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Forum Index : EV's : Tesla Powerwall for EV???
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| UselessK Newbie  Joined: 05/05/2015 Location: AustraliaPosts: 1 |
Hi All, So I'm in the early stages of researching and designing an EV for a daily commuter maxing 100KM a day if I'm being generous. So far I've seen a lot of battery solutions that are really expensive and require substantial amounts of configuration and wiring. Which in itself is not a big deal however there has to be a better way. Then, while watching Elon Musk's announcement of the powerwall and idea came to me that you could deploy one or two of the daily cycle 7KWh battery packs into an EV and achieve similar or better cell figures off to a AC or DC motor. What do you guys think of this concept? Cheers, Alex. |
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Trev Guru  Joined: 15/07/2006 Location: AustraliaPosts: 640 |
The thing to work out is if the pack voltage is going to work. The powerwall has a voltage range of 350v to 450v. That's a scary voltage! https://www.teslamotors.com/en_AU/powerwall Is the speed controller input voltage in that range? How would you charge the powerwall?? Does anyone know if these powerwall's are available yet?? Check out other EV conversions. Look at what what vehicles, motors, speed controllers and battery packs they use. With more information of what has been achieved, you will be better equipped to know if your ideas will work. http://evalbum.com/ Have a look at my EV Hilux, here is the link to EV 7 Might be worth your while to read all pages, EV Conversion, EV 2, EV 3, EV4 etc, up to EV 7. Trev @ drivebynature.com |
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KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
NO the tesla powerwall uses cell no better than recycled (but otherwise new) 18650 type cells ie give or take 8Wh/cell. roughly 3.6-3.7V nom and 2.2AH each. you can buy these from otherwise new laptop packs, salvaged and in single cell format from $1.1ea on ebay delivered in AUS. High performance cells such as Samsung 18650 29-E are capable of higher C rates and have higher capacity available = smaller and lighter. 18650 type cells are typically NCM/NCA chemistry which is good for either massive rates of discharge or massive Wh capacity for their size - cant have both! I have a 3.0kWh 18650 NCM battery smoothing system (connects to grid/house and discharges simply based on the time of day when power is 50c/kWh) This is the most economical method of using battery technology. total is 7S54P - Very close to the powerwall at 2 units each 7S 60P. This is 378 cells for ~$400 and $200 in materials to assemble and 3kWh = $200/kWh vs $1200 / kWh commercially available stuff. SO why wouldn't you do this? $200/kWh storage at lithium = rough 400 cells x .50g each = 20kgs! here is why lappie cells happy at 0.5C charge/discharge will do 1C but get warm = cycle life hurting Ebike experience Samsung 20R cells do 5C like having a poo and 10C very well (warm but not hot)this is 20A/cell!!! vs the lappie stuff at ~2A/cell. ebay cells may have been sitting around for 3 years = some failures.... have to test each and every one of them. can do some bulk charging (use foil and group 50+ cells together with books sitting ontop and power supply chucking out 10-15A @ 4.2V (use neo magnets to hold wires onto foil :) ) then use Watt hour or MAH counter to measure discharge from every cell repeat step 1 to recharge wait 4 weeks and then thow away any that have a significant voltage drop (self discharge caused by dendrites formed by being flat too long) What kind of car?? Me i want 200kW peak 100kW cont but this is close budget options = ~$6K Kostov dual motor setup + controller another 4K+ so we need to be able to deliver some 300V (under load) and 400A+ lets call it 70 cells in series at 3.7V nom and 4.2 =294V max for this to wok with lappie cells at $1.1 each and 0.5C i'd need 400/1.1 (2.2Ah cell) =363 x 70 = 25454 cells which is NUTS at near $30K or lets call it peak discharge 1C (and most of the time this WILL be true) gives 400/2.2 = 181(cells in parallel to provide the current) x 70 (cells in series to provide the voltage) =12727 cells = *3.7*2.2 = 103.5kWh @ $14K cells and 6K in "stuff" to assemble them for $200/kwh Option B use new kickass cells like the 29E, 1/4 the QTY/Weight/capacity for ~25kWh for about the same money and a HELLUVA LOT LESS WORK! all that said LIfepo4 cost basically double c/Wh BUT are twice the size and weight BUT have double the cycle life and available in 100AH+ sizes= much less pack building to do. hope you learned something! DIY OK for small stuff BUT takes a LONG time!!! Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
FYI 100kms range is typically 20kWh pack at a minimum! at 20kWh / 100km commute depends on how fast you want to go but skimping. 20000/7Wh = 2857 cells = 70S 40P gives 280V under load and 348A assuming 2.9AH/3C. =98kW peak and 30kW continuous. My guy in china would assemble as smaller packs each BMS protected at ~$5-6AUd/cell. give or take $15-16K +GST i make that not bad ... again LIFE PO4 CALB much easier but tougher to customise pack as bigger formats Luck favours the well prepared |
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