Charing strategies for an infrequent driver that drives lots of miles

[shred86]

And by “this thread” I meant: Let the hacking begin... (Model S parts on the bench)

 

[wcorey]

Well, I can address this part, and it's kind of in between. The "otherwise", which you seem to think is a rhetorical that doesn't happen, is exactly what happens in some circumstances, though. People who have connected to something like a low power J1772 station that was only supplying 30A have had it do no charging at all for sometimes a half hour or entire hour if it was far below freezing. It's doing nothing but run the battery heater with that 30A for quite a while first.

The way you stated this shows that you're thinking of it in a binary state:
0 = too cold = no charging
1 = warm enough = charge as fast as possible

It's not like that, because it's a gradual sliding scale of how many amps the battery can safely charge at based on temperature. There is a temperature point below which it is just too cold, and there can be no charging without damage. And the Tesla cars do prevent charging at those temperatures, unlike most other electric cars. But it can get up to a temperature where it can do some slow charging that is below the damage threshold, and that keeps rising to allow more amps as the temperature continues to get higher. That is illustrated in the progress of no regen versus limited regen versus full regen. That is what rate of charging it can allow based on temperature.

Of course the Model 3 has no battery heater. I DO charge using my Prius Plugin's Lvl 2 charger via the J-1772 adapter. What I see is, esp when I connect upon return from a trip the charge rate is generally 21-22 miles/hr if the car is cold it starts at a rate of 3 mi/hr and eventually goes up to maybe 11 or 15 mi/hr. That is, again, no battery heater.

 

[StealthP3D]

I think you could also make the argument your efficiency is better driving with a battery pack that is closer to optimal temperatures and you get full regenerative braking.

I've found that even when the regen is limited due to being parked for hours in the 20's and 30's (degrees F), there is still enough regen for most normal braking. It's rare that I need to use friction brakes, even when regen limited, because I look/plan ahead.

My point is that I don't think avoiding a reduction in available regen is a valid reason for charging in the morning rather than when you get home. Tesla has designed a practical, easy to use charging system, it's best to not overthink it, just plug it in when you get home and go about your other life functions without worrying about your "optimal" charging strategy.

 

[StealthP3D]

Of course the Model 3 has no battery heater. I DO charge using my Prius Plugin's Lvl 2 charger via the J-1772 adapter. What I see is, esp when I connect upon return from a trip the charge rate is generally 21-22 miles/hr if the car is cold it starts at a rate of 3 mi/hr and eventually goes up to maybe 11 or 15 mi/hr. That is, again, no battery heater.

The Model 3 does have a battery heater function and it will be activated whenever the Battery Management System (BMS) determines it's beneficial to heat the batteries. It does this by passing current through the electric inverter and motor such that the motor heats up but does not apply a torque to the driveshaft. As the motor/inverter become warm, it pumps heat transfer fluid through them which carries the heat throughout the battery pack which warms it up.

 

[N..8]

Please don't quote my numbers someone here I'm sure knows them and will post. I think that the battery heat comes on and stays on no matter what until the battery reaches half regen which is about 58 degrees. (Range Mode Off) So timing your charges to end right before you leave with a warm battery does save energy. Battery heater is 6kw I believe.

 

[wcorey]

The Model 3 does have a battery heater function and it will be activated whenever the Battery Management System (BMS) determines it's beneficial to heat the batteries. It does this by passing current through the electric inverter and motor such that the motor heats up but does not apply a torque to the driveshaft. As the motor/inverter become warm, it pumps heat transfer fluid through them which carries the heat throughout the battery pack which warms it up.

Yes, I understand there is heat scavenging.

 

[StealthP3D]

Yes, I understand there is heat scavenging.

It goes beyond simple heat scavenging because it uses the components to CREATE the heat from battery electrical energy (or grid power if plugged in). While it does scavenge waste heat while driving, it also actively heats the battery while parked if the BMS determines it's beneficial to actively heat the battery.

 

[StealthP3D]

Please don't quote my numbers someone here I'm sure knows them and will post. I think that the battery heat comes on and stays on no matter what until the battery reaches half regen which is about 58 degrees. (Range Mode Off) So timing your charges to end right before you leave with a warm battery does save energy. Battery heater is 6kw I believe.

While there might be a scenario in which timing your charging to coincide with your departure might save electricity, in general it will consume more electricity overall vs. charging when your battery is already warm from driving home. That's becasue, in cold climates, your battery will cool off overnight. If it's cold enough in the early morning when your charging might be scheduled to begin, it will have to actively warm the battery before charging at higher cuurrents. However, if you charge upon arriving home, this won't be necessary. Sure, your battery will colder when you depart in the morning but cold batteries are better at supplying current than recieving current (charging). So you can still use a limited amount of regen on a battery that would be too cold to charge at a higher rate. And the battery will be warmed using waste heat from driving it. So evening charging is more efficient in a cold climate than charging right before departure.

 

[wcorey]

It goes beyond simple heat scavenging because it uses the components to CREATE the heat from battery electrical energy (or grid power if plugged in). While it does scavenge waste heat while driving, it also actively heats the battery while parked if the BMS determines it's beneficial to actively heat the battery.

That's good to know...thank you. So, by definition then, by having the Model 3 plugged in it will use wall voltage to keep the battery warm, If not plugged in it will use battery voltage to provide heat to keep the battery warm. Esp in the latter case this contributes to 'phantom' drain then.

 

[Rocky_H]

That's good to know...thank you. So, by definition then, by having the Model 3 plugged in it will use wall voltage to keep the battery warm, If not plugged in it will use battery voltage to provide heat to keep the battery warm. Esp in the latter case this contributes to 'phantom' drain then.

Well, it could, but not necessarily that it will. It isn't going to just keep using energy to keep the battery warm all the time for no reason. It will certainly let it get below freezing without heating it if it's just sitting there off, and it's not trying to charge or anything. But if you plug it in to make it charge, it will have to heat up the battery some to get itself ready for charging.

 

[StealthP3D]

That's good to know...thank you. So, by definition then, by having the Model 3 plugged in it will use wall voltage to keep the battery warm, If not plugged in it will use battery voltage to provide heat to keep the battery warm. Esp in the latter case this contributes to 'phantom' drain then.

As Rocky said, it won't keep the battery "warm" for no reason (the car can be driven with a cold battery). It will only heat a battery if it's asked to charge a cold battery or if it's "super" cold. I don't know exactly where "super" cold starts but it is temperatures most of us never experience.

 

[wcorey]

It isn't going to just keep using energy to keep the battery warm all the time for no reason

Understood. I didn't mean to imply it would. I've seen fluctuating morning battery levels. I've not correlated them to ambient temp. From watching the Ben Sullins show others have too. What I'm not clear anyone's done is correlate drain to external factors. Although I imagine some of these third party programs for iPhone/Android could as they have access to cabin temp. I've only had the car two months now and, in that time, there have been mild days and fridged days. I'd guess come mid Apr or so the behavior will become more predictable. I should look into Tesla API, after all, that's what I have done for 45+ years.