Claims for 1min EV charging time

[jjjord]

I've been thinking for a while about all the promises from Fisker and other (future) EV manufacturers about a 1min charging time. Not that much about the vehicles themselves or their batteries, but the infrastructure required to do that. Let's do some assumptions:
200Wh/m (very optimistic efficiency - assuming groundbreaking in aerodynamics, tires, etc)
300miles range - that's what they usually promise
So the battery should be able to discharge at least 200*300=60KWh

To simplify let's use an ideal case - there are no losses in the charger, battery chargers from 0 to 100% in a linear manner. Or the battery is 100KWh, but it's only used between 20-80% that's not relevant. The bottom line is you have to transfer 60KWh to the car in 1min. If it was 1h it is easy math - 60KW for 1hour (that is 600V, 100A - very reasonable). Now if you want to transfer 60KWh in 1min it would be 60 times more - 3600KW=3.6MW

I am not sure what are the requirements for high voltage insulation, but my bet is no manufacturer would go more than a 1000V system (it will probably be DC, otherwise you should carry some solid charger in your trunk). That means the current would be 3600KW/1KV = 3600A. For reference if voltage is 10KV, current would be 360A

I am not in a close touch with latest tech in high power transfer, but one way to go is using multiple conductors, another way would be some kind of magnetic conversion - you park above a plate that lifts close to the battery and does some magic to transfer 60KWh in 1min...

Any ideas? Or maybe you have read more info on the subject somewhere else? Do you care to share?
Thanks

 

[mspohr]

I've been thinking for a while about all the promises from Fisker and other (future) EV manufacturers about a 1min charging time. Not that much about the vehicles themselves or their batteries, but the infrastructure required to do that. Let's do some assumptions:
200Wh/m (very optimistic efficiency - assuming groundbreaking in aerodynamics, tires, etc)
300miles range - that's what they usually promise
So the battery should be able to discharge at least 200*300=60KWh

To simplify let's use an ideal case - there are no losses in the charger, battery chargers from 0 to 100% in a linear manner. Or the battery is 100KWh, but it's only used between 20-80% that's not relevant. The bottom line is you have to transfer 60KWh to the car in 1min. If it was 1h it is easy math - 60KW for 1hour (that is 600V, 100A - very reasonable). Now if you want to transfer 60KWh in 1min it would be 60 times more - 3600KW=3.6MW

I am not sure what are the requirements for high voltage insulation, but my bet is no manufacturer would go more than a 1000V system (it will probably be DC, otherwise you should carry some solid charger in your trunk). That means the current would be 3600KW/1KV = 3600A. For reference if voltage is 10KV, current would be 360A

I am not in a close touch with latest tech in high power transfer, but one way to go is using multiple conductors, another way would be some kind of magnetic conversion - you park above a plate that lifts close to the battery and does some magic to transfer 60KWh in 1min...

Any ideas? Or maybe you have read more info on the subject somewhere else? Do you care to share?
Thanks

Sounds unpossible because of physics and math colliding with the real world

 

[Saghost]

Well, 360 A is only slightly more than Superchargers deliver now - but like you I have trouble believing anyone will put a 10 kV system into a car.

The battery chemistry that can safely take a 50C charge rate doesn't exist to my knowledge.

I think it's more likely that you'll get a car with a thousand or fifteen hundred mile range that makes the charge speed question nearly irrelevant than that you'll get one that can charge to 80% in one minute.

 

[mongo]

An 8 mile (usable) range 3 could fully charge in a minute...

Even if your charge voltage was 10kV, you would need the pack to also be 10kV, that would difficult to support electronics wise. You would need roughly 2,750 cells in series to hit that level, which then puts the pack only 4 cells wide (relative to Tesla), which would not support a 360A charge rate.

To get to 360 A, you need the ~80 cell wide pack that Tesla has, say their chemistry can charge at double the rate: so 40 * 2,750 = 110,000 cells. Assume the energy is half due to higher power, 7 Wh per cell = 770 kWh pack.

My numbers may be a little off, but that is roughly correct.
The other may to look at it is C rate, 3.6 MW at even 10 C needs a 360 kWh pack.

My guess: Semi will be around 800kWh in 4 200kWh packs that charge independently. ~500 kW rate using 4 superchargers and 4 cables.

 

[Saghost]

An 8 mile (usable) range 3 could fully charge in a minute...

But only if it's carrying the full 300 mile pack with the upper half and most of the bottom marked as unusable...

 

[mongo]

But only if it's carrying the full 300 mile pack with the upper half and most of the bottom marked as unusable...

Yah, hence my use of "(usable)"

 

[11thIndian]

Well, 360 A is only slightly more than Superchargers deliver now - but like you I have trouble believing anyone will put a 10 kV system into a car.

The battery chemistry that can safely take a 50C charge rate doesn't exist to my knowledge.

I think it's more likely that you'll get a car with a thousand or fifteen hundred mile range that makes the charge speed question nearly irrelevant than that you'll get one that can charge to 80% in one minute.

Agreed. At a certain point you pass range any individual is going to drive in a day, unless you’re doing a marathon trip across country with multiple drivers.

I just moved across country and drove 2600mi in 2.5 days (Ontario to California). You need to stop every 3-4 hours for food or other necessities. I think and even 600-800mi vehicle solves this problem for nearly everybody as long as charging time is roughly an hour.

 

[jjjord]

Many good points here. About the 360A current - insulation will be much different (I suppose) at 10KV than the <400V on the superchargers. And there are a lot of variables as mentioned above - capacity of the batteries, operating voltage etc.
But the bottom line is you have to transfer 60KWh in 1min... I don't see that happening anytime soon though.

 

[Darmie]

Even if these companies can get there on paper and let's face it, that's all it is at the moment. we don't know how it's going to work until you have some proof of concepts running around. When and if we see this, how many different recalls and back to the drawing boards will we see before they have paper meet reality. Look at EA having issues with their fast charger cable. Yes it may be corrected now, but how well will it work when it starts being used? I'm not saying it can't happen. Look, we had one shot at the atomic bomb, so anything is possible.

 

[Mixdup]

80% in one minute would beat the refueling time of a gas car. it would be cool to reach that level of charging but it's unrealistic.

I also think it's a little harmful to the adoption of EVs if companies make wild claims that cannot possibly be met, at least within any reasonable time frame. This is just going to turn people off when promises aren't met ("what else are they not going to be able to do" or "what else are they lying about")

All of that damage to the perception of EVs for what, the promise that you'll *beat* the refueling time of a gas car? That no one is asking for? getting the time as close as possible to an empty-to-full refill of a gas car should definitely always be the goal, but be reasonable and measured about how you go about it

 

[david_42]

I have some high power experience from the Navy and I'm not certain there is an insulation that can handle 10,000 volts in a single cable at the required amperage. Sure you can use multiple cables, but it would take longer to connect and disconnect the cables than to deliver a one minute charge. Some companies are already experiencing cable problems at much lower power levels.

 

[Casmium]

You could develop a way for the for the battery pack to switch the different cells or groups of cells from being parallel to in series for fast charging mode.

 

[mongo]

You could develop a way for the for the battery pack to switch the different cells or groups of cells from being parallel to in series for fast charging mode.

That helps with charge current, but doesn't change the C rate of the charge.

 

[ItsNotAboutTheMoney]

Easy:
1) 120kWh battery capacity
2) 120kW charging
3) 2kWh usable capacity

 

[Saghost]

Easy:
1) 120kWh battery capacity
2) 120kW charging
3) 2kWh usable capacity

Yup. We talked about that upthread a month ago.