RAN charging curve?

[johnbro23]

With 6 stations deployed, curious if anyone can share the charging curve they're getting. I see one mention on the forums of 215KW which is great.. that's over 8 miles per minute. What are others seeing in terms of charging speed, and what does the charging curve look like? I believe Rivian has told us to expect a better curve than Tesla, holding 200KW+ through 60% state of charge, and I'm curious how that looks in real life. And how fast does it taper off from there.. what speed are we pulling at 80% SoC?

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[Khaneric]

So i've charged at RAN stations a few times but the Rivian app doesn't show the charge cause it's free and honestly i never sat around and did it. I can tell you i hit 215 for a while and it was WELL over 100 all the way to 80%.

 

[pc500]

So i've charged at RAN stations a few times but the Rivian app doesn't show the charge cause it's free and honestly i never sat around and did it. I can tell you i hit 215 for a while and it was WELL over 100 all the way to 80%.

Easier thing is to just record a video, go grab lunch, toss it on Youtube. Someone else will make the spreadsheet

 

[SeaGeo]

holding 200KW+ through 60% state of charge

I haven't seen this claimed from Rivian. Are you able to point to it?

The truck charging curve is the same on RAN or a 350kw station with EA as long as you can get a charger that doesn't derate due to thermals (or just shitty hardware). Conceptually speaking, it pulls 500A from about 0% to about 50% so roughly 190kw to 220kw over that range and voltage increases, and then it starts dropping off in steps.

 

[Guy]

I haven't seen this claimed from Rivian. Are you able to point to it?

The truck charging curve is the same on RAN or a 350kw station with EA as long as you can get a charger that doesn't derate due to thermals (or just shitty hardware). Conceptually speaking, it pulls 500A from about 0% to about 50% so roughly 190kw to 220kw over that range and voltage increases, and then it starts dropping off in steps.

Does it have to start dropping at 50% or is that a conscious decision of Rivian’s?

 

[SeaGeo]

Does it have to start dropping at 50% or is that a conscious decision of Rivian’s?

Great question. I'm going to caveat this statement that this is based on consumer level digging into charging strategies for similar batteries. tl;dr they can't do a lot without risking damage to the batteries.

The charging curve Rivian has enabled is broken into two phases, a constant current phase (governed by the 500A CCS limit), followed by a constant voltage phase. They're following the constant current phase up until the point where the battery pack voltage is close to the nominal voltage, or seemingly commonly around 50% SOC. The idea here is to prevent accidentally overcharging (and inducing overvoltage) the batteries.

So they're switching from a constant current to a constant voltage framework at about 50% to protect the battery. I don't think there's a ton they can do without exposing the batteries to risk other than potentially smoothing out the ramp for current.

I've plotted the charging data from three real charging sessions with amperage and voltage tracked. Two of them are Ioniq 5 curves, one is the 500A 450v curve, and another is sort of a theoretical 800v Rivian curve to see the potential impacts/differences.

I've included two ioniq5 curves because they have a couple of charging pauses slowdowns, which I think is handy to show that as you crank a lot of amperage into the pack, that amperage spikes the voltage as well. So if you look at Ioniq 5a plot at 50% you see the current drop, which caused the voltage to drop from 97% nominal to 95% nominal (728 down to 710v). You can see a similar drop at about 82% for the other Ioniq 5 curve. I provided that to show why they have the constant voltage phase and how increasing/reducing current impacts the voltage, and how reducing current helps maintain a constant voltage during the constant voltage phase of charging.

The left y-axis is % of the nominal voltage of the packs at 100%, the right y-axis is the current from the tests. You can see that the voltage increase as a percentage is fairly similar between packs, but you can also see how the Rivian seems to have more current induced voltage in the 45-70% range than the Ioniq pack.

For shits and giggles I also pretended that I know what an 800v Rivian pack may behave like with a 350kw limit. With that I plotted up what the current would look like, and then assumed above 50% it would follow closely to the current CV phase.

That theoretical charging curve would look like this:

The 800v curve is obviously just educated guessing, and heat in the battery pack would still be a big issue and probably control a lot of the real world behavior. Practically speaking the nice thing (in my mind) is that the 800v system would allow you to pull 280kw with an amperage that most of the existing fast chargers seem to be able to reliably maintain.

 

[Guy]

Great question. I'm going to caveat this statement that this is based on consumer level digging into charging strategies for similar batteries. tl;dr they can't do a lot without risking damage to the batteries.

The charging curve Rivian has enabled is broken into two phases, a constant current phase (governed by the 500A CCS limit), followed by a constant voltage phase. They're following the constant current phase up until the point where the battery pack voltage is close to the nominal voltage, or seemingly commonly around 50% SOC. The idea here is to prevent accidentally overcharging (and inducing overvoltage) the batteries.

So they're switching from a constant current to a constant voltage framework at about 50% to protect the battery. I don't think there's a ton they can do without exposing the batteries to risk other than potentially smoothing out the ramp for current.

I've plotted the charging data from three real charging sessions with amperage and voltage tracked. Two of them are Ioniq 5 curves, one is the 500A 450v curve, and another is sort of a theoretical 800v Rivian curve to see the potential impacts/differences.

I've included two ioniq5 curves because they have a couple of charging pauses slowdowns, which I think is handy to show that as you crank a lot of amperage into the pack, that amperage spikes the voltage as well. So if you look at Ioniq 5a plot at 50% you see the current drop, which caused the voltage to drop from 97% nominal to 95% nominal (728 down to 710v). You can see a similar drop at about 82% for the other Ioniq 5 curve. I provided that to show why they have the constant voltage phase and how increasing/reducing current impacts the voltage, and how reducing current helps maintain a constant voltage during the constant voltage phase of charging.

The left y-axis is % of the nominal voltage of the packs at 100%, the right y-axis is the current from the tests. You can see that the voltage increase as a percentage is fairly similar between packs, but you can also see how the Rivian seems to have more current induced voltage in the 45-70% range than the Ioniq pack.

For shits and giggles I also pretended that I know what an 800v Rivian pack may behave like with a 350kw limit. With that I plotted up what the current would look like, and then assumed above 50% it would follow closely to the current CV phase.

That theoretical charging curve would look like this:

The 800v curve is obviously just educated guessing, and heat in the battery pack would still be a big issue and probably control a lot of the real world behavior. Practically speaking the nice thing (in my mind) is that the 800v system would allow you to pull 280kw with an amperage that most of the existing fast chargers seem to be able to reliably maintain.

Many thanks for this. The Ioniq has much
More area under the curve between 50 and 80%, would be good if Rivian can close that gap a little.

A second charging question I have is I know batteries can be rated for a certain number of charging events and that charging can cause degradation over time. Is it therefore better, for a normal week of commuting, charge once from 10 to say 70% rather than charging 10-12% every day? The weekly approach reduced the number of charging instances by c. 5 fold and could that extend the life of the battery in any meaningful manner? Sorry for the questions but the R1S will be my first EV.

 

[SeaGeo]

The Ioniq has much
More area under the curve between 50 and 80%, would be good if Rivian can close that gap a little.

I think you're referring to area under the curve on the last plot I made. I *think* the only reason they have that is because of the voltage difference basically. I could be wrong, but I don't think Rivian has much room to increase charging in that range with the current voltage of the pack. If they can, I suspect it will be very dependent on collecting a large amount of data.

A second charging question I have is I know batteries can be rated for a certain number of charging events and that charging can cause degradation over time. Is it therefore better, for a normal week of commuting, charge once from 10 to say 70% rather than charging 10-12% every day? The weekly approach reduced the number of charging instances by c. 5 fold and could that extend the life of the battery in any meaningful manner? Sorry for the questions but the R1S will be my first EV.

A battery engineer from GM posted a thread on twitter a few weeks ago. Basically he said don't worry about it, that's the job of the BMS, but if you are going to go the extra mile, the larger swings in charging are harder on the batteries than smaller swings. So doing 60 to 70% every should be less hard on the battery than 10 to 70% once a week. And avoid letting it sit high or low SOC for very long.

 

[Guy]

I think you're referring to area under the curve on the last plot I made. I *think* the only reason they have that is because of the voltage difference basically. I could be wrong, but I don't think Rivian has much room to increase charging in that range with the current voltage of the pack. If they can, I suspect it will be very dependent on collecting a large amount of data.


A battery engineer from GM posted a thread on twitter a few weeks ago. Basically he said don't worry about it, that's the job of the BMS, but if you are going to go the extra mile, the larger swings in charging are harder on the batteries than smaller swings. So doing 60 to 70% every should be less hard on the battery than 10 to 70% once a week. And avoid letting it sit high or low SOC for very long.

Many thanks, this is all really helpful information.
For the area under the curve from 60-80% other companies like Ford seem to have higher charging across that range and they are 400V architecture. So that is what led me to think Rivian may be conservative as they collect data. The new BMW iX seems to have a high rate of charge up until 95%.

 

[SeaGeo]

Many thanks, this is all really helpful information.
For the area under the curve from 60-80% other companies like Ford seem to have higher charging across that range and they are 400V architecture. So that is what led me to think Rivian may be conservative as they collect data. The new BMW iX seems to have a high rate of charge up until 95%.

Overall they're very similar. Where Rivian can probably improve is smoothing the curve out. They basically make bigger drops than I'd like starting at 70% and then end up following a very similar backbone curve. That being said, I'll take that any day over Ford's curve. I plotted them up for you for comparison. The 500A and 450A curves are Kyle's two test curves he published. You'll likely notice, the slope of the curve is similar.

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