Aotema Hub Motor Technical Information

Motor power ratings are specified in watts. Watts(W) = Volts(V) x Current(A). For example, a motor running at 36V and 21A would about 750W. The thing that most people don't realize is that motors don't have an exact value for watts. Consider the specified rating to be a general value as each motor will have a power range. Sometimes motors are purposely under-rated as in the case of electric bikes sold to Europe which by law are limited to 250W. Ever wonder why there are so many motors rated for 250W ? Taking one of these motors as an example, first calculate the current. 250W/36V = about 6.9A. That current is too low for 90% of ebikes so it doesn't add up. The absolute minimum current for an ebike is 10A, and many are 15A. So 36V x15A = 540W, twice what the specified rating is. Of course you can run at a lower voltage, and 24V is still common, especially for smaller bikes. In that case you have 24V x 15A = 360W, and if you lower the current to 10-11A, you would get your 250W.

Another thing to keep in mind is that hub motors are about 70-80% efficient under load so the power you get to the wheel is the calculated power times efficiency. A 500W motor produces 350W of usable power (70%). The point is that motors can be run at different power levels. They will be most efficient at a specific power level. Below this level ,they will bog down and waste power for example when they are going slow under heavy load. At the higher point of the power range, the motor will start to get hot as it can not dissipate the heat and will waste power.

The Aotema motor is rated at 750W, how did we determine that? The standard way to rate a motor is test it on a sophisticated motor testing apparatus. It puts it under measured loads and plots the various parameters including efficiency and output power. The power rating corresponds to the point of peak efficiency. The Aotema results show good efficiency at that power range. There's actually a simpler method anyone can do, while not exact, it gets you in the ballpark. Simply increase the power level supplied to the motor while under load and measure the temperature of the motor. The power level at which point the motor is slightly warm when run continuously (under load) is the maximum power level. The peak power would be another 40% of that value.

You will see motors advertised as 1000W on sites like Ebay and you might think, wow what a great deal on a powerful motor! The problem is any power level can be slapped on a motor. Most of these are actually 500W motors. At 1000W, they are operating beyond the efficient range, will run hot and waste power. So don't get hung up on power ratings or fooled by exaggerated advertising claims. For more information on your power requirements, contact customer support at Aotema-USA.