EndlessPlaid
⚡EV/Tesla Nerd 🔋
Additionally, no one (especially Tesla) rate their cars at the wheel. They always take the bigger number for marketing.
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Model S Plaid Battery Details, sourced from EPA Docs, Vehicle Observations, & Supercharging/Charging data
- Thread starter AlanSubie4Life
- Start date
Hello, this is Keith Ritter. Just joined TMC and started following this thread.
George S Bower and I do a lot of reverse-engineering technical analysis on Tesla products, especially on the packs and drive trains and write our findings on InsideEVs. We've been trying to figure out the new MS pack/drive train and get it dialed in.
First, kudos to those that zeroed in on the pack S and P configuration. I'm about 99% sure you got it right at the 108S72P configuration. Getting it down to 72P was vital to building this new pack. I'll post something later on other aspects of the pack innards I think we'll find when Sandy Munro or others do an actual teardown. How the modules are likely built and the cooling details and why.
Second, regarding the apparent discrepancy between the pack kW output and the motor ratings at peak acceleration. The pack kW output is almost exactly what I'd expect for 1,020 HP motor load. Let's not forget that engineers who want to build light, cost-effective products do not design systems for peak efficiency at the extreme condition. They engineer for the system to survive and drive another day. Efficiency is for the "most-likely" condition...i.e. highway speeds. I believe Tesla's engineer also follow that mantra.
Let's walk through where power losses will occur between the pack itself and the motor shaft.
HV Busbars/HV connectors/HV cables from pack to DU: resistance is probably about 3 milli-ohms, based on the conductor sizes and connectors they use. 2300 amp, I x R = about 7 VDC or about 2% loss. Doesn't sound like much, but this a short burst of 15 kW of heat...like about 10 plug-in wall heaters.
Drive unit inverter: They have SiC, which is about as good as you get. these are typically about 99% efficient at "design" load. But this is way higher than design. Figure 98%. So another 2% loss.
Motor windings/rotor: Tesla did change from induction to PM rotor, which got them about 3% more efficiency and more consistent torque. The carbon sleeve doesn't buy any more efficiency. It just was imperative to hold the rotor together at the higher redline RPM. It wasn't clear if Tesla changed from round wire windings to square hairpin to improve fill, but I'd think it would be required to reduce winding losses at high amps. PM motors built that way can get 96-97% efficiency. Say 3.5% losses here.
Reduction gears: The last part of the drive unit before you get to the axle driveshaft HP. Double-reduction helical gearset. 98% efficient. 2% losses.
Adding up the losses: 2 + 2 + 3.5 + 2 = 9.5% losses. about 77 kW subtracted from the 818 kW leaving the pack. So the net is about 741 kW output or just under 1000 HP.
George S Bower and I do a lot of reverse-engineering technical analysis on Tesla products, especially on the packs and drive trains and write our findings on InsideEVs. We've been trying to figure out the new MS pack/drive train and get it dialed in.
First, kudos to those that zeroed in on the pack S and P configuration. I'm about 99% sure you got it right at the 108S72P configuration. Getting it down to 72P was vital to building this new pack. I'll post something later on other aspects of the pack innards I think we'll find when Sandy Munro or others do an actual teardown. How the modules are likely built and the cooling details and why.
Second, regarding the apparent discrepancy between the pack kW output and the motor ratings at peak acceleration. The pack kW output is almost exactly what I'd expect for 1,020 HP motor load. Let's not forget that engineers who want to build light, cost-effective products do not design systems for peak efficiency at the extreme condition. They engineer for the system to survive and drive another day. Efficiency is for the "most-likely" condition...i.e. highway speeds. I believe Tesla's engineer also follow that mantra.
Let's walk through where power losses will occur between the pack itself and the motor shaft.
HV Busbars/HV connectors/HV cables from pack to DU: resistance is probably about 3 milli-ohms, based on the conductor sizes and connectors they use. 2300 amp, I x R = about 7 VDC or about 2% loss. Doesn't sound like much, but this a short burst of 15 kW of heat...like about 10 plug-in wall heaters.
Drive unit inverter: They have SiC, which is about as good as you get. these are typically about 99% efficient at "design" load. But this is way higher than design. Figure 98%. So another 2% loss.
Motor windings/rotor: Tesla did change from induction to PM rotor, which got them about 3% more efficiency and more consistent torque. The carbon sleeve doesn't buy any more efficiency. It just was imperative to hold the rotor together at the higher redline RPM. It wasn't clear if Tesla changed from round wire windings to square hairpin to improve fill, but I'd think it would be required to reduce winding losses at high amps. PM motors built that way can get 96-97% efficiency. Say 3.5% losses here.
Reduction gears: The last part of the drive unit before you get to the axle driveshaft HP. Double-reduction helical gearset. 98% efficient. 2% losses.
Adding up the losses: 2 + 2 + 3.5 + 2 = 9.5% losses. about 77 kW subtracted from the 818 kW leaving the pack. So the net is about 741 kW output or just under 1000 HP.
TorqueMonster
Member
Keith,
What a pleasure to have you post on this forum!! Thanks for your in-depth technical explanation of losses throughout the powertrain. I now see how losses are being booked, and the number make a lot of sense. When i was thinking of losses I was only thinking from the motor output power (motor load) and rotors through the reduction gears. thanks for the info !!
What do you speculate on the roadster (or plaid+) powertrain in terms of power output? Do you think they can really achieve 1300 HP??? I am assuming that it will be using the 4680's.
EndlessPlaid
⚡EV/Tesla Nerd 🔋
Totally with @TorqueMonster on his post! So great to see you here Keith.
I was literally reading your analysis just yesterday! This info is beyond helpful! We were speculating from the battery to wheels, when we should've used motor output to wheels. Thanks again! Ecstatic that this is sorted out now.
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EndlessPlaid
⚡EV/Tesla Nerd 🔋
Hi Keith, if you don't mind, I have a question:
How do you think Tesla achieved this power curve?
The car definitely has this curve based on how it's performing at high speeds. I saw in your InsideEvs article that you suggested that maybe Tesla was overamping due to the extra cooling, and how there are always losses at higher RPMs. I was thinking that overamping may be quite unlikely though, due to the system being made to have great longevity, and the stress put on the system regardless of cooling ability. Plus, like you stated, Tesla tries to engineer the system to survive and drive another day.
They would definitely not want to be honoring their 8 year/150,000 mile warranty all of the time.I've also seen another theory that these motors may feature an extremely low V/RPM figure.
Quoting @mongo here: "The Plaid curve shows a higher max power which indicates pack improvements allowing higher pack current. Then follows a really shallow slope indicating either a very low Volt/RPM figure or possibly, V/RPM is low enough that it never hits voltage saturation of the inverter. In that case this may be loss of power due to the increased number of switching events of shorter duration vs motor inductance which could reduce the effective power output."
This curve clearly does in fact show losses at higher speeds, they are just heavily minimized to maybe 40-50 hp lost at 200 mph. How do you think Tesla managed to minimize these losses at high RPM? Is it the really efficient EM-field created by the combination of the carbon-wrapped rotors, and tight tolerances those rotors allow for?
It would be really great to have your input on this, and if you have an updated theory to share, I would love to hear it!
Greatly appreciated,
2021plaid
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Hello! Great to have you here as other have stated! Curious on your take on the carbon sleeving. If the sleeve helps control back EMF and therefore help the motor maintain power at higher RPMS, wouldn't this also make it more efficient? I thought I remember that the sleeving was for both holding the rotor together AND limiting backflow, but I could be remembering wrong. Welcome to the forum!
EndlessPlaid
⚡EV/Tesla Nerd 🔋
Beautifully put! Elon himself stated that the carbon-wrapped rotors allowed for tight tolerances as super high rpm, and that in turn allows for a massively efficient EM field.
EndlessPlaid
⚡EV/Tesla Nerd 🔋
Hi Keith, some things have occured since I first asked you about the power curve. Our dutiful member @omarsultan has presented some new graphs, and a video of his run where he made 818 kw:
Graph of battery current and voltage:
2021 Tesla Model S Plaid - osultan
This video hosted by SmugMug; your photos and videos look better here.
osultan.smugmug.com
If you look at the graph and video, this all but confirms that there is no overamping going on to get the power curve. If there was, than the battery would have to be making substantially more power.
Now that we know that overamping is not occuring to get that curve, how do you think Tesla has managed to mitigate the losses in the curve?
Something that I should've included in my original post are these tweets from Elon, which further go into detail on the construction and benefits of the carbon-wrapped rotors:
Once again, I would greatly appreciate your input and time on how Tesla has achieved this incredible feat.
Thank you so much,
2021plaid
Yes, the carbon fiber, though not interacting with the EM field, reduces rotor expansion at 20K+ RPM and allows the engineers to keep the the field gap between the rotor and stator tighter than would otherwise be required at these high RPMs, reducing magnetic losses. But mere- mortal-level PM EV motors also have extremely tight gaps to reduce magnetic losses (albeit operating at lower RPMs, so usually using metallic magnet containment sleeves). .
I'm not familiar enough with the intricacies of the inverter electronics and motor windings to comment on whether the reduced V/rpm is also a factor.
Tesla has some things going on here I just can't explain. The comparative older MS motor map curves in that illustration fit classic induction motor behavior, with a short flat-HP section, then about 30% peak HP sag at redline. Typical PM EV motors have typically a longer flat spot and then about 10-15% sag as RPMs really pick up- mostly the gear box drive unit, bearing rolling resistance and gear tooth loading friction, windage, etc.
I here Munro is now fully funded for buying a Plaid. Hopefully his teardown will illuminate us!
EndlessPlaid
⚡EV/Tesla Nerd 🔋
Keith, thank you so much for your well thought out reply! There definitely has been some efficiencies that have been made to the powertrain as a whole. Tesla has pretty much been able to cut those losses in half, to a 7% loss at top speed. Regardless, I think this is an incredibly impressive advancement that Tesla has achieved. Once again, thank you for the reply!
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New here, didn't see if there was an edit mode a reply after posting. I mis-spoke above about the carbon sleeve. The carbon sleeve does not interact with the EM field, but that is a +. As noted in that twitter thread, steel sleeves attenuate the field strength some.
EndlessPlaid
⚡EV/Tesla Nerd 🔋
Hi small question, the new Plaid pack seems to have internal cell connection of 108s (110s) which leads to a maximal charging voltage of around 460V. I assume that there is no problem with charging on the SuC V2, which according to the label has an output range of only 50-410V? Thx.
Thanks for the info. This problem was also related to the issue of opening the SuC network for other car manufacturers, where I considered that the voltage limit of 410V for SuC V2 is the main technical reason and was waiting for the V3, which has 500V support from the beginning. However, Tesla was obviously able to solve it.
Yeah, Tesla is doing some wizardry there--thinking is maybe the superchargers is more capable than published.
EndlessPlaid
⚡EV/Tesla Nerd 🔋
EndlessPlaid
⚡EV/Tesla Nerd 🔋
So this is interesting! Always awesome to see battery details:
EndlessPlaid
⚡EV/Tesla Nerd 🔋
@Aleks0404 just posted this excellent video from Ingineer! Finally the first teardown and look at the Plaid pack!
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