Experts needed for technical puzzle question.

[Bigfoot]

I have asked some club members this question. They have said this is
impossible but they have failed to convince me by any technical logic.

Very high power/weight ratio electric models have fairly short duration
flights. However, they often only use full power in relatively short bursts
and I suspect a lot of the battery power is lost in heat in the speed
controller during low throttle spells.

Now I guess there is all sorts of electronic wizardry inside speed
controllers so why can they not include voltage conversion circuits?

For example, full throttle sends maybe 98% of battery volts to the motor and
perhaps 94% of battery current (6% keeping Rx and servos alive?). Now at
reduced throttle (slow inverted passes?) the motor may only need 49% of
battery volts. Normally I guess the remaining 51% of volts is reflected in
heating in the speed controller. 100% of the reduced motor current is being
drained from the battery. Now with conversion circuitry, at the reduced
motor voltage, only 50% of the motor current needs to be drained from the
battery as the battery is chucking out this current at 98% battery volts and
therefore chucking out all the electrical power necessary to supply power to
the motor at 49% battery volts. This should be possible using a
power-capable diode between the motor terminals of the speed controller, and
perhaps a capacitor and inductance. For the same amount of time spent at
full power, the reduced power period would be doubled, flights would last
longer and the speed controller would not have to dissipate much heat.

[Ollie]

The electronic speed control dissipates the least heat when it is fully on or fully off. Therefore it is designed to be fully on or fully off as much of the time as possible. The power dissipated in the ESC is the voltage drop across the ESC times the current through the ESC. When the ESC is switched on The voltage drop across it is nearly zero. When the ESC is switched off the current is near zero. It is only when the ESC is very briefly switching between on and off that there is much instantaneous power dissipated in it. By switching almost instantaneously, the ESC has a very low average power dissipation. The motor (load) responds to the average voltage over a long series of rapid switching cycles. The ESC controls the average voltage and thus the motor speed by varying the duty cycle between on and off.

[steve lewin]

You may want to look a bit more carefully at exactly how ESCs work. Just to clarify what Ollie is saying, ESCs do not "reduce the voltage" to the motor to reduce speed. What they actually do is switch the full voltage to the motor but for only part of the time. I.e. if you are using 1/4 of the power (half voltage and therefore half current) the full voltage is switched on 50% of the time. The only heating effect is because the switching effect is not perfect and takes some power, but it is a tiny amount of power.

If you're thinking of the very high power hotliner type electrics they almost never run on partial throttle anyway. On to go up then switch off. Some considerable power is lost heating the motor and battery, almost none in the ESC.

Steve

[KillerWatt]

yup yup.. it's digital baby.. you know, 1's and 0's, On and Off, full blast or nothing, just not on all the time at reduced speed setting, RPM/time averaged by prop loading to Appear like an analog (say voltage dropping, power wasting, series resistor) speed controlling effect ........... kw