Back in the day I was running Orion R10 speedos and would cut the caps off of them. I just installed a hobbywing into my 17.5 buggy and thru the years there seems to be less and less room to work. My question is, Can I still take the cap off and the speedo be fine? I never noticed a difference in feel with or without the caps attached to the speedos....

If you want to burn up the FET's then go ahead by removing the capacitor.

In my wet car i run a QuicRun ESC without capacitors, as I understand it the capacitors help smooth/supply the power to the control unit if/when the motor is hogging it all. It has run two years without a glitch.

I tried to run my Trackstar Tubro esc the same in my TC but kept getting loss of control at full throttle - I was also running an Orange RC receiver. I changed to a Futaba receiver and also added the capacitors back on and no more issues - but not sure which sorted it.

i applaud you brave guys to test this stuff heh. kinda like those guys who cut the antennas off their receivers i guess.. the cap is there to smooth the power and prevent massive voltage sags and bad ripple currents. esc is quite sensitive to this kinda stuff and might shut down under a brutal load like a mod motor or stock motor poorly tuned. add in fans and a powerful servo and it might be a bad time.. i guess if you have the most tits batteries all the time you could get away with it.. ill tpyically run a LARGER cap to try to take some of the strain off the batteries as chemistry isn't instant.
ill also add that my experience comes from the older hobbywing 3.1 and xr10 series. those i would use a larger cap to get a bit more punch without sacrificing batteries.. the new orca escs i use now have TINY little caps.. kinda similar in size the current hobbywing sport caps ect. i dont really see any reason to delete somthing that small. esp if it comes preinstalled as it does on hobbywing.

As an electrical engineer I've never really thought too hard about what the caps do in our ESCs. I understand in theory a cap works by storing charge on the plates and that lets you do some useful stuff in electronic circuits but now I'm curious as to what exactly they're doing and whether or not the "common knowledge" I see passed around on-line regarding their operation is accurate.

The first question that strikes me as worth asking is "how much useable current can a capacitor provide in high load conditions?" That's a pretty straightforward question to answer. The amount of charge stored in a capacitor can be calculated using Q = C * V. Plug in typical numbers for our ESCs and you get Q = 8.4V * 900uF, which works out to roughly 0.0075 coulombs of electrical charge. An ampere is an electrical flow rate defined as a of 1 coulomb of charge over 1 second of time. If we assume an amp draw of maybe 30A when a car accelerates from a standstill, that 0.0075 coulombs of charge gets used up in 0.00025 seconds. Now, that assumes all of the 30A comes from the cap first, then the battery. That's not how it will really work - based on the impedances of the cap and the battery it will be a mixture of amps coming from the battery and the cap at the same time, possibly with the rate of charge coming out of each varying over time. But lets assume maybe it's a 50/50 split - battery provides 15A and the cap provides the other 15A? That's still 0.0005 seconds. Okay, so let's look at it from another angle - if we want 900uF of capacitance to provide current over a useful period of time to us, say maybe half a second, how much current would that be? 0.015A.

So the idea that caps are doing any kind of work to prevent the battery's voltage from sagging under heavy load or really helping our car to accelerate faster is looking pretty shaky.

The next interesting question to ask would be "how much capacitance is required to have some kind of meaningful impact to our car's acceleration?" So lets use the same assumptions here - we want the cap to provide 30A over half a second. We can use that to calculate how much capacitance we'd need using the same two formulas. 30A over half a second is 15 coulombs of charge. A cap that can store 15 coulumbs of charge at 8.4V would need to be 1.78 F, roughly 2000 times the capacitance of what you get with an ESC.

Interestingly, capacitors with that much charge do exist at not very exorbitant rates or sizes. A 4F cap rated for 8.4V is only $15 on mouser and roughly 1/4" x 1/4" x 1/2" in size. Unfortunately the ESR of the cap I'm looking at is rated at 45 ohms. A lipo cell is somewhere in the .02 to .04 ohm ranges so that means in practice the ESC will pull the overwhelming majority of current flow from the battery, but it's possible the cap could provide just enough current to help with voltage sag in some meaningful way.

Anyway, this was mostly a post to satisfy my own curiosity and nothing else really.

Yes, that is the simple explanation of the working of a capacitor. But the story is a bit different.

The resistance of a capacitor is frequency depending. The higher the frequency, the lower the resistance or acually called the impedance. X = 1 / (2 x pi x f x C)

So a high frequency ripple on the powerline will get a low resistance load and so will be faded away from the power line giving a much cleaner DC voltage. That is better for the FET's

Because the internal resistance of the capacitor plays a role as well in how low the total resistance/impedance can become the effect will be much better with so called low ESR capacitors but also with parallel stacking you can get the resistance lower. The new non polarized capacitors are made of a huge amount of parallel stacked ceramic capacitors. My made 900uF ceramic capacitor shows on the ESR meter a 5 times lower impedance than with a normal module with 2x 470uF electrolyc capacitors and that is a huge and even noticeable difference knowing from the few guys who tested them.

^Much appreciated. Never bothered to crunch the maths, despite working with electronics daily.

I though they were there to absorb the ripple currents.
https://www.radiocontrolinfo.com/rip...to-improve-it/

So I decided to do an extremely rudimentary circuit analysis to see if I could gain a better understanding of what's happening.



I've made some pretty major simplifications - the transistors have been swapped out for simple switches, the motor windings are shown as just resistors, and there's probably all sorts of other things I should technically add, like the windings probably have some amount of capacitance between them, or a resistor to represent the IR of the battery, etc. But for the most part I was looking to get the basic gist of what's going on and I think this helps in that regard so hopefully it's not too gross of an oversimplification.

The graph of the voltage between points A and B on the circuit over time isn't necessarily to any kind of scale - what I don't know without some serious calculating/simulating is 1) how far the voltage actually drops when the switches are closed and 2) how long the voltage actually takes to drop. Thinking about it now, if I go with the numbers I used in my last post, an 8.4V battery with a 0.02 ohm IR should have a 0.6V drop when outputting 30A. That seems pretty realistic from what I remember seeing on battery discharge curves.

Intuitively, a cap with more capacitance will take longer to discharge so you'll have a higher average voltage over the duration of the switches being closed. And capacitors with a lower ESR will have less of a voltage drop which should also equate to a slightly higher total average voltage over the timespan the switches are closed. So in that regard, I could see how it's theoretically possible that a larger cap could provide performance gains by keeping the average line voltage slightly higher over the duration of a PWM pulse.

Some ESCs have adjustable PWM frequencies, but I wouldn't look at that as a way to increase the average voltage over the duration of a PWM pulse - windings are inductors and they have higher impedance at higher frequencies so you'll just end up heating up your motor more.

Anyway, all that said, my best guess is the real purpose of the capacitor is to prevent the switching transistors from seeing instantaneous voltage changes. Without a cap the voltage drop in my graph when the switches close would be instant, and voltage impulses contain lots of high frequency noise that probably isn't good for the transistor.

You just have to see it as a RC low pass filter.



Where R is the resistance of the cable (+ connector) and the internal resistance of the battery.
https://www.allaboutcircuits.com/tec...ive-RC-filter/

^ Drops the mic and walks out the door.

Sometimes, extremely sometimes I feel a ET4 knows more than an EE or EET.

We all have our backgrounds, degree or otherwise. Mine stems from a childhood surrounded by practical consumer electronics and industrial relics.

I had considered that, but I'm not sure how that would affect anything. Specifically what would change about my analysis or my voltage graph sketch that would impact performance?

I did find a pretty interesting video on youtube. It's a guy with a mini pro dyno and he actually tests one of those massive 2,500 uF capacitor banks to see what affect is has. Unsurprisingly there's 0 detectable difference on the dyno between the stock cap and the massive 2,500 uF cap.


I can't find a clear "smoking gun" in the engineering that would make me confident in saying there's performance gains to be had with different caps, and a guy with expensive testing equipment can't detect any performance gains from switching caps either. For me, that's enough that I can confidently ignore any marketing hype around capacitors.

Anecdotally, I also built myself a ceramic capacitor bank for my Mini-B. Not because I was chasing performance but because the smaller form factor was a major benefit in such a small car. Going from the stock electrolytic caps to the ceramic caps made no detectable difference to anything other than how easy it was to get the body on the car.

Interestingly when you use higher PWM frequencies it's the ESC that runs hotter and the motor runs cooler.

And how many of you ran the esc with a bad power so I never knew about it? I did ran mod for an entire season with a non working power cap 🤷‍♂️. Ran a 5.0t in mod tc never had an issue. Replaced the cap and the esc still works like a charm

Well, with 99% of the racers with no background of electronics you can sell them anything with the right marketing story.
With capacitors there is a line of enough is enough so more will not help, but again with the right story more capacity will sell.

From what I hear is that my bank did provide a better brake feeling and a stronger brake and one guy made a personal best laptime on some indoor track. The brake I can understand it comes from the capacitor, the better laptime can come from any track condition but can also come from the capacitor.