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800V fast charging discussions

ajdelange

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I just want mid-gate, high AC power output and 800V fast charging.
Curious as to why you care what voltage the charger runs at as long as it pushes the amps required. The cables on the V3 super chargers are liquid cooled and much skinnier than the non cooled cables on the V2's even though they carry 600A.
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Max

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Curious as to why you care what voltage the charger runs at as long as it pushes the amps required. The cables on the V3 super chargers are liquid cooled and much skinnier than the non cooled cables on the V2's even though they carry 600A.
A GM video gave me the impression that flipping the connections to turn 400V into 800V for charging makes it faster. Didā€˜t really look into alternative tech. I really donā€™t care about the voltage. I just care about the ability to fill up a large battery pack as fast as possible when I am towing. Any tech that get me there and is readily available is cool with me.
 
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ajdelange

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What determines charging speed is the ratio of the charger's power output to the battery capacity. One can configure the pack in several ways (i.e. as 400 or 800V) and if a higher voltage is chosen then less current needs to be passed. This has advantages in that less copper is required in the charging cable and less in the vehicle wiring between charge port and inverter (and copper is expensive) etc but as long as the current delivered to each cell is sufficient it doesn't matter how the pack is organized.
 
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Zoidz

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A GM video gave me the impression that flipping the connections to turn 400V into 800V for charging makes it faster. Didā€˜t really look into alternative tech. I really donā€™t care about the voltage. I just care about the ability to fill up a large battery pack as fast as possible when I am towing. Any tech that get me there and is readily available is cool with me.
800 volt charging has a few benefits, the biggest is time to charge is cut in half, possibly slightly less than half. That's because there is less heat generated, both in cabling and in the battery pack, at 800v vs. 400v due to half the current flow at 800v. Less heat means more power transferred and retained in the battery, and less weight due to cable/wire size requirements, with a potential net result of a little more range.

A rough analogy is your home uses 120/240 VAC power, but the utility and transmission distribution systems use anywhere from 600 volts to hundreds of thousands of volts. Higher voltage improves efficiencies.
 

Max

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800 volt charging has a few benefits, the biggest is time to charge is cut in half, possibly slightly less than half. That's because there is less heat generated, both in cabling and in the battery pack, at 800v vs. 400v due to half the current flow at 800v. Less heat means more power transferred and retained in the battery, and less weight due to cable/wire size requirements, with a potential net result of a little more range.

A rough analogy is your home uses 120/240 VAC power, but the utility and transmission distribution systems use anywhere from 600 volts to hundreds of thousands of volts. Higher voltage improves efficiencies.
It makes sense. I assume less heat means less waste too. I was surprised how much loss there was when Tommy was charging that R1T.
 

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ajdelange

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800 volt charging has a few benefits, the biggest is time to charge is cut in half, possibly slightly less than half.
Come on now.

That's because there is less heat generated, both in cabling and in the battery pack, at 800v vs. 400v due to half the current flow at 800v.
True less heat is generated in the cabling - in fact 1/4 as much but the current in each cell is the same whether the cells are in parallel or series. As the losses outside the cells are relatively small cutting them down by even a factor of 4 has only a small effect on the overall efficiency (heat production).

Less heat means more power transferred and retained in the battery, and less weight due to cable/wire size requirements, with a potential net result of a little more range.
. True but nothing like a factor of 2. The main benefit of 800V is in the charger with the secondary ones being in the OEMs ability to reduce some copper weight in the car itself. But note that the Tesla chargers are expected to now top 300 kW soon. Do we think they will be retrofitting our cars with 800V batteries? Or that the CT will have 800V architecture? Isn't that second question an interesting one?
 

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These chargers can put out about 500amps regardless of voltage. What you want in the end isn't current (amps), but power (kW). Power equals current times voltage. If you double the voltage with the same current you double the power.
 

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Are we talking about CCS chargers or Superchargers? CCS standard is limited to 500A currently, right @ajdelange? That's a legitimate confirmation and question - not snark. In case it came off snarky.


As you noted, what the end users really is going to care about is V*A. As you noted, higher voltage has some benefits for efficiency through less heat loss.

True 800v systems require more than just a battery pack sitting sitting in parallel to accept 800v. GM's "800v" system is 800v charging through a split pack (as I understand it). But *I think* (marginal confidence level) porsche and Hyundai have true 800v systems that should result in less current draw for a given output to the motors.

I think the general context that people want an 800v system is because of the 500amp limit of CCS chargers as they are currently implements. Other than for the CT, I don't think the supercharger capabilities aren't really relevant.

Edit: answered this myself. The current CCS standard is limited to 500A (at least per Wiki... I don't feel like chasing it down further right now)
https://en.wikipedia.org/wiki/Combined_Charging_System

Basically I think people want to have a peak charging rate faster than ~200kw when these batteries are >~100 kwh so with a target charging rate equivalent to something like 200ish miles in 20 minutes. This is just a soft observation based on the charging times that people seem to be happy with that aren't historic tesla drivers.
 
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ajdelange

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These chargers can put out about 500amps regardless of voltage. What you want in the end isn't current (amps), but power (kW). Power equals current times voltage. If you double the voltage with the same current you double the power.
These chargers put out the current the car wants and the car requests additional current by asking for additional voltage for as long as those requests stay within the envelope of the charger and that depends on the charger. An HPC350 charger will put out 500 amps at any voltage below 700V at which point it is putting out the maximum 350 kW that class of charger is capable of. As the vehicle asks for higher voltage the current drops following a hyperbolic trajectory which "bites the corner" Off the envelope. At 920 V (the maximum) the current is limited to 380.4 A which still gives 350 kW. Where we are in the charger envelope depends on the car's "load line" a nearly horizontal line starting at the left of the envelope and extending towards the right. Probably too deep into the weeds already but if anyone wants more I'll answer if I can.
 

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Is the goal of this thread to pat Rivian on the back for using an outdated system or try to pretend it's not outdated?

800v and 900v have a ton of benefits and can charge much faster more reliably. This has been proven in real world applications, vs the selective theoretical science you're using to talk away 400v being a worse option.
 

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ajdelange

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Are we talking about CCS chargers or Superchargers? CCS standard is limited to 500A currently, right @ajdelange? That's a legitimate confirmation and question - not snark. In case it came off snarky.
It doesn't and I'm not sure which we are talking about here as these posts got moved here from another thread which is labeled "800V charging" so I guess we are talking CCS although the SC are similar.


True 800v systems require more than just a battery pack sitting sitting in parallel to accept 800v. GM's "800v" system is 800v charging through a split pack (as I understand it). But *I think* (marginal confidence level) porsche and Hyundai have true 800v systems that should result in less current draw for a given output to the motors.
I guess some definitions are required here. To my way of thinking a "true" 800 volt system would be one like Lucids where the battery is permanently configures with modules interconnected so that the pack has two terminals 800V apart. No series parallel switching. It also has 800V inverters and 800V motors. The Rivian patent was a clever scheme in which the pack was split in 2 and the halves connected in series for 800V charging and reconnected in parallel to run the 400V motors.


I think the general context that people want an 800v system is because of the 500amp limit of CCS chargers as they are currently implements. Other than for the CT, I don't think the supercharger capabilities aren't really relevant.
I mentioned in the previous post that the HPC350 looks like a rectangle with the upper right hand corner bitten out by a parabolic arc representing the 350 kW limit. Any vehicle load line which intersects that arc can get the maximum power. As mentioned in that same post that can be had at as little as 380A (@ V 920 V) or as high as 500 A (@700V). Obviously you can't charge an 800V battery from a 700V supply so the minimum current for 350 kW is going to be less than 500A.


Edit: answered this myself. The current CCS standard is limited to 500A...
...at less than 700V and further limited at voltages above 700.


Basically I think people want to have a peak charging rate faster than ~200kw when these batteries are >~100 kwh so with a target charging rate equivalent to something like 200ish miles in 20 minutes. This is just a soft observation based on the charging times that people seem to be happy with that aren't historic tesla drivers.
I think people would like to charge at an average rate of 2C (15 minutes for 50% charge) but I don't think we are going to get that. For a 180 kWh battery that's 360 kW - beyond even the HPC350 class. But it's clear that we can build chargers that approavh that rate. I just don't think today's batteries can withstand it. I think 1.2C (60% in half an hour) is more like what we'll se for a while. That means averge of 216 kW. Chargers can certainly be built that will do that but they'll have to throw a heck of a lot of current at a 400 V battery (over 500A) which the new Tesla chargers can do.
 
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Is the goal of this thread to pat Rivian on the back for using an outdated system or try to pretend it's not outdated?

800v and 900v have a ton of benefits and can charge much faster more reliably. This has been proven in real world applications, vs the selective theoretical science you're using to talk away 400v being a worse option.
Yes, forget all this science and engineering junk. 800V is clearly superior because 800 is a big number. Big numbers are better!

/S
 
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ajdelange

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Is the goal of this thread to pat Rivian on the back for using an outdated system or try to pretend it's not outdated?
It's to have an intelligent discussion of the merits of 800 V systems. In the Rivian context it's to recognize that their years old design is, of course, no longer bleeding edge and to discuss the disadvantages of this, if any.

800v and 900v have a ton of benefits and can charge much faster more reliably. This has been proven in real world applications, vs the selective theoretical science you're using to talk away 400v being a worse option.
As the discussion is intended to be intelligent of course the science needs to be considered. So let's have the "science" behind the tons of advantages.

For the more rational - yes there are some and I think they have been touched on but I'm not sure it has been mentioned in this thread that the principal one is to the charger manufacturer. What good does it do an OEM to build a car that charges 2C if no one can build the charger to charge it?
 

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It doesn't and I'm not sure which we are talking about here as these posts got moved here from another thread which is labeled "800V charging" so I guess we are talking CCS although the SC are similar.
in what I think is a first for you is your quotes got messed up.

A couple of follow-ups:
1. from what I see the CCS2 standard is currently limited to 500A (or less). You don't think that's the case?

2. Yes, the chargers themselves are currently limited to less amperage higher voltages as you noted.

3. This is where I think we may be speaking slightly differently. So I'm going to pull in a video recording of a few systems quickly here. In it are an EQS, E-tron GT (same 800v platform as the taycan), Mach e, and a model S.

The E-tron GT does 10 to 60% in 12 minutes. and 10 to 80% in 19 minutes. The EQS (400v) gets to 60% in 20 minutes, and the model S in 25 minutes. So starting at 10% they're picking up the first 50% with an average C rate of 2.5, 1.5, and 1.2C. The EV6 and Ioniq 5 also hit that 10% to 60% number in about 11 minutes as well for ~2.5C on average. And then they proceed to shave about a minute or two off the E-tron GT in the 60 to 80% portion of the curve. The Lucid does 0 to 50% in less than 20 minutes as well.


For a full charge, I agree something like 1C is probably about as good as you'll get. But for the "optimal" charging range of a battery 2C isn't unheard of.
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