# Electric Bikes - More Watts or Volts = Faster Speed?

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lildragon555
04-11-10, 04:20 PM
Is it the number of Watts (ex: 1000 W) or Volts (ex: 36V) that determine how fast the electric motor can go up to?

yopappamon
04-11-10, 04:36 PM
Watts = power

More volts usually means more power until you let the smoke out.

Watts = volts x amps, so they are directly proportional

lildragon555
04-11-10, 05:02 PM
ok thanks a bunch

rscamp
04-11-10, 07:25 PM
Is it the number of Watts (ex: 1000 W) or Volts (ex: 36V) that determine how fast the electric motor can go up to?

The unloaded RPM is the motor speed constant times the voltage. i.e. 80 RPM/V X 36V = 2880 RPM. The motor doesn't start to consume any significant electrical power or produce any mechanical power until it is loaded...

morph999
04-11-10, 09:52 PM
Also, bigger tire usually means faster speed on an electric bike. Smaller tires usually mean longer range. You can increase your range sometimes up to about 8 miles more just by going to a smaller tire. Like a 26" to a 20". There is a point at which if the tire is too big for the motor to spin easily then it can diminish your results.

Going to a smaller tire though decreases your speed though. And going to a bigger tire will decrease your range so there is trade-offs.

dumbass
04-12-10, 08:33 AM
Morph.....your correct but only when speaking about a hub motor because you can not adjust for the ratio. Whereas, with a non-hub that is driving through the bikes gear system you have the best of all worlds. When you need torque or range you can gear down. When you need more speed you can gear up. Hey, that sounds just like riding a bike!

Geekybiker
04-12-10, 01:51 PM
Both- sort of on a hub motor

Watts is like HP on a car. Ultimately it determines your top aero limited speed

Volts works more or less like gearing to a hub motor. Winding out at too low of a speed, but have plenty of power? You need more volts. (Note no mechanical advantage of real gears.

Amps work more or less like torque on a car. The more amps, the quicker off the line you are.

Just like a car can make HP through RPM or Torque, a electric motor makes watts through volts or amps.

lildragon555
04-12-10, 04:48 PM
Would 3 12 Volt 18 AH Batteries power a 1000W 36V Motor pulling around 35 amps?

morph999
04-12-10, 05:35 PM
Would 3 12 Volt 18 AH Batteries power a 1000W 36V Motor pulling around 35 amps?

Sure it would. A 36v 18AH SLA would be more like a 36v10AH lfepo4, though. You typically only get about 70 % of the usable capacity out of an SLA battery. You get about 95 % out of lifepo4.

lildragon555
04-12-10, 06:04 PM
How long would it last though?

yopappamon
04-12-10, 06:15 PM
18AH / 35A = .514hours = ~30.8 minutes

The batteries would need at least a 2C rating to supply 35 amps.

lildragon555
04-12-10, 06:35 PM
Ill just get this 35 AH one, cause I need at least an hour

morph999
04-12-10, 10:02 PM
I recommend 36v of lifepo4 from here
http://elitepowersolutions.com/products/product_info.php?cPath=16&products_id=74

cost about \$360 + shipping which is usually about \$20. A better investment than SLA.

Geekybiker
04-13-10, 12:22 PM
Ill just get this 35 AH one, cause I need at least an hour

How far you need to go is a better indicator than how long.

AH X Volts = Watt hours.

Most people don't seem to use more than about 22-23ish watt hours per mile from what I've seem (That's all motor, no pedal)

ebikes.ca has great page on choosing your battery.
http://www.ebikes.ca/batteries.shtml