Miles per gallon equivalent

[longsundayrun]

Hi y'all....I'm a teacher in Rhode Island.....and my students and I have built a small Electric Vehicle with a Magic Pie III....we tested it this past Sunday on the track...we ran it for 17 miles and only used 3.6 volts (started with 39) ... performed outstanding to me...I expected it to run down to 24 volts...does anyone have any insight in how to calculate miles per gallon equivalent ??....any comments !!!....I would appreciate it !!!..thanks !!...Ed Fernandes, Tiverton High School, Tiverton, RI

[Morgen 3Eman]

Hi Ed,

Is that made from PVC pipe?  What does it weigh?  Could we have a closeup of the steering?   It looks like a pretty cool way to interest kids in engineering careers.

 I have no answers for your questions, but I'm sure that Alan will be able to help.  He is pretty much the genius in residence here..... Welcome aboard.

TTFN,
Dennis

[longsundayrun]

Hi Dennis....yes, it's 1" PVC pipe....bought the plans from Dan Fleishman in Florida....Americanspeedster.com....it weights about 110 pounds....a great school project for my engineering kids....it uses an old kingpin design for the front end with aluminum tie rods...here's a pic...

[longsundayrun]

Dennis....here's a you tube link that briefly shows us testing it on our track
Ed

http://m.youtube.com/watch?v=egZYDnjBLNo

[sixty_cycle_hum]

Cool project and great question.  I was curious about this earlier today and figured it out.

To begin with, the EPA defines MPGe as 33.7 kWh being equal to one gallon of gasoline.  Knowing that, you will just need to know what kind of power over time is needed to recharge the batteries after a given distance is traveled.  Remember that there are inefficiencies in charging and discharging the battery and the motor itself, so metering the power use of the vehicle is not really good enough.  You need to know the total power supplied at the charge point, because in the end, that's where the juice is coming from right?

My example:

I commute 13 miles exactly to work one way with my Magic Pie 3.  I know from my kill-a-watt meter http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU
 that if I begin my 13 mile ride with a full charge, it takes another ~1.75 hours to get the battery back to a full charge, and an indicated .3 kWh used shows on the meter.

So if I use .3 kWh for 13 miles, then I can simply divide .3/13 to give me .023 kWh / mile... Or 23Wh per mile.

From there, you can use the proportion of 1 Mile per 23 Wh = x Miles per 33,700 Wh

solve for x and you get MPGe, which works out to be about 1465 MPGe!

Hope that helps.  If there are any errors above, I hope someone can catch them.

-sixty

[sixty_cycle_hum]

Oh, and don't use MPGe except to impress your Prius driving friends.  http://www.popularmechanics.com/cars/news/4324986

Also, the cost of a gallon of gasoline is much more volatile than a kWh from the utility company, so the MPGe figure is always obsolete.

My $0.02

[longsundayrun]

Hello !....Thanks so much for the info and especially the effort....your figures are correct...and based on how my EV performs, I am getting about 783 MPGe...I hope my Prinicipal believes it !!!...thanks again !!

[Zero]

You murricans should abandon all those middle-ages units, here in Europe, we use Liters/100km, its quite simple, and easier to use with EV's too, you just calculate the cost of money per 100km, my ebike uses 0.15€ per 100 km, and if my car uses 10L/100km, and with the petrol costing roughly 1,5€/L, then I can say that my ebike is 100 times more efficient than car

[longsundayrun]

First of all, Zero, I respect your right to your opinion....but to use a slanderous name like "murrican" to describe me ....when you don't even know me...when all Im asking is friendly discussion about something educational, speaks to your subterranean ilk and obvious low self respect. I feel sorry for you and hope you seek the help you obviously need. Zero sounds about right.

[sixty_cycle_hum]

Haha, yeah "murricans" isn't very nice.  Thankfully it only describes part of the population here - and not likely anyone interested in EVs.  I'm personally not offended, but it definitely perpetuates the stereotype of fat, lazy, uneducated mouth-breathing American rednecks. , and that's not cool.

Zero is right, though.  The MPG measurement is asinine, and that was the purpose of my second post.  It really does not describe efficiency in a way that is intuitive.

While we're at it, we should all be using SI measurements, metric sockets, and 24 hour clocks.  FOR SCIENCE!

-sixty

[longsundayrun]

Hi sixty cycle !,...yes, I would agree that the mpg is quite outdated...even Zero was right about that part...I still use the MPG for this project because when I present my EV to the school board next week, they only can relate to mpg...thanks for your support !!!

[Morgen 3Eman]

Hi Folks,

A quick question.

I have metric and SAE tools in my garage.  I used to speak Spanish, French, and Chinese as well as my native English. (If you don't use a language for a long time, you loose it) (Same as tools)  One of my professors taught me that if your only tool is a hammer, you tend to see every problem as a nail.  Now I'll admit I'm just a dumb Yank, so please help me to understand why having differing units of measurement across the world is a bad thing?   Could you please  frame your explanation in terms of the value of a group of nations requiring citizens to speak French, German, Italian, Greek,Polish,Romanian, Spanish, Portuguese, et al in an area the size of Alaska?

i'd just like to understand the logic system you use in everyday life.

Have a nice day.

TTFN,
Dennis

[GM Canada]

At my age MPG is all I can understand. Litres per 100 km means nothing to me. But If I can go 20 miles on a gallon of gas that I can relate to. The easiest thing for me to relate to is 12 inches to the foot. Since my shoe is 12 inches long its very easy to pace things out. Just last week I needed to estimate how many yards of soil I needed for a certain area. I measured it out heel to toe. Figured out the width and length very easily. I needed 4 inches thick of dirt so I multiplied it out by length times width divide by 3 and voila!

Great looking project. The mileage you are getting is awesome. I told you the e-geeks in the forum could help with the calculations. Whoops, is e-geeks offensive? 

Gary

[longsundayrun]

Hi Gary !....thanks for the nice complement on the EV. It's been a great, positive project in engineering with some fantastic students. Love this forum also. The chatter and experiences are refreshing and have been wonderful to read. It's clear the Magic Pie is really getting some positive attention and making a difference in the way we think about transportation and engineering solutions. I especially enjoy reading all the questions and responses from many different places in the world. So when somebody throws out a shot, I'm more disappointed than offended simply because negativity on this forum is not necessary. I'm a teacher so I've heard it all from bad to good and I am not thin skinned by any stretch of the imagination. Its no wonder people can't get along. Enough on this point.

The MPG is what we use in the US...the auto makers have no other way because we still have the gallon....and yes, it's easy to understand...I like the MPGe math because it helps newbies see the simple elec/gas comparison and it makes sense. But I also see the need to have different measurements in other countries because its what they are used to. And it's interesting to see how it all compares to the same point...measuring distance, energy used and cost.

Hopefully, the negativity is behind us and we can go back to being inventive and supportive of each other. It's a lesson I constantly teach in my classroom. We are, as adults, supposed to set a good example !!!....And I'm proud to be an E-geek !!!

Sincerely,
Ed

[sixty_cycle_hum]

Dennis, I think being multi-lingual both literally and figuratively with respect to measurement is a really good thing.  I wish I would have studied another language more seriously.  In the real world, while I would love to deal only with SI measurements, I also have SAE tools in my shop and at my job.  I have to, because that's the way things are - especially dealing with older vehicles as I sometimes do.  As Gary said - everything is easier to estimate in the units that we're comfortable with (I still estimate in gallons, feet, etc).  But, if you can start when you're little (like I try to do with my kids), you can be bilingual.  You can "think" in other languages.  A GOOD thing.

I think the best argument for a universal "language" for measurement is the reduced chance for error in conversion or "translation" as it were.  Surely we've all heard the phrase "lost in translation".  Mistakes happen, and it costs money.  See the famous NASA metric mixup http://en.wikipedia.org/wiki/Mars_Climate_Orbiter#Cause_of_failure

If for no other reason, simple calculations within the SI measurement system are ridiculously easy.  It all makes sense because it's designed to make sense.  I'm just an idiot, but talk to someone who deals with the math of SI every day, and I think they will give you similar reasoning.

In the end, if we can all become proficiently "bi-lingual", the best system will prevail given the chance to do so.  Logically speaking, the internationally standardized system WILL prevail, and when it does?  I don't want my kids only knowing how to speak a dead language while everyone else is collaborating and doing inter-galactic super rocket surgery studies.

You're professor was right about the hammer; we need all the tools.