Graph of Consumption vs. Speed ?

[AlanSubie4Life]

Something I’ve noticed since we have both a single and dual motor cars is that the consumption goes sky high (370wh/mi+) past 75-80mph on the dual motor cars but that the front motor seems to make a lot more noise as well. Too big of a correlation to be coincidence, I think.

I can't imagine that it would be engaging the front motor at those speeds unless you are accelerating. Even at 350Wh/mi at 85mph, that's only 28kW, which the rear motor is easily able to produce. In this speed area though, aero losses are really going to be dominant, even in winter time, so your efficiency in Wh/mi will be going up with pretty close to the square of velocity. The baseline 70-100Wh/mi is still there, but the term proportional to 1/velocity due to accessory use has really become very small at that speed.

Can't really explain why it wouldn't be even more noticeable on a single motor car, though (it should be, since the baseline rolling resistance is really low on those cars!).

 

[ElectricIAC]

All the more reason it was perplexing to me as everything I’ve read points toward the rear motor being the dominant mover. Maybe it’s just drag noise but the sharp increase in consumption on a side by side test was hard to ignore.

 

[Daniel in SD]

usually alternating between full throttle and full brake at speeds significantly greater than 18 MPH.

It takes 360Wh to accelerate to 60mph (ideal kinetic energy) so if you were to do this on a 6 second cycle (assuming you have P3D!) for 4 minutes straight you would travel approximately 2 miles and use 14.4kWh of energy (and that's neglecting drivetrain loss!).

 

[ZOMGVTEK]

It takes 360Wh to accelerate to 60mph (ideal kinetic energy) so if you were to do this on a 6 second cycle (assuming you have P3D!) for 4 minutes straight you would travel approximately 2 miles and use 14.4kWh of energy (and that's neglecting drivetrain loss!).

Yikes, that likely means in the neighborhood of ~25kwh consumed from a cold battery. This road is nearly perfect for aggressive snow driving, so it ends up making me drive at the limit when its snowy. But this means its far from a 6 second cycle, its just a blinking traction light or ABS the whole time. And the heat needs to be hammered to keep the glass vaguely clear. Still waiting on that party box...

 

[AlanSubie4Life]

Yikes, that likely means in the neighborhood of ~25kwh consumed from a cold battery.

I think he was trying to explain that this use was barely possible...

I suppose I ended up being a bit misleading on that one. The 10-12% is repeatable, but its total consumption including HVAC use when its snowing, cold, and the battery is cold enough there is almost no regen. This means ~10+ minutes preheating on HI, leaving the heat on HI for the 10ish minutes it takes to pick up food, and usually alternating between full throttle and full brake at speeds significantly greater than 18 MPH.

The interesting bit is that it appears to zap less range now that the car near enough always preheats the battery. It sure looks like i'm seeing a bit less consumption doing the same thing, but with a battery that was warmed from its own energy. I don't think its just the enhanced regen, so it could be the energy inst really fully consumed and the BMS ticks off a bit too much? It's only really super noticeable when the battery is below freezing, right around when the little snowflake shows up.

This is still unbelievable. I'd need to see some pictures, and really I'm only interested in the usage/pictures while you're in drive (one picture right before going into drive, one right after going to park... and of course the starting rated miles, the Wh/mi, and the ending rated miles (% is not very useful particularly in the case of a cold battery since each % continuously changes in energy content as the battery warms/cools) ). Speculating about energy use while in Park is unfortunately just that - speculation. I've never seen the energy meter deviate significantly from my expectations, though I do actually expect that you might use rated miles at a LOWER rate than the normal ~230Wh/rmi (Dual Motor) when the battery starts cold, due to the battery warming up and recovering available energy over the course of a drive. I've just never had a chance to check that case & behavior myself.

To really isolate the efficiency loss effect of a cold battery, of course you have to complete your drive without using the HVAC, without pre-warming, and without using the friction brakes.

 

[Daniel in SD]

I think he was trying to explain that this use was barely possible...

Oops. I was off by a factor of two. 1/2 m*v^2 not m*V^2. So 7.2kWh of energy to travel 2 miles alternating between only full acceleration to 60mph and full brake to 0.

 

[ZOMGVTEK]

That's the thing, the Wh/mi isn't reported as all that high. Maybe 600ish? I don't typically use the trip meter unless its a longer trip, so this is a guesstimate from when I glance at the graph. I'd guess the heat accounts for a fair bit of the consumption, usually the SOC drops quite a bit by the time I get in the car. I'm going off the SOC displayed in the app when I open it, to when I get back and look at the car's indicated SOC. Scientific it ain't, but I get back home wondering what happened to the juice. It could be the SOC drops suddenly right away or something, I don't really look too closely.

Not using heat when the conditions are poor is barely possible, the glass frosts over on the inside quickly. And the distance required to stop using regen alone when the battery has the little snowflake at high SOC is pretty much the entire drive. It's not really possible to recoup the energy anyways since the rolling resistance is quite high on fresh snow. But preheating now heats the battery, and even if I let it go for 20-30 minutes, the consumption is totally reasonable and expected. It's only when the battery is super cold that the apparent consumption is absurd.

 

[AlanSubie4Life]

It's only when the battery is super cold that the apparent consumption is absurd.

Genuinely curious about how this all works. I think you could do a scientific experiment and use the heat, to make sure rated miles work correctly. You can even preheat. Just have to take that picture immediately as you put it in drive and immediately after you stop.

Generally my sense is that it sounds like everything is perfectly accounted for. But would have to gather data to be sure.

As I said, if anything, I suspect rated mile use will be lower than expected, when looking at kWh used, in these conditions. But no way for me to know; it is just my guess. I guess it is slightly off topic but I guess on topic it would be interesting to see how high that warming and battery warming drives that inverse velocity term.

 

[ZOMGVTEK]

Sure, so just reset a trip meter? The weather is kinda nice right now, so the pack takes a long time to cool down. I’ll wait for a day that’s super chilly with good snow and won’t preheat.

 

[bedoig]

I can't imagine that it would be engaging the front motor at those speeds unless you are accelerating. Even at 350Wh/mi at 85mph, that's only 28kW, which the rear motor is easily able to produce. In this speed area though, aero losses are really going to be dominant, even in winter time, so your efficiency in Wh/mi will be going up with pretty close to the square of velocity. The baseline 70-100Wh/mi is still there, but the term proportional to 1/velocity due to accessory use has really become very small at that speed.

Can't really explain why it wouldn't be even more noticeable on a single motor car, though (it should be, since the baseline rolling resistance is really low on those cars!).

The front motor is powered when warming the battery and makes a distinctly more noticeable whine, but I can't hear it over the road noise past 35-40 mph. I've observed both motors pulling 3 to 3.5 kW while conditioning for supercharging even while parked.

 

[tivoboy]

I think I recall somewhere that the most efficient speed for the M3 is 31 mph. At that speed the WHm per mile is like 110-120. that should give one over 600 miles of range. I've managed to get even lower WHm by really working on the hypermiling and curves and leveraging slight changes in elevation as much as possible, but it's not sustainable on a flat surface of course.

 

[QS01]

I think I recall somewhere that the most efficient speed for the M3 is 31 mph. At that speed the WHm per mile is like 110-120. that should give one over 600 miles of range. I've managed to get even lower WHm by really working on the hypermiling and curves and leveraging slight changes in elevation as much as possible, but it's not sustainable on a flat surface of course.

I believe the record was set at 606 miles at a speed between 20-30 mph over 32 hours (no A/C). Average of 110 wh/m

 

[AlanSubie4Life]

I believe the record was set at 606 miles at a speed between 20-30 mph over 32 hours (no A/C). Average of 110 wh/m

I checked this again today - it was 19mph (32 hours), as I said above (I assume they drove continuously since that would make sense!). If you look at my model it is not far off. I don’t have the minimum calculated but you can plug it into Wolfram Alpha and it will tell you.

 

[AlanSubie4Life]

I've observed both motors pulling 3 to 3.5 kW while conditioning for supercharging even while parked.

Sure, but other than conditioning for Supercharging does this happen any other time? (I have zero experience with the cold obviously...but it seems like it would not be very beneficial from an efficiency standpoint to warm the battery unless you needed it warm. I understand it lowers resistance (and is required for charging and regen) but it would take so much energy to warm it...). It sounds like the answer is yes based on @ZOMGVTEK comments, but how do we know the battery heater is on for his case?

 

[AlanSubie4Life]

Sure, so just reset a trip meter?

You should be able to do the “Since last charge” or just use the standard “since time x” meter, which is from the last time you sat in the driver’s seat (it restarts when you leave the seat, though the last result is visible until you next exit Park). But you could reset a trip meter if you have multiple short segments. But then you have to be careful...because it doesn’t count energy use when you’re in park. So you have to take pictures at the beginning and end of each segment which is basically a huge pain. Anyway, you mentioned a specific segment so it seems fine to wait until it gets chillier and then take careful pictures for that single segment, being careful to only track the start and end miles from when you enter drive until you enter park (and not from any time outside of that where there could be significant power consumption which is not counted). Ideally, you start with a deep snowflake and maybe end without one. Be sure to capture miles before and after; % is not useful.

 

[ZOMGVTEK]

My car only heated the battery while driving once, and I’m not really sure why. It was chilly, but not all that cold at the time, and I think the car was parked for a day or two beforehand. I preheated it from the app for a few minutes, and it continued heating during the drive. You can tell since the car drives differently while heating, you can hear the inverter carrier frequency in the front motor, and the drive unit oil pumps buzz like crazy. The car appears to limit peak power while heating, and when approaching zero the car is very rough and sometimes abruptly stops from ~1mph. If you navigate to a nearby supercharger and exit the car without opening the drivers door you can hear it. The pumps ramp up as the motor stators heat, it takes maybe 30-60 seconds to hit full speed. But the buzzing starts immediately and it’s fairly noticeable. It now also does this when you turn the keep climate on, and starts when you exit the car and shut the door. It heats until there’s maybe 3 regen dots most of the time. It’s pretty aggressive with the heating now, so the pack temperature is much less commonly an issue unless the car sits a while and I don’t preheat. I wish it would just go ahead and preheat while driving when there’s near zero regen. The car drives like garbage when the pack is super cold, it’s worse than the Leaf. I assume this is an efficiency thing mostly, since the motors are used to heat the singular glycol loop. The entire motor casing, contents, and oil needs to be heated. So at speed the chilly air really pulls most of the heat out before the little heat exchanger has a chance to dump it into the main loop. When parked it works well though.

 

[AlanSubie4Life]

What is so bad about the way the car drives when it is really cold, exactly?

The pumps ramp up as the motor stators heat, it takes maybe 30-60 seconds to hit full speed. But the buzzing starts immediately and it’s fairly noticeable.

It heats until there’s maybe 3 regen dots most of the time.

I have noticed the spool up of that pump (but I don’t hear the associated pre-heat motor noise at the same time). However, when I am at a fairly high SoC, the front motor sounds a bit louder anyway (presumably due to the higher voltage...but it definitely isn’t preheating for this specific motor noise; it is a bit different noise).

Generally I do notice this louder pump sound when I am 1) at relatively high SoC and 2) I ask a fair amount out of the car from the beginning. Generally I feel if I don’t give it the beans, it won’t tend to spool up the pump.

I’ll have to pay closer attention to exactly when I hear this noise, in future. Of course, I never preheat my car and I would not even know how to tell from the app that the battery is being pre-heated (never paid attention in SD of course). When driving, I’m reasonably sure I could reliably tell if the motor is being used to heat the pack, as I am fairly familiar with that noise, from some of my more recent Supercharging events.

The pump spool-up is something related, but different AFAIK. Maybe it only spools up the pump if there is actually excess heat that can be used to warm the pack (that would make sense)?

Again, I have a hard time believing it is energy efficient to warm the pack. It makes sense if the car is plugged in of course, but I can’t imagine it’s a net win otherwise.

I could imagine they might make efforts to shunt waste heat to the battery at relatively high SoC, if there is limited regen. That results in pump spooling. But in my modest temps, it doesn’t seem that it is cold enough to require actual supplemental heat by running the motors non-optimally to generate heat (and again, I’m not convinced it is beneficial to do so unless the car detects it is being driven aggressively).

It seems like a complicated problem to determine the optimal course of action, and I would not be surprised if the behavior is dependent on driver demands on the vehicle.

 

[bedoig]

Sure, but other than conditioning for Supercharging does this happen any other time?

No idea, I don't have a lot of experience in real cold either, but thought it could explain what was being seen/heard.

 

[ZOMGVTEK]

What is so bad about the way the car drives when it is really cold, exactly

Quite a few relatively minor things I had hoped would be less noticeable. The windshield defroster isn’t terribly powerful, the coverage is average at best and the air temperature isn’t super high when it’s cold outside. I presume this is a bad sign for how it’s going to perform in the occasional double digit negatives. It takes a fair while to clear the windshield and it appears to fog up much more often than most cars. The auto mode appears to try and combat this with intermittently moving air to the defroster and hammering the fan speed before going back. But its apparently temperature dependent, and when set to HI if it’s cold outside, the air temperature exiting the vents isn’t great when in auto since it wouldn’t let you put in in recirc before. They changed this in a recent software update and you can use recirc in auto now, but it’s been warm lately so I don’t know if this helps. In cold weather the HVAC is very loud when set to HI since it appears to need to run very high fan speed for full heater power, possibly to limit the peak temp the heater is exposed to? Either way, the separate coolant loop with a conventional heater core would easily maintain full heater power at a low and quiet fan speed. I’m not sure if this is a design choice or limitation. You can only get high air temperature from the vents in some conditions, and the heater isn’t powerful enough to do this at any reasonable fan speed when pulling in cold outside air. But when you put it on HI, it really just targets 82 and the air temp from the vents is controlled to maintain cabin temperature. When the battery is very cold, the throttle feels very slow like it’s in chill mode. The power has an apparent ramp to it, but maybe it’s just me and it’s slow AF. Either way, the car feels slow with a very cold battery, not like ‘slower than usual’ slow, but really kinda slow and bland. The vehicle dynamics fall apart on the dual motor with a cold battery. Some of the surfaces take longer than other cars to come up to temperature, even on HI. The headlights are apparently far more efficient than the ones in my Leaf, since they never melt ice. The total lack of regen with a cold battery kinda sucks too, and the brake pedal does a clicking thing when you press it under light regen when cold for some reason. My Leaf did this as well, but it was only once after turning the car on with a cold battery and much worse. It appears to be the brake booster doing some sort of adjustment, but I don’t see why.

Mostly, I would like the heater to be more powerful, allow much higher vent air temps, allow for cabin temps significantly beyond 82, have less noticeable power limit and more regen with a cold battery. They did massively boost power with a cold battery a bit ago, I think it was V10. It’s much improved, but still kinda bland driving when cold. If you’re driving slow, you probably wouldn’t notice any difference though, so this isn’t really a problem for the majority. And at least now they’re allowing for auto pack heating without having to live near a supercharger and map to it. This helps a lot since the pack takes a bit to cool down, and even after a few hours it’s usually OK if it was warmish earlier. It’s SUPER clear when the dual motor is heating the battery. Press the preheat button in the app and the drive units come to life, and start buzzing and whirling. It stops when you open the drivers door, and if you press the brake pedal too fast the front drive unit is disabled and shows turtle mode.

 

[AlanSubie4Life]

And at least now they’re allowing for auto pack heating without having to live near a supercharger and map to it. This helps a lot since the pack takes a bit to cool down, and even after a few hours it’s usually OK if it was warmish earlier. It’s SUPER clear when the dual motor is heating the battery. Press the preheat button in the app and the drive units come to life, and start buzzing and whirling. It stops when you open the drivers door, and if you press the brake pedal too fast the front drive unit is disabled and shows turtle mode.

Thanks. But as you stated above, this pack heating does not occur when driving (unless going to a Supercharger), right? For the purposes of the model, I'm trying to figure out whether there is ever a case when we need to add that ~6kW of power to the "accessory" use coefficient in the model (except when navigating to a Supercharger of course).

If there were, we could get accessory use up to something like 15kW worst case. And I think that would make the "optimal efficiency" speed something like 65mph! Of course, that would only be temporary (the 9kW heat + AC could be a steady state 9kW in frigid temperatures but I doubt the battery would need continuous 6kW of heating even in extreme cold).