way wrong.

 

[pdt]

8 kWh

The Energy density in the battery will be 16kwh. GM said recharging the batteries will take 6 hours at 110V and 15 amperes. But 110V * 15A *6H= 9.9kwh
So it should take 16000/(110*15) = 9.7 hours to recharge the batteries instead of 6 hours.
Could somebody explain this difference?

Only 8 kWh of the battery will be used (maximum charge 80%, minimum charge 30%).

 

[Joshua Bretz]

The Energy density in the battery will be 16kwh. GM said recharging the batteries will take 6 hours at 110V and 15 amperes. But 110V * 15A *6H= 9.9kwh
So it should take 16000/(110*15) = 9.7 hours to recharge the batteries instead of 6 hours.
Could somebody explain this difference?

From what I gather, there is a 16kW battery, but it is only charged to 80%, and discharged to 30%, so it's only 8kW that you have to put in the battery to get the 40+ mile electric range. I would guess that this is to improve battery life. But also, imagine that you plugged in at the top of Mt. Washington & then went down the auto road. The potential energy times 0.8 is about 15% SOC, so it keeps from overcharging the battery. Probably likewise going up an extreme grade where the ICE might not be able to keep up.

 

[Jason M. Hendler]

If the Volt only uses 8 kWh of its battery pack for 40 miles, then it gets 5 miles per kWh. Tesla Motors gets 225 miles for its 56 kWh, which is 4 miles per kWh. I wonder how the Volt achieves better efficiency, as both vehicles have regenerative braking and a single gear.

Oh, perhaps Tesla only depletes 80% of its battery. Still, I thought the Tesla Motors vehicle had a more efficient motor design.

 

[Tom]

Tesla and Volt Contrasts.

Jason,

Tesla depletes their battery to a lower state of charge, SOC. The decrease battery voltage and efficiency with this lower SOC. To get to higher power levels for their higher hp motor, the Tesla runs at higher current than the Volt, more I^2R losses. My simulation shows that at 55 mph the larger weight of the Volt is equaled by the higher wind drag losses of the Tesla to give approximately equal losses for wind drag versus tire dissipation totals at cruise. I suspect the driving range of the Tesla, a sports roadster, is established with a more aggressive driving profile than the Volt. The Volt, with its 200+ man design team, probably has ten times as much engineering simulation/optimization work (reduced inverter power dissipation losses, better heat design) than the Tesla. Eventually it will also use more advanced technology (SiC on Si power electronics, advanced heat exchangers, dual side cooling, custom caps with reduced ESR, and custom ICs with increased UpIntegration. One result is less power is required to run fans.). I also suspect Volt will use hybrid magnetic and variable reluctance motors for increased motor efficiency.

 

[Jason M. Hendler]

Tom,

I get all that, but I thought Tesla had a "secret sauce" for their motor in particular, that made it more efficient. Perhaps they only improved the power to weight ratio, as opposed to efficiency.

 

[Mausoldj]

If the Volt only uses 8 kWh of its battery pack for 40 miles, then it gets 5 miles per kWh. Tesla Motors gets 225 miles for its 56 kWh, which is 4 miles per kWh. I wonder how the Volt achieves better efficiency, as both vehicles have regenerative braking and a single gear.

Oh, perhaps Tesla only depletes 80% of its battery. Still, I thought the Tesla Motors vehicle had a more efficient motor design.

I apoligize if this has already been mentioned, but the Tesla is a 100-0 discharge and the Volt is a 80-30(20?). I don't have the sheet in front of me, but that should be correct.