On Sat, Jul 9, 2011 at 7:16 AM, Bill Bradburry <bbradburry@bellsouth.net> wrote:
This is not a big problem since I can not
hear the hum when in flight, but I thought someone might be able to tell me how
to stop it. I have the Renesis and I am using the stock capacitor that is
attached to the engine. When I turn on the alternator, there is a slight
buzzing hum that appears in the headset and the frequency goes up and down with
the engine. It is pretty obviously the alternator I think.
Does anyone have any suggestions?
Bill B
That is a really common and difficult problem. I still have an alternator buzz. I fly a certified Navion that has a buzz worse than mine. Almost all aircraft have it to some extent. Here are some things to look into and try.
Besides the alternator, look into contributing sources. For me, it is an interaction between the alternator and the intercom. Turn off either device, and the buzz goes away. So if I am solo, I can turn off the intercom. For me, the buzz through the intercom is only weakly dependent on intercom volume. So I can turn down the volume on the headsets and up the volume on everything else, and it minimizes the buss.
I also got small improvements from each of the following: Installing an noise choke on the power supply to the intercom. Turn up the music :-) Moving the power supply for the alternator field off the main buss (that included the avionics) into an engine compartment buss near the main alternator power out.
Using shielded wire for the entire run of the alternator field wire. (to the switch and back). But then better than that, I installed a relay near the alternator so that the field power only travels a short distance and the only connection to the alternator switch is the trigger for the relay. That also improved an alternator over-voltage issue.
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