We have access to the Tesla Roadster and some of its components as a "black box." We can certainly gather some clues about the insides by reading specifications from various OEMs, such as the makers of the individual battery cells. But as Tesla Motors points out in their engineering blogs, even the battery manufacturers do not document the performance of their product under all conditions. Tesla Motors learned a great deal about Li-ion batteries by operating them outside of the specifications. They ended up restricting the operating parameters to be significantly less than what the manufacturers allow (e.g. the Roadster never charges the cells to their full 4.2 V, instead stopping at 4.15 V range, or 4.1 V standard). In other words, we most certainly do not have all of the information that Tesla Motors has available to them.
My point is that we have no idea what Scott's "cool down" feature is actually doing to the battery on the inside. We can make reasonable guesses, and we can observe certain externally visible parameters, but Tesla Motors certainly has more information. Perhaps the very first thing they tried was Scott's technique, and perhaps they discovered that it creates a very undesirable tradeoff that makes some other aspect of battery performance or longevity suffer.
In any case, thanks for the answers! Now I understand how it works, and I might even experiment with a combination of manual charging and time-of-use rate charging. At least I have the vehicle log files to show the resulting temperature swings.
When I first got my roadster, I was able to get my work to install a 14-30 outlet in the parking lot of my building. So, I did all of my charging at work and virtually none at home (free gas!). I have a fun 7 mile drive to/from work/home, so I usually heat up a fully charged battery on the way home. I noticed (in the old FW) that if the last blue bar on the battery was on, the pump would usually run all night or at least until 1am or 2am in the morning. I discovered that if I plugged in my MC240, set the current to 12A, set the timer on my stopwatch, and manually stopped the charge after 20 minutes, battery would cool enough (I now know <30C) to stop the pump. The tatter does this automatically. It uses 13A so you can see that it is running. (I wanted to use 11A, but the PEM doesn't allow it)
Additionally, the pump was one of the main reasons I upgraded to a 2.5. While I was working on the log_parser and pre V4 HW version of the tattler, I would borrow Richard's Sport (#595). We would swap cars for a day or two and I would do my data collecting/analysis on the 2.0. I would usually marvel how much quieter the 2.0 was than my 1.5. Over the next 9+ months, it just kinda wore me down. The first EOL 100 announcement got me started looking at used 2.0s and demo 2.25s (2.0 with a 2.5 front). I wanted a sport 2.x with the same color, and finally just ordered a custom one. I waited three months. The last month was the hardest, even though I already had a roadster! They initially said they could have it done by the end of June, in time for Laguna seneca(sp). But they missed that date and I picked up my car the following weekend.
Last edited by scott451; 08-06-2011 at 11:55 PM.
Doubtful... (No FUD about the tattler, please ), The tattler just starts a low current charge and lets it run for up to 45 minutes. It's probably more "If you follow [Tesla's] advice, and always keep your car plugged in and charged" you don't need cooldown. Which is true if you are non-TOUPerhaps the very first thing they tried was Scott's technique, and perhaps they discovered that it creates a very undesirable tradeoff that makes some other aspect of battery performance or longevity suffer.
The "significant hurdles", I believe are related to the user experience. Already, amoungst the beta testers there was confusion about how cooldown works (a bug made it more confusing). If tesla had a cooldown feature and a non-tech user unknowingly turned it on, the car would look and sound like it was charging, but not actually charge! There is no easy way around this. Additionally, how do you explain to a non-tech user how/when he should and should not use cooldown? Very confusing. Richard and I have been using Tattler cooldown for +6 months and I seriously considered leaving it out of the tattler for exactly this reason. In the "shipped" version of the tattler, cooldown will be off by default and will not showup in the status until enabled. I will probably remove it from the main help menu. So "HELP" will not show cooldown but "HELP COOLDOWN" will give you all the settings and commands.
Last edited by scott451; 08-06-2011 at 11:58 PM.
Tesla already says to plug the Roadster in, if you can, when it's not being driven. With delayed charge start enabled, I already notice that the car makes different fan noises when I plug the car in. Heck, it makes different noises when I come back a couple hours later and open the trunk.
So, you plug the car in, the VDS says "preserving battery," and the 45 minute 13 amp cooldown begins. When it's done, the VS says the usual about when charging will begin.
In other words, cooldown should be automatic - the user only needs to remember what he's already been told: plug the car in if you can when it's not being driven.
What am I missing?
There are currently 1 users browsing this thread. (0 members and 1 guests)