Charging overhead - why L1 is so inefficient.

[jadnashuanh]

The i3 has active cooling which may account for some additional energy use, depending on when the car was used and how hot things are.

 

[bwilson4web]

. . .
o i forgot

The volt reported 24,8km and 2700-2800watt/h its only displays 2.7 so it can be almost 2.8
thats a calculated 2700 to 2800 / 24,8 = 108,87 to 112,9 watt per km.

the i3 reported 24,8km and 11.2kwh/100km or 112 watt per km.

and at the socket after charging 3300 for the I3 en 3200 for the volt.

again 37,8kmph average speed.

I did the following by monitoring the average speed. If it was below 26 mph (41,6kmph) from a stop, I would resume at a higher speed 30-35 mph (48,0-56,0kmph) until it was back to 26 mph (41,6kmph). No heating or A/C with cabin temperature controlled by partially opening windows as needed. There were two segments:

• Lat 34.652870 Lon -86.571707 Elevation 183m Temp 66 F (18,9C)
• Lat 34.714168 Lon -86.669213 Elevation 201m Temp 61 F (16,1C)

Here is the source data:

• 14.6 mi (23.4km)
• 25.4 mph (40,6kmph)
• 6.8 mi/kWh (10,9km/kWh or 91,7kWh/km)

• 21.4 mi (34,2km)
• 26.3 mph (42,1kmph)
• 7.9 mi/kWh (12,6km/kWh or 79,4kWh/km)

• Segment 1 - 91,7kWh/km * 23.4km = 2145,8kWhr
• Segment 2 - 79,4kWh/km * 34,2km = 2715,5kWhr
• Vehicle = 4.9 kWhr, EVSE = 5.8 kWhr ~84% efficiency, ~0.9 kWhr lost
• 5.8 kWhr / (14.6 + 21.4) = 161.1 kWhr / mi.

My EVSE can handle up to 40 A charging but the BMW i3-REx only draws 30-31 A, ~7.2 kW/hr.

In my normal commuting, speeds are significantly higher. I estimate:

• ~0.5 mi @25 mph, ending in long stop light delay
• ~6 mi @55 mph, ending in long stop light delay
• ~1.5 mi @45 mph, ~1 stop light delay
• ~1 mi @65 mph, 1 stop light delay

I can replicate this benchmark and set the EVSE maximum charge rate to 12 A. This will simulate using the L1 charger that comes with the car. However, I suspect we won't see a significant change in the round-trip efficiency because the built-in charger is likely the greatest source of loss. Converting AC to DC is difficult to do efficiently.

Bob Wilson

ps. I used 1.6 km/mi for conversions. Standard units used "," for decimal point; nothing used for 1000 unit marker, and no " " between quantity and units. Results were rounded to nearest 0,1. If non-USA numbers use "," as the decimal place maker, what do they use for 1000 unit marker. For example, does 2145,8kWhr becomes 2,145,8kWhr?

 

[GI3L]

. . .
o i forgot

The volt reported 24,8km and 2700-2800watt/h its only displays 2.7 so it can be almost 2.8
thats a calculated 2700 to 2800 / 24,8 = 108,87 to 112,9 watt per km.

the i3 reported 24,8km and 11.2kwh/100km or 112 watt per km.

and at the socket after charging 3300 for the I3 en 3200 for the volt.

again 37,8kmph average speed.

I did the following by monitoring the average speed. If it was below 26 mph (41,6kmph) from a stop, I would resume at a higher speed 30-35 mph (48,0-56,0kmph) until it was back to 26 mph (41,6kmph). No heating or A/C with cabin temperature controlled by partially opening windows as needed. There were two segments:

• Lat 34.652870 Lon -86.571707 Elevation 183m Temp 66 F (18,9C)
• Lat 34.714168 Lon -86.669213 Elevation 201m Temp 61 F (16,1C)

Here is the source data:

• 14.6 mi (23.4km)
• 25.4 mph (40,6kmph)
• 6.8 mi/kWh (10,9km/kWh or 91,7kWh/km)

• 21.4 mi (34,2km)
• 26.3 mph (42,1kmph)
• 7.9 mi/kWh (12,6km/kWh or 79,4kWh/km)

• Segment 1 - 91,7kWh/km * 23.4km = 2145,8kWhr
• Segment 2 - 79,4kWh/km * 34,2km = 2715,5kWhr
• Vehicle = 4.9 kWhr, EVSE = 5.8 kWhr ~84% efficiency, ~0.9 kWhr lost
• 5.8 kWhr / (14.6 + 21.4) = 161.1 kWhr / mi.

My EVSE can handle up to 40 A charging but the BMW i3-REx only draws 30-31 A, ~7.2 kW/hr.

In my normal commuting, speeds are significantly higher. I estimate:

• ~0.5 mi @25 mph, ending in long stop light delay
• ~6 mi @55 mph, ending in long stop light delay
• ~1.5 mi @45 mph, ~1 stop light delay
• ~1 mi @65 mph, 1 stop light delay

I can replicate this benchmark and set the EVSE maximum charge rate to 12 A. This will simulate using the L1 charger that comes with the car. However, I suspect we won't see a significant change in the round-trip efficiency because the built-in charger is likely the greatest source of loss. Converting AC to DC is difficult to do efficiently.

Bob Wilson

ps. I used 1.6 km/mi for conversions. Standard units used "," for decimal point; nothing used for 1000 unit marker, and no " " between quantity and units. Results were rounded to nearest 0,1. If non-USA numbers use "," as the decimal place maker, what do they use for 1000 unit marker. For example, does 2145,8kWhr becomes 2,145,8kWhr?

GREAT

well i did have lower temp. 12c ( 53,6f )
that would account for a lower watts per km/mile in my case compared to yours.
is was also cloudy
and of course we can not simulate the exact road conditions and stoplights etc.

i guess elevation is not that important because it is a electric car?

thats are high loss in charging i did see a PDF where they say more like 90%+

 

[bwilson4web]

...
GREAT

well i did have lower temp. 12c ( 53,6f )
that would account for a lower watts per km/mile in my case compared to yours.
is was also cloudy
and of course we can not simulate the exact road conditions and stoplights etc.

i guess elevation is not that important because it is a electric car?

thats are high loss in charging i did see a PDF where they say more like 90%+

I would not rule out the cooler temperatures as possibly allowing more passive temperature control versus having to run the A/C to deal with the charger and battery heat. Sad to say we don't have enough metrics about the BMW i3-REx to make an accurate model, yet.

In my case, I have a couple of 'test routes' that I use to eliminate stops. In this case, I used ordinary streets of Huntsville which for the most part asphalt paved. I did select streets to minimize lights and delays (i.e., we have right turn on red after stop which in practice is 'Yield to traffic on a right turn.'

Elevation is important as on the return I got better performance. I see a similar effect when benchmarking our 2010 Prius.

The only advantage I see with L1 charging at 12 A is reduction of (I**2)*R losses and possibly passive cooling as opposed to active cooling at a higher rate. But I'll have to test to find out.

As for the built-in charger efficiency and battery characteristics, I'm not ready to dive into that area, yet.

Bob Wilson

 

[GI3L]

how long do you have the i3?

 

[bwilson4web]

how long do you have the i3?

May 27, 2016, 6:00 PM (Eastern Daylight Time)

Bob Wilson

 

[jadnashuanh]

The only real effect on elevation in a BEV is the energy required to climb up or coast down...unlike an ICE, where it may or may not be as efficient at altitude (a turbocharged engine may have enough excess boost to not show much of any differences). Yes, the air might be a little less dense, but it's typically colder, so that makes it a bit more dense, so the effect isn't as great.