Battery tech aside, how does any auto maker plan to get 10 minute charge time when just getting they much power through a cable is a huge challenge.
Battery tech aside, how does any auto maker plan to get 10 minute charge time when just getting they much power through a cable is a huge challenge.
This is not an issue because, even if a small wire is used, the efficiency loss is not all that considerable. Energy is cheap, so liquid cooling the cables and dissipating i.e. 5% of the energy into the conductor is a straightforward trade-off.
Compare that trivially to petrol, which costs petrol (diesel) to move to petrol stations, and it's actually not that surprising.
Additionally, there has recently been a lot of investment into EV chargers with built-in batteries that charge at slower rates when a vehicle is not present, and operate independently from the grid once a vehicle is connected. This answers the obvious question about infrastructure to deliver the power required.
Two such chargers:
https://freewiretech.com/products/dc-boost-charger/
https://insideevs.com/news/398348/eon-volkswagen-fast-chargi...
Is this even going to be required in most cases? Charging at that speed is only really useful for road trips where you're sitting there waiting for charging to complete so you can go. If you're charging while the car is parked at home for the night, what does it matter if it's ten minutes or ten hours?
So then you only really need the very fast chargers at truck stops on the highway and the like, and then couldn't those chargers just be given a hefty grid connection? The high voltage lines already run parallel to major highways.
Increasing I^2R heat loss by 5% doesn't let you shrink the cable much. You go from "humongously phat cable" to "really phat cable". The problem remains.
Also remember that the cost of the petroleum distribution infrastructure is shared between in-town drivers and road-trip drivers. If these "fast chargers" are only supposed to be used by people who need more than one batteryful of driving in a given day (i.e. people on a road trip), the budget available to pay for the refueling infrastructure is going to be tiny compared to the petroleum infrastructure. EVs will simply never "catch on" for non-commuter use if we go down that road.
Also note that 1000V isn't an upper bound; many vehicles under design now will be ~1000V, and I expect that to push up to at least 1500V within the next few years.
Imagine we used 35mm2 at 0.55 Ohm/km and we have 2 poles. If the charging cable is 3m including inside the device, that’s 2x3 = 6m. That’s 6.6 mOhms total, so I2R on that at 500A is only 1.65kW, which is nothing.
As for chargers with batteries, I don’t see how that’s viable. 75kWh would require each charger to have 6 powerwalls just to store 75kWh. If you wanted to dispense that amount of power in 10 minutes you would need 60 powerwalls per charger. Maybe a battery could be designed to provide higher power output, but it’s going to have the same issues that car will have when attempting to charge at a fast rate. Even with storage in the charger how quickly can it recover? Tesla superchargers run non-stop on busy travel holiday. Relying on a onsite battery would do no good on high demand days.
A quick search tells me that 1000 kcmil wire is rated for 450 amps [1].
Another quick search finds that reasonably sized 1000 kcmil rated for 15000 volts are available and reasonably sized for a vehicle charger [2].
[1] http://wiresizecalculator.net/wiresizechart.htm
[2] (note that kcmil and mcm mean the same things) https://www.lighting-gallery.net/gallery/displayimage.php?po...
I can't bend a 24mm-diameter solid copper rod with my bare hands. Can you?
Going stranded enough to feel even remotely like a "cord" or "cable" will bloat that diameter far, far beyond 24mm.
I used to work with ~9mm diameter solid copper and even for that I treated it like EMT and used task-specific benders to shape it.
1000 kcmil cable x2 +ground and insulation is going to be one beefy cable. I’m not saying it can’t be done, just that it’s not a trivial problem to solve. Add to this an environment with a wide range of ambient temperatures and untrained humans sure to be yanking on stuff.
I just would like to see some details on exactly how these claims will be achieved rather than some marketing puff piece. And Toyota is not alone here, GM pulled the same with the hummer EV and “watts to freedom” marketing buzz with no explanation of what that even means.
http://www.ecswire.com/mmspecs/Specsheets/Belden/leadWireSel...
So you don’t actually need so big a cable. You also wouldn’t normally be using MV cables for a car charger — getting 15kV safely through a car charger terminal sounds like an interesting challenge. But 450A at 1kV doesn’t sound like a particularly big deal.
Keep in mind that there’s potentially a free factor or 2 available. I don’t know how actual DC chargers work, but I imagine you could supply -1kV and 1kV relative to ground without too much trouble, resulting in effectively 2kV while only operating at 1kV relative to ground. AIUI you trigger rather more onerous NEC rules if you get to much higher voltages relative to ground.
It's not a general safety code.
It's 80% about making sure buildings don't burn down, and 20% about peoples expectations about what parts of their house can shock them if a fork is stuck into them. That's it.
Regardless of how anyone may feel about the NEC, this is a field installation that needs to follow the rules. So those big cables will be sized per the NEC ampacity tables, and they will follow NEC rules based on their operating voltage.
[0] I randomly stumbled on one under construction.
The contacts are on the roof of the vehicle and the charger drops down onto them.
I'm not sure how that adapts for smaller vehicles, but they aren't starting from nothing.
Since this thing is meant not to charge a single bus, but rather a fleet of buses, it's almost certainly not safe for the general public to get anywhere near it.
This thing is in the same class as transmission line transformers.
https://new.siemens.com/global/en/products/energy/medium-vol...
The 450 Kw charger can be setup standalone, it doesn't have to be in a charging depot. It charges 1 bus at a time. The design is focused on installation at locations along a bus route where the bus pauses. If the bus automatically charges during the pause, it can operate with a smaller, cheaper battery.
I admit I’m rather impressed that the connectors can handle this amount of current, but they don’t seem to have a problem with it.
https://www.greencarreports.com/news/1125436_the-most-powerf...
I'm not an electrical engineer; I don't know what the proper cable size is for this application with all the correct safety margins, but it doesn't seem too terribly unreasonable as long as the voltages are pretty high and the battery can tolerate it. If heat is a problem, then water cooled cables can help.
... for a very brief period of time.
Please don't use horsepower as a measure of electrical power, it's misleading. All the stuff around us that is commonly measured in horsepower is fossil-fuel-burning equipment with fossil-fuel-levels of energy density at any given cost point. They make hard things seem easy because they don't have to be rechargeable.
With electric motors it seems to be at least fairly common to refer to an electric motor's mechanical power output in kilowatts rather than horsepower. In a lot of ways that makes sense, but horsepower is a unit that more people are familiar with.
By comparison a normal 200HP engine at 30% efficiency is producing 667kw of waste heat into the air with a tiny percentage of that going out the exhaust pipe.
An average ICE is only producing 200HP at a specific RPM, for short period of time. Red-lining any sedan while being stationary will probably overheat the engine pretty quickly, as the on-board radiator fan either electric or mechanical will not provide enough airflow. They are designed to be cooled by incoming air while driving.
With electronic ignition, you usually have a way to limit max RPM by stopping ignition, so you're not producing work (and heat) either way.
This isn't really a fair comparison. Cooling capacity goes up with the temperature difference to ambient. It's a lot harder to cool 8kw of heat at 20C above ambient compared to 8kw at 200C above ambient.
The majority of that heat is removed via the radiator which uses a liquid coolant which should not exceed 105C even when the outside temperature is 45C so that’s only 60C of wiggle room.
Though it’s a fair point batteries have lower maximum temperatures, at worst reducing charging rates when outside temperatures exceed ~(110C or 43C) is hardly deceptive or particularly relevant to most people. High end cars could even use the car’s AC in extreme situations.
Just to be clear, you'd ordinarily have the cells themselves in series or a bunch of parallel groups in series to reach high voltages, and as far as the charger is concerned it's just one big battery with a single positive and a single negative terminal.
On the other hand, if you're suggesting balance charging where you have an individual connection with the charger between each cell, that's not really practical to do with large batteries because the current would be very high and the voltages very low, which, as far as cabling goes, is the worst-case scenario. Charging a single cell at 100 amps and low voltage requires basically the same size cable as charging a bunch of cells in series at 100 amps and high voltage. If you need a big, thick cable for each cell, that gets unwieldy very quickly.
Another unpractical option is to switch the battery into a single parallel group during charging and charge the whole group as if it was a single low-voltage high-amp-hour cell. That's unpractical for the same reason; low-voltage charging is an inefficient way to move energy around. Also, switching from series to parallel would require a lot of high-current contactors (basically, electro-mechanical relays), which are kind of expensive.