# tesla observations



## dcb (Dec 5, 2009)

was catching up on ivans site a bit, and saw this (annotated screen shot attached)
https://www.youtube.com/watch?v=NaV7V07tEMQ

443 lb/ft torque, 416hp. (290kw, 375v batt, > 773 amps in the slots? single turn?)
so, what's up with the airgap irregularities?


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## mora (Nov 11, 2009)

Maybe this clears the airgap questions:

https://youtu.be/ZOriitPjlcw?t=343

Single turn. Stator seems loosely wound but doesn't seem to affect performance. Resin holds it in place.


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## dcb (Dec 5, 2009)

nice vid. Adding some mass to the end turns looks like a good idea (potting?)

I think it just dawned on me what happened, when they cut the hole, they cut partway into a stator lamination, and tore off the pole ends irregularly on that lamination in the process.


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## kennybobby (Aug 10, 2012)

Looking at the motor assembly video, appears to be 25 in hand, wrapped 2 turns per coil, with 3 coils per pole pitch...? i'm thinking the pole slot spacing is at 8-10-12, correct me if wrong.

Earlier this year i was trying to estimate R and L--maybe Michal will measure it for us.
-----
For a 3-phase, 4-pole wye motor with the poles wired 2s2p, and using 16 AWG copper wire 25-in-hand:

phase inductance ~ 493 nH
phase resistance ~ 5.3 mR

This gives an L/R time constant of 93 usec. If we use 3 tc to reach full current, then the motor max speed ~ 26,858 rpm. With a 9.73:1 gearbox the theoretical max speed would be 228 mph.

For a P85D to reach 155 mph the motor(s) will need to spin at 18,200 rpm and make at least 50 kW each, or just the front motor make 100 kW. The inverter would need to be generating a current waveform of 606 Hz, and the per phase L/R time constant would have to be less than 138 usec.

Send data when you get some…


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## istemihan (Jan 2, 2017)

kennybobby said:


> For a 3-phase, 4-pole wye motor with the poles wired 2s2p, and using 16 AWG copper wire 25-in-hand:
> 
> phase inductance ~ 493 nH
> phase resistance ~ 5.3 mR


Hi Kenny,

I am new to this forum and you statement is the actual reason why I registered to this forum. I've been looking for phase inductance values of Tesla motors. Finally first and the only information was yours.

I need to verify this information. But it seems very low to me for a powerful electric motor. I would expect it to be at least a few mH's. You are referring to stators winding inductances right?

Thanks.


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## kennybobby (Aug 10, 2012)

Howdy istemihan,

welcome to the forum.

That does seem to be low, and the reason being that it doesn't account for the increase in inductance that the backiron would contribute (reluctance of the iron laminations)-- that number i estimated was purely an L based upon # of turns and approximate dimensions of the motor coils since i have no data on the iron. The R was a similar calculation using a length of parallel wires, etc.

i was hoping and hinting that someone (Eldis) who owns one of these motors and separated it from the inverter would actually measure the R and L of the windings to give us some real data...

if you find anything please share and post it up here.


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## istemihan (Jan 2, 2017)

kennybobby said:


> Howdy istemihan,
> 
> welcome to the forum.
> 
> ...


Thanks for the answer Kenny. 

I also asked about this on Quora. Here is the link: https://www.quora.com/What-is-a-typical-stator-winding-inductance-of-electric-car
A guy says that the typical electric car motor inductance is about 500 mH. I'm gonna start a topic on this issue.


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## kennybobby (Aug 10, 2012)

The problem with such a high inductance as 500 milliH is that the current wouldn't be able to flow in and out the windings at the level necessary to make the torque and hp that has been demonstrated.

e.g. at 100 mph the motor must spin at ~11,740 rpm, and the current waveform for the 4 pole motor would be about 391 Hz.

The impedance would be on the order of 1228 Ohms.
The L/R time constant would be on the order of 94 seconds.
So it just can't be that high.


But 500 uH (microH) does seem to fit the data better.

The impedance would be 1.2 Ohms.
The L/R would be 0.42 seconds, 3 time constants ~ 1.3 seconds. See how this compares with the current ramp up during a WOT acceleration run.


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## okashira (Mar 1, 2015)

I have measured the inductance of a small DU stator and it's 72uH.
(phase to phase is 144uH)
Resistance is about 0.007 Ohm.

I would not bother trying to calculate these values from an accel run. The ramp up is limited by controller logic not by L/R constant.

The only way you could guess at inductance is with torque vs motor current, since torque is a function if I*L


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## istemihan (Jan 2, 2017)

okashira said:


> I have measured the inductance of a small DU stator and it's 72uH.
> (phase to phase is 144uH)
> Resistance is about 0.007 Ohm.
> 
> ...


Thank you so much for the information. This is good news.


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## electro wrks (Mar 5, 2012)

I was doing some research on cobalt recently and noticed its potential application in high-end electric motors: http://www.protolam.com/page9.html

The alloy noted has ~50% cobalt and could be used in light weight, high output motor stator(rotor?) laminations. Does anybody know if any EV manufacturers uses this in its motors? I'm thinking the "T" word here.


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## okashira (Mar 1, 2015)

electro wrks said:


> I was doing some research on cobalt recently and noticed its potential application in high-end electric motors: http://www.protolam.com/page9.html
> 
> The alloy noted has ~50% cobalt and could be used in light weight, high output motor stator(rotor?) laminations. Does anybody know if any EV manufacturers uses this in its motors? I'm thinking the "T" word here.


Highly doubtful. That alloy would sacrifice inductance (permeability) and possibly more hysteresis for a slightly higher saturation limit. It would reduce efficiency at lower loads.
I am sure Tesla uses iron with the highest possible permeability with good saturation characteristics.
Not to mention cost.


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