Surely MPGe can't be accurate? 194 MPGe?

[Depauwler]

 

Instead of taking the interstate (which I did on my way to my destination, using EV later at the higher speeds and got 44 MPGe) on my way back I tried another route which took me through residential areas, so it was all 35-40 MPH with occasional stop signs.

 

I understand I got 2.8 miles for free, but I'm just having trouble believing the conversion is correct.  Is EV just that good?

[larryh]

The MPGe reported by the car is not correct.  When computing MPGe, you are supposed to measure the amount of electricity consumed at the wall outlet.  The car measures the amount of electricity that is extracted from the battery.  There are losses associated with charging the battery and then with discharging the battery to propel the vehicle.  If you are using the 120 volt charger that came with the car, the actual amount of electricity from the wall outlet used to charge the car is 1.4 times that reported by MyFord Mobile.  So, in your case, it will require 1.5*1.4 = 2.1 kWh of electricity to recharge the battery.  Your actual MPGe is 194 / 1.4 = 139 MPGe.

Edited July 27, 2013 at 04:39 PM by larryh

[Depauwler]

Ahh, okay.  That's still impressive though. ;)

 

Actually I've noticed that every car I've driven (including those not mine) that reports MPG overestimates.  My last car was a Cruze and it always gave a better MPG and reported fewer gallons used than my numbers showed.  So I'm not surprised.

 

BTW larryh, I've been wondering how you track MPGe in Fuelly?  Do the math yourself to figure out how much gas you would have used to produce the same amount of kWh you used?

[larryh]

The MPG reported by the car seems to be accurate.  I reset the trip 1 odometer whenever I refuel.  Last time, the pump shut off 0.1 gallons before the amount shown on the odometer.  So I simply added an additional 0.1 gallons to match the amount displayed on the console.

 

I have a spreadsheet that calculates the amounts to enter in Fuelly.  It takes the gallons of gas G, amount paid for the gas C, kWh of plug-in energy displayed on the trip 1 odometer since I last refueled E, the distance traveled on the trip 1 odometer D, and the rate for electricity R. 

 

The equivalent gallons of electricity is:  Ge = 1.4 * E / 33.705.

The cost for electricity is:  Ce = 1.4 * E * R,

The total energy cost is Ct = C + Ce (gas cost plus electricity cost),

So, I enter in the Fuelly gallons field:  Gt = G + Ge (the gallons of gas plus equivalent gallons of electricity),

I enter in the Fuelly Price/Gallon field:  Ct / Gt (the total energy cost divided by the total equivalent gallons).

 

I determined the 1.4 factor by plotting the plug-in energy displayed on the console vs. how much electricity, measured using a Kill A Watt meter at the outlet, is used to recharge the battery over a two month period using the 120 volt charger.

 

Edited July 27, 2013 at 06:23 PM by larryh

[Depauwler]

I just realized why that is the only thing that makes sense.  I was going to be lazy and just report the gallons from the pump until I realized if I filled up this weekend instead of next (when I'll be going on a road trip and will need to use hybrid mode), I'd get a different result, since I could go all week without using any gas.

 

I'll have to steal your formulas.  I wonder if that 1.4 is really consistent across cars though?  Probably since it's all assembly line, standarized equipment, ya?  I reset Trip 2 when I took possession and was planning to reset it with each refill.

[Depauwler]

Unfortunately I'm in an odd position.  I currently have to rent a garage from my apartment complex for a flat rate per month.  The electricity is free, however.  The best I can figure now is that my electrical cost would be $55 * numDaysSinceLastFillup / AverageDaysPerMonth.  If I filled up today, that would be just over $45.  I think I'll try to find a standard rate for my area and use that instead.

[larryh]

If you look in the C-Max forum, you will see that may people get identical results to what I get.  They all get 1.4.  At least for the 120 volt charger, the results are consistent. 

Edited July 28, 2013 at 05:43 PM by larryh

[larryh]

You could use your actual electric rate which is zero.  You have no electricity costs so you will have very low operating costs for the car.  I get a lot of free electricity too.  But I haven't taken that into account in Fuelly.  I simply use my standard electricity rate for all the plug-in energy.

Edited July 29, 2013 at 09:16 AM by larryh

[Depauwler]

Ah, actually you're right.  I didn't consider that; there's a free charger near Meijer's I always use, and I don't have an easy way to account for the pay stands.  Still, I think I'd rather estimate it.  Apparently the average residential rate around me is .1151 per kWh.

 

I'll just use that since it's really the MPGe I'm interested in, not the cost per mile.

[ChuckJ]

Does anyone know if you get a better efficiency using the 220 system?

 

ChuckJ

[murphy]

It takes 2 hours with the 240 volt system versus 7 hours with the 120 volt system.  Just based on heat loss the 240 volt system is more efficient.

[apm]

It takes 2 hours with the 240 volt system versus 7 hours with the 120 volt system.  Just based on heat loss the 240 volt system is more efficient.

 

Hi Murphy,

 

My car takes 5 hour 50 minutes to charge using a 120V charger, from a completely discharged big battery (5.2kWh).

 

At my last full battery recharge the Kill-A-Watt reported usage of 7.6 kWh, so it seems that the formula above is about right.

 

Regards,

APM

[ChuckJ]

I know this is probably dumb, but I can't get the MPGe rating in empower while driving.  It that an option?

 

ChuckJ

[Russael]

Yes it is.  You need to select Fuel + Electric in the left screen.  You should find it under Display -> Units -> Fuel Economy -> Fuel + Electric.

[shaggy314]

IIRC, your 110 charger from Ford is 1.3 KWh whereas the 220s get the full 3.3 KWh the car can take.

[ChuckJ]

Yes it is.  You need to select Fuel + Electric in the left screen.  You should find it under Display -> Units -> Fuel Economy -> Fuel + Electric.

Thanks, Russael.  I now have that selected but it doesn't give me an opportunity to input the cost of electricity and I thought that would be a component.  Is it not?

 

ChuckJ

[murphy]

Thanks, Russael.  I now have that selected but it doesn't give me an opportunity to input the cost of electricity and I thought that would be a component.  Is it not?

 

ChuckJ

The cost of electricity or gasoline does not matter in MPG or MPGe calculations.

What you are missing is the fact that one gallon of gasolins contains a fixed amount of energy.

I think the number Ford uses is 33.7kWh per gallon of gasoline.

There is disagreement on this number.  I have seen it given as high as 34.02 kWh / gallon.

That may be due to the difference between pure gasoline and the stuff we have now with alcohol in it.

Edited September 3, 2013 at 10:13 AM by murphy

[ChuckJ]

The cost of electricity or gasoline does not matter in MPG or MPGe calculations.

What you are missing is the fact that one gallon of gasolins contains a fixed amount of energy.

I think the number Ford uses is 33.7kWh per gallon of gasoline.

There is disagreement on this number.  I have seen it given as high as 34.02 kWh / gallon.

That may be due to the difference between pure gasoline and the stuff we have now with alcohol in it.

Thanks, murphy.  I thought there was an easy way to calculate the money saved by using electricity rather than fuel. And I'm really confused as to the 100MPG rating on the car if that's not the case.

 

ChuckJ

[murphy]

Thanks, murphy.  I thought there was an easy way to calculate the money saved by using electricity rather than fuel. And I'm really confused as to the 100MPG rating on the car if that's not the case.

 

ChuckJ

The gasoline only combined city/highway rating for the car is 43 MPG.

The electricity + gasoline combined city / highway rating for the car is 100 MPGe.

MPG and MPGe are different metrics.

 

MPGe involves assigning 33.7 kWh to a gallon of gasoline to compute the MPGe.

 

Whether or not electric operation is cheaper depends on the cost of gas and electricity where you live.

[ChuckJ]

 

 

Whether or not electric operation is cheaper depends on the cost of gas and electricity where you live.

Yep, I get that Murph.  I just thought there was a way to show if you were optimizing the mix.  I'm reading that some people are paying $.30+ for a kWh.  I was thinking there would be a way to let people know if they should be running on pure hybrid vs plug in.  You can figure that out manually, of course.

 

So not to beat a dead horse, but what's the advantage of tracking MPGe?

 

ChuckJ

Edited September 3, 2013 at 07:11 PM by ChuckJ

[murphy]

So not to beat a dead horse, but what's the advantage of tracking MPGe?

 

I have used about 4 gallons of gasoline since April.  Tracking MPG would be meaningless.  I'm sure if I switched the screen to MPG it would say 999.9 MPG which is clearly impossible.  If the HVB was never charged, then MPG would be valid.  If two sources of energy are being fed to the car they both have to be accounted for in the mileage calculation.  Only MPGe does that.

[ChuckJ]

Got it, thanks Murphy.

 

ChuckJ

[jsamp]

The gasoline only combined city/highway rating for the car is 43 MPG.

The electricity + gasoline combined city / highway rating for the car is 100 MPGe.

 

murphy, I believe that is incorrect.  The electricity only combined city/highway rating is 100MPGe.  That is without using any gas.  The combined electricity/gas mileage will be somewhere between 43 and 100 but that is by mixing different metrics as you pointed out.  This also shows in your long-term results on fuelly at 78.3 mpg (tracking MPGe, not MPG)

[murphy]

Those numbers are taken directly from my Window sticker.

[jsamp]

Those numbers are taken directly from my Window sticker.

 

True, that's what the sticker says.  However if you notice it also says to the right that it used 0.0 gallons of gas.  I guess it's because there is a limited top speed on electric they have to say "electricity and gas" because the Volt does not say that.  Prius Plug-in is the same as Energi on the sticker, but it actually used 0.2 gallons of gas for the EPA test.  Take a look at the sticker images attached.