Firstly, whats legal?
How is that power is that measured?
Considering the law was most likely based on the output of a petrol engine, it would seem appropriate to measure the power output at the wheel. And since the power output is a curve, with a peak, it would seem appropriate to take some kind of average as the “normal” power output.
So how do you work out the power at the wheel?
There are energy losses all the way through an electric bike system. So what you start with at the battery might be considerably less by the time it gets to the wheel. Most of this loss is heat.
Lucky for us there is an e-bike calculator to work this all out.
The above graph is based on a 36v battery, 25amp controller and a 2807 motor.
While the peak output is just under 500w, it would be reasonable to say that 300w is available for an average of the bikes speed range.
I know from experience that when climbing a steep hill with the above system, the bike slows to 10km/h, which is an output of 300 watts at the motor. (50% efficiency)
If you were to multiply the battery voltage with the controller current draw eg, 36v x 25a = 900 watts, you might think you were well over the legal output, but you would be wrong.
EVLAB’s recommendations for a useful system with reasonable climbing ability and legal power characteristics.
36v LifePO4 15ah battery, 25amp controller, Nine Continent motor. (Nominal 300w peak 500w)
or if you want to push it a bit,
48v LifePO4 10ah, battery 20amp controller. Nine Continent motor. (Nominal 400w peak 600w)
Want more power?
Above 300 watts not exceeding 2000 watts is classed a moped. For this your bike must be registered with license plate, have front and rear lights, a horn, indicators, rear view mirror, not exceed 50km/h. You must wear an approved DOT4 helmet and hold your car license. You do not need a WOF or insurance.
2000w on a bicycle is exciting. You will accelerate with the cars at the lights and leave most scooters wondering what just happened. How ever, you now move into an area of exceeding limits. Limits of your bike’s brakes and frame, limits of your batteries, limits of your motor and limits of your own ability to maintain control.
If you plan to use your bike for off road, by all means build the system of your dreams. But respect the law.
Here are some thoughts.
If you want more power, increase your voltage.
Increasing the amps, gives you more torque off the mark and helps with hill climbing, and to small extent acceleration, but mainly just increases losses and stresses the system.
After 40-50 amps there is very little to gain from Nine Continent motors as the motor is saturated. Raise your voltage and go to a smaller wheel or larger winding motor.
Crystalite X5 motors can handle larger currents.
EVLAB wont fulfill a warranty on a motor that has been pushed beyond its rating. Use a temperature monitor to protect your motor from over heating.
By choosing a higher discharge rate battery, or monitoring your system you may be able to use a smaller capacity battery.
Want even more insane power!
Yes it can be done. Legally over 2000 watts is classed as a motorcycle. You would need to build quite a system to achieve over 2000 watts constant at the wheel. From e-bike parts this would require custom work and on board monitoring to most parts to ensure reliability.
Spend time at the endless-sphere forum and see what can be done.
Otherwise its time to move to motorcycle type motors and controllers and larger battery packs!
EVLAB can source motorcycle parts for you.
