T200 efficiency at different voltages

Blue Robotics Products Thrusters and Motors
1

Hi,

I was viewing the T200 thruster Excel technical data when I start thinking about relation about the data values in it

From what I understand the relation between RPM and thrust seems to be fixed (accounting for statistical errors)

So I started comparing similar RPM/Thrust values from 3 different voltages on T200 like this:
(I choose to compare this part of data because is at the maximum PWM for 12v but of course less than maximum for other voltages)

PWM RPM A V W Kgf g/W
1900 2995 16.91 12 202.9 3.71 18.3
1816 3002 13.54 16 216.6 3.74 17.3
1800 2985 13.12 18 236.2 3.72 15.8
1792 3013 13.47 20 269.4 3.72 13.8

The first thing that i noted is that, for the same RPM/Thrust, as voltage increases the amperage decrease but not proportionally so the power consumption is higher and the efficiency is going down

  • Where is these energy wasted? Losses of the motor or ESC that tends to be less efficient at less than 100% throttle?

From technical data:
Full Throttle Current (Power) @ 12 V 17 Amps (205 Watts)
Full Throttle Current (Power) @ Nominal (16 V) 24 Amps (390 Watts)
Full Throttle Current (Power) @ Maximum (20 V) 32 Amps (645 Watts)

  • Why if is the voltage increasing the Full Throttle Current is increasing too?
    If I understand correct the ESC only limit and regulate the voltage but not the current

I read that more than 20v is not recommended
- Is it possible for example supply it with 20v and just limit the maximum output of PWM ex. 1792 for 20v?

  • Could the power control reduced range is bad affecting piloting and maneuvering?
  • Is it still less efficient than use a lower voltage, right?

You will forgive me but my knowledge of electric motors is still WIP :slight_smile:

Thank you

2

Hi @Maw -
Brushless motor ESCs do not regulate voltage - they switch the connection of the battery to the motor very quickly, matching the rotation rate of the motor, to send pulses of current to keep things turning. You can learn more on Wikipedia.

For a fixed thruster, the same RPM will generate approximately the same thrust, regardless of voltage.

Higher voltage drives higher flow of current, when more current flows more resistive losses are present. Due to the KV value of the motor, the rpm per volt, maximum rpm increases with voltage. You can think of higher voltage as higher pressure in a water hose, which means more water can flow when an output valve is opened (flow = current.)

Using 20v and higher is not recommended as this can damage the motor itself. Limiting the throttle value when used at higher voltage is required as a result. This generally doesn’t affect piloting, as the limited throttle value corresponds to similar power levels that lower voltages would reach at full throttle.

3

Thank you Tony for your accurate response

Just one last little doubt:
The amount of increase in current as consequence of increasing voltage (and also the change of efficiency) is like a percentage predictable for every thruster, it depend on KV value and other data specific to a single motor or can only be discovered experimentally?