I have recently watched a video about a powerful Octa-copter that uses 30,000 Volt brushless motors to propell, the batteries however look quite small about a 19v laptop battery. How is the voltage increased to suffice the voltage requirements? where does the extra electrical energy come from or what is the tradeoff for stepping up the voltage? and if the batteries are at most about 19V how does it obey ohms law?
$\begingroup$
$\endgroup$
0
Add a comment
|
3 Answers
$\begingroup$
$\endgroup$
2
The $KV$ in $30KV$ refers to the motor velocity constant $K_v$. It does not refer to kilovolt $kV$, cf. comments by John Rennie.
-
$\begingroup$ Ahh so it was just a bad misinterpretation on my part(or theirs). $\endgroup$ Sep 4, 2014 at 17:21
-
$\begingroup$ Note - we think it's 330KV... 30KV would be a very slow motor (unloaded, it would give 600 rpm at 20 V input). $\endgroup$– FlorisSep 4, 2014 at 17:40
$\begingroup$
$\endgroup$
0
It is quite easy to use a step-up converter to generate almost any voltage. The question is "voltage at what current". The power a battery can deliver is finite (power = voltage times current), but you can convert voltages in many different ways. The most obvious is an oscillator (inverter) followed by a transformer and a rectifier, but there are more efficient systems out there.
How do you think a CT scanner produces 140 kV for the Xray tube using the power coming from the mains supply?
If you are interested in the details of a circuit that can do this I would recommend asking on our sister electrical engineering site.
There is some value in using higher voltages in a motor, but usually you want greater voltages to achieve some special purpose (like voltage needed to accelerate electrons in tubes, or power transmission where resistive losses are smaller when you use higher voltage and lower current). I can't see a good reason to step the voltage up to 30kV for the application you describe - the losses in efficiency from the converter are significant.
$\begingroup$
$\endgroup$
0
I seriously doubt that the batteries were putting out 30 kV. You surely misread or misheard something.
The chemistry of batteries is such that individual cells produce from a few 100 mV to a few volts. A 30 kV battery would require 1000s of cells, which would make no sense at all. In addition, 30 kV is much more difficult to handle and would be much less efficient.
Just think of the arcing distance alone, and consider how a motor would have to be designed around that.
answered Sep 4, 2014 at 12:35