ESC power capacitor question
 

Is there any advantage/disadvantage of using a capacitor of higher value than what came stock with my esc? I am using a Speed Passion Reventon Pro. It came with a 2200uf 16v 105* capacitor. Would a capacitor with a higher uf and/or voltage value help/hurt or not make a difference? Is there an advantage of using multiple capacitors vs 1 of equivalent value?

If it matters, the car is 2wd, 17.5 "blinky" buggy, w/ 5.05 FDR, 3" battery leads, and 70C batteries.

Higher voltage or capacitance ratings will increase the ripple current capability, which is very important in this application. This lets the capacitors run cooler and extends their life. Make sure you use capacitors designed for high ripple current! Most manufacturers have at least one type that is optimized for this.

Multiple smaller capacitors (of the same total value and rating as a single large capacitor) have a higher surface area / volume ratio, and this also lets them run cooler. They might be easier to fit into tight spots, too!

Higher capacitance low ESR is certainly good, several ESC manufacturers offer higher capacity caps as an upgrade. At least some are multiple caps in parallel. Should lower ESC temps and improve braking feel and consistency as I understand it.

Does a higher voltage rating help?

Higher voltage ratings will prevent the cap from undergoing electrolysis at the plates when high-frequency garbage (like ripple currents) hit the caps. Electrolysis = Gas = Boom!

Higher capacitance will only help to a degree, and you probably won't really notice it, but your ESC might stutter less. Low ESR will help keep temps down.

Yes, higher voltage ratings give higher ripple current capability and longer life.

But the uf has to be at least the same if not higher correct? Also, what is ESR?

equivalent series resistance

http://www.radio-electronics.com/inf...ial-basics.php

also pretty good definition and breakdown here, a little more in depth

http://www.illinoiscapacitor.com/pdf...or_fiction.pdf

Correct.

Can someone put links to online sales of this items?

King regards.

OK, guys, please forgive the repetitive questions. I am still trying to wrap my head around the esc cap issue. It's been literally 40 years since I installed maintained, troubleshot, and qc'd voice and data communication circuits, so my basic electricity is a little foggy. The stock cap is rated at 2200uf 25v (not 16v like I posted earlier) 105* high temp.

From a rc car perspective, will I gain noticable more punch, smother braking, and lower temps from running a single aftermarket cap rated at 2200uf, 35v, ESR 0.1206 ohms and a ripple current of 2880 ma, or four 470uf 35v ESR 0.494 ohms and a ripple current of 900ma wired in parallel. OR, am I over thinking the problem, and just run the stock cap or their high power 4 cap bank (four 470uf 16v caps) :confused:

Thanks for any feedback

Ok so. I guess back to even more basics to help my understanding.

DC powered battery (supply) goes through the esc comes out as 3 waves phase shifted 120 degrees (ac?) Clipped as a trapezoid wave with no negative alternation?

If that statement is true then the ripple current seen is usually from ac to DC conversion in power supply circuits. Therefore where are we seeing ripple current from? A back feed from the motor?

And to muddy the water more resistors in parallel divides resistance. So putting caps in parallel makes the ESR divide as well??? Lowering ESR will give a small bump in current adding to the "punch"? Based on lower resistance increases current?


Lost in electrons
Gary

I would choose the four caps, since their combined ripple current rating is substantially higher, making them more reliable. But I don't think you will notice any difference in the performance of the car or the ESC, as the ESR is about equal.

If the battery ESR and MOSFET on-resistance are sufficently low, then the voltage output from each ESC terminal will be at either zero or the full battery voltage while the MOSFETs are on. They essentially act only as switches. At full throttle, they are on for the entire length of each commutation phase (no PWM).

The motor back-EMF is sinusoidal for each phase. Commutation makes this appear to the battery as a rectified 3-phase signal (DC with the tops of each sinusoid superimposed). The current has a similar appearance, but with maximums where the back-EMF is minimum (disregarding other effects from inductance, etc.) Again, this is for full throttle (no PWM).

Putting caps in parallel does divide the ESR for the combination. But this usually won't result in any perceptible increase in "punch" (power), as the commutation frequency is too low for the caps to supply current for a significant length of time.

Correct me if I'm wrong, but wouldn't adding a small receiver battery eliminate all of these concerns?

No, that can only power the receiver and other electronics. A receiver battery isn't allowed to supply power to the motor. The main battery still sees all of the high currents drawn by the motor.