Avionics: Installed alternator filter

Update 23-Oct-20:  This was a bad idea.  View the last picture in this post.

Update 21-Aug-22:  The filter was moved when I installed a backup alternator.  View that post to learn more.

 

I have a little bit of alternator whine that comes through my headsets.  It's not noticeable in flight, but it is noticeable on recordings of the intercom through my canopy cam.  Interestingly, I do not hear any whine when my LEMO headsets (to which I also added a filter cap last year) are disconnected from ship's power.

So I decided to try an alternator filter (note, they are much cheaper sourced elsewhere).  Nothing special about these.  It's just a capacitor.  It ended up reducing the whine a little, but it didn't eliminate it.

I mounted mine as shown in the following images.

There's a hole on the alternator's metal shield that is just a bit larger than an AN3 bolt.  Adding some washers made it viable.

I could get in there with a 1/4" ignition wrench to work the bolt.

Here it is from a view looking up.

Update 23-Oct-20:  This was a bad idea.  When I went to change the oil 7 months later, I found this.  Turns out that the metal hood that I bolted the filter could not be recruited into the task of holding this relatively heavy filter in the punishing environment of an IO-390.  I'm quite fortunate that the filter didn't completely separate from the airframe and depart the cowl in flight, doing damage to something or injuring someone.  This was a very educative experience and a potent reminder to stay within the bounds of my knowledge:  Don't do something like this that hasn't already been shown to be safe.

Update 21-Aug-22:  The filter was moved when I installed a backup alternator.  View that post to learn more.