Ebike Battery Pack Energy Density Talk

[emtbeast]

The issue I'm seeing is that each of these Wh/ km charts show useage/ efficiency at max power output. Anytime you go faster, you burn more energy per km.

So, unless I am misunderstanding, for these range tests to be valid the testers would need to normalize for input pedaling assistance AND output power, to properly access efficiency.

Hey, yes in a way you are correct, as you said the faster you go the more power is needed, more power = more torque × rpm.
More torque = more current, and more current = higher consumption/worse efficiency.

I actually don't like to talk about efficiency in Wh/km, I prefer Wh/100m altitude gain. Now if you look at the right side of the chart they provide the incline 0% and 10%, that's how they say Wh/100m also but in a different way.

Now the second part of your question, yes a stronger 90Nm motor at the same voltage(36V) will use more than an 80Nm motor.
Like you suggested if they would even out the input and output bettwen the systems yes we would see the actual differences but mostly due to how the system is built and how good the components are,etc...

Now I still believe that if we see a difference at max power then that difference would grow bigger at a lower power setups.

Motor engineers try to create a motor system that in their opinion is the best, some choose a low grunt motor(Older Giant PW-X2), some go for high rpm/grunt(Bosch SX), some take a midway approach,...what I am saying is that every motor is built and its firmware programmed for a specific way of riding-thus the differences in feel. The testers would need to know the optimum point of each motor to see where it works most efficient, that's is basically impossible to do and so the max power approach imo is good enough to see the overall difference and I also feel that if a motor can provide it should be tested at what it can provide.

The: Wh/100m is universal, it just shows how much a system is capable of in it's max settings.

In my opinion it would probably be pretty interesting and more of real life picture if they would use a preprogramed trail that incorporates different trail conditions(Uphill, downhill, motor assistance off/on, stop&go,...), basically an good mix of everything, then we would see the real picture.

 

[TheKaiser]

90Nm motor at the same voltage(36V) will use more than an 80Nm motor.

I like your idea of the Wh/100m measurement. I may be missing something, but it seems like measuring the energy required to gain altitude (and thus stored potential energy) is a cleaner way of measuring, with fewer variables, than flat terrain, especially if doing a real world test. They'd of course need to specify the system weight, but that could allow for easy conversion for riders/bikes of other weights if you wanted to figure out what you might achieve in the real world.

Quick question on the above quote though, regarding the 90Nm motor vs the 80Nm motor. Earlier in the thread, a post from another user mentioned doing a ride at a higher power than usual, and thus in less time than usual. The casual observer might assume that would use more battery juice, but this person mentioned finishing the ride at the same battery level as when doing the ride at a lower power level, and if I understood correctly, they were attributing this to the fact that the motor did the same amount of "work", but just concentrated into a shorter time period. That actually makes good sense to me, in terms of your Wh/100m measurement, where, all else being equal, you could dole those Watt hours out slowly or quickly, but the same amount of energy will be required to lift the system weight up 100m. So, getting back to the 90Nm vs. 80Nm motor scenario, the 90Nm motor will be able to drain a given battery in less time, but the achievable range between the 2 motors should be just about the same, assuming they have an equivalent Wh/100m measurement, correct?

 

[emtbeast]

I like your idea of the Wh/100m measurement. I may be missing something, but it seems like measuring the energy required to gain altitude (and thus stored potential energy) is a cleaner way of measuring, with fewer variables, than flat terrain, especially if doing a real world test. They'd of course need to specify the system weight, but that could allow for easy conversion for riders/bikes of other weights if you wanted to figure out what you might achieve in the real world.

Quick question on the above quote though, regarding the 90Nm motor vs the 80Nm motor. Earlier in the thread, a post from another user mentioned doing a ride at a higher power than usual, and thus in less time than usual. The casual observer might assume that would use more battery juice, but this person mentioned finishing the ride at the same battery level as when doing the ride at a lower power level, and if I understood correctly, they were attributing this to the fact that the motor did the same amount of "work", but just concentrated into a shorter time period. That actually makes good sense to me, in terms of your Wh/100m measurement, where, all else being equal, you could dole those Watt hours out slowly or quickly, but the same amount of energy will be required to lift the system weight up 100m. So, getting back to the 90Nm vs. 80Nm motor scenario, the 90Nm motor will be able to drain a given battery in less time, but the achievable range between the 2 motors should be just about the same, assuming they have an equivalent Wh/100m measurement, correct?

I have seen some videos of the testing bench, they strap the bikes down with a strap and so create a similar amount of weight to the bike. What I have wondered, does the bike suspension design and the whole bike design also affect the efficiency in some way, what I have noticed on my bike that has a climb/firm setting on the shock better efficiency when in that setting, basically better suspension parts give better grip uphill on the trails, so if we put this variable into play, it takes the conversion about efficiency to the next level.

For the second question. Yes you are correct, for the same distance the rider had a higher energy consumption in less time(he was faster) or the opposite he had lower energy consumption in more time(he was slower).
One thing to note here, this is true only in really all the same conditions for both rides, especially trail and environment conditions and the start battery SOC needs to be the same for both rides, it is definitely possible.

 

[TheKaiser]

I have seen some videos of the testing bench, they strap the bikes down with a strap and so create a similar amount of weight to the bike. What I have wondered, does the bike suspension design and the whole bike design also affect the efficiency in some way, what I have noticed on my bike that has a climb/firm setting on the shock better efficiency when in that setting, basically better suspension parts give better grip uphill on the trails, so if we put this variable into play, it takes the conversion about efficiency to the next level.

For the second question. Yes you are correct, for the same distance the rider had a higher energy consumption in less time(he was faster) or the opposite he used lower energy consumption in more time(he was slower).
One thing to note here, this is true only in really all the same conditions for both rides, especially trail and environment conditions and the start battery SOC needs to be the same for both rides.

Yeah, that makes sense to me. In regard to the effect of suspension on pedaling efficiency, that has been debated for over 30 years with analog bikes, and I can certainly attest to the more efficient "feel" when the suspension is firmed up or locked out, however quantifiable data is surprisingly hard to come by, even after all these years. When adding an e-bike motor into the mix, I had been inclined to think that suspension anti-squat, bob, etc...would be less of a concern, not just because of the plentiful power output, but more because of the smoothing effect that the motor has over the dead spot in the pedal stroke. Even with minimal overrun settings, the motor is going to eliminate a lot of that pulsative effect of a normal cyclical pedal stroke, and I would imagine it will keep the suspension a lot more stable than the same frame design without a motor. That's not to say that you won't still notice the "feel" but I would guess, and I emphasize "guess" that the actual measurable losses due to suspension bobbing would be a smaller percentage of total power output on an e-bike than on an analog bike.

 

[emtbeast]

Yeah, that makes sense to me. In regard to the effect of suspension on pedaling efficiency, that has been debated for over 30 years with analog bikes, and I can certainly attest to the more efficient "feel" when the suspension is firmed up or locked out, however quantifiable data is surprisingly hard to come by, even after all these years. When adding an e-bike motor into the mix, I had been inclined to think that suspension anti-squat, bob, etc...would be less of a concern, not just because of the plentiful power output, but more because of the smoothing effect that the motor has over the dead spot in the pedal stroke. Even with minimal overrun settings, the motor is going to eliminate a lot of that pulsative effect of a normal cyclical pedal stroke, and I would imagine it will keep the suspension a lot more stable than the same frame design without a motor. That's not to say that you won't still notice the "feel" but I would guess, and I emphasize "guess" that the actual measurable losses due to suspension bobbing would be a smaller percentage of total power output on an e-bike than on an analog bike.

Yes you are correct, there is a difference, but it's minimal, I tried to test in a few times on the same trail, but never really put the results into numbers, just by feel of the average consumption I can say better suspension does aid to better efficiency, especially when climbing steep and blocked terrain.

 

[Suns_PSD]

Hey, yes in a way you are correct, as you said the faster you go the more power is needed, more power = more torque × rpm.
More torque = more current, and more current = higher consumption/worse efficiency.

I actually don't like to talk about efficiency in Wh/km, I prefer Wh/100m altitude gain. Now if you look at the right side of the chart they provide the incline 0% and 10%, that's how they say Wh/100m also but in a different way.

Now the second part of your question, yes a stronger 90Nm motor at the same voltage(36V) will use more than an 80Nm motor.
Like you suggested if they would even out the input and output bettwen the systems yes we would see the actual differences but mostly due to how the system is built and how good the components are,etc...

Now I still believe that if we see a difference at max power then that difference would grow bigger at a lower power setups.

Motor engineers try to create a motor system that in their opinion is the best, some choose a low grunt motor(Older Giant PW-X2), some go for high rpm/grunt(Bosch SX), some take a midway approach,...what I am saying is that every motor is built and its firmware programmed for a specific way of riding-thus the differences in feel. The testers would need to know the optimum point of each motor to see where it works most efficient, that's is basically impossible to do and so the max power approach imo is good enough to see the overall difference and I also feel that if a motor can provide it should be tested at what it can provide.

The: Wh/100m is universal, it just shows how much a system is capable of in it's max settings.

In my opinion it would probably be pretty interesting and more of real life picture if they would use a preprogramed trail that incorporates different trail conditions(Uphill, downhill, motor assistance off/on, stop&go,...), basically an good mix of everything, then we would see the real picture.

If we can't normalize for input/ output as each motor is programmed differently, then the next best thing is same rider/ weight/ load and then include the average speed at which each motor completed its range run. If the average speed was higher, we can conclude that it's a more powerful unit that used more power for that reason.

 

[Suns_PSD]

I like your idea of the Wh/100m measurement. I may be missing something, but it seems like measuring the energy required to gain altitude (and thus stored potential energy) is a cleaner way of measuring, with fewer variables, than flat terrain, especially if doing a real world test. They'd of course need to specify the system weight, but that could allow for easy conversion for riders/bikes of other weights if you wanted to figure out what you might achieve in the real world.

Quick question on the above quote though, regarding the 90Nm motor vs the 80Nm motor. Earlier in the thread, a post from another user mentioned doing a ride at a higher power than usual, and thus in less time than usual. The casual observer might assume that would use more battery juice, but this person mentioned finishing the ride at the same battery level as when doing the ride at a lower power level, and if I understood correctly, they were attributing this to the fact that the motor did the same amount of "work", but just concentrated into a shorter time period. That actually makes good sense to me, in terms of your Wh/100m measurement, where, all else being equal, you could dole those Watt hours out slowly or quickly, but the same amount of energy will be required to lift the system weight up 100m. So, getting back to the 90Nm vs. 80Nm motor scenario, the 90Nm motor will be able to drain a given battery in less time, but the achievable range between the 2 motors should be just about the same, assuming they have an equivalent Wh/100m measurement, correct?

A better comparison is your car.

You already know that driving your car, electric or ICE, if you travel faster, your MPG/ eMPG drops rather quickly. As in, you burn more energy per mile. NO way around it, efficiency is lost.

The same is true on our e-bikes. Traveling faster burns more Wh/ mile or any other parameter you want to use such as Wh/ 100m.

 

[Waynemarlow]

Just to support just how complex this subject is ( and it always fascinates me how someone can ride the trail twice and profoundly say that X setting on his motor is more efficient without a single piece of monitoring equipment attached ) then have a look at this formulae

Which is the basic calculation for leg power to maintain a constant speed. Add in the motor parameters and settings and you can probably dedicate a university mathematics graduates masters degree thesis and still not get a good answer.

One of the the outcomes of that formulae is
One of the scary implications of this equation is that at high speed, the power you have to produce is proportional to the cube of your velocity. So, to increase your speed by 25%, you need to nearly double your wattage!

For a bit of bed time reading and fun for those inclined heres a pretty good website

An interactive model-based calculator of cycling power vs. speed

An interactive calculator that lets you explore the relationship between cycling power and speed.

www.gribble.org

 

[timo2824]

Just to support just how complex this subject is ( and it always fascinates me how someone can ride the trail twice and profoundly say that X setting on his motor is more efficient without a single piece of monitoring equipment attached ) then have a look at this formulae
View attachment 152859
Which is the basic calculation for leg power to maintain a constant speed. Add in the motor parameters and settings and you can probably dedicate a university mathematics graduates masters degree thesis and still not get a good answer.

One of the the outcomes of that formulae is
One of the scary implications of this equation is that at high speed, the power you have to produce is proportional to the cube of your velocity. So, to increase your speed by 25%, you need to nearly double your wattage!

For a bit of bed time reading and fun for those inclined heres a pretty good website

An interactive model-based calculator of cycling power vs. speed

An interactive calculator that lets you explore the relationship between cycling power and speed.

www.gribble.org

This is interesting! My experience in the real world is if I ride faster, I finish the trail in a shorter duration, but end with similar battery level as I do riding the same trail slower. So it seems like I use more watts per hour, but the total watts to move my bike and I along the trail remains constant.

 

[Waynemarlow]

This is interesting! My experience in the real world is if I ride faster, I finish the trail in a shorter duration, but end with similar battery level as I do riding the same trail slower. So it seems like I use more watts per hour, but the total watts to move my bike and I along the trail remains constant.

I think you might be entering into rolling tyre resistance and the likes of momentum giving energy efficiency gains over bumps as examples, more so than actual motor efficiency. The laws of physics are quite well known and for you to get there using less energy solely from the motor is just not feasible if we know that virtually every current bike motor are going to be pretty similar in actual efficiency of converting stored battery energy to rotation. There has to be other factors.

However I may be wrong and DJI have cracked how to create energy from nothing, look up liberty engines on YouTube as examples.

 

[emtbeast]

I think you might be entering into rolling tyre resistance and the likes of momentum giving energy efficiency gains over bumps as examples, more so than actual motor efficiency. The laws of physics are quite well known and for you to get there using less energy solely from the motor is just not feasible if we know that virtually every current bike motor are going to be pretty similar in actual efficiency of converting stored battery energy to rotation. There has to be other factors.

However I may be wrong and DJI have cracked how to create energy from nothing, look up liberty engines on YouTube as examples.

I also agree, that it's a complex measurment if it's even possible to do, probably not, so the simplified testing they do on motors is good enough in my opinion and yes rolling tyre resistance is an interesting thing in cycling, where in some cases a wider fatter tire is faster than a skinny one, etc...

Hahaha a good one for 》Energy creation《 If that would be true then a certain company or country would probably need some eagle like freedom... or they would just dominate the world with limitless energy...

 

[Suns_PSD]

This is interesting! My experience in the real world is if I ride faster, I finish the trail in a shorter duration, but end with similar battery level as I do riding the same trail slower. So it seems like I use more watts per hour, but the total watts to move my bike and I along the trail remains constant.

When I ride with my family on my non e-bike, I swear it's more tiring going their 6 mph than my 11 mph on the same trail. It's about momentum over rocks and what not.

But I think what we are talking about is different, steady climb or the like. Going faster WILL use more energy, just like in your car going faster uses more energy.

 

[Suns_PSD]

Just to support just how complex this subject is ( and it always fascinates me how someone can ride the trail twice and profoundly say that X setting on his motor is more efficient without a single piece of monitoring equipment attached ) then have a look at this formulae
View attachment 152859
Which is the basic calculation for leg power to maintain a constant speed. Add in the motor parameters and settings and you can probably dedicate a university mathematics graduates masters degree thesis and still not get a good answer.

One of the the outcomes of that formulae is
One of the scary implications of this equation is that at high speed, the power you have to produce is proportional to the cube of your velocity. So, to increase your speed by 25%, you need to nearly double your wattage!

For a bit of bed time reading and fun for those inclined heres a pretty good website

An interactive model-based calculator of cycling power vs. speed

An interactive calculator that lets you explore the relationship between cycling power and speed.

www.gribble.org

For sure, scientifically accurate numbers are a bit harder to create, but we can certainly do some 'Bro-Science' and learn some things.

For instance, consistently the DJI motors appear to be less efficient than the Bosch. But we need to see if the Amflow bikes are just going faster and completing the same trails faster, to really make sense of this trend.

 

[Waynemarlow]

Sorry Bro Science doesn't work for me. In this situation the numbers of parameters outside of the influence of the motor will vastly outweigh anything Bro Science can throw at any discussion on the efficiency of said motor.

 

[Suns_PSD]

I hear you. That said I get surprisingly consistent results for e-bike battery usage under certain conditions. Both alone and compared to other e-bikes.

 

[Waynemarlow]

At a minimum do you log the input battery Wh's when you are charging, its about the only way that you can reliably work out just what the motor is using without having onboard data logging. The % or bars on a display are so variable that they are almost only a rough guide. When we are getting down to small % between motors as to actual efficiency over a distance, then rough guides are not going to tell you anything that is meaningful.