Alternator Noise Revisited

[breister]

I've read the old threads, and think I have a diagnosis but want to confirm my expected cure.

I have alternator noise (varies with engine speed and only occurs when alternator is switched on) which is annoying on some radio freqs (some freqs will break squelch just from the noise; on others I hear it "overlayed" on other's transmissions). Intercom alone does not have the noise, only perceivable when receiving on radio (may be in outbound, too, but I can't hear that).

Alternator = Van's 60 amp internally regulated, purchased last year.
Battery located a long way from the alternator, on the other side of Avionics bus

Suspected solution: Install a honkin' big capacitor between alternator B-lead and Ground, as close to the alternator as possible.

Questions:
- How much difference does it make moving the capacitor closer to the alternator (e.g. is mounted on the firewall behind the engine just as good as glued to the alternator)?
- Is there such a thing as "too big" for the capacitor (e.g. someone suggested a couple of hundred thousand microfarads, but for $25 I can get a 1 farad (1,000,000 microfarad) capacitor meant for huge stereos and already having really nice attachment terminals and mounting bracket)?
- If this DOESN'T fix the problem and I have already spent an excruciating amount of time tracing ground runs, what to try next (e.g. is the Van's alternator a particularly bad generator of noise, and would upgrading to an externally regulated alternator have any effect on this)?

Thanks,

Bill

[L.Adamson]

I have the Van's 60 amp internally regulated alternator. I've used ground wiring just about everywhere, that ends up back at the firewall. Only the navigation lights use the airframe (wing) as a grounding source; but the wing is also attached to a ground wire. All wires that require a shield have them.

The bottom line --------------no noise, what so ever. And the new audio panel even takes care of the squelch duties automatically.

L.Adamson -- RV6A

[breister]

lol - lucky you, but that doesn't answer my questions!

[glider]

Before you start spending time and money, make sure the alternator/regulator isn't dead. Hook up an oscilloscope and take a look at the output, there is always some ripple but if you are missing an entire 'peak' then your alternator/regulator is busted.

We found a screwdriver tip in our alternator!!
(I was the only one complaining about whine though..)

http://www.bcae1.com/charging.htm

[L.Adamson]

Originally Posted by breister

lol - lucky you, but that doesn't answer my questions!

Sure it did. This one...

(e.g. is the Van's alternator a particularly bad generator of noise, and would upgrading to an externally regulated alternator have any effect on this)?

L.Adamson --- RV6A

[breister]

Originally Posted by L.Adamson

Sure it did. This one...

(e.g. is the Van's alternator a particularly bad generator of noise, and would upgrading to an externally regulated alternator have any effect on this)?

L.Adamson --- RV6A

Fair enough - yours doesn't cause you a problem.

Mine still does. I'm pretty sure it doesn't have a broken regulator because it is brand new (and another logical question is, do alternators "break in" over time?).

This weekend I'll try the "big honkin filter" approach and report back...

[az_gila]

Originally Posted by breister

.....
Suspected solution: Install a honkin' big capacitor between alternator B-lead and Ground, as close to the alternator as possible.

Questions:
- How much difference does it make moving the capacitor closer to the alternator (e.g. is mounted on the firewall behind the engine just as good as glued to the alternator)?
- Is there such a thing as "too big" for the capacitor (e.g. someone suggested a couple of hundred thousand microfarads, but for $25 I can get a 1 farad (1,000,000 microfarad) capacitor meant for huge stereos and already having really nice attachment terminals and mounting bracket)?
- If this DOESN'T fix the problem and I have already spent an excruciating amount of time tracing ground runs, what to try next (e.g. is the Van's alternator a particularly bad generator of noise, and would upgrading to an externally regulated alternator have any effect on this)?

Thanks,

Bill

...bypass a large capacitor.... try something like a 0.1 uF ceramic and a 10 uF small electrolytic in parallel (an admitted SWAG at values).

The big honking capacitor will prevent possible short term drops (spikes) in voltage when the load changes, but won't remove high frequncy stuff.

Note that the AK 950-FTR1 filter is 6,800 uF and is advertised to "smooth out low frequency ripple"

http://www.chiefaircraft.com/airsec/...FIFilters.html

..and the LON LS03-01004 appears to be 15 uF...

Try the 2 capacitors - use a conservative voltage rating - at least 50 volts and even 100 volts - and see what that does to your noise. It's a cheap experiment...

NOTE uF = microFarad

UPDATE - Interesting Sacramento Sky Ranch article here... agrees with my guesses above...

http://www.sacskyranch.com/altnoise.htm

[dilamipo]

Originally Posted by az_gila

...bypass a large capacitor.... try something like a 0.1 uF ceramic and a 10 uF small electrolytic in parallel (an admitted SWAG at values).

The big honking capacitor will prevent possible short term drops (spikes) in voltage when the load changes, but won't remove high frequncy stuff.

Note that the AK 950-FTR1 filter is 6,800 uF and is advertised to "smooth out low frequency ripple"

http://www.chiefaircraft.com/airsec/...FIFilters.html

..and the LON LS03-01004 appears to be 15 uF...

Try the 2 capacitors - use a conservative voltage rating - at least 50 volts and even 100 volts - and see what that does to your noise. It's a cheap experiment...

NOTE uF = microFarad

UPDATE - Interesting Sacramento Sky Ranch article here... agrees with my guesses above...

http://www.sacskyranch.com/altnoise.htm

Hi az_gila, I have this problem and I like to know how I have to install those capacitors on my alternator. My alternator is the Van's one with 60 amps.
I have all the units grounded to the battery directly, but when I put on the alt field I have whine in my headset.

thank you

[RV10inOz]

Have you got an ipod connector into your audio system? These are great alternator noise antenna and don't ask me how I found it. It took 50 hours of frustration.

[dilamipo]

Originally Posted by RV10inOz

Have you got an ipod connector into your audio system? These are great alternator noise antenna and don't ask me how I found it. It took 50 hours of frustration.

Thank you David for your help, yes I have an cable for the ipod, but it's shield to ground and the ipod it's not connected.