Flux FPV

Multirotor Tech and DIY

Fix Little Bee Voltage Spikes

The FVT Little Bee ESCs, also known as the MRM Zeus, are very popular ESCs for mini quad pilots right now, and for good reason. They perform very well and at a reasonable price. However, there is one issue with these ESCs – they cause some nasty voltage spikes that can fry FPV cameras and video transmitters. I will try to explain why this issue occurs as well as how to fix it. Feel free to skip the next paragraph if you want a fix without any of the technical details.

Most ESCs have one common feature – they have a large electrolytic capacitor sticking out of the back. This is to absorb the voltage spikes that come from the operation of the ESCs. However, to make these ESCs smaller and lighter, FVT used surface mount ceramic caps instead of electrolytic ones. Usually, these would be more effective at absorbing spikes due to the lower ESR, but they aren’t. This is because these capacitors may not have been sufficiently derated. Derating is when you use a capacitor rated for a voltage 2-3 times the maximum you expect the capacitor to see since the effective capacitance decreases as you get closer to the max. operating voltage. This is significantly worse for ceramic caps than for electrolytic ones. All ESCs with active braking generate these voltage  spikes, but it especially bad with the Little Bees due to the combination of extremely strong braking and insufficient filtering. A huge thank you to mnemennth at RCGroups for the explanations.

Red Brick 20A Plane ESC with Electrolytic Capacitor Highlighted

Red Brick 20A Plane ESC with Electrolytic Capacitor Highlighted

Now for the fix itself: One option is to add one large capacitor (1000 uF or more) where your battery wires connect to the PDB. Make sure the voltage rating is high enough! You can also add small capacitors (around 330 uF) where each ESC connects to the PDB. The exact values are not crucial but should be in this range. Ideally these should be low-ESR caps of a good brand like Panasonic, Sanyo, Nichicon or Rubycon. Basically what you are doing is compensating for the insufficient filtering by adding more (to soak up the spikes). I have not tried this method myself but have heard from reliable sources that it works.

An easier method which worked equally well (for me) was to power the FPV gear from a small variable buck converter like this. It is a good idea to buy a 5 pack since they are dirt cheap and super useful to have around. Note that this is a buck converter, which means that the input voltage should be higher than the output voltage for a stable output (usually about 1.2V higher). I set the voltage on it to 9V to be safe as I run both 3S and 4S which means that the input voltage may sag up to 10-11V during hard flying. Do make sure that whatever output voltage you set is at least 1V above the minimum voltage required by your video transmitter and FPV camera to avoid blackouts. I also put a 470 uF capacitor on the output of this regulator for more filtering. I get nice clean video feed and haven’t fried anything so this method seems to work for me. Ideally, you should still use a 1000uF low ESR cap on the power rails in order to protect the regulator itself.

Example of a variable voltage regulator.

Example of a variable voltage regulator.

15 Comments

  1. What about the vbat on a naze32? will the voltage spikes kill the naze through the vbat?

  2. Hi this is a great article. By mistake I bought a 1000uf low esr 16 v instead of 25v cap. Since I’m using 4S lipos, can I still use these 16v caps , what happens if I use it? Thanks .

    • SK1701

      22nd August 2016 at 4:47 PM

      Hi. A fully charged 4S LiPo is 16.8V, but your cap is only rated for 16V. That should not be enough to immediately burn your capacitors (Electrolytic caps actually go pop rather than burn), and I think I’ve seen some people on RCGroups using 16V caps with 4S on really tight builds. However, the capacitor will no longer be as effective at absorbing the spikes if you are using a voltage above the maximum (like what I mentioned about derating, but worse since you a crossing the specified limit). It may also lead to internal damage/ degradation of the capacitor over a period of time, which further reduces its effectiveness. I would just get a 25V (or even 35V if it fits) capacitor. However, you could perhaps test with this capacitor with all other parts disconnected at first, and use it if it works until you get higher rated caps. Just don’t blame me if something blows up 😛 😉

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  4. Hi I just have a quick question. I;m actually making a very tight build that only has 10mm of clearance and as a result I’m not able to fit a 1,000uF capacitor. Would something like a 680uF capacitor connected directly to the PDB still work? Please let me know as the only other option I have would be to solder the capacitor while soldering the xt60 and bring it to the outside of the frame. Any help would be appreciated. Thank-you

    • SK1701

      28th May 2016 at 9:18 AM

      Hi.
      I really am not sure what exact amount will be enough or not. 680uF will definitely be less effective than 1000uF but if you can get a good low-ESR 680uF cap it might be enough. I can’t really say for sure.

  5. Really nice article, thanks.

    But I have one question, what is the differnce when powering FPV gear (let’s say both vtx and camera are for 5v) from a 5v BEC on a PDB, than using this small regulator?

    • SK1701

      17th May 2016 at 6:48 AM

      No difference really. It is just that 5V is on the lower end for most video transmitters and cameras and it is usually recommended to power them slightly higher than the minimum operating voltage. This regulator just lets you vary the output voltage. Otherwise in theory they are almost the same: both are just switching regulators.

  6. Thanks for the article Oscar. A couple questions.

    What is the actual voltage spike that these ESCs generate? Are we talking about 2x the input voltage, 3x? I want to know because [my VTX](https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=76394) handles 6V to 30V (much larger range than typical), so should mine be safe from spikes without additional filtering?

    If we want to add a capacitor to each ESC or one on the Vbat line going to whatever equipment needing that voltage (VTX for me), we should choose a cap that is rated for 2 to 3 times the charged voltage of the battery?

    • SK1701

      21st April 2016 at 8:54 PM

      Hey.
      I am not sure if anyone has measured the actual value of the voltage spikes. I think Mini Quad Test Bench had some data on massive current spikes with these ESCs, though that was during acceleration/ braking. I have an oscilloscope on the way and I will try to measure the spikes once I get it. I would still run a capacitor to be safe as the spikes may exceed 30V (my guess), if only for a fraction of a second.
      I use a 1000uF 25V cap at the BATT terminals (along with a regulator). This should suffice even for 4S. Capacitors rated for higher voltages may be better but they will also be significantly larger.

      PS: This isn’t Oscar’s blog. Though I’m honoured you thought it was 😉

      • Whoops. Sorry Flux. Think I assumed you were Oscar because the page alignment seemed similar Oscar’s posts that I was reading in other windows, lol. I am very curious what the true max spike voltage is. I bet it depends on motor size and inertia as well as input voltage. I’m running tiny 3020 props on 3S 1105 4000kv motors which only pull about 5 amps, so perhaps my setup won’t see spikes as large as a 4S Cobra 2204 2300kv motors spinning 5040 triblades… Quite a complex issue. Do you know if the Zeus V2 eliminates the spikes? http://www.multirotormania.com/20-amp/1366-mrm-zeus-v2-20-amp-esc.html

        PS: What language does this site use so I can condense hyperlinks?

        • SK1701

          2nd May 2016 at 8:27 AM

          Hi.

          Sorry for the extremely late reply. To the best of my knowledge, the only change in the Zeus V2/ Little Bee 20A Pro is that it has an F39x MCU instead of the slower F330 in the regular LB/ Zeus. Unless they have added filtering caps (I am not sure if they have), the voltage spike issue will remain. Once more people start running these, we will know for sure. It would also be interesting to see if and how the spikes vary with different setups like yours.

          Also, I am not sure what you mean by which language the site uses?

    • SK1701

      2nd May 2016 at 3:48 PM

      Well it looks like someone has tested the spikes- http://www.rcgroups.com/forums/showpost.php?p=34668187&postcount=2259 and they go up to 29V!

  7. Hi thanks for this Fix! First of all I really like your Blog! I also have a few questions about this topic. I will use this PDB( http://www.banggood.com/CC3D-NAZE32-F3-Power-Distribution-Board-PDB-With-Filter-BEC-Output-5V-12V-3A-for-QAV250-p-1023543.html ) in the description it says that the power outputs are already filtered. Will this be enough to protect my FPV gear? And if this voltage spikes burn out the fpv gear does it also burn out the Flight controller? Im using the Naze32 Rev5 and it’s only rated for 5v so if there is a voltage spike from the littlebee esc’s this would mean I also have to protect the Naze32 not only the FPV gear? Thanks for any help.

    • SK1701

      9th March 2016 at 7:03 PM

      Hi.
      I’m glad to hear you found this post helpful.
      As for your question, yes powering your FPV gear from the regulator on the PDB should be enough to protect it. However, I would still recommend soldering a good 1000uF 25V low-ESR capacitor on the battery leads/ pads. Also watch out – if you are using the 12V BEC on that PDB you must ensure the battery voltage does not drop below 13.2V or so. Also, the Naze32 is unlikely to burn out since it is usually powered from a 5V BEC. The parts that are at risk of damage are those that are connected directly to the battery voltage (via the PDB or otherwise).

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