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-   -   esc kv motor limit? (https://www.rctech.net/forum/radio-electronics/972364-esc-kv-motor-limit.html)

Speed Chaser 12-27-2016 05:03 PM

esc kv motor limit?
 
Excatly what do they mean by esc kv motor limit? I was looking at this
Motor Limit: Brushless Motor Limit with 2S LiPo / 6 Cell NiMH: KV≤6000 (3656 size motor)
Brushless Motor Limit with 3S LiPo / 9 Cell NiMH: KV≤4000 (3656 size motor)
Brushless Motor Limit with 4S LiPo / 12 Cell NiMH: KV≤3000 (3656 size motor)
From a EZRUN MAX10-SCT, my question is what would happen if i plug lets say a motor that is 4400Kv and has a max continuous current of 60 amps with a 3s lipo. Can this motor still be used with this esc?

the rc guy 12-27-2016 05:42 PM

most esc have a 3500kv limit on 3 cells..esc would or could probably thermal..and shut down till it cools

on your esc it says less than 4000kv on 3 cells

Speed Chaser 12-27-2016 05:52 PM

Why do they have that limit? I dont think it should be due to thermal problem when the esc can handle 120 amp continuous current, double the motor.

ta_man 12-27-2016 07:08 PM


Originally Posted by Speed Chaser (Post 14781079)
Why do they have that limit? I dont think it should be due to thermal problem when the esc can handle 120 amp continuous current, double the motor.

Hint: Maye the ESC can't really handle continuous 120 amps.

robert@castle 12-28-2016 12:31 AM


Originally Posted by Speed Chaser (Post 14781079)
Why do they have that limit? I dont think it should be due to thermal problem when the esc can handle 120 amp continuous current, double the motor.

It's not necessarily a question of how many amps the motor is pulling. They could say that is the limit to prevent customers from running a bad setup, but typically KV limits are due to the firmware on the ESC's processor. The firmware controls the pulses being sent to the motor generally following a 6 step commutation pattern. The faster the motor can spin the faster the ESC has to turn on and off the MOSFETS in order to apply power to the correct phase to keep the motor spinning. Firmware efficiency, hardware optimization, and processor clock speed all play a role in how fast of a motor the ESC can run.

Castle car ESCs generally have a max Electrical RPM limit of about 120k. Electrical RPM is calculated by (Motor KV * Max Pack Voltage * Pole Count) / 2. So if you had a 3500KV 2 pole motor on 3s it would have an Electrical RPM of (3500*3*4.2*2)/2 = 44100. If that truly is their limit, then they may be running their processor at a lower clock speed.


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