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Rotax 912 Noisy Regulator

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Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Tue Sep 29, 2015 3:49 pm Post subject: Rotax 912 Noisy Regulator

A brief problem description: I changed from a fried Key West voltage regulator on the front of my firewall to a Rotax VR on the back of my firewall. (Kitfox w/ 912ULS.) Now the music input to my intercom (SLA-400 TSO) is muted because of noise coming into the intercom via the IC-200 radio. So far I've shielded the input all the way to the VR, tried a noise filter right in front of the DC bus, and a faraday cage over the VR. I've improved the problem to the point that I can hear the music up to about 3000 rpm, then it mutes. So I bought an oscilloscope and took some measurements today. I'm seeing a weird 20Hz 360mv spike downstream of the VR, and the VR input (generator output) looks terrible. (I thought it was a kind of square wave.) I can't seem to find what the 912 generator output is supposed to look like online. Any ideas? Any ideas what the downstream voltage spikes are?



Thanks,

A VR Out B Bus - 2490 RPM.jpg

Description:

A trace - VR output voltage
B trace - Ground bus voltage

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206.73 KB

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8026 Time(s)

A VR in - B VR in braid 2200 rpm.jpg

Description:

A trace - VR input voltage
B trace - VR input braid voltage

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217.6 KB

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8026 Time(s)

A Main bus + B - 2310RPM.jpg

Description:

A trace - Voltage at main bus
B trace - Ground bus voltage

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240.81 KB

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8026 Time(s)

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Sep 30, 2015 12:16 pm Post subject: Rotax 912 Noisy Regulator

At 06:49 PM 9/29/2015, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Guy Buchanan" <gebuchanan(at)cox.net>



 A brief problem description: I changed from a fried Key West voltage regulator on the front of my firewall to a Rotax VR on the back of my firewall. (Kitfox w/ 912ULS.) Now the music input to my intercom (SLA-400 TSO) is muted because of noise coming into the intercom via the IC-200 radio. So far I've shielded the input all the way to the VR, tried a noise filter right in front of the DC bus, and a faraday cage over the VR. I've improved the problem to the point that I can hear the music up to about 3000 rpm, then it mutes. So I bought an oscilloscope and took some measurements today. I'm seeing a weird 20Hz 360mv spike downstream of the VR, and the VR input (generator output) looks terrible. (I thought it was a kind of square wave.) I can't seem to find what the 912 generator output is supposed to look like online. Any ideas? Any ideas what the downstream voltage spikes are? 	


  The fact that you didn't have noise . . . an now you

  do suggests a change in WIRING of the alternator

  and rectifier/regulator. I'm guessing on where and

  how the various components are grounded.



  Electro-static shielding of wires, magnetic shielding

  of the rectifier/regulator are almost guaranteed

  to be no help with what appears to be a ground-loop

  situation.



  The 'noises' you observed are all quite normal

  for the components of an engine driven power

  generation system. The alternator is the most

  trashy device in any airplane but the noise levels

  are limited, known and easily managed in the

  design of potential victims.



  The now-you-have-it and then-you-didn't points

  strongly FIRST toward a change in grounding

  and SECOND toward an interference coupled

  magnetically between adjacent wires bundled

  together.



  ALL potential victims (radios, nav, entertainment

  systems should ground together ON the panel with

  a single robust ground feeder extending down to

  DC system grounds on the firewall.  See View-A

  of  http://tinyurl.com/6m3bk8k



 

   Bob . . .    [quote][b]

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Wed Sep 30, 2015 2:42 pm Post subject: Re: Rotax 912 Noisy Regulator

Bob,



Thanks for the response.



I have no "firewall ground bus" but do have the "Panel Ground" forest of tabs inside the firewall. The engine ground strap is passed through the firewall with a brass or bronze bolt. The few grounds I have from the engine side pass through the firewall to the forest of tabs. The penetration for these grounds is away from the penetration for the VR, but they then pass near to the VR, as do the wires from the battery to the positive bus. I have an avionics ground forest of tabs on the panel, but I think the only thing connected are the headset grounds. I don't think I connected the radio and intercom grounds to it. (Checking) 



As to wires bundled together, the VR input and output go through the same firewall penetration. That's bad, isn't it? They're together for a distance of maybe three inches, then separate. I think I could separate them completely if necessary.



This same system worked fine with my Rotax 582 with the VR forward of the firewall. Replacing the 582 with the 912 with its VR behind the firewall seems to have resulted in more noise.



I have tracked one possible ground loop with the tachometer ground. I'll check it for continuity and will try to update my wiring diagram and post it.



Thanks again.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Wed Sep 30, 2015 6:29 pm Post subject: Re: Rotax 912 Noisy Regulator

 	  Quote: 	
		  the VR input and output go through the same firewall penetration. 	


Does the voltage regulator output have to go through the firewall?

Can it be connected directly to the main power bus though a fuse?

Are the AC wires from the dynamo to the voltage regulator twisted?

If they are too big to twist, how about using two pairs of smaller wires?

Is the faraday cage made from steel or aluminum?

Joe

_________________
Joe Gores

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Thu Oct 01, 2015 12:36 pm Post subject: Re: Rotax 912 Noisy Regulator

OK Bob,

     You got me of my sorry, no good, lazy butt and checking ground loops. Starting at the inside firewall ground tabs I found the following loops:



1) 0 Ohms: Com ground (Normally attached to tabs) -> IC-200 radio neg. -> (Not sure of this link) -> IC-200 chassis body -> com antenna braid -> airframe at com antenna -> firewall -> tabs.

2) 1800 Ohms: Transponder ground (Normally attached to tabs) -> Transponder neg. -> Transponder case -> carbon fiber panel -> (Not sure of this link) -> airframe -> firewall -> tabs.

3) 1800 Ohms: Engine Information System (EIS) ground (Normally attached to tabs)-> EIS neg. -> EIS case -> carbon fiber panel -> (Not sure of this link) -> airframe -> firewall -> tabs.

4) 0 Ohms: Intercom ground (Normally attached to tabs)-> panel tabs -> (Not sure of this link) -> IC-200 chassis -> com antenna braid -> airframe at com antenna -> firewall -> tabs.



I think I can isolate the transponder from the carbon panel, if it matters to com noise. Clearly I have two whopper ground loops in the com system which I'm not sure how to rectify, since the com antenna braid is grounded both to the com chassis and the airframe. The one wiring variation from your design was that for some reason I carried the com ground back to the firewall forest of tabs instead of grounding it at the panel tabs. I'll fix that. However I think I'll still have the ground loop through the antenna shield. (I'll check continuity between the antenna braid and IC-200 ground tomorrow.) Any suggestions regarding that loop?



Thanks.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Thu Oct 01, 2015 1:52 pm Post subject: Re: Rotax 912 Noisy Regulator

OK I went out and confirmed that the IC-200 com antenna ground is connected to the radio chassis and on to the power ground. Therefore in order to avoid a ground loop I've got to break either the antenna ground or the power ground. (Right now the antenna braid is attached to ground at the radio chassis and the airframe at the antenna. It's attached at the antenna presumably to make the ground plane on my rag and tube aircraft.)



Not sure how to avoid a ground loop here.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Tue Oct 06, 2015 7:44 pm Post subject: Re: Rotax 912 Noisy Regulator

Score another one for Bob. Cleaned up three of the ground loops, including the intercom and radio and voila, the audio noise is gone and my music is no longer muted. Amazing. (Not really.)



Thanks Bob.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

jwd3ca(at)gmail.com
Guest

Posted: Wed Oct 07, 2015 6:59 am Post subject: Rotax 912 Noisy Regulator

Hi Guy... just out of curiosity, can you explain how you test for ground loops? Using an ohm meter, apparently, but hoe exactly? Thanks!

On 6 October 2015 at 23:44, Guy Buchanan <gebuchanan(at)cox.net (gebuchanan(at)cox.net)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "Guy Buchanan" <gebuchanan(at)cox.net (gebuchanan(at)cox.net)>

 

 Score another one for Bob. Cleaned up three of the ground loops, including the intercom and radio and voila, the audio noise is gone and my music is no longer muted. Amazing. (Not really.)

 

 Thanks Bob.

 

 --------

 Guy Buchanan

 K-IV 1200 / 912Uls / Warp / 500 hours and flying again.

 Now a glider pilot too.

 

 

 

 

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-- 

Regards,  J.

-----------------------------

J. Davis,   



- Zenith STOL CH750 C-FJNJ: Jab 3300, Whirlwind GA prop, Bing

- Sonex #325 (ex)C-FJNJ, Jab 3300a, Prince P-Tip, Aerocarb

- former C-IGGY CH701 owner/builder

- see these and more at 'www dot cleco dot ca' web page



 

  [quote][b]

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Wed Oct 07, 2015 8:11 am Post subject: Re: Rotax 912 Noisy Regulator

I have the ground tab forest on my inside firewall. I wired the aircraft so that theoretically if you pull the ground wire from its tab, there should be no continuity between the wire and the firewall. (Nothing is grounded to the airframe.) If there is, then I've got another path to ground, and therefore a ground loop. (Two separate paths connected at one point, the tabs, make a loop.) I don't know what you do if you're using the airframe to ground stuff, since there's no way to isolate the ground. However if the item you're grounding is attached right to the airframe, making the ground, I suppose there's no way to have a "loop", since the entire airframe is energized. If you run a wire from the item to the airframe then you could feasibly make a small ground loop.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 12, 2015 5:00 am Post subject: Rotax 912 Noisy Regulator

At 09:57 AM 10/7/2015, you wrote:

  	  Quote: 	
		  Hi Guy... just out of curiosity, can you explain how you test for ground loops? Using an ohm meter, apparently, but hoe exactly? Thanks! 	




   A 'ground loop' is said to exist when a potential

   antagonist (most often an alternator, motor or 

   sometimes a strobe) shares a ground path with a

   potential victim (most often an audio system or

   some instrument that responds to millivolt level

   signals).



   Hence, the victim's performance is compromised

   by the DC/AC components of the antagonist's

   functionality. Ground loops are avoided with

   judicious attention to architecture where failure

   to 'avoid by design' cannot be readily detected

   except for the victim's mis-behaviors.



   I'm not sure how any sort of instrument or 

   other measuring process would be useful in

   detecting/analyzing a ground loop.



 

 

   Bob . . .    [quote][b]

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