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Physics is a harsh mistress. Back of the envelope numbers: Tesla uses 75KWh batteries at 400vDC to go 250 miles. Trying to refill that in 5 minutes is going to

by gvb 9y ago

Physics is a harsh mistress. Back of the envelope numbers: Tesla uses 75KWh batteries at 400vDC to go 250 miles. Trying to refill that in 5 minutes is going to be dumping some serious power into the battery in a very short time. To recharge 75KWh in 5 minutes (1/12 hour) at 100% efficiency would take: (75,000 / (5/60)) / 400 = 2,250 amps (900KW) That is going to be one BIG connector and cable going into the car... and the battery's internal wiring will need to be increased by 10x (or more) to carry that current to the cells. For comparison, the Tesla SuperCharger uses 400v at 250 amps (100KW). To do the charge in 5 minutes would be an order of magnitude more power. It's a pretty good bet that the SuperChargers are close to the max charge current the batteries can accept. Any inefficiencies in the system will result in waste power that will also have to be dissipated - if the charger were 90% efficient, it will have to get safely dissipate 100KW (1MW * 0.1) for the duration of the charge. A quick google search indicates lithium ion batteries are close to 100% efficient in charging(!) so that really good - the charge won't be cooking the cells themselves, although the battery's wiring and charge current control circuitry will need to be kept cool. Ref: * https://en.wikipedia.org/wiki/Tesla_Model_S#Battery https://en.wikipedia.org/wiki/Tesla_Model_S#Battery * https://teslamotorsclub.com/tmc/threads/model-s-battery-voltage.22341/ https://teslamotorsclub.com/tmc/threads/model-s-battery-volt... * http://www.motortrend.com/news/tesla-supercharger-an-in-depth-look/ http://www.motortrend.com/news/tesla-supercharger-an-in-dept...

hwillis 9y ago
It's not so bad- the connector would be tricky, but you can fit that much power in a normal sized connector[1]. For a real charging network you would need supercapacitors at the stations, not a 1 MW feeder per car, since people won't be constantly charging. You would need a very large capacitor for this purpose, but that wouldn't really be a problem. It wouldn't even be that expensive relative to the cost of a car. You'd have to scale up the size of the internal wiring, but not that much. The wires are sized for efficiency, not heating. For extreme speed charging it's acceptable for them to heat up briefly. Finally, a 5 minute charge would be an average of 12 C (1 C means charging in an hour, .5 C means 2 hours, etc). This is high, but there are plenty of batteries that can do it- there are batteries that can charge/discharge up to 40 C. Even if it isn't good for the batteries, that's not really a problem since it would be needed pretty rarely. [1] These can handle 260 amps per .4 square inches of connector- 3.5 square inches in total: http://www.molex.com/molex/products/family?key=extreme_ten60power_highcurrent_connector http://www.molex.com/molex/products/family?key=extreme_ten60...

by gvb 9y ago

hwillis 9y ago

It's not so bad- the connector would be tricky, but you can fit that much power in a normal sized connector[1]. For a real charging network you would need supercapacitors at the stations, not a 1 MW feeder per car, since people won't be constantly charging. You would need a very large capacitor for this purpose, but that wouldn't really be a problem. It wouldn't even be that expensive relative to the cost of a car. You'd have to scale up the size of the internal wiring, but not that much. The wires are sized for efficiency, not heating. For extreme speed charging it's acceptable for them to heat up briefly. Finally, a 5 minute charge would be an average of 12 C (1 C means charging in an hour, .5 C means 2 hours, etc). This is high, but there are plenty of batteries that can do it- there are batteries that can charge/discharge up to 40 C. Even if it isn't good for the batteries, that's not really a problem since it would be needed pretty rarely. [1] These can handle 260 amps per .4 square inches of connector- 3.5 square inches in total: http://www.molex.com/molex/products/family?key=extreme_ten60power_highcurrent_connector http://www.molex.com/molex/products/family?key=extreme_ten60...