Thread Tools
Dec 30, 2008, 02:51 PM
WarClouds Online Dogfights
IL2windhawk's Avatar
Discussion

ESC capacitors. What do they do?


Please bare with me on this short story. I think I've finally solved a mystery that has puzzled me all summer, and I'm hoping one of your electronic masters can confirm my suspicion:

The first ESC I bought was a Castle Creations 80. It's been in quite a few airplanes now, and it's also been through a few crashes. I've had great reliability with it until the last plane I put it in. I was running a med-size motor (about .25 power class) with strong thunderpower batteries and I was carefully monitoring watts & current to make sure I was not exceeding any of the component specifications. I was safe by a factor of 2 on all components, so it seemed that I had everything checked and re-checked. But for some reason the motor would drop to half-power during flight or stop entirely (in both cases always when I was running near full power). When this happened I would cut the throttle in flight, thereby reseting the ESC, and then I would crank it back up and sometimes it would work flawlessly, other times it would just repeat the problem.

Well just yesterday I discovered that one of the capacitors has at some point become disconnected from one of the contacts. It is disconnected, but still very close to the solder joint such that it could potentially vibrate in and out of contact with the joint. I do not know when this damaged happened, but I'm wondering if this has been the problem all along. Would a reduction of 1/2 capacitance cause these intermitten failures at high throttle settings? And why: what is the function of those capacitors?

Strangely, the ESC will still power on and run a smaller motor. So apparently the problem does not impact lower-current operations.

Thanks in advance for any opinions. I'll have the ESC repaired for sure, but I'd love to prove to myself that I've finally found the source of this problem before risking any more dead sticks.
Sign up now
to remove ads between posts
Dec 30, 2008, 03:09 PM
Space Coast USA
hoppy's Avatar
http://www.teamnovak.com/tech_info/p...power_caps.htm
Dec 30, 2008, 03:14 PM
Space Coast USA
hoppy's Avatar
dupe]
Dec 30, 2008, 03:23 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Novak page is ok, just ignore the 'more power' marketing nonsense.

Other manufacturers:
https://www.rcgroups.com/forums/show...highlight=kill

Vriendelijke groeten Ron
Last edited by Ron van Sommeren; Dec 30, 2008 at 03:30 PM.
Dec 30, 2008, 05:07 PM
Registered User
This statement:
Quote:
Originally Posted by IL2windhawk
But for some reason the motor would drop to half-power during flight or stop entirely (in both cases always when I was running near full power).
and this statement:
Quote:
Originally Posted by IL2windhawk
Strangely, the ESC will still power on and run a smaller motor. So apparently the problem does not impact lower-current operations.
are reminiscent of hitting low voltage cutoff. Have you ruled this out by checking your power system with a wattmeter and verifying the cutoff settings on your ESC?
Dec 30, 2008, 06:15 PM
I havent decided yet
the caps just smooth out the dc ripples on the input side.... makes the voltage "smoother" and eliminates spikes. the caps should not cause the trouble that you have described. they can be removed safely but not recommended.
Dec 30, 2008, 07:26 PM
sneu's Avatar
Quote:
Originally Posted by dmiller746
the caps just smooth out the dc ripples on the input side.... makes the voltage "smoother" and eliminates spikes. the caps should not cause the trouble that you have described. they can be removed safely but not recommended.
I would say that you are incorrect in suggesting that the caps can be removed safely. In fact without them the spikes from the switching will likely exceed the voltage limits for the FETs--which can lead to a melt down(aka fire). On a 20 volt system I measured spikes in excess of 100 volts. The caps are there for a reason!

Steve Neu
Dec 30, 2008, 07:45 PM
Registered User
If it was me I would call castle and ask them how much they would charge to fix it..
Dec 30, 2008, 10:07 PM
I havent decided yet
I dont think it is a good idea to remove them but I have removed one before and didnt see the symptoms on my system that he is seeing. I saw no difference but I know that is rolling the dice. I finished the flying session and retired the ESC. I do have alot of respect for Steve Neu and am certainly not disagreeing with him. He know his stuff here and in the industrial arena ( my field of employment). Take his advice above all others but I did remove a cap from an old EFlite ESC ( it removed one leg by itself) and it did continue to operate for the rest of the day. Fix your cap and see what happens but we might need to keep looking for the cause of the symptoms that you describe.
Last edited by dmiller746; Dec 30, 2008 at 10:44 PM.
Dec 31, 2008, 05:57 AM
Registered User
vintage1's Avatar
The trouble is the ripples you will see - and the spikes - depend on many variables.

Motor inductance.
Wire inductance.
Pack resistance
wire resistance.
and so on.

I.e. YMMV to a huge extent.
Dec 31, 2008, 05:24 PM
Registered User
Sabrejock's Avatar
Quote:
Originally Posted by IL2windhawk
Please bare with me on this short story.
Well, now, that would depend on what we would be 'baring'.

Hey, Happy New Year. Tex.
Dec 31, 2008, 06:40 PM
7000mw of raw power!
rich smith's Avatar
Thanks to Theunissen and Konze here at RCG and Atmel/Microchip app notes I've been able to aquire enought knowledge of BL ESC to design several models from scratch. Spent many hours staring at scope traces. High voltage noise was observed with brushed motors but with BL negative spikes were the problem. Specially if both FETs were turned on at same time due to firmware bug.

Major reason those large caps are present is to reduce impedance due to battery internal resistance and long leads. This is particularly important when high Kv motors are used with marginal batteries (old or small). Otherwise the FETs pull down the supply resetting the micro or other voltage sensitive circuits.

I've removed them for reasons of weight on many occasions and it worked fine, mainly because my motors draw such little power. With bigger motors I'd expect exact same symptoms OP observed. Or in cases where you extend power leads too much. Then you might want to put the caps back in.
Dec 31, 2008, 09:24 PM
Registered User
During some test I made at very high currents the caps did get warm if not hot so they were supplying large currents. I had three 470ufd, 100 volt caps on the ESC and any less would have been a smoke bomb.
Jan 01, 2009, 10:41 AM
7000mw of raw power!
rich smith's Avatar
I noticed this on high power setups. They smooth huge ripple currents which are worst at 50% throttle. Very cool at %0 and %100 though. Same for FETs. Also affected by PWM freq.


Quote:
Originally Posted by mjsas
During some test I made at very high currents the caps did get warm if not hot so they were supplying large currents. I had three 470ufd, 100 volt caps on the ESC and any less would have been a smoke bomb.
Jan 01, 2009, 01:20 PM
WarClouds Online Dogfights
IL2windhawk's Avatar
LOL, well- as usual when I ask an electronics question I 've received several differing/contradictory answers. Thanks for taking the time to offer up your opinions, and for the educational links. It looks like it may just come down to a repair followed by thorough testing to know for sure if this was my problem.

Mrforsyth, I will test for those ESC settings - thanks.

Happy New Year


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion ESC timer - what do these DIP switches do? foxkilo Control Line 4 Sep 15, 2008 04:18 PM
Eflight brushless ESC's what do you think of them??? crash test dummy Power Systems 10 Aug 09, 2005 01:36 PM
Hitec #SP1010 ESC question, what do I do with the skid wires? mrebman Power Systems 3 Nov 20, 2004 07:50 PM
3 motors...what can they do? NitroSpazzz Scratchbuilt Indoor and Micro Models 0 Jan 18, 2004 06:28 PM
Have ESC/Bat - What do I fly? IncredibleITGuy Electric Ducted Fan Jet Talk 1 Sep 02, 2002 08:19 AM