Reserve after "empty"

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KarenRei

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#1
So, I got a bit of flack the last time I suggested this - but good to see that it's confirmed:


That said: don't chance it, of course. Charge estimation is a tricky task (particularly if you don't hit charge extremes very often); there's not even any guarantee that you'll make it all the way to 0%, let alone below it.
 

SoFlaModel3

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#2
So, I got a bit of flack the last time I suggested this - but good to see that it's confirmed:


That said: don't chance it, of course. Charge estimation is a tricky task (particularly if you don't hit charge extremes very often); there's not even any guarantee that you'll make it all the way to 0%, let alone below it.
it makes sense that there would be a reserve. People like to somehow run out of gas in ICE cars even with stations literally everywhere. :)
 

KarenRei

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#3
The problem has been that occasionally someone reports running out above 0, or exactly at 0, and people interpret that as meaning "there's no buffer". What it actually means is "charge estimation is difficult". Some people might go 30 miles after it reads 0. Others might run out of charge with 10 miles left showing. It's just how it is. The more frequently you charge high and run low, the more accurately it'll be able to estimate, but it'll never be perfect.

But, in general, it should go 5-15 miles below 0.
 
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#4
So this below zero reserve might be 1-4 kWh. If the battery is 80.5 kWh total, 75kWh is usable and there's not top end buffer, then the bottom end buffer is 1.5-4.5kWh. Does that sounds about right?
 

roflwaffle

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#5
So this below zero reserve might be 1-4 kWh. If the battery is 80.5 kWh total, 75kWh is usable and there's not top end buffer, then the bottom end buffer is 1.5-4.5kWh. Does that sounds about right?
Yup. The only thing I can think of adding is that available battery capacity is a function of the average discharge rate. If someone drives on the slow side, ala the EPA range test, they'll likely get +/- 78 kWh out of the pack, just like Tesla did on the EPA range test. If someone drives on the fast side, they'll likely get less than 78 kWh out of the pack, and how much less depends on how much higher the current draw is because they're going faster.
 
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#6
Yup. The only thing I can think of adding is that available battery capacity is a function of the average discharge rate. If someone drives on the slow side, ala the EPA range test, they'll likely get +/- 78 kWh out of the pack, just like Tesla did on the EPA range test. If someone drives on the fast side, they'll likely get less than 78 kWh out of the pack, and how much less depends on how much higher the current draw is because they're going faster.
How would you explain the recent hypermiling test in Colorado where the guys went ~25mph over more than a day but only got 66 kWh from the battery?
 

roflwaffle

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#7
How would you explain the recent hypermiling test in Colorado where the guys went ~25mph over more than a day but only got 66 kWh from the battery?
I'm not sure offhand. They didn't use anything to measure current/voltage, and the onboard energy estimates could be off. Or there may have been some issue with the battery that cut their run short. Or something else?
 

SoFlaModel3

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I'm not sure offhand. They didn't use anything to measure current/voltage, and the onboard energy estimates could be off. Or there may have been some issue with the battery that cut their run short. Or something else?
Well something is definitely wrong as the car won’t charge now and has been sent to Tesla service.
 

littlD

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#9
Just wondering about that "it won't hurt the pack" statement...


And that makes two members of #TeamMidnightSilver flat bedded... Although I didn't run Middie down to 0%, I just did a manual update after driving her home on Delivery Day.

UPDATE: Middie is still unresponsive after 5 hours of Engineering trying to figure out why. Seeing that it started with the manual update, I'm thinking it's firmware that just needs to be reset. But Engineering is trying to get to root cause, which I support. Don't want others having similar issues.
 
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KarenRei

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#10
Just wondering about that "it won't hurt the pack" statement...


And that makes two members of #TeamMidnightSilver flat bedded... Although I didn't run Middie down to 0%, I just did a manual update after driving her home on Delivery Day.
I imagine that they're been *very* few people outside of Tesla to flatline a Model 3 before. Tesla will make good use of this data to improve charge measurement on slow drains and prevent whatever is stopping the charge.
 
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SimonMatthews

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#11
Well something is definitely wrong as the car won’t charge now and has been sent to Tesla service.
Years ago, there was a story published that the Roadster battery pack would be permanently bricked by running it flat. There were multiple reports of this, but they all went back to the one story.
 

SoFlaModel3

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#12
Years ago, there was a story published that the Roadster battery pack would be permanently bricked by running it flat. There were multiple reports of this, but they all went back to the one story.
I definitely remember that or something like that. Basically — never go to zero is locked into the back of my mind :)
 

littlD

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#17
Surely there's a HV-12V converter onboard...?
I'm not sure about that.

Here's what the owners manual says concerning what happens to the 12V battery under low battery conditions if Model 3 has been sitting for a long time.

NOTE: The battery it mentions being damaged is the 12V battery, not the 75kwh battery pack:

"Discharging the Battery to 0% may permanently damage the Battery. To protect against a complete discharge, Model 3 enters a low-power consumption mode when the charge level drops to 5%. In this mode, the Battery stops supporting the onboard electronics to slow the discharge rate to approximately 4% per month.
Once this lowpower consumption mode is active, it is important to plug in Model 3 within two months to avoid Battery damage. Note: When the low-power consumption mode is active, the auxiliary 12V battery is no longer being charged and can completely discharge within 12 hours. In the unlikely event that this occurs, you may need to jump start or replace the 12V battery before you can charge. In this situation, contact Tesla."