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From what I've heard, you need at least one capacitor on the ESC of a drone so that it can smooth out the voltage spikes to prevent electrical noise and improve the longevity of the ESC. If this is the case, wouldn't having more than one capacitor wired in parallel help further smooth out voltage spikes? Say on a 5'' drone, would it be worth the extra weight to have 3 capacitors instead of 1?

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Capacitors come in various sizes and values, so one big capacitor could equal two smaller ones in value; I do not know for certain if this offers a weight saving, but can reduce PCB footprint size by being 'taller' (although, you can stack capacitors of the same footprint.)

A reason to have more than one would be to adjust the frequency response, as a capacitor's reactance is related to the frequency and the capacitance: $$X_c=\frac{1}{2\pi fC}$$ where $X_c$ is the capacitor's reactance, $f$ is the frequency of the spike/noise and $C$ is the capacitor value.

To this end, you often see multiple capacitors for decoupling or filters; however, in an application where the aim is to decrease voltage sag it is less crucial. There are almost certainly more capacitors on the board, which may be in parallel to the larger capacitors (design dependent), but positioned close to the ICs and other parts so that each component gets the voltage it requires.

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  • $\begingroup$ parallel vs series is important to mention. I am not sure how overflow operates, as in when you reach capacity and fall over to the next cap. $\endgroup$ – Marc the Janitor Oct 13 at 18:49
  • $\begingroup$ @kralc In your last paragraph, you mention something about the aim being to reduce voltage sag. I don't think this is correct. The main purpose of the capacitor is to act as a sort of power filter, it would require much larger or many more capacitors to deal with voltage sag. With the few capacitors on a drone, if the battery were unplugged they couldn't power it for even a split second, so it's unreasonable for them to be able to provide any significant amount of extra power when the battery sags. Correct me if there's something I'm not understanding. $\endgroup$ – Jacob B Oct 13 at 19:51
  • $\begingroup$ Motors are very inductive, which means they have intermittant high current requirements. These are more accurately called transients, and cause very short duration changes in voltage due to non-perfect conductors and limitations of battery chesmistry, which the capacitors provide the reactive power help to smooth out. They are not designed to act as a power source instead of a battery, although capacitors (called 'supercapacitors') specialised for this purpose do exist for low current devices. $\endgroup$ – Kralc Oct 13 at 20:23

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