Cold Weather Observations

[larryh]

The following plot shows kWh/mile vs. outside temperature for my 8 mile city commute to and from work in EV mode.  Climate is off.  At 70 F, it requires 0.230 kWh/mile of energy from the HVB for the commute (or a total of 8*0.230 = 1.8 kWh).  At 0 F, it requires 0.317 kWh/mile (or a total of 8*0.317 = 2.5 kWh).   So it requires 0.317/0.230 = 1.38 times as much energy for the commute at 0 F vs. 70 F.

 

It I go to Tesla's web site, they have a calculator for estimated range vs. temperature.  For city driving with climate turned off, the estimated range is 347 miles at 70 F and 337 miles at 0 F.  They show very little reduction in range.  You get 97% of the range at 0 F vs. 70 F.  That seems strange since I would expect aerodynamic drag alone to cause a greater reduction in range than that.   Even on the highway at 70 miles per hour, they show the range at 0 F to be 93% of the range at 70 F. 

 

For the Fusion Energi, the energy capacity of the HVB is reduced 15% at 0 F.  So rather than about 5.7 kWh of usable energy, the usable energy is 0.85 * 5.7 = 4.9 kWh.  The Tesla must have a heater for the HVB so they do not lose range in cold weather.

 

The range of the Energi at 0 F, is thus 4.9 / 0.317 = 16 miles.  The range at 70 F is 5.7 / 0.23 = 25 miles.  So the range at 0 F is 65% of the range at 70 F.   Tesla does significantly bettery with 97% of the range at 0 F vs 70 F. 

 

15% of the difference (97% - 65% = 32%) can be attributed to the Energi lacking a heater for the HVB.  The remaining 17% must be due to significantly higher friction with the Energi vs. the Tesla in cold weather.  So the question is why does the Tesla do so much better in colder weather?  The 1.38 addtional energy factor required for the Energi at 0 F vs. 70 F causes a significant reduction in range. 

 

Being a hybrid, the Energi has the additional overhead of the eCVT.  I wonder how much impact that has on performance in cold weather.  It must add a significant amount of additional friction in cold weather over pure electric cars.  If that is the case, the eCVT is the big hit to MPGe in cold weather.  I wonder how other purely electric cars do in the winter?

 

Other than the eCVT, I have no other explanation why the Energi requires so much more energy at 0 F vs 70 F.  I suspect the increased friction contributions from greater aerodynamic drag and greater tire rolling resistance at 0 F are responsible for less than half of the increased energy demand. 

 

 

Edited March 8, 2015 at 04:27 PM by larryh

[murphy]

The Tesla battery has a liquid temperature control system.  Sustained high current loads on the battery cause it to heat up.  However if it has been allowed to cold soak in low temperatures regenerative braking is disabled, regardless of the SOC, until it warms up.

[larryh]

When the HVB temperature falls below 0 F, the Energi also disables regenerative braking. 

 

Aerodynamic drag increases about 15% when the temperature falls from 70 F to 0 F.  Thus I would expect the energy required for the 8 mile commute to work to increase from 1.8 kWh to 1.15*1.8 = 2.1 kWh.  So there is an another source of friction causing the 2.5 - 2.1 = 0.4 kWh of energy loss.    The commute takes about 15 minutes, so there is roughly (probably not very accurate) 60/15*0.4 = 1.6 kW of power loss due additional frictional losses above what I would expect. 

Edited March 8, 2015 at 07:09 PM by larryh

[rbort]

Maybe all the loss difference in the energi vs the tesla is due to the cvt drag in cold weather.  I noticed my Cmax doesn't roll as far in the winter months as it does in the summer.  The tesla doesn't have a cvt, so that might be the whole difference in the world, not battery temp.  If they had a battery heater that would take power to use and lose range doing it, I would think that would be counter productive.

 

-=>Raja.

[larryh]

 

The Tesla has a battery heater. See the following link. While the car is plugged in and when you first start out, it warms the battery. A cold battery has significantly less energy.

 

http://www.teslamotorsclub.com/entry.php/194-Cold-Weather-Driving

Edited March 9, 2015 at 05:17 PM by larryh

[Hybridbear]

The Focus Electric also heats the battery. It doesn't like to let the HVB temp drop below 50 F and it doesn't let it go above 98 F. Like a Tesla it also has no eCVT to have increased drag.

 

I wonder if the Tesla calculator online is just overly optimistic because they want to sell cars.

[larryh]

Some things to note about the Tesla in the link provided in post #330. 

 

Regenerative braking is disabled in the Tesla when the battery temperature falls below freezing to protect the battery.  Charging the battery when it is too cold with damage it.  The Tesla uses a resistive heater to warm the battery prior to charging with an EVSE when the battery is too cold.

 

The Energi also disables regenerative braking when the HVB is too cold (below around 0 F).  If you attempt to charge the HVB with an EVSE when the HVB temperature falls below 0 F, it uses a fraction of the normal power used to charge the HVB at warmer temperatures.  It is probably not a good idea to let the HVB sit in cold weather too long when it is discharged and in hybrid mode, allowing the HVB temperature to fall below 0 F.

 

To precondition the car, the Tesla draws up to 12 kW of power, 6 kW for the battery heater and 6 kW to heat the cabin.  The Energi draws up to 3 kW to heat the cabin, but lacks a battery heater.  It takes a lot of energy to warm both cars.

 

To warm the cabin, both cars uses a resistive heater.  The Energi supplements the electric heater by pulling in coolant warmed by the ICE.  The electric heater is going to have a hard time keeping up when it is below 0 F.  That is why the ICE starts.   Since the Tesla doesn't have an ICE, it uses the coolant warmed by electric motor and inverter instead.

Edited March 9, 2015 at 09:35 PM by larryh

[Rhynri]

Unless I'm mistaken, doesn't the Tesla also use waste heat from the motor(s) to keep the battery warm in cold weather?  That would help save considerably on the energy to keep the battery warm. 

[Hybridbear]

Unless I'm mistaken, doesn't the Tesla also use waste heat from the motor(s) to keep the battery warm in cold weather? That would help save considerably on the energy to keep the battery warm.

Yes, but this is much less than the waste heat from an ICE.

[Rhynri]

Yes, but this is much less than the waste heat from an ICE.

Well, yes.  But it's still free!

[Russael]

On fairly rare occasion, like this morning, my car seems to abort preconditioning for no apparent reason.

 

Came out this morning and my car was warmer than ambient (freezing), charging indicator was lit on my EVSE, but the blower was off and the car wasn't doing anything.  The coolant was apparently cooling off too, as when I left, I did turn the heat on but it took about 3 minutes or so before the blower started circulating air.

 

It's not often it happens (maybe once every 2 months?) so it's something a dealership would blow off and not be able to replicate.

 

I had left on time as well.  Go time set for 7:30, I was in the garage at 7:30.  My Go Times will go 15 minutes beyond my departure time if I don't quite get out there at 7:30 and am running a little behind.

[Hybridbear]

On fairly rare occasion, like this morning, my car seems to abort preconditioning for no apparent reason.

 

Came out this morning and my car was warmer than ambient (freezing), charging indicator was lit on my EVSE, but the blower was off and the car wasn't doing anything.  The coolant was apparently cooling off too, as when I left, I did turn the heat on but it took about 3 minutes or so before the blower started circulating air.

 

It's not often it happens (maybe once every 2 months?) so it's something a dealership would blow off and not be able to replicate.

 

I had left on time as well.  Go time set for 7:30, I was in the garage at 7:30.  My Go Times will go 15 minutes beyond my departure time if I don't quite get out there at 7:30 and am running a little behind.

Some Focus Electric owners report that their cars also periodically skip Go Times. My parents have indicated that this has happened a few times in their C-Max. I have not yet experienced it in the Focus Electric or Fusion Energi and my wife has never commented about it either.

[FordService]

On fairly rare occasion, like this morning, my car seems to abort preconditioning for no apparent reason.

 

Came out this morning and my car was warmer than ambient (freezing), charging indicator was lit on my EVSE, but the blower was off and the car wasn't doing anything.  The coolant was apparently cooling off too, as when I left, I did turn the heat on but it took about 3 minutes or so before the blower started circulating air.

 

It's not often it happens (maybe once every 2 months?) so it's something a dealership would blow off and not be able to replicate.

 

I had left on time as well.  Go time set for 7:30, I was in the garage at 7:30.  My Go Times will go 15 minutes beyond my departure time if I don't quite get out there at 7:30 and am running a little behind.

If you do decide to head to your dealer, please let me know. I can look into some additional assistance, :)

 

Meagan

[Russael]

If you do decide to head to your dealer, please let me know. I can look into some additional assistance, :)

 

Meagan

 

My car will be 2 years old in May and will be due for an oil change and tire rotation.  One thing I mentioned a while back is that when I do take it in, I want every computer module in that car flashed with the most recent software, but I don't believe a dealership will touch anything unless it's considered broken, or if a Ford TSB says to upgrade the software.  My computer gets a patch at least once a week for security, remove bugs, and improve performance.  Individual softwares get patches.  My car's software hasn't been touched since it rolled off of the assembly line, except for Sync, which allows users to upgrade.

 

I've been pretty lucky to have been virtually trouble-free all this time, sans a glitch here and there.

[rbort]

Russael,

 

Cars are not like computers, hence if it ain't broke don't fix it so to speak.  The car runs a limited amount of software and if everything is working properly then its good.  If there is a new flash it might take out or add new features, but its not going to fix anything unless something was broken and they made a tsb for it to fix it.

 

Your computer runs alot of software, there are viruses out there, you need to update it to protect against the constant threat from those.

 

A different thing than cars in my opinion.  My 2013 Cmax has been great for me since day 1, the only thing I had to fix was the GPSM module which caused the GPS to run parallel on roads that the car was on.

 

-=>Raja.

Edited March 14, 2015 at 02:57 AM by rbort

[Russael]

I do not agree.

 

This isn't the thread to have this discussion, so I'll keep it brief.

 

Ford has had over 2 years to scour the software, remove the bugs, and optimize (they don't need to combat viruses... yet).  Bugs that may not be immediately apparent are still in the car and, with my luck, will surface once the warranty is gone.  Tesla did it right and gives everybody the latest calibrations OTA.  That has fixed many, many issues that others would still be driving around with if they owned a Ford or other make.

 

I haven't had any problem with the car yet.  Never had a warning light, never had a failure.  Have had the infotainment system go in to battery shut down mode nearly every time I turn the car off, but I've never had it not start.

[larryh]

Some things to note about the Tesla in the link provided in post #330. 

 

Regenerative braking is disabled in the Tesla when the battery temperature falls below freezing to protect the battery.  Charging the battery when it is too cold with damage it.  The Tesla uses a resistive heater to warm the battery prior to charging with an EVSE when the battery is too cold.

 

The Energi also disables regenerative braking when the HVB is too cold (below around 0 F).  If you attempt to charge the HVB with an EVSE when the HVB temperature falls below 0 F, it uses a fraction of the normal power used to charge the HVB at warmer temperatures.  It is probably not a good idea to let the HVB sit in cold weather too long when it is discharged and in hybrid mode, allowing the HVB temperature to fall below 0 F.

 

To precondition the car, the Tesla draws up to 12 kW of power, 6 kW for the battery heater and 6 kW to heat the cabin.  The Energi draws up to 3 kW to heat the cabin, but lacks a battery heater.  It takes a lot of energy to warm both cars.

 

To warm the cabin, both cars uses a resistive heater.  The Energi supplements the electric heater by pulling in coolant warmed by the ICE.  The electric heater is going to have a hard time keeping up when it is below 0 F.  That is why the ICE starts.   Since the Tesla doesn't have an ICE, it uses the coolant warmed by electric motor and inverter instead.

 

One more thing to note is that the specifications for the Tesla HVB state that the car should not be left outside when the temperature is below -22 F for more than 24 hours.  I assume that the Tesla does not use the battery heater when it is unplugged so the HVB temperature will fall well below 0 F when temperatures are this cold.  This suggests that extreme cold temperatures will damage the HVB.  It is probably not a good idea to leave the Energi outdoors for an extended period of time, with the car off, when temperatures fall below -22 F either.

Edited March 14, 2015 at 12:48 PM by larryh

[larryh]

I have had no problems with preconditioning.  The car has always been preconditioned in the morning for my commute to work. 

 

I had several of the modules reprogrammed by the dealer in the car:  BCM, BECM, PCM, and SOBDMC.  You can see the affect the this programming on the 12 V battery in this post:  http://www.fordfusionenergiforum.com/topic/1683-obd-ii-data-for-hvb/?p=19490

Edited March 14, 2015 at 12:51 PM by larryh

[stevedebi]

I do not agree.

 

This isn't the thread to have this discussion, so I'll keep it brief.

 

Ford has had over 2 years to scour the software, remove the bugs, and optimize (they don't need to combat viruses... yet).  Bugs that may not be immediately apparent are still in the car and, with my luck, will surface once the warranty is gone.  Tesla did it right and gives everybody the latest calibrations OTA.  That has fixed many, many issues that others would still be driving around with if they owned a Ford or other make.

 

I haven't had any problem with the car yet.  Never had a warning light, never had a failure.  Have had the infotainment system go in to battery shut down mode nearly every time I turn the car off, but I've never had it not start.

It is a matter of user choice. Personally, I agree with you, and want the latest modules flashed in my car. But I know Ford doesn't tend to do that unless they are doing some work and having to flash anyway - or at least that seems to be the case at my dealer. But I imagine they would flash the modules if you asked.

[Hybridbear]

When we bought our Energi I requested that they update all the modules and they said that they could not. Ford will not reimburse them to fix a problem preemptively before vehicle sale and Ford will not reimburse them to update modules after vehicle sale without a specific reason to update the module. If you want your modules updated, search the SSMs & TSBs section of this forum and the FFH forum and make a list of SSMs and TSBs that update modules. Then you can bring those to the dealer and mention those specific complaints to get the modules updated.

[larryh]

The following plot shows the effect of temperature on my 8 mile commute to and from work in EV mode.  I have plotted kWh/mile consumed by the car vs. temperature.  At 75 F, I get about 0.225 kWh/mile (150 MPGe).  At 0 F, I get about 0.310 kWh/mile (109 MPGe).  It appears that it takes about 0.310 / 0.225 = 1.38 times more energy at 0 F vs. 75 F.

 

Edited April 25, 2015 at 02:21 AM by larryh

[larryh]

The following chart shows the percentage of energy recaptured via regenerative braking vs. temperature during my 8 mile commute to work in EV mode.  At 75 F, 30% of the total energy used to propel the car is recaptured via regenerative braking.  At 0 F, 15% of the total energy is recaptured.  Cold weather significantly impacts regenerative braking.  In this case, the effectiveness of regenerative braking is halved at 0 F vs. 75 F. 

 

Edited April 25, 2015 at 02:21 AM by larryh

[larryh]

kWh/mile is computed as the net plug-in energy consumed by the car divided by the total distance traveled.  Thus the net plug-in energy consumed for my commute is kWh/mile times the number of miles traveled.  The actual distance of my commute is 7.8 miles.  So the net plug-in energy (NE) consumed for my commute is (see post 346 above):

 

At 0 F, NE = 0.310 * 7.8 = 2.42 kWh, and

at 75 F, NE = 0.225 * 7.8 = 1.76 kWh.

 

If the percentage of energy recaptured by regenerative braking is R, then the total energy (TE) used to propel the car is TE = NE/(1-R).  This is the net plug-in energy plus the energy recaptured through regenerative braking (see post 347 above):

 

At 0 F, TE = 2.42 / (1-0.15) = 2.84 kWh, and

at 75 F, TE = 1.76 / (1-0.30) = 2.51 kWh.

 

In this case, the total energy used to propel the car is 2.84 / 2.51 = 1.13.  That means it requires about 13% more energy to propel the car at 0 F vs. 75 F.  This is due to increased air density, increased tire rolling resistance, and increased internal friction at 0 F vs 75 F. 

 

 

The energy recaptured through regenerative braking (RE) is R * TE:

 

At 0 F, RE = 0.15*2.84 = 0.43 kWh, and

at 75 F, RE = 0.30*2.51 = 0.75 kWh.

 

Regenerative braking is significantly less effective at colder temperatures.  Much of the kinetic energy that would otherwise be available for regen is lost due to increased friction from higher air density, increased tire rolling resistance, and increased internal frictions, among other factors. In addition, if the battery is cold, then it can't accept as much regen as when it is warm. Any regenerative braking above the maximum charge limit of the battery is lost and cannot be stored in the battery.

 

It is because of the significant impact of cold temperatures on regenerative braking that the kWh/mi at 0 F is 1.38 times that at 75 F.  13% of the increase is due to increased friction required to propel the car at colder temperatures and the remaining 38% - 13% = 25% is due to less effective regenerative braking. 

 

During my city commute to and from work with many stop lights and a 55 mph speed limit, regenerative braking is critical to attaining good mileage. In the winter, the effectiveness of regenerative braking is cut in half. The very feature that makes EVs so efficient in the first place is rendered significantly less effective by cold weather.

Edited April 25, 2015 at 02:15 AM by larryh

[larryh]

The following is a simplified analysis of why regenerative braking is less effective in the winter.  The actual analysis is much more complicated.

 

At 75 F, the total amount of energy required to propel the car for my commute is 2.51 kWh, the energy recaptured by regenerative braking is 0.75 kWh, and thus the net plug-in energy used is 2.51 - 0.75 = 1.76 kWh.

 

At 0 F, the total amount of energy required to propel the car for my commute is 2.84 kWh, the energy recaptured by regenerative braking is 0.43 kWh, and thus the net plug-in energy used is 2.84 - 0.43 = 2.42 kWh.

 

It requires 2.84 kWh / 2.51 kWh = 1.13 times more energy at 0 F to overcome increased friction. 

 

In the summer, 0.75 kWh / 2.51 kWh = 30% of the total energy used to propel the car is recaptured via regenerative braking.  In the winter time, 13% more energy is required to overcome additional friction and is not available for regenerative braking.  Thus of the 2.51 kWh of energy to propel the car in the summer, 13% * 2.51 kWh = 0.33 kWh is lost to additional friction and can no longer be used for regenerative braking.  That leaves 0.75 kWh - 0.33 kWh = 0.42 kWh available for regenerative braking. 

 

So now only 0.42 kWh / 2.84 kWh = 15% of the energy is recaptured by regenerative braking in the winter. 

 

Whatever energy is lost to overcome additional friction is not available for regen.  This greatly impacts the efficiency of regen and overall MPGe of my commutes. 

Edited April 25, 2015 at 01:46 PM by larryh

[larryh]

I believe this chart explains much of the energy losses at colder temperatures.  It shows the power from the HVB required to propel the car at 30 mph vs. Transmission Fluid Temperature (TFT).   The outside temperature is 30 F.  It takes 1.5 times as much power to propel the car when the car is cold (TFT is 30 F) vs. when the car is warmed up (TFT is 110).    When it is cold out, it is going to take many miles for the car to warm up (TFT to reach 110 F).  It will take much longer when running in EV mode without the help of the ICE to warm things up. 

 

Pure EVs don't have an eCVT like the Energi.  In cold weather when running in EV mode, I suspect the eCVT is a useless appendage that wastes a significant amount of energy.  Pure EVs will probably not see as much of a dramatic reduction in mileage that I observe in the chart in post 346 above.

 

Regen during cold temperatures works just as well as it does at warmer temperatures (provided the HVB is not too cold).  The reason for significantly less regen in post 347 is the eCVT (and the rest of the car's transmission system) is siphoning away energy that would otherwise be available for regen. 

 

Edited April 27, 2015 at 09:17 AM by larryh