250W vs 500W

[Russell]

Hi Russell,

Ahhh okay.. I'm starting to see the light here with some of the confusion here. I suppose you do not own a Cycle Analyst?!? You do know that you can use the CA to do the throttle controlling for you automatically?

Did you know that the Cycle Analyst comes with a rudimentary cruise control function built into the box?? They call it the "limiting features" (page 12) and you also have the ability to tune the feedback loop of this cruise control to maintain the transition between on and off smoothly (page 13). So in effect, you can turn a rather dumb ebike into something similar to a Bionx system. It's actually pretty cool to feel the motor turning on and off, to maintain a fixed cruising speed with you pedaling with it the same time. I also limited the current draw too, so it climbs rather anemically without sucking a lot of amps (current limit feature on CA) and it helps conserve the battery usage quite a bit. Downside is that, it pretty much limits your bike to doing a certain speed. You need to restore those limits to higher values if you want the beast of the 9C to return and I find them tiring after doing a while. I much prefer Bionx assist 1 to 4 with a 1 button touch. I wish Justin would incorporate a "Cruise Control" function separate from the current limiting features and can only be engaged with a touch of a switch. The kill switch for this throttle on control would be the brake lever. JVBIKE sells the Bionx brake sensor.

Battery consumption is not a function of speed though. It's a function of acceleration and hill climbing and is controlled by the current draw of a set system, because once you achieve your cruising speed, current draw would be minimal right. Yes, you can somewhat control the throttle to minimize current draw, but if a computer does this for you like the Cycle Analyst or the Bionx, wouldn't that be even better?

I agree with you that the Bionx system is expensive and it doesn't have the guts to go head to head with more powerful motors out there, but I am actually looking into expanding the capacity of my Bionx system to include one of those LIFEPO4 24V 12ah battery ebike.ca has for sale. All I have to do is disable the regenerative braking so it doesn't charge the battery and then I'm set. Part of it is inspired from Denis who also owns the same bike as I do. But learning from his experience, I'm trying it on my out of warranty Bionx battery that I think is no longer 8ah -- probably closer to 6ah. Still 18ah in a nice light package is going to be cool!

Thanks for the reply Russ..

DE.

I have a Watt's-Up meter mounted on my handlebars to monitor power consumed. Again I don't need a CA to limit current because I use 15A controllers and limit current with the throttle. Because I use a trigger throttle I am able to finely adjust power on a continuous basis and after a while just like driving a car it become second nature. I use the motors for assistance so I have no need for high current. My legs can provide very good torque for acceleration and up hills I gear down and pedal vigorously with the motor providing a nice boost.

I of course was being simplistic when I said battery consumption was all about SPEED but that's the bottom-line; how fast you get up to SPEED (accelerate), your SPEED up a hill and the SPEED you run on the flats, so YES it's all about SPEED. Again it's very simple...when my average trip speed is high I use more power. If I want to use less power I go slower. I have a record of every ride I do and it's pretty clear cut...and of course it makes perfect sense.

In the end it's all about personal preference so if you're happy with the BionX that's great but for me it offers no real advantage. As I said one day I may try the kit and find I like it best of all but for now I like the set-up I have and am not done experimenting.


-R

 

[silentflight]

The Bionx can be modded in a few significant ways. I ride a 50 volt Bionx with an 8Ah A123 battery, for example.

 

[liveforphysics]

Even with my normal 1.8kwhr pack, which would be like having a pair of 48v 20Ah ping packs, I had trouble running out of juice when I went on a long training ride with a buddy who does competetive long distance cycleing. Anytime I wanted to get ahead of him, it was effortless, as my bike will still do 50mph, even on a low pack, however, the goal was to ride as efficiently as possible to try to cover the same distance he does. I didn't even have my pedal chain on the sprockets, as I was trying to show him that electric bikes can cover big distances on there own power. I was getting close to the danger 3.2v/cell area by the time we finally got back home. He was also pretty tired from trying to run my e-bike out of juice with his legs.

If you want to be able to hang with a "Lance" level rider, I would start with at least 40Ah at 48v, and 60Ah would likely be better if you don't want her to worry about her hubby needing to cut his rides short for your battery.

 

[DahonElectric]

Hi Russell,

While speed does have a detriment to power consumption, this is not due to speed but rather due to aerodynamic drag. In order to move forward, the cyclist has to push through the mass of air in front. The faster the cyclist moves, the more he or she has to push that mass of air in front. This is called wind resistance. In human cycling, there is almost a limit on how much power you can generate to overcome this resistance and accounts for 70-90% of resistance felt during pedaling. The only other real resistance is climbing a hill.

Here's an example.

A 150lbs human cyclist traveling at 16mph with a wind resistance of say 2mi/h riding a grade of say 0% (flat) will need to output 70w of power (making all assumptions static). At 20mph, 125watts will be needed to push the bike forward. Raise the grade to 1% at 20mph, it will need 230 Watts. Raise the grade to 2% riding at 20mph, you will need to output about 333 watts. Same grade but now at 24mph will require around 485watts of power. So really, the determining factor in energy expenditure is speed, rider weight and gradient as well as wind direction (head or tail wind). However, this calculations are based on an assumption of a ride on a normal race bike. Electric bike is heavier and has more drag partially on the type of motor used and more bags used (battery container/carry items), so obviously more energy will be needed to overcome rider friction, bike friction and air pressure drag. And it doesn't help battery efficient for some people to be riding full suspension bikes either as it is high off the ground and puts the rider in an upright position, thus creating even more drag.

What I have found riding the 9C is that, if I dial my hybrid bike to max out at 20mph and operating at the max amp of 10A (I have a 20A controller), it makes the bike easier to pedal and the ramping up to cruise speed so much smoother. I get good mileage under these conditions. The beauty of the Cycle Analyst is that with its ability to do cruise control and the setting of oscillation points from response to recovery set by iTermMax, iTermMin, IntSGain, PAGain, IntAGain, PVGain etc... By playing with these values, I managed to get a really smooth, I mean smooth transition from throttle down to throttle on just like a car in Cruise Control with acceptable lag time. Unlike you having to variably adjust the throttle by looking at your Watts-Up meter, the Cycle Analyst does this automatically. I think this is a more efficient way to handle power consumption and is similar in how the Bionx works -- fine digital proportional control.
Except, the only difference is that, my Cycle Analyst bike keeps maintaining the cruising speed regardless if I add pedal power or not. If I add pedal power and cruise pass 20mph, the motor gradually turns off.
Whereas with the Bionx, less pedal power means less assist. I can manage say around 8wh/mile, or 9wh/mile on hilly terrain with 100% throttle set to on with my CA bike. If I drop the cruise speed down to 16mph set in Speed Limit function, I get even better mileage. If I set the Max Amps to 5A, the 9C will start feeling like a 200W motor! More exercise!

DE.

 

[Russell]

Hi Russell,

While speed does have a detriment to power consumption, this is not due to speed but rather due to aerodynamic drag. In order to move forward, the cyclist has to push through the mass of air in front. The faster the cyclist moves, the more he or she has to push that mass of air in front. This is called wind resistance. In human cycling, there is almost a limit on how much power you can generate to overcome this resistance and accounts for 70-90% of resistance felt during pedaling. The only other real resistance is climbing a hill.

At low speeds, say less than 10 mph, rolling resistance, a function of tire design, road surface and weight is the predominant force. At roughly 15 mph, depending on the individual bike and rider, rolling resistance and air resistance are roughly equal. At 20 mph air resistance is close to two-thirds of the total resistance felt and at 30 mph air resistance is about 80% of the total. Losses due to mechanical components are generally less than 5% for a well-tuned bike and this remains essentially fixed.

Here's an example.

A 150lbs human cyclist traveling at 16mph with a wind resistance of say 2mi/h riding a grade of say 0% (flat) will need to output 70w of power (making all assumptions static). At 20mph, 125watts will be needed to push the bike forward. Raise the grade to 1% at 20mph, it will need 230 Watts. Raise the grade to 2% riding at 20mph, you will need to output about 333 watts. Same grade but now at 24mph will require around 485watts of power. So really, the determining factor in energy expenditure is speed, rider weight and gradient as well as wind direction (head or tail wind). However, this calculations are based on an assumption of a ride on a normal race bike. Electric bike is heavier and has more drag partially on the type of motor used and more bags used (battery container/carry items), so obviously more energy will be needed to overcome rider friction, bike friction and air pressure drag. And it doesn't help battery efficient for some people to be riding full suspension bikes either as it is high off the ground and puts the rider in an upright position, thus creating even more drag.

Because you did not take into account the forces besides air resistance your figures are off. Assuming the same svelte 150 pound rider on a lightweight flat-bar bike with slicks the power needed to ride at 15mph is closer to 100W and at 20mph it's about 200W. Most ebike riders will need quite a bit more power especially if they're running knobbies.

Once in cycling shape I can sustain about 150W power output which on my Kona Smoke sans motor and battery gets me about a 15.5 mph trip speed at best. Converted to an ebike and riding at 18.0 mph requires about 200 total watts on the flats. I use approximately 7.3Wh/mi from the battery at that speed or 131W. Adjusted for motor and controller efficiency that means about 100W from the motor leaving 100W from me, a 50-50 split. Of course I don't ride under ideal conditions, there's wind and hills and acceleration, so in practice my contribution is likely closer to my sustainable limit of 150W. Therefore when I go out and ride at 18.0mph on my ebike I get a really good workout which equals what I would get riding without the motor at 15.5mph, the difference is I don't have the extreme heart rate peaks with the ebike as I do on the regular bike.

To tie all this back into the original theme of the thread is to say that I use the same amount of power from the battery using my "250W" motor as I do my "500W" motor since I ride at a speed that only demands about 131W on average.

-R

 

[DahonElectric]

At low speeds, say less than 10 mph, rolling resistance, a function of tire design, road surface and weight is the predominant force. At roughly 15 mph, depending on the individual bike and rider, rolling resistance and air resistance are roughly equal. At 20 mph air resistance is close to two-thirds of the total resistance felt and at 30 mph air resistance is about 80% of the total. Losses due to mechanical components are generally less than 5% for a well-tuned bike and this remains essentially fixed.

Absolutely, because the main resistance is the human body.

Because you did not take into account the forces besides air resistance your figures are off. Assuming the same svelte 150 pound rider on a lightweight flat-bar bike with slicks the power needed to ride at 15mph is closer to 100W and at 20mph it's about 200W. Most ebike riders will need quite a bit more power especially if they're running knobbies.

Once in cycling shape I can sustain about 150W power output which on my Kona Smoke sans motor and battery gets me about a 15.5 mph trip speed at best. Converted to an ebike and riding at 18.0 mph requires about 200 total watts on the flats. I use approximately 7.3Wh/mi from the battery at that speed or 131W. Adjusted for motor and controller efficiency that means about 100W from the motor leaving 100W from me, a 50-50 split. Of course I don't ride under ideal conditions, there's wind and hills and acceleration, so in practice my contribution is likely closer to my sustainable limit of 150W. Therefore when I go out and ride at 18.0mph on my ebike I get a really good workout which equals what I would get riding without the motor at 15.5mph, the difference is I don't have the extreme heart rate peaks with the ebike as I do on the regular bike.

To tie all this back into the original theme of the thread is to say that I use the same amount of power from the battery using my "250W" motor as I do my "500W" motor since I ride at a speed that only demands about 131W on average.

-R[/quote]

I know this is simplistic, because I used an average constant shape of a human body as an example, because the calculations I used above is the same rough calculations people use to size racers on triathlon bikes or time trial bikes, but if you want accuracy, probably a wind tunnel test would be the best choice.

The wattage of the ebike's motor is simply what it is capable of generating. To reach a given speed in general using the same battery voltage pack, the 500W motor does accelerate quicker than a 250W motor at the expense of current draw. What I was relaying in the original theme is that with aerodynamic drag, the faster you go the more power you need to generate to maintain that speed for a period of time, unless you're riding a HPV or a recumbent low enough to the ground and with built-in fairings. I don't disagree with you Russell that riding a 500w motor like a 250w does extend battery endurance, but this is not a function of reducing speed, because comes night time when the winds died down a bit, you do use less wattage to propel you forward at the same speed. I've commuted during the night as well (around 8-9 PM) and I do find, at least according to CA, that I'm saving roughtly 20watts/mile. Besides, it felt easier riding fast in the night as well so I don't think it is psychological either.

DE.

 

[dogman dan]

Great discussions guys, but back out in the world, on a real road, when the wind catches me out there, I much prefer the 700 watt aotema, that can go ahead and get me there at 20-25 mph. The 350 watt bike in the same wind will bog right on down to about 14 mph, and god help you if you are climbing a hill too.

This makes riding a 500 watt bike using 250 watts to save power much much much more practical and usefull since the extra 250 watts is there when you do need it. Controllers with amp limiting switches are avalilable if you want to have that feature.

A good kit that has that stuff, is the Fusin, which is not sold in the 350 watt version anymore. But it's a nice gearmotor, like the bafang, and the three speed switch allows an efficiency mode riding if you need it. World Wide Electric Bikes is the vendor.

 

[Russell]

Great discussions guys, but back out in the world, on a real road, when the wind catches me out there, I much prefer the 700 watt aotema, that can go ahead and get me there at 20-25 mph. The 350 watt bike in the same wind will bog right on down to about 14 mph, and god help you if you are climbing a hill too.

This makes riding a 500 watt bike using 250 watts to save power much much much more practical and usefull since the extra 250 watts is there when you do need it. Controllers with amp limiting switches are avalilable if you want to have that feature.

A good kit that has that stuff, is the Fusin, which is not sold in the 350 watt version anymore. But it's a nice gearmotor, like the bafang, and the three speed switch allows an efficiency mode riding if you need it. World Wide Electric Bikes is the vendor.

Yes you definitely have to match the motor to the job. You don't find too many people running Bafangs continuously at high speeds because they simply can't dissipate that kind of power. I’m running mine at 48V/15A for the capability to go faster but I don’t use full throttle much. On my trips I average 17-18 mph and contribute at least half the work so the Bafang is a perfect fit. The 9C is a bit of overkill for this type of riding plus it’s more conspicuous…and I simply like the bike the Bafang is on better.

I recently moved to a hillier location with some 6-8% grades and a few short 12% hills compared to 4-6% at my last location but the Bafang does handle them, albeit with plenty of pedaling. There are no hills I can't get over in a few minutes so the duty cycle isn't high; it's basically up 100 ft, down 100 ft a few times over the round trips. If someone is looking to average over 20 mph or has longer grades then they should look to a higher rated motor. The guy who fed 2KW into a Bafang then asked "what happened" when it smoked cracked me up.

-R

 

[DahonElectric]

Dogman,

Thanks for the tip on the Fusin motor. The 9C motor definitely is a great workhorse to get from one locale to another in a zippy! My 250W Bionx, while efficient in one thing is pretty much gutless compared to the 500W motor. If there's a geared motor in the future that is as low cost as the 9C and as powerful, I will consider swapping.

Again, great discussion thread..

DE.

 

[silentflight]

Interesting to follow along with the discussion here. The Bionx performs much better on hills at 48 volts, so while you still don't get the efficiency of running the motor through the gears, you may enjoy the ride. Like both of you, I like to manage my amp-hours and often ride on pedal power alone until I am fifteen or twenty miles from home, then turn on the Bionx for a fast trip back. Sometimes 250 watts is enough power, but it really is nice to have more on tap when you need it.

At 48 volts my watts up says the Bionx is drawing 1200+ watts on the half-mile 10% grade that is often on my route. That changed my opinion of what a Bionx is capable of.

Scott

 

[deardancer3]

Just Got home with a 250w bionx on a 7 speed Aluminum Folder.

It is basically a Dahon 7 speed aluminum frame, it is replacing the old Giant Revive semi-recumbent that weighed 42 lbs with no ebike kit, and with a 36v NIMH pack on it with a Bionx motor, 57 lbs.

I have a few final nit picky cosmetic things to handle, (shorter screws in some places, pretty up some rough places on adapter plate) but performance wise, wife (50 y.o. 5'3") is elated to have an ebike that she can actually lift in and out of the car by herself, can pedal up a small hill with no assist, yet will do 20mph with little effort and climbs all the hills. 39 lbs with kit and battery with rear rack, kick stand, water bottle and holder, fenders, bells, lights. Top speed is set at 20mph of course.

Now she says she feels as nimble riding this as on a regular bike.

I am not allowed to work on her bikes unless requested but I might go looking for a nice Big Apple or equivelent as the 20" Bionx is now laced radially, no more 2 cross. we shall see what is around locally.

d

 

[dogman dan]

Perfect, That weight is only a few pounds heavier than most full suspension mtb's. My commuter, with motor battery, a quart of water, tools, lights, and whatever I bought on the way weighs 80 pounds or more! Sucks to try to put it on the bus bike racks for sure. Right now I have my fusin on a heavy but nice cruiser frame, but I'd like to try one on a 700c aluminum frame sometime, along with some fatpacks or lipo for a bike with a total weight of under 40 pounds. All my ebikes are far too heavy to pedal anywhere without the motor unless it's downhill.

 

[liared]

I use a standard bicycle converted to an E-bike using a DIY kit from China.
I have just bought a stronger motor for my E-bike - changing to a 36V 500Watt front direct drive hub motor from an earlier 24V 250 Watt front hub motor.
I use my E-bike primarily for commuting. I have a 10AH lithium battery that will hardly support me the full commuting distance if I go full speed all the time with the new stronger motor.
I see from the Cycle Analyst specifications that it allows me to set the maximum AMP power that goes to the controller from the battery.
A small part of my commute is rather hilly and the rest is rather flat so I would like to set the Cycle Analyst to give me max AMP:s during the hilly part and when entering the flat part adjust the Amp delivered setting to a lower “economy ride” value thus saving my battery so it will last the whole distance.
I use the pedal assist function (pedal sensor) and like to get some exercise too during my commute. It keeps me warm and healthy!
Is it easy to change the max amp setting as described above?
I imagine I stop riding when doing this max Amp change. Can it be done by a few simple clicks or turns by hand on the Cycle Analyst unit?
Will I have to disconnect the power from the battery in order to do this?
If it is a simple thing to do I will buy the Cycle Analyst right away.