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BigJohn

Well Known Member
Here's a mystery for you who are electronically inclined. You know who you are;) I have recently resumed fighting the alternator whine war. I have identified the whine in the intecom as definitely coming from the alternator. As per Rotax recommendation, Van's included a 22,000 mfd capacitor in the fuse panel in parellel with the power bus to smooth the noisey output from the regulator/rectifier. I reasoned that if extra capacitance (another 22,000mfd cap) was installed right at the regulator output forward of the firewall the noise would be killed before it entered the avionics bay. I checked with Van's tech support and they didn't see any problems with this idea, in fact they asked me to report back results.

So I ordered and installed the extra capacitor, right at the firewall, with nice short leads. Negative side grounded to the firewall mounting bolt. Very proud of myself for the really neat and professional looking installation! Problem is, now there is NO alternator output!:eek: Was aghast thinking I had ruined the regulator or worse, the alternator! Unhooked the new capacitor and operation returned to normal. Phew!

So, can anyone think of why the regulator doesn't like 44,000mfd instead of 22,000mfd across its ouput? I'm stumped. And oh yes, I'd still like to get rid of the whine before I have to listen to it all the way to Oshkosh!

BTW, I called Dean at Lockwood and he has no idea why this would happen either.
 
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Hey BigJohn - -

You did not say if the whine went away with the second capacitor ? ? Did you put a volt meter on the battery direct ? The Dynon may not have shown charging, but it may have actaully been charging. I didn't go back and look, but I'm sure you eliminated the one "extra" wire going to the Reg ? ? ?

John Bender
 
Perhaps the regulator is seeing what it thinks is a "short" on the output and is shutting down. Capacitors can accept a huge inrush current due to their low internal resistance until they are charged. Most electonics that use large filter capacitors have an inrush current limiting circuit to prevent power supply damage due to the large initial current draw.

You might try putting a resistor in series with the cap (perhaps 5 or 10 ohms) and see what happens. The resistor should not affect the ability of the cap to filter the supply but will limit the inrush current.

I would also check all your power/battery/ground connections, the ships battery is one of the best filters there is, a high resistance in this circuit can cause noise on the bus.
 
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BigJohn,
Do you have a picture of the installation?
What regulator terminal did you connect the capacitor to?
What was the engine RPM and system voltage with the capacitor connected?
What symptoms indicated no regulator output?
Does the whine go away when heavy loads such as lights and fuel pump are shut off?
Consider installing the capacitor right at the power input to the intercom. It is possible that a large inrush current could blow the avionics fuse. But I think it is worth a try.
Joe Gores
 
Be very careful when handling that big cap, it can kill you!! I would wire a 1K resistor in parallel to the terminals to discharge it when its not being used as a safety precaution.

Are you sure the polarity is correct?

With it safely discharged check the cap with an ohmmeter, it should have a very high resistance if not reading open.
 
The best way to remove alternator whine from audio electronics is not to just use a simple big honkin' capacitor across the alternator output or across the power feed at the audio device... but rather to use a filter circuit with a choke coil and a reasonable sized capacitor in the power feed to the audio device (radio, intercom, etc). Radio shack used to sell such a 10amp self-contained alternator noise filter for car stereos, for about 16 bucks, but discontinued it a few years ago. You can still find these kinds of filters at most car audio specialty shops, and also Lonestar Aviation makes an FAA-PMA'ed certified unit for big bucks

Here's an example schematic of what's typically inside. Personally, I'd use a higher voltage-rated capacitor myself.:
37182d1338041954-alternator-whine-filter-works-but-what-does-do-filter.jpg


If you want to make a really crude, home-brew filter, here's a tutorial (personally, I'd buy a factory-made choke, not wind my own :D ):
http://www.worldwidedx.com/home-brew/31492-building-simple-alternator-whine-ignition-filter.html
 
rocketbob said:
Be very careful when handling that big cap, it can kill you!! I would wire a 1K resistor in parallel to the terminals to discharge it when its not being used as a safety precaution.
Click to expand...

Come on Bob, lets not be scaring folks now....

Unless you are tightening the terminals holding an all metal screwdriver in your mouth while your sweat covered chest is grounded against the fuselage, the chance of electrocution from 12 volts is probably impossible (even with the above worst case conditions it probably impossible).

People smarter than me have said there has never been any recorded electrocution death attributed to a voltage under 25 Volts (I would have been dead a long time ago).

Sounds like a good one for "Myth Busters" or have a look at THIS report (gotta love the internet).
 
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As usual, thanks to all you guys for lending me your brain power. The problem has been solved, and it wasn't the capacitor's fault! Got to go fly now, more later............
 
OK, here's the scoop.....

In pulling wires in and out of the connector on the rectifier/regulator while trying to isolate the source of the noise, I inadvertently broke the locking tabs off the female spade terminals. So instead of sliding onto the contacts they were butting up against the ends of them. This caused intermittent contact, which led me to draw some incorrect conclusions, such as that the capacitor was causing the regulator to shut down the alternator. When I got the contacts firmly seated operation returned to normal, even with the capacitor installed. And, the noise level is significantly reduced, although not entirely eliminated.

For pictures go here.

Thanks to all for the support. Hope I didn't strain anybody's brain.
 
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