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Old 12-18-2016, 04:11 PM   #38 (permalink)
thingstodo
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Quote:
Originally Posted by sendler View Post
This 350kW number is fun for them to throw around and get people excited about but no car can use this much charge rate. It would need a 1000v battery to keep the current down to 350 amps. And full liquid cooled contacts and cables.
Agreed that none of the present EV's may be able to charge at 350KW.

Fast-charging a 100 KW-H pack in 20 minutes needs 300 KW. But there is a point of diminishing return, just like all engineering. If 200 KW or 250 KW is reasonably priced and does most of what is needed, that's a good place to start. Having the charging standard impose the limits is short-sighted ... and they have all done that at least once already. If we can't get to 350 KW for a while - that's fine by me.

700V for a DC bus voltage is quite common in the US when fed with 480/460V three phase. 1000V DC bus is common in Canada with 600/575V three phase. I don't have experience in Europe, but we have some european equipment that runs up to 690V three phase, so that's over 1000V DC.

My point - these are already common voltages in industry. It will take some engineering to make that safe for vehicles. Again - avoid building the limitations into the charging standard. Aim HIGH. Let the designs strive to reach them.

350A is only 400 HP at 600 VAC. We would normally run parallel 2/0 conductors so that they are easier to handle, but single conductor 500 MCM cable will run 350A 24/7/365, with a 110F ambient temperature. The cables are hard to handle - I would expect an automated system to engage the charger to the vehicle. If you are expecting intermittent use (like a charger does) with temperature monitoring of the conductor a single run of 2/0 is reasonable. But as you mention further down, the connector is the issue.

My point - the cabling is not particularly difficult. A cable-way can take most of the weight, like the monster-sized TV mounts that let you raise/lower/swing the TVs. The difficulty is in the connectors and the user interface. And I'll repeat myself a bit - aim HIGH and let the designs or the materials or the connectors be the limitation - NOT THE STANDARD

Quote:
350kW at 1000V. This was not mentioned. At 400V it is just 140kW. Slightly faster than Supercharger.
BUT that speed is only possible with liquid cooled pins in the plug. Without that extra it is less than 100kW.
I guess that is for smarter people than I to deal with. Maintaining a large enough contact surface to prevent heating while making the connector light enough for a consumer to move around ...

Quote:
1000V packs are big questionmark on small vehicles due to extra complexity.
You have mentioned complexity a few times. There is more insulation at 1000V than there is at 400V. Above 1000V there are corona issues that need to be dealt with. The techs that troubleshoot need better equipment and a bit more training. The contactors and electronics are more expensive. But I'm obviously missing something on the complexity.

Quote:
Also charging at 350kW is not possible due to thermal limitations (car is not capable to extract heat
at that speed from the pack). Imagine at 90% efficiency 35kW of heat. Not going to work.
Even with absurdly massive AC compressor there is not enough surface area for radiators.
I'm not familiar with this issue.

If your battery is charging at 90% efficiency ... it's time to retire it! I would expect 97% would be a bad day. Again - I must be missing something.

Quote:
Also another limitation of the lithium chemistry itself. 100kWh battery can do around 120kW (Tesla).
200kWh pack could do around 240kW. But 100kWh pack (no matter the voltage) will not charge at 240kW rate without
MASSIVE improvement. Voltage per cell would tip safe limit instantly.
This is not consistent with my limited experience. You are listing charge rates just over 1C. NiCd, NiMh, LiFePO4, LiMnO(whatever the Leaf uses), Lithium Polymer ... every rechargeable chemistry I can come up with ... can charge faster than 2C. I must be missing something.
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