Quote:
Originally Posted by roderick
I hate to point out that some one is wrong...but here are mixed up facts with both posche and toyota:
They use their capacity of between 80~90% to 20~30%. (Soc wise)
Their battery system without cooling weights about 60~80KG (very heavy!)
The difficulty with 24 hrs is to manage the cell temperature (keeping their cells balanced is easy)
Porsche this year sees to be having some trouble with keeping the cell cool (guessing 40~70C)
Toyota hasnt reported any battery problems. However, I'm guessing they have gained some weight compared with Capacitor.
PS: their charge and discharge system is regulated by software mostly likely doing distance traveled vs allowed total discharge per lap.
Oh, and the fun part is...in the qualifying, They can keep the battery at almost full capacity and use as much as they can on the last corner to gain speed till the finish line.(this will reset the allowed battery energy at the finish line)That's how they get super fast time.
sorry about the long post  |
What exactly is wrong about what I said?
Everything you posted here seems to agree. High current (recovery and deployment) causes the cell heating issue. You control it by deploying less power though a software current limit in the battery management system.
I'm not sure what the point about a 60-80 kg battery is. They have constructed a 60-80kg battery
WITH cell temperature issues when running. This tells you that they are on the low end of the spectrum with regards to battery size. Lets say you need 100 amps. From a 1 Amp hour battery this is 100C. From a 200 Amp hour battery this is 0.5C. The 200amp-hour battery runs cooler but is MUCH HEAVIER assuming the same battery chemistry....extrapolate this to what porsche are doing. There cell temperature issues will go away with a battery pack double the current size and weight. But who is going to run an overweight battery in a race? They designed a system on the limit for weight reasons, and as you would expect, we see the negatives of doing such (temperature)
When you take a lithium battery and deep cycle it (80% to 20-30%) for a long time, you reduce the energy and power density of the cell over time. The way that lithium redeposits or binds to the cathode is controlled by the chemistry and kinetics so it's not always what you want and there can be side reactions producing "dead" deposits which don't hold any energy and just increase internal resistance inside the cathode. Cell manufacturers will have experimentally derived data on this specific to each program. A good designer only builds a battery to last a race distance and some change (i.e safety factor) and no longer. Any longer and it's just more weight when you fully consider the design of the pack and how it operates.