This is a BLDC motor with the magnets on the shaft and the windings near the casing. The casing doesn't get hot only the shaft. Also my ESC shuts the motor down after a few seconds, if I throttle down then throttle up again it will run for a few more seconds. The ESC does not get hot at all but the motor shaft is getting very hot. I will list the components, I'm using a 6s 8p battery, the voltage is 24.4, at full throttle it drops to 23.9. Everything is connected well with 8 gauge wire what could be the problem?

Motor- SSS 56104/500KV Brushless Motor 6 Poles W/O Water Cooling For RC Boats Specification: 56104 6 Poles Inner Runner Brushless Motors

Model No. Tum KV Max Amps(A) Max Voltage(V) Max Power(W) Idle Current(A) Max RPM Shaft(mm) Motor Dimension(mm) Weight(g) 56104/500kv 8Y 500 116 88 11000 1.4 45K 8 56*104 980 Length of extend shaft:25mm

ESC- 300A BOAT ESC 12S R-SNAKE 300A Electronic Watercooled Speed Controller Suitable for catamaran with a motor size of 1.4 meters or more High continuous amp: 300A Programmable via USB Link and Programming-Box (available at our Ebay store) Included 8mm Bullet Connectors Includes USB LINK* to set it by PC (only windows) Flier warranty *Program and manual available at fliermodel website

SPECS 300A BOAT ESC Flier mod. R-Snake Voltage (LiPo): 3-12S Voltage: 12V to 50V Anti-spark cable: yes Wires: 8AWG Connectors: 8mm Bullet BEC: No Size (mm): 2405735 Weight: 387g

Battery- 6s 8p


  • \$\begingroup\$ Your BLDC does not have any water cooling, therefore getting too hot: (1) rcgenesis.net/…, (2) process-cooling.com/articles/…. \$\endgroup\$
    – tlfong01
    May 20, 2021 at 3:43
  • \$\begingroup\$ Propeller? No propeller? \$\endgroup\$
    – DKNguyen
    May 20, 2021 at 4:05
  • \$\begingroup\$ "the motor shaft is getting very hot." - exactly how hot is 'very hot'? Can you measure battery current? Is the prop shaft connected? How easily can the shaft be turned by hand? \$\endgroup\$ May 20, 2021 at 8:18
  • \$\begingroup\$ I found out why, I sealed the motor for underwater use it is for a trolling motor for my kayak. The rubber seal around the shaft was doing it. I took it apart and ran it hard no heat whatsoever. I thing if I get an aluminum prop and only run it in the water it will be fine I didn't realize the seal would create that much friction. Thank you all. \$\endgroup\$
    – edrummer
    May 21, 2021 at 2:15
  • \$\begingroup\$ So the cause was described in my answer. Please accept my answer, to close this session. \$\endgroup\$ May 21, 2021 at 8:29

1 Answer 1


A BLDC has a rotor with a permanent magnet. The induction motor (IM) has a squirrel cage and the rotor flux is due to induced current in the cage. In the IM most heat is produced in rotor, then transferred to the stator and through a shaft. When the IM is hot when you touch the outer stator casing, it means that the rotor is glowing red.

A BLDC is a different since the magnetic field as seen from rotor is DC, so no eddy currents are present that can heat the rotor. All the heat produced in BLDC is due to stator resistance and stator eddy currents, therefore when you touch the stator outer casing you have touched the hottest point. The heat is transferred to the rotor through the air gap (in the reverse direction as in IM).

To conclude, in the BLDC the stator shall be hotter than the shaft unless the heat is produced due to friction of the shaft - shaft bearings, load bearings, ... or transferred from the load.


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