fitting bigger capacitor to tekin rs pro? or glitch elsewhere

[johnnygibbon]

hi fellas i have just put a 2nd hand tekin rs pro in my xb4 however i found that yesterday it was glitching with my savox servo an the reciever ( spectrum) was flickering on an off. endpoints are set corrctly as well
i tried 2 recievers and it still did it . i had tested the tekin in my drift car beforehand and it was fine working order
then i added a capacitor to the reciever ( glitch buster) which helped until the latter part of the race as the batteries lost a bit more charge and then about 4 min in to the race it would glitch again and turn off and on again
i thought it might be the savox but its pretty new and has worked fine for months
however on closer inspection this morning i found the little silver capacitor that comes with the esc had come away on 1 leg so was not connected so .......
1. could this be the source of the glitch or does it not make much differance , as i said the glitch happens when the batteries get to about 8 volts near the end of the race and while doing a lot of steering on throttle
2. i am going to replace this capacitor with a new one , but can i replace it with a larger one or 2 wired together to increase the capacity and help prevent it drainig as quickly under load
3. what capacity is reccomended for the power cap for the esc and for making a new glitch buster

thanks in advance
johnny

[shaine]

There has been loads written about this issue on a large U.S site.

From what i can gather Savox and Spektrum dont play well with certain ESC's due to a weak BEC. The Savox servos are said to draw a lot of current starving other components in the process.

I totally bypassed the savox servos when shopping because of this reason and went with a
Xpert RC SI-3401 Brushless Servo 12.47kg 0.080 Sec

which draws a lot less current.


Another option although more expensive is to change your radio gear in the hope that solves it.

[mpg200]

Hi,

A savox will pull spikes of 3.5A which can upset weak BEC circuits causing the receiver to 'brown out' (glitch)

The capacitor on the speedcontroller is there to handle the ripple current so the large ripple is not seen by the cells, having this diconnected will cause high ripple in the cells which can cause the speedo to brown out.

So replace the cap/caps on the speedo, yes if you have space you can add 2 together.

This together with keeping the receiver capacitor should solve your problem.
I run spektrum and savox with 2200u 25V cap on the receiver (rubycon ZLH series I think) i'll check.
I have no issues with brown out on Durango 410. My speedo is a Nosram matirx which although is rated at 3A BEC, I know its good for 4A I tested it. Won't do 4A for long though I had it run 4A for 3 min continuous, it got a bit hot.
As for a speedo cap, I've used 1600u and 2200u and they have all been fine. but the bigger the better just make sure its at least 16V better if its 25V. use ones with low internal resistance Rubycon ZLH for example.

[DCM]

Right chaps, lets get some things straight from the get go...

The capacitor on the ESC is there to drive the FET gates open and shut and has nothing to do with 'ripple currents', trust me, I know having been involved in testing ESC's since the early 90's....

If the ESC is disconnected from the capacitor, it can cause drive issue's on the ESC side.

BEC circuit in the Tekin, it is has a high current rating.

Savox, this is where the crux lies, they are glitchy, noisey and hungry servo's which can AND DO cause brownouts. I have even had a small 12th Savox cause system shutdowns in a GT12 on 2S.

If you re-attached/replace the ESC capacitor, fitted a capacitor to one of the receiver ports, changed the receiver, I would then look at the servo, check for free movement etc.

[johnnygibbon]

thanks guys, thats all good advice , i will source some good caps and get soldering,
so 16v or 24v is fine and about 1800 to 2200 uf
ive generally run lrp speedos and savox servos where i could so this problem has been rare
i also have a low profile savox running on a reventon s and spectrum in my drift car and thing this may also need a cap making to,
im a bit gutted though i always liked savox servos ive had one 4 or 5 years now and its still spot on , and i also like spectrum radio gear
but maybe time to change servo brands
in the 4wd anyway

[Dombrasky]

just to add another angle to this I've ran the RS ESC(not pro) in my dex210 and previously losi 22 with a Savox servo with NO cap on the ESC or reciever for
over 3 yrs now
with no problems at all,fitted wth KO receiver is the key point

[mpg200]

Originally Posted by DCM

The capacitor on the ESC is there to drive the FET gates open and shut and has nothing to do with 'ripple currents',

DCM all of your post is valid and correct, But I disagree here. You still need the caps on the ESC oh yes, What the purpose is can be open to debate. At the moment from the simulations i've done on brushless FET drive it looks and behaves like a ripple current filter. But i'm happy to educated otherwise by a convincing alternative.

But the main points here are the same..
Caps needed...yes
Savox power hungry...Hell yes.

[johnnygibbon]

Thanks guys the info is very helpful and may save me a fortune replacing gear and a headache
Mattr is this the receiver I need
http://bit.ly/1g1zuvJ
Hope so
It's a cheap fix to stay running with my current gear
That I'm quite happy with up till now
And on another note I was a bit worried about tekin esc s but I must say it felt really nice when it was going
Smooth and fast
But will it last

[DCM]

Originally Posted by mpg200

DCM all of your post is valid and correct, But I disagree here. You still need the caps on the ESC oh yes, What the purpose is can be open to debate. At the moment from the simulations i've done on brushless FET drive it looks and behaves like a ripple current filter. But i'm happy to educated otherwise by a convincing alternative.

But the main points here are the same..
Caps needed...yes
Savox power hungry...Hell yes.

As you push power through a FET, it heats up, as we are driving the gates open and shut at a high rate, the heat builds up resistance which builds up heat. A battery, whether NiCd, NiMH or LiPO can't give that instantaneous burst to fire the gate side of the FET open or shut fast enough, a capacitor can, and the higher the quality, the better it works, hence why the capacitor is there, it makes the esc more powerful but what it does is make the FET work more efficiently.

[badger5]

As mentioned above Spektrum and Savox don't really seem to mix well, from my understanding it's caused by the Savox servo drawing higher currents than other servos and the Spektrum receivers having the failsafe voltage cut off set higher than Futaba or Sanwa. The RS Pro's weren't know to having the strongest BEC's either! I had the same issues with an 1/8th electric buggy then I switched to Futaba servos and Sanwa radio and never had an issue again.

For the Tekin speedo it does need a capacitor on it, Tekin mount it directly on the speedo as the shorter the wiring the better the effect it has, many people also mounted two caps on the RS Pro for 4wd trying to keep the speedo cooler.