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Charging of Li-Ion batteries
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Written on: 19 November 2008 [11:25]
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ecoadmin
Administrator
Topic creator
registered since: 20.07.2007
Posts: 583
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To all battery experts: The charge time of an electric vehicle largely depends on the charger used and the power available at the power socket. Assuming we have a powerful charger and many amps available at the socket, could such a fast charge pose a problem to lithium batteries? If so, is it the temp rise of the cells the main threat? Twike 890
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Written on: 21 November 2008 [04:47]
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Lensman
 registered since: 31.05.2008
Posts: 75
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Keep in mind that waste heat means you're wasting the electricity you're using to charge the batteries. Yes, there's a limit on how fast you can charge the batteries. If I understand it correctly. the faster you try to charge them, the greater the percentage of power is wasted as heat. So it's not just a linear progression; trying to charge the batteries too fast wastes electricity. And different battery chemistries have different characteristics. Some can be charged faster, and some don't generate as much heat when charging and discharging. Some auto makers are claiming that they are developing an EV can be fully charged in as little as 4 hours with a 220 volt outlet. It remains to be seen how well that stands up to real world usage; manufacturers are generally rather optimistic in claims about their product. |
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Written on: 25 November 2008 [23:27]
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childress
Administrator
registered since: 14.08.2007
Posts: 140
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I personally think that a 'universal battery system' would be a more acheiveable goal than rapid charging from an efficiency point of view. Think of it: You pull-in and hot-swap your batteries for ones that have been slow-charged on a nice solar/wind "gas" station. Granted, it's a logistical nightmare... Commute suck? Twike it; You'll like it!
http://www.uiuc.edu/goto/twike |
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Written on: 27 November 2008 [09:45]
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Lensman
registered since: 31.05.2008
Posts: 75
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I've been dismissing the idea of swapping out batteries in a car, but I've changed my thinking on that. I've recently read a long interview with the guy running the Project Better Place company, and he seems to really have thought this idea through, with plans to start a project in Hawaii. So I'm now hopeful this is a lot more practical than I previously thought. One reason I've considered it impractical is because a battery swap station would require a small building with the footprint and mechanical complexity of an automated car wash. But it just occurred to me a couple of days ago: What if the battery swap mechanism could be *added to* an existing automated car wash? Many larger gas stations already have those anyway. If that could be done, that may well make it practical. Perhaps a bigger concern is that it will be difficult to persuade the car makers to standardize battery packs and connections. If battery swap stations are proprietary and will only handle one brand of car... then the system won't succeed. [This article was edited 2 times, at last 27.11.2008 at 09:47.] |
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Written on: 07 December 2008 [15:46]
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Franko30
Administrator
registered since: 08.09.2007
Posts: 88
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Lensman wrote: If I understand it correctly. the faster you try to charge them, the greater the percentage of power is wasted as heat. Correct. When a battery gets warmer/hot the internal resistance gets higher thus creating more heat... But, as you said, it depends on the battery type. In the Twike, the NiCd batteries would really get warm when charging with the maximum of 16 A that the German 220V system allows. Depending on the outside temperature the temperature increase over a charging cycle would be as much as 15° Celsius, whith battery ventilation running at its max. Whereas the maximum temperature increase my Twike had this summer with the new LiIon-Manganese batteries (see: http://www.twike.de/index.454.html) was around 5° Celsius per cycle. And that is without any battery ventilation! The reason for the lower temperature increase is the much lower internal resistance of LiIon batteries compared to NiCd. Lensman wrote: Some auto makers are claiming that they are developing an EV can be fully charged in as little as 4 hours with a 220 volt outlet. It remains to be seen how well that stands up to real world usage That depends on the capacity of the batteries. Again: The Twike. My Twike has batteries with 20 Ah at 360 V (nominal voltage) - about 7,2 kWh of energy in the batteries, maybe 8 kWh when considering losses (charger, AC/DC conversion etc.). A complete charge with 220 V and 16 A takes me 2 1/2 hours. Theoretically it should only take a little over 2 hours (220V*16A=3,52 kWh). So, if a car manufacturer creates a car and the batteries run at 360 V and the car uses up to 16 kWh/100 km, plus the car only has a battery pack for 100 km, we could just double the Twike example and we're almost at "full in 4 hours". Cheers Franko30 [This article was edited 2 times, at last 07.12.2008 at 15:51.] Mitsubishi i-MiEV + Citysax 002, davor/formerly Twike 808 and 891
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