Electric Vehicle charging

Thread Starter

Ian0

Joined Aug 7, 2020
2,192
How many kWh does it take to charge a 100kWh vehicle battery?
There's a few factors involved:
Resistive losses, transformer losses, switching losses.
Lithium ion batteries charge at 4.2V but discharge at 3.7V, but that's not true for the entire charge-discharge cycle.
Does anyone have an approximate figure for the charge efficiency?
On pay-chargers, which side of the charger circuitry is the meter? On the mains side or on the output side?
 

sagor

Joined Mar 10, 2019
439
Many EV cars have a 120V or even a 240VAC charging port. Those cars that are pure EV, may require overnight charge at 120V, but only a few hours at 240V.
At 240V and 20A charge (very conservative value), you are charging close to 5kw per hour. Most EV cars have a battery in the 18 to 24kwh range, not 100kwh. Exceptions exist of course.
At 240V and 40A, you would be charging close to 10kw per hour, and that would charge a 100kwh battery in about 10 hours, excluding efficiency losses.
 

Thread Starter

Ian0

Joined Aug 7, 2020
2,192
Absolutely not! They discharge from 4.2V down to 3.0V. 3.7V is about half a full charge.
That's what I meant - perhaps I could have put it better. Charge goes in at an average potential of 4.2V - charge comes out at an average potential of 3.7V.
 
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Thread Starter

Ian0

Joined Aug 7, 2020
2,192
He means KWh per hour, which can be simplified to KW.

Bob
Like I said. Power is measured in Watts, so kW/hour must be rate of change of power or dP/dt.
I can excuse some of the dim witted “scientific” journalists on the daily newspapers for failing to understand the difference between power and energy, but I’d hope we could manage to get it right on AAC!
 

Irving

Joined Jan 30, 2016
1,497
My wife's i-Pace has a 74kW battery pack. On a 3.8kW charger it takes 15h to go from 30% to 100%, that's about a 10% overhead. This is similar to my 24v/200Ah LiFePO4 packs, which take on average 202Ah to charge from 10% to 100%, about an 11 - 12% overhead.

My 24v charging setup goes 240v/5.4A (1296W) to 24v/50A (1200W) into the charger, 28V/40A (1120W) out of the charger- so about 13% losses. Coupled to the 11% charging overhead that's 6500W input to realise 4800W storage, about a 30% overhead.

I'd expect the i-Pace charging to be more efficient as the i-Pace has a 388V battery so the single step conversion from 240v rms (340v pk) is more effective, say 95% so overall about a 15% overhead.

Incidentally the i-Pace is returning approx 4miles/kWh (stored) or 3.4miles/kWh (input) and a kWh costs me 12.6p, so about 3.7p/mile, compared to her previous petrol-powered Audi Q5 at 7.7miles/litre @ 121p/litre = 15.7p/mile...... Mind you, its unlikely she'll manage to do the 225,000 miles necessary to reconcile the difference in the price of the vehicles (but there are cheaper EV cars than the i-Pace!).
 
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andrewmm

Joined Feb 25, 2011
1,466
And so is the foot-pound

sorry , I thought you asked what it was,

Interesting fact,
a French foot was longer than a UK foot,
So I'd guess a French foot pound was also larger,

Thank you french for the Si unit system,

I note even the later star treks use Km for distance, ( the prequil enterprise used miles I think )
 

Thread Starter

Ian0

Joined Aug 7, 2020
2,192
sorry , I thought you asked what it was,

Interesting fact,
a French foot was longer than a UK foot,
So I'd guess a French foot pound was also larger,
unless the French pound was lighter! Then they might have been the same. It would be a pied-livre!
 

Irving

Joined Jan 30, 2016
1,497
Many EV cars have a 120V or even a 240VAC charging port. Those cars that are pure EV, may require overnight charge at 120V, but only a few hours at 240V.
At 240V and 20A charge (very conservative value), you are charging close to 5kw per hour. Most EV cars have a battery in the 18 to 24kwh range, not 100kwh. Exceptions exist of course.
At 240V and 40A, you would be charging close to 10kw per hour, and that would charge a 100kwh battery in about 10 hours, excluding efficiency losses.
In the UK the home-chargers are 240v/16A single-phase (so-called '3kWh' chargers) or 240v/32A 3-phase ('7kWh', but that involves the householder in significant additional expense). Most public chargers are 7kWh; there are 10kWh and higher though not all cars can use 10kWh+ and will revert to 7kWh max.
 
How many kWh does it take to charge a 100kWh vehicle battery?
There's a few factors involved:
Resistive losses, transformer losses, switching losses.
Lithium ion batteries charge at 4.2V but discharge at 3.7V, but that's not true for the entire charge-discharge cycle.
Does anyone have an approximate figure for the charge efficiency?
On pay-chargers, which side of the charger circuitry is the meter? On the mains side or on the output side?
Here, make it easy on yourself: https://www.caranddriver.com/features/a36062942/evs-explained-charging-losses/
 

Thread Starter

Ian0

Joined Aug 7, 2020
2,192
Thanks.
I find it rather difficult to believe that they are getting 99% efficiency. That would suggest that the cells can discharge at only 1% lower voltage than the charge voltage. Charging at an average of 3.74V and discharging at 3.70V? Really? And that would require zero losses in the circuitry.
I'm rather more inclined to believe @Irving and @BobTPH.
 
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