350 kW superchargers

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j.emerson

Member
Joined
Jan 19, 2017
Messages
11
350 kW supercharges are on the horizon. Elon Musk is hearing the competition and has said he plans to install a Tesla
V 3.0 supercharger with 350kW capacity. It is said that a 90 kW battery can charge from empty to 80% in 15 minutes.
I have one question.

If I remember high school chemistry and thermodynamics right, pumping in 350 kW of electrical energy into a battery is going to create a hell of a lot of heat. What is the strategy for compensating for this? I know that EV batteries have cooling systems, but I doubt if they were designed for cooling a 350kW infusion of energy.

Any thoughts on this?

I don't want to upgrade to a DC fast charger if one of these monsters might severely reduce the life of my Rav4 EV battery.
 
First, I’m going to be saying this a lot in the coming years:

The placarded maximum charge rate of the station has very little to do with how fast it will charge your car. Those are the maximum LIMITS of the charger.

So, while the charger is technically capable of 350 amps multiplied by 1000 volts = 350kW, it's going to charge most modern EVs at a wee bit under 50kW maximum, including a Tesla using the CHAdeMO adaptor. All that capability goes to waste without a car that can use it.

Secondly, Elon Musk did *not* say that he would build a "350kW" charger. He said what they would build would make 350kW look like "child's play". The internet ran wild with that, hence all the crazy speculation.

CHAdeMO is officially:
350a * 1000v = 350kW

CCS isn't publically specified, but I believe is will be:
350a * 1000v = 350kW
400a * 1000v = 400kW, power limited for up to 30 minutes, requires liquid cooled plug

Tesla Supercharger is capable of:
365a * 400v = 147kW

I predict Tesla will offer:
500a * 2000v = 1MW, primarily for trucks

If Tesla wanted to call their chargers "350kW" tomorrow, all they need to do is make them 1000 volt capable. They already have all the amps they need.

This does not mean that a Porsche MissionE car is going to charge at 350kW any more than a Tesla can. If the Porsche car indeed has an 800v battery, that logically indicates that it will charge at its highest current and highest power level between 650v and 750v:

400a * 650v = 260kW

400a * 750v = 300kW

If you go to the Porsche website, they make a lot of references to 220kW, so again, don't hold your breath on this one charging much over 300kW at 400 amps, and only for a VERY short amount of time. The same is true of Tesla, which can handle 330-365 amps from 0% to about 20%.

They can say, however, that the new Porsche car can *use* a 350 kW station, but then so can a lowly Nissan LEAF, Volkswagen eGolf or BMW i3 at 45kW.


********

There is absolutely no way that Porsche can accomplish the stated goal of 80% in 15 minutes with today's tech and with cost effective cells that can power a car in all temperatures and last 150,000 miles without adverse degradation. This is assuming 80% of a 100kWh battery. It's not going to happen.

The mainstream EV cars like the Chevy Bolt EV, Nissan LEAF, BMW i3, or eGolf, or any number of other vehicles are usually restricted to 125 amps.
 
Our JdeMO fast charge equipment for the RAV4 EV is limited to 125 amps, like virtually all existing cars that can use CHAdeMO public chargers.

Regardless of what machine you plug into, it will never exceed 125 amps. In the future, we will experiment with higher amps, and possibly offer a software upgrade to take advantage of higher output chargers on the horizon.

Currently, the maximum charge rate is about 45kW = 360v * 125a

As to heat dissipation, i would probably design an off-board cooling system that you link up to when connecting electrically for these really fast charge rates of the future. Just two pressurized fluid couplings should work. Then, you can make as big of a heat exchanger as required, but mounted on the ground, not in a car.
 
Thanks for the explanation Tony. You are a wealth of information. You reminded me that any EV will only allow so much elec. flow to charge the battery so the additional capacity of these superchargers is of no consequence for my Rav4 EV (or for most EVs today).

But I still would like to know if the 45kW inflow rate you say is currently allowed by the Rav4 EV on the DC fast charger creates more heat stress on the battery than a 10kW level 2 and is the liquid cooling system designed to handle that additional heat flow evenly across the battery cells to avoid hot spots?

Thanks helping me understand this.
 
j.emerson said:
But I still would like to know if the 45kW inflow rate you say is currently allowed by the Rav4 EV on the DC fast charger creates more heat stress on the battery than a 10kW level 2 and is the liquid cooling system designed to handle that additional heat flow evenly across the battery cells to avoid hot spots?

Yes, of course, charging any modern battery more quickly will create more heat, as well as "stress" on the cells. So does operating the battery outside of 50% State Of Charge (SOC), or operating the battery too hot or cold.

The ideal modern lithium cell parameters for long life would be neither charged, nor discharged (no cycling), while kept at 50% SOC, in a near frozen state at about -25C. Everything outside of those parameters puts more "wear and tear" on the cell.

Only Tesla or maybe Panasonic could answer your question about hot spots within cells. That is well outside our work.

The RAV4 EV liquid battery cooling has proven adequate at 530 amps discharge (Sport mode), as well as 125 amps continuous while charging with JdeMO. In normal use, the battery frequently operates between 25C and 40C (77F to 104F) observed.

JdeMO monitors pack temperature every 1/10 of a second, and adjusts charge rate to the following. Any time that the green LED push button is quickly blinking, that indicates that the JdeMO software has automatically slowed the charge rate below 125 amps:

90 amps - 45C / 113F degrees battery temp
60 amps - 47C / 117F degrees battery temp
30 amps - 49C / 121F degrees battery temp
OFF ------ 51C / 125F degrees battery temp

Max published cell temperature by Panasonic is 60C.

When at ambient air temperatures above 25C / 77F, it is strongly recommended that the cabin climate control be left in AUTO mode when either expecting to be using JdeMO, or while using JdeMO. Do not use OFF, ECO LO or ECO HI.

Should the battery be too cold, at apparoximately 15C / 60F, the onboard battery heater will warm the cells. JdeMO will also reduce charge rate below 10C and 0C until the battery warms. Most of your CHAdeMO public charging will be done after driving the vehicle some distance, therefore the cells will likely always be at the ideal temperature for charging of 25-40C.

Tesla dedicated battery heater for RAV4 EV:
http://phillipsandtemro.com/wp-content/uploads/2016/11/2016-Zerostart-Catalog.pdf

page 86, Circulation heaters, industrial, tank
 
Thanks again for a very complete explanation. It appears that charging strategies carefully take into consideration the temperature of the battery. I can only assume that Tesla has figured out how to evenly distribute the cooling liquid to address the challenge of avoiding hot spots in a large battery array.

I may have a bit more concern about exceeding design specs. than most as I was a mechanic 40 years ago and witnessed Volkswagen pushing their Beetle beyond its design limits resulting in disastrous consequences for the consumer.

The Volkswagen Bug had a governor to keep the vehicle below a set speed so that it could keep the air cooled operating temperature down enough to accommodate a hot oil cooler sitting right next to the #3 cylinder. It was slow but it keep trucking along.

In the infinite wisdom of the marketing division (I am sure they never consulted with the engineers) Volkswagen decided that they wanted to reach to the younger demographic with more sporty performance and took off the governor. I seem to remember an ad with a policeman giving a Beetle driver a speeding ticket.

Well, no surprise, the little buggers blew up. It didn't help that you had California smog control regulations that wanted engines to run hotter to reduce emissions. Beetle engine rebuilds were 1/2 of our shop's business as the #3 cylinder overheated and swallowed the exhaust valve. Smart Beetle owners re-plumbed an oil cooler away from the engine.

Physics has a way of tempering our wills and wishes.
 
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