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I shared my review with some people that I know associated with Tesla - they are disappointed in my review - but do not dispute my findings.
they have also shared the following
1. Randy Pobst only gets 1 or 2 laps to set his times - 3 at most - there is no "duration" characteristic to any of their reviews
2. they claim most street cars will degrade in a similar if not more spectacular fashion to my experience with the Model 3
3. they called out the Alfa Romeo Quadrifoglio - as having worse degradation than the Model 3 - their test drive only go one lap before the brakes "gave up 100%" at Laguna
they are apparently aware of my critique, and nothing here is news to them - I've instructed some of them in past events and they are aware of my bonafides as an advance track amateur…but yeah the Model 3 is no track car.
brakes shouldnt "give up" with the right pads and driver, to run a 1:46 ... ive run that without even using brakes!
here is the apex pro lap times for the 3rd session - 4 laps (50% - 21% battery w/overheated brakes)
Interesting report. keep in mind, you have proved you can rally a GT3, and a cup car to a decent lap time. (only around 4 seconds off the pro times) Since you are on street tires, that's a huge variable. keep in mind, top pros ran World challenge GT in the 1:39 for the winning and top times. (vipers, C5 c06s, M3s, cup cars ) so, tires are a HUGE difference. second of all, there are the top mustangs in t2 or specifically , spec mustang are 3500lbs and they run in this range too. simple, normal stoptech or brembo brakes with 14" rotors and probably PFC11s. Brakes are not taxed and there are not fade issues. times are also in the 1:39 to 1:40 for top drivers. so, the car has the power, a little more weight and can reach those times with the right tires . Pads, should be at least a performance pad. so, i disagree with the fact that your car fails as a track car because it lasts 5 laps. you have something totally unique. an electric car that is on the track. you are part of the trail blazers. its fine. 5 laps and I'm usually good in a qualifying. (5-8 laps and im good, but ive been doing this for 20 years) but you get to go out 4-5 times and that gives your TOTAL laps well over what i usually see in a weekend , and that goes for track nuts that are racers too. )
so, work through the issues , cooling , get the right pads. learn how to manage heat in the pads by changing braking style, and get some dual purpose street/race tires and have fun. the car is going to be easy to grow into without the variables of gear changes. (an traditional automatic has the drawbacks, which the electric doesnt have so that is an advantage.) HP is not equal on a gas car , vs the electric because you ACTUALLY need a second gear to be on par with power ( 400hp vs 400hp gas) because the EV loses HP at a higher rate over 80mph.... in other words, what you are equal to out of the corners, you lose a LOT after 75-80mph, which is a good portion of the track.
anyway, enjoyed the report. i have a real interest in electric cars and a lot of experience in the motor/battery field. have fun and keep the stories coming!
edit: reviewed your video--- Try more trail braking and start out wider for turn 2, turn 7 and especially into the corkscrew. you are overslowing for many of the turns and not letting the turns slow you down (putting it simply , putting more burden on the tires that the brakes.
HP is not equal on a gas car , vs the electric because you ACTUALLY need a second gear to be on par with power ( 400hp vs 400hp gas) because the EV loses HP at a higher rate over 80mph.... in other words, what you are equal to out of the corners, you lose a LOT after 75-80mph, which is a good portion of the track.
Because a EV has a broad HP curve, doesnt preclude it from needing a gear box to keep the accelerative forces optimized. if you look at the EV HP curve you see it fall dramatically off as it approaches about 50% of its max RPM capabilities. (this is due to electrical time constants that keep current from rising to full potential and eddy current losses which eat away at the HP at higher RPM)
so, if the tesla could have a 2nd gear , like models many years ago, it could be shifted into a taller gear and take advantage of its HP potential.
From the graph, you can see the rear wheel torque values over a wide speed range for a 5 speed gas engine and a tesla of a similar HP ( notice that at about 70 mph, how the gas engine is still able to keep in its power range, while the tesla is falling off, and getting worse as speed increases. since, on the race course you spend most of the time accelerating at above 70mph , it is a major factor in its ability to produce better lap times for its HP . This is because HP is a vehicle's capacity to accelerate at any vehicle speed. maximize hp, and you maximize forces at the rear wheels at any speed .
from the below graph, you can see at 100mph, the tesla has about 100less HP , even if the started out at the same max hp.
if you look at the gold and the orange HP curves for the tesla and the Challenger, you see the tesla has a big advantage from 0 to 55mph, where the challenge has the same advantage from 55 to its top speed. had the tesla had a 2 speed gear box, it would have the ability to keep the same HP levels as the challenger to top speed. You can also clearly see the small gains of the tesla in the lowest speed you ever see on a race track, of around 45 to 50mph on the slowest turns. However this is a huge advantage in drag racing as seen by the heavy tesla's 0-60mph times but we are talking road racing here.
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Last edited by mark kibort; 11-20-2018 at 03:48 AM.
It's all a function of vehicle weight and drag, since the EV motor and its controller efficiency is negligible compared to those losses. Yes, the power losses of the battery (I^2 x R)
are a factor, but most all LI batteries will have similar internal resistances. The Porsche EV will benefit from using a 800 volt system, which will help reduce the (I^2 x R) losses
of the battery and reduce charging times.
please explain. keep in mind, with the higher voltages, comes higher switching losses. how does the 800 volt system reduce the power losses? power loss are due to (I^2R), so high current through lower resistance can equal low current through higher resistance . or, are they increasing the capacity, so that they can have faster charging ... (i.e. more batteries in parallel, eg: xC charge rates)
brakes shouldnt "give up" with the right pads and driver, to run a 1:46 ... ive run that without even using brakes!
Cameron's 1:46 lap was most likely on racing pads, fluids, and hoosiers - and he disabled the nannies by disconnecting the wheel speed sensors - I'm guessing all this because that's what he did to run his 1:48.xx lap at Laguna - I've done a lot of internet sluthing and can't actually find the setup/config changes that were done the car for the 1:46.xx time, but there is a detailed break down for the 1:48.xx lap time…the car is pretty heavy - so the stock brakes fading at Laguna after a few laps isn't a surprising out come.
had a great time at Laguna Monday with PCA Diablo crew in my GT3!! Nice to be in a car that can run full out for the entire session! No brake fade on stock pads, upgraded fluid, gyro-disc street rotors…other than that stock!
super fun day at Laguna - had fun with both the Model 3 and the GT3 - both cars have 3 in their names - heh!!!
Because a EV has a broad HP curve, doesnt preclude it from needing a gear box to keep the accelerative forces optimized. if you look at the EV HP curve you see it fall dramatically off as it approaches about 50% of its max RPM capabilities. (this is due to electrical time constants that keep current from rising to full potential and eddy current losses which eat away at the HP at higher RPM)
so, if the tesla could have a 2nd gear , like models many years ago, it could be shifted into a taller gear and take advantage of its HP potential...
A few very early Roadsters did have a two-speed gearbox. However they had a hard time designing the gearbox so it wouldn't fail. Fortunately some improved IGBTs (power transistors) became available for the inverter such that they didn't need the second gear. So they designed a one-speed gearbox and it worked fine. The early Roadsters were retrofitted with the new gearbox and electronics, and the rest is history.
The dual motor Teslas essentially do have a second gear. The front motor is geared differently than the rear motor. With the S and X, both motors are induction motors. The software can 'torque sleep' one or the other to optimize performance, efficiency, etc. It is why the dual motor cars get better range than the single motor cars. With the Model 3, the rear motor is a variant of a reluctance motor with added permanent magnets for higher efficiency. The front motor remains an inductance motor. So the tradeoffs are different since presumably only the front motor can be put into torque sleep mode.
Because a EV has a broad HP curve, doesnt preclude it from needing a gear box to keep the accelerative forces optimized. if you look at the EV HP curve you see it fall dramatically off as it approaches about 50% of its max RPM capabilities. (this is due to electrical time constants that keep current from rising to full potential and eddy current losses which eat away at the HP at higher RPM)
so, if the tesla could have a 2nd gear , like models many years ago, it could be shifted into a taller gear and take advantage of its HP potential.
From the graph, you can see the rear wheel torque values over a wide speed range for a 5 speed gas engine and a tesla of a similar HP ( notice that at about 70 mph, how the gas engine is still able to keep in its power range, while the tesla is falling off, and getting worse as speed increases. since, on the race course you spend most of the time accelerating at above 70mph , it is a major factor in its ability to produce better lap times for its HP . This is because HP is a vehicle's capacity to accelerate at any vehicle speed. maximize hp, and you maximize forces at the rear wheels at any speed .
from the below graph, you can see at 100mph, the tesla has about 100less HP , even if the started out at the same max hp.
if you look at the gold and the orange HP curves for the tesla and the Challenger, you see the tesla has a big advantage from 0 to 55mph, where the challenge has the same advantage from 55 to its top speed. had the tesla had a 2 speed gear box, it would have the ability to keep the same HP levels as the challenger to top speed. You can also clearly see the small gains of the tesla in the lowest speed you ever see on a race track, of around 45 to 50mph on the slowest turns. However this is a huge advantage in drag racing as seen by the heavy tesla's 0-60mph times but we are talking road racing here.
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Yes, most on this thread know all the BASICS of EV technology! So again, clarify your numbers numbers (400hp) below:
Originally Posted by mark kibortHP is not equal on a gas car , vs the electric because you ACTUALLY need a second gear to be on par with power ( 400hp vs 400hp gas) because the EV loses HP at a higher rate over 80mph.... in other words, what you are equal to out of the corners, you lose a LOT after 75-80mph, which is a good portion of the track.
please explain. keep in mind, with the higher voltages, comes higher switching losses. how does the 800 volt system reduce the power losses? power loss are due to (I^2R), so high current through lower resistance can equal low current through higher resistance . or, are they increasing the capacity, so that they can have faster charging ... (i.e. more batteries in parallel, eg: xC charge rates)
Using 800 volts as the system power reduces the battery current versus using 400 volts. Thus the I^2 x R losses of the battery are reduced. Yes, the series resistance of the battery resistance will increase,
but the net effect is less battery power dissipation. Furthermore, the switching devices in the controller will dissipate less power, i.e. lower on-voltage (Vsat) of the switching devices. Using higher voltage
results in less current for the same capacity in energy (kWhrs), thereby reducing the charging time for a given range.
Yes, most on this thread know all the BASICS of EV technology! So again, clarify your numbers numbers (400hp) below:
Originally Posted by mark kibortHP is not equal on a gas car , vs the electric because you ACTUALLY need a second gear to be on par with power ( 400hp vs 400hp gas) because the EV loses HP at a higher rate over 80mph.... in other words, what you are equal to out of the corners, you lose a LOT after 75-80mph, which is a good portion of the track.
Please avoid the hyperbole!
the "400HP vs 400HP" was only to show equal power levels of each style of powerplant which, in the balll park of most high performance EV's. in the diagram's comparison, its a 650hp (peaky hp curve) challenger with a 550hp Tersla, maybe it was done to match the HP in the 0-60mph range so the curves would stradle each other in the beginning. the point is, after 75mph, the gas will have advantages in HP , which make it much better suited for track use. however, if a second gear is used, that could be avoided as it would retain it's hp in the track speed range.
Using 800 volts as the system power reduces the battery current versus using 400 volts. Thus the I^2 x R losses of the battery are reduced. Yes, the series resistance of the battery resistance will increase,
but the net effect is less battery power dissipation. Furthermore, the switching devices in the controller will dissipate less power, i.e. lower on-voltage (Vsat) of the switching devices. Using higher voltage
results in less current for the same capacity in energy (kWhrs), thereby reducing the charging time for a given range.
Can you clarify some more? lowering current while keeping power the same, doesnt reduce I^2R losses because as you say, the resistance goes up by a factor of 4 ot keep power constant. motors work on amper/turns for power output. just raising the voltage doesnt change the power equation or conservation of energy so there is no real free lunch (or power)
As far as the batteries, if you put more in series to raise voltage, but keep capacity the same, the charging rate should be the same, as that is generally a function of capacity , correct ? but i understand if the current discharge rate , which would be lower at higher voltages, would be easier on the batteries, and could extend capacity for the same power output.
. However, the switching losses are higher with the higher voltages as well and current rise times can be enhanced being faster for PWM drivers.
edit: Im reading what you wrote again about the losses in the battery being less because the current goes down by half and the resistance only goes up double, so less power losses...... i was speaking to the motors........... is that the big advantage?
again:
Using higher voltage
results in less current for the same capacity in energy (kWhrs), thereby reducing the charging time for a given range
when you increase series voltage of batteries, the capacity stays the same as you say, but higher voltages are required just to keep the current rate the same (not less as you say) and that would result in the same charging time.. after all, the batteries are fuel tanks, rated in amp/hours. you have a 100amp/hour battery, and it will take 1 hour at 100amps. this is regardless of the voltage .correct?
Last edited by mark kibort; 11-20-2018 at 03:29 PM.
the "400HP vs 400HP" was only to show equal power levels of each style of powerplant which, in the balll park of most high performance EV's. in the diagram's comparison, its a 650hp (peaky hp curve) challenger with a 550hp Tersla, maybe it was done to match the HP in the 0-60mph range so the curves would stradle each other in the beginning. the point is, after 75mph, the gas will have advantages in HP , which make it much better suited for track use. however, if a second gear is used, that could be avoided as it would retain it's hp in the track speed range.
Thanks. The value of 400hp is about 300kW. For the M3's 400V system, that's about 750 amps from the battery. Assuming the battery resistance of about 100 milliohms (.100 ohms),
that's about 56kW of peak battery power dissipation. That battery current results in a battery voltage drop of 75 volts, so the power to motor is then reduced and not supplying 400hp.
The low range (~ 210 miles) M3 has about a 60-70 kWhr battery. You can calculate how many laps the M3 can do when one considers trying to maintain an average track HP of just 300hp,
notwithstanding getting even close 400hp. Obviously, the battery can get "cooked" by the power it delivers and the number of laps attempted.
Can you clarify some more? lowering current while keeping power the same, doesnt reduce I^2R losses because as you say, the resistance goes up by a factor of 4 ot keep power constant. motors work on amper/turns for power output. just raising the voltage doesnt change the power equation or conservation of energy so there is no real free lunch (or power)
The internal battery power (loss) is I x I x R (I^2 x R);
I(new) = I(old) / 2, R(new) = 2 x R(old)
Power(new) = ( I(old)/2) ^ 2) x 2 x R(old) = (I(old) / 4 ) x 2R(old) = I(old) x R(old) /2
So the new battery power loss is 1/2 the original loss.
Originally Posted by mark kibort
As far as the batteries, if you put more in series to raise voltage, but keep capacity the same, the charging rate should be the same, as that is generally a function of capacity , correct ? but i understand if the current discharge rate , which would be lower at higher voltages, would be easier on the batteries, and could extend capacity for the same power output.
When you double the voltage, you double the capacity, i.e. assuming the same Ahr capacity. But the goal/desire is to keep the kWhr (energy) capacity the same
while reducing Ahrs - less amps to charge for a given/same capacity/range.
Originally Posted by mark kibort
However, the switching losses are higher with the higher voltages as well and current rise times can be enhanced being faster for PWM drivers.
That's only the case for the same dv/dt and the origin peak current. But since the peak current is less (less power when switched "on")
and the switching devices will be smaller/faster and the area under their power dissipation curve will be less.
11-19-2018, 05:49 PM
HP is not equal on a gas car , vs the electric because you ACTUALLY need a second gear to be on par with power ( 400hp vs 400hp gas) because the EV loses HP at a higher rate over 80mph.... in other words, what you are equal to out of the corners, you lose a LOT after 75-80mph, which is a good portion of the track.
