Today's Message Index:
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1. 01:16 PM - Re: Rotax 912 Noisy Regulator (Robert L. Nuckolls, III)
2. 03:44 PM - Re: Rotax 912 Noisy Regulator (Guy Buchanan)
3. 07:53 PM - Re: Rotax 912 Noisy Regulator (user9253)
Message 1
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| Subject: | Re: Rotax 912 Noisy Regulator |
At 06:49 PM 9/29/2015, you wrote:
>
>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 . . .
Message 2
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| 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
K-IV 1200 / 912Uls / Warp / 500 hours and flying again.
Now a glider pilot too.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=447572#447572
Message 3
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| Subject: | Re: Rotax 912 Noisy Regulator |
> 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
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=447574#447574
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