What kind of performance would the Tesla have

[t-maxxracer32]

Originally Posted by lutach

Battery technology is only getting better. It's how you use it that will determine if it'll catch fire, vent, puff and fail. Manufacturing defects can also be a factor, but most of the stuff I've seen is either user error, pack build issues, people just doing stupid stuff like hooking a lipo up to a car battery and lipo sack marketing. Would you like to see a race car running on lipos: http://www.proev.com/ (It uses 565lbs of lipos). They could've gotten better performance even with the now older A123 2.3Ah cells that we use in our R/Cs. The LiFePo4 chemistry does show it's safer, but it also has its trade off. My point is, for a car such as the Tesla, they need to use better cells and not just some laptop energy cells. Now how do you feel having 1000lbs. of non high discharge rate cells behind you? That's what you get with the Tesla at $120k.

your right. for 120k you should be getting some sick battery of the future or at least something that is high quality. Im not saying that lipos are unsafe its just that they have more of a chance to explode, burst, catch fire, or something along those lines than lets say a nimh batt. Sure most of the problems are user errors, but those small amounts of manufacturer defects would grow once you throw hundreds of lbs of the stuff in the trunk of a car. There has got to be a number of tests that the tesla manufacturers will go through to prevent this stuff so it wont happen, and it is unfortunate that they are not using the higher grade batteries, but maybe when you get the car you can mod it to use half the weight and produce double the power.

im excited to see this

[lutach]

Originally Posted by t-maxxracer32

your right. for 120k you should be getting some sick battery of the future or at least something that is high quality. Im not saying that lipos are unsafe its just that they have more of a chance to explode, burst, catch fire, or something along those lines than lets say a nimh batt. Sure most of the problems are user errors, but those small amounts of manufacturer defects would grow once you throw hundreds of lbs of the stuff in the trunk of a car. There has got to be a number of tests that the tesla manufacturers will go through to prevent this stuff so it wont happen, and it is unfortunate that they are not using the higher grade batteries, but maybe when you get the car you can mod it to use half the weight and produce double the power.

im excited to see this

Lipos are safe, but LiFePo4 has shown to be safer. Have you even seen a NiMH or NiCD cell blow? I have and some even right in front of me. Never had a lipo do that. A good pack design for a full size car would eliminate any fire hazard and I know the places that does just that. All I know is Tesla will probably use the same cell for their new car, but at least that one will be cheaper.

[othello]

Lutach i can understand your feeling that considering Teslas car price level you want the best cell powering this car. C rate of the cells used is only one criteria when it comes to define "best" cell. Of course a higher C rate allows higher power levels and an efficient cool running battery pack also translating in a higher range. On the other side Teslas rather small motor can't cope for long with high power levels. The motor if i recall it right is only air cooled and will simply overheat when pushed to hard (one of the reasons why they limited top speed to around 120mph which requires around 80KW according to their mathematical model). Pushing a street legal car to 60mph in around 4 seconds is not that bad after all ;-)

When reading articles about their battery pack and cell choice i got the impression that many other criterias (beside C rate) had to be considered: safety, cycle life, energy density are among the important ones. Don't forget that their cell tests, R&D of battery pack, passing safety tests and so on dates already a few years back and implied high costs. You can't simply switch to another cell now that the car is beeing sold and every component is optimised around a certain cell design.

Facts gathered from Teslas articles about their battery pack:
. Cells have a capacity of 2.2Ah
. 99 cells in series: around 366.3V (3.7x99)
. 69 bricks in paralel: around 151.8Ah (69x2.2)
. 151.8 x 366.3 = 55.6KwH on board (roughly comparable to 8 liters of gasoline)

Tesla states that the battery pack is able to provide up to 200KW.
. 200 / 69 = 2.89KW per paralleled string
. 2890 / 366.3V = 7.88A

If those cells were able to hold voltage at 3.7V each string must provide less then 8A to achieve a power level of 200KW (or 544A @ 366.3V).

To optimise cycle life cells are operated between 3.0V and 4.15V. To achieve 200KW with a minimum cell voltage of 3V (system pack @ 297V) one would need 673A (673 / 69 = 9.75A per cell). Amp draw per cell should never exceed 10A under those circumstances.

Lutach, i'm looking forward seeing your built.

[lutach]

Originally Posted by othello

Lutach i can understand your feeling that considering Teslas car price level you want the best cell powering this car. C rate of the cells used is only one criteria when it comes to define "best" cell. Of course a higher C rate allows higher power levels and an efficient cool running battery pack also translating in a higher range. On the other side Teslas rather small motor can't cope for long with high power levels. The motor if i recall it right is only air cooled and will simply overheat when pushed to hard (one of the reasons why they limited top speed to around 120mph which requires around 80KW according to their mathematical model). Pushing a street legal car to 60mph in around 4 seconds is not that bad after all ;-)

When reading articles about their battery pack and cell choice i got the impression that many other criterias (beside C rate) had to be considered: safety, cycle life, energy density are among the important ones. Don't forget that their cell tests, R&D of battery pack, passing safety tests and so on dates already a few years back and implied high costs. You can't simply switch to another cell now that the car is beeing sold and every component is optimised around a certain cell design.

Facts gathered from Teslas articles about their battery pack:
. Cells have a capacity of 2.2Ah
. 99 cells in series: around 366.3V (3.7x99)
. 69 bricks in paralel: around 151.8Ah (69x2.2)
. 151.8 x 366.3 = 55.6KwH on board (roughly comparable to 8 liters of gasoline)

Tesla states that the battery pack is able to provide up to 200KW.
. 200 / 69 = 2.89KW per paralleled string
. 2890 / 366.3V = 7.88A

If those cells were able to hold voltage at 3.7V each string must provide less then 8A to achieve a power level of 200KW (or 544A @ 366.3V).

To optimise cycle life cells are operated between 3.0V and 4.15V. To achieve 200KW with a minimum cell voltage of 3V (system pack @ 297V) one would need 673A (673 / 69 = 9.75A per cell). Amp draw per cell should never exceed 10A under those circumstances.

Lutach, i'm looking forward seeing your built.

Yes, the motor is an AC Propulsion designed motor. They can get the same amount of energy from other better suited cells. They use lithium laptop cells which are not the best for safety. Since they are lithium laptop cells, they won't provide the life cycle many hopes for. The cells I can get are used in some very serious machines and have the capability of over 5000 cycles for the Lithium Ion and way more then that for the Lithium Iron Phosphate cells. I don't think the cells they use can handle many 9A cycles. I don't think the Energy type cells should be used in a vehicle and that's the reason there's Power type cells.

For my race car since it won't be a mass production type vehicle, things will be expensive. One of the reasons I'm looking for investors to jump in, but they don't get all this stuff and just claims it won't work.