I have read many posts here that mention the gearing problems of using an outrunner motor - of having to gear a motor down that is 2,000+ rpms for a wheel that only needs to turn at 400 rmps. I have noticed that the specs on the motors usually list a voltage range for the motor yet in all of the builds I have seen here, the builder has used 48v or more. My question: why don't people use, say, 36v instead of 48v to reduce the rpm of the motor? By doing that the weight of the gearing system could be reduced. The lower voltage batteries are also a little cheaper than the 48v.
Power is directly proportional to RPM and these motors are designe to turn in the range of 6-7.5K RPM for the most efficient operation, the voltage should be setup to match and then the reduction allows the RPM to be streetable but without allowing outrunners to get into their efficient RPM band, they will run warm and inefficient.
Once you spool them up - they run quite efficiently and much lighter than equivalent or lower powered hub motor drives.
48/50v is 12S lipo and when using RC controllers like ICE HV 160 or the like, they are limited to 12S - you can use an infineon with halls to get around the voltage when using a lower kV motor in the 130/170kv range - on those motors to acheive 7500 RPM would require 12s for the 170 but the 130 would require more voltage.
Actually this is a good point. I was under the impression the efficiency range of a given motor is based on the input voltage, so that if you put 30V in then the motor will have peak efficiency at 80ish percent of max RPM. I thought it didn't matter what the voltage was? I understand if you want more watts of output, you need to step up voltage, but why COULDN'T we run 24V for an inexpensive setup with just a ton of amps?
Motor handling voltage, kV and current are all based on the number of turns and percentage of copper filled. With a constant motor (no change) higher voltages will yeild higher RPM and higher efficiency rates under continual use (our application).
Running lower efficiency causes the shedding of more heat - in your suggestion, we would run maybe 2-3S lowering our RPM but also limiting the power we can muster, no matter how many amps that motor trys to draw it will never reach an efficient and powerful output level and will cause major heating.
Thanks! I am glad I asked this question. If the majority is correct, I will get a longer lived outrunner if I run 48v because 48v yields less heat? and will also get more miles per kw because it is running at a more efficient stage? I am looking for power, like a Turnigy 80-100-B in the hopes that it will yield more dependability. Please feel free to dialog more about this.
Thanks! I am glad I asked this question. If the majority is correct, I will get a longer lived outrunner if I run 48v because 48v yields less heat? and will also get more miles per kw because it is running at a more efficient stage? I am looking for power, like a Turnigy 80-100-B in the hopes that it will yield more dependability. Please feel free to dialog more about this.
Give us an idea what application you plan to use this outrunner in?
The turnigy would work but there are more efficient options (expensive too) out there if your lookign for uber reliable setups.
In either case, the theory is - with higher voltage, less current (sustained) is required for the same power and thus less heat... Provided the bearings are in shape (meaning they are good bearings) spinning at 6000 or more RPM shouldn't be an issue for a quality outrunner (check the feedback on the turnigy motors).
What bike is this intended for, what size wheel and what type of speed are you looking for?
Well, simply put, high amps are inefficient. And you need higher amps when running a lower voltage for the same power output.
High amps = heat = efficiency loss.
Although I'm guessing you can get away with a lower voltage setup if it's low power, such as < 1000watts. I just wouldn't put >100amps into a 5s setup.
pengyou, the 80-100 can probably handle much more power than you might ever ask it to. You may be better off with an 80-85 (available with a 170-Kv), it is the same diameter, but slightly shorter, lighter, and less expensive than the 80-100...but it will also still provide a great deal of power.
