Using wh or ah for calculating range

[Tats]

Interested in real world experience on this one - let's say I have two identical watt hour batteries but at different voltages. eg. 840wh at 36v (23.33aH) and 840wh at 48v (17.5aH).

I know I'll get more real world speed and less range from the higher voltage battery if I'm riding hard because I'm fighting wind resistance etc - but in general normal speed riding will it be the same situation?

e.g. 1C discharge at 36v I assume would be 1.33C at 48v so therefore the lower voltage battery with less C would be giving me the better range if I was working at the same speed?

So, I'd just check the discharge curves to get the relative loss of range? I know there's all the lurking variables like slope, pedalling etc - that's why I'm interested in a real world view not a theoretical one only.

 

[docw009]

Actual wh will depend on the riding habits of the user, I ride my e-bikes in PAS mode at relatively modest (turtle like) speeds.

I do have a watt meter, and I do have a bike that I run on different batteries (36v, 48v, 52v). My small amount of empirical data suggests for the same average speed and PAS level, I'll burn about the same watt-hr per mile (within 10%) at 36 or 52 volts.

If I recall my college level physics classes correctly from long ago, I think that is expected.



.

 

[Drunkskunk]

Watt hours is the actual way to calculate range. I'm sure you already know, but for those who find this question on a google search, Watt hours (Wh) is the actual amount of energy a battery has. If you think of a battery like a barrel, then voltage is how tall the barrel is. Amp hours are how wide the barrel is. And watt hours is how much energy is actually in the barrel.
So at the same speed you will use the same amount of watts regardless of the voltage or amperage.

Except for the Yeehaa factor.
The Yeehaa factor is the brain's inability to ride as slowly, cautiously, and boringly when you have more power available. Stick a higher voltage battery on an otherwise unchanged bike, and you won't be able to resist goosing the throttle, or taking a section of road just a little faster. Even when you are well disciplined, it still will effect your power usage. For some, this might only change their usage by a few dozen watts per ride. For others like me, ....... wewll, YEEHAA!

 

[amberwolf]

Yes, regarding that: On my typical work commute, I have many stops and starts ile (half a dozen per mile at least). But on a longer trip I have much fewer of them, so that even though I am at about the same average speed, it takes much more total Wh/mile (up to twice as much, more with some loads!) for the shorter trip than the longer one, because I usually peg the throttle to get up to speed from a stop as quickly as possible, partly because it's more fun, but mostly so I don't get run over from behind by the cars waiting behind me in line at the traffic lights or other stops.


But either way, Wh is the measure to use to determine pack capacity, and thus range you'll get out of it, as a basic estimate.

Actual range will depend on how you ride, terrain, wind/weather, load, etc.

 

[wesnewell]

Simple answer is ah are relative, while wh are finite. 10ah@36V=360wh. 10ah@48V=480wh. if you ride at the same speed, wh per mile is the same, with maybe a small deviation for motor efficiency, so you'll get more range with the 48V battery pack. There are all kinds of other factors involved like the extra voltage loss of the lessor voltage battery to maintain the same speed with a lessor voltage battery compared to a higher volatge, etc., etc., etc., but all in all, the higher voltage pack will have ~25% more range.

 

[dogman dan]

As long as you ride the same,,, getting the same watt hours per mile, then range will be the same if the batteries have the same actual, real world, watt hours in them.

But the yeehaa factor is hard to keep in check, at the higher voltages, especially if there are more starts and stops.

On a long cruise, limit speed to keep the yeehaa factor toned down, and you will get the good distance you need for the long ride. This is why the kits with some kind of power level selections, or having a DP CA, 3 speed switch, or whatever is so nice when you need that range. Very easy to let the speed creep up.

If you pedal, you can just set a lower gear, pedal in that gear comfortably, and just adjust the throttle to keep your cadence comfy. That will limit speed. Much harder to keep the throttle mellow if you are not pedaling.

 

[footloose]

The Yeehaa factor is the brain's inability to ride as slowly, cautiously, and boringly when you have more power available.

+1 on that, and thanks... I always wondered what the proper technical term was

 

[Salman]

I would also like to ask a question regarding range,

If the simulation from ebike dot ca is telling me that I will get a range of 20km at 30mph with xxx battery, controller amps and tyre diameter. Etc etc .
In the real world how much will I get?
Very few start and stops
Will paddle, so the hub will not use more amps on start and stops.
Slowly accelerate to top speed.
100% flat roads
No, off roading




Sent from my SM-T800 using Tapatalk

 

[Ykick]

There becomes a point where it makes most sense to get into CA (Cycle Analyst) and let all the Wh/mi calculations be done for you. Wired into throttle you can merely adjust simple limit parameters to better insure extreme range extension.

 

[Salman]

All cycle Analyst will perform this way or there are any specific version..

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[wesnewell]

CA's are not fortune tellers. They can't tell you jack about something you haven't done yet. And if you've done it, it doesn't take a genius to do the math. If it takes 200wh to ride 10 miles without a ca, it will take the same with one, assuming the same conditions. Actually, since the CA does use a little power, it will take a little more power using a CA. But you can then brag about having a $150-$200 watt meter. Even if you can't program it correctly. It's a nice accessory, but it's not a necessity by any means. Yep, I had a watt meter for a while when I first started. Just wasted space on the handlebars imo.

 

[Ykick]

CA's good limiter when you wish to maximize range. Also excellent power, odometer, speed, voltage, Ah, Wh meter and cycling computer - but you need to have actually owned and used one to know anything rational about the CA.

Salman - CA V2.4 - all the same with main differences about how they’re wired/connected.

Lowest price $95 USD I’ve ever seen for base model - http://www.ebikes.ca/shop/electric-bicycle-parts/cycle-analysts/ca-dp.html

Depending on your controller it may be possible to connect, hardwire or maybe require external shunt if you’re not comfortable/able to rework shunt connection into your current controller?

The speed sensor is another variation. Gonna depend on your motor? Sometimes with DD motor speed sense can be pulled from Hall Sensor. Any wheel speed sensor tends to work so if you can solder it’s all very configurable.

Feel free to open a thread with your bike and setup? Get some specific ideas if you wish to investigate. This one is probably going to go off rail anyway and we shouldn’t hijack it anymore than we already have/will. Oy vey!

 

[wesnewell]

CA's good limiter when you wish to maximize range. Also excellent power, odometer, speed, voltage, Ah, Wh meter and cycling computer - but you need to have actually owned and used one to know anything rational about the CA.

Well, I guess if you have no self control, it will limit your power usage. It can't increase power, only limit it. A $3 cycle computer gives me odometer, trip meter, speed and average speed, etc., and still works without the battery pack A $3 voltmeter gives me pack voltage. and makes an excellent fuel gauge. Your last comment is just ridiculous. You don't need to own or use something to find out what it can and can't do. You can look up almost anything on the net and find out everything about it without ever having used or owned one. Like I said, it's a nice unnecessary piece of equipment. If you want one, buy it.

 

[Ykick]

I’ve bought 4-5 CA’s. Couple of ‘em went with bikes I sold and a couple I still use.

Years ago I was skeptical but once I researched what they sell used for (check/search marketplace) it’s obviously a sought out and loved device. Never going to lose much money buying a CA if you decide you don’t like it.

But, most folks will find that it adds considerably to their eBiking “experience” and eventually feel naked without one.

 

[Doctorbass]

VERY simple answer:

here is mine:

Ah is not Energy

Wh is.. and it can be converted to Joules, BTU or whatever energy unit you want.... but not Ah

and to determine a given distance you need energy data:wink:


even more:

Wh is Ah x average Voltage ( nominal voltage)... Also the first half of Ah of a battery is at higher voltage (full charge to half charge) than the last half of Ah of the battery.. so the last 50% Ah of a battery countain less energy than the first half

Also.. the last half of Ah is at higher internal resistance so it will output more energy in heat than the first half.

if you plan a trip by using the Ah measurement, you better have to slow down for the return! :wink:

Doc

 

[dogman dan]

Yes,, think in watts and watt hours, and things get much easier to understand.

But you can think in ah for very rough estimates. Useful for making sure your idea for a certain length commute is total fantasy, or might work. 20-23 mph,, 36v,, you should use one ah per mile or less. But not more unless its all uphill or something. Using that crude rule of thumb, you can figure out that your 20 mile daily commute needs a 20 ah battery, or a charge at work with a 10. But your real world results will be different depending on lots of things. Good enough only for knowing a 10 ah won't get you there and back at 20 mph. It might at 17 mph though.


Very hard to predict actual real world range with the sim,, because it's not real easy to guess how hard you pedal. Because your batteries real world watt hours is not always what the ah would indicate, and it can vary quite a bit depending on how the battery is discharged.

I'm weak, a sometimes sick old man. So I tend to pedal at less than 100w. A pretty fit guy might go at 150w all day, and an average joe ( not fit, but not sick) can pedal 100w for an hour or even two.

It does not have to be a CA,, any cheap watt meter will do. The CA is costly, and does not do all it's functions on most e bikes. But they have a nice display, a good mount, and don't lose the data when the battery is disconnected.

But even if you have a cheapo watt meter, then you can tell what your pedaling amounts to. Hit cruise speed on the flat, pedaling like you can for hours. note the watts the motor is pulling. Then stop pedaling. you should have to increase the throttle to keep going exactly the same speed. Now note the watts.

Now you know how much your pedaling amounts to, and can use the sim by using their watt hours number, then subtract yours. Easy math,, say the trip should take 500wh, and 45 min. You pedal at 125 w for 45 min. So that's 125 wh in one hour. 45 min will be about 90 wh. Your trip should take 410wh with your pedaling added.

Once you have any kind of watt meter, then you can know what your typical watthours per mile is, including your pedaling. You will also be able to find out what your batteries real world capacity is,, when discharged using your bike.

Mental calculations while you ride are fun for some,, torture for me. I really like my CA for it's display of my average watthours per mile for the trip. I can calculate at home, that to ride from home to whatever and back, on X battery, I need to get Y watthours per mile. Say that is 25wh/mi. As I ride,, If I start seeing 30 wh/mi on the display,, I won't make it.. Maybe its windy that day. Or my pedaling is not doing shit. So I slow down some, get closer to 25, and then I can relax and enjoy the ride without having to worry or do math in my head.

 

[Tats]

Thanks everyone for your answers - I've been riding using the aH on my CA v2 as my range indicator as its on the primary display screen. But, I've been using average Wh/km as my go to indicator of efficiency.

I average between 13.5 and 14.9 Wh/km with my BBS02 at 36v and my guess based on all the info here is as long as I don't hit the yeehaa button too hard I'll pretty much average the same. Therefore going the higher volts allows a corresponding drop in aH. At the moment I have 90 cells of Samsung 32E - 10s9p so if I went 14s then the 7p would give me ample range being 98 cells.

Not planning on the change of battery now, but a friend is looking at a similar setup with a higher voltage.

 

[dogman dan]

Once you start thinking in wh, it becomes really clear. 48v x 15 ah = 720 wh. 36v x 20 ah = 720 wh. As long as your configuration has the same number of cells, it will have the same wh.

But,,, it's possible the higher voltage sags more under load, resulting in less usable wh for the pack. IF,, you ride so it sags that is.. If you ride so it does not sag, it should discharge the same real world wh.

Once you have the pack built,, and see how many ah it can give,, no reason not to just watch the ah used display on the CA for most of your trips. Its conveniently there on your screen, along with other stuff you want to know.

But for your calculations,, use the wh used compared to the known capacity in wh, and your wh/km, and you will know to the km what your remaining range is. This is not set in stone though,, that is your range at X wh/km. Lower that wh/km, and the battery coughs up more wh,, and your pedaling is more of the total.

For me,, the magic number is 25 wh/mi. If I can hit that,, all my batteries together can go 80 miles. With the next town, drink of water, or plug up to 70 miles away, this can be crucial to hit that 25 wh/mi. On a shorter trip,, obviously I can afford to haul ass, not pedal at all, etc. No range anxiety on short trips.

 

[Ykick]

The way I use CA as limiter or rather (range insurance) is to test enough to find “worst case” Amp limit.

For example, if 25Wh/mi is my consumption which will deliver worry free range for a given battery pack - I simply adjust CA throttle Amp limit until my worst case WOT (wide open throttle) consumes 25Wh/mi.

In the case of my usual long range bike, that’s about 8-9A peak. Now, majority of the time I don’t need to be that conservative and I would prefer more “Yeehaw” for my shorter trips so a simple change in the CA menu bumps that up to whatever my controller Amp limit happens to be.

But when faced with 25 mi ride on 700Wh battery pack it’s nice to know the CA can be utilized to transparently insure I’m going to have enough battery for that trip.

Of course, knowing your power consumption, using a speedometer, calculating in your head and then disciplining your throttle use can accomplish the same thing. If that makes you happy, go for it.

But for myself, that’s a lot of extra BS when I’d rather be paying attention to a long ride.

Coupled with the fact that used CA’s are basically a form of currency around here - net $$$ cost is actually very low.

For example, I’d be hard pressed to lose more than $40 buying a new CA then turning around and selling it here in marketplace. Don’t take my word for it, do a search history of the few used CA’s that have sold and you’ll see what I’m saying…

I’m bringing up a methodology that works well for me. To each their own, I hope some of my journey(s) can/will help others.

 

[Tats]

Interesting setup on your CA - WOT equalling your range requirements. When planning on longer runs I've used the satiator simulator to give me an indication of wH in the pack at a given voltage multiplied that by 80% and that's given me the average wH/km and I've cycled to that. Must admit the adaptto range feature, initial PAS settings upon power-up and string voltages are the features I'd like a CA type device to have in a future release.

 

[dogman dan]

Absolutely,, if its flat you can use a DP CA to limit amps,, thus ensuring a slow enough ride to make your range. You can also limit speed, but I don't like the way that surges and dies, surges and dies.

Since many of my bikes have a display, I can just use that displays power levels to limit speed when I need to,, then instantly punch up full power when needed to climb a mountain.

Definitely harder to ride in the bottom quarter of the throttle, and hold it steady, so lowering the power and riding closer to WOT is nicer.

Another option that works for speed limiting is to just build a slower bike. 20" wheel makes it more efficient on starts and a better climber, and combined with a less than the fastest rpm winding, you end up with a bike with tons of power to climb, but a more like 20 mph top speed. Of course,, if speed is crucial to surviving where you ride,, that idea sucks.