What technically would need to happen to get the P85D the 691 hp?

[sorka]

If we extrapolate 3.5% loss from battery to motor shaft based on their 463 hp and assuming they mean that at 30% where we know the battery is outputting 357KW(480hp at battery vs 463 at shaft), then we'd need 716 hp battery power or 534 KW.

 

[lolachampcar]

Silly,
Doing a boost dc-dc for those kinds of amperage would likely weight near that of the SCs
I'm more a fan of some high discharge rate (high C) batteries in parallel with the Tesla pack. Actually, my recommendation to my bud was simply to use a smaller very high discharge rate pack to reduce mass (1/4 mile runs) then use a generator to recharge it between runs. We figured somewhere less than 1.5 KW-Hr per run (which assumes somewhere around 750hp for a full 11 second run which is not possible given the way motors work).

 

[sillydriver]

Silly,
Doing a boost dc-dc for those kinds of amperage would likely weight near that of the SCs
I'm more a fan of some high discharge rate (high C) batteries in parallel with the Tesla pack. Actually, my recommendation to my bud was simply to use a smaller very high discharge rate pack to reduce mass (1/4 mile runs) then use a generator to recharge it between runs. We figured somewhere less than 1.5 KW-Hr per run (which assumes somewhere around 750hp for a full 11 second run which is not possible given the way motors work).

Fair enough. Well, it seemed like a good idea at the time. :smile:

 

[mikes_fsd]

Quick and dirty, back of the envelope answer: You would need a current draw of 1500 to 1700 amps from the 7104-cell pack at ~6000rpm, 51mph.

Show your work on how to get 691hp at the motor shaft from an awd tesla.

What do we know about the motors?

from post by Dennis
Max hp on the rear engine is at 5950 rpm and 6100 rpm for the smaller front motor on the p85d

from the tesla website for the performance model (latest data P90D?)
front 193 kW (259hp)max at 6100 rpm, max speed 18000 rpm, max torque 330 mN
rear 350 kW (469hp)max at 5950 rpm max speed 16000 rpm, max torque 600 mN

motor rating 320V
overall final drive ratio: 9.73:1


from R&T article for P85D

front 221 hp 165 kW, 244 ft-lbs
rear 470 hp 351 kW, 443 ft-lbs
total 691 hp 516 kW, 687 ft-lbs

Assume the front and rear motor power peaks are at the same rpm for the 85 and 90 based upon post by sillydriver about the numbers:
"Next, the manual says the max ‘net power’ for the ‘performance’ rear motor is 350Kw @ 5950RPM (divide by .7457 to get 469HP), and the front ‘performance’ motor is 193Kw @ 6100RPM (259HP). This disagrees with the 503HP for the rear now on the website, but DOES agree with the 259HP for the front. Discrepancy unexplained. Note that the ~6000RPM for peak powers in each = 51MPH. It sounds like the MS, with its single gear, begins to fall out of its power band over 51MPH, but how this interacts with max battery power is unclear."


So use 6000 rpm for both front and rear to get the 691 hp (516kW)

for 516 kW output, and 95% efficiency of inverter => 543 kW input power

543kW/360V = 1509 Amps (using 10% sag on full pack voltage)
543kW/320V = 1697 Amps (using motor rating voltage)

Extra Credit:
Use cell test data graph from wk057 to account for cell internal resistance.

Hmm, I was under the impression, that in this day and age 95% efficient inverter for the ~400V dc is kinda the low end...

This next one if from Fuji Electric

And I would be disappointed/surprised to see that Tesla cant get better efficiency then what an random google search can return... But, then again, does someone know the Tesla's inverter efficiency numbers? Any independent testing?

I would bet it is 97%+
so, for 516 kW output and 97% efficiency of inverter => 532 kW input power

532kW/360V = 1477 A ... so possible in a Ludicrous car with smart fuse?

Can someone point me to the internal resistance graph that is mentioned here?

 

[kennybobby]

Take a look at the whiz-kid's graph and discussion in that thread:

P85D Power draw numbers do not add up... - Page 8

As for efficiency, probably only Michal Eldis or Jack Rickard have the right kind of maple to be able to answer this question. Both of these guys bought a used complete drive unit (inverter, motor and gearbox) for testing and experiments.

Michal designed a separate controller board to run any inverter. He took a tesla inverter apart on the maple floor of his apartment and then ran the motor with his card, so he would have access and could make the necessary measurements.

Jack has his mounted on a maple-top work bench and used some tools developed by Collin Kidder to run his motor using commands over the CAN bus. i think Jack has a dyno also so he might be able to measure efficiencies.

 

[jerjozwik]

*posting for subscription to thread, carry on.*