I know if possible you should have the caps as close to the noise point as feasible.  But, if you chose to mount the cap away from the proper point, how far can you do that before you defeat the purpose of the cap?

As I posted in another question I want to mount the 4in1 ESC 90* out.  Doing this puts the battery pads on the right side of the quad.  Putting the cap there would defeat the purpose of rotating the ESC which is for aesthetics anyway.  A big ol' cap sticking out in the wind will look crummy.  So if I mount the cap remotely, will 1 1/2 - 1 5/8 inch leads from the battery pads on the ESC to the cap be too long to allow the cap to be effective?  If not, what is the max distance, for future reference?

The leads that comes with the cap are crappy. So you don't want to run any length using those leads, otherwise you diminish the low ESR. If you solder a good wire as close as possible to the base of the capacitor, you can run wires 1-2 inches away without a drop in the low ESR. The Raceflight people discovered this, but the video is no longer available. And I can't find anything other video. So you just have to take my word for it.

Hey, you've never steered me wrong or anyone else on the forum that I know of...so I trust you.  

Thanks for the info...remote mounting it is.

Oscar also mentioned this in his blog.

https://oscarliang.com/capacitors-mini-quad/

So all this discussion got me to looking at specs of different capacitors.  It appears that some ceramic disk caps have low ESR as well.  But yet all the stuff used in the FPV world are electrolytic caps, why?  Using a ceramic disc cap or similar would be so much more convenient due to smaller size for a given load/voltage.

I've used the pigtail with cap unit on a couple builds on a couple builds and seems to work just fine.
https://www.racedayquads.com/collections...tail-combo

(07-Aug-2019, 01:46 PM)RENOV8R Wrote: I've used the pigtail with cap unit on a couple builds on a couple builds and seems to work just fine.
https://www.racedayquads.com/collections...tail-combo

And your power lines are likely more than 2 inches long....right?

And using that as a template, I should be able to put the cap back at the batter connector that I posted about on my build post.  That would be so clean looking, if it would work, I'm in....

This is why we use electroytic. Quote from this website.
https://itstillworks.com/difference-betw...32763.html

Electrolytic capacitors are typically used in power supply applications for voltage filtering, but are also used frequently in audio frequency amplifiers. Ceramic capacitors are often used for radio frequency and in some audio applications. Generally the ceramic capacitors are small and are not constructed with an internal coil; this is why they are preferred in the high frequency applications. They are usually used in circuits which circumvent high frequency signals to ground.

(07-Aug-2019, 12:45 PM)Krohsis Wrote: So all this discussion got me to looking at specs of different capacitors.  It appears that some ceramic disk caps have low ESR as well.  But yet all the stuff used in the FPV world are electrolytic caps, why?  Using a ceramic disc cap or similar would be so much more convenient due to smaller size for a given load/voltage.

To be effective, the capacitor in a quad needs to have a relatively large value of capacitance -- typically, 470µF to 1000µF.  Only electrolytic capacitors are manufactured in such large values, because electrolytics can pack a lot of capacitance into a small volume (at some sacrifice of other characteristics such as ESR).  Ceramic capacitors of comparable physical size have 2-3 orders of magnitude less capacitance.  You can't buy a 470µF ceramic capacitor, and if you could then it would weigh more than your quad.

(08-Aug-2019, 05:34 PM)SJChannel Wrote: To be effective, the capacitor in a quad needs to have a relatively large value of capacitance -- typically, 470µF to 1000µF.  Only electrolytic capacitors are manufactured in such large values, because electrolytics can pack a lot of capacitance into a small volume (at some sacrifice of other characteristics such as ESR).  Ceramic capacitors of comparable physical size have 2-3 orders of magnitude less capacitance.  You can't buy a 470µF ceramic capacitor, and if you could then it would weigh more than your quad.

True, I have been doing some reading since the post....but what I have found is the need for the amount of capacitance like a 470uf electrolytic cap isn't needed for filtering like we need.  Most of the 4in1 ESC have numerous caps, none of which are electrolytic.  Those caps do such a good job of filtering there is almost no need for adding a electrolytic cap on the ESCs or the PDB or FC.  I believe most of the caps on a 4in1 ESC board are ceramic....just many small ones...so I guess there is truth in electronics that there is strength in numbers....  

Power supplies, like the one on your computer, or the stereo system I had in the 70s and 80s use electrolytic caps for filtering, but that is trying to filter out noise from the A/C input.  The noise produced from ESCs and other electrical devices in the FPV system, may not need that level of filtering.  Clearly, people much more experienced than me came up with using the electrolytic caps for noise filtering, and they work.  But it seems to this novice they may not be needed.....anyway, I'm still learning.......

(08-Aug-2019, 06:23 PM)Krohsis Wrote: True, I have been doing some reading since the post....but what I have found is the need for the amount of capacitance like a 470uf electrolytic cap isn't needed for filtering like we need.  Most of the 4in1 ESC have numerous caps, none of which are electrolytic.  Those caps do such a good job of filtering there is almost no need for adding a electrolytic cap on the ESCs or the PDB or FC.  I believe most of the caps on a 4in1 ESC board are ceramic....just many small ones...so I guess there is truth in electronics that there is strength in numbers....  

Power supplies, like the one on your computer, or the stereo system I had in the 70s and 80s use electrolytic caps for filtering, but that is trying to filter out noise from the A/C input.  The noise produced from ESCs and other electrical devices in the FPV system, may not need that level of filtering.  Clearly, people much more experienced than me came up with using the electrolytic caps for noise filtering, and they work.  But it seems to this novice they may not be needed.....anyway, I'm still learning.......

With modern ESCs you can sometimes get away without using external electrolytics, and sometimes not.  It depends on many things: how much current your motors draw, the quality and age of your batteries (i.e., how much they sag on current bursts), how aggressive your props are, etc.  I have a quad that performed flawlessly until I mounted a GoPro on it.  Then I started noticing yaw twitches at high throttle.  Adding a 470µF low ESR capacitor across the battery fixed it.

Anytime there is a sudden increase in the current drawn from a system, energy is drawn from the system and the voltage tends to sag.  Part of the sag is from the internal resistance of the battery and the resistance of the wires and PC traces.  But for rapid current changes, most of it comes from the inductance of the traces and wires.  For the purpose of this discussion you can think of inductance as being like a resistance that is higher in value for rapidly changing currents than for slowly changing currents.

The purpose of the capacitors is to supply the missing energy until the current stabilizes and the inductive effects diminish, and also until the voltage regulator has time to respond.  On digital electronics (including ESCs and flight controllers), standard practice is to put a ceramic capacitor, typically 0.1µF, next to each chip, as close as possible to the power pins of the chip.  This supplies the needed energy to the associated chip and keeps it from getting confused by electrical noise.  A capacitor that small can't supply very much energy but it can supply it very quickly, and a chip doesn't need much.  Generally there are also one or more larger electrolytic capacitors to stabilize the circuit board as a whole.  (Look at a computer motherboard and you'll see them scattered about all over the board.)  These can supply much more energy and for a longer time, but they can't supply it as quickly as the ceramic capacitors.  That's because electrolytics have more inductance internally, and also because they're physically larger and therefore need longer wires or PC traces leading to them -- which means more inductance.

I don't have a 4-in-1 ESC to look at without dismantling a quad, so I can't say for sure.  But I'd be pretty surprised if a 4-in-1 didn't have at least one large-ish electrolytic capacitor on board.

I haven't seen any electrolytic caps on my 4in1.....

I appreciate the long narrative.  Like I said I'm new to this topic and learning more all the time.

(08-Aug-2019, 06:23 PM)Krohsis Wrote: But it seems to this novice they may not be needed.....anyway, I'm still learning.......

Maybe I've just been lucky with the electronics I've chosen, but I haven't needed to add any caps to any of my quads yet.