Electric Vehicle Charge Rate

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alboities

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Hi, my name is Albert and I currently working on a project in one of my undergrad classes.

For my project, we are looking into finding how long a car needs to be charged in order to reach a certain mile distance. My specific portion is to find how fast the car charges over time under lvl 1 (120V 15A) and lvl 2 (240V 60A) charging. I have searched the web and have only been able to find how much time is needed to recharge the entire battery using these two levels.

However I need specific data for the intermediate charging area (between max and min). We assumed that the charge rate is non linear so that the time it takes to charge a car from 40% to 60% state of charge is not the same as charging the battery from 60% to 80%. (Assuming other variables, temperature/heat are constant)

I was using the specific car the Nissan Leaf as my specific example which has a Lithium-Ion 24kWh battery and a 80% depth of discharge.

The ultimate goal is to write a program in MatLab which recieves two inputs: current state of charge and target state of charge) and then outputs the required time to reach the target state of charge under lvl 1 and lvl 2 charge rates for an electric vehicle.

I am currently very lost and have been unable to find relevant data and was hoping if any of you could help or point me in the right direction.

I have already looked at discharge/charge cycles for various batteries and am getting confused with all the varying terminolgy (I'm a MechE not a EE, sadly :(). I was considering looking at charge/discharge rates vs state of charge for smaller sized batteries and then scaling these to electric vehicle rates, and was wondering if this was the right direction?

Any help would be greatly appreciated, but if anyone could find a graph or tabulated data on this that would be amazing.
 

beanland

Senior Member
Location
Vancouver, WA
Charging

Charging

The time is going to depend on the charger design. You need to put energy into the battery to restore the charge. If you use a constant-voltge charger, as the battery charges, the voltage rises, and the charge rate drops, so each additional increment of charge takes longer. if you use a constant-current charger, the voltage from the charger rises as the battery gets charged, so the charge rate (couloumbs of charge) is constant. I am no expert on the physics of charging but I believe there are some elegant techniques to speed up charging with out damaging the battery.

The problem is that some of the energy going into the battery is not stored chemically, it is turned into heat. In fact, this is a problem under discharge, too. So, how fast you can charge a battery is also affected by how fast you can get the heat away from the battery.

An elegant charger would monitor the temperature of the battery and then regulate the charging current to maximize the charge rate without overheating the battery. The charger should also stop charging periodically to test the state-of-charge of the battery and then start charging again based on that feedback.
 

gndrod

Senior Member
Location
Ca and Wa
Charge Rates

Charge Rates

For my project, we are looking into finding how long a car needs to be charged in order to reach a certain mile distance. My specific portion is to find how fast the car charges over time under lvl 1 (120V 15A) and lvl 2 (240V 60A) charging. I have searched the web and have only been able to find how much time is needed to recharge the entire battery using these two levels.

However I need specific data for the intermediate charging area (between max and min). We assumed that the charge rate is non linear so that the time it takes to charge a car from 40% to 60% state of charge is not the same as charging the battery from 60% to 80%. (Assuming other variables, temperature/heat are constant)

I was using the specific car the Nissan Leaf as my specific example which has a Lithium-Ion 24kWh battery and a 80% depth of discharge.

The ultimate goal is to write a program in MatLab which recieves two inputs: current state of charge and target state of charge) and then outputs the required time to reach the target state of charge under lvl 1 and lvl 2 charge rates for an electric vehicle.

Any help would be greatly appreciated, but if anyone could find a graph or tabulated data on this that would be amazing.

To be able to formulate EV charge rates may be difficult due that the new EV charge controls are designed into each brand of EV system setup. Another words the charge control rate for the Leaf is going to be different than that of a Tesla. Battery technology has become a complex variable due to supply sources applied (I.e. energy draw limits from source capacity, phase and voltage) and the battery temperature charge control will need to be addressed for EV Supply Equipment interfaces.

Level 1 (slow), Level 2 (normal) and Level 3 (fast) source capacities are the standards available but not established for a qualified charge rate for all brands.
As mentioned, I believe that defining the type battery and the manufacturer's vehicle controller will be the best approach to graphs needed for your project.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110417-2220

alboities:

I would suggest you contact each of the auto manufacturers and see what information they might be willing to provide. Also contact the battery manufacturers. At the Automotive Testing Expo last fall there were a number of vendors relating to your subject area. See http://www.testing-expo.com/usa/ for this year's show announcement.

The Chevy Volt charger is internal to the car. The battery is rated at I believe 16 KWH. But it should be rated at 10 KWH because they only use part of the range to maximize battery life. Thus, if you want to estimate range upon the available energy, then you need to use the 10 KWH. Also charging should be done just before use because the battery needs to be operated warm or hot, I do not know the desired temperature. By charging just before use one takes advantage of the already warm battery, and extra energy does not need to be provided to keep the battery warm from the end of charge until use. Thus, the charger must be smart and know the charge level at the start of charging, and the time when the car will be used after charging.

You also should go to your engineering library and search IEEE Journals for EV charging and battery information.

.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
1210418-1334 EDT

alboities:

If you are anywhere near Detroit, MI tomorrow you might want to try to attend this event
http://www.eng.wayne.edu/page.php?id=6239
The lower left of this page is the Registration tab. Very confusing web site.

The Volt plant tours are full. Battery plant tour is not.

The conference and meals are free. Paid by DOE and other tax dollars.

.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110430-1027 EDT

alboities:

Yesterday at the "Electrifying the Economy and Educating the Workforce" at Macomb Community College I met and talked with Dr. Gholam-Abbas Nazri of General Motors.

In his presentation he had indicated there were very few textbooks on the electrochemistry of lithium ion batteries. He is co-author of one, and another not yet available.

Following are references to some of his publications:
PUBLICATIONS

Books
1. Science and Technology of Lithium Batteries (text book)

G.A. Nazri, and G. Pistoa, Kluwer Academic Publishers, 2002

(in Press)

2. Materials Design and Optimization for Solid State Batteries (text book)

C. Julien and G.A. Nazri, Kluwer Academic Publishers, 1994.

3. Solid State Ionics, MRS Proceedings, Vol. 135, (1989)

G.A. Nazri, R.A. Huggins, M. Balkanski

4. Solid State Ionics II, MRS Proceedings Vol. 210, (1991)

G.A. Nazri, D.F. Shriver, R.A. Huggins, M. Balkanski

5. Solid State Ionics III, MRS Proceedings Vol. 293 (1993)

G.A. Nazri, J-M. Tarascon, M. Armand

6. Solid State Ionics IV, MRS Proceedings Vol. 369 (1995)

G.A. Nazri, J-M. Tarascon, M. Schreiber

7. Solid State Ionics V, MRS Proceeding, Vol. 548 (1999)

G.A. Nazri, C.Julien, A. Rougier

8. Electrochemical Society Proceedings Vol. 99-24, 1999

Intercalation Compounds for Battery Materials

G.A. Nazri, M. Thackeray, and T. Ohzuku

9. Electrochemical Society Proceedings Volume, 000, 2001 (in Press)

G.A. Nazri, B. Scrosati, R. Kotz, E. Takeuchi

This is the site from which the above information was extracted.
http://web4.uwindsor.ca/units/mater...4733d4a657f2fce485256c8d005ad36e!OpenDocument

I believe he is not directly involved in the Volt project, but is more into basic research.

He could not tell me if a heater was used in the Volt battery pack.

.
 

Besoeker

Senior Member
Location
UK
One of the things that concerns me about EV charging is how the utilities will cope with the extra loading on the network if there is significant uptake of them.
Here's something I posted elsewhere to quantify the problem:
The average household in UK consumes about 13kWh per day. The Mitsubishi i MiEV has a 16kWh battery capacity. Allowing for the inefficiencies of the charger and the battery this would take maybe around 20kWh for a full recharge. Based on that and sort of average mileage, it would increase domestic energy consumption by about 55% for the average household.

The TATA has a slightly greater range (100 miles as opposed to 93) and a 26.5kWh battery so the increase for the average household would be about 80%.


Charging at off-peak times when there is spare capacity might help some but if everybody charges at off-peak times then ot will no longer be off-peak.
I'm not averse to EVs. We make components for them. The more the better.

But I'm also a pragmatic old fellow. And I think sometimes we need to look at the bigger picture.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110420-1744 EDT

Besoeker:

In the near future, meaning 5 to 10 years, there is no problem with respect to the grid and generation capacity in the US. There may be localized points in the distribution that need larger pole transformers, this is easily handled. The load will be largely nighttime. A little analysis will demonstrate this. Also confirmed by the president of DTE Energy on one of the discussion panels.

Because a car has a battery rated at 16 KWH does not mean you will put 16 KWH back into it. Consider the Volt. Its battery is rated at 16 KWH, but the electronic control only allows you to use the middle 10 KWH of charge. Therefore, I really think it should be rated at 10 KWH. Some of the references below are 8 KWH.

An official GM site is http://www.chevrolet.com/volt/ . The web site is very poorly designed. It is extremely slow and I could not find any information on charging requirements. I did run across the following two comments at http://www.chevrolet.com/volt/features-specs/ :

Charge Control
Programmable time of day with charging indicator light

Battery
16-kWh Lithium-ion, Rechargeable Energy Storage System, includes liquid thermal management system with active control

This probably means there is some degree of temperature control of the battery.


Use --- chevy volt charging requirements --- to search in google. Following are a couple results. There are many more.

http://www.mychevroletvolt.com/chev...40v-installation-costs-rebates-and-incentives
http://www.mychevroletvolt.com/chevy-volt-home-charging-grants

Suppose we use 16 A at 240 and 3 hours charge time, this is 11.52 KWH. or a power level of 3.84 KW.

I might point out that I have no intention of getting a Volt or any other EV at this time. My new F150 is just fine and the Volt could not do the things my F150 can. The Volt could save on gas but would be a liability otherwise.

To see what effect an EV charging system would have on the local grid consider my home power system. The pole transformer is probably 25 KVA, and my main panel is 200 A. Roughly speaking the transformer could provide 25 KW continuously. My night time load is about 1 KW. I have one neighbor that shares this transformer with me. If we both had the same nighttime load and both had a Volt charging, then the transformer would be seeing roughly a 10 KW load. No problem. Put 5 customers on this same transformers and the night load for maybe 3 hours is 25 KW. Still not likely a problem. I do not think our area has more than five homes on a single transformer.

There is a government goal to get 1,000,000 EV cars on the road in the US by 2015. This is unlikely to occur, although the higher current gas prices might help this. But this number of EVs is an insignificant load on the grid.

However, the early adopters will probably cluster in certain neighborhoods, like mine. Within 30 or so houses we have maybe 3 Prius, 3 Escapes, 4 Jeeps, 2 Suburbans, 3 F150s, a Fiesta and Focus (retiree of Ford, new every 2 years), another Hybrid, a Cadillac, 2 Navigators, and numerous medium and small front-wheel drive cars that get stuck in the snow. There are many liberal college professors in the area and these are the ones that will be attracted to the Volt. I doubt that very many Volts will show up in our area very soon. Maybe three. That would present no appreciable load on the grid. Of this group who are the likely buyers of a Volt? I suspect it would be the Prius drivers. Probably none of the four wheel drive users would change. What the large vehicles need is engine shutdown at standstill, and low cost regenerative braking would be desirable.

In one of the smaller group meetings yesterday one person asked why you could not do a fast charge in 5 minutes. I illustrated why by this example:
Suppose the normal charging load is 20 A and to fully charge the battery takes 8 hours. I then asked the questioner what the ratio of 8 hours to 5 minutes was? He quickly said 96. So I said round this to 100 and multiply by 20 and the result is 2000 A, and that is just economically impossible. I further said, the battery would explode because of the high power dissipation in the battery.

With anything known today you can not charge a reasonable size battery with the energy content of 20 gallons of gasoline in 5 minutes. But in 5 minutes you can load 20 gallons of gas into a car's gas tank.

Last night for the dinner talk Dr. David E. Cole was the speaker. He is the son of a former President of General Motors, 1960s. This association and for other reasons he would have an early Volt. His home is about 2 miles closer to the meeting place than my home. My round trip mileage for the meeting was 110.1 miles and with my F150 and I got 19.1 MPG at 70 MPH 33 deg F, and rain, and I can go 6 times this distance or more on one tank of gas. If I had the EcoBoost engine instead of the 5.0 L, then my mileage would probably be about 20% higher, maybe 23 MPG. Dave Cole commented in his speech that his Volt ran out of battery charge part way to the meeting. We can figure his one way mileage was about 53 miles. So maybe 10 miles from the meeting his Volt switched to gas. His return trip would also be gas.

Dave Cole is very much a believer in the concept of the Volt, and he hopes the public does not get too excited too soon before this type of vehicle becomes economically viable, which it is not presently. I agree with him on the concept, but for me it has to do whatever job I need done and has to be economical. Incentives only help to get an industry started. A product has to stand on its own or it won't be successful.

An old, 1995, but interesting reference:
http://www.osti.gov/bridge/purl.cov...65CEB007D61E?purl=/279700-LzNz2M/webviewable/

.
 

Besoeker

Senior Member
Location
UK
110420-1744 EDT
Interesting post, gar. Thanks.
Besoeker:

In the near future, meaning 5 to 10 years, there is no problem with respect to the grid and generation capacity in the US.
I agree. In that sort of time frame I wouldn't expect there to be such a huge uptake of EVs.

There may be localized points in the distribution that need larger pole transformers, this is easily handled.
Then the larger pole transformers will need a higher capacity to them. If/when EVs become mainstream, then capacity limitations might kick in.

The load will be largely nighttime. A little analysis will demonstrate this. Also confirmed by the president of DTE Energy on one of the discussion panels.
Yes. and that would mitigate the problem to some extent.
Because a car has a battery rated at 16 KWH does not mean you will put 16 KWH back into it. Consider the Volt. Its battery is rated at 16 KWH, but the electronic control only allows you to use the middle 10 KWH of charge. Therefore, I really think it should be rated at 10 KWH. Some of the references below are 8 KWH.
That doesn't change the problem. You just have to recharge more often. Take 8kWh every other day. Your neighbour does the same on alternate days. Same result as far as the network is concerned.

In one of the smaller group meetings yesterday one person asked why you could not do a fast charge in 5 minutes. I illustrated why by this example:
Suppose the normal charging load is 20 A and to fully charge the battery takes 8 hours. I then asked the questioner what the ratio of 8 hours to 5 minutes was? He quickly said 96. So I said round this to 100 and multiply by 20 and the result is 2000 A, and that is just economically impossible.
Had a similar discussion in another thread and I made a similar point to the one you did. And idea that was floated around was the possibility of a refueling station having a a quick battery swap system the idea being that you drop off your discharged battery and pick up a fully charged unit. A bit like on a cordless drill but scaled up some. I suppose the idea has some merit. It would need agreements on standardised battery configurations both physically and electrically and that might be hard to achieve. Probably impossible in your 5-10 year time scale. But possibly the ball breaker is getting the required power to the charging to deal with the volume of customers at a typically busy fuel station. Do a few simple calculations and you'll see what I mean.

With anything known today you can not charge a reasonable size battery with the energy content of 20 gallons of gasoline in 5 minutes. But in 5 minutes you can load 20 gallons of gas into a car's gas tank.
Yes. Part of the range/recharge time limitation of EVs.


Last night for the dinner talk Dr. David E. Cole was the speaker. He is the son of a former President of General Motors, 1960s. This association and for other reasons he would have an early Volt. His home is about 2 miles closer to the meeting place than my home. My round trip mileage for the meeting was 110.1 miles and with my F150 and I got 19.1 MPG at 70 MPH 33 deg F, and rain, and I can go 6 times this distance or more on one tank of gas. If I had the EcoBoost engine instead of the 5.0 L, then my mileage would probably be about 20% higher, maybe 23 MPG. Dave Cole commented in his speech that his Volt ran out of battery charge part way to the meeting. We can figure his one way mileage was about 53 miles. So maybe 10 miles from the meeting his Volt switched to gas. His return trip would also be gas.

Dave Cole is very much a believer in the concept of the Volt, and he hopes the public does not get too excited too soon before this type of vehicle becomes economically viable, which it is not presently. I agree with him on the concept, but for me it has to do whatever job I need done and has to be economical. Incentives only help to get an industry started. A product has to stand on its own or it won't be successful.

I pretty much agree with that. At present performance limitations, primarily range and recharge times, for EVs limit their appeal. And they are generally expensive compared to more conventional vehicles.
Rising fossil fuel prices might have some impact on a push for EVs. But maybe it will just move the market towards more efficient IC powered vehicles.

I used to have the blue car in my avatar. It had the 5.3 litre V-12 engine. Smiles per mile...awesome. Fuel consumption per mile....awful. On a long run I might get 18mpg. Locally, it did well to get into double figures.
A few cars later....
My current car is a four pot Diesel with a manual six speed box. Certainly it is different from the V-12 Jag but it is far from being crude and noisy. If you stop at traffic lights, though far from intrusive, you can hear that the engine is running. In the Jag, you had to look at the rev counter to know.
On the plus side it has all the boys toys.
Somewhat academically, top speed is about 135 mph.

But, more importantly, fuel consumption is amazing. On my round trip to the office today it was 66mpg. I stayed more or less within legal speed limits - 70mph on the motorway - and crawled around in low gears and started and stopped at lights in the built up areas.
 
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