Test: 200w electric bicycle efficiency = 1512 MPG equivalent
 

The best efficiency I've been able to squeeze from the ForkenSwift so far this winter is 107.7 equivalent MPG (US), or 311.5 Watt hours / mile if you speak EV.

http://forkenswift.com/album/21-fs-pedal-boat.jpg

bennelson says an efficient run on his electric Kawasaki motorcycle is 15 miles and about 1 kWh to recharge. That works out to 67 Wh/mi, or 503 eMPG, by my formula.

You big tease. :p


BTW, what is your formula for calculating equivalent mpg?

Conversions:

1 kWh = 3412 BTU
1 gal (US) gasoline = 114,500 BTU

EDIT: and the electric efficiency figures quoted are energy use "at the wall" (including charging inefficiencies), not just energy drained from the pack.

How are you measuring the "at the wall" number and how efficient do you think your charger is?

At the wall measurement is from a Kill-a-watt meter.

I'm not really sure how efficient the charger is because I don't have on-board instrumentation to tell me how much I've fed into or drawn from the pack.

EDIT: but I have seen references of 70-80% charger efficiency chucked around.

Oh my...

8.7 km (5.4 miles)
0.12 kWh to recharge

= 22.2 watt-hours/mile

= 1512 MPG (US) equivalent

Note: obviously it's not a direct comparison. The car & motorcycle are faster than the e-bike. So their efficiency is calculated at a higher average speed.

But the imbalance is countered somewhat by the fact that we're comparing the best case efficiencies of the car & motorcycle, vs. a flat-out worst case run on the e-bike.

Yes, I avoided using the brakes as much as possible, but I did not drive for load or accelerate gently to minimize resistance & Peukert losses, as I try to do in the car. No, I pretty much had the twist grip pinned on "GO!!!" for the full 8.7 km.

Also worth noting: if I'd pedalled some, maybe I could have doubled the electric efficiency. Not an option (yet! :p) in the ForkenSwift or on the motorbike.

Call some charger mfr.s and ask them if they'd like to provide you with models to test for your EV web site. Then just accidentally lose the best one. ;)

1512? Nice... with lights on or would that have cost 100 MPG?

Nice, I'm gonna try to get the wife a little e-scooter sometime. I think I can handle a 500-700mpg equivalent. Much better than her Cavalier is doing...

E-bikes really are insanely efficient!

One thing you do have to watch is what charger you use.

I did some tests on my cycle using a cheapo 1.5A 36V trickle charger that came with my electric bike hub wheel kit. Man does it charger the cycle slow!

However, I also tried charging my batteries with a couple big old "charge your car batter" 12v chargers which were higher amp. They were about HALF as efficient as the little solid-state trickle charger!

A Killawatt is a great device for measuring electric use. I have slain phantom power in my house down to a $30 a month electric bill.
I think measuring power use at the wall is the only fair way to do it, because it builds in charger efficiency into all the equations. This encourages people to use better chargers!

I saw an E-bike that ran off a couple of DeWalt Lion batteries - that was pretty cool too!

I'll throw mine in here for some more data if someone wants to figure it out since I'm smart enought. It consistantantly takes 3.7 hours to recharge after a 26 mile ride with assist and a average speed 19 mph.

So if it charges at 46 watts/hour and takes 3.7 hours thats 170.2w

26 miles
.170kw to recharge

6.55 wh/m

I don't have charger numbers, just amp meter and volt meter numbers from the bikes on board meters, cruseing up and down my mostly flate road my very rough amp average is 12, with my voltage droping to 28 volts, my speed is averaged at 22mph with a 27mph top speed (digital bike speedometer) without pedaling and starting from a dead stop.
so I have 12 amps times 28 volts (poorly built 32v pack) is 336 watts while crusing at 22mph comes to... 15 watts per mile, I haven't used it enough to have charging numbers, but my DeWalt batteries that are going on in the spring take 100 watts (Kill-a-watt meter) each to charge a 79.2 watt hour battery pack... yes I know there is some fuzzyness in there, right now my driveway and road are both covered with ice, when that changes I'll get better numbers, but from what I can tell my 22mph crusing speed uses a nice 15 watts out of the battery, ad 20% for charging, then a little more for float and self discharge, and it's I figure 20-22 watts per mile is a safe number... pretty close to Metro's number.
I have a brushless 3 phase motor, so it's a more efficent design then the schwinn, and more powerful to boot, from a dead stop going up a hill without pedaling I've seen the amp meter jump to 28-30 amps or around 1,000 watts.

By my calculations, that works out to 5130 mpg (US) equivalent. You're obviously doing a lot of assist!

Yes and no i do hypermile the pack. It's just like driving the car. I engauge once I get up to speed, off on descents and hills. :turtle:

So what would the formula be to convert kWh/mile into mpg? Or kWh/km into L/100km. :p

Conversions:

1 kWh = 3412 BTU
1 gal (US) gasoline = 114,500 BTU
The bike went 8.7 km (5.41 miles) on 0.12 kWh

0.12 kWh = 409.44 BTU (0.12 * 3412)

409.44 BTU = 0.003576 gal (US) (409.44/114,500)

5.41 mi / 0.003576 gal (US) = 1512.9 mpg (US) equivalent

You can do the mpg/L 100k conversion. :)

So I guess the formula for mpg (US) equivalent is:

mi. / kWh * 3412 / 114,500

Might have been my bike. Built it as soon as I was able to get hold of the batteries at a reasonable price a year and a half ago. As far as I know, it was the first seventy two volt Dewalt setup in the country. That has been long surpassed now and some of my ebike friends are building their own BMS's and chargers for the A123 cells that are used in the Dewalt chargers.
All right. Can't figure out how to load images here. I think I have it as an attachment though.

As for MetroMPG's formula it helps to remember that we can cancel labels when we do the math.

For example: 1 mile/20Whr x 1000Whr/3412 BTU x 114500 BTU/1 Gallon

These are all conversion factors except for the first term which is an actual measurement from one of my own rides. You can see that the Whr terms and the BTU terms will cancel when multiplied out and all that is left is numerical values and miles/gallon. From there it's just a simple matter of punching the numbers into a calculator.
JJ

Thanks for correcting my laziness, JJ. I can still hear my high school physics teacher shouting, "UNITS!!!"

Wow, I didn't realize they were quite that efficient. I've got to get on that and get one built. Some days when it is sunny, we have extra power from our pv panels, that could be put to use in this manner. For some reason I thought that they would need to be charged w/250 watts for 10 hours or something rediculous.

I think you may end up quoting miles per dollar or miles per KW-hr to compare with any energy source because the power plant is burning some fuel at 30 to 40% efficiency by the time it get to the battery. So we might want to stay away from any miles per gallon numbers. Evenually miles per unit of energy from any source will be similiar i suppose but until then miles per dollar is about as fair as you could get. Even windmills and pv panels cost dollars. What do you think about this approach?
How do we add enviromental costs to this?

It's quite hard to do that considering the power source varies from place to place. The gas I use versus what they use in down south isn't even the same right now, and ergo has a different amount of energy. Realistically it will vary from station to station based on the amount of ethanol added too. And how would you treat sources such as the captured methane from cow's feces that Vermonter's buy and would otherwise cause more environmental harm? I guess we would get infinite values since it's reducing methane which is many times worse than CO2.

"Only?" Even at only 30 to 40% efficiency at the power plant, electric drive is far more efficient than internal combustion.

That's problematic. Don't forget: some people will pay more for efficiency; the bottom line isn't always cost.

On top of that, people pay anywhere from 5 or 6 cents all the way up to 20+ cents per kWh for electricity, so quoting a MP$ figure for electric falls apart there. The price of fossil fuel doesn't see the same kind of spread across the country (some, but not that much).

I bought a windmill which will take 7 years to pay for itself, just to save from buying 17,500 kw-hrs @ $0.10 over that time. That's the cost I'll pay.

I was just looking at the bigger picture, it's good that electric cars fit the job in a lot of places. But for the sake of comparison the dollar is fairly consistent over the US at least. That's how i will know what some people will pay for efficiency.
If i say my energy cost is 16 miles per $. Then everyone can compare their cost in their location.

Would it be easier to quote miles per kw-hr, rather than trying to figure out how many gallons the power plant had to burn?

Since this post is about an efficiency test of an electric vehicle, I don't know how to convert that to other energy sources for the purpose of comparison.

Here is a link to energy unit conversions.
http://www.cogeneration.net/FuelAndE...quivalence.htm

There are many of them out there.
JJ

I am hinting that to get gallons, i would need to know the efficiency of the power plant and transmission to the battery.
311 watt-hrs / mile i understand.
At my electricity cost that would about 32 miles per $.
In contrast to my car at 16 miles/ $.

Ah, now I see what you're getting at. You're opening that can of worms.

EPA doesn't use power plant or efficiency of transmission to determine MPG equivalent of electrics. It uses power usage from the wall (which factors in charger in/efficiency).

If we're going to force electrics to factor in power plant to wheels, then to be fair we must also change the way we measure fossil/liquid fueled vehicles, ie. factor in energy use in refining and/or transportation of the fuel to the pump.

I think it's best to stick with the way the EPA does it.

It would take a team of scientists to calculate the cradle to grave path for a drop of energy. By cost i didn't mean that was the only cost. (e.g. enviromental) i just thought converting to currency would make it easier to compare the direct economic forces. Economics tends to influence the direction unless the feds intervene forcefully. That means we need pioneers like the ecomodders all the more.

MPG vs Watt Hours / Mile
 

While this thread is a bit dusty, I typically use the dollar/gallon VS btu/kWh because people always ask one of two questions -

How many MPG does it get?

How much does it cost to run?

Unfortunately, most people aren't familiar with btu's or kilowatts.

If you equate MPG based on what it costs to fuel an IC car, VS the price of electricity, than I use the present cost of gasoline (today it is $4.56 / gallon for regular) and the present cost for electricity to charge my EV (6.5 cents / kWh - 80 % geothermal here, balance is other renewables plus natural gas peaker plants).

Using the numbers above, the 'fuel' cost per mile to operate my Citicar is 1.625 cents a mile at 250 watts hours/mile.

It gets about 280 MPG when comparing today's gasoline cost. But as stated, this is a moving target, and has the effect of making electric cars appear more 'efficient' every time the price of gas goes up.

Using the BTU information, it gets 134 MPG. Seems to me that 134 MPG is rather understated... Feels like my 'MPG' is much more than that as the cost per mile is almost nothing.

IMHO it seems that the best way to keep records is watt hours/mile since price is a moving target, but MPG based on the current price of gas is more accessible to the unwashed. Is the standard here to use BTU equivalents?

easiest way it to calculate the amount of energy in a gallon of gas , then go by that for your electric usage.. as for the efficiency of the electric plant.. hard to tell unless you ask them and they tell you, usually they're more efficient than a IC engine by a long shot.

I have been doing my electric motorcycle fuel economy based on converting both gasoline and KWh into BTUs.

Electricity is measured from the wall, which takes charger efficiency into account - which is good, it encourages people to use an efficient charger.

My cost per mile is right about at 1 cent, so figuring economy based on price of gas is real easy - just move the decimal point in the gas prices over two places.

I usually state my economy based on the electric to BTU conversion as stated in MPG - right around 300 MPG. Then I say that "but based on the COST of gasoline, it gets the equivelent of..."

I also mention how electricity can be made from solar, wind, etc. while gasoline cannot.


There really doesn't seem to be any good standard to stating "gas mileage" of an EV to the masses. Watt-hour per mile is good to use for electric vehicle folks, but I think it is worth it to convert to MPG for everyone else.

Tom: I don't think there's really a "standard" here ... but:

I tend to agree that eMPG based on BTUs is the best way to catch people's attention, even if kwh/mi (or km) is a better measure.

The most common question I get regarding efficiency is "how much does it cost to recharge," followed closely by, "and how far can you go on a charge?"