Battery voltage confirmed: 400V-450V

[DucRider]

At 400V, can you explain RJ's comment about being able to charge at over 300kW at the peak? if not, then either RJ was confused or there must be another explanation. This would be a way that could happen creatively.

Like other things they hoped to provide, that did not make the cut (electrochromic roof, powered tailgate, etc).

All specs now point to 225 kW peak (500A @ 450V - the pack is most likely to be 108 cells in series).

They were testing 400A and 500A during the cold weather. Neither of those are possible at 800V, but do get you to the quoted 200 kW at 400V (nominal), so that is what they are utilizing.

I can't think of a single reason to have 500A capability in the vehicle if you could utilize 800V charging. Can someone come up with a scenario where that would be useful/required? It would not be necessary at Electrify America or RAN locations (or from any current DCFC equipment that I am aware of).

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[mkennedy1996]

They were testing 400A and 500A during the cold weather. Neither of those are possible at 800V, but do get you to the quoted 200 kW at 400V (nominal), so that is what they are utilizing.

You are making the assumption that the vehicle shown in the cold weather testing has the final configuration and was not an earlier prototype or one of several different current prototypes being tested to evaluate each under cold weather conditions.

You seem to have a conclusion and then select that matches that conclusion as proof and then discount evidence to the contrary as inaccurate / out of date.

I don't know whether they intend to use the patent that they filed, but it is not as clear cut as you make it out to be that the vehicles will be standard 400V 500A.

All specs now point to 225 kW peak (500A @ 450V - the pack is most likely to be 108 cells in series).

With the quoted charging speeds, there is a real question in my mind about a peak of 225kW in a 400V system being able to charge 140 miles in 20 minutes. This would be dramatically different than my years of experience with 400V BEVs and the real world performance for every other 400V BEV that I can find.

Adding 140 miles in 20 minutes at an approximate efficiency of 430 Wh/mi, you would need to sustain an average of 180.6 kW into the battery for the full 20 minutes. Do you know of another 400V BEV that can sustain that level of kW for that long?

 

[azbill]

You are making the assumption that the vehicle shown in the cold weather testing has the final configuration and was not an earlier prototype or one of several different current prototypes being tested to evaluate each under cold weather conditions.

You seem to have a conclusion and then select that matches that conclusion as proof and then discount evidence to the contrary as inaccurate / out of date.

I don't know whether they intend to use the patent that they filed, but it is not as clear cut as you make it out to be that the vehicles will be standard 400V 500A.



With the quoted charging speeds, there is a real question in my mind about a peak of 225kW in a 400V system being able to charge 140 miles in 20 minutes. This would be dramatically different than my years of experience with 400V BEVs and the real world performance for every other 400V BEV that I can find.

Adding 140 miles in 20 minutes at an approximate efficiency of 430 Wh/mi, you would need to sustain an average of 180.6 kW into the battery for the full 20 minutes. Do you know of another 400V BEV that can sustain that level of kW for that long?

The Audi E-Tron has a 84KWH battery that can be charged from 0% to 80% in 30 minutes. It maintains the full 150KW rate up to 70%. The charge rate of the E-Tron is 150/84 = 1.8C, basically it can charge at 180% of its rated capacity for an extended amount of time, yes >20minutes.

The Rivian has a 135KW pack (approximatley). Charging at 200KW would be 200/135 = a charge rate of 1.5C, which is less than the E-Tron C rating. So it is easily achieved.

The Taycan, which has an 80KWH battery has peak charging at 270KW, but only up to about 25%. The reason is simple, they are pushing the battery at a very high C rating, 270/80 = 3.4C. Tesla does something similar, that is why they have to back off and taper much earlier in the charge cycle.

If you do not understand C rating, it is explained pretty well in this article:

https://circuitdigest.com/article/an-overview-of-li-ion-batteries

When lithium batteries were first introduced, the norm was to charge them at a 1C rate, i.e. that means a 100KWH battery would charge at 100KW, but even then they have to taper near the end, thus for the E-tron it significantly reduces above 80%, as do all other EVs. As technology has improved, batteries can now be charged at higher C ratings.

The bottom line is that charging at a 1.5C rate up to 70-80% is possible with battery technology that exists today.

 

[DucRider]

I don't know whether they intend to use the patent that they filed, but it is not as clear cut as you make it out to be that the vehicles will be standard 400V 500A.

This late in the game, I think the chances of them intensively testing charging characteristics that will not be on the production vehicles are zero.. There is no benfi to them to find out how well it charges at very high amperages if the production vehicles will not have the wiring and other components to handle it.

With the quoted charging speeds, there is a real question in my mind about a peak of 225kW in a 400V system being able to charge 140 miles in 20 minutes. This would be dramatically different than my years of experience with 400V BEVs and the real world performance for every other 400V BEV that I can find.

Your experience with Tesla is with 350V (nominal) battery packs with a max charge voltage of ~400V. The Rivians are most likely to be 400V nominal and ~450V max charging (108s configuration vs Tesla 96s).
There are EVs that have a charge curve that closely follow the classic cc cv model (i3, etron, etc):

Others use a modified version with set steps (Bolt EV, etc):

500A capability and 800V charging will not coexist in a vehicle coming out in the near future. Your premise that they are currently testing 500A charging under a variety of conditions (and posting about it publicly) but will not be implementing it in their vehicles I find to be extremely unlikely.

Adding 140 miles in 20 minutes at an approximate efficiency of 430 Wh/mi, you would need to sustain an average of 180.6 kW into the battery for the full 20 minutes. Do you know of another 400V BEV that can sustain that level of kW for that long?

Tesla pushes their 350V system to 250 kW. Nobody else does that, so it's not possible?

 

[mkennedy1996]

The charge rate of the E-Tron is 150/84 = 1.8C

The bottom line is that charging at a 1.5C rate up to 70-80% is possible with battery technology that exists today.

Thanks for the link and the information on the E-Tron charging. I am familiar with the power in and out limitations of lithium ion batteries, but the context of those limitations in relation to the size of the battery pack had escaped me. The E-Tron was the comparable that I was looking for. Thanks again.

 

[mkennedy1996]

that they are currently testing 500A charging under a variety of conditions (and posting about it publicly) but will not be implementing it in their vehicles I find to be extremely unlikely.

Probably the same likelihood of the CEO stating that the vehicles will charge at up to 300kW in a public interview and then not implementing it.

Tesla pushes their 350V system to 250 kW. Nobody else does that, so it's not possible?

Is that a question? Tesla plays games. A lot of smoke and mirrors. They get up to 250kW for 5 minutes, but by the end of 20 minutes they are down to 85kW. The average time from 20 to 80% is not much faster than their 150kW chargers.

 

[DucRider]

Probably the same likelihood of the CEO stating that the vehicles will charge at up to 300kW in a public interview and then not implementing it.

An unofficial video released by a non-Tesla employee with off the cuff comments before they started building and testing production intent vehicles?
That carries a lot less weight in my book than an official video released close to launch backed up by written specs published on their website.

And as a note: 400V vs 800V is independent of the ability to charge at a given kW rate.

 

[mkennedy1996]

An unofficial video released by a non-Tesla employee with off the cuff comments before they started building and testing production intent vehicles?
That carries a lot less weight in my book

We can do this all day I guess, but I will stop now with this:
Random "tech" making an off the cuff statement about amps in a Cold Weather testing video vs. The CEO directly answering a question in a recorded interview.

 

[mkennedy1996]

And as a note: 400V vs 800V is independent of the ability to charge at a given kW rate.

Turns out, I wasn't done. Is it correct to say that 400V vs 800V is independent of the ability to charge at a given kW rate? My understanding is that one of the practical limitations of BEV charging is the heat generated. Doesn't the same kW at 800V generate less heat than at 400V, which increases the practical charge rate?

 

[azbill]

I firmly believe that Rivian has a "plan" to get to 300KW, we just do not know the timeframe or exactly which batteries will be capable of that. In the end it may only be the Max Packs that can take that charge rate. Nothing is in writing, except that they plan on 140 miles in 20 minutes for the initial deliveries. The 300KW was a verbal statement and is not written anywhere, therefore it is not binding or meaningful.

Other manufacturers have been a bit more clear on voltage and KW charge rates, but nobody has published any charging curves yet.

 

[azbill]

Turns out, I wasn't done. Is it correct to say that 400V vs 800V is independent of the ability to charge at a given kW rate? My understanding is that one of the practical limitations of BEV charging is the heat generated. Doesn't the same kW at 800V generate less heat than at 400V, which increases the practical charge rate?

Actually there is a practical limit of 500A, so at some voltages higher KW is not possible. That limit is determined by wire size and the need for liquid cooling.

Thus at 400V, 200KW is possible, at 800V 400KW would be possible. But so far chargers have been limited to 350KW. I did see a spec for a new ChargePoint design that claimed 500KW, but those have never been delivered or installed.

 

[DucRider]

Turns out, I wasn't done. Is it correct to say that 400V vs 800V is independent of the ability to charge at a given kW rate? My understanding is that one of the practical limitations of BEV charging is the heat generated. Doesn't the same kW at 800V generate less heat than at 400V, which increases the practical charge rate?

Not at the cell/module level. The initial wiring (and other components) required to get the juice to the pack needs to be beefier, but the C rate doesn't change with voltage. The heat generated within the pack is the same.

 

[mkennedy1996]

Not at the cell/module level. The initial wiring (and other components) required to get the juice to the pack needs to be beefier, but the C rate doesn't change with voltage. The heat generated within the pack is the same.

So your statement that "400V vs 800V is independent of the ability to charge at a given kW rate" would not be correct. The voltage is NOT independent of the charge rate in real world applications.

An 800V charger at about 437 amps provides 350kW, while that same 350kW in 400V would require 875 amps, which is not available in an EV charger and not practical for an EV charging application. For the voltage to be independent at a given kW, in this case 350kW, you would have to be able to complete the charge at either 800V - 437 amps or 400V - 875 amps interchangeably, which can not be done, therefore the voltage used is not independent and is directly related to the kW rate that can be achieved in a real world setting.

 

[DucRider]

So your statement that "400V vs 800V is independent of the ability to charge at a given kW rate" would not be correct. The voltage is NOT independent of the charge rate in real world applications.

you would need to sustain an average of 180.6 kW into the battery for the full 20 minutes. Do you know of another 400V BEV that can sustain that level of kW for that long?

My statement was in response to this.
Sustaining 180 kW is not affected by voltage.

Higher voltages allow for faster charging due to amperage limitations on cables, connectors and other hardware. Sustaining a given charge rate is not tied to voltage.

 

[mkennedy1996]

My statement was in response to this.
Sustaining 180 kW is not affected by voltage.

Higher voltages allow for faster charging due to amperage limitations on cables, connectors and other hardware. Sustaining a given charge rate is not tied to voltage.

That is all pretty obvious. That is why the question was narrowed to 400V BEVs, since their maximum kW is less than that of an 800V BEV.

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