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Again, I do not get the point. It sounds like you are making a hyper technical esoteric argument. How many people know exactly all the nuances of an ICE? I can tell you my Tesla has "instant" torque and very smooth linear power. We have All seen the videos of the Tesla S Plaid. Why does it accelerate so quickly? Why does Tesla say it has over "1000 hp? Is that a myth? What is the hp? I do understand that power in an EV can drop off at something less than full charge. That also tells me battery size matters. That is why for the ERay I would like to see a 10 kWh + battery size vs those who are not in favor of any electrification of the Corvette want something less than 2 kWh. So my real technical question would be, what would be the added benefits of using a 10 kWh battery vs a 2 kWh battery in the ERay? I know the downside - weight (costs is de minimis). Wouldn't the larger battery be able to allow the electric motor to produce more hp? And for a longer time?
Without knowing the specs of the battery it is hard to know. Batteries have different discharge rate ratings. It might be 20C or 50C or 100C. At 50C a 2kWh battery would theoretically discharge at a rate of 100 kW for a brief period of time. that is about 134 HP. When it is at half capacity it would support about 67HP. It would not take long to drain the battery at all, probably less than 2 minutes, and it would be VERY hard on the battery. So if you were trying to support 100 HP with a 2 kWh battery it would be do that until about 75% of capacity. So somewhere less than a minute. 10 kWh would give you 5 times that. and or support 5 times the HP. Keep in mind that is at 100 HP constant and no conversion losses. The reality is on a road course, you would be using regenerative braking that would boost the battery back up for part of that. On a drag strip it would be plenty if you could recharge between rounds.
The theoretical calculations are relatively easy. In real life there are lots of factors that affect the outcome. Heat hurts and helps the batteries, there are practical current limitations. Rapid charge and discharge of batteries shortens battery longevity.
Other than the aural aspects, the problem with EVs are not the electric motors. it is supplying the motors with current and voltage. It is the storage of the energy that is the problem. The current batteries have lots of limitations as storage and delivery as compared to the energy storage that is gasoline. Gasoline is way more energy dense and has few flow limitations. Batteries of the same capacity are huge and heavy. A car would not need the same energy capacity because electric motors are at least 2-3 times as efficient in energy conversion as gas. Even with that advantage batteries still suck, right now.
The bold is the point. In the real world as installed and controlled the results are not the same. Excuse me if I am doubtful of the dynos charts from Tesla. It kind of reminds me of the 60's when the manufacturers use gross horsepower, bare engine on the dyno with dyno exhaust, but when you measured them as installed in a car with accessories and as installed exhaust and intake, the real numbers were very different.
Your point on the dyno problem is fair. I don't know what type of dynos they are running, The point of power being limited by state of charge of the batteries is real. The torque and power being limited by the controller is real.
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When using a variable frequency drive, the motor has an infinite number of torque curves. Each of the lines in this graph represent a different drive inverter excitation frequency, with motor rpm on the x-axis. By increasing the drive frequency as the motor RPM increases, we can make the torque curve flat. (the overall torque curve rides on top of all of the dashed lines). As you may notice, at 0 RPM, by picking the correct excitation frequency, I can generate max torque at 0 rpm. Other tricks can be played to get (110%, 120%) of rated torque at 0 rpm. For all intents and purposes, these systems deliver massive torque at 0 rpm on up.
You and I are in pretty strong agreement with respect to the battery being a part of the power system, and not just a gas tank. The battery provides the push to get current into the motor; the inverter just tailors the current profile for best response, torque and power. Both battery and inverter strongly impact the torque production ability of the motor. I would comment more but am running short on time.
Without knowing the specs of the battery it is hard to know. Batteries have different discharge rate ratings. It might be 20C or 50C or 100C. At 50C a 2kWh battery would theoretically discharge at a rate of 100 kW for a brief period of time. that is about 134 HP. When it is at half capacity it would support about 67HP. It would not take long to drain the battery at all, probably less than 2 minutes, and it would be VERY hard on the battery. So if you were trying to support 100 HP with a 2 kWh battery it would be do that until about 75% of capacity. So somewhere less than a minute. 10 kWh would give you 5 times that. and or support 5 times the HP. Keep in mind that is at 100 HP constant and no conversion losses. The reality is on a road course, you would be using regenerative braking that would boost the battery back up for part of that. On a drag strip it would be plenty if you could recharge between rounds.
The theoretical calculations are relatively easy. In real life there are lots of factors that affect the outcome. Heat hurts and helps the batteries, there are practical current limitations. Rapid charge and discharge of batteries shortens battery longevity.
Other than the aural aspects, the problem with EVs are not the electric motors. it is supplying the motors with current and voltage. It is the storage of the energy that is the problem. The current batteries have lots of limitations as storage and delivery as compared to the energy storage that is gasoline. Gasoline is way more energy dense and has few flow limitations. Batteries of the same capacity are huge and heavy. A car would not need the same energy capacity because electric motors are at least 2-3 times as efficient in energy conversion as gas. Even with that advantage batteries still suck, right now.
Thanks for the math. In my layperson conclusion it confirms my prior belief that an Eray with a @2kWh battery would, borrowing your term "suck" and be a wasted engineering exercise. I believe the Ferrari SF90 has an @ 8 kWh battery. I would like to see the ERay at 10+ kWh.
When using a variable frequency drive, the motor has an infinite number of torque curves. Each of the lines in this graph represent a different drive inverter excitation frequency, with motor rpm on the x-axis. By increasing the drive frequency as the motor RPM increases, we can make the torque curve flat. (the overall torque curve rides on top of all of the dashed lines). As you may notice, at 0 RPM, by picking the correct excitation frequency, I can generate max torque at 0 rpm. Other tricks can be played to get (110%, 120%) of rated torque at 0 rpm. For all intents and purposes, these systems deliver massive torque at 0 rpm on up.
You and I are in pretty strong agreement with respect to the battery being a part of the power system, and not just a gas tank. The battery provides the push to get current into the motor; the inverter just tailors the current profile for best response, torque and power. Both battery and inverter strongly impact the torque production ability of the motor. I would comment more but am running short on time.
I saw that exact graph as I was doing research on the topic.
Your comments are always welcome and informative. It has been a long time since I studied how these things work, mostly in a non-automotive world. The controller systems have certainly gotten more sophisticated since then. These are not your old slot car controllers and transformers. And there are more and more motor configurations (I played with DC brushed and brushless motors). Dealing with relatively low voltage and power is different than what they are putting in cars today.
At 50C a 2kWh battery would theoretically discharge at a rate of 100 kW for a brief period of time. that is about 134 HP. When it is at half capacity it would support about 67HP. It would not take long to drain the battery at all, probably less than 2 minutes, and it would be VERY hard on the battery. So if you were trying to support 100 HP with a 2 kWh battery it would be do that until about 75% of capacity. So somewhere less than a minute. 10 kWh would give you 5 times that. and or support 5 times the HP. Keep in mind that is at 100 HP constant and no conversion losses. The reality is on a road course, you would be using regenerative braking that would boost the battery back up for part of that. On a drag strip it would be plenty if you could recharge between rounds.
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Really, the bolded hits the nail on the head and sums up why a 2KWh battery would be undesirable for a performance application, although it would theoretically work for driving around town slowly at low load.
Folks will argue that regen will recharge the battery. On a road course like the Ring, regen won't be adequate. Regen can only recover kinetic energy, which is a reversible loss. On a road course, irreversible losses greatly increase in magnitude, and a good deal of the motor's power is expended irreversibly, mainly in the form of overcoming aero and rolling parasitic losses, but also copper and iron losses. These irreversible losses will stack up quickly. I was happy to see what I think is the Eray at the Ring, since I suspect they're looking for performance over a 7+ minute timeframe.
Really, the bolded hits the nail on the head and sums up why a 2KWh battery would be undesirable for a performance application, although it would theoretically work for driving around town slowly at low load.
Folks will argue that regen will recharge the battery. On a road course like the Ring, regen won't be adequate. Regen can only recover kinetic energy, which is a reversible loss. On a road course, irreversible losses greatly increase in magnitude, and a good deal of the motor's power is expended irreversibly, mainly in the form of overcoming aero and rolling parasitic losses, but also copper and iron losses. These irreversible losses will stack up quickly. I was happy to see what I think is the Eray at the Ring, since I suspect they're looking for performance over a 7+ minute timeframe.
So what would be a good minimum/adequate size battery? And I know that depends on what the use is for, but as an example projected street use? And for the Ring?
well.. the only thing I can see is that the E-ray smoked the Z06 at the track and they dont want to release it. Allocations now out and still not lap time. All of us here can feel at easy picking the best option c-8. The sad part is they forced and forced the z06 to come out first and its been nothing but wtf's..lol
All they had to do was hire me.. I could have hit other places to do mfg contract work for parts.
btw: Everyone go to the Reg C8 area and see my post of the new Dodge... GM now has comp.. Im not a normal fan but this looks pretty goo.
So what would be a good minimum/adequate size battery? And I know that depends on what the use is for, but as an example projected street use? And for the Ring?
A question that I've asked myself and I'm sure the Eray team has asked themselves, is should the Eray be capable of completing a 20-minute HPDE session? Or should it be targeted more for the street; the battery sizing can vary all over the map since this represents such a wide difference of performance requirements on the battery. The SF90 demonstrated a hero lap at Indy but that was only a minute and a half - and hero laps don't mean much to me unless I can have some fun on the road course for more than 1 lap.
I think for the street, 8-12 Kwh is fine. You could theoretically get away with much less on the street. My issue with very small batteries on the street is that IR losses go up and temps go up, and you'll go through much deeper discharge cycles, and even if regen eventually brings it back up, you've shortened the battery life. For a 7-minute Ring lap, and assuming the worst for regen, a 8-10KWh battery gets there with a decent-sized discharge and 50% throttle duty cycle @ 120hp. Larger batteries also spread the heat generation out over a larger area for a given discharge rate and have more cooling capacity. Increase the motor power and everything changes- For an HPDE session, you probably need a good bit more, but could compromise with less and let battery performance drop off ....., and this may be outside GM's targets for the car........but they're good at compromising, so anything's possible.
My general 10,000-ft view is that once you've made the leap to adding small batteries and motors to an ICE platform or in general, you shouldn't then try to save weight by going backwards and trimming battery capacity or motor performance; IMO you should go in the opposite direction, and ensure you have enough motor and enough battery, and if you don't, go ahead and pay another small weight penalty to get it.
I think battery size will be limited to what fits in the tunnel, along with the control module and cooling. At some point, someone had measured the tunnel and posted it. Maybe someone can find it. Keep in mind there is already stuff in there. With the volume, battery capacity can be estimated from known information. I think the tunnel bottom plate will become an integral part of the battery cooling system.
I think battery size will be limited to what fits in the tunnel, along with the control module and cooling. At some point, someone had measured the tunnel and posted it. Maybe someone can find it. Keep in mind there is already stuff in there. With the volume, battery capacity can be estimated from known information. I think the tunnel bottom plate will become an integral part of the battery cooling system.
I agree that should be the primary limiting factor. And if I recall, based on the size of the Ultium batteries, someone did the math and they should be able to get at least 10 kWh in there.
The problem I'm having is that they can't build a small-capacity 10KWh battery from the already-announced Ultium cell, and get 400V. These cells each have a physical dimension of 23x4x0.4 inches, and each cell is 3.7V, and 0.37KWh.
When they connect these Ultium cells in series, they need 108 (3.7V) cells in series, to get 400V. However this yields 40KWh of capacity. Each cell has about 0.37KWh. Could do this, but then weight and cost go up.
If they were to build a 10KWh pack from these cells, they'd need 27 cells in series, but this would only yield 100V which reduces motor power.
Which leads me to believe that there's another unannounced cell physical dimension option for small battery packs.
It is frustrating to wait for the performance figures to see the light of day. The Z06 has an embargo set for October, and since the E-Ray will not yield any serious stats until around 2Q next year, the comparison of the two is a long way off, plenty of time for the Z owners to see delivery while the rest of us contemplate our navels. Now I know the mantra is the Z is a track car and the E-Ray a street racer, but that 0-60 time and quarter mile will be of great interest to compare when the time finally comes.
https://www.autoblog.com/2022/08/20/...ic-car-motors/ "Yasa, an Oxford, England-based manufacturer of motors used in Ferrari’s SF90and 296 GTB plug-in hybrids, uses just a few kilograms of iron for its stators, reducing the mass of the machines by as much as 85%". "Mercedes announced it had acquired Yasa for an undisclosed sum and would put its motors in AMG models slated to launch starting in 2025"
These are the GM motors that have been announced
180 kW front-drive permanent magnet motor
255 kW rear- and front-drive permanent magnet motor
62 kW all-wheel drive assist induction motor
fascinating
You suppose GM will introduce an axial flux motor on the hybrid Corvette? They are testing the SF90..
How much HP can 2--62kW motors produce (noted by Kodiak) w/ a 10-12kwh battery? According to some calculations (https://www.google.com/search?client...hp+conversion;https://www.rapidtables.com/convert/power/kw-to-hp.html), 62kW should yield 83.1434hp; doubled would yield 166.278. Adding 166 to 495 (assuming no tuning to the base Stingray LT-2), yields 661hp; but this does not take into account power to the wheels only at the motor shaft. Now as has been noted above, the available battery current will determine the actual kW/hp value, and since GM may try to avoid overshadowing the LT-6, we may see de-tuning of the LT-2 (hp/torque curves to synergize w/ the motors) or limited power to the front motors for a lesser number as has been stated in above posts. Speculation abounds...
The point is electric car fan”s ideas about how electrics motors work in the real world are wrong. Tesla don’t make full torque at zero RPM or even 1 RPM. It is clearly shown in a Tesla dyno. Because they are generally direct drive (Tesla is) with no clutch they don’t function in the same way as a gas car.
Also the motors alone don’t determine the HP electric cars make. The batteries and controller does too. Why do you think Teslas make less HP at half capacity. Whereas a gas car will make the same power with half a tank of fuel.
Oh and motor torque alone does not determine acceleration. Otherwise diesel trucks would out accelerate Corvettes, and they don’t.
It is very clear many posters don’t understand basic physics, and believe many myths.
line the new Zo6 up next to a plaid. There is your answer.
We know what that will yield; with a Plaid putting out 1020hp awd, a drag race from a stop will give the EV such a large lead as to make a 1/4 mile race an foregone conclusion, now at 1/2 mile or above where the Plaid tops out at 200mph, we may see a Z06 reach its sweet spot and make some serious gains but it can only max out at 188mph. Factoring in a long track, the Plaid in track mode would see heat limits to hp output and some severe strain on the brakes to cope with its 4766-4940lb. curb weight (depending on your source). A good head to head will not favor the Z in a quarter mile, while a 1 mile drag will be more even, and a race circuit like VIR could be more favorable to the 'Vette.
https://www.caranddriver.com/news/a3...vir-lap-time/; here the Tesla used aftermarket brakes vs. the base set up of the Porsche Taycan Turbo S (750hp awd at 5199lbs.). One could argue that Tesla is capitalizing on "hero laps" by modifying its cars, and so a more even comparison with a production Plaid may produce a much different result. The Z is at least 1000lbs. lighter than the Plaid, but that FPC has to be kept in a high rev. band to keep its advantage.
https://www.autoblog.com/2022/08/20/...ic-car-motors/ "Yasa, an Oxford, England-based manufacturer of motors used in Ferrari’s SF90and 296 GTB plug-in hybrids, uses just a few kilograms of iron for its stators, reducing the mass of the machines by as much as 85%". "Mercedes announced it had acquired Yasa for an undisclosed sum and would put its motors in AMG models slated to launch starting in 2025"
These are the GM motors that have been announced
180 kW front-drive permanent magnet motor
255 kW rear- and front-drive permanent magnet motor
62 kW all-wheel drive assist induction motor
fascinating
You suppose GM will introduce an axial flux motor on the hybrid Corvette? They are testing the SF90..
The new Lyriq will have an AWD version next year that GM says will produce 160 hp more vs the RWD. So where is that motor? I would not consider those leaked motor numbers as the only ones available.
line the new Zo6 up next to a plaid. There is your answer.
Plaid over 1000 HP and AWD. Put the Plaid against a 1000+HP Nissan GTR or Porsche 911 Turbo (AWD) and it is a different discussion. And if you were driving a Plaid you would be driving an ugly car, and the other guy would not.
08-18-2022, 12:00 PM
