Test: 250w electric bicycle efficiency = 1512 MPG equivalent

[MetroMPG]

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.

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.

I've been wondering how an electric bicycle compares to these. So I went for an 8.7 km spin on the 250 Watt electric Schwinn. No pedalling. Top speed seen was about 28 km/h (17 mph) - but it's more like 22 km/h (14 mph) on the level.

It's recharging now. I'll post back later with the results.

[Daox]

Originally Posted by MetroMPG

It's recharging now. I'll post back later with the results.

You big tease.


BTW, what is your formula for calculating equivalent mpg?

[MetroMPG]

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.

[Who]

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

[MetroMPG]

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.

[MetroMPG]

Oh my...

8.7 km (5.4 miles)
0.12 kWh to recharge

= 22.2 wH/mile

= 1512 MPG (US) equivalent

[MetroMPG]

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! ) in the ForkenSwift or on the motorbike.

[Who]

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?

[AndrewJ]

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...

[bennelson]

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!

[Lazarus]

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

[Ryland]

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.

[MetroMPG]

Originally Posted by Lazarus

I'll throw mine in here for some more data if someone wants to figure it out

6.55 wh/m

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

[Lazarus]

Originally Posted by MetroMPG

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.

[Thalass]

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

[MetroMPG]

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

[jjackstone]

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

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

[MetroMPG]

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

[james]

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.

[diesel_john]

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?