Reported Trip Energy Used vs Energy required to recharge car

[larryh]

For the past two weeks, I have been keeping track of the total amount of energy consumed as reported in the Trip Summary/Odometer vs. how much energy is required to recharge the battery using a Kill A Watt electricity usage meter.  I reset the trip odometer with a fully charged battery at the start of the day.  Then when I arrive home to recharge, I keep track of the energy with the Kill A Watt meter required to fully recharge the battery.  I do not include the energy required for pre-conditioning the car.  The following plots the results:

 

 

 

 

 

I suspect the car is under reporting the energy consumed.  The battery holds 7.6 kWh, of which, 1.1 kWh is reserved for hybrid use.  So if I deplete the battery, I would expect that I would have used at least 6.5 kWh of energy.  The most the trip odometer shows that I have consumed is 5.6 kWh.  Of course, the charging process is not 100% efficient.  Some of the energy used to charge the battery is wasted as heat or used to power the cooling fans for the battery.  So I would expect it to take a bit more than 6.5 kWh to charge.  According to the plot above, the amount of electricity required to power the car is under reported by about 44%.  For a fully depleted battery, it requires about 7.8 kWh.  I wonder if the results would differ with a 240 volt charging station.  I am using the 120 volt charger that came with the car.  I also wonder if the current outside temperature makes a difference.

 

I need to redo this chart.  I set the charging to "Value Charge" for several of the charges.  Value Charge consumes 60 watts of power while waiting to charge.  So, if the car waited 10 hours to charge, the measured energy to charge the battery will be off by 0.6 kWh.  "Charge Now" will use less electricity to charge the car.

Edited June 25, 2013 at 08:14 PM by larryh

[larryh]

Note that this would imply that the MPGe values shown on the console are overly optimistic.  The true MPGe is probably lower.

Edited June 22, 2013 at 10:36 AM by larryh

[larryh]

If I look at my commute to and from work on Monday of 15.5 miles, as reported by the trip odometer, the car consumed 3.5 kWh.  So my MPGe for that trip, using this value, was (15.5/3.5)*33.7 = 149 MPGe (which matches what I see at the MyFord Mobile web site).  However, the true energy consumed was approximately 3.5*1.44 = 5.04 kWh.  (The actual amount was 5.44 which is much more than normal for some reason).  Using the correct energy consumption, the mileage was actually (15.5/5.04)*33.7 = 104 MPGe. 

 

So, rather than substantially exceeding the EPA ratings, I am actually only just matching them. 

 

The MPGe shown on the console and at the MyFord Mobile web site make the car look like it is getting much better MPGe than it really is.

 

Note that the amount of energy to charge the car (for the same amount of battery depletion) varies considerably from day to day for some reason.  So I am not sure how to properly measure the amount of energy required to recharge the car when computing MPGe.

Edited June 22, 2013 at 10:52 AM by larryh

[murphy]

Please tell us what the numbers you are using are.

What is 33.7?

What is 1.44?

 

There are 34.02 KWH in a gallon of gasoline.

 

https://en.wikipedia.org/wiki/Miles_per_gallon_gasoline_equivalent

[larryh]

The EPA uses 33.7 kilowatt-hours (33,705 watts) of electricity equivalent to one gallon of gas.  That is also the number used at the Wikipedia link:

 

, where wall-to-wheel electrical energy consumed (Wh per mile).

 

The 1.44 is from the plot in the first post.  The amount of energy required to charge the car is 1.44 times the amount of energy reported by the Trip Summary/Odometer or MyFord Mobile.  Basically, I can conclude from the chart, that the MPGe reported by the Trip Summary/Odometer/MFM must be divided by 1.44 to determine the true MPGe.

 

I believe the EPA computes MPGe as follows:

 

"The EPA fully charges an EV and then lets it sit overnight. The following day the vehicle is driven through successive test cycles until it is no longer able to perform the test cycle. Then the vehicle is brought back to a fully charged state, and the energy used to recharge the vehicle is measured at the wall because that is the energy usage that will appear on the consumer's utility bill."
 

Edited June 22, 2013 at 12:12 PM by larryh

[Russael]

I noticed my MPGe numbers seem to go up the warmer it is.  When I go to work in the morning (usually around 60 degree temps), I'll get an average of somewhere in the 150's according to the computer, but when I travel back home when the temps are somewhere in the 70's to 80's, plus with having the car in the sun the whole time, the trip computer says I'll get somewhere around 170 to 190MPGe.  I don't drive any differently and in fact I would expect the number to be lower since I seem to spend more time at red lights.  Only accessory I use is the stereo.

 

I remember in another thread that someone mentioned that the car was consuming 60 watts of energy as soon as he plugged it in with a value charge profile set, and it would stay there until charging actually occurred.  However, when his actual charge was done, it would drop to near 0.

 

So if you spend the entire 7.5 hours to charge your car and consume somewhere around 7.5kw, if we add an additional 450 watts for the fans, brings us to 7.95kw consumed.  On top of this, I don't know how efficient the charger is. 

 

I found this link:  http://evbatterymonitoring.com/WebHelp/Section_3.htm

 

That says a charger can be around 85% efficient but then battery efficiency lowers it even more... they say the overall % of efficiency is 64%.  If we do 85% efficient, we get: 7.95kwh * 1.15 (adding 15% energy consumed), which comes to 9.1425kwh consumed to charge 7.5kw. If we do it at 64%... 7.95 * 1.36 = 10.812kwh consumed. 

 

That gets really close to your numbers.  5.5kw + 330w(fan) = 5.83kw * 1.36 = 7.9288kw  However, that link apparently was charging a much lower voltage battery pack (36v).  I googled around for a few minutes looking for an inverter charger efficiency rating and can't find squat at the moment.  You're taking 115 volt AC household current and inverting it to 300 volts DC.  I have zero idea how efficient that is.  But if that article is any indication, that may explain your electrical consumption.  I would be curious to know if 240v is more efficient (it should be... higher voltage is typically more efficient for heavy duty appliances).  Too bad Scooter80 isn't still around since he has a 240 station hooked up to a meter.

[larryh]

My commute is city streets at 55 mph, so I won't get the best MPGe numbers. I generally get better numbers in the morning when its in the 60's rather than my commute home in the 70's.  Probably, because there is much less traffic in the morning vs. the afternoon commute home so I have more control over how I drive (the other drivers are not forcing me to be inefficient, i.e. more room for braking, etc.). 

 

The 60 watts of energy prior to the value charge time is used to slowly charge the battery.  I have asked Ford why it is doing this, but I have not yet received a response.  It should not use any energy until the value charge time.  After the battery is fully charged, the charger consumes a minimal 1.8 Watts of energy waiting for the next charge.

 

I will be getting a 240V charger next month and a submeter from the electric company, so I will find out if it is any better then.

 

Note that the actual charging efficiency varies significantly.  The multiplier factor varies from a minimum of 1.36 (the value you computed above) to a maximum of 1.55 over the two week period.  The average was 1.44.  I have no idea why it varies so much.

Edited June 22, 2013 at 01:07 PM by larryh

[murphy]

I have a meter on my 240 volt charger.

The only time I ran my battery down to the point where the car switched into hybrid mode it took 7.09 KWH to charge the battery.

 

That is the highest reading in 63 charges which total 169.51 KWH.

13 of those readings were to precondition the cabin.

[larryh]

For the 120 volt charger, the minimum amount I have recorded to charge the battery after it has been depleted is 7.57 kWh.  The maximum is 8.21 kWh. 

 

The 240 volt charger could possibly be more efficient.  So that would imply that the true MPGe values for the car depends upon the charger being used.  I wonder what charger the EPA used to rate the car?

Edited June 22, 2013 at 02:02 PM by larryh

[Russael]

The MPGe numbers you're receiving from the car should be accurate - it doesn't factor in charging inefficiencies since that is not the true amount of energy that was used to move the car.  It is not factoring in the charging inefficiencies.  We're used to putting gas in the tank as 1 price and then seeing that turned in to an MPG number, since that amount of gas is what moves the car (it's 99.9% efficient to pour gas from the pump in to the tank with some lost as vapor).  With electrical MPGe, it is only ~64% efficient to pour power in to the battery tank.

 

I never did actually research this kind of efficiency before buying the car.  I'm surprised the numbers are that poor.

[larryh]

The MPGe computation is supposed to include power from wall to wheel:

 

EPA's miles per gallon equivalent metric MPGe is determined in a manner similar to MPG for a conventional internal combustion engine vehicle. In both cases the metric only considers the pump-to-wheel or wall-to-wheel energy consumption, i.e. it measures the energy for which the owner usually pays. For EVs the energy cost includes the conversion from AC from the wall used to charge the battery.

 

The MPGe computed by the car is missing the energy losses associated with conversion from AC from the wall to charge the battery.  So what the car is reporting cannot be compared to the EPA rating on the window sticker.

 

Note that the EPA ratings do not account for the energy consumption upstream, which includes the energy or fuel required to generate the electricity or to extract and produce gasoline; the energy losses due to power transmission; or the energy consumed for the transportation of the fuel from the well to the station.

Edited June 22, 2013 at 03:31 PM by larryh

[Russael]

Found that statement on Wiki...

 

Wiki: 

Pump/Wall-to-wheel

EPA's miles per gallon equivalent metric shown in the window sticker does not measure a vehicle's full cycle energy efficiency or well-to-wheel life cycle. Rather, the EPA presents MPGe in the same manner as MPG for conventional internal combustion engine vehicles as displayed in the Monroney sticker, and in both cases the rating only considers the pump-to-wheel or wall-to-wheel energy consumption, i.e. it measures the energy for which the owner usually pays. For EVs the energy cost includes the conversions from AC from the wall used to charge the battery^[27] The EPA ratings displayed in window stickers do not account for the energy consumption upstream, which includes the energy or fuel required to generate the electricity or to extract and produce the liquid fuel; the energy losses due to power transmission; or the energy consumed for the transportation of the fuel from the well to the station.^[8][28]

 

Considering this... at least for your 120v charger, doesn't seem to jive. 

 

If Murphy has time, I'd like to see what his car states for energy use for the day (kw consumed) and then see what his charger says it dumps in to the battery pack that night.  Considering he has mentioned that on a dead battery his charger reported 7.09kw to put back in where your car is going over 8 without a fully discharged battery screams that 110v is inefficient.  But I'd like Murphy to look at the numbers to reinforce it.

[larryh]

I wonder if the car just measures the energy used to power the wheels.  So the losses associated with charging the vehicle and converting the battery charge to mechanical energy are not taken into account.  Hence I put in 7.8 kWh of energy and only get 5.6 kWh of useful work out.

[larryh]

I see in Scooter80's review of the 240 V GE Wattstation, charging a fully depleted battery required 6.8 and 6.9 kWh (vs. 7.8 kWh for the 120 V charger).   So that provides more evidence that a 240V charger is more efficient. 

[Russael]

Are you sure your Kill-A-Watt meter is accurate?  I've read a handful aren't so much, but it's a pretty rare occurrence.  May be worth hooking it up to a vacuum cleaner and see what it says, since those typically max out at 12 amps, the same as the Ford charger is supposed to be at.  Worth a shot next time you clean your house.

 

Aside from that, I'm quite surprised the 110v charger has that much loss putting juice back in to the battery.  I wonder if Ford only gives 1 calculation at 240 volt for MPGe and not a second one for 110v since losses seem SIGNIFICANTLY greater.

 

If you have 120 volt at your plug (not 115 or 110) and the charger consumes 1500 watts (typical rated maximum) at 100% efficiency to charge 7.09kw (Murphy's example) should only take 4.73 hours at 120v. 7.5 hours at 120v  with 1500 watt draw calculates out to 11250 watts, which FAR exceeds battery capacity.  In order to have 120v charge 7.09kw in 7.5 hours, the charger should only draw about 945 watts at peak, or about 7.9 amps at the outlet at 100% efficiency.

 

What does your kill-a-watt meter say about the maximum current being pulled by the charger during charging, not just the total energy drawn?

[murphy]

The charge profile is not linear.  It starts out high and then tapers off near the end.  It is very dangerous to overcharge a Lithium-ion battery so they have to sneak up on the full charge state. 

 

I posted a charge graph back in April of a completely discharged battery.

 

http://www.fordfusionenergiforum.com/topic/740-graph-of-charging-a-completely-depleted-battery/?do=findComment&comment=3098

[larryh]

The Kill A Watt meter seems to be accurate.  The current when charging is 11.52 amps and the power is 1355 watts.  The last full charge for a depleted battery took 5 hours and 47 minutes.  Multiply that by 1355 watts and I get 7.84 kWh.  Since the charge tapers off at the end, the actual energy consumed to charge the battery was 7.75 kWh. 

 

Note the maximum rated amperage of the charger supplied with the car is 12 amps. 

Edited June 23, 2013 at 03:11 PM by larryh

[Russael]

I know the charge ramps down when it gets near the end, but it seems to only do a ramp down for about the last 10 - 15 minutes.  It also continues to run the fans for a few minutes after charging is complete as well.  Overcharging Lithium batteries typically means exploding batteries.

 

Larry, your last full charge for a 'depleted' battery... depleted how far?  Was that your 5.5kw to be replaced or was that after you hit hybrid mode?  If that was your 5.5kw and it ate 7.75kw to recharge it... that's pretty bad especially with your crazy electrical rates. :)

 

I don't have a meter on my 240 charger but I can sort of figure out what the car is consuming using the MyFord trip and charge website.  I just completed about a 22 mile segmented trip... 8 miles to the parent's home, 1.6 miles to the restaurant and back, a stop at the megamart, and then another 8 miles home.  I had about 10 miles left on the battery, and the website says I consumed about 3.6kw for those trips.  Car is on the charger now, so we'll see how long it takes to recharge the thing.  It SHOULD take around 1 hour 10 minutes.  We'll see what it says in a bit.

[larryh]

Yes, that battery was depleted.  I drove 56.5 total miles on Freeway/Highway.   The first 24.4 miles were in EV mode after which the battery was depleted and the ICE turned on.  The car then consumed 0.73 gallons of gas during the remainder of the trip.  The car claimed to have used 5.6 kWh of charge from the battery.  It required 7.75 kWh to recharge the battery.  Actually, that was one of the more efficient trips.  The efficiency was then 5.6 / 7.75 = 72%.  I got 72% of the electrical energy put into the car as work to propel it.

Edited June 23, 2013 at 07:56 PM by larryh

[Russael]

Hmmm... something is interesting with the reporting.  I went back through my trip logs and looked at the one where I drove 26 miles, all EV, and had drained EV mode and half the hybrid battery... and the MyFord trip thing says I consumed a total of 5.2KWh.  I would've expected a report of at LEAST 6.5KWh since it's said that the system reserves 1.1KWh for Hybrid mode.  Maybe there's another reserved part of the pack for engine starting or something that we don't see.

 

My other long trip (had about 1 mile left on the battery) says 5KWh consumed.

 

I wonder if anybody has anything greater than 6KWh used according to the car...?  Maybe EV mode is between 5.5 and 6KWh and Hybrid mode is actually between 1.5KWh and 2?

 

My car finished charging.  1 hour 25 minutes to completion... so there was an additional 15 minutes in there for something (probably the ramp-down and cooling).

[larryh]

I suspect some of the variation that I see in the amount of energy to charge the battery has to do with the level of depletion of the hybrid portion of the battery.   The level of the hybrid portion of the battery varies from 1/4 to 3/4 of its capacity when I plug it in.  So that could explain about 0.5 kWh of the variation to charge the battery.

 

I also suspect that what is reported by the Summary/Trip odometers is the energy applied to the wheels and not the amount withdrawn from the battery.  Since the conversion from the energy stored in the battery to mechanical energy is not 100% efficient, you probably lose 1 kWh or more which would explain why the car reports 5.4 kWh when it actually draws 7.6 (total battery capacity) - 1.1 (hybrid portion) / 2 = 7 kWh from the battery.  The most that I have seen for a trip is 5.8 kWh. This too might have something to do with how much of the hybrid portion of the battery has been consumed before the ICE turns on.   I know that this value decreases when going down a hill as the battery recharges.  So who knows what other factors affect it.  Does it include climate?

 

Also I suspect the electricity has higher octane in Michigan :hysterical:

Edited June 23, 2013 at 10:59 PM by larryh

[larryh]

I have determined a source of some of the charging inefficiencies.  I used the Value Charge option for several of the charges.  While waiting to charge, the car consumes 60 watts of power for the 12-volt battery and the on-board battery charging control module.  So I am going to have to collect more data using "Charge Now" rather than "Value Charge".  If you want to achieve the highest MPGe, then you don't want to select "Value Charge."

[larryh]

The following is an updated chart showing the actual kWh consumed by the car as measured with a Kill A Watt electricity meter connected to the wall outlet vs the kWh of Energy Use (the amount of plug-in energy the car claims was consumed) as displayed on the car's Trip Summary/Odometer console display.  I am using the 120 volt charger that came with the car.  Also, I am now using the "Charge Now" setting to charge the car and not the "Value Charge" setting.  There is now a lot less variation in the data.  Any remaining variation is now probably due to round off error.  The reported kWh on the car's display console shows values only to one decimal point.

 

 

 

I start with a fully charged battery in the morning.  At the end of the day, I record the kWh of Energy Use displayed on the console using a trip odometer.  I then recharge the battery and measure how much electricity was required using a Kill A Watt meter.  The car is allowed to sit overnight until I take the next trip the following day.  This is the correct procedure to measure MPGe.

 

As illustrated in the chart, the actual energy consumed by the car is 1.4 times what the car reports.  So if the car displays an energy use of 5 kWh, the amount of electricity consumed by the charger to charge the battery for that trip was 5 * 1.4 = 7.0 kWh.

 

This implies that for a trip entirely in EV mode, the true MPGe for the trip is the value reported by the car divided by 1.4.  So if the car reports 140 MPGe, the true MPGe is 140/1.4 = 100 MPGe.  I am adjusting the values that I enter into Fuelly to account for actual kWh consumed from the power company to charge the car.  The true MPGe readings are lower that what is reported by the car.  So for the last 1170.1 miles since I previously refilled the fuel tank, the car reported 70.8 MPGe.  Using the 1.4 adjustment factor, I compute the actual MPGe to be 63.4. (Note you can't simply divide by 1.4 in this case because gas and electricity were both consumed.)

 

Note that the fuel consumption reported by the Trip Summary/Odometer seems to accurate and can be trusted.  It claimed for the 1170.1 miles that I used 11.35 gallons of gas.  When I filled the tank with gas, the nozzle shut off at about 11.2 gallons of gas.  I added a little more to bring the total to 11.35.

Edited July 27, 2013 at 06:41 PM by larryh

[Taylorjd]

....

, where wall-to-wheel electrical energy consumed (Wh per mile).

....

 

So if the 2 trains let the station at the same time and one was going west at 80 mph with a tail wind of 10 mph and the other was going ..... 

 

 

This is to much like school  :banghead:  :redcard:   lol

[larryh]

I did a simple experiment to further determine the efficiency of the car in EV mode with climate control off.  I drove the same stretch of roads, in both directions, for a short distance, with the cruise control set to speeds from 20 mph to 70 mph.  I reset a trip odometer at the start of the trip and observed the MPGe at the end.  I averaged the results at the same speed going in both directions (the roads were not perfectly level so you get better MPGe in one direction vs. the other).  I did this during early morning hours when the winds were calm, temperature around 70, and there was no traffic to interfere.  Note is very hard to get consistent results at low speeds.

 

 

 

The relationship between speed and MPGe appears to be linear between 20 and 70 mph.  Based on MPGe values and the maximum plug-in energy displayed by the console in the Trip Summary/Odometers that I have observed after a depleted battery, 5.8 kWh, the estimated range of the car at the various speeds is computed as (MPGe / 33.705 kWh / gallon equivalent) * 5.8 kWh:

 

Speed (mph) Distance (miles)

20                 43.2

30                 37.9

40                 32.6

50                 26.9

60                 22.8

70                 18.0

 

The estimates for low speeds are more uncertain than for higher speeds.  Of course, the temperature, grades of the roads, wind, and other factors will influence the actual miles achieved for a fully charged battery.  The results above seem to be consistent with what I have observed for the car. 

Edited July 7, 2013 at 12:48 PM by larryh