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It is absolutely constant-current (or current limiting as you say) for the majority of the charge profile. I don't want to go into the weeds into explaining it, you can do your own research and figure out why it's that case.
That's not how it works. See the charge curves below.
The cell can't handle higher than 4.2V voltage. If one charges it at higher voltage first it just ages faster, and if the voltage is too high, it goes on fire. So ultimately a battery charging is voltage limited. The current follows the voltage and the SoC (State of Charge). When the battery is empty the current is very high, when the battery is full the current is very little.
It is however common practice to protect the battery or the circuitry from high current in the initial phase so it is limited at a lower value. Hence the constant current.
Look at the voltage (blue curve). When starting the charging the voltage is raised up to the point where the charge current (green curve) reaches the predefined maximum current. This is what I call current limiting. As the battery gains charge the voltage needs to be raised slowly to keep the current at the predefined maximum value, see the rising blue curve. But once the voltage reaches 4.2V the system switches from constant current to constant voltage. The voltage has reached its maximum value and can't be raised further. The currents keeps dropping as the SoC increases.
Now what the V3 supercharger does is that it immediately raises the voltage to maximum and it remains there for the whole charging time. This is why I say most of the charging is voltage limited. The charge current starts at a very high value and keeps dropping slowly. There is no constant current past 20%. When you see the charge curve in kW dropping, that means the current is dropping.
As the battery gains charge the voltage needs to be raised slowly to keep the current at the predefined maximum value, see the rising blue curve. But once the voltage reaches 4.2V the system switches from constant current to constant voltage. The voltage has reached its maximum value and can't be raised further. The currents keeps dropping as the SoC increases.
Yes, this is the most simplistic and naive charging mechanism as I mentioned before. The bare fundamentals. It's enough for most consumer electronics and has been employed for a couple decades. When long term pack longevity is not a major concern this may be all that's needed.
Originally Posted by acoste
Now what the V3 supercharger does is that it immediately raises the voltage to maximum and it remains there for the whole charging time. This is why I say most of the charging is voltage limited. The charge current starts at a very high value and keeps dropping slowly. There is no constant current past 20%. When you see the charge curve in kW dropping, that means the current is dropping.
Nope, that's not how it works when supercharging. And the voltage does not rise that fast in terms of portion of total charge time - no matter how many amps you dump in it. And the charge current is not dropping because of the simplest method of keeping voltage constant until the end of the charge. There are other variables that effect the charge curve such as internal resistance of the cells and heat buildup, pack temp, etc. It is only switched to C-V near the end.
Yes, this is the most simplistic and naive charging mechanism as I mentioned before. The bare fundamentals. It's enough for most consumer electronics and has been employed for a couple decades.
Nope, that's not how it works when supercharging. And the voltage does not rise that fast. And the charge current is not dropping because of the simplest method of keeping voltage constant until the end of the charge. There are other variables that effect the charge curve such as internal resistance of the cells and heat buildup, etc.
What you see up there is actually the Tesla battery cell. So please, if you are so clever, explain me how you keep the current constant beyond the point where the charger has reached the maximum voltage??? You can't raise the voltage any more!!!
Also power = current x voltage. P=U*I
Look at the second half of the curve. The voltage is constant, the current is dropping. Ergo the power is dropping. Now go back to the Supercharger's charge curve. From ~18% the power is dropping. With your false logic the power shouldn't drop there.
Or imagine your false assumption that the current is constant, the power is dropping. Due to P=U*I equation the only way this would be possible if the voltage is dropping. Yet in my life I have never seen a battery charging where the voltage is dropping and it is the lowest when the battery is fully charged!!!!
I've said this before and I'll say it again - to date Tesla is the _ONLY_ EV that routinely charges at 120,000 watts (or soon more) and does it reliability and often in a pretty extensive charging network - from a practical point of view it's the only charging network that actually works that has cars that match the network capabilities - and Tesla is investing aggressively at keeping it "fresh" and functional and growing…pretty much every other EV doesn't charge at high rates, or is shipping in such limited quantities that it basically doesn't matter.
Kudo's to Tesla for not standing still and coming up with V3 supercharging, and having actual products in the market place (the Model 3) that can actually use the ability - I look forward to using V3 supercharging for my long distance travel needs, and from a practical point of view I will do so much sooner than Porsche will even actually ship a single customer Taycan or an Audi E-Tron or Electrify America will have a reliable or functional network.
Porsche system may be better on paper, but so far Tesla is the only one I see with anything actually in the market place and the credibility that will actually work - supercharging is one area in which Tesla's execution has been pretty good…
go back to Jack Rickard's video when he charged the Tesla cell,
Here is the link to my post above, 2nd video: "Testing Tesla Model 3 2170 Cells - Battery Nerd **** with Full Frontal Nudity" https://rennlist.com/forums/showpost...&postcount=634
He starts charging at 1:15:00
Start voltage 3.8V, current is set to constant 10A (little over 2C)
after start the voltage increases slowly and the current remains at 10A
then at 1:33:00 the voltage reaches 4.2V; at this point he switches to constant voltage
he keeps the voltage near 4.2V and the current keeps dropping
at 1:39:00 the voltage is at 4.2V and the current is at 5A.
at 1:44:00 the voltage is at 4.2V and the current is at 2.6A
I've said this before and I'll say it again - to date Tesla is the _ONLY_ EV that routinely charges at 120,000 watts (or soon more) and does it reliability and often in a pretty extensive charging network - from a practical point of view it's the only charging network that actually works that has cars that match the network capabilities - and Tesla is investing aggressively at keeping it "fresh" and functional and growing…pretty much every other EV doesn't charge at high rates, or is shipping in such limited quantities that it basically doesn't matter.
Kudo's to Tesla for not standing still and coming up with V3 supercharging, and having actual products in the market place (the Model 3) that can actually use the ability - I look forward to using V3 supercharging for my long distance travel needs, and from a practical point of view I will do so much sooner than Porsche will even actually ship a single customer Taycan or an Audi E-Tron or Electrify America will have a reliable or functional network.
Porsche system may be better on paper, but so far Tesla is the only one I see with anything actually in the market place and the credibility that will actually work - supercharging is one area in which Tesla's execution has been pretty good…
Prior the V3 charging Tesla Model 3 charged max at 120kW. Having a 80kWh battery, this means 120/80 = 1.5C charge rate.
BMW i3 22kW charging at 45kW: 45/22 = 2C
Hyundai IONIQ Electric (28 kWh usable) 65kW charging 65/(~32) =2C
Both these cars are charging at a higher C rate than the v2 superchargers. If these cars were using 80kWh batteries like Model 3 LR, this would mean 160kW charging speed..
said something about a car that can't be road tripped using a non-existing fast charging network and claiming it was more functional than the actual product that is shipping and using a fast charging network that has been proven effective at fast charging 100,000's of EV's driving long distance
I yawn'ed and did not care. Once again Acosta missing the point caused ya'know he hates Tesla and can't believe they are still in business.
He starts charging at 1:15:00
Start voltage 3.8V, current is set to constant 10A (little over 2C)
after start the voltage increases slowly and the current remains at 10A
then at 1:33:00 the voltage reaches 4.2V; at this point he switches to constant voltage
he keeps the voltage near 4.2V and the current keeps dropping
at 1:39:00 the voltage is at 4.2V and the current is at 5A.
at 1:44:00 the voltage is at 4.2V and the current is at 2.6A
I don't really have time for this back and forth and it's obvious you are still learning very basic Lithium battery fundamentals so this will be my last reply on this topic. What you're doing is applying the basic Lipo charging method and shoehorning it to what you think the Superchargers are doing (such as assuming the current is dropping because the maximum voltage has been reached - this has long not been the case for a long time with more sophisticated charging algorithms that need to take many other variables into account as I mentioned). Just quickly to your points - I never suggested you will charge past 4.2 volts. When the cell is at 4.2 volt you switch to constant voltage. What I'm saying is the voltage does not rise immediately to 4.2v within the first 10-20% of the charge (and thus quickly being at CV as you think) and additionally when the current starts tapering in supercharging it does not necessarily mean the cells has now reached 4.2 volts as you think it does.
As for your video, if he starts at 3.8 volt then depending on the chemistry the battery is roughly 65% capacity so he will reach target voltage and thus CV quicker than from low SOC. In reality, using this same simple charging method CC is the majority of the charge time from an empty cell. And his charge method is not even close to what the actual Superchargers are doing. He just wants to simply demonstrate the cells can take 2C charge and record some temperature. It has very little to do with what a real battery engineer employed at Tesla or other EV manufacturer would be doing in evaluating optimal and max charge rates and the charge profile in the real world with temp, internal resistance, future degradation, etc into account.
Lastly, you're attempting to get into the technical weeds in some attempt to show other manufacturers are more competent than Tesla (which - as a fan of EVs from any company - is simply not true) when customers in the end only really care about these three things:
1). How many miles of range do I get per X minute of charge. This takes both vehicle efficiency AND charge rate into account.
2). How easy is it to navigate, do road trips and access the fast chargers. What is the availability of location of those fast chargers.
3). How long is my battery going to last when I take advantage of those fast chargers.
When the cell is at 4.2 volt you switch to constant voltage. What I'm saying is the voltage does not rise immediately to 4.2v within the first 10-20% of the charge (and thus quickly being at CV as you think) and additionally when the current starts tapering in supercharging it does not necessarily mean the cells has now reached 4.2 volts as you think it does.
On the V3 supercharger the charge voltage reaches 4.2V at around 12%. I was exaggerating when I said immediately. From there on it is contant-voltage mode.
Originally Posted by doshc
As for your video, if he starts at 3.8 volt then depending on the chemistry the battery is roughly 65% capacity so he will reach target voltage and thus CV quicker than from low SOC.
You are mixing charging voltage with battery voltage under load.
Originally Posted by doshc
In reality, using this same simple charging method CC is the majority of the charge time from an empty cell. And his charge method is not even close to what the actual Superchargers are doing.
In regular slow charging the current is limited at a low value, so it is charging in CC method for 80% of the time.
This doesn't apply for the supercharger which wants to maximize the current instead of limiting it.
So, Tesla is doing tricks again!!! Based on the power curve the charger spends 42 seconds at maximum speed in total.
As for the power curve I guess they are showing total power delivered from the charger but this is not equal to the total usable energy delivered to the battery. See "effective charge speed" below. They keep using tricks like this, which made me turn away from Tesla.
Discrepancy between power curve vs Soc and SoC vs time. The latter doesn't show any sign of super fast initial charge.
I calculate the power curve first.
Tesla Model 3 battery capacity: 72kWh usable, 80kWh in total.
V3 charging, power vs SoC curve:
from 8% SoC to 12% SoC, avg charging power ~200kW, 4%*72kW/200kW*60*60 = 52 seconds correct: 60 seconds
from 12% SoC to 16% SoC, avg charging power 250kW, 4%*72kW/250kW*60*60 = 41.5 seconds
from 16% SoC to 50% SoC, avg charging power ~200kW, 34%*72kW/200kW*60 = 7.3 minutes correct: 7.7 minutes.... look how different is that from the 2nd graph. I have to add 20% inefficiency to reach the 2nd curve. This confirms that Tesla reports charger speed, and not effective charge speed.
EDIT: I made a mistake earlier here. And found the trick. This last line can't be calculated like this because the x axis is SoC, not time.
but the 2nd line is correct. The charger spends 42 seconds at the maximum speed. (adding the 20% inefficiency will put it to around 1 minute)
These are effective charge speeds so the charger may run at 20% higher, for the 154kW section at around 154*1.2 = ~185kW on average from 25%-50% SoC.
This is equivalent of 663mph charging speed (based on 310mi range on 72kW, 154kW charging speed)
"A Tesla engineer executive indicated that the time to charge the car from 20% to 60% battery at a V3 supercharger would be about 15 minutes."
This ^^ guy is more honest than Tesla, 20%-60% = 40% of 72kW = 28.8kWh. 29kWh in 15 min = 116kW effective speed . Given the losses when charging and discharging, the charger needs to deliver ~140kW power to achieve that assuming 80% efficiency.
Using these more realistic numbers the charger is in CC mode until 50% of SoC.
Something isn't true. Either the power vs SoC graph or the SoC vs time. This latter can easily be verified later.
One more example, BMW i3
BMW i3 22kWh model, battery capacity: 19kWh usable, 22kWh in total.
BMW i3 charging, power vs time curve:
0-20min, avg charging power 39kW, 0.333h*39kW = 13kWh
20-30min, avg charging power 24kW, 0.17h*24kW = 4kWh
This is in total 17kWh.
The SoC shows 84% that means 16kWh.
The charger used (car reported) 17kWh to add 16kWh usable capacity, that would mean 94% roundtrip efficiency (car reports 100% speed, real speed is 94% of it). This is very good!, BMW is pretty honest about charging speeds.
I'm not gonna weigh in, beyond commenting that much of the faster charge claim is coming from a battery Elon assumes is colder, to begin with. Still, with the SCs around much of the US, it has never been easier to put miles in a (30-40%) more efficient EV, and be on your way. For many of us, this thing is the price of a beater.
I'm not gonna weigh in, beyond commenting that much of the faster charge claim is coming from a battery Elon assumes is colder, to begin with. Still, with the SCs around much of the US, it has never been easier to put miles in a (30-40%) more efficient EV, and be on your way. For many of us, this thing is the price of a beater.
Acoste is trying to dig up conspiracy theories with his very limited grasp of battery engineering and it's quite hilarious (and even a bit sad given he has so much idle time to do this). Tesla never said the battery was going have 250kw charge for the entire charge with 100% efficiency - something he believes Tesla is 'tricking' users with. Tesla's marketing:
"A new 1MW power cabinet with a similar design to our utility-scale products supports peak rates of up to 250kW per car. At this rate, a Model 3 Long Range operating at peak efficiency can recover up to 75 miles of charge in 5 minutes and charge at rates of up to 1,000 miles per hour. Combined with other improvements we’re announcing today, V3 Supercharging will ultimately cut the amount of time customers spend charging by an average of 50%, as modeled on our fleet data."
He didn't include the Tesla customer who tried a V3 supercharger and made those graphs quotes about his experience:
"Here is my supercharger v2 vs v3 chart. 15-80% within 24 min feels unreal." That is indeed about a 50% reduction and is what ultimately matters to the customer. Even faster charge speeds via new hardware and effortlessly deployed over-the-air fleet updates to existing cars.
03-07-2019, 07:26 PM
