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Hi all,
Need suggestion from the experts here.

My Servocity pan and tilt servos(Hitec HS 785 HB) are putting interference back into the 12v power line and it creates white patterns on my monitor. Interference is visible only when the servos are moving or jittering or if i try to move my tracker forcefully by hand

I am feeding 12v from a 3S battery to my monitor,pitlab groundstation and to switching mode Ubec which converts 12v to 5 volts for servos.All servo leads are twisted and i have tried using ferrite rings,LC filters, low ESR caps and nothing is working. If i use seperate 12v battery to feed the Ubec that supplies 5v for the servos then i get no interference on my video.

If i use older hitec heli esc instead of ubec to feed the servos from the same battery, then i get much less interference .I think its probably due to the fact that heli esc has a 5v LDO instead of switching regulator.

So is there any way to isolate the servo power so that servos can't feed interference back into my 12v rail?How about isolated 12v to 5v converters? Please suggest. Thanks.

Edited by ninja_zx11
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Since the Hitec ESC's 5V LDO works well then that seems to confirm your suspicion that the issue is related to the UBEC's 5V switcher.

Have you tried a different ESC/BEC that has a switcher VReg?
Have you tried a standalone BEC switcher VReg rather than an ESC/BEC combo?
Have you investigated the wiring layout for ground loops?

Assuming the UBEC can be salvaged, I have some questions about your LC filter.
1. What L and C values did you use?  Please post a photo of the LC you built so I can see the physical size of the components.
2. Where did you install the filter? On the 3S input or 5V output?
3. Was the LC filter's inductor in series with the positive rail or ground rail?
 

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Thanks Thomas for your reply.

14 hours ago, Mr.RC-Cam said:

Have you tried a different ESC/BEC that has a switcher VReg?

No I have not tried different ESC/BEC that has a switcher VReg but i will find and try.

 

14 hours ago, Mr.RC-Cam said:

Have you tried a standalone BEC switcher VReg rather than an ESC/BEC combo?

Yes i have tried different BEC that has a switcher but same issue.Using Hitec ESC's LDO BEC,it gets much better but i can still see some interference but that i can tolerate.

 

14 hours ago, Mr.RC-Cam said:

Have you investigated the wiring layout for ground loops?

No I have not but i will post my wiring diagram here. Sorry I don't have expertise to pinpoint ground loop issue.

 

14 hours ago, Mr.RC-Cam said:

. What L and C values did you use?  Please post a photo of the LC you built so I can see the physical size of the components.

I am attaching a picture of my LC filter that i tried. I tried low esr 470uf,680uf,1000uf and even 2700uf on the 12v power rail and 5v servo rail.

14 hours ago, Mr.RC-Cam said:

2. Where did you install the filter? On the 3S input or 5V output?

I tried to install filter on 12v just before the switching BEC and i also tried to install it on 5v output of BEC but same thing.

 

14 hours ago, Mr.RC-Cam said:

3. Was the LC filter's inductor in series with the positive rail or ground rail?

I think the LC filter i used is in series with the positive as ground goes through.

 

I also monitored my 5v output from the switching BEC and its quite stable even under full servo load.It remains at 5.02 volts

 

One more thing i noticed. If i power my system by 12DC ,AC wall charger, I get no interference. So does that mean interference is getting grounded to my house ground? Does that mean there is no ground loop issue?  Thanks.

IMAG2731.jpg

Edited by ninja_zx11
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I am attaching a picture of my LC filter that i tried.

That's a very "lightweight" LC filter. It looks similar to those sold for FPV drone installations (for video camera and vTx). Don't use it on the 5V to the servos (it isn't designed for the peak servo loads). No promises, but it might help to use it only on the power leg that serves the lower current video devices, such as the monitor and vRx.

Quote

One more thing i noticed. If i power my system by 12DC ,AC wall charger, I get no interference. So does that mean interference is getting grounded to my house ground? Does that mean there is no ground loop issue? 

Interesting find. Especially if you are connecting the wall adapter to the exact same place (and same way) that was connected to the 3S LiPO. I would expect a good performing 3S LiPO to work better than some randomly chosen wall adapter. FWIW, I've seen ground station noise troubles when using a low capacity LiPO or if it was old and tired (high ESR).

During the testing I suggest using a good high capacity 3S with a full charge on it. This might help the Switching BEC's transient response characteristics.

I suspect you need better LC filtering on both input and outputs of the UBEC. And maybe revised power/ground routing. I recommend you post a detailed sketch and a photo that gives me an idea how everything is currently connected.

 

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