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Thank you. So 80% is all that can be expected from first generation EV :(


True that range is king at the current moment in time, but it shouldn't be. Part of the movement into EV is about getting more out of energy, so I think efficiency should be king.

If the shorter range, but better engineered car will meet my daily range needs or my usual long journey hop length, whichever longest. If there's sufficient charging infrastructure and it recovers the hop length in sufficient time. I would actually choose the shorter range car.

But I understand my way of thinking is minority. Perhaps this is why people buy stupidly big "tractors" for local trips to the school.
Precisely why I deliberately chose the 28kWh Ioniq (Classic) in preference over newer models and longer-range competitors: it has plenty of range for daily use, superb efficiency and very fast-charge recovery when on long journeys.
 

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Discussion Starter #23
In 30 kWh Soul charger efficiency @ full whack (6.6 kW) is around 90 %. Using granny charger it's only around 75%. Both values can be seen using Torque pro via OBD port.
This would suggest AC-DC chargers are actually over 90% efficient as previously mentioned, it's the car electronics that brings down calculated charging efficiency for slower charging cars.

Thank you for clearing this up. Conclusion is, buy cars with fast AC-DC charger built in.

I wonder what sort of efficiency Renault Zoe charging on 22 or 43 kW can achieve........
 

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The faster you charge the more heat is generated, i.e. the more energy is lost to heating.

The granny charger result is odd. I wonder if some of the energy was used to run the battery heater. Does the Soul have a battery heater?
 

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The faster you charge the more heat is generated, i.e. the more energy is lost to heating.

The granny charger result is odd. I wonder if some of the energy was used to run the battery heater. Does the Soul have a battery heater?
It's not that odd if there are fixed overheads outside of the onboard charger itself - which there are. Start with an assumed 95% efficiency at all power levels (optimistic) for the on board charger, and add a constant ~300 watt parasitic power draw from the rest of the car during charging.

Charging at 2kW - 95% efficiency means 1900 watts DC out of the charger, 300 watts wasted elsewhere (not going into the battery) gives 1600 watts. 1600/2000*100 = 80%.

Charging at 3kW - 2850 watts out of the charger, 300 wasted = 2550 watts. 2550/3000*100 = 85%.

Charging at 6kW - 5700 watts out of the charger, 300 wasted = 5400 watts. 5400/6000*100 = 90%.

Lines up pretty well with observed figures ?

Think of it like the heater in the car. Once up to temperature it takes the same amount of power (more or less) to keep you warm whether you're doing 30mph or 60mph, so the heater is a fixed overhead. At 60mph you'll get to your destination twice as fast so the heater runs for half the length of time and consumes half the total energy. Therefore at higher speeds the range loss from the heater for a given journey distance as a percentage is smallest and the penalty for turning on the heater is the greatest at slower speeds.
 

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Discussion Starter #26
The faster you charge the more heat is generated, i.e. the more energy is lost to heating.
This is also very true. So Zoe 43 kW charging may not be as efficient. But the internal resistance also relates to C number when charging does it not? Low C number means less heating of the battery?

I feel 7 or 11 kW is probably the most efficient charging speed for today's 50 +-10 kWh cars: doesn't heat up the battery but still quick enough to minimise the fixed overhead.
 

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This is also very true. So Zoe 43 kW charging may not be as efficient. But the internal resistance also relates to C number when charging does it not? Low C number means less heating of the battery?
Cell internal resistance doesn't change much with the C rate, its determined primarily by the size and design of the cell, also state of charge and cell temperature. (Also battery age as resistance gradually goes up as batteries age and degrade)

Unlike wires which increase in resistance when they get hot, Lithium Ion cells actually have their lowest resistance when they're fairly warm (somewhere around 40C) and higher resistance when they're cold. So rapid charging a battery which is cold can cause it to warm up and drop in resistance improving efficiency slightly.

Most of the losses at 43kW are going to be in the charger itself I'd say - I calculated that even on the tiny 16kWh battery in my Ion, when charging at 43kW the losses in the battery due to cell resistance (of a nice warm 30-40C battery where resistance is lowest) are only about 3%, which isn't that much when you think about it.
I feel 7 or 11 kW is probably the most efficient charging speed for today's 50 +-10 kWh cars: doesn't heat up the battery but still quick enough to minimise the fixed overhead.
I haven't tried to calculate it but my gut feeling is that you're probably right and around 7-11kW is the most efficient charging speed for today's EV's.

Go too low and the fixed overheads start to eat into efficiency as was just discussed - go too high and the charger itself starts to become a bit less efficient due to I^2*R losses, along with things like cables and connectors. Anything with resistance has I^2*R losses that increase with the square of the charge current. You end up with with losses that look roughly like an inverse bell curve with losses increasing at both slow and fast ends.

Of course with DC rapid charging only the battery cell resistance losses and part of the cable/connector losses are in the car - the AC/DC conversion losses are now the problem of the rapid charger which is doing the legwork and dissipating the lost power... one of the many reasons why DC rapid charging is superior to AC. (Make that bulky, power dissipating charger "someone else's problem" outside of the car itself)
 

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Most of the figures shown on a Leaf dashboard are wildly optimistic but assuming their miles/kWh (from battery) is anywhere near accurate then dividing that by my own miles / metered kWh supplied should give an indication of charger efficiency. On my 40kWh that figure gave : 1.020 (average of last 3 months) but on the e+ it's 1.141 (average of first 3 weeks).
 

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The faster you charge the more heat is generated, i.e. the more energy is lost to heating.
True, but batteries and semiconductors often behave in a non-linear fashion and may be less inefficient at higher rates.
 

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Discussion Starter #30
Most of the figures shown on a Leaf dashboard are wildly optimistic but assuming their miles/kWh (from battery) is anywhere near accurate then dividing that by my own miles / metered kWh supplied should give an indication of charger efficiency. On my 40kWh that figure gave : 1.020 (average of last 3 months) but on the e+ it's 1.141 (average of first 3 weeks).
1.24 for my Leaf 24 at 3.3 kW charging :(

Cell internal resistance doesn't change much with the C rate, its determined primarily by the size and design of the cell, also state of charge and cell temperature. (Also battery age as resistance gradually goes up as batteries age and degrade)
Thank you for another great explaination.

Is it right to say as cells degrade, they are essentially building internal resistance on top of loosing ability to charge. So a 60% degraded battery will become less efficient take more than 60% of original capacity to charge?
 
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