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Power limiting while track lapping

Discussion in 'Model S: Driving Dynamics' started by brianman, Apr 12, 2016.

  1. brianman

    brianman Burrito Founder

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    #1 brianman, Apr 12, 2016
    Last edited: Apr 12, 2016
    (A bit rambly post but wanted to drop down my thoughts before I forgot to post.)

    For those not familiar, lapping is "at speed" / high speed track driving but cooperative -- coordinated passing -- with no racing or timing.

    On rainy days, the acceleration limiter isn't really much of a problem at the track for me. Perhaps it's because I'm still in the early days of building up experience. Perhaps it's because I really don't want a 5-digit repair bill (or car replacement) on any track day ever. But let's talk about sunny days...

    I've driven the following tracks in lapping sessions:
    1. The Ridge (Shelton, WA) - P85, P85D, P85D
    2. Pacific Raceways (Kent, WA) - P85
    3. PIR (Portland, OR) - P85, P85D
    4. ORP (Grass Valley, OR) - P85, P85D, P85D
    5. Laguna Seca (Monterey, CA) - P85, P85D

    For all 5 in the P85, it's very easy to reach the first acceleration limiter (160 kW, "half power") within 2 laps -- even with 80+% SOC. If you "take it easy" (regen setting at low, coast in the straights, take corners at speed) you can avoid the limiter for 3-5 laps -- perhaps even a full 20+ minute session.

    With the insane-flavored P85D, the first ("half power") limiter comes much later (within 4 laps) for me when pushing the vehicle. Also, it's much less punishing -- 240kW is less "limpy" than 160kW. If you continue to push it, the second limiter (25%) will arrive -- and it feels like Valet Mode. I try to avoid it as much as possible. Knowing all of the above, I tend to use the same "take it easy" approach as with the P85 but have "a little more fun" on the straights -- accelerate some, just not full out -- which buys me a full session of "at speed" just not "at Insane speed".

    Now let's talk about Ludicrous. The first ORP event I had a lot going on in my head (new group, telemetry distraction, other RL stuff) so I wasn't really going all out. The next event was at The Ridge and was wet -- not always raining, but always a wet track. Finally, back at ORP this weekend it was beautiful. Dry the whole time. Sunburn...well that part sucks. Anyway, where was I ... oh right, dry and pretty. Clockwise on Saturday (not my first time) and counterclockwise on Sunday (my first time). Both days, I did set the regen to Low but otherwise drove it without regard for the limiter -- until I felt the limiter. The good news: I didn't see the limiter at all until SOC was below 50%. That's better than I expected by a long shot. Note that on Sunday I didn't "go nuts" on the downhill of Valkyrie (it's still a bit intimidating) but I did push it pretty heavy on the 1-16 straight much of the time.

    One more note... "How was traffic? Was that giving the car some breathing room?" On Sunday, no. For 3 of the 4 sessions, I lined up first in grid and was free for nearly 2 laps before executing a few passes; traffic wasn't really an issue. For the 4th session, I lined up behind a friend and we immediately hit traffic -- that cleared within the 2nd lap; after the 2nd lap traffic was a non-issue.

    A second note... "How much range is used per session?" The most aggressive 25 minute session used ~100 rated miles. It's a 2.3 mile course and I think we were getting about 10 laps per session -- though I didn't actually count the laps. IIRC, the energy app was reporting a little over 1100 Wh/mi. pretty much steadily so ...
    (a) (1.1 kWh/mi) * (2.3 mi) * 10 = 25.3 kWh
    (b) 85 kWh * (100 rmi/253 rmi) = 33.59 kWh
    ... those look pretty far off, let's try some adjustments...
    (a2) (1.1 kWh/mi) * (2.3 mi) * 12 = 30.36 kWh
    (b2) 80 kWh * (100 rmi/253 rmi) = 31.62 kWh
    Yah, those look closer. So 12 laps and a 5kWh battery buffer line up decently.
     
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  2. brianman

    brianman Burrito Founder

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  3. EarlyAdopter

    EarlyAdopter Active Member

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    This bodes well. Have to see how it holds up in warmer weather.

    While I could see the limiter kicking in to protect a dumb fuse from blowing under heavy heat load and the ludicrous smart fuse not needing that limitation (same for the main pack contactor), that wouldn't explain the difference in limiting between the P85 and P85D. Still seems like it's motor related.

    Any luck getting some CAN logging going? Would love to see some numbers on heat from the motors and other components.

    Also, I bought some water sprayers end of last season that the Audi R8 and Nissan GTR folks were recommending for dealing with their heat limiting (yes, this isn't just a Tesla problem). Haven't hooked them up yet. Maybe this summer.

    Got mine back today from ludicrous upgrade. Should be a fun summer!
     
  4. brianman

    brianman Burrito Founder

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    My working theory was that (a) dual motors mitigated motor overheating by spreading the load across the two motors and (b) fuses mitigated overly-conservative battery output power governing.
     
  5. disillusioned

    disillusioned Member

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    I know literally nothing about track racing, though I had heard that Tesla's definitely start limiting you at some point due to heat. Were you pegged at the max speed to hit the 1100wh/mi number so consistently, or pretty close, excepting the turns? You mention coasting with low regen, so I guess I'm wondering what part of what you were doing causes such heat build up, and where the threshold is: if I'm on an interstate doing 90mph nonstop for an hour, will I hit the limiter? Apologies for stupid questions, this is way out of my wheelhouse.
     
  6. Saghost

    Saghost Active Member

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    Very interesting. It sounds like all those complaints about the S not being a track car may be about to end (though of course that was never really relevant to the way 99% of them get driven.)

    I wonder if one of our European friends has a Ludicrous car they can take to the Ring with a dash cam to match against the video from a couple years ago....

    (The theory about limiting to protect the fuse makes sense to me, actually - the various posts I've seen on the subject seemed to make it clear the car was using some sort of a power over time map that wasn't greatly affected by outside temperature, and staying on the safe side of a 600A fuse you're sometimes drawing 1300A through fits. Though in that case, I wonder why Tesla wasn't clearer about the difference Ludicrous makes in Track/sustained high power performance - all the press I remember focussed on 0-60 and quarter mile times.)
     
  7. Denarius

    Denarius Active Member

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    Awesome news! Can't wait to get back out to the track!
     
  8. brianman

    brianman Burrito Founder

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    Not at all. I'm still learning counter-clockwise ORP. I definitely wasn't at full throttle (driver wasn't ready), but I definitely wasn't holding back to keep the limiter at bay (car was ready).
     
  9. 3mp_kwh

    3mp_kwh Member

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    My experience is on east coast tracks, not with a Tesla. I'm glad you experienced more latent over-heating, but expect that you weren't getting much power out of turns, until the wheel was straight. Correct? Maybe at some speed, everything I've experienced stops happening, like a >50mph apex to track-out. But with really basic "in slow, out fast" technique, coming out of a turn becomes a dead pedal zone for AWD. This is fast for the street, but still slow enough the tires aren't beginning to squeal.
     
  10. scaesare

    scaesare Active Member

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    Interesting.

    Some recent references I came across led me to believe that the IGBTs used in the inverter had a constant-power rating significantly less than what the full power capability of what the model S is capable of. For that reason I assume that the inverter can deliver higher peak power only for bursts before heat becomes an issue.

    Perhaps that's not the only limiting factor, but I suspect it may be as much anyone as the fuse, if not more. It also meshes with the fact that the dual motor cars don't limit as quickly, given there are 2 inverters to spread the power handling load over.
     
  11. Saghost

    Saghost Active Member

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    Huh. If the IGBTs were the limiting factor, I'd expect to see the limits respond more to differing conditions - we know they are actively cooled and Tesla monitors them in real time from the diagnostics screen, right?

    So I'd expect them to only limit the power when the IGBTs are overheating, and what I've read about the power limiter seems to suggest it's acting more like a power over time look up - as in, you hit is at about the same point on a freezing cold day and a scorching hot one. I think, from my forum reading anyway. I don't have any personal experience with it, yet.
    Walter
     
  12. scaesare

    scaesare Active Member

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    Yeah, good question.

    I wish I could find the reference to the IGBT's I was reading. It may have been that they were only rated to produce peak power as a function of time, rather than strictly heat (as fuses often are). That might be a factor for the behavior you are describing.

    The other thing I suspect is that, when pushed hard, the system moves to active chilling of the coolant delivered to the drive unit pretty quickly. As such, the total cooling that can be delivered may depend on the HVAC system, and there may not be a lot of variance as to how low it can go, despite outside temps.
     
  13. brianman

    brianman Burrito Founder

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    #13 brianman, May 9, 2016
    Last edited: May 9, 2016
    Saturday, May 7th, was another lapping day at ORP - counterclockwise. It was in the 70s with a track temperature around 120F.

    The first session was a warmup and was intentionally very light, with lots of traffic. Many in the run group were new to counterclockwise at ORP so there was a lead follow that I caught up to, etc. No big.

    The second session I could let it out a bit, and had quite a bit of fun with very little limiter involvement. I spent the last 2/3rd of the session following a friend* that I met at the event, and we had basically no traffic to deal so it was a lot of fun. I was comparing his line to mine while we went. I did my best to make it obvious that I wasn't "presenting" / requesting a let-by. (In the 'download' discussion after the session, he confirmed that it was clear.)

    The third session I hit the first limiter within a few laps and then got hit hard with the 2nd limiter. This session I happened to start the group (with my new friend behind me to compare lines from swapped positions) and I took off like I was in a hurry (oops...). I didn't see another car for at least 3 laps. When the 2nd limiter hit I figured "surely the passing flood should begin soon". Two laps later I got caught by my friend and he had let another car by so I let the two of them by. After 4 more laps of 1st or 2nd limiter (it fluctuated), I decided to exit track to get some charge (and stop fighting the uphill battle) and saw the white flag (session nearly done but not checked) as I exited.

    Here was the energy app after I parked to charge at the 14-50R:

    20160507_ORP_After3rdSession_Limiter.png



    * Friend's ride for the curious (basically totally different ride than the Model S - loud, hot, open air, 1400 pounds):

    20160507_ORP_Friend.png

    I skipped the 4th session to charge (which left me with 150 rated miles for the 5th session) to ride with him. He skipped the 5th session to ride with me. Was really interesting comparing notes.


    After a little bit more charging during the skipped 6th session, I left for The Dalles supercharger with 70 rated miles (plenty of buffer) right before that session ended.


    I keep plugging for them to get some 80A HPWCs at ORP but it's going to takes some time. They're already at/near electrical capacity there and the power company is asking them to pay $1mil for a new substation.
     
  14. Denarius

    Denarius Active Member

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    @brianman on your third session when you saw the first limiter what was your battery %?
     
  15. brianman

    brianman Burrito Founder

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    I didn't remember to look (and retain) while driving. :( I suspect below 50% but more than 20%.

    I might be able to make an educated guess once I run the numbers a bit more (and use SWAGs from what I recall of when I plugged and unplugged).
     
  16. bhzmark

    bhzmark Active Member

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    Any update?
     
  17. brianman

    brianman Burrito Founder

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    #17 brianman, Sep 26, 2016
    Last edited: Sep 26, 2016
    Here's (screenshot) the worst limiter I've seen on my P85D w/L. This is from ORP on 09/24/2016 (Saturday) after exiting to the paddock after a painfully slow CW lap from turn 10 and beyond. I was about 3 turns beyond any traffic behind me but they caught up rapidly after this limiter hit.

    20160924_ORP_Limiter.jpg


    For me, the limiters and the "Electronic stability control systems"* are the big deal breakers for having more fun at the track.

    * This is the icon that means "the car is unhappy, power cut briefly" that double-punishes:
    ElectronicStabilityControlSystem.png


    And for the follow-up question:
    Why not just turn it off?


    Consequently, from the driver perspective this represents a downgrade from the RWD vehicles:
     
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  18. Denarius

    Denarius Active Member

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    Ludicrous upgrade destroyed time to limiter. I've hit the limiter while driving aggressively on the road. I never did pre-ludicrous.
     

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