Quote:
Originally Posted by Lauri
My point was that for passanger car you'd need to have battery capable of no more than 0.5C because you'd like to drive at least 2 hours - that is 110 mile / 180 km range on average cruising speed.
Most batteries are capable of higher burst currents. And you don't need longer bursts than 10 seconds. 10 seconds will get up over the legal speed limit anyway.
Maybe we'll see cars with some supercaps that are able to give boost to the main battery. They'd only have to help for few seconds.
So for my passanger car I see no reason to have battery thats capable of more than 1C discharge. The same thing applies for charging. You just can't get enough power from the power grid to charge batteries with 1C or even 0.5C currents.
So charging max 0.25C and discharging max 0.5C and very high power density - this would be the ideal batt for passanger car in my oppinion.
BTW - I know about the power sag / voltage drop under load. But when talking about C-values one could assume that the battery does handle it without too much voltage drop ;)
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I understand, but most of the EVs need to have the appropriate cell used, not just common laptop cell designed for longer lasting low energy consumption application. You know EVs are not low energy consumption products like a laptop. You can try this in a smaller scale if you want and you will see my point. Before high discharge rate lipos came out, I was messing with high energy lithium cells and guess what, they all failed in a R/C, now think what can happen in a full size car. The cell used in the Tesla in my opinion is not safe. The people I speak to know that a EV to be compatible with the I.C. version, needs a battery capable of more the 0.5C. Why you ask, fast charging. The current grid can support such fast charging if you move away from the 110 or 220 standards. You can have a higher voltage coming from the grid set up to offer the fast charging. A lot of the energy produced by current power plants is wasted anyways. I think of things ahead instead of thinking of common things that we see. Now in order for your 0.5C discharge to work, you will need a much higher voltage then current EVs are using. A few set ups I know of can handle up to 960VDC, but some can go up to 1200VDC. Also, to have a battery only put out 0.5C for a EV, you need to look at the whole vehicle and not just at the battery. How much will the vehicle weigh, how aerodynamic is the vehicle and how much power will the motor need to maintain a certain speed? When you figure all those in, you will then see why you will need a battery capable of more then 0.5C. Even at the weight of 1000lbs., the Tesla pack can't handle the load as it needs water cooling. When a battery can't deliver the current asked, it'll overheat and that causes a very short life cycle. Tesla could've went with SLA batteries at the same weight which would offer better performance, faster charging capabilities and would be much safer.
So do a little test in your R/C with plain energy cells. Example, get a few of the Panasonic cell used in the Tesla and wire them in the voltage you use in your R/C, then do the same with similar sized cell from A123 or K2 (Not the 26650 sized, but the 18650 1100-1200mAh cells) and see which ones will perform better. Also, try charging the Panasonic cell at the same high rate as the A123 or K2 cells. Let us know your results.