Nav on AP and Vampires

February 3, 2019

Time to provide some Tesla observations for my friends and family. This blog commentary speaks to two separate issues/features: charge retention and Navigation on AutoPilot.

Charge Retention

We had planned a long January 2019 vacation about two years prior. We knew would be away from home for 17 days. No one would be driving our EVs nor recharging the batteries. An option to leave both vehicles plugged in was overturned, considering the remote possibility of spurious electrical spikes during our absence.  There was no sense in taking chances. Better to leave the cars unconnected to any charging system.

I expected some loss of battery energy (vampire drain) or phantom discharge while just sitting in our unheated garage. But with a reasonable charge at the start of our vacation, I’d expect plenty of energy to be retained through our absence.  I equate battery energy with calculated or expected mile range, since that is the primary purpose of the battery.  On Day 0 of the test, the Model S had 203 miles calculated range and the Model 3 had 263 miles calculated range. 

I expected both cars (Model S and Model 3) to behave similarly. Both battery packs are rated at 75 KWh.  Different design years, vehicle weight, and different motor styles mean different mile range capability. The charge loss at rest should be similar, so I thought.

The phenomena of phantom loss is known. Vampire circuits and devices pull current from the battery. Every time I logged into the Tesla app, I am “waking up” both cars to interrogate their status. The onboard computers read out basic vehicle parameters: range available in miles (battery charge capacity), internal car temperature, lock status, location, controls, and service scheduling options. Waking up the computers consumes battery capacity.  It is also possible that the cars may be attempting to download map updates via WiFi.  All activities that may drain battery current.

During our vacation absence, I periodically logged into the Tesla app and extracted the expected mileage range of both cars. The plot of this data is below.

What was surprising was the rate of loss difference between the two vehicles. The Model 3 lost approximately 30% of it's expected range, or 5 miles range per day of dormancy.  The Model S lost 16% of its expected range, or only 2 miles range per day of dormancy.  What would cause the Model 3 to lose at a faster rate than the Model S?  And why is the rate of loss flat on the Model S for the first 8 days and then essentially matching the Model 3 rate after day 8?

Some have speculated that the newness of the Model 3 may have the battery system settling in or calibrating.  I'm not sure that I buy this.  The Model S has a setting for Energy Saving that I had not activated during our vacation absence (forgot) which has been eliminated on the Model 3.  I'll need to do a bit more research into this puzzlement.

Navigate on AutoPilot

Today we took the Model 3 (Erik the Red) on a quick road trip to Milwaukee. We started with a full charge - expected mile range of 306 miles. The temperature was about 45 F. The round trip was 183.8 miles, and the end of trip “calculated full range capability” was 232 miles.  Since actual range efficiency is affected by external temperatures, I expect a reduced range at the lower temperatures. The calculated reduction in range was roughly 25% due to the lower temperatures.

A new feature added to the Model 3 several months ago is Navigation on AutoPilot. This feature lets the onboard computer system merge the “navigate to” location with the AutoPilot feature. After selecting the target end destination, the computer paints a blue path to follow when AutoPilot is engaged.  

But in addition to the convenient ease of AutoPilot drive “without hands”, the Navigate on AutoPilot  feature recommends lane changes based upon the navigation path. The feature recommends an action, requests driver confirmation, and executes if confirmed. The computer system looks at the road, senses vehicles nearby, judges whether a lane change is needed and actually executes the lane change without additional driver involvement. Blue lines on the car/road image on the monitor indicate what is happening on the road. Simple.

On the cars monitor below, the left-hand side of the display shows the red Model 3 with a blue path.  The feature is actually indicating that the vehicle should change to the right-hand lane (shown with a grey path shifting to the right).  The navigation path was indicating an right off-ramp change in direction.  The car will automatically make this lane change after driver confirmation (note the Confirm lane change note below the Model 3 image).

In general, the new feature was quite good. It recommended lane changes at several interchanges, and executed flawlessly. The challenge was with ongoing road construction that caused lane restrictions and narrowing. This always complicates the AutoPilot feature.  

It comes down to a confidence in the system.  With miles of driving using the AutoPilot feature, I have become quite confident in it's capability.  The AutoPilot 2 enriched capability with the Model 3 (more cameas and sensors) makes the AutoPilot performance even more exact.  The Navigation extension is natural, given the strong GPS function in the Tesla.  Time will provide more driver confidence and vehicle knowledge. 

Made the trip to Milwaukee and back without the need to SuperCharge along the route.  This is thanks to the longer range capability of the Model 3.

By the way, the Milwaukee Art Museum (MAM) is a wonderful destination.  Great architecture housing many interesting and well-known pieces of art.  Plan a visit at your earliest convenience!

MAM Calatrava wing exterior design 

MAM hallway to exhibitions

Eastward view of Lake Michigan

A few pictures of the collection