how fast can a 38.4 volt 500 watt motor make an e-bike go at

elvispilot

10 mW
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Jul 15, 2013
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can a 38.4 volt 12ah battery and a 500 watt motor make a bicycle that weighs 65 pounds and myself (165 pounds ) go at 45kmh for 20km?
 
elvispilot said:
can a 38.4 volt 12ah battery and a 500 watt motor make a bicycle that weighs 65 pounds and myself (165 pounds ) go at 45kmh for 20km?

500W actual output will give you maybe 35km/h at the high end on level ground with neutral wind. Range is always a function of battery capacity, but if you can get a true 12Ah at an average of 38.4V, then your range at 35km/h would be about 32km.

Motor and battery capacities are always nominal, and subject to many variables.

You'll need at actual 1kW of output to sustain 45km/h on the flat.
 
thanks for the quick reply
http://www.youtube.com/watch?v=nfoRtqvx76o
what do you think of this? this bike has a 500 watt motor and it's going at 50kmh, is that possible?
 
elvispilot said:
thanks for the quick reply
http://www.youtube.com/watch?v=nfoRtqvx76o
what do you think of this? this bike has a 500 watt motor and it's going at 50kmh, is that possible?

Check it out for yourself:
http://kreuzotter.de/english/espeed.htm

This power and speed calculator will give you a good idea what you can expect from a given bike setup and a given amount of power. Maybe the guy in the video has a motor that really makes 1000W, or maybe he has a downhill and a tailwind helping him.

500W of mechanical power will not carry you at 50km/h by itself, unless you're riding some sort of queer bike that sacrifices both pedal power and decent handling in exchange for improved aerodynamics.
 
The question has been stated in a way making it nearly impossible to answer.

How fast can that motor go? Depends on the winding it has, the rim size, and more importantly, what the actual voltage and amps you feed the motor. You can feed a "500w" motor 4000w, and double the voltage, and perhaps hit 75 KPH. It might melt the motor after a few miles, but you asked how fast, not how long.

Chalo has it exactly right what wattage it takes to make any ebike motor at any voltage go a certain speed. I often use 400w= 20 mph as a rough rule of thumb. Or, depending on conditions it could take double that. But flat ground, no wind, regular bike, rider not terribly more heavy than 200 pounds, 400w will get you 20 mph.

But depending on the motors exact winding, it's max no load rpm at 38.4v could be 200 rpm, or 400. And that rpm produces different travel speeds on different size wheels.

Now, if I make about 50 assumptions, I can say you will go 20-25 mph. The main guess, is that you are referring to a typical direct drive humbotor kit in 26" wheel. Often a 28mm wide rotor about 9" in size, the typical 7 turn winding goes about 22 mph at 36v. Some have a 6 turn, and go closer to 25 mph. This is with the typical 20-25 amps controller that actually limits at 22 amps. About 800w is the maximum wattage, so 30mph doesn't happen in most cases.
 
It's also worth mentioning that getting maximum motor power at maximum speed requires careful matching of motor voltage (and rpm per volt) to wheel diameter, and this ideal ratio varies according to power demand-- e.g. rider weight, riding position, tire type, etc. A crank drive like the one in the video allows you to use the bike's gears to change the motor reduction in real time.

Usually getting a good match of top speed and max power means that performance at lower than top speed will be compromised. That is, if you set up your bike for top speed alone, acceleration and hill climbing will be impaired, along with cruising efficiency.
 
thanks for the answers guys...i'm no pro so can you guys tell me what motor and battery would be ideal to get a steady 45kmh and a 40km range irrespective of hills and wind?
 
also how good are the 26*4inch surly tires for ebikes, can i get a range of 35km at 45kmh with a 750watt motor and a 38.4v 12ah battery
i really want to increase the speed of my prodeco phantom x2
 
My bike is 2WD with 2 small 250W motors.

The bike pull 30A max @12s lipo

Topspeed is 42km/h and then ~ 15A ~ 700W

So i think 750W can be good for 45km/h.
But you want some more for fast acceleration ;)

44.4V 20Ah is good for 45km range.

12Ah 38,4V to low for 35km

At 45km/h the bike wil use ~ 20wh/km. You battery only 460wh so max 23km.

The voltage is low to if you want 45km/h with 26inch you need reeel fast wind motor.
 
7 turn direct drive 28mm motor, often called a 9 continent, or 9 continent clone. Other brand names are yes, conhis, golden, muxus, or about a zillion others.

Run it on 48v, that will get you 45kph. to go 40 k at that speed will take slightly more than 15 ah of "48v", so get a 20 ah battery.

You will slow down some from that top speed if it's windy, or very steep hills. But you will more or less have 45kph for as much as 45 k.

Not spouting theory here, just what I did for about 10,000 miles. "36v" will be closer to 35kph, at that speed 20 ah of 36v will do.

48v 20 ah is a bitch to carry, won't fit well on most bikes unless you split the pack and pannier each half. So you might consider 48v 15 ah, and slow down for the longer rides.
 
Do you have a pilots certificate? If so, that's proof to me that you are smart enough and careful enough to go past the beginner type batteries.
 
thanks erikjan and dogman that was some really useful information. and yes i am a qualified private pilot working on my commercial pilot license now.
i need to commute 17.4km to reach the airport so i travel on my prodeco phantom x2 ebike (2013 version) but the problem is that it only goes at 32kmh and i really need to get that speed up to 45kmh and get a range of 35-40km. if you guys could tell me an ebike in the range of $1500-$2500 that does 40km at 45kmh i would be really happy
here's a pic of my 38.4 volt 12ah phantom x2 battery
 

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also this ebike has a ridiculous watt hour per mile @ 29.742 i get just 25km full throttle on the windiest days. i carry 2 of these batteries to commute 35km :( i really really need to get a fast ebike. i weigh 165 pounds + 20pound backpack .
 
dnmun said:
ok, it is 12S lifepo4 so you can use a 36v lifepo4 charger to charge it.
i want to know what i can do to get this battery to run at 40-45kmh and give me a range of atleast 20km
 
Ok, I'll assume if you can pass a pilots certificate test, you are plenty smart to handle RC lipo without burning the house down. You don't need to buy a new bike, you just need to modify it.

Start reading about this chemistry, often bought from Hobby King in china. It has a c rate much greater than the typical for lifepo4 bike batteries. This allows the use of any hot rod controller you like, and as a bonus, it's smaller and lighter too.

18s would be a good voltage, 63v minimum at the end of the ride, That would get your motor to go close to 50kph at the very end, and likely 55 kph as you leave the garage. Most "72v" controllers have a low voltage cutoff at about 60v, so just about perfect for a drop dead stopping point for 18s lipo. 15s could work too, depending on the exact winding your motor has. That should get you about 40-45 kph, using the controller you have now.

Backing up a bit, you might try dipping your toe in lipo by adding a 3s lipo pack in series to your existing batteries. See if that is fast enough. If so, then you could leave your bike stock, and just add 12v more for a small increase in speed.

Hauling ass, you will never get good wh/mi. Period. So just accept that it will take a fairly big battery to go 20k at 50kph. 40 wh/mi is not that unusual, for a bike that goes fast. 18s lipo in 15 ah size should do the trick. 18s 15 ah would be 9 of the 6s 5000 mha packs. 3 sets of 3 packs in series, each set made from 3 6s packs connected parallel.

BTW, I have a LTA certificate, hot air. If a dumbass balloon pilot can figure out lipo, surely a fixed wing pilot can. Like aviation, it's dangerous, but safe if you just follow established safe routines.
 
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