# Why is the ESC not giving enough current for my propeller?

So I have a Hobbywing Skywalker 80 amp ESC and Sunnysky X3520-720 that I just did a ground test with a power meter. Results gave only about 31 amps at 16.3V which is way under what I was expected (around 60-80 amps).

Any ideas on what's behind this?

• What propeller do you use? How do you determined the expected power? Jun 28 '21 at 11:27
• 720kv on 4S with (I'm guessing) somewhere around a 15" prop, 31 amps seems like a reasonable (maybe slightly low) current draw. Note that's 16 * 31 = ~500 watts or 2/3 of a horsepower Jun 28 '21 at 15:25
• SunnySky's data predicts 72amps with a DXL14*8 at 16.8v sunnyskyusa.com/products/sunnysky-x3520-brushless-motor About the only mistake you can make is the wrong size of prop. Jun 29 '21 at 7:59
• @254 Labdawan Putra Karsa The relationship between different thrusters are not straightforward, as you have to consider their efficiency. The efficiency of a propeller depends on the speed (in this case the rpm), so you cannot make this direct relationship, but you must analyze the propeller efficiency data and see in which region it will work to be able to estimate the consumed power. Jun 29 '21 at 12:57

The 80 amps on the ESC is its rated (maximum) current not what it consumes. The maximum current draw of the motor should be less than the rated current of the ESC. Otherwise the ESC will heat up and stop working. 30 amps sitting on the ground might be reasonable as the motors are spinning but not providing any lift.

• "but not providing any lift" doesn't make sense - the motor will be working hardest when the plane is static and will draw less power when the plane is moving, as the air arriving at the prop will already be moving. I agree with everything else though. Aug 18 '21 at 8:16
• You are right, I was assuming a copter. However the OP said ground test so no lift in any case. Aug 18 '21 at 13:12