Electric Vehicle Battery specification (very basic)

[Topher925]

You were aware, and yet you still posted in this forum https://www.physicsforums.com/showpost.php?p=2666688&postcount=43" that Li-Ion had '100 cycles' (unless one derates it)?

You're taking what I said out of context. The specs that were determined in previous posts were assuming deep cycling along with heavy transient operation with discharge rates greater than 1C. That will kill a cell fast, especially if the cell isn't adequately cooled. The graph which you posted, and I always I have to explain, is for a steady state cycling at a charge/discharge rate of 1C. This will never happen in a real automotive application. Thats like saying someone who can run 1 mile in 5 minutes, can run 10 miles, up and down hills, in 50 minutes. Graphs such as the one you posted provide little information on the actual lifetime performance of a battery. When you start to consider harsh conditions, plus transient operation, plus actual time, the slope of that curve gets a lot steeper.

What constitutes 'significant degradation and performance' loss? Reference?

Depends on the application. For cars, 5,000 hours of discharge operation with less than 30% loss in capacity is a good bar.

Dell laptop batteries are not really a relevant to the topic of this thread which is 'Electric Vehicle Battery' specs.

Yeah, but they are. There's not a whole lot of difference between batteries used in laptops and batteries used in cars. The Tesla Roadster for example uses glorified laptop batteries.

http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf

I'm not saying you're going to find laptop batteries in every hybrid or electric car, but there isn't really that big of a difference between the designs in most cases except for the packaging and maybe slight modification of the materials. Battery manufacturers like to make lots of small cells and likes to make them cheaply. This revolves around reliability standards. Its not to often you find a manufacturer making one large specific cell for one specific customer.

 

[mheslep]

...Yeah, but they are. There's not a whole lot of difference between batteries used in laptops and batteries used in cars. The Tesla Roadster for example uses glorified laptop batteries.

http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf

I'm not saying you're going to find laptop batteries in every hybrid or electric car, but there isn't really that big of a difference between the designs in most cases except for the packaging and maybe slight modification of the materials. [...]

Not so. The difference is large as a little background reading would quickly show. Laptop batteries use Co chemistries which have a fairly weak bond with the Oxygen atoms, worsening at high temperatures. It is the unbinding of O that contributes to the thermal runaway and subsequent fires. The newer Li Ion design uses FePO; P binds tightly to O, won't let it go. Commercial EV's do not use laptop chemistry, the Tesla being the only exception as it was early out of the gate, and Tesla used a sophisticated thermal system to compensate.

 

[mheslep]

You're taking what I said out of context. The specs that were determined in previous posts were assuming deep cycling along with heavy transient operation with discharge rates greater than 1C. That will kill a cell fast, especially if the cell isn't adequately cooled. The graph which you posted, and I always I have to explain, is for a steady state cycling at a charge/discharge rate of 1C. This will never happen in a real automotive application.

In this thread the https://www.physicsforums.com/showpost.php?p=2658594&postcount=6" a 15kWh pack with a 40kW motor load at max power/acceleration (2.7C), and with an average discharge over several hours at highway speeds, thus ~0.5C average. With an extremely heavy accelerator foot and poor heat dissipation on the battery pack, we can expect Li Ion to lifecycle to drop by perhaps half down to maybe 1500, but '100 cycles' is off by an order of magnitude.

 

[xxChrisxx]

No offence to anyone in the profession. But the above few posts outlines quite nicely why mechanical engineering is more cool than electrical engineering.

 

[pchoopanya]

Hello,

I know this is rude but I do have the same kind of project which is to propose the powertrain design of an electric bus.

I am kind of lost, do not where to start. Of course, I have read so many articles though. So I think I have some background knowledge, but I just want someone to point out how I can put these jigsaw pieces together.

Is it possible to tell me how I can calculate how big the motor will need to be? Are we talking about its delivered power in kW? Is rated power simply a maximum power?

All so, how do I do the same for a battery and a fuel cell?


Thank you very much

 

[mgb_phys]

I assume this is just a school project and somebody isn't trying to design an electric bus based off advice on the internet...

Find out how many HP a bus engine has.
Convert that to kw
Find out what range you need - how many hours.
Work out how many batteries you need for that number of KW-hours.
Realise why there aren't (m)any battery powered busses.

 

[pchoopanya]

1. The original bus (diesel engine) deliveres 170 kW of maximum power

2. But this whole powertrain is to be replaced by a hybrid fuel cell/battery electric powertrain

3. The bus is to be operating in Bangkok, Thailand. So, for each one round trip, without re-fuelling between the rout, it will be on the road for 3 hours and only covers about 50 km before returning to the start point where it can recharge its battery.

 

[mheslep]

Hello,

I know this is rude but I do have the same kind of project which is to propose the powertrain design of an electric bus.

...

China built a small E-bus fleet for the Olympics. You might try to get information from the manufacturer.
http://www.sinautecus.com/products.html#hybrid

 

[Ken Freeman]

I think one thing that's missing in both design exercises is a good analysis of the bus/other vehicle mission profile: speeds, accel/decel, climbing delta-H and climb speed, and find out what is actualy the reason for the necessary propulsion torque and power, and at what road speed. The comfort, convenience, and safety (lighting, electric braking, electric steering) and other vehicle controls subsystems need the same analysis to deternine how much to add into provide those services, and whether diversity of load can be used to reduce the actual system rating. The mission profile should include service/battery condition assessment intervals, as well as customer total mission duration (10years, 1.2M miles is not out of line for a heavy commercial vehicle, and buses might be in the same megamile ballpark).

Clearly, battery recharge is a key requirement that also needs to be understood.

 

[mheslep]

I think one thing that's missing in both design exercises is a good analysis of the bus/other vehicle mission profile: speeds, accel/decel, climbing delta-H and climb speed, and find out what is actualy the reason for the necessary propulsion torque and power, and at what road speed. The comfort, convenience, and safety (lighting, electric braking, electric steering) and other vehicle controls subsystems need the same analysis to deternine how much to add into provide those services, and whether diversity of load can be used to reduce the actual system rating. The mission profile should include service/battery condition assessment intervals, as well as customer total mission duration (10years, 1.2M miles is not out of line for a heavy commercial vehicle, and buses might be in the same megamile ballpark).

Clearly, battery recharge is a key requirement that also needs to be understood.

Carnegie Mellon has an online research project that provides much of that information.

 

[Ken Freeman]

What's it called? Some brief Googling is turning up a wide range of stuff, not obvious if they're what I'm thinking of.

 

[mheslep]

Carnegie Mellon has an online research project that provides much of that information.

What's it called? Some brief Googling is turning up a wide range of stuff, not obvious if they're what I'm thinking of.

http://chargecar.org

To role your own driving profile:
http://chargecar.org/participate/how_to

There are plenty of canned driving profiles uploaded to the site, eg:
http://chargecar.org/data/327

Driving Date: 2009-11-05
Location: Rockville, MD, US
Traffic Type: Light
Route Type: Commute
Route Setting: Urban
Car Type: Compact
Car Make: Saturn
Car Year: 2004

with these stats

Total Distance: 3.13 miles
Trip Duration: 0 hrs 4 mins 21 secs
Time Idle: 0 hrs 0 mins 12 secs
Net Elevation Change: -74.32 feet
Average Speed: 32.17 mph
Max Speed: 69.3 mph

Which, if traveled using CM's E-car model would use energy accordingly:

Energy Consumed: 1.06 kWh
Total Charge: 0.05 kWh
Total Discharge: -1.1 kWh
Percentage of Power Regenerated: 4.09%
Peak Power Usage: 85.31 kW

There are numerous online plots available as well - acceleration, speed, etc.

http://chargecar.org/data/do_graph?meta_data_id=327&data_type=gps_datas&graph_type=power_over_time&file_name[name for the profile above.

 

[mheslep]

...I do have the same kind of project which is to propose the powertrain design of an electric bus.

I am kind of lost, do not where to start. Of course, I have read so many articles though. So I think I have some background knowledge, but I just want someone to point out how I can put these jigsaw pieces together.

Is it possible to tell me how I can calculate how big the motor will need to be? Are we talking about its delivered power in kW? Is rated power simply a maximum power?

All so, how do I do the same for a battery and a fuel cell? ...

Montreal committing to all electric bus fleet (1300 strong) by 2025.
http://gas2.org/2010/05/25/montreal-buses-to-be-completely-electric-by-2025/#more-8096

Montreal is looking at fast-charge buses that can store enough power for a 20 kilometer route before recharging in 10-15 minutes at either end of the route.

which are fairly tame (unrealistic?) requirements. Twelve miles would require a very small battery pack, say 6 kWh assuming 2 miles per kWh in a bus with good regeneration braking, plus some margin, call it 10 kWh. Such a pack would cost maybe $5000, weigh 100kg. To charge in 15 minutes would require a 40 KW line (480 V at 83A). Might be easier to go with a battery exchange. Replacement cost is a problem though with these small batteries. Assuming a maximum of 3000 deep discharge cycles for any size battery and three charges a day, they'd get no more than three years out of the battery, worse with the quick charge stress.

 

[Sixdeuce062]

So to be blunt yes u can build it to do that but keep in mind u will have lots of batteries ( half the cars worth) every thing in the car will have to be light as possible ( the lighter it is the more dangerous it gets think about it ) and it gets very expensive but it is possible.

I was in a high school class that build one of a go kart out of used and donated parts form an electric fork lift and other stuff in 03 got 10 mi. before batteries died and top speed of 20 mph so yeah you can but its not going to be very cost effective