EV Motorcycle Build (in my head)
 

So I have looked into building an electric motorcycle for getting around town, and back and forth from work. I don't have the funds yet, but I am still in the planning stages so that isn't and issue, but I think I ran into some issues. I have been running the numbers for a while and after looking at some other EVs it seems I may have my numbers off... According to my math this electric motorcycle I have thought out should be able to achieve 357.04mpg at a cruising speed of 55mph. Something must be wrong here though because I haven't seen any other home-made EV motorcycles get numbers these high and I hardly know jack about EVs... Even crazier is that I want to fully enclose this motorcycle to get as close to about .35cd as possible, which (according to my math) bumps the mpg up to 492.42.

I have attached the file of the entire build.
Can somebody tell me where I went wrong?

It'd seem like you're planning on using some sort of Lithium chemistry. Did you account for ~80% allowable Depth of Discharge? That won't affect your MPGe rating, but it will change your range.

Not sure how to factor that in. Most of this spreadsheet was from another person who made his own ebike and I have made a few changes and additions to it. He did not opt to use lithium, so the math on that may be off, I just dont know what I would need to change.

Is my formula for MPGe correct?
(Driving Range x Gas kWh) ÷ (Voltage x Amp-Hrs/1000) = MPGe

My math:
74.59miles x 33.7kWh ÷ 7.04kWh = 357 MPGe

This also shows that if my driving range is lowered (say due to the ~80% Depth of Discharge) my MPGe will also be reduced.

Your notes on the Excel sheet say your batteries are rated for 44 Ah, and you're figuring 3.2V nominal per cell.

70.4 V * 44 Ah = 3097.6 Wh (or 3.0976 kWh). At 80% DoD, that gives a usable figure of 2478 Wh. At 65%, you'd get 2013.44 Wh.

AHA! FOUND IT! H/I/J 32-34 aren't quite right.

If putting all 22 batteries in series to get 70V, you don't increase the capacity at all. You've still only got 44 Ah. Voltage * Amp-hours = Watt-hours.

Cars are between 200 and 400 Wh/mile. A motorcycle is probably around the same; Ben Nelson would probably have the best numbers.

65% DoD was 2013 Wh. At 400 Wh/mile, that's 5 miles range; 200 Wh/mile, it's 10 miles range. Not even close to your 75 miles.

I'm still working out what exactly is wrong in your sheet, but I wanted to try and get a reply up kind of quick.

Thanks for looking into it. Idk why the sheet your looking at says 44AH batteries. Mine says 100AH, but regardless I see what you mean about H/I/J. If I change I-34 to 100AH it brings me down to a puny 3.39miles and that is without changing the WH/Mile. If I change that to 400 as well I might as well just walk, heck its only .8miles away right? Wow I thought I made a little mistake, but I seem to have made a HUGE one and made this whole thing pretty pointless. Sad face :(

Dang, what a sad waste of time.

Okay, here goes. Your note on the cell said 44 Ah - but maybe that's from previous spreadsheet user.

EV-calculations

Therefore, the Wh/m usage = Voltage x ( Current / Speed ) = X Wh/m

K21 in your sheet is wrong. It should be A34 * (J19/I14).

I34 is wrong, too. Your total amp-hours is the same as amp-hours of single battery. I32:I34 should be deleted.

*IF* you can really get it to work out at 94 Wh/mile, you still get ~48 miles at cruise on 100Ah at 65% DoD. After losses and Peukert; you'd probably get 85% of that 48; giving ~40 miles total range.

94.39 Wh/mile seems really, REALLY efficient! I'm not sure that you can get that low.

If it's only 0.8 mles, why not an e-bicycle?

I've made some changes to your sheet (as described) and have attached a new copy.


*EDIT*

I messaged Ben Nelson on Twitter and asked him to weigh in. :)

Thanks for the info. Did you double check the Driving Range (K-34) formula to verify that it is still correct after the changes you have made? If so, I would still be very happy with 48.48 mile driving range at a cruising speed of 55mph. My goal is 300MPGe so if I end up getting 48.48 and add a full fairing to lower my cd down to .35 that still puts me at 67.94 miles and 325.21 MPGe.

I will be using LED's for all lighting other than the headlight, which will help the Wh/m usage, but I think most of the electrical power needed is going to be from the mechanical power required to drive the motor. So far, I haven't touched those formulas.

Looks like some good thoughts flying around here.

To start with, 357 MPGe is NOT way off.

The very first thing I did after I built my electric motorcycle was reset the trip odometer, go for a ride, come back and recharge it with the charger hooked to a Kill-a-watt to track the energy used.

With the distance tracked by the trip odometer and the energy to recharge tracked with the kill-a-watt, (including charging losses and/or inefficiency of the charger) I could calculate the electrical equivalent MPG. On my very first ride, it clocked in at 321 MPGe.

M.I.T. has a nice fact sheet on energy conversions.
http://www.mitenergyclub.org/assets/2008/11/15/Units_ConvFactors.MIT_EnergyClub_Factsheet.v8.pdf
Download it, save a copy, and print it out. It's good info to have.

On that sheet, it lists how much energy is in a gallon of gasoline (and diesel, and bio-diesel, and ethanol, and uranium.......)

Using that info and knowing how far you can go on a set amount of electricity, you can do a little algebra to figure out your real MPGe. Getting over 300MPG or about 100 watt-hours per mile is NOT unreasonable.

Electric motorcycles have the ability to be amazingly efficient compared to gas cycles or even electric cars.

Also, keep in mind that the real world is a very different place than a spreadsheet. Spreadsheets don't have hills and bad weather. And I've never fallen off a spreadsheet and broken my ankle.

There are other weird variables too. I've noticed that the most efficient charging is in the middle of the pack. If I use the "middle of the pack", that is if I take trips that are a middle distance of what my pack can handle (not really short trips, not really long ones) the batteries soak up the charging energy the most efficiently.

There are so many different variables, all of which will only work to bring your efficiency down.

But really, all that said. EV Motorcycles are great! Build one! They are fun and efficient

PS: If you want to know more about my cycle, you can read about it at 300MPG.org I named my blog that based on the extreme fuel economy of my electric motorcycle. 300 MPG seemed high enough. I don't think anybody would believe 321!

I did check it - and the numbers for Wh/mile and driving range didn't change, even after replacing them with new formulae. The big thing was the oops with Amp-hours.

Ben - thanks for coming by ;) If ~100 Wh/mile is good, then that's super awesome! I've never looked at motorcycle numbers, so I was scared and wanted to be conservative until an expert came by. :)

VERY glad to see that my goals seem reasonable. You had me down for a bit with the 400 Wh/m thing. I thought I was going have to be swapping the ebike idea for just building a recumbant reverse trike (pedal power). I realize that this is all theoretical for now and the actual results will definitely vary, but I am just making my shopping list and crunching the numbers right now.

Thanks for the help. If all of the numbers seem to be ok now (thanks again for the edit) I guess all that is left is to build this thing (when funds permit).