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Help debugging an alternator noise problem

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a.s.elliott(at)cox.net
Guest

Posted: Tue Dec 02, 2008 1:17 pm Post subject: Help debugging an alternator noise problem

I submitted this before, but am now including much more information, per  Bob's request.

  

  Problem - I am getting a lot of clearly alternator (or voltage  regulator noise) on the receive side of my radio. There is no noise on only  battery power, or with the alternator disconnect relay unpowered.  The  noise is very low at idle, and increases in both volume and frequency as RPM  increases, At high RPM makes it very difficult to understand  transmissions.  Radio is a Terra 760D fed from the main bus.  I have  checked to be sure that the problem persists even with no other equipment  powered up (not coming somehow from lights or avionics).

  

 System - The system is pretty similar to Z-17, except that I have two  batteries (PC-680) connected through a marine selector switch (A-B-Both-Off) and  no master relay.  

  

 There is a secondary EFIS bus which can be powered through a DC-DC  regulator, but the problem does not depend on whether this bus is powered up or  not.  

  

 In place of the SD-8, I have an 18 amp John Deere permanent magnet  alternator feeding through a 4-wire motorcycle voltage regulator  (Crane Fireball, installation doc here http://tinyurl.com/17a), connected to the main  bus using the B&C relay/overvoltage protection kit as shown in the diagram,  which includes a big filter capacitor.

  

 Bus voltage is fine with the alternator connected (about 14V) and the  charging portion is working OK.  

  

 Questions: 

 [1] Should not the big capacitor be filtering out this noise?  

 [2] Could the capacitor be bad? Can I test it?

 [3] What would happen if I wired the cap backwards?

     (I will check ASAP.)

 [4] Is there other or additional filtering I could put on the

     feed?  If so, what?

 [5] Are there other things I could check/test?

  

 Thanks,

 Andy Elliott, Mesa, AZ

N601GE,601XL/TD,Corvair



  

  

   [quote][b]

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klehman(at)albedo.net
Guest

Posted: Fri Dec 05, 2008 7:15 am Post subject: Help debugging an alternator noise problem

Andy

I don't see a reply to you so I'll add a little incidental info.

I can confirm that the 20 amp nominal single phase (two output wires) 

John Deere permanent magnet alternator should not add noticeable noise 

to your system. I do not use a capacitor and my batteries are smaller 

than yours. I use the John Deere regulator which works fine as long as 

it is not disconnected from the battery while the engine is running. In 

fact mine is hard wired to the battery because it will fail (max 

charging and no regulation) if disconnected with the engine running. I 

don't know if your battery switch could be an issue but it doesn't sound 

likely. My Overvoltage relay is between the alternator and the 

regulator. I do have a small filter on the strobe power supplies. In 

general a large electrolytic capacitor will tend to destroy itself 

visibly if wired backwards. Capacitors can certainly be tested if 

someone has a tester. However if it holds a charge it is probably fine. 

By that I mean if you see a spark when you connect it to a battery and 

it retains voltage after being disconnected for a minute or more. 

Generally it is recommended that a small resister (a few ohms) be put in 

series with a large capacitor to slow the charging or discharging 

(reduce wear and tear) when testing like this although often folks just 

look for the spark to confirm current going in and then again back out 

when the terminals are shorted. Reversing the polarity may make the 

capacitor explode so keep positive terminal to positive battery 

terminal. A large capacitor when charged can provide a momentary large 

current so it is good to discharge them before handling them or 

installing them.



I'm not familiar with your regulator so I'd be suspicious of it unless 

you know others are using it with no problem. My radio is an icom but I 

would not expect yours to be more sensitive to noise.



Ken



Dr. Andrew Elliott wrote:

 	  Quote: 	
		   I submitted this before, but am now including much more information, per 

 Bob's request.

  

 Problem - I am getting a lot of clearly alternator (or voltage regulator 

 noise) on the receive side of my radio. There is no noise on only 

 battery power, or with the alternator disconnect relay unpowered.  The 

 noise is very low at idle, and increases in both volume and frequency as 

 RPM increases, At high RPM makes it very difficult to understand 

 transmissions.  Radio is a Terra 760D fed from the main bus.  I have 

 checked to be sure that the problem persists even with no other 

 equipment powered up (not coming somehow from lights or avionics).

  

 System - The system is pretty similar to Z-17, except that I have two 

 batteries (PC-680) connected through a marine selector switch 

 (A-B-Both-Off) and no master relay. 

  

 There is a secondary EFIS bus which can be powered through a DC-DC 

 regulator, but the problem does not depend on whether this bus is 

 powered up or not. 

  

 In place of the SD-8, I have an 18 amp John Deere permanent magnet 

 alternator feeding through a 4-wire motorcycle voltage regulator (Crane 

 Fireball, installation doc here http://tinyurl.com/17a), connected to 

 the main bus using the B&C relay/overvoltage protection kit as shown in 

 the diagram, which includes a big filter capacitor.

  

 Bus voltage is fine with the alternator connected (about 14V) and the 

 charging portion is working OK. 

  

 Questions:

 [1] Should not the big capacitor be filtering out this noise? 

 [2] Could the capacitor be bad? Can I test it?

 [3] What would happen if I wired the cap backwards?

     (I will check ASAP.)

 [4] Is there other or additional filtering I could put on the

     feed?  If so, what?

 [5] Are there other things I could check/test?

  

 Thanks,

 Andy Elliott, Mesa, AZ

 N601GE,601XL/TD,Corvair

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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