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Old Apr 04, 2012, 12:07 PM
Pursuit of Happiness
Ron101's Avatar
Brentwood, California
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Adding Capacitors - A good time to revisit the issue

Hey guys,

This is an old issue that has come up from time to time over the years. I thought with the recent recall scare and Castel now offering a cap pack. That it would be a good time to cover the issue again.

First off here is an old thread of mine that had great info about adding caps... The experts jumped in to save the day:

http://www.rcgroups.com/forums/showthread.php?t=905356


So if you read through the thread you can see that added caps, really lowers the voltage ripple and can save a ESC. As a precaution I will go back and add a few caps to my setups.
Castel offers a new cap pack... but I've done it myself, it's so easy and cost a few bucks. I won't pay $22 for a cap pack. But if your in a rush here is a link to the cap pack.

http://www3.towerhobbies.com/cgi-bin...&I=LXBVNB&P=FR


Or you can just buy 50 caps for $33 and have enough for many planes

here is the link (thanks to Tom B.): http://search.digikey.com/us/en/prod...2402-ND/613763

You want the caps as close to the ESC as you can get them. Just clean off a small area of the main power leads insulation. Polarity is written on the side of the caps... you can add four like Castel or more if your leads are long. They say 4 for every 8 inches (seems like over kill) but I'm sure they are worried now.
So just rap the leads from the cap around the ESC main power leads on there correct polarity and solder in place... cover wire with tape or heat shrink.

another option I'm going to check on... I was told long ago that you can multiply the UF and use less larger caps. So in our case Castel is useing 330 UF caps....330uf x 2 = 660 uf. I found a 50v 680 uf the mohm is a little lower..so I need to check that this is ok. (or maybe one of our pros knows?)

here is the link to the larger cap:
http://search.digikey.com/us/en/prod...2402-ND/613763

You should be able to add two of these instead of four and have the same result as the Castel cap pack..... it would cost you $2 and 15 minutes worth of work.

I have to run, but will call Castel later to confirm we can use these.... I'm going to add caps to all my controllers.. I used to do it only on long lead setups. But it's cheap insurance and may save a plane.

later
Ron
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Old Apr 04, 2012, 01:32 PM
deltas are cool
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yeah im with you ...im tried og CC ESc flaming ...i have 5 of these esc's and 3 are shot. i just got a CC cap pack ,need to send in all my burned up ESC's what are you'll feeling about smaller 4s / 5s set up is it still needed.
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Old Apr 04, 2012, 01:46 PM
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rodger,

Did you lengthen the leads on all 3 that flamed? I have only ever lengthened the motor wires and have been ok(knock on wood) so don't know if it is just dumb luck or there is just no need to add extra caps with the standard leads. Castle told me i did not need them.

Brian

Quote:
Originally Posted by AIR SALLY View Post
yeah im with you ...im tried og CC ESc flaming ...i have 5 of these esc's and 3 are shot. i just got a CC cap pack ,need to send in all my burned up ESC's what are you'll feeling about smaller 4s / 5s set up is it still needed.
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Old Apr 04, 2012, 01:47 PM
Its a Condition not Addiction
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[QUOTE=Ron101;21234358]Hey guys,

another option I'm going to check on... I was told long ago that you can multiply the UF and use less larger caps. So in our case Castel is useing 330 UF caps....330uf x 2 = 660 uf. I found a 50v 680 uf the mohm is a little lower..so I need to check that this is ok. (or maybe one of our pros knows?)


Hey Ron,

Problem with most caps and they way the work is...

Let say I have blown caps on my motherboard in my PC...blown ones are 6v 2200uf....I can only increase the voltage, but not the uf. So I dont think you would want to just buy a larger uf cap. The CC cap sets are actually using all 4 to smooth out the ripple...each cap only does so much, so with 4...it is taking out the ripple more and more...

just my .02 cents

But you are correct...you can make theses cap sets yourself....but the CC are nicely packaged...( PUN intended )

James
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Old Apr 04, 2012, 03:02 PM
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The voltage rating on a cap is the peak voltage it was designed for. So for typical 12s HV case you'll want at least 50v rated caps.

In terms of the capacitance, measured in micro/milli farads, the larger the total value you have(caps in parallel) the longer it takes to charge and discharge. So the larger, the better for ripple voltage control until you get to a point of diminishing returns where the physical size is not practical. One word of caution, when you start getting to these size of caps at these voltages they hold a fair bit of energy so be careful with instantaneous discharge and resulting sparks.
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Old Apr 04, 2012, 03:41 PM
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I have spent alot of time with castle on the phone discussing this and here are my findings and this has worked great for me:

You first need to establish a baseline of ripple current using some fresh batteries. Start by running up a simulated short flight on the ground.

Pull up the data from the logger and only view Voltage and ripple current

Use your curser to "box" the flight from the moment the voltage drops till it goes back up, this will remove the dead time and highlight only the flight its self.

Now take the avg ripple and divide it by the average voltage, this will be your baseline average ripple current. Ideally you want this number as low as possible (.01-.02 etc.) If it is over .05 or just under then you will have issues in the future (here is why) anything under .05 is fine but as batteries get older the average ripple current will increase, so if you are at let say .045 to start you will be fine for awhile but as the batteries age you will go over .05 and that can lead to problems in the ESC.

So lets say you have fresh battery packs but you are at .04 average ripple current. The solution is to add Caps,

You want to keep the caps as close to the ESC as possible, I use the meathod that Ron mentioned which is to slice off the top of the wire insulation, solder in the cap wires and then coat them heavily with Liquid Electric Tape. Works great.

I would start with 1 cap then run the flight test again and see how that helped the average ripple current.

My Falcon 120 has the ESC in the thrust tube back in the nacelle, The battery wires are pretty long but I soldered in 2 caps and with a slightly worn set of packs I am getting .023 Average Ripple current.

Now you need to monitor this over time and keep your eye on the average ripple current, you dont want to keep adding caps just becasue the ripple goes up, this is going to happen as the batteries wear. Ideally when you get to .05 its time to retire those packs. If you are at .05 with new packs then the caps are the solution.

Going the digikey route is great if you solder well, the castle route makes things easier but does cost more.

There are several guys that will come on here and balk about this post but here is the bottom line, if you want to play with CC ESC's then you should use their advice!! If you set it up this way and are monitoring temps, extending the fan spool up time, etc.. You should never have a problem, if you do its on them!

I watched a ICE2 HV 160 get pushed to 204 amps and 8600 watts fly a 25lb EDF this morning and it had a ripple of .018 and the max temp of the ESC is 124 and it worked flawlessly.
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Old Apr 04, 2012, 04:23 PM
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Quote:
Originally Posted by bri6672 View Post
Now you need to monitor this over time and keep your eye on the average ripple current, you dont want to keep adding caps just becasue the ripple goes up, this is going to happen as the batteries wear. Ideally when you get to .05 its time to retire those packs. If you are at .05 with new packs then the caps are the solution.

.
Is there a limit on how many caps one could add and does it have a negetive effect once a certain amount of caps are added. If no negtive effecs maybe adding a couple more caps as batteries age will be cheaper then retiering a whole set of batts.

Just a thought.
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Old Apr 04, 2012, 04:46 PM
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Falcon5, I would call Castle Tech Support on that one. I know that cheaper batteries have a tendancy to have a higher ripple as well, I noticed even with the Hobby king packs that the Turnigy's seem to be better than the Zippy's but not a drastic difference.

I think the reality is if you are at .05 and already have caps then those packs are pretty darn old and they should just be retired!

My 12s 5000 setup for my Falcon 120 only has about 6 flights in my Falcon but individually they have been used for almost 1 year in my habu32 and they are only at .023! Now keep in mind I dont charge them faster than 1.5c and I usually bring them down to about 3.74 per cell and I ALWAYS leave them at 60% even if they are going to sit for just a week.
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Old Apr 04, 2012, 05:29 PM
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All great info..thanks
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Old Apr 04, 2012, 05:48 PM
Aka: Tom Jenkins
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Palm Beach County, Fl.
Joined Aug 2008
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Say! I had a dirt nap and my esc sorta went thru a bulkhead and severely distorted 4 of 6 caps, one started oozing so, I found and ordered a 10 pack off ebay matching numbers and manufacturer, the fellow sent a 14 pack so its alive again!

Question: I would like to know if its ok to liken voltage ripple and spikes to water hammer in laymans terms.
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Old Apr 04, 2012, 05:51 PM
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Brian
Quote:
I watched a ICE2 HV 160 get pushed to 204 amps and 8600 watts fly a 25lb EDF this morning and it had a ripple of .018 and the max temp of the ESC is 124 and it worked flawlessly.
curious to know what that was? airframe and the power setup
how many flights at that level?
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Old Apr 04, 2012, 05:53 PM
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Quote:
Originally Posted by jcdfrd View Post
Brian


curious to know what that was? airframe and the power setup
how many flights at that level?
Hey John,

Not mine so I am not spilling the beans but I can say the amount of runs has been very limited so we will see if it stands the test of time...
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Old Apr 04, 2012, 07:12 PM
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Hobart, Tasmania, Australia
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I would like to offer an alternate view going back to here:

http://www.rcgroups.com/forums/showthread.php?t=42110

Particularly Post 2 with the instructions from Jeti - to place the caps half way between the battery and ESC. I have done this on a couple of models, even having 3 caps placed at intervals of 150 to 200 mm along the leads. In practice it appears to work OK, but its a method not usually talked about when this issue comes up.
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Old Apr 04, 2012, 07:27 PM
Capt. Z
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Makes a little sence I guess, putting caps mid way in theory could knock down a spike befor it got to large, then another set of caps right at he ESC. but I am sure the engineers would have somthin' to say about it.

Maybe it's like this,if one set of caps is used put them close to the ESC, if multiple sets are used put one set close to the ESC and the other mid streem but that is just a guess.
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Old Apr 04, 2012, 07:46 PM
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My 2 cents worth

Form what I have read on this issue, most all of your are correct. There is one important issue your missing. Its the ESR (Equivlant Series Resistance) of the Cap. Cap's that are uses in swtching power supplys all use low ESR Cap's. Using any aluminum cap can cause a stability problem that I really don't want to go into here. If any of you design Switching Power Supplys, you will know what I'm talking about. One more issue ALL CAP's, especially electrolytic's, loose capitance with heat and age. This is an issue seen a lot on PC mother boards. Down the road, your not getting the total capitance you started out with. You can get around this by adding more cap's. The caps should be as close as possible to the ESC. Putting them in the middle can cause a stability problem with the inductance of the wire. I have seen this happen years ago with brushed motor. It can still happen with a brushless too.

My 2 cents worth
Larry E.
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