Cost of charging?

[broosth]

One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.

 

[WetEV]

One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.

Efficiency is higher at higher charge rates.

 

[SparkE]

A 240V EVSE (the "charger", which converts AC to DC current, is in the car) is generally slightly more efficient than a 120V EVSE.

Suppose it is 10% more efficient to use 240V (which is over-stating it). In order to make up the approx $500 for the EVSE (i.e., break even), a person would have to suck up $5000 worth of electrons at 120V. At $0.20 a kWh (I'm just making that up) that is 25000 kWh (enough to drive over 100,000 miles in a Bolt). At $0.10/kWh : 50,000 kWh.

Don't sweat it.

 

[broosth]

Thanks. I am not sure why it would be more efficient, but I have not seen any technical discussion of the process. I see lots of explanations of charging rates, but nothing about the AC/DC converter process nor the issues of cell charge balance. As a person with an EE degree (albeit 48 years out of date) i'd like to see more detail.

 

[BarfOMatic]

start reading through the last few years of posts - the topic(s) has/have been covered before.

Edit: Oh, and since this is NOT AT ALL specific to the Bolt, can this thread be moved out of the Bolt-specific part of the forum? Pretty please?

 

[WetEV]

Thanks. I am not sure why it would be more efficient, but I have not seen any technical discussion of the process.

This isn't a graph of the Bolt's charger, which is just a high power DC to DC converter with an adjustable output voltage and current limits, but is of a more common part with much lower power output.

Do you really want to dive into DC to DC converter design? I've designed some low power ones, but not a 7kW one...

 

[SparkE]

Moving to "off-topic" area ...

And WetEV - did you mean AC-to-DC converter?

 

[SparkE]

An article :

Understanding AC/DC power supply efficiency : https://www.xppower.com/Portals/0/pdfs/TA_Understanding%20ACDC_0810.pdf

 

[WetEV]

And WetEV - did you mean AC-to-DC converter?

Done in two steps for every system I've looked at.

Rectified and filtered to DC with some ripple, then put into a DC to DC converter.

Amusing. A Youtube teardown of a power supply, including a "cat move a little bit. Go go go."

https://www.youtube.com/watch?v=B19rB_FR5Mk

 

[theothertom]

One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.

Heat looses due to resistance tend to be higher with lower voltages. So 240V is more efficient than 120.

 

[like2bike]

I think the difference between L1 and L2 is much more the than most people would guess. I am working on doing a comparison study but don't have very accurate numbers yet. One thing I noticed was that the Bolt L1 cable uses 16 gauge wire while my 2013 LEAFs L1 used 12 gauge. I calculated the Chevy L1 would use 15 watts more in cable loss at 12 amp charging. My present estimate for the charging efficency is as follows:

Measured from breaker box to DC into battery on the Bolt, 12A Chevy L1, 7.2KW L2:
L2: 94%
L1: 88%

Admittedly, one big factor is the L2 was installed next to the breaker box to minimize wiring loss and the L1 is coming from an existing 15A outlet on the far end of my garage. I did change the outlet receptacle to a commercial grade one though.

Hopefully, I'll have more accurate data soon.

 

[GetOffYourGas]

Taking your numbers at face value:

To charge at L2, you need roughly 60/.94 = 63.8 kWh
To charge at L2, you need roughly 60/.88 = 68.2 kWh

The difference is 4.4kWh, or $0.53 at $0.12/kWh.

Even charging fully twice a week (that's a lot of driving!), it's $1.06/wk or $55.12/year. It would still take 9 years to break even with SparkE's $500 L2 EVSE. And that number is low if you need to call an electrician.

 

[Arob216]

Power companies transmit at very high voltage to overcome resistance\loss en-route. As a % of power delivered, resistance consumes a bit less power.

Also, with a shorter charge time, if battery conditioning kicks in due to extreme temperatures, the shorter charge time translates to less conditioning time. So in extreme hot or cold, the efficiency of L2 improves even more than in 60-80F temps.

https://www.veic.org/documents/default-source/resources/reports/an-assessment-of-level-1-and-level-2-electric-vehicle-charging-efficiency.pdf

 

[like2bike]

I have more confidence in my measurements now and I still have similar results. I will also show results without the house wiring loss:

Breaker Box to DC into battery: 87.8% for Bolt L1, 94.1% for Schneider L2.
Wall plug to DC into battery: 89.6% for L1, 95.3% for L2 (actually hard wired).

For me the cost difference for a full charge would be $1.01
$0.22 x (60/87.8 - 60/94.1) = $1.01

Surely not a great payback. But here are the other advantages of L2:

• 
  Safer, no 120V outlet used.
  Faster charging (this is more often an advantage with the LEAF)
  Money going to EV infrastructure instead of electric.

When you realize you're not going back to ICE, it's time to take the plunge.

 

[Rowlemi]

One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.

If my knowledge is correct...Your friends are probably misinformed. The cost per kilowatt hour is the same whether you charge at 120V or 240V - the only difference is the charging speed. Faster charging may be more convenient, but it does not affect the price of electricity...

 

[ClarD]

The cost per kilowatt hour is the same whether you charge at 120V or 240V

You're only counting the kWh delivered to the battery.
You are missing the overhead of having the car "on" for twice as long.

In Car Scanner, I see a loss of 384 watts from the AC input to the DC received by the battery. My voltage drop from the AC meter to the EVSE wall plug indicates another 118 watts lost. Some of that is charger efficiency, some is the overhead of the supporting electronics.

 

[BillM]

The onboard inverter is more efficient at 240 Volts input so there’s also that improvement multiplied by the duration of the change cycle. The power loss in the wiring feeding the outlet or connected to the charger is related to the current squared times the electrical resistance of the wire. The power loss in the wire is greater at the higher level-2 current, but that is offset by a shorter charge duration. The wire loss is not insignificant, but is probably a wash comparing level-1 and level-2.

Over all, you’re better off with level-2 charging. I use the EVSE cord which was supplied with my Bolt and a 240 Volt socket adapter. I am limited to 12 amps which is programmed into the cord’s control box and appropriate for the fairly small gauge cable of the car cord. The Bolt charges in somewhat less than half the time at 240 than it does at 120 using the same cord. Even though the charge current is “only” 12 amps, it is enough for the way I drive and ai didn’t have to install an expensive high current level-2 charger.

I had the electrician install a good quality four prong Hubbell 1450 240 volt outlet, so I am ready if I decide I need the speed of a higher current EVSE.