| littlegiant |
05.29.2009 03:34 AM |
Quote:
Originally Posted by big greg
(Post 290996)
i have never noticed the mmm getting any warmer dropping the epa, ive heard that about old speedos but dont agree with it on the mambas, ive heard multiple others say the same thing but never noticed this among me and a dozen or so others around here doing it
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Dropping EPA is a method of limiting the power of the motor but there is this concern that it may lower efficiency in the motor or esc. To my understanding, the motor will not be affected much as long as it is running within its optimum rpm range - where there is no significant predominately iron or copper loss.
As for the esc, switching loss of the mosfets is the main cause of concern when lowering the EPA. According to my findings, other than switching to rotate the magnetic field within a brushless motor, the esc varies the input power to the motor by doing pwm switching when powering each phase of the motor coils. Usually pwm is done at a constant frequency - only the duty cycle is varied. But at 100% duty cycle, the mosfets are turned on all the time. Anyway, a well designed esc will operate its mosfet at an efficient pwm frequencies while maintaining good performance. And to top it off, with advancement in mosfet technology, good quality mosfets can switch at high frequency with minimum switching loss as long as the switching current is of an acceptable range. Switching loss goes up as switching frequency goes up/switching current goes up. Switching loss due to gate capacitence is neligible at constant on or off state but becomes significant when switching at high frequency. This explains why mosfets heat up more when running at a lower than 100% duty cycle. At 100% duty cycle, the mosfets are still switching to rotate the magnetic field of the motor around the rotor but the switching frequency of the mosfets is reduced.
I doubt that there will a big difference in esc temp by lowering the EPA in todays well designed escs with quality mosfets. Many reported that running their brushless setups at half throttle seems to heat up the motor/esc more.
I am thinking that maybe there is lesser air flow (lower speed) or that the motor's efficiency is lowered due to it running at a lower than optimum RPM (copper loss). But then again, I highly doubt that the temperature increase will be a lot. Probably just 1 or 2C depending on the setup. I will test out different EPA values once I get my HW150A.
Slap me hard if I got it wrong. :D
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