Charging Question

[tim@groundwork]

OK, so when I'm charging (refreshed Model S LR) it pulls 30amps at 200volts. If I'm at 10% SoC it will charge to 20% in about an hour. If I'm at 80% it will charge to 90% in about two hours. My question is, is it more expensive to charge my car when it has a full charge (since it takes so much longer at a higher SoC)?

 

[GtiMart]

Look at how many kW your car is pulling while it charges. You are paying electricity per the kWh. 30A @ 200V makes 6kW, assuming these are the real values you see in the car as it charges. Plugged in a 6kW for one hour consumes 6kWh.
How big is the battery? A refreshed LR S might have a 100kWh battery. 6kWh only represents 6%. You can't go from 10% to 20% in an hour with that setup. If you gain 10% in one hour, it means you used at least 10kWh, your charging configuration must provide more power than what you indicated.

 

[leapingwhale]

OK, so when I'm charging (refreshed Model S LR) it pulls 30amps at 200volts. If I'm at 10% SoC it will charge to 20% in about an hour. If I'm at 80% it will charge to 90% in about two hours. My question is, is it more expensive to charge my car when it has a full charge (since it takes so much longer at a higher SoC)?

No. If you have a typical residential setup that only meters energy (i.e., no demand charges), then the cost only depends on the amount of energy (i.e. kilowatt-hours) that you consume which is essentially not dependent on charging speed (i.e. power). For commercial fleets, especially for heavy duty vehicles, demand charges are usually a prime consideration. In these cases, so-called demand management may be used to intentionally slow charging. The point is worrying about slow charging being costly is either irrelevant (most residential applications) or wrongheaded since faster charging is the true driver of cost in applications with metered demand.