The guy who did this mod did not report any catastrophic accident, and was extremely satisfied eventually. He had several additional mods for improving cooling ready, but he judged that oil alone was more than enough. I did not do this myself (no need) so I cannot speak for myself. Let me say again, though, that it was a geared hub.
Hub Motor Cooling Idea
- Thread starter Metallover
- Start date
John in CR
100 TW
I recall someone trying an oil bath in a direct drive hub. No long-term results. I think filled a motor with oil in an effort to keep water out for a submersible bike. It was all low speed stuff, I can't imagine it for a geared hub with a rotor turning 4-5 times as fast as the wheel and in the opposite direction. Just imagine friction from an oil filled air gap even in a slow rpm hub. Flow of oil over the spindly hall wires isn't appealing either. Each of those who tried an oil bath reported significant reductions in performance, which means friction. Sure there's a much better pathway for heat dissipation, but if you're decreasing efficiency by even 1%, which is more realistically 10-20% or more, then it's a negative overall effect. That's because you're still stuck with dissipating the heat through the outer surface of the motor to air in the outside environment.
The only way to improve continuous performance is by sending some fluid inside to capture some heat and bring that heated fluid to the outside and dissipate it in some manner that isn't through the exterior surface area of the hub. I ignore the small heat transfer through the axle and spokes. Personally I like air just fine, and with an open system I don't have to worry about any additional heat exchanger, and best of all any performance hit is just a handful of watts. I haven't melted a motor yet, but have exceeded 6kw continuous on many occasions. If I want to go crazy, I'll add a blower. In the meantime I'm going to increase flow greatly by boosting the rpm.
Some have talked about a sealed system with a liquid flowing through tubes and and exterior heat exchanger, but I just don't see much point with our small motors. That kind of stuff might make sense for a car size motor or racing motorcycle where you have to shed quite a few thousands of watts of heat. If you look at the highest power density motors in the world, they're designing rotors to stimulate air flow through the motor, so I'll stick with the experts, and wait patiently for more efficient motors.
John
The only way to improve continuous performance is by sending some fluid inside to capture some heat and bring that heated fluid to the outside and dissipate it in some manner that isn't through the exterior surface area of the hub. I ignore the small heat transfer through the axle and spokes. Personally I like air just fine, and with an open system I don't have to worry about any additional heat exchanger, and best of all any performance hit is just a handful of watts. I haven't melted a motor yet, but have exceeded 6kw continuous on many occasions. If I want to go crazy, I'll add a blower. In the meantime I'm going to increase flow greatly by boosting the rpm.
Some have talked about a sealed system with a liquid flowing through tubes and and exterior heat exchanger, but I just don't see much point with our small motors. That kind of stuff might make sense for a car size motor or racing motorcycle where you have to shed quite a few thousands of watts of heat. If you look at the highest power density motors in the world, they're designing rotors to stimulate air flow through the motor, so I'll stick with the experts, and wait patiently for more efficient motors.
John
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