ESCs and extended power wires: Should we add capacitors?

[Motopreserve]

Thanks for the clarifications. Just one more....

when you describe how to solder the caps on (if using multiple caps), are you saying to put the cap pins almost touching - so that they act almost like a single unit - or the opposite (staggered by a hair)? I understand parallel vs serial, but I have also seen premised units (like the ones castle sells) that are physically staggered because they're on a PCB.

I dont know that I need this after reading your assessment - but it's helpful actually knowing which caps would be best, and how to do it - since I wondered down the path of this research inadvertently

 

[econfly]

Thanks for the clarifications. Just one more....

when you describe how to solder the caps on (if using multiple caps), are you saying to put the cap pins almost touching - so that they act almost like a single unit - or the opposite (staggered by a hair)? I understand parallel vs serial, but I have also seen premised units (like the ones castle sells) that are physically staggered because they're on a PCB.

I dont know that I need this after reading your assessment - but it's helpful actually knowing which caps would be best, and how to do it - since I wondered down the path of this research inadvertently

It's not necessarily a huge deal, but ideally they would all attach directly to the same load points. Physically, that's hard to do. I just checked out that Castle cap pack, and to my mind that is not the ideal way to do it (pretty much what I was saying to avoid). But I'm sure they know what they are doing, so maybe it just doesn't matter much. Because I think a single additional cap is almost surely good enough for all but extreme cases, I would pick a single cap of suitable size and solder it right to the same pads used by the power and ground wires coming into the ESC.

 

[Motopreserve]

It's not necessarily a huge deal, but ideally they would all attach directly to the same load points. Physically, that's hard to do. I just checked out that Castle cap pack, and to my mind that is not the ideal way to do it (pretty much what I was saying to avoid). But I'm sure they know what they are doing, so maybe it just doesn't matter much. Because I think a single additional cap is almost surely good enough for all but extreme cases, I would pick a single cap of suitable size and solder it right to the same pads used by the power and ground wires coming into the ESC.

I thought I had that right - just wanted to check.

Thanks!

 

[jes1111]

Great info here

Couple of things to add:

Capacitor Voltage Rating: the higher, the better. The cap is having to deal with the induced voltage peaks, so higher voltage rating will be able to do that better. My rule of thumb is to use double the battery voltage.

Capacitor Count: the caps will get hot when they're working hard, so multiple smaller components will be able to dissipate the heat better than a single larger one.

Wires: twisting the power feed wires is better than running them parallel, to reduce radiated interference.

Component Life: I treat ESC capacitors the same as motor bearings - replace them on an "hours flown" schedule, even if they look okay. They take a hammering and WILL eventually fail.

Brand: Rubicon is the default choice for China-made ESCs, but there are many fakes around. No problem if you're buying from Digikey, etc., of course. Panasonic FR Series are my choice - available widely from the big suppliers. I replace the caps on new ESCs on receipt.

 

[Motopreserve]

In sticking with the specific links theme: would THESE be the appropriate caps? I have seen the suggestion of doubling the voltage. These would be for a 4S setup. Does it hurt a 4S build to go to the larger voltage capacity/size to make them appropriate for the possible future swap to 6S setup?

also, when you talk of ESCs as consumables - how many flight-hours are we talking here???

thanks

 

[jes1111]

In sticking with the specific links theme: would THESE be the appropriate caps? I have seen the suggestion of doubling the voltage. These would be for a 4S setup. Does it hurt a 4S build to go to the larger voltage capacity/size to make them appropriate for the possible future swap to 6S setup?

also, when you talk of ESCs as consumables - how many flight-hours are we talking here???

thanks

Yes - those linked are good. I buy from Mouser UK: http://uk.mouser.com/Panasonic/Alum...rs-Leaded/FR-Series/_/N-1yzvjj0Z75hqwZ1yzv4gr. Datasheet: http://www.mouser.com/ds/2/315/ABA0000CE132[1]-293385.pdf

AFAIK there's no problem with over-specing the caps, only under-specing

Hours: I've set my limit at 30 hours (or whenever the machine is in bits). They also get checked after each flight: any sign of bulging on the top of the can and they'd be replaced immediately (hasn't happened to me yet).

 

[Motopreserve]

Appreciate the clarity folks. I feel like I should go back to that old thread on rcgroups and just link to here

 

[econfly]

Yes - those linked are good. I buy from Mouser UK: http://uk.mouser.com/Panasonic/Alum...rs-Leaded/FR-Series/_/N-1yzvjj0Z75hqwZ1yzv4gr. Datasheet: http://www.mouser.com/ds/2/315/ABA0000CE132[1]-293385.pdf

AFAIK there's no problem with over-specing the caps, only under-specing

Hours: I've set my limit at 30 hours (or whenever the machine is in bits). They also get checked after each flight: any sign of bulging on the top of the can and they'd be replaced immediately (hasn't happened to me yet).

I agree with there being no issue with over-rated caps, just as long as choosing higher voltage or more capacitance does not have a material negative impact on the impedance value (voltage significantly in excess of system power is fine, but if it comes with more resistance it can be detrimental).

One thing I wonder about, however, is the notion of replacing caps at 30 hours. It can't hurt, of course, but are there objective data to support this?

For example, the Rubycon ZLH spec sheet rates the series at 6,000 to 10,000 hours at 105 degrees C. That's pretty robust -- thousands of rated hours at temperatures that will boil water. The impedance and rated ripple current values are specified at 100kHz -- well in excess of the 8-16kHz fluctuations we expect in an ESC. The only reason I can see to replace caps due to expected wear would be one where the temperature during flight exceeds the rating. And if that's happening, the best approach is to fix that problem by adding capacitance or improving the build (removing unnecessarily long wire runs, etc.). Put another way, any build that has a non-trivial chance of blowing an ESC capacitor at 30+ hours (or even much longer) is a build that should be reconsidered and improved.

 

[jes1111]

I agree with there being no issue with over-rated caps, just as long as choosing higher voltage or more capacitance does not have a material negative impact on the impedance value (voltage significantly in excess of system power is fine, but if it comes with more resistance it can be detrimental).

One thing I wonder about, however, is the notion of replacing caps at 30 hours. It can't hurt, of course, but are there objective data to support this?

For example, the Rubycon ZLH spec sheet rates the series at 6,000 to 10,000 hours at 105 degrees C. That's pretty robust -- thousands of rated hours at temperatures that will boil water. The impedance and rated ripple current values are specified at 100kHz -- well in excess of the 8-16kHz fluctuations we expect in an ESC. The only reason I can see to replace caps due to expected wear would be one where the temperature during flight exceeds the rating. And if that's happening, the best approach is to fix that problem by adding capacitance or improving the build (removing unnecessarily long wire runs, etc.). Put another way, any build that has a non-trivial chance of blowing an ESC capacitor at 30+ hours (or even much longer) is a build that should be reconsidered and improved.

No objective data, just a low-cost precaution. I chose 30 hours to coincide with the rest of the maintenance schedule: complete strip down and rebuild @ 30 hours. The caps keep the machine in the air, so why skimp? Glad to report not even a hint of glitch in over 100 hours logged hours so far.

 

[econfly]

No objective data, just a low-cost precaution. I chose 30 hours to coincide with the rest of the maintenance schedule: complete strip down and rebuild @ 30 hours. The caps keep the machine in the air, so why skimp? Glad to report not even a hint of glitch in over 100 hours logged hours so far.

I understand. What you are doing works for you, and it should.

What I'm trying to do is keep this as objective as possible for those reading along and trying to decide what to do. And objectively, I can't see a reason to replace capacitors on schedule or at all.

One would have to fly 8 hours a day, 365 days per year, for a few years to reach the rated life of the capacitors. If, for sake of argument, capacitor replacement at 30 hours (or 50 or 100, etc.) actually were necessary then there would be something seriously wrong with the build in the first place. A capacitor with any significant chance of failure at hour 31 is a capacitor that is massively stressed and thus just as subject to fail at hour 29 or even hour 1. That's a build that needs to be fixed, and you can't do it by replacing the capacitors alone.

What makes this problem compelling is the almost complete disconnect between practice and results. By the nature of the problem, just about any prescribed "solution" is harmless. So there is plenty of subjective opinion out there about what to do and why to do it, but no clear proof that we need to do anything at all or that in the absence of doing anything we can expect predictable negative results.

More objective data would help. I would love to hear from someone who has experienced a blown ESC capacitor, what their build details were, etc.

Also helpful would be some temperature data during or after flight. I'll start measuring this myself and I hope others will do the same. This doesn't have to be complicated. Use an infrared thermometer (they are pretty cheap these days) and measure the temp of the ESC capacitor(s) immediately after landing. Post up what you find along with close-up photos of the capacitor (or specs if you can find them). It would be really neat to get a significant number of responses here.

 

[jes1111]

And objectively, I can't see a reason to replace capacitors on schedule or at all.

There's plenty of anecdotal evidence that capacitor failures bring down aircraft - plus one's general knowledge that capacitors deteriorate and die. In this application the capacitors are worked hard - very hard. So it entirely makes sense to replace them on a regular basis.

 

[econfly]

There's plenty of anecdotal evidence that capacitor failures bring down aircraft - plus one's general knowledge that capacitors deteriorate and die. In this application the capacitors are worked hard - very hard. So it entirely makes sense to replace them on a regular basis.

Fair enough. I'm not trying to question your judgment. What I am trying to do is collect as much objective data and insight as possible on this topic.

I really want to encourage those following this thread to post up capacitor temperature data as I suggested earlier. I will be collecting data in the coming weeks, hopefully, if weather and time allow some flying.

If anyone can report real world experience with a failed ESC capacitor that would be helpful too.

 

[RotoTwit]

I assume these are electrolytic capacitors, the normal rule of thumb is use 'at least' twice the voltage rating for the capacitor as the capacitor will EVER have applied across its terminals, & for safety/reliability even more is better (overbuild).

So fundamentally - 3.7 volts x #S battery size times 2, 3 or more!

ex: 6s - 6 x 3.7 volts = 22.2 volts x 2 = 44.4 volt capacitor with rating OR higher! - this is true for ANY size/type capacitor small or large.

So really, the OP's 6s battery usage is actually NOT safe if the caps are 35v !! (as in many things you can get by for a while before failure occurs or caps are better than labeled !!)

And also, I am talking CONSTANT DC voltage, but if you have 'noisy' voltage with spikes above the norm battery DC voltage, then THIS should be the voltage used for the capacitor NOT the steady DC voltage - thus 3x or 4x is MUCH safer - if you care for ultimate reliability.

This 'noise' is 'induced' voltage into wires from some electrical noisy producing device - likely the ESC itself via radiation/induced into the battery lead wires (shielded wires could be used - both for input to ESC and its output)

FYI: I am sure Amazon will overbuild their delivery copters in most/all ways if they really desire reliability !

Since it seems ALL ESC's are multi-voltage input (multi battery sizes can be used), then the ESC should be 'engineered/built' to the highest voltage that can be applied times 2 or more (x3 or x4), or it is poorly built and can really fail.

Any/all capacitors are obviously imperfect, meaning they have small imperfections throughout their layers and surfaces, it is when a 'hole/imperfection' occurs that allows current to flow too fast which will then cause their destruction - too much current flow (temp increases) and can literally explode - the usual cause of failure is too much voltage across it or age.

A capacitor acts much like a battery, but it only acts to store/maintain voltage - very little current will/should flow, a battery stores both voltage and current - which is power or amp/hours @ some voltage = watts.

So a capacitor is 'trying' to maintain a voltage, but its voltage 'storage' will be 'drained/released' quickly depending on its 'load' ie energy sucked from it by ESC which is what OP is doing - supplying a given voltage 'longer' before decreasing - making a more perfect battery as far as ESC is concerned!

FYI: Audiophiles have worked for VERY many years, trying to improve their music sources, pre-amps and power amplifiers by trying to 'stabilize' the power/voltage throughout their systems - similar to the OP's effort, the diff is that they can spend money for big heavy capacitors and huge 120v line filters/regulators (electronic and Inductors/capacitors) in order to have 'pristine' spike free constant voltage/power allowing the system to delivery ONLY an 'amplified' signal and nothing extra OR less - from the music source to the speakers - I have personally seen $200,000 sound systems (2 speakers!). Audiophiles use shielded wire/cables for EVERYTHING if possible - no stray voltage - perfect voltage & 99.99999999999 % pure copper wires/cabling !! (not that most of us could hear it really - no mp3's here !!!! )

 

[econfly]

The above just isn't helpful. Feel free to start your own thread on capacitors and ESCs (or on Amazon, audiophiles, general and obvious electronics observations, etc.). I very much want to keep this thread to a tight and orderly objective discussion. I will address the one quantifiable (and unsupported) statement made:

So really, the OP's 6s battery usage is actually NOT safe if the caps are 35v !! (as in many things you can get by for a while before failure occurs or caps are better than labeled !!)

In the OP you can find a link to a review I did here that included three very popular ESCs (by Jeti, T-Motor, and Castle), all rated to 6s, and all using capacitors rated at 35v. So while you can believe anything you want, what you can't do (and did not do) is offer objective evidence that all three ESC makers don't understand their product and used the wrong components. In addition, I can say that my observations of voltage fluctuations on the oscilloscope and with no capacitors at all did not reveal voltage fluctuations at 6s power (25.2v at full charge) anywhere near 35v.

Please, let's keep this objective and on point.

 

[jes1111]

econfly - I appreciate what you're trying to do but I believe you're defending the wrong hill: your suggestion is that there's no need to change capacitors unless objective data proves otherwise. Simple knowledge of capacitors and their issues suggests (to me) the exact opposite: you should change the capacitors frequently unless objective data proves otherwise.

 

[econfly]

econfly - I appreciate what you're trying to do but I believe you're defending the wrong hill: your suggestion is that there's no need to change capacitors unless objective data proves otherwise. Simple knowledge of capacitors and their issues suggests (to me) the exact opposite: you should change the capacitors frequently unless objective data proves otherwise.

How frequently should we change the capacitors? And what do you have to back up your answer?

 

[jes1111]

How frequently should we change the capacitors?

That's what I'm hoping you can tell us

And what do you have to back up your answer?

Just common sense

A few pages back it was suggested that temperature should be the focus and I'd agree with that: temperature is what destroys the caps, thereby exposing everything else to danger. Observing voltages may lead to an understanding of what's happening (with different lead lengths, cell counts, ESC ratings, etc.) but the final goal must surely be to provide a mechanism for estimating the appropriate replacement schedule for any given setup.

 

[econfly]

That's what I'm hoping you can tell us

Just common sense

A few pages back it was suggested that temperature should be the focus and I'd agree with that: temperature is what destroys the caps, thereby exposing everything else to danger. Observing voltages may lead to an understanding of what's happening (with different lead lengths, cell counts, ESC ratings, etc.) but the final goal must surely be to provide a mechanism for estimating the appropriate replacement schedule for any given setup.

Say you were a reader of this thread and trying to decide what do. How compelling would it be to see one poster claiming that we should replace our ESC capacitors every 30 hours when his only argument is "common sense"? Why not every 10 hours? Every 2 hours? Why do it at all when caps have rated lives measured in thousands of hours?

My answer regarding capacitor replacement (a topic I didn't bring up or even consider) is (a) approximately never, or (b) now. And the reason for that is you are either operating within spec, which means thousands of hours of capacitor life (from the objective source: the manufacturer's spec sheets). Or, you are out of spec, which means you need to fix the problem. In no state of the world can I comprehend the logic of swapping out capacitors ever X number of hours. That's your idea, and you have offered no objective reason for the idea nor for the completely random 30 hour interval you prefer.

 

[econfly]

Just to add -- I don't want to be rude or difficult, and arguing with people on the internet just about never seems work out well, so I'm not going to go too far down that path. Any objective comments are welcome and helpful. This is a topic with lots of opinion and very little evidence. We can go on for pages and pages with people posting up unsupported or subjective ideas. I hope, however, that we can keep this discussion limited to objective facts and reasoning. To that end, I will once more ask that readers post up ESC temperature data as I described earlier. That is the clearest path to a better understanding of this issue. Thanks.

 

[fltundra]

I agree with there being no issue with over-rated caps, just as long as choosing higher voltage or more capacitance does not have a material negative impact on the impedance value (voltage significantly in excess of system power is fine, but if it comes with more resistance it can be detrimental).

One thing I wonder about, however, is the notion of replacing caps at 30 hours. It can't hurt, of course, but are there objective data to support this?

For example, the Rubycon ZLH spec sheet rates the series at 6,000 to 10,000 hours at 105 degrees C. That's pretty robust -- thousands of rated hours at temperatures that will boil water. The impedance and rated ripple current values are specified at 100kHz -- well in excess of the 8-16kHz fluctuations we expect in an ESC. The only reason I can see to replace caps due to expected wear would be one where the temperature during flight exceeds the rating. And if that's happening, the best approach is to fix that problem by adding capacitance or improving the build (removing unnecessarily long wire runs, etc.). Put another way, any build that has a non-trivial chance of blowing an ESC capacitor at 30+ hours (or even much longer) is a build that should be reconsidered and improved.

I recap vintage tube gear on average every 10 to 15 years max. 30 hours is unrealistic.