I am currently working on my second build, which will be a Caddx+KISS 5" 6S quad, and I purchased several types of 50V capacitors with varying capacitance ratings; 330uf, 470uf and 1000uf. The ESC is a KISS 2-5S 25A (40A limit) 32bit 4-in-1 and requires a capacitor when using anything above 5 cells. I understand that a 50V capacitor is the safest way to go, however, what about the capacitance?

My number one goal is to obviously have a working quad, but I am really hoping I can fit everything within the frame. The 1000uf capacitor is too large and would need to be fixed to the XT60 with a Wafl cap, or fixed to the frame externally. Those methods worry me as it places the capacitor in harms way and will increase the risk of a puncture. The 470uf capacitor will fit within the frame, albeit barely, and is also the same capacitance rating of the capacitor in my Betaflight 5" 6S build. With that said, my KISS ESC is rated for 2-5S and there are no capacitor recommendations in the ESC's documentation, so would this cause any issues?

Note that I am very new to this hobby and everything involved (one month in), so any answers given with additional details attached regarding why you chose X rating over Y rating, is seriously appreciated. Though any and all answers are appreciated regardless!

You can try without capacitor and see how things flies and how clean your video is. If it is fine with you, then you don't need a capacitor. If you want a cleaner video feed and possibly twitches, then you will need to add a capacitor. 1000uf is the recommended size, but you can always try less.

One of the reason KISS do not usually need a capacitor, because they run on much lower PID and gyro loops than BF. BF will inherently have more noise due to the higher sampling.

(07-Feb-2021, 04:23 AM)voodoo614 Wrote: You can try without capacitor and see how things flies and how clean your video is. If it is fine with you, then you don't need a capacitor. If you want a cleaner video feed and possibly twitches, then you will need to add a capacitor. 1000uf is the recommended size, but you can always try less.

One of the reason KISS do not usually need a capacitor, because they run on much lower PID and gyro loops than BF. BF will inherently have more noise due to the higher sampling.

Well, at the moment the noise aspect is less of a concern than serious voltage spikes that could damage the circuits/on-board capacitors. Is the reason for KISS devs recommending a capacitor when attaching a 6S lipo to the ESC their concern of the aforementioned voltage spikes, or is it the minor noise related spikes that interfere with signals? I think I am going to apply a capacitor regardless, because it should increase the life-span of the on-board capacitors (or so I have read.) I can understand a higher capacitance being the safest bet, but is it equivalent to installing a 50 gallon gas tank on small sedan? You can't go wrong with the larger tank, but if it's completely unnecessary, then you wouldn't have to install the tank externally.

I have read 470uf to 1000uf rated capacitors are recommended for 6S, but does this change when the ESC is only rated up to 5S?

If your esc is only rated for 5S, using 6S will toast them regardless if you have cap or not. Cap also have voltage rating. If you plan to use 6S, i recommend at least 35V rated caps.

The bigger capacitance in theory can smooth out bigger spike.

You can check Rotorbuild for quite a few Apex/Kiss build.

https://rotorbuilds.com/search/Apex+kiss


I use Fettec F7 FC and 35A 4 in 1 ESC with 6s. Fettec does recommend capacitor for 6S and the ESC actually came with a 470uf 50v which I use next to an arm close to the battery pads. And I use a Fettec Spike absorber with a smaller cap placed within the frame behind the DJI camera for extra peace of mine.

Mr Steele actually did not use a cap on his build video from 2019 and he's flying 6s with his 5S rated 4 in 1 KISS ESC

According to Flyduino, the reason for the 5S rating is due to the 25v capacitors and 30v fets. They have stated the ESC could get a 6S rating, but felt it more responsible to rate it for 5S. And Jasper is correct; Mr Steele does not use a cap. I also spoke with someone who built a near identical quad to mine, with the only difference being a DJI Air Unit instead of a Caddx Vista, and they've been flying it capless on 6S for months without issue.

I was able to fit the 50v 1000uf cap into the frame with it soldered directly to the underside of the lipo pads. It fits just BARELY and is touching the camera a little bit. The operating temperature of the capacitor is ~50' - ~105' C, which has me worried given its contact with the back of the camera. Worst case scenario is I'll have to switch to a Rubycon 470uf. I also purchased a Panasonic 680uf cap, but it's larger than the current 1000uf. The other solutions would be using a custom camera mount (like this) or purchasing a Caddx Nebula Nano, which is considerably smaller than the DJI camera.

(07-Feb-2021, 10:33 AM)jasperfpv Wrote: I use Fettec F7 FC and 35A 4 in 1 ESC with 6s. Fettec does recommend capacitor for 6S and the ESC actually came with a 470uf 50v which I use next to an arm close to the battery pads. And I use a Fettec Spike absorber with a smaller cap placed within the frame behind the DJI camera for extra peace of mine.

I probably could have saved myself the headache by using Fettec, but I really wanted to clone that Steele build. By the way, doesn't placing the cap further away from the ESC greatly reduce its effectiveness? I was reading about this, but it was from a single source and I haven't done any other research on the matter.

(12-Feb-2021, 12:03 PM)Woogie Wrote: I probably could have saved myself the headache by using Fettec, but I really wanted to clone that Steele build. By the way, doesn't placing the cap further away from the ESC greatly reduce its effectiveness? I was reading about this, but it was from a single source and I haven't done any other research on the matter.

Yeah the ideal placement is direct to the ESC battery pads but I made a compromise  here and I had no issues so far.

So the main reason for fitting a cap is just to clean the video feed...?
And if so.. going lower in capacity is better than nothing?
And if no video problems... don't bother fitting a cap??
I've fitted one to mine not knowing why.

(03-Mar-2021, 08:55 AM)Titanv11 Wrote: So the main reason for fitting a cap is just to clean the video feed...?
And if so.. going lower in capacity is better than nothing?
And if no video problems... don't bother fitting a cap??
I've fitted one to mine not knowing why.

It's used to help mitigate any excess electrical noise in the system which can affect not only the video feed but any data flowing through the board including the important gyro data. It can also help so suppress voltage spike to a certain extent, although a capacitor isn't as good as a TVS diode device for doing that.

Some people only fit a cap if necessary, especially if they are trying to save weight. I recommended always installing a cap unless you have a good reason not to because it's easier to plan that at the initial build stage than to have to pull a build apart again afterwards and then try and shoe-horn one in later. Treat fitting a cap as a sort of insurance policy.

(03-Mar-2021, 10:17 AM)SnowLeopardFPV Wrote:  insurance policy.

Very clear