1. May 24, 2013

### nchin

The Nissan leaf is powered by 107 hp electric motor, kept alive by a pack of batteries, It takes 79.85 kilowatts to run the motor, assuming 100% efficiency.

a) The Nissan contains a 24kWh battery pack and its estimated that using a 220V charging dock at home. The leaf can be charged in 8 hours. What the current as the leaf is charging?
b) if it cost 11 cents perkilowatthour, how much does it cost to fully charge the leaf?

a) i = P/V =>(24000*8)/220 = 872.7 A
b)79.851 x 8 hours = 638.808
638.808 x .11 = \$70.26

is this right?

2. May 24, 2013

### rude man

Not right.

If the battery can supply 24 kW for 1 hr then if it had to be recharged in 1 hr it would take how many amperes to recharge? And if we can take 8 hrs to recharge, would that take more or less current?

3. May 24, 2013

### nchin

i dont understand. (24 kW times 8 hours to recharge)/220V?

4. May 24, 2013

### CWatters

Think about the units for kWh

= Watts * time(in hours)/1000
= Current(Amp) * Voltage(volts) * time(in hours)/1000

PS I believe a Leaf can be charged from a normal domestic socket so 800-900A is unlikely

5. May 24, 2013

### nchin

24000 * 8 hours /1000 = 192 W

current=192W / 220Volts = 0.87 amps?

6. May 24, 2013

### CWatters

No you missunderstood my post totally.

I start from the beginning ...

The battery stores a quantity of energy. I wish they would specify that in Joules but they used kWH instead which is ok.

kWH means kilo Watt Hours so a sum that gives an answer in kWH will involve multipling power(in Watts) by time(in hours).

Specifically...

Energy (in KWH) = Power(in Watts) * time(in hours)/1000..................(1)

but as you know

Power(in watts) = Current(in Amps) * Voltage(Volts)...........................(2)

substitute to give..

Energy (in KWH) = Current(Amp) * Voltage(volts) * time(in hours)/1000

The question asks for the current so rearrange that to give

Current = (Energy * 1000) / (Voltage * time)

Then plug the numbers in.

Last edited: May 24, 2013