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Discussion Starter · #1 ·
I've seen a number of discussions on this. Thought that this statement from GM's Chief Engineer for Electrified Vehicles hit the spot:

Efficient Charging
 

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jashev - good question.
Earlier this year was, I part of a data logging trial for 3 months, a study done by FleetCarma. On my 2012 Volt, here's what I observed:

Miles driven: 4,863
Electric %: 100%

Total charge events: 269
Level 1 charges (120V): 78
Level 2 charges (240V): 191

Total energy (kWh): 1,242
Total charger loss (kWh): 160 (12.9%)

Level 1 energy (kWh): 385.8
Level 1 charger loss (kWh): 55.68 (14.4%)

Level 2 energy (kWh): 856
Level 2 charger loss (kWh): 104.1 (12.2%)
 

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Yet another reason for installing aL2 EVSE
 

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Discussion Starter · #6 ·
jashev - good question.
Earlier this year was, I part of a data logging trial for 3 months, a study done by FleetCarma. On my 2012 Volt, here's what I observed:

Miles driven: 4,863
Electric %: 100%

Total charge events: 269
Level 1 charges (120V): 78
Level 2 charges (240V): 191

Total energy (kWh): 1,242
Total charger loss (kWh): 160 (12.9%)

Level 1 energy (kWh): 385.8
Level 1 charger loss (kWh): 55.68 (14.4%)

Level 2 energy (kWh): 856
Level 2 charger loss (kWh): 104.1 (12.2%)
2.2%! That's pretty significant. Very interesting!
 

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jashev,
I diced my data some more. For L2 charging events greater than 2.0 kWh (119 events), charger loss averaged 12.1%.

Similarly, L1 charging events greater than 2.0 kWh (56 events), charger loss averaged 14.6%.
 

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From my perspective It matters very little, since 99% of the time when I'm charging on my Level 1 unit I'm not paying for the electricity.
 

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L2 still doesn't pan out for me, I'd only save about $50 a year between the 2% charger loss and off-peak vs. super-off peak rate differences. Installation cost aside, an L2 EVSE alone would take close to 10 years to pay for itself in my garage. I rarely drive more than 40 miles in a day and I sleep during nighttime when the car charges- so I don't see the point of installing L2 at home, at least for the way I use my Volt.
 

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A couple of reasons come to mind that the 240 Vac system would be more efficient:

  • Less power loss in the line cord
  • Better efficiency in the AC-DC charger in the car

Line cord: Total energy delivered during a charging event would be Volts x Current x Time. If you double the voltage and keep the current the same, then you can deliver the same charging energy in half the time. Energy loss in the power cord will be ((Resistance x Current) x Current x Time). At 240 Vac, with the same current but half the charging time, you cut your line cord energy loss in half.

Charger: Energy loss in the AC-DC charger in the car will be due to a variety of factors. The unit converts 120 Vac / 240 Vac to DC, and steps it to up approximately 380 Vdc. Charger energy loss will be related to both operating voltage and current. As a generalization, the charger operates more efficiently at a step up ratio that is closer to one. 240 Vac gives a step up ratio closer to one.

The shorter charge time with 240 Vac is beneficial for me for a couple of reasons. On weekends I can drive the car in the morning, top off the charge, then drive with full range in the afternoon. Another consideration is that my utility has a very low electrical rate from midnight to 7 AM. With 240 Vac, I can do a full charge at the cheapest rate. With 120 Vac, I’m buying part of my charging power at ~2.6x higher rate. I would agree with other posters that they payback time on the 240 Vac system is relatively long.
 

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Discussion Starter · #11 ·
jashev,
I diced my data some more. For L2 charging events greater than 2.0 kWh (119 events), charger loss averaged 12.1%.

Similarly, L1 charging events greater than 2.0 kWh (56 events), charger loss averaged 14.6%.
Even more impressive. Since I am pretty much retired, I also find it convenient to be able to run around in the morning, get home and charge, then have full range again in the afternoon.
 
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