T200 Overvoltage Power Efficiency

[adam]

Hi @dobelz,

First, I believe this explanation of mine will clarify the expected behavior of the T200 in beyond supported voltages:

I need more THRUST from the T200

Hi @ghammerle, The T200 is designed to run best at 16V, and is rated to run well up to 20V. Beyond that, long term performance and durability has not been tested, though I can say at 27-28V there is imminent danger of overheating and burning out the thruster in minutes or less. Running beyond 20V will increase wear and significantly reduce efficiency, there will be some boost in thrust but most of the additional power will be wasted as heat. However, independent of the 26V rating of the Basic E…

The previous discussion you linked is quite old and dated back to only a few months after the launch of the T200. Since then, there has been a lot more knowledge gained and testing carried out.

Everything you say is true- torque is proportional to current only, and torque dictates propeller RPM and thus thrust. Since Ohm’s law (V=I*R) states there is direct relationship between current, voltage, and resistance, current must go up as voltage goes up since resistance (stator windings) remains the same. Also, as you correctly suggest, the plot you linked does show the T200 uses appropriately the same amount of power for a given thrust at both 12 V and 16 V. This is the expected behavior.

However, there is one more critical factor that must be considered, that @nick-wernicke actually points out in the original thread you linked- the ESC and how throttle is modulated. Critically, the voltage at the stator windings is not just V_supply, but V_supply * Duty Cycle, or the average PWM supplied voltage, AKA V_apparent. The ESC reduces “throttle” by literally chopping down the average voltage by only powering a phase a certain percentage of the time. Thus even though the supply voltage may be 16 V, the apparent voltage at the thruster will only be ~16 V at full throttle 100% duty cycle. At lower throttle, say 50% duty cycle, the apparent average voltage will be 16*0.5= 8 V. This is how an ESC can control “throttle” in the first place- by reducing duty cycle, apparent voltage, and thus current/torque/RPM/thrust are reduced.

In the T200 12 V and 16 V thrust vs. power chart you posted, note the purple 16 V line is significantly longer than the brown 12 V line, corresponding to a greater range of thrust due to a greater range of voltage. When powered at 16 V, the ESC does not actually feed 16 V to the thruster until duty cycle/throttle exceeds 75%. At 100% throttle and 12 V, apparent voltage is the same as 75% throttle and 16 V (0.75*16=12). Therefore regardless of V_supply being 12 V or 16 V, approximately the same amount of power will be required for a given thrust.

I hope this explanation helps!

-Adam