Battery Preheat - Down side

[init6]

That graph appears to show it preconditioning below 20%, or am I interpreting in wrong?

Min SoC was 49% The y-axis is for the speed (unless you're a traffic cop )

 

[GeorgeSymonds]

Isn’t it only Cabin preheat before driving that won’t engage below 20%, similar to sentry mode turning off. I thought this was to protect the state of charge on an unattended car, not to prevent features when you’re driving

 

[Davva]

That's doesn't mean the battery heater is on. Here's a trip where the preconditioning message was on for the whole trip:
View attachment 1020456
Interestingly the state of charge doesn't drop dramatically when the heater is on.

Are you sure? I think that graph is telling us something very different from your summary.

If you look around the middle of the graph there is a section where the speed is jittering around 70mph - I'm looking around the time frame of 12:26 through to 12:40. During this time there is a section from 12:26 to 12:34 where the battery heater is off, and then a section from 12:34 to 12:40 where the heater is on.
It's a little difficult due to the granularity of the SOC graph, but I look at the graphs and see:
Period 12:26 to 12:34, SOC: 56% -> 50% so 6% drop in 8 minutes (no battery heater)
Period 12:34 to 12:40, SOC: 50% -> 43% so 7% drop in 6 minutes (with battery heater)

Assuming 75kwh battery, and same average speed:
No heater: 4.5kwh used in 8 minutes, so 0.5625kwh per minute
With heater: 5.25kwh used in 6 minutes, so 0.875kwh per minute
So around 1.5x energy usage with heater than without.

If you were averaging 300wh/mile without the heater, you'd be then getting around 465wh/mile with the heater on.

I've got a Model Y LR - and that pretty much matches with my experience of what heating the battery results in.

 

[Davva]

Are you sure? I think that graph is telling us something very different from your summary.

If you look around the middle of the graph there is a section where the speed is jittering around 70mph - I'm looking around the time frame of 12:26 through to 12:40. During this time there is a section from 12:26 to 12:34 where the battery heater is off, and then a section from 12:34 to 12:40 where the heater is on.
It's a little difficult due to the granularity of the SOC graph, but I look at the graphs and see:
Period 12:26 to 12:34, SOC: 56% -> 50% so 6% drop in 8 minutes (no battery heater)
Period 12:34 to 12:40, SOC: 50% -> 43% so 7% drop in 6 minutes (with battery heater)

Assuming 75kwh battery, and same average speed:
No heater: 4.5kwh used in 8 minutes, so 0.5625kwh per minute
With heater: 5.25kwh used in 6 minutes, so 0.875kwh per minute
So around 1.5x energy usage with heater than without.

If you were averaging 300wh/mile without the heater, you'd be then getting around 465wh/mile with the heater on.

I've got a Model Y LR - and that pretty much matches with my experience of what heating the battery results in.

Sorry - my numbers will be off, only realised the scale for the SoC graph isn't what the label is. I'll redo the numbers again as the figures I've quoted above aren't correct. However, the ratio should be the same I think (the gradient of the SoC is the important bit, which should remain the same regardless of the absolute numbers I used).

 

[Kenners]

I never seem to get the fastest charge speeds at superchargers anyway, well very rare anything close to the max. So not sure what I’m giving up with preheating. If I’ve been driving for a few hours the battery will already be quite warm, even in winter.

 

[init6]

I wouldn't bother re-doing the figures as there are too many unknown variables such as power, incline, weather etc to make direct comparisons between the parts of the graph.

 

[Davva]

I wouldn't bother re-doing the figures as there are too many unknown variables such as power, incline, weather etc to make direct comparisons between the parts of the graph.

Yup, fair enough.

From my own experience I've seen battery heating for preconditioning take a very significant amount of power. I basically just don't let the car do it anymore.

 

[ewoodrick]

I never seem to get the fastest charge speeds at superchargers anyway, well very rare anything close to the max. So not sure what I’m giving up with preheating. If I’ve been driving for a few hours the battery will already be quite warm, even in winter.

What vehicle do you have and what Superchargers are you using. Are you aware of the limitations of V2 chargers? And what state of charge do you start with?

 

[Kenners]

What vehicle do you have and what Superchargers are you using. Are you aware of the limitations of V2 chargers? And what state of charge do you start with?

Y LR, I am aware if the limitations of V2 etc, just never noticed any real difference in charge speeds from preheating and can’t really see any benefit. It never really hits the max, normally anyway, so battery temp does not seem to matter much. The car charges pretty quickly still anyway. Tbh i don’t really get the obsession with charge speed, I have had more problems with it charging too quickly (have to move car halfway through coffee) than too slowly. I guess its to convince all the people with ICE cars that think they will spend their whole lives waiting for the car to charge.

 

[ewoodrick]

Y LR, I am aware if the limitations of V2 etc, just never noticed any real difference in charge speeds from preheating and can’t really see any benefit. It never really hits the max, normally anyway, so battery temp does not seem to matter much. The car charges pretty quickly still anyway. Tbh i don’t really get the obsession with charge speed, I have had more problems with it charging too quickly (have to move car halfway through coffee) than too slowly. I guess its to convince all the people with ICE cars that think they will spend their whole lives waiting for the car to charge.

A Model Y should absolutely be able to hit 250kW and over 1,000 mph at a V3 supercharger.

You will have to be well below 30% to see this speed though.

If you aren't seeing that speed, then it may be time for a service request.

 

[CyberGus]

Theoretically, preconditioning can be partially achieved without using extra power by simply not cooling the pack, but I suppose that's only useful at higher ambient temperatures.