EVSE 120 VAC Charging Efficiency

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MrDRMorgan

Well-known member
Joined
Oct 30, 2013
Messages
1,211
Location
Manteca in Central California
What is the charging efficiency of the EVSE charger? Said another way, for 10 kWh into the car's battery how much power must be supplied from the wall? I need this number to estimate how much of my solar system output will be consumed by charging the car.

28 June 2015: It is looking like the 120 VAC charger supplied with my Spark EV is averaging about 69% charging efficiency as calculated using a power meter at the wall outlet and the Energy Used value found on the Energy Info screen under Energy Details.
 
For future reference charging efficiency is not dictated by the EVSE but rather the cars on board charger and the vehicles auxiliary loads (fans, pumps, electronics etc.)
 
^^^
Yep. L1 and L2 EVSE efficiency is actually very high due to them being not much more than a smart safety switch. Almost all of the losses are in the above, as Jedi2155 stated.
 
Thanks. I knew the charger was onboard in the car and I caught my error after reading many more posts. I have a lease pending and I wanted to make sure I made a reasonable estimate of how much of my home PV solar system output would be consumed by the car considering my usage was approximately 30 miles per day average. The standard 120 VAC Level 1 charger should be adequate. I do not use a TOU electrical rate schedule as my PV solar system currently covers 100% of my home's annual power requirements and I have net metering. The car would add 8579 kWh annually and, after factoring in my solar system output and my home's power consumption, I would, at the end of 1 year, owe my power company for 2791 kWh at a total annual cost of $460. Not bad considering my 2002 Honda Accord would consume about $1631 in gasoline for the same number of miles.
 
MrDRMorgan said:
What is the charging efficiency of the EVSE charger? Said another way, for 10 kWh into the car's battery how much power must be supplied from the wall? I need this number to estimate how much of my solar system output will be consumed by charging the car.

For the first year I owned my Spark EV I measured the input energy and took note of the energy consumed as shown on the internal display. Most of my charging was from Chargepoint stations but some was from 120V with a "Watts-Up" to measure the energy consumed in charging.

From my measurements the efficiency using L2 charging is ~83% but ~78% using L1 (usually at the 12Amp setting).

I suspect the main loss is the power consumed by cooling circulation and the various parasitic loads that are on when charging. Since they will be the same for L1 and L2 that will reduce the efficiency when using L1.

kevin
 
Thanks Kevin. It looks like your data supports using 75% charging efficiency for the L1 charger in the vehicle. I am looking to take delivery of my Spark EV this week. It was in transit as of yesterday.

Dennis
 
NORTON said:
You could get all your usage data on 120V charging with one of these: http://smile.amazon.com/P3-Internat...UTF8&qid=1432515292&sr=8-2&keywords=killawatt
As much as I like the Kill-A-Watt (I have the original http://www.p3international.com/products/p4400.html, as that was about all that existed when I got mine), I wouldn't want to use it for a car charging continually at 12 amps. It'd be fine for a few minutes...

There have been reports of melting like these below:
http://www.mynissanleaf.com/viewtopic.php?p=173354#p173354
http://www.mynissanleaf.com/viewtopic.php?p=320201#p320201
 
There have also been reports of EVSE's melting old wall outlets.
I had my Killawatt in daily service for a couple of months with my Volt before getting an L2 at home.
Never had a problem. Always at 12 A. Of course I had it plugged into a brand new dedicated 120V wall outlet.

It allowed me to see I was spending $39 per month to drive my Volt. $0 per month at the gas station!
Then I also got access to plug in while at work, so my data gathering came to an end and I just enjoyed EV travel.

My Spark EV has the DC Fast charge option and the fact that my town has a pioneering Free DC Fast charge network, (14 CCS Combo/Chademo and dozens of L2's),
I may ramp up the OCD and never charge at home! .
I can see myself saying in 6 months, "I never spent a dime on powering this thing" !
 
Thanks Norton. I do have one of these Kill-A-Watt EZ power meters which I will use just to verify my power consumption estimates. Given what I have read, I too would be reluctant to continuously run my charging through the meter. However, it is possible that a bad (resistive) AC outlet is the real cause of the problem and not the meter itself. I have had some experience with AC outlets going bad and had to replace them.

In my garage I have a dedicated 20 amp outlet that is currently used for my built-in house vacuum system. This outlet is not used at night so I plan to use it to charge the car.
 
I don't know if efficiency is relevant in estimating solar. SparkEV L1 has two modes: 8A mode and 12A mode. Obviously, 12A mode will be less efficient. At 8A mode at 120V, it's slightly under 1kW. I measured about 80% with 8A L1. My measured data along with house wiring loss is at

http://sparkev.blogspot.com/2015/05/spark-ev-efficiency.html
 
Great information. Thanks so much. I use 4 mi / kWh average to determine what my daily in-town kWh consumption will be; my baseline usage is 10,000 miles per year. The efficiency factor is needed to calculate how many kWhs I need to supply from my home in order to fully recharge the car.

Post note: Your BlogSpot suggests the 4 mi / kWh number already includes the loss factor. Therefore, at 75% charging efficiency, the actual car usage would be more like 5 mi / kwh. Am I understanding that correctly?
 
SparkevBlogspot said:
... Obviously, 12A mode will be less efficient.......
You should research that. Most have found !2A puts more in the pack. L2 puts more in the pack. There is a fixed 'overhead' for the processing and Thermal Management System (When required).
This overhead is steady, so 8A charging sends the least % of the current to the battery pack.
 
SparkevBlogspot said:
I don't know if efficiency is relevant in estimating solar. SparkEV L1 has two modes: 8A mode and 12A mode. Obviously, 12A mode will be less efficient. At 8A mode at 120V, it's slightly under 1kW. I measured about 80% with 8A L1.
I'm not sure your assertion is correct.

I posted http://www.mynissanleaf.com/viewtopic.php?p=155305#p155305 earlier. The thinking about why the efficiency is higher as the wattage goes up is that the fixed overhead (e.g. pumps) has to run for less time.
 
MrDRMorgan said:
Post note: Your BlogSpot suggests the 4 mi / kWh number already includes the loss factor. Therefore, at 75% charging efficiency, the actual car usage would be more like 5 mi / kwh. Am I understanding that correctly?
You are correct. 4 mi/kWh is what actually goes into the car as seen at the outlet using Kill-A-Watt. This includes all losses in EVSE and onboard charging, but does not include house wiring losses. I was getting 4.8 mi/kWh as reported by the car. Therefore, you can treat SparkEV as blackbox, and you don't have to know its charging efficiency.

4.8mi/kWh is in the blog; this is how I can estimate efficiency by knowing what the car thinks it spent and what I measured in putting into the car.

If you use 4mi/kWh, you should be safe for all but the most extreme case. I live 2000 ft above sea level, and that number was achieved by going down to the dog beach and back through variety of conditions. Driving steady at 55 mph gets close to 4.6 mi/kWh, but that was using DCFC. Although not in "freeway efficiency" blog post, normalizing for house charging from DCFC would make it close to 4.3 mi/kWh.

http://sparkev.blogspot.com/2015/05/freeway-efficiency.html
 
cwerdna said:
SparkevBlogspot said:
I don't know if efficiency is relevant in estimating solar. SparkEV L1 has two modes: 8A mode and 12A mode. Obviously, 12A mode will be less efficient. At 8A mode at 120V, it's slightly under 1kW. I measured about 80% with 8A L1.
I'm not sure your assertion is correct.

I posted http://www.mynissanleaf.com/viewtopic.php?p=155305#p155305 earlier. The thinking about why the efficiency is higher as the wattage goes up is that the fixed overhead (e.g. pumps) has to run for less time.
Thanks. I'm going to have to research actual charging with 12A. In my blog post, 12A being less efficient was based on loss in house wiring (50% current, double the power loss).

NORTON said:
SparkevBlogspot said:
... Obviously, 12A mode will be less efficient.......
You should research that. Most have found !2A puts more in the pack. L2 puts more in the pack. There is a fixed 'overhead' for the processing and Thermal Management System (When required).
This overhead is steady, so 8A charging sends the least % of the current to the battery pack.
This is only for L1 charging, and efficiency was only in relation to house wiring. L2 charging should be more efficient due to higher voltage, but I don't have L2 charger to test this. As mentioned in my blog, few pennies of estimated savings from using L2 charger cannot justify $500 L2 EVSE, let along trenching and running wires and permits, which could run over thousand dollars.

By the way, I also discuss why I may not want to charge at home to 100%. Living high up and always going downhill from home, I can easily overcharge the battery. First time this happened, I got a call from GM via on-star; they hung up right away after I said hello. For me, slow charge is actually advantageous. See the second point of this blog.

http://sparkev.blogspot.com/2015/05/sparkev-suggestions.html
 
MrDRMorgan said:
my baseline usage is 10,000 miles per year.
If you plan to use DCFC with NRG eVgo, it may be cheaper to DCFC rather than charge at home. This is because after you pay the membership fee, $ per kWh comes to slightly less than SDGE base rate, yet charging efficiency is higher. The more you use, the more spread out your membership fee will become. If you pay membership fee, and still charge at home, you're actually wasting money. This is only true for DCFC to 80% SoC, not L2, and not topping off will be better for the battery longevity, too.

http://sparkev.blogspot.com/2015/05/public-chargers-in-socal.html

And this limits the lowest energy cost for SparkEV. If you use DCFC more than 2 times a month and enroll in eVgo OTG plan, your maximum MPGe goes down to 77.5 MPGe (5 mi/kWh) or 62 MPGe (4 mi/kWh) with 10K miles / year. Still, I highly recommend that you get eVgo OTG plan. Since getting SparkEV and eVgo OTG plan, I haven't even started my gas cars thanks to DCFC. It's become a real car. I even took couple of trips to LA. If (when?) Chevy put DCFC in all their dealers, I might even try for 1000 miles in one day challenge with SparkEV.

http://sparkev.blogspot.com/2015/05/dcfc-quick-charge-and-driving-from-la.html
 
Thanks to you all for the great information.

I used all of this information to work backwards in order to estimate the percentage of my daily PV solar system kWh production that would go towards the car and what percentage would continue to go to my home. Using 10K miles per year, 4mi / kWh and 75% L1 charging efficiency, it looks like 57% of my PV solar system production would go to the car and 43% to my home. Currently, my PV solar system covers 100% of my home's annual power requirements thanks to net metering. Note: my current home power consumption is approximately 5200 kWh per year.

Most of the driving my wife and I do is in town with short freeway hops. When I totaled all of the costs for the Spark - lease costs, license costs, insurance costs and added home power costs for the 39 month lease period, and factored in the state and county rebates available, I still come out ahead of the total cost of gasoline to operate our 2002 Honda Accord over the same 39 month lease period. I made my calculation using a gasoline cost of $3.50 per gallon.
 
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