P85D Power draw numbers do not add up...

[Bighorn]

Watch The Fast Lane video on Youtube trying to do 0-60 runs in the Challenger Hellcat. Staff couldn't break 5 seconds and the pro from Dodge couldn't beat 4.7. Makes all the commenters putting down the Model S saying the Dodge can do 2.9 seem a wee bit delusional. Traction and the 1st-2nd transition seemed to be bugaboos. Launch control showed no benefit.

We test the 2015 Dodge Challenger Hellcat from 0-60 MPH over over again - YouTube

 

[Todd Burch]

Ouch! So easy to put up consistent (and faster) times with the S.

(How were they struggling to even get a time slower than the P85?!?)

 

[linkster]

Watch The Fast Lane video on Youtube trying to do 0-60 runs in the Challenger Hellcat. Staff couldn't break 5 seconds and the pro from Dodge couldn't beat 4.7. Makes all the commenters putting down the Model S saying the Dodge can do 2.9 seem a wee bit delusional.

WOW! Thanks for the YouTube link. I hadn't seen this video. The Hellcat will be lucky to get 0-60 in under 6 secs. on the street. I can't tell y'all enough how much stickier that concrete prepped drag launch strip is with rubber and VHT vs. plain ol' street asphalt.

 

[Olle]

Is your pack with the 650A fuse from an 85 or a P85?

 

[Olle]

WOW! Thanks for the YouTube link. I hadn't seen this video. The Hellcat will be lucky to get 0-60 in under 6 secs. on the street. I can't tell y'all enough how much stickier that prepped drag strip is with VHT.

So the hellcat does 0-60 in 4.7 with street tires and P85D 3.2. No contest. With radials the hellcat did 2.9, once. I wouldn't be surprised if the P85D would do 2.5 on tires optimized for the strip. Imagine the ultra precise traction control on four wheels and all that torque on four wheels.
In real life its pretty nice with 0-60 as well as passing power 40-70. I hope the P85D will shine there, even more so than the P85 which is already brilliant. 1/4 mile and ability to go a few laps on the track is fun, but seriously, who buys a 5 to 7 seater to do that?

 

[Juanmax]

Oh that's a good data point hidden between the lines.

So at a nominal pack voltage of 346 you were pulling ~925 Amps or 4.2C during that 7 seconds at top speed.

Based upon that power consumption an S85 could run at top speed for about ~16 minutes, full pack to empty.

wrong. The 85 does not need 300kW+ to keep up to top speed. he said while accelerating to top speed he saw it at max power during 7 seconds.

I do not assume that it needs north of 80kW to keep the speed. So it actually gets around 120miles on a charge at full speed.

I actually drove an 85 loaner as my roadster was getting sport suspension, and maxed it in the German autobahns. I cannot say for sure the number, but I am pretty confident it was below 100kW.

 

[WarpedOne]

My previous car had 88kW and 120mph max speed.

 

[wk057]

I'll have to video next time... but no, it was not a constant 320kW. Pretty sure it was under 100kW holding top speed also.

 

[Torben_E]

Interesting how this thread died out long ago... I find it more interresting than ever....

We definitfly know that the P85D does not deliver more than 420 kW (before inverter/motor losses) by now. And that a 1.500 A is needed over the 1.300 A fuse to deliver more power. And that current in Ludicrous is still not going to deliver the 691 hk claimed in for the Insane.

WK057... i see a missing link between 630 A and the 1.300 A and now the 1.500 A. To be honest I assumed it was 2 x 630 A fuses... but you restated that it is only 1x630 A, right ?

Why then did EM say we have replaced the 1.300 A with a 1.500 A ?

Torben_E

 

[PRJIM]

the fuses are slow-blow, i believe tesla is stating the max fuse rating rather than the nominal current.

 

[tom66]

the fuses are slow-blow, i believe tesla is stating the max fuse rating rather than the nominal current.

They are fast blow fuses. But all fuses have an I2t curve, which means the rated current can be exceeded for some time without failure. Generally, a fuse is specified with two main specifications: a guaranteed to withstand current (for this one it would be ~500A or so) and a guaranteed to interrupt current (e.g. 5000A will blow in 0.1 seconds.) The 630A rating will generally be some specification like 30 seconds continuous operation, 175C case temp, worst case rating etc. depending on the manufacturer.

This is why the electronic fuse that Tesla are introducing is necessary, to get that extra 1500A out of the pack would require changing the fuse but that would compromise things like the short circuit blow time, which could (potentially) lead to a fire or serious battery pack damage due to shorted inverter etc.

 

[lolachampcar]

Drove ludicrous two days ago. Was #1 on the upgrade list before the test drive and told the manager I'm definitely keeping that position.

The PD performs and the PDL ups the game by performing significantly better above 30 mph then my PD.

..... not really sure how the fuse size plays into the game but, given all the controversy over ratings and the such, I'll simply continue to base my decisions on experience and quoted performance (0-60, 1/4 mile) when I can not test drive before committing.

 

[darthy001]

Drove ludicrous two days ago. Was #1 on the upgrade list before the test drive and told the manager I'm definitely keeping that position.

The PD performs and the PDL ups the game by performing significantly better above 30 mph then my PD.

..... not really sure how the fuse size plays into the game but, given all the controversy over ratings and the such, I'll simply continue to base my decisions on experience and quoted performance (0-60, 1/4 mile) when I can not test drive before committing.

Dang, I was secretly hoping that you would be disappointed with it It seems like I will have to schedule a test-drive when the 90 gets to Norway....

I assume this was a P90D?

Any news on the actual upgrade timing?

 

[lolachampcar]

It was a PDL. The upgrade works for me but you may have different requirements/standards. Definitely test drive it first.

As for timing, the Service Center still had no clue so it remains "Tesla Soon". I try not to concern myself with when anymore and try to look at it simply as a treat I will get in the future.

 

[darthy001]

It was a PDL. The upgrade works for me but you may have different requirements/standards. Definitely test drive it first.

As for timing, the Service Center still had no clue so it remains "Tesla Soon". I try not to concern myself with when anymore and try to look at it simply as a treat I will get in the future.

As pointed out by you and several others my quota of buying without testing with Tesla is over so no upgrade until I've actually tested ludicrous, and even better if I've gotten to test an upgraded P85D.

So hopefully we will get some P90Ds or upgraded P85Ds to test here in Norway soon.

The difference must be very noticable for me to even consider this expence given my level of "satisfaction" with Tesla at the moment. Of course they could give me a nice deal due to the seat-fiasco and I would consider it that much more

 

[Torben_E]

They are fast blow fuses. But all fuses have an I2t curve, which means the rated current can be exceeded for some time without failure. Generally, a fuse is specified with two main specifications: a guaranteed to withstand current (for this one it would be ~500A or so) and a guaranteed to interrupt current (e.g. 5000A will blow in 0.1 seconds.) The 630A rating will generally be some specification like 30 seconds continuous operation, 175C case temp, worst case rating etc. depending on the manufacturer.

This is why the electronic fuse that Tesla are introducing is necessary, to get that extra 1500A out of the pack would require changing the fuse but that would compromise things like the short circuit blow time, which could (potentially) lead to a fire or serious battery pack damage due to shorted inverter etc.

Thx Tom66, very usefull.

Torben_E

 

[Zetopan]

We definitfly [sic] know that the P85D does not deliver more than 420 kW(before inverter/motor losses) by now. And that a 1.500 A is needed over the1.300 A fuse to deliver more power.

I am unsure who your "we" is, but I am pretty sure that it does not include me. Firstly, as was quite correctly previously stated, fuse ratings actually allow for relatively short term overloads that far exceed their nominal ratings. Hence the fuses that Tesla is using on the P85D allows for up to about 1,300 amps for many seconds without self destructing (see message #22). Tesla had to limit the maximum current draw to 1,300 amps on the P85D because most fuses have a rather wide resistance and I^2*R tolerances. The "typical" fuse would handle higher current than 1,300 amps, but for reliability the worst case has to be used in the design. If that were not the case some Tesla owners could find themselves stranded with blown fuses even though the "typical" fuse would have easily survived under the exact same conditions. Tesla did not replace a 1,300 amp fuse with a 1,500 amp fuse. They replaced a wide tolerance fuse (having a much lower nominal rating than 1,300 amps) with a much tighter tolerance fuse. The latter fuse, because of its tighter tolerances, lets Tesla increase the current and still avoid blowing the fuse with worst case fuse resistance and I^2*R tolerances.

And that current in Ludicrous is still not going to deliver the 691 hk [sic]claimed in for the Insane.

Secondly, lets do a little simple math. 691 HP = 515486 KW (I am using a slightly higher wattage per HP than reality due to rounding). Now we can divide that wattage by 1,500 amps since that is the maximum current draw. The result is 344 volts (rounded). That assumes 100% efficiency for the inverters and motors. Induction AC motors with copper rotors (what Tesla uses) are more efficient that most industrial motors and this is why Tesla actually manufactures their own motors. A very good industrial induction motor can be 97% efficient at its maximum load. I don't know the efficiency of the Tesla inverters but I suspect that it is very good. Lets assume for the sake of argument that it is only 90% (it is likely better than that). Given those numbers, the battery voltage would need to be 394VDC (rounded) to deliver
691 HP.
If I instead use 95% efficiency for the motors and 95% for the inverter, the battery voltage would have to be 381 VDC. Note that the nominal terminal voltage of the P85D battery is 400 VDC. At that voltage and 1,500 amps the battery output power is 600 KW but it will drop pretty rapidly from there to a slightly lower voltage under load. That electrical power translates to 804 HP. Since the P90D "Ludicrous Mode" rating is 762 HP, that allows for only a 2% efficiency loss, unless the terminal voltage has increased somewhat on the higher capacity battery.
Manufacturer internal combustion engine HP and torque ratings are measured at the crankshaft, these do not include the losses due to the transmission and drive axel gearbox (usually a locked up differential). Since Teslas have a simple gearbox rather than a complex transmission the motor gearbox transmission losses will be lower than your common automotive internal combustion engine power transmission losses. Hence the Tesla will be placing more of the generated power to the automobile axels than an internal combustion engine.

 

[lolachampcar]

Zeto,

First, thanks for taking the time to show that Tesla's numbers may be possible on the existing L battery.

Second, I somehow came away from the Elon fuse discussion thinking Tesla was employing active "pyro" fuses which have circuitry on board to monitor instantaneous current (within the sample time frame of the circuit) and "blow" the fuse link in a fault condition. It is my understanding that these fuses allow (1) much lower resistance values as you are using pyrotechnics to sever the link instead of I2R losses to melt it and (2) higher continuous loads due to the active nature of the fuse allowing you to run much closer to your fault point without the fuse melting. Do you have a reference for the fuses still being set to 1300 amps?

 

[wk057]

I am unsure who your "we" is, but I am pretty sure that it does not include me. Firstly, as was quite correctly previously stated, fuse ratings actually allow for relatively short term overloads that far exceed their nominal ratings. Hence the fuses that Tesla is using on the P85D allows for up to about 1,300 amps for many seconds without self destructing (see message #22). Tesla had to limit the maximum current draw to 1,300 amps on the P85D because most fuses have a rather wide resistance and I^2*R tolerances. The "typical" fuse would handle higher current than 1,300 amps, but for reliability the worst case has to be used in the design. If that were not the case some Tesla owners could find themselves stranded with blown fuses even though the "typical" fuse would have easily survived under the exact same conditions. Tesla did not replace a 1,300 amp fuse with a 1,500 amp fuse. They replaced a wide tolerance fuse (having a much lower nominal rating than 1,300 amps) with a much tighter tolerance fuse. The latter fuse, because of its tighter tolerances, lets Tesla increase the current and still avoid blowing the fuse with worst case fuse resistance and I^2*R tolerances.



Secondly, lets do a little simple math. 691 HP = 515486 KW (I am using a slightly higher wattage per HP than reality due to rounding). Now we can divide that wattage by 1,500 amps since that is the maximum current draw. The result is 344 volts (rounded). That assumes 100% efficiency for the inverters and motors. Induction AC motors with copper rotors (what Tesla uses) are more efficient that most industrial motors and this is why Tesla actually manufactures their own motors. A very good industrial induction motor can be 97% efficient at its maximum load. I don't know the efficiency of the Tesla inverters but I suspect that it is very good. Lets assume for the sake of argument that it is only 90% (it is likely better than that). Given those numbers, the battery voltage would need to be 394VDC (rounded) to deliver
691 HP.
If I instead use 95% efficiency for the motors and 95% for the inverter, the battery voltage would have to be 381 VDC. Note that the nominal terminal voltage of the P85D battery is 400 VDC. At that voltage and 1,500 amps the battery output power is 600 KW but it will drop pretty rapidly from there to a slightly lower voltage under load. That electrical power translates to 804 HP. Since the P90D "Ludicrous Mode" rating is 762 HP, that allows for only a 2% efficiency loss, unless the terminal voltage has increased somewhat on the higher capacity battery.
Manufacturer internal combustion engine HP and torque ratings are measured at the crankshaft, these do not include the losses due to the transmission and drive axel gearbox (usually a locked up differential). Since Teslas have a simple gearbox rather than a complex transmission the motor gearbox transmission losses will be lower than your common automotive internal combustion engine power transmission losses. Hence the Tesla will be placing more of the generated power to the automobile axels than an internal combustion engine.

Just a technical note.

I don't think you, like many others, understand how voltage drop works in the battery. Under a 1500A load the voltage of the pack as a whole is going to plummet due to the internal resistance of the cells. It's not "slightly lower under load," it's MUCH lower under this load, nearly 100V lower by my calculations.

I would redo this with kW as the measure, but we all know 1 HP = 746W, so here is the graph I made that takes into account voltage drop of the battery pack:

First thing you'll notice is that this curve is not V*A linear. You'll see that at a full charge, under 1500A load, the voltage drop is going to cause the power output to be around 600 HP max, or around 450kW. You'll never see 691 HP out of the pack because that would require amperage beyond what the cell level fuses can handle, literally destroying the entire pack as a whole almost instantly. Once one pops it increases the load on the other 74 in the group and a chain reaction would ensue in every group until they were all popped.

This is data from the 85 kWh pack cells, so the 90 kWh pack would be about 5% better, in theory. They may also have beefed up the cell level fuses in the 90 pack as well, I don't know. However the 1500A cap puts the power cap around 600HP/450kW from the battery, and I'll say +/- 5% to account for potential differences in the 90 kWh pack cell chemistry.

I should probably do up a technical thread on battery voltage drop.

 

[Lanber]

And please note, 600 HP is from the battery, then it goes to the inverter to change into AC power and then to the motor, then a transmission and out to the tires.
It`s anyone`s guess as to losses combined there. 15% minimum. 20+% in reality.