My potential charging miles disappeared

[larrykoch100]

Not a good title but anyway. I charged at my cabin at 249 miles. Leaving it going downhill usually adds about 12 miles to my range if my battery is low. At the bottom my miles still said 249. Were the braking charge mile just ignored? Where did they go.
What I could do is to increase my charging miles say to 265 and recover the 12 miles. That's a hassel so I proably won't. Any suggestions?

 

[Rocky_H]

Jeez. This was certainly different than I was expecting. Usually these threads are about "my rated miles are decreasing faster than real miles". I think this is the first time I have seen someone's complaint be that their car is not gaining miles!

But now to give some answers to this. They've always built in a little fudge factor on that display to make it act mostly like a fuel gauge. They don't want it acting flaky and jumping up and down based on going a little bit uphill or downhill, so they just will not show every single 1 rated mile of increase. They save it up a bit. On my 2014 Model S, I have been able to see this for years. On a long downhill, the display will just sit there at the same number for quite a while, with it being blocked from showing an increase until it gives up and realizes there is enough to make it worthwhile, and it will jump up by 3. And then after a while, it will jump up by another 3-5 or so. So the car is built with some logic to save them up a little bit.

But now about your 12 miles:

Leaving it going downhill usually adds about 12 miles to my range

You say "usually". In what months were you "usually" seeing this? Do you see where I'm going?
What was the temperature back then when you "usually" saw it gaining more miles? Is it colder now than it was back then, where you might be using up more energy from running the heat in the car? You say it's a long downhill from your cabin, so your cabin is at high elevation, so here at the end of September, it's getting colder up there.

People new to electric cars don't usually realize this. That display isn't just "miles". That is a measure of all energy in the battery that has to supply everything. There isn't a really hot engine to siphon heat off of, so for heating the cabin, it's like running an electric space heater. And that's not just for the cabin. It's warming up the battery pack some too. So the battery is having to supply energy for HEAT + MILES. So that's where your 12 rated miles went that you were expecting to have.

 

[Gasaraki]

If you moved 12 miles and your charge level stayed the same, doesn't that mean you "charged"?

 

[Rocky_H]

If you moved 12 miles and your charge level stayed the same, doesn't that mean you "charged"?

No, this is about continuous downhill. You could sit in a little red wagon and go down the hill for 12 miles, and it wouldn't be getting charged. So even with no regen at all, the display could stay the same. This is asking about: since there IS some regen effect, where is it going?

 

[larrykoch100]

@rocky For years I have charged at home so when I go to cabin the battery was always low so with 100% consistency I always saw a gain of about 12 miles with the regular 3 mile jumps. My tier 3 electric skyrocketed so I decided to charge at my garage and over two separate days the downhill didn't add to my 249 full tank. At the bottom the tank should have read 262. The 12 missing miles weren't hidden somewhere becasue on the flat my tank immediately started lowering from the 249 base.

 

[AlanSubie4Life]

The 12 missing miles weren't hidden somewhere becasue on the flat my tank immediately started lowering from the 249 base.

I think @Rocky_H is simply saying that you probably used that energy for something else, on your last two trips. The test to do would be to turn off the HVAC entirely (or at least ensure that both heat and AC are off) and redo the experiment.

12 displayed rated miles in an LR AWD is about 12rmi *(230Wh/rmi) = 2.76kWh

This is what you will gain by descending about 1700 feet in an LR (unrealistically assuming no losses - probably more like 2k feet). Obviously the height in your case is greater than this, since this number assumes zero miles are traveled.

What is the elevation of your cabin relative to your chosen hill end point? (Pomona is at about 1000 feet I think.)

What is the distance from your cabin to the bottom of the hill?

Did you carefully check your miles display before you left the cabin to be sure it actually charged to 249rmi?

In any case, let's say it was a 20-mile downhill drive at 50 mph. That's 24 minutes.

To use 2.76kWh in 24 minutes that would be 2.76kWh/0.4hr = 6.9kW

That's definitely high for heat use in California at this time of year. But it is possible. If the time is different (let's say it takes 48 minutes to drive down), then 3.5kW could be a reasonable number on a chilly morning drive down from the mountains.

 

[larrykoch100]

13 miles from my cabin at 5280' (chimney anyway) to Starbucks in San Bernardino, about 1100' I drive at night, midnight to 4am, to avoid traffic. No systems running because its about 60 degrees. My tier 3 electric jumped becasue of running AC in Pomona because of multiple 100 degree days. I actually saw 121 temp on the Tesla, but I think the oficial estimate was 119, keeping us out of the record books.

 

[AlanSubie4Life]

13 miles from my cabin at 5280' (chimney anyway) to Starbucks in San Bernardino, about 1100' I drive at night, midnight to 4am, to avoid traffic. No systems running because its about 60 degrees. My tier 3 electric jumped becasue of running AC in Pomona because of multiple 100 degree days. I actually saw 121 temp on the Tesla, but I think the oficial estimate was 119, keeping us out of the record books.

Check your trip meter next time! If you typically add 12 miles on the trip, it should read roughly:

-12rmi*230Wh/rmi/13mi = -212Wh/mi

Since your rated mile display was unchanged on these particular trips, it should have read ~0Wh/mi.

I can't explain where all that energy went, but it went somewhere. It's too much to be explained by AC use, unless you take 2 hours to drive the 13 miles. Either that, or it's possible your car was not charged to the initial value you thought.

I'd just double check the starting and ending miles on your next trip, right before exiting park, and right after entering park. And look at the trip meter results too. As @Rocky_H has indicated, the miles tend to get banked in 3-4 mile increments during regeneration, but this is not the core issue here as has been discussed already. I am not sure whether an unbanked amount of energy (if there is some that has not yet been added) gets added when you transition to park. (This is important for aligning the trip meter & understanding the consistency with the rated miles number.)

 

[Rocky_H]

midnight to 4am, to avoid traffic. No systems running because its about 60 degrees.

I'll bet the battery heating is running, though, and that's not a system you get to see or control except in the observed efficiency numbers.

 

[webbah]

I'll bet the battery heating is running, though, and that's not a system you get to see or control except in the observed efficiency numbers.

You can see a lot of detail if you install the right adapter and a bluetooth OBDII diagnostic dongle to the diag port and use ScanMyTesla on Android or iOS. With the Model 3 PVC heater and depending on weather conditions and what temp you are trying to keep the cabin at (if in Auto) the PVC heater can use 2-6 kW power.

 

[AlanSubie4Life]

I'll bet the battery heating is running, though, and that's not a system you get to see or control except in the observed efficiency numbers.

Definitely a possibility. If it was truly 60 degrees at the top (I can't imagine it being much cooler than that at 5300' right now), it seems a bit unlikely though. Unless perhaps you're navigating to a Supercharger and it want to prewarm? Doesn't sound like that's what was going on here though.

Maybe it attempts to heat the battery if it starts encountering limited regen on the downhill?

 

[smatthew]

With the Model 3 PVC heater and depending on weather conditions and what temp you are trying to keep the cabin at (if in Auto) the PVC heater can use 2-6 kW power

Perhaps you meant PTC, not PVC?

 

[webbah]

Perhaps you meant PTC, not PVC?

Indeed. Brain fart.

 

[TheRFMan]

@rocky For years I have charged at home so when I go to cabin the battery was always low so with 100% consistency I always saw a gain of about 12 miles with the regular 3 mile jumps. My tier 3 electric skyrocketed so I decided to charge at my garage and over two separate days the downhill didn't add to my 249 full tank. At the bottom the tank should have read 262. The 12 missing miles weren't hidden somewhere becasue on the flat my tank immediately started lowering from the 249 base.

Seems fairly straightforward to me. Previously, you charged at home at the lower altitude, drive to uphill to your cabin without charging once there, and left the cabin with a fairly depleted battery and regained charge via regen on the way down.

Now, because of high electricity rates at home, you decided to charge at the cabin, leaving for the downhill trip home with a full battery.

The issue is that you can't add energy to a battery that's already full, and likely didn't regen at all on the way down. Any deceleration required to maintain constant speed would have been done of by the friction brakes. As you said, you left with a "full tank". You can't fill the tank to more than its capacity.

If you want to make use of regen energy capture on the way down, don't charge to 100% at the cabin. Charge to 80 or 90%, and leave some room in the battery for the energy from the downhill regen.

 

[Rocky_H]

@TheRFMan Oh, good eye! I missed that detail of the variable that changed. I hadn't noticed that he didn't normally charge at the cabin, and now he did. So yes, of course that makes sense that it wouldn't have room in the battery to store the extra energy. And that's not an all or nothing thing either. Regen can be about 30-60kW of recharging power on a pretty steep hill if the battery is warm, so if you have your battery at 80% or 90%+, it just will not allow that high of a charging power, so it might be limiting the regen to maybe 10 or 20kW power, which would probably mean it's supplementing with the brake pads, losing some of that extra energy.

 

[AlanSubie4Life]

I missed that detail of the variable that changed. I hadn't noticed that he didn't normally charge at the cabin, and now he did.

Sometimes these questions are like brainteasers...."Where did they bury the survivors?"

I just figured that if the OP had been riding the brake on the way down they would have noticed and said something. Clearly not!

It also seemed like he had a new car with only 14 posts, and 249 miles would have been ~80% SoC. But clearly he may have a 2019, and is a very infrequent poster, and that's more like 85-90% on an older battery.

So certainly 90% at the top of a 5000-foot descent would explain it. Even 80% could relatively quickly max out regeneration due to saturation of the anode with ions, with no battery warming, even with temperatures in the 70s to 80s.

 

[TheRFMan]

I just figured that if the OP had been riding the brake on the way down they would have noticed and said something. Clearly not!

Perhaps not as noticeable with TACC/Autopilot on?

 

[AlanSubie4Life]

Perhaps not as noticeable with TACC/Autopilot on?

Yeah, entirely possible, though frankly on those mountain descents it would be pretty darn unpleasant to try to use either TACC or Autosteer.

 

[drtimhill]

No, this is about continuous downhill. You could sit in a little red wagon and go down the hill for 12 miles, and it wouldn't be getting charged. So even with no regen at all, the display could stay the same. This is asking about: since there IS some regen effect, where is it going?

As other note, the car is still using power for various systems even going downhill (heating, computer, lights etc etc). So depending on environment the regen energy might be going to those systems.

 

[AlanSubie4Life]

(heating, computer, lights etc etc)

Heating/cooling (battery heating and cabin heating) is the only consumption item that is of any significance here. All the other systems' power requirements are quite negligible for the numbers we are talking about here. (The net power generation for the OP on his typical drive was something like 8kW average.)

Computer, lights, are not zero, but they can be neglected for this particular discussion.