What exactly is "preconditioning" and how does it actually work?

What exactly is "preconditioning" and how does it actually work?

I apologize in advance if this has been discussed to death already, but I have searched the forum threads, used volkerize and read the owners manual and can’t figure out precisely what “preconditioning” is and how it works.

I am preparing to take my first long trip in my P85D away from supercharges and want to maximize my driving range, so I want to do everything “right”.

There are two different things people seem to conflate (or perhaps they are the same?) when discussing preconditioning: 1) Getting the cabin to a comfortable temperature before leaving and 2) Getting the battery to operating temperature before leaving

I’m not concerned about #1 – my car is in a garage at 55 degrees and I can use the phone app to set the temp a bit before I leave and will be fine.

#2 is where I would like a lot more specific information. Threads indicate warming can occur from driving the car, charging the battery or by the onboard warmers. It appears to be far more power intensive (one thread indicated the draw could outstrip a 40A connection) and potentially a big contributor to initial power use.

Suggestions in threads range from:
• Timing charging so the car hits 100% just seconds before you get in and drive off
• Warming the cabin up to 70 degrees an hour early and this warms the battery as well
• Get in the car an do something to wake the car up
• Just leaving the car plugged in overnight (this one doesn’t seem correct to me)

1) What is the “preconditioned” operating temperature of the battery?
2) Assuming the garage and battery are at 55 degrees, how much energy is expended to warm the battery?
3) Does charging the battery always get the battery to operating temperature? Or only if it’s for long enough and the outside temp isn’t too low? For example, is saving the last 10% of the charge for just before you leave sufficient or might that not fully warm the battery?
4) Does preconditioning get the battery to a minimum temperature or a range of temps?
5) Does charging hit that minimum temp or actually get the battery much warmer than that?
6) Could a big charge actually get the battery warm enough that the battery would need to cool initially using battery power to do that?
7) If the battery is “fully preconditioned”, how much temp does it lose per hour (Assuming it’s in a 55 degree garage)?
8) Does the fact that the car doesn’t seem to take power from the wall until it loses 3% mean you could lose this to preconditioning without taking it from the wall?
9) Once the battery is preconditioned is there any way to enter a "hold" mode when plugged in to keep the battery warm?

I know that I am likely totally overthinking this, but from reading the forums I know there are plenty of smart and dedicated (and curious!) MS owners and I’m betting someone might definitive answers!

Bighorn | March 9, 2015

Short answer is that it shouldn't matter at 55deg. You can judge if the battery is being used to heat itself by looking at the energy "speedometer" at rest or in neutral (with the climate off). There's some correlation between limited regen and a battery needing some warming. Generally, this would start to occur around 50deg. If you don't have a dotted line restricting regen, there's no need to precondition.

DLebryk | March 10, 2015

That's a ton of questions. My experience is from the Chicago area this winter.

Oddly 50-55 degrees is almost the exact spot where you won't spend much energy heating the battery. That's the temperature where things are almost normal.

When it is below 50, more like 45 and a lot colder - the only trick that reliably works is to charge the car to the 85 or 90% level overnight. An hour before you leave, change the charge level to 100%. That will heat the battery some, but not all the way. You will still see some limited regen (that yellow dashed line on the lower side of the speedometer energy side) and the energy consumption chart will show a good sized spike for about 5 miles. If you did nothing and had a cold battery, the car will start out with Regen disabled or limited (the yellow dashed line is very close to the 0 spot). The battery is fully warm when the yellow dashed line is gone. In the cold that can take over 10-15 miles to go away.

Turning on the climate control to heat the interior doesn't do a lot of good to warm the battery.

In the winter, you'll never see the battery getting too warm and trying to cool off from charging.

This also assumes you have 220V at 40 Amps available and aren't trying to do all this with 110V (that won't heat the battery at all).

Range mode helps spread out heating the battery - you won't see a huge energy spike, but will see higher energy use over a longer period of time (in practice that is more efficient than lots of heat all at once from the battery). Range mode only works if you are taking a fairly long trip, like 100 miles. There's no advantage with a short 15 or 20 mile trip.

Your last question 9 - no there is nothing like that. You mostly have to trick the car into getting warm while plugged in.

mclary | March 14, 2015

jeffjo - You answered your own question at the end:

I know that I am likely totally overthinking this

Ask your masseuse!

Brian H | March 14, 2015

CC is now supposed to warm the battery at all settings, but you may have to give it enough time.

inconel | March 22, 2015

I would like to know as well. If the car is plugged into a 110V and I use the climate control from a smart phone app to warm up the interior 1 hour before leaving, does it also warm the battery up allowing the car to start right away without the limited regen yellow line?

Tesltoronto | March 22, 2015

The climate control warming turns off after 30 minutes or so.

I have not found a way to warm the battery - other than to complete the charging to coincide with the the time you are ready to leave.

I just mentioned in another thread that thought I have an HPWC, I charge the car at 30 amps and start the charging around 2 a.m. It reaches full charge around 7 a.m. (for my daily commute) and the battery is warm enough for me to drive away without much loss around 8 a.m.
(I would have adjusted the time to complete the charge at 8 a.m. but I would have to pay a higher rate for the electricity after 7 a.m.).

Brian H | March 23, 2015

Check. Elon said the battery warming now occurred with any cabin heating/prewarming now.

BrassGuy | March 24, 2015

As others have suggested, you won't have a problem at 55 degrees.

The word I've read is that the battery heater and the cabin heater each can take as much as 6kW. On a 40A 240V circuit (9.6kW), that's not enough to power both and the excess would be drawn from the battery. However that much power won't be used unless the battery and cabin are really frozen.

According to the release notes, if the car is plugged in then using the app to preheat the cabin will preheat the battery if needed. It's my observation that the battery heater pretty much gets the regen to about half way, around 30kW. Driving will get rid of the rest of the regen restriction.

If the battery is cold soaked, charging the last 10% may not be long enough to heat the battery completely either. I usually set the charge timer. Each 10% is a bit less than an hour (at 40A), so it's easy to calculate when to start charging. Even 45 minutes after charging has completed, the battery will probably not have cooled too much; so the timing is not that critical.

That leads into the comment about leaving seconds after the charge has completed. All you really want to do is avoid range charging and abandoning the car. If it sits at 100% for a half hour, it's really not going to matter. Obviously the battery will be at optimum temperature when the charge has just completed.

You asked a lot of questions, I'll try to touch some that were not discussed yet:
6) The battery won't need cooling while charging, maybe except during supercharging. I don't know about using 80A, since I don't have dual chargers.
7) At 55 degrees, there may not even be regen restriction. Nonetheless, it will take quite some time for the battery to cool significantly at that temperature.
8) If the car is plugged in, preconditioning will draw power from the wall up to the max allowed with your connection. Using a 110V outlet to preheat will use range. (Speculation, I have not tried this.)

Brian H | March 24, 2015

Sounds about right.

GAGSTESLA | March 24, 2015

Using 120V does not use range. I had a 90% charge, plugged into 120v, no juice moving into the car. Turned on the climate via app and watched the umc come to life when the climate turned on. 15 minutes later, car was nice and warm and still at 243 miles of range.

PV_Dave @US-PA | March 25, 2015

@GAGSTESLA: I think it depends on how much it needs to draw for the conditioning. When I was plugged into 120V last summer at the beach, my recollection is that running the A/C for 20 mins to cool the car off not only drew from the grid, but also pulled a tiny bit from my battery.

Tropopause | March 25, 2015

Also preconditioning requires some sort of patterned driving for the software to function accurately.

JeffreyR | March 25, 2015