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Required DC gearmotor horsepower to push a bicycle?



 
 
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  #11  
Old January 12th 16, 08:22 AM posted to rec.bicycles.tech
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Default Required DC gearmotor horsepower to push a bicycle?

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  #12  
Old January 13th 16, 12:07 AM posted to rec.bicycles.tech
Andre Jute[_2_]
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Default Required DC gearmotor horsepower to push a bicycle?

On Monday, January 24, 2011 at 8:06:01 PM UTC, John Doe wrote:
Specifically... What is the approximate required horsepower for a DC
gearmotor to push a bicycle at 20 mph or less on terrain less hilly
than San Francisco.

Thanks.


Mmm. I'm 205 pounds and my bike, fully trimmed up with luxury gear and carrying all my painting equipment weighs at least a quarter that much again, call it one-eighth of a ton all up. A 250W high-torque front motor (Bafang 8FUN QSWXK) I fitted had no problem moseying bike and gear and me along at the 15mph legal limit, at which point it would throttle itself back to maintain 15mph. Also good uphill if fitted with a big enough battery. (You have to understand that the size of the battery and the quality of the cells not only regulates the endurance of the battery as in distance it can cover before it becomes dead weight, but also its instantaneous discharge capability, which you can guess at from the C rate of individual cells.)

The 250W also did well enough on slopes but I live and ride among hills (my town is known as the Rome of West Cork...), where a bigger centre motor (Bafang BBS350) is good for well over the legal limit on the flat and, again noting the caveat of the battery being big enough to deliver the necessary current for the length of your longest hill, lets you storm up hills quite exhiliratingly. Of course, the battery for such antics is bigger, heavier and more expensive.

So I would say that on the flat 250W will do you fine, and in San Francisco 350W would be better. If you're lighter, disciplined about luggage, and willing to pedal a bit as well, a high-torque 250W motor with a high quality Panasonic or Samsung cell battery will very likely be good enough for San Francisco as well, though 20mph would wear it out fast. My QSWXK wore out in 3 years and about 3500km of hard use, and I still thought it a bargain; others are also beginning to understand that electric motors on bikes are a consumable item. (The motor itself is the cheapest part of the system, less than a hundred bucks for a quality front motor, and the tools for opening it are more expensive than a new motor, so you just trash the old motor and buy a new one.)

Here's the expected speed freak piccie (2nd photo down) of my bike this past autumn, not too far from where I live --
http://thorncyclesforum.co.uk/index....82377#msg82377
-- which also shows the sort of hills that differentiate between a 250 and a 350W motor.

Here is a photo-essay on my bicycle site which explains some of the considerations in choosing an electric motor for your bike, and shows the fitting procedu
http://coolmainpress.com/BICYCLING.html

Good luck.

Andre Jute
HiTorque
  #13  
Old January 17th 16, 01:13 PM posted to rec.bicycles.tech
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Default Required DC gearmotor horsepower to push a bicycle?

On Monday, January 24, 2011 at 3:06:01 PM UTC-5, John Doe wrote:
Specifically... What is the approximate required horsepower for a DC
gearmotor to push a bicycle at 20 mph or less on terrain less hilly
than San Francisco.

Thanks.


Fully depends on rolling resistance.
(and weight of rider etc)
A factory stock Currie Ezip Trailz (450w dc chain drive PM motor) which is more or less a beach cruiser.
74lbs bike, 26x1.9" 65psi tires etc.
And this 200lb rider etc uses about 9.5-10A wide open on the flat w/o wind.
24V times 10A=240 watts.
It also means if you could get all 10Ah out of factory battery you would go
close to 15mi (15-16mph wide open) Reduction of throttle to 10-11mph vs 15-16
drops current draw by almost half! (extending range)
A 700c road bike, 250w motor 85psi tires can do this on maybe 6amps @ 24v or 150w (never had the meter on that bike to tell, just guessing based on range and feel)
Hope this helps.
 




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