RWD on route battery warming vs AWD

[SigNC]

So we went on medium length road trip on the weekend. I left the house at 100% charge from the triangle area and my garage was about 55 degrees when i left going by the temp the car displayed when i left. shortly into the the drive i had full regen and the on route battery warming didn't really pop on until about 15 minutes before we got to the supercharger on route. When I plugged in however at about 25% charge i only pulled about 100kW. We had driven a little over 2 hours at interstate speed, had about 15 minutes of on route warming and initially left with a battery at 55f. IMO it seems like we would have a plenty warm battery for full speeds. I tried 3 different stalls as I was the only one charging and they all had about the same speed. After I landed on the 3rd one and decided it wasn't the stall another 3 pulled in, dual motor, and plugged in and pulled 145kW right at the start.

On the way home, inverse of the trip we started off with a very cold battery, about 25f, and drove for a little over an hour before we got to the supercharger. However, this time the on route battery warming kicked in almost immediately and was on for over an hour before we got there. Again however, the car only pulled about 100kW at about 25% charge.

So my question, any thoughts on if the car is smart enough to start battery warming earlier in a rwd than an awd since it, from what i've read, has about half the heating power? I have a fairly early model # and I know there have been some charging pin updates so i'm going to get those looked at as well but just seems like it must be more temp related since we've never had issues chaging before unless it was cold.

 

[derotam]

So in the RWD car it only has the one motor to provide power for battery warming. For a recap, it does this by sending a purposefully inefficient waveform to the motor that does not provide motion but gets converted to heat. At a standstill, preconditioning will push up to approx 3.5kW max to the stator in order to provide battery heating. While moving, evidently, is seems it might be hard to mix the motion and non-motion power waveforms, so as you speed up the battery heating waveform is reduced.

Now in an AWD vehicle, the forward motor is not used a lot in "normal" driving conditions, so you can still get up to that 3.5kW heating power to the front motor.

To your question about starting the warming earlier in a RWD vs AWD, it is a good idea, but the way the warming power is reduced/non-existent at highway speeds in a RWD vehicle, it wouldn't matter much.

Here are some graphs of some data I have captured...

Imgur Time is in seconds, Temperatures are in Celsius. This was a short 3 mile drive, speeds up to 60mph. In the graph notable points are: R Stator temp plateau is me stopped in McD's drive-through. Temperature increases at the end was me initializing Battery Preconditioning(by routing to a supercharger). I would have let it go a while longer but turns out watching Netflix deactivated the routing which in turn deactivated preconditioning, and sorry but watching Netflix on my lunch break was more important then further data.

* Here are two graphs and one spreadsheet. Imgur First one is my first 6 minutes driving this morning, no HVAC, no Battery Preconditioning. Second is next 10 minutes not in motion, no HVAC, Battery preconditioning ON. I then turned on HVAC, turned off BP, and finished my drive to work(about 10 min of 45-50mph with stop lights, 15 min highway 60-75mph, 5 min <20mph). Temp data after I got to work is in the table in the 3rd pic. Speed in Graphs is in km/h here.

 

[SigNC]

Ah that makes a lot of sense RE: getting basically full warming from the front motor at highway speeds vs almost none from rear. Surely 2+ hours of highway driving would be enough to heat a battery up enough for full charging from a start of 55f right?

 

[justsomeguy]

Ah that makes a lot of sense RE: getting basically full warming from the front motor at highway speeds vs almost none from rear. Surely 2+ hours of highway driving would be enough to heat a battery up enough for full charging from a start of 55f right?

The problem is the overall the drivetrain is rather efficient. Any heat generated is waste and is unwanted in most situations. At 60mph for 2 hours assuming baseline efficiency of 240Wh/mi you're expending 28.8kWh of energy. At 85% drivetrain efficiency that's less than 5kWh converted to heat over two hours. Depending on how well insulated the battery is, that's probably not enough to get it warm and keep it there.

Someone is going probably going to correct all the numbers I just threw out because they're probably quite a bit off, but it gives you a basic idea of how little heat is generated in normal driving.

 

[derotam]

The problem is the overall the drivetrain is rather efficient. Any heat generated is waste and is unwanted in most situations. At 60mph for 2 hours assuming baseline efficiency of 240Wh/mi you're expending 28.8kWh of energy. At 85% drivetrain efficiency that's less than 5kWh converted to heat over two hours. Depending on how well insulated the battery is, that's probably not enough to get it warm and keep it there.

Someone is going probably going to correct all the numbers I just threw out because they're probably quite a bit off, but it gives you a basic idea of how little heat is generated in normal driving.

Nope, no numbers correction here, I have no input to that. I do agree that it is very efficient and there is not a lot of waste heat generated.

 

[SigNC]

I will say, when we left on the return trip with a battery at 25f it was able to get the battery warm enough in an hour to get the same charge rate that was seen on the outgoing trip where i drove for 2 hours and left with a battery 30f warmer. who knows. Wish I had an easy way to see the battery temp so I could tell what the limiting factor is. Better yet, it would be nice if tesla told you why you aren't getting full charge rate.

 

[SigNC]

Would be nice if i could toggle on battery warming before I leave via the app to get a head start on the warming.

 

[diamond.g]

I will say, when we left on the return trip with a battery at 25f it was able to get the battery warm enough in an hour to get the same charge rate that was seen on the outgoing trip where i drove for 2 hours and left with a battery 30f warmer. who knows. Wish I had an easy way to see the battery temp so I could tell what the limiting factor is. Better yet, it would be nice if tesla told you why you aren't getting full charge rate.

Are you interchanging C and F in your temps? AFAICT based on Bjorn Scan my Tesla app the batteries like to be ~55C not 55F to get full power charging.

 

[SigNC]

Are you interchanging C and F in your temps? AFAICT based on Bjorn Scan my Tesla app the batteries like to be ~55C not 55F to get full power charging.

no i'm not. I'm saying when i left the house it was 55f I then went on a 2 hour drive and navigated to supercharger which tripped on battery warming. I'm sure it needs to be 55C to get the levels of charging bjorn is seeing in europe but to max out a level 2 charger it shouldn't need to be that high I wouldn't think. Either way, if i started at 55f and drove for 2 hours I'd think it would be at least above 90 with battery warming. Who knows. I need to by a OBD2 module so i can just see

 

[Rogue one]

We own a long range RWD and had to hit a super charger on a return trip today. Left the hotel it was around 30 degrees F out car was cold soaked plugged in the super charger as destination about an hour away started pre condition right away. We drove 75-80 MPH bassicly the entire hour drove and the supercharger topped out at 100KW at 25 SOC so while I love the efficiency of the RWD it does have the down side of being so efficient it struggles to heat the pack when it need to. You can cheat and do some 0-60 hard accelerations but with a car load of people that isn’t something I was willing to do.

 

[SigNC]

We own a long range RWD and had to hit a super charger on a return trip today. Left the hotel it was around 30 degrees F out car was cold soaked plugged in the super charger as destination about an hour away started pre condition right away. We drove 75-80 MPH bassicly the entire hour drove and the supercharger topped out at 100KW at 25 SOC so while I love the efficiency of the RWD it does have the down side of being so efficient it struggles to heat the pack when it need to. You can cheat and do some 0-60 hard accelerations but with a car load of people that isn’t something I was willing to do.

Sounds like you had about the same experience as me.

 

[dontblinkdoc]

Just to add another data point, I have been doing a few drives around -2 C. I still get ~140 kW within a min of plugging in. One trip I arrived to Supercharger with 4% SOC and the second one I arrived with 30%. In both cases I saw preconditioning for roughly 15 min. Car is 2018 LR RWD. The difference might be that i may have been going somewhat above the speed limit (130 km/hr) and I do love a good bout of acceleration.

Are all these cars in the above examples LR? Your explanation for the difference between RWD and AWD seems plausible (but I know nothing about the tech), but it doesn't seem to match with my experience (unless the difference had to do with speed).

 

[camalaio]

Missed this thread the first time around, but another datapoint to add:

LR AWD. -10C (14F), but the battery was probably at +9C (48F) at departure due to garage parking. Set destination to Supercharger just over an hour away and took backroads to get there (less traffic to deal with, more fun in the snow). Even with a lot of accel/decel due to backroads and it preconditioning all but two minutes of the drive, I arrived and it struggled to hit 110kW. It was almost warm enough.

Turns out it takes a lot of energy to heat a 1000lb battery by a very large amount in cold weather. I expect the smaller SR+ pack would make up for some of the difference of not having effectively two heaters.

 

[ralph142]

some more variation:

LeMR, rwd. last saturday, cold soaked pack 45F ambient. 10 min / 30 mph trip to sc, 15-60 % charge, never cracked 100 kw. 3 hrs later, after some stops, ambient down to 35/ snowing. Nav on to next sc, preheat on for the last 25 minutes at 65-70 mph, arrived with 12%, hit 145 kw immediately. Charged to 60% had tapered down to 100kw. different SCs since this was a one leg trip.