Miles per amp hour

C

chrisvw

10 W
Joined
Feb 12, 2009
Messages
72
Location
Ft. Collins Colorado
I thought it would be a good idea to share ebike range information. I've certainly noticed that your performance will vary (considerably) based on how fast you ride, weather, terrain and how much you pedal. Regardless, this seems like a useful topic. I struggled with the most useful means to log this and decided simpler is probably better. Inputs on the best way to do this are appreciated.

My latest stats:
3.6 miles/amp hour average in the following conditions
average speed 19mph
48V lipo pack
Crystalyte 5303
Always pedal - moderate effort
bike plus rider approx 250lbs
warm (85 deg F) and flat
7 stops in 22 miles
(294W hours in 22.3 miles or .076Wh/mile)

I've usually used 3 miles/amp hour as my rule of thumb to decide whether I need to carry my charger for longer trips.
Apologies in advance to the kilometer/kilogram inclined.
 
Also see:

Watts at speed:
http://endless-sphere.com/forums/viewtopic.php?f=5&t=14786
 
Amp Hours are not a measure of energy consumed, only a measure of current. It's like miles per 1/4 tank in your car. While it can be meaningful to you because you know your battery, it's not valid for comparative purposes. This is a carry over from the old days of electrics that is better forgotten. Watt hours per mile, or watt hours per kilometer, are the common measures.

With my new pack I'm quite confident that I could easily exceed 5 miles per amp hour at 20mph with no pedaling. Do I think my bike is more efficient than yours? Absolutely not, because in actuality I'd be using about twice the energy as your bike, not 50% less. That's because my pack is at much higher voltage. In useful terms for comparison purposes you're doing about 13wh/mi (not .076), which is great for a big motor, and I was predicting 25wh/mi was possible for me.
 
Chris

..The measure that makes most sense is WattHrs per mile. That takes account of the voltage of your battery. 3.6 AmpHrs/mile at 59.6 Volts is a LOT more energy than 3.6 AmpHrs /mile at 29.8 volts. Most meter systems give you WattHrs as well as AmpHrs. If your meter doesn't, multiply the AmpHrs by the "typical" voltage available to your motor. The real voltage available changes over time and distance traveled but "typical" is a good approximate.

..Doing this would allow a meaningful comparison of energy used.

Don
 
Almost any reporting of energy used or watts-at-speed is better than nothing.

Distance/Ah with a note on system voltage and speed has most of the vitals; a description of the EV puts meat on the bones for others to compare.

I prefer watts-at-speed and a description of the EV. That format includes enough variables for a reasonable comparison to other setups, unless the speed is way outside the norm.
 
Thanks for all the feedback.

I understand Watt-hours per distance is the "correct" measure, but if you know your battery voltage it is easily calculated. I chose miles/amp hour because it is a really easy "figure of merit" for a given battery voltage. Also, as I'm riding, I use amp hour consumption as my battery guage, so it's really easy to calculate if you're having a good or bad day of energy consumption. I can't do the miles/Wh calculation in my head and Wh isn't one of my default measures on the cycle analyst that many of us use.

I was making the assumption that the majority of ebikers are at 36 or 48V and this is a simple 4 to 3 conversion to see if you are in the neighborhood.
 
Fine. If you're going to force people to convert, why not make most learn something in the process. I ride pretty fast, normal cruise in the 35-40mph range. My electrical consumption is consistently in the 20-25 joules/link range.

BTW, It's absurd that the CA doesn't do Watt Hours.
 
John in CR said:
BTW, It's absurd that the CA doesn't do Watt Hours.
Click to expand...

The CA does do watt hours. I rely upon this measurement more than the others for distance information. It even reports the WH/per mile, and I don't do a bit of math.

TJG
 
so my CA says i used 20w per KM...this with a 40 amp controller set to 38 amps...is that a lot?
 
chrisvw said:
I understand Watt-hours per distance is the "correct" measure, but if you know your battery voltage it is easily calculated. I chose miles/amp hour because it is a really easy "figure of merit" for a given battery voltage.
<snip>
I was making the assumption that the majority of ebikers are at 36 or 48V and this is a simple 4 to 3 conversion to see if you are in the neighborhood.
Click to expand...
Sort of. One issue with this is that not everyone's 36V pack is really 36V nominal; I have a 10-cell TS pack that would be 33V, an SLA pack that would be 39V, and a NiMH pack that would be 36V. The differences seem minor but will make good comparisons more difficult.

Another problem is that this only gives you the nominal voltage of your pack, not the actual voltage it is at over time as you use the current; the voltage can sag quite a lot during high acceleration / high current use, making it significantly less Wh than if you calculate via nominal voltage. And while riding long stretches of low current use, it may be much higher voltage than nominal, making the Wh use there higher than if you used nominal.

It *might* average out to be close, but it might not, depending on your trip and riding style. So if you can, using actual Wh readout from a wattmeter (like the CA has) is more accurately representative of your system's power usage.

FWIW, I don't do math in my head either; I have to do it on paper or with a calculator--numbers just don't work right in my brain. :)
 
moostrodamus said:
so my CA says i used 20w per KM...this with a 40 amp controller set to 38 amps...is that a lot?
Click to expand...


My CA reports an avg of 30 wh/per mile doing an avg of 30 mph using the 5303 motor over the course of about 16 miles. I have my CA to limit amps to 40 max.

You'd have to do the math to convert to KM values to see how this compares with your readings.

When I'm easy on the throttle and cruising at 20-22 mph, then my usage is at 22.4 wh/mile.

TJG
 
Doing some conversions....

I have a 2807 9C motor, I average about 35km/hr (21.74mph) over a 20km (12mile) Distance and use 20Watts/Km (12 watts per mile?)

Sound about right? Shouldn't have had that third beer...but its HOT here...

Moo
 
Sounds right to me. Don't forget that when we want answers like this one, the solution is not a simple one.

You have to remember, I weigh more than you (probably), I tow a trailer most days, my terrain is not the same as yours, and the wind conditions are going to be different than what you encounter.

Add to those things that your motor is probably more efficient in conserving power than mine is. When I made my build, I wanted the biggest, most powerful hub motor that I could afford. I did not count the WH/per mile cost, nor do I now.

TJG
 
The Journey Guy said:
John in CR said:
BTW, It's absurd that the CA doesn't do Watt Hours.
Click to expand...

The CA does do watt hours. I rely upon this measurement more than the others for distance information. It even reports the WH/per mile, and I don't do a bit of math.

TJG
Click to expand...

Great. It was absurd that he said it then, because it really would have been absurd if the CA didn't.
 
I use about 9amps going too work(uphill 12 miles) and about 6 amps going home (12miles downhill). I have a 48v 20ah Ping v2.5 and do 30mph on the flat stretches. The most i have used is about 12 amps. I try not to horse the battery too much because the ping cost 800bucks. I have had the new 40amp controller for a week now, with my old crystalye 30amp controller i used about 18 Watts per KM.

New controller lets me maintain 30mph (50KM/H) in stronger winds, longer hills. It remains to be seen if the ping will hold up to that.

I guess that is what stats like Watts/km/miles are for...Maybe 20watts per KM is too much...we shall see yes?
 
moostrodamus said:
so my CA says i used 20w per KM...this with a 40 amp controller set to 38 amps...is that a lot?
Click to expand...
Whr?...

Watts get you speed, Whr gets you distance. (power vs. energy)
 
Is there a CA for dummies guide somewhere here? I'd love to read that thread.
 
moostrodamus said:
Is there a CA for dummies guide somewhere here? I'd love to read that thread.
Click to expand...

The reality of this sport/lifestyle is that there is a lot to learn when you are new to it. One needs to be careful when expressing ideas and asking questions. The terms need to be learned, and applied in the right way. When you said that you used 9 amps getting to work, in reality, you would have been correct in saying that you used 9 Ah (amp hours) getting to work.

Much of understanding what we want to know is just to get a handle on the terms that are used. Learn the difference between amps and amp hours. Watts and Watt hours.

I suggest that you do what you are doing. Read, read, read. Take notes. Most of the things in the beginning will not make sense. Make notes of what does not make sense. The more you read, then little things will start to make sense. Then go back to your notes, and see if the things that did not make sense to you in the past, are starting to make sense after you read and study.

Or, just get on your bike, and have a GREAT time of it! There are times when I believe that some folks have to break things down to a level that is so detailed, it leaves much to be desired for the pure enjoyment of our chosen sport/lifestyle. Of course, there are times to be detailed, and there are also times to just invest in an expensive battery, put it on a e-bike, and just go out and have some fun!!

Sooner or later, all our components break down and fail. No matter how detailed we get in the analysis of things, they will fail sooner or later.

Enjoy 'em in the meantime. :lol:

TJG
 
TJG,

If you're going to lecture someone at least get it right and tell them to use watt hours. Talking in amp hours is like 2 people comparing gas usage as follows: Bob brags that he uses only a 1/2 a tank of gas per week, and Joe responds that he only uses 1/4 of a tank, but they don't know each other's car and Bob drives an econobox with a 12gal tank, and Joe drives a 2 ton truck with a 50gal tank.

Amp hour usage is only useful as a gauge to the owner, because they know their pack, not in posts on the forum unless it's a discussion about battery capacity where the voltage accompanies it.
 
John in CR said:
TJG,

If you're going to lecture someone at least get it right.
Click to expand...

Well, John, what is right? Is it right because you say it is? Is it right because I say it is?

And who is lecturing who here?

But you know what? Thanks for your opinion. I'll certainly give it careful consideration.

TJG
 
Hey

Today I saw sunshine almost all day. My neighbor said "too bad, it's so rainy".. ?

Don
 
TJG,

When you explain to me how watt hours isn't a correct measure of electrical energy consumption, then I'll eat my bike. Amp-hours clearly isn't. Does your electric bill come in kilowatt-hours or kiloamp-hours?
 
John in CR said:
TJG,

When you explain to me how watt hours isn't a correct measure of electrical energy consumption, then I'll eat my bike.
Click to expand...

I do not recall saying that watt hours isn't a correct measure of electrical energy consumption. Matter of fact, I don't recall saying anything at all to you that you could have even interpreted as being close to that statement.

The only thing I recall saying to you, in this thread or any other, is that the CA does measure watt hours. I did not share that information with you in an attempt to make you look stupid, unawares, or even un-informed. Perhaps something in my statement to you has lead to you believe that you need to continue with this diatribe.

What I'm going to do here might make it easier for you to resolve your issue. Ready? Here we go: " John, you are, and were, completely correct, right, and overwhelmingly informative."

Thanks for this opportunity to get to know you better, and my wishes for you remain totally affable.

TJG
 
TJG,

Sarcasm is unbecoming of you, and I'm sorry if you've taken my written words in a way other than intended. ES is a place of learning and sharing, one of the best in the world for EV's, especially ebikes. In that vein it is a disservice to the community to promote or otherwise encourage inaccurate information, and this is a topic that is often confusing. The unit of energy is the joule, which is equal to 1 watt-second, and also equal to 1 newton-metre, but the joule is too small to be truly useful to us as a common measure for our bikes, since we'd be looking at 5 and 6 digit numbers over the common distances of the mile or kilometer. Plus we typically don't have the means to directly measure joules anyway. We do however get all the info quite easily for watt-hours with no tedious conversions. Not only is watt-hours quite useful and easy to obtain, but it also allows direct comparisons of energy usage between all EV's, ebikes, emotos, ecars, etc.

Amp-hours can be a useful number, but really only to the user, like a gas gauge, and sharing miles per amp hour or amp hours per mile with others is incomplete, because it's a meaningless number without voltage. Adding the voltage to the statement completes it, but why force those you're sharing the info with to do the math themselves. That's like starting a discussion about gas mileage and reporting "I average 225 miles using 5.4 gallons."

Another example is that I personally use voltage as my fuel gauge, because it's easy and the discharge curve of my LiMN batteries make it accurate enough to be useful. However, it would be totally inappropriate for me to report that I average a drop in resting voltage of 6.5 volts over 20 miles even if I did provide all of the other details needed for someone to make sense of those numbers.

Watt-hours per mile or per kilometer is the common measure that is useful to all for comparative purposes.

John
 
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