motor/kv/ system question

[BrianG]

Why does an ESC run cooler at WOT than at partial throttle? Simple; fewer on/off pulses. To get variable power, the FETs switch on and off. However, a FET does not switch on and off instantly - there is a ramp up and down. This ramping is where the power is lost as heat. When at partial throttle, the ESC sends more of the on/off pulses to limit the average voltage. Think of it this way, if the ESC is 10% of the time "on" and 90% of the time "off", the motor will see an average of 10% of the battery voltage. At WOT, the ESC is sending full battery voltage, so there are no on/off switching cycles (well, not counting the switching between the phases).

I hope that made sense.

FYI, there is no difference between setting the EPA at something less than 100% and not using the full throttle trigger throw. So, you can have the EPA set at 100%, but if you are only using 1/2 the throttle trigger throw, it's the same amount of losses as setting the EPA at 50% and using full trigger throw.

If the setup is too fast, reduce gearing (will increase torque), get a lower kv motor (may increase torque), or reduce battery voltage.

[littlegiant]

Originally Posted by BrianG

Why does an ESC run cooler at WOT than at partial throttle? Simple; fewer on/off pulses. To get variable power, the FETs switch on and off. However, a FET does not switch on and off instantly - there is a ramp up and down. This ramping is where the power is lost as heat. When at partial throttle, the ESC sends more of the on/off pulses to limit the average voltage. Think of it this way, if the ESC is 10% of the time "on" and 90% of the time "off", the motor will see an average of 10% of the battery voltage. At WOT, the ESC is sending full battery voltage, so there are no on/off switching cycles (well, not counting the switching between the phases).

I hope that made sense.

FYI, there is no difference between setting the EPA at something less than 100% and not using the full throttle trigger throw. So, you can have the EPA set at 100%, but if you are only using 1/2 the throttle trigger throw, it's the same amount of losses as setting the EPA at 50% and using full trigger throw.

If the setup is too fast, reduce gearing (will increase torque), get a lower kv motor (may increase torque), or reduce battery voltage.

Hi there. thanks for the explaination. Correct me if I am wrong. So you mean that there is some actual pwm switching of the fets when powering each phase to vary the power delivered to each motor phase right? Doesn't the esc just rotate the magnetic field to get variable speeds by just switching the fets just on and off without pwm?