I presume Porsche will design their battery pack and cabling to take advantage of the 800V. 15 minutes to 80% charge on a 400 mile pack would be AWESOME. Basically rivals ICE cars. Tesla needs some competition, it will be good for Tesla loyalists.
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I presume Porsche will design their battery pack and cabling to take advantage of the 800V. 15 minutes to 80% charge on a 400 mile pack would be AWESOME. Basically rivals ICE cars. Tesla needs some competition, it will be good for Tesla loyalists.
JRP3
Hyperactive Member
You're missing the point. The bottleneck is the cell C rate, 800V is meaningless.
JeffK
Well-Known Member
If we assume that 400 mile requires 130 kWh such as Lucid implies. Then 80% of 130kwh is 104 kWh, lets say 100kWh for easier math you'd need a 400 kW charging station to charge 80% in 15 min assuming a linear charge rate (which won't happen becuase it's best to lower the charge rate with higher SoC). As far as I know the largest charging stations planned are 350kW so realistically you'd be looking at 17-20 minutes with the fastest chargers and at nearly 2.6 C.
Keeping in mind Tesla's like the P100D are usually charged near or below 1 C especially at a higher state of charge..
Porsche was looking at a 310 mile range, so 100 kWh meaning 80 kWH in 15 min which might be doable at cost to the battery life. Most lithium Ion manufacturers recommend 0.5 - 1 C charge rates but you'd be looking at 3.2 C to get 80 kWh in 15 min
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As several of us are trying to explain... simply quoting higher voltage #'s as if that automatically guarantees faster charging is not necessarily the case. Remember, it's current flowing in to the pack that dictates overall charge rate. @JRP3 and I trying to point this out.
The 85-100kWh Tesla packs are somewhere in the neighborhood of 225-265Ah, with a nominal voltage of ~375V (max 400V). At ~330A charging, they are already pushing a 1.25-1.5C charge rate. And depending on ambient conditions, they are also working overtime to shed heat while charging (car's thermal management system kicks in to high gear).
For a pack of similar capacity but rated at 800V max, the pack's current capacity would be halved, so ~112-132Ah. So at the same C-rates the pack would only be able to safely draw ~165A or so. For those above-mentioned supposed 350kW stations, you are talking ~440A @ 800V... greater than 3.5C as @JeffK. That implies very large conductors and connectors, a lot of thermal management capacity, and a cell chemistry that may not be well suited for other aspects of automotive applications.
Even charging at the same ~330A capacity as Telsas do today is a ~3C rate. Now the as-of-yet vaporware vehicles could have larger packs (say ~125), but that doesn't change the fundamental issues all that much...
Greater voltages do have some advantages for the same given power, namely smaller conductor sizes. There are also some disadvantages, such as greater insulation required (negating some of that conductor advantage), and the need for higher rated components.
Increasing voltage is not a magic bullet..
alseTrick
Active Member
Two 400V batteries in series gets you to 800V. Not sure what the C value has to do with charging two batteries in series.
Porsche's 800-Volt fast charging for electric cars: why it matters
Porsche's 800-Volt fast charging for electric cars: why it matters
JeffK
Well-Known Member
You might want to google c-rate, here's a source Charles-Augustin de Coulomb's C-Rate for Batteries
Note that even in the link you posted, the graph clearly reads charge time limited by "battery cell". The notion that it could theoretically charge to 80% in 15 min is mostly hype.
Keep in mind that Porsche is owned by VW and VW is not above fudging numbers...
JRP3
Hyperactive Member
I'll try to give a simple example.
I can build a 100kWh pack two different ways.
400V x 250Ah or 800V x 125Ah
To charge the 400V in one hour, at a 1C rate, takes 250 Amps
To charge the 800V in one hour, at a 1C rate, takes 125 Amps
Now since both packs are the same capacity they both have the same number of cells. The 400V pack has twice as many cells in parallel and half as many cells in series, the 800V pack has half as many cells in parallel and twice as many cells in series. Because cells in parallel are additive in capacity the 400V pack can take twice the current at a given C rate as the 800V pack. The only way the 800V pack can charge at a faster rate is if the basic cell chemistry is capable of charging at a higher C rate. The voltage of the pack is irrelevant, only the C rate of the basic cell chemistry matters.
I explained that two posts above yours.
Short version for those not wanting to read:
For a given capacity pack, configuring it at double the voltage means it has half the current capacity. Current capacity determines rate of charge it can accept.
Red Sage
The Cybernetic Samurai
I presume/predict/prognosticate Porsche will charge at least as much for Mission-E as they did for the Panamera Turbo S Exclusive Series (and likely a whole lot more) for the 'privilege' of getting their 800v battery pack, won't have a '400 mile pack' anywhere on offer, and thus will not be 'competing' with Tesla Motors at all.
Even assuming the salesman is correct - that means it costs significantly more than a P100DL, while being much slower and having only fractionally more range - and showing up at least two years later. Doesn't seem very persuasive to me.
There is a good reason the household power supply is kept between 110 - 240v. Tesla has not gone for 800v and again, quite certain it is a well considered compromise. As another poster has said, it is quite straight forward to increase the operating voltage by connecting cells in series and Tesla could have even gone all the way to 2400v if required and technically, everything from inverter current handling requirements to charge cable thickness could have been reduced but if you are accidentally exposed to that level of high voltages, the reactionary safety cutouts will be unable to react fast enough to prevent injury or death.
So it is easy for Porsche to come up with headline grabbing figures but they have to be very careful not to get too carried away. We are talking about the very fundamentals of safety.
All true. But I tend to think the limitations on the power transistors in the inverters are a bigger factor. If you can't get the power out of the pack quickly and efficiently, it isn't useful to you anyway. I think most high quality high voltage IGBTs are rated for 600V these days...
A fully loaded MX can get you to $160K. A little premium for Porsche makes sense. If it charges twice as fast and has the sustained performance promised . . . Tesla better worry.
3Victoria
Active Member
The whole problem is that "if". If pigs could fly ....
Its all vapourware at this point. Let's worry about it when we see some real evidence it is going to happen.
JeffK
Well-Known Member
It won't, we've already established that. It'll charge at nearly the same rate, it'll have worse performance 0-60, and it won't seat as many people.
...but it'll look cool.
Dan Detweiler
Active Member
If, if, if...
When and if these things actually hit the road then we can discuss and compare. Until then it's just really cool vaporware. Not knocking it, just saying that right now the only thing Tesla needs to worry about is ramping up for their delivery of of their car that is just as fast, can drive coast to coast with ease, and will be able to drive itself (all of which has been documented and demonstrated) and oh...will cost about 1/3 that of the Porsche.
I don't think Tesla's sweating in their boots.
Porsche is touting sustained performance vs. the Tesla 0-60 that can be done no more than twice before the battery needs time to cool. I suspect that Porsche is concentrating on cooling to make faster charging safer for the battery and be able to perform in a continual way.
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