Capacitors For Noise Filtering in Mini Quad

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Capacitors For Noise Filtering in Mini Quad


Capacitors can make your FPV video signal cleaner, and your mini quad fly better. In this tutorial we will explain what types of low ESR capacitor you should get and why low ESR is important, and where to install the caps in a racing drone.

Here are some reliable sources you can get your low ESR capacitors from:

Solder to XT60 pads:

Solder to ESC power pads:

Noise is caused by quickly varying voltages, current and frequencies in an electrical circuit, even a motor running smoothly can cause these fluctuations.

When you think of the changing conditions all the motors on a multirotor experience, you realize that the electrical environment of a mini quad can be described as downright hostile. Your FC, VTX , camera and other peripherals all need stable electrical conditions to run optimally, which places them firmly in enemy airspace, literally surrounded by bogies!

As technology advances allowing for more powerful motors and ESC’s, the problem becomes even more pronounced.

The noise issue is absolutely crucial, it can mean the difference between a fantastic FPV mini quad and something that is completely unflyable.

There are many forms of capacitors and they are one of the most components in electronics.

The main use of capacitor in FPV is for filtering out ripples and noise in the power supply. It acts like a tiny battery, when there are voltage spikes, it absorbs it like charging a battery; when there is voltage drop, it’s discharged by releasing the energy. Overall the voltage level is more smooth.

Adding more capacitors can help clean up our power a great deal, which gives you the following benefits:

  • Reduced video noise in your FPV feed
  • A reduction in noise that can corrupt motor, ESC and radio signals
  • Improved flight characteristics and performance, by “cleaning up” the noise in the power to the Gyro sensor
  • It might even save your electronics from being damage by voltage spikes caused by Active Braking (Damped Light)

We prefer low ESR capacitors for our purposes. ESR stands for “Equivalent Series Resistance“. Capacitors with lower ESR show better filtering capability as demonstrated in this video.

LC filters are often used in FPV systems to combat video noise as well, but it only protects the system after the noise is induced. Adding capacitor at the source of the power on the other hand, protects the entire system by preventing the noise from being induced in the first place.

Here is an example showing how much improvement it made to my FPV video feed after installing a capacitor at the XT60 power input.

You don’t have to use caps, but we recommend it. As mum says:

“Put a cap on, it’s noisy out there!”

If you have a noisy quad (lots of oscillations and hard to tune PID), or noisy video feed, adding capacitors would probably be the first thing to try.

Here is how you can decide whether your quad is too noisy and need cap.

  • Listen to the motors and see if there are oscillation that you can’t tune out with PID
  • Check for hot motors
  • Noise in your video feed is another sign of electrical noise in the power
  • In extreme cases, you can get ESC/motor desync and “death of roll” and cause you to crash to the ground. Noise can corrupt your ESC signals

Even if you don’t have a noisy build, it’s still good practice to add caps. Better safe than sorry right? 🙂 Bent and misshapen props can introduce noise in your power, the adding caps might actually help with that too.

First of all, it’s extremely important to understand the polarity of a capacitor, which leg is positive (+) and which is negative (-). If you make a mistake, the capacitor won’t work and can even explode, please work carefully! The shorter leg indicates negative, if you cannot see the negative label on the body.

How to Read Capacitor Spec

How to Read Capacitor Spec

Solder the capacitor to either the ESC power or XT60 solder pads. Negative to negative, positive to positive. Make sure you secure the capacitor with ziptie, double-sided foam tape, or glue after soldering.

There are 3 places where you can add your capacitors for them to be effective. Be aware that you only need to install caps in one of these locations.

1. On the PDB, where XT60 pigtail is soldered.

Solder capacitor on PDB in mini quad

2.Where the ESC power leads are soldered to the PDB.

3. Or on the power terminals of each ESC (the best choice IMO).

The closer your capacitors are to the source of the noise, the more effective the filtering will be. The ideal place to solder your capacitors is on the pads of the ESC power terminals (option 3). However you’ll need to solder 4 individual capacitors, one for each ESC, small ones such as 330uF should be fine.

If a cap on each ESC takes up too much space, you can solder 1 or 2 larger caps to the PDB (e.g. 1x1000uF or 2x470uF). It might be less effective as the caps are further away from the source of the noise, but I have tried this solution on a few of my quads and it works well enough for me.

Cut the legs of your caps as short as possible for the best results, and to minimize ESR, these tiny leads don’t conduct high current very well.

Thicker wires such as 20awg can be used for extension if there is no space for the cap at the joint, and this doesn’t actually seem to increase ESR by any noticeable margin.

Capacitor Removes Lead and solder wires

If your mini quad still has issues with oscillations and hot motors after adding caps to the XT60 and ESC’s power, you might want to consider adding a small capacitor directly to the Gyro’s power supply. This can reduce the excessive amount of noise present in the Gyro’s power more effectively.

This hack is for experienced users only. It’s not easy finding where to solder the capacitor to, and it also requires good soldering skill.

Adding Cap to 3.3V

The Gyro (IMU sensor) on our flight controllers is powered by a 3.3V LDO regulator, so you just need to solder a capacitor to the 3.3V pin of the Gyro, or the 3.3V output of the LDO. The other end of the cap solder to ground.

Popular options are 4V 220uF – 400uF tantalum capacitor: https://amzn.to/2MiaOXi

[Diagram of where the LDO for Gyro is]

The 3V rail should be filtered as close to gyro as possible for the best result.

Very few FC’s share the same 3.3V rail with the MCU and spektrum receivers, so you might be able to access the 3.3V rail on an external solder pad. IMO this is not a good design not having a dedicated low noise regulator just for the gyro sensor, but it does make it easier for you to solder the capacitor to if required.

Adding Cap to 5V

The 3.3V LDO for the Gyro gets power from the 5V rail, so some people chose to filter the 5V rail and claimed to have success cleaning up noise in the gyro. That doesn’t always work but worth a try.

Popular options: 6V 220uF – 400uF tantalum capacitor: https://amzn.to/2O7mEEb

Is it necessary to add caps to the Gyro’s Power?

You don’t have to worry about it if you don’t have issues. If you do, try other easier methods first and treat this tutorial as the last resort.

Anyway, I wish all FC manufacturers in the future can provide proper filtering in the gyro power in their designs. It’s good to know that many latest FC now have capacitors on the Gyro’s power, including Airbot. So hopefully we won’t need to DIY in the future.

I linked to some cap options at the beginning of this article in case you don’t know what to get.

It’s not just capacitance value, you also have to take into account the size and weight of the cap, whether it will fit inside your quad.

25V rated caps should be enough for most 4S builds, though you may want to consider 35V just to be safe, as voltage spikes can on occasion reach higher than 25V.

For 5S and 6S builds, it really depends on your setup. A lot of people are using 35V cap without issues, but for a powerful build, the voltage spikes might be too much for a 35V cap to handle, in this case it’s safer to use a 50V one.

If you are not sure, give 35V a try first, since they are smaller and easier to mount. If you find it getting hot after a flight, or exploded, then you should definitely use a 50V cap.

If the capacitor in your build keep getting hot after every flight, it could be an indication that the cap is too small.

Here’s a great list of low ESR capacitors from a google spreadsheet, as well as their size and weight so you can pick one that best suits your needs.

25V

Brand Series Size (D X L) Impendance (Ω/100 kHz)
Panasonic FM 10×12.5 0.038
Elna RJF 10×12.5 0.039
Vishay 160 RLA 12.5×25 0.04
Panasonic FM 8×15 0.041
Samwha ML 10×12.5 0.053
Nippon KZE 10×12.5 0.053
Panasonic FR 8×11.5 0.056
United Chemi-Con (UCC) KZH 8×11.5 0.062
Nippon KZH 8×11.5 0.062
Samwha MZ 10×12.5 0.08
Panasonic FC 8×15 0.085
Panasonic FC 10×12.5 0.09
Nichicon PW 10×12.5 0.09
Samwha MK 10×12.5 0.098
Panasonic TP 10×16 0.13
Elna RJ4 10×12.5 0.81

35V

Brand Series Size (D X L) Impendance (Ω/100 kHz)
Panasonic FM 10×16 0.026
Elna RJF 10×16 0.028
Panasonic FM 8×20 0.03
Samwha MZ 10×16 0.038
Nippon KZE 10×16 0.038
Vishay 160 RLA 12.5×25 0.04
Panasonic FR 10×12.5 0.043
United Chemi-Con (UCC) KZH 10×12.5 0.045
Nippon KZH 10×12.5 0.045
Panasonic TP 10×20 0.052
Samwha ML 10×12.5 0.053
Panasonic FC 8×20 0.065
Samwha MK 10×16 0.065
Panasonic FC 10×16 0.068
Nichicon PW 10×16 0.068
Elna RJ4 10×12.5 0.7

25V

Brand Series Size (D X L) Impendance (Ω/100 kHz)
Panasonic FM 10×16 0.026
Elna RJF 10×16 0.028
Vishay 160 RLA 16×25 0.029
Panasonic FR 8×20 0.03
Samwha MZ 10×16 0.038
Panasonic FR 8×15 0.041
Nippon KZE 8×20 0.041
Panasonic FR 10×12.5 0.043
United Chemi-Con (UCC) KZH 10×12.5 0.045
Nippon KZH 10×12.5 0.045
Samwha ML 10×12.5 0.055
Samwha MK 10×20 0.06
Samwha MK 10×16 0.065
Panasonic TP 8×20 0.067
Panasonic FC 10×16 0.068
Nichicon PW 10×16 0.068
Panasonic TP 10×17 0.13
Elna RJ4 10×12.5 0.57

35V

Brand Series Size (D X L) Impendance (Ω/100 kHz)
Panasonic FM 10×20 0.019
Elna RJF 10×20 0.02
Nippon KZE 10×20 0.023
Samwha MZ 10×20 0.027
Panasonic FR 10×20 0.028
Panasonic FR 10×16 0.028
Panasonic FR 8×20 0.03
Nichicon UHW 10×16 0.03
Nippon KZH 10×16 0.032
United Chemi-Con (UCC) KZH 10×16 0.032
Vishay 160 RLA 18×20 0.035
Panasonic TP 12.5×20 0.038
Samwha ML 8×20 0.038
Samwha ML 10×16 0.041
Samwha MK 10×20 0.05
Panasonic FC 10×20 0.052
Nichicon PW 10×20 0.052
Samwha MK 8×20 0.088
Elna RJ4 10×16 0.5

25V

Brand Series Size (D X L) Impendance (Ω/100 kHz)
Elna RJF 12.5×20 0.017
Panasonic FR 10×25 0.018
United Chemi-Con (UCC) KZH 10×25 0.018
Nippon KZH 10×25 0.018
Panasonic FR 10×20 0.02
Nichicon UHW 10×20 0.02
Nippon KZE 12.5×20 0.021
Samwha MZ 12.5×21 0.025
Vishay 160 RLA 16×31 0.027
Samwha ML 10×20 0.033
Vishay 136 RVI 12.5×25 0.034
Panasonic FC 10×30 0.035
Panasonic FC 12.5×20 0.038
Nichicon PW 12.5×20 0.038
Panasonic FC 16×15 0.043
Samwha MK 10×25 0.045
Samwha MK 10×20 0.05
Elna RJ4 10×20 0.27

35V

Brand Series Size (D X L) Impendance (Ω/100 kHz)
Panasonic FM 12×25 0.015
Elna RJF 12.5×25 0.015
Nichicon UHW 12.5×20 0.017
United Chemi-Con (UCC) KZH 12.5×20 0.017
Nippon KZH 12.5×20 0.017
Panasonic FM 12.5×20 0.018
Nippon KZE 12.5×25 0.018
Samwha MZ 12.5×25 0.022
Vishay 160 RLA 18×35 0.024
Samwha ML 12.5×20 0.026
Panasonic FC 16×20 0.029
Samwha MK 12.5×25 0.029
Panasonic FC 12.5×25 0.03
Nichicon PW 12.5×25 0.03
Samwha MK 12.5×20 0.043
Elna RJ4 12.5×20 0.23
  • Panasonic EB, EE, HD, NHG,GA, M, SU, KA and KS series are not low ESR
  • Samwha SD, BH and RD series are not low ESR, WL and WF are mediocre
  • United Chemi-Con (UCC) with KZM series is comparable to KZH
  • There are much more low ESR Vishay capacitors, but they are just too big
  • Rubycon low ESR capacitors go only up to 220uF – thus not show here
  • Elna RJ3 and RJ4 are comparable

Edit History

  • May 2017 – Article created
  • Oct 2017 – Updated cap options, uploaded a video to show the effectively of adding cap
  • Apr 2018 – Added section “Does my Quad Need Capacitor?”
  • Aug 2018 – Added section “Adding Cap to Gyro’s Power”
  • May 2019 – Updated capacitor introduction
  • Jan 2020 – Added info on cap getting hot, cap size consideration



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