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Old 19-01-2019, 13:11   #1
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Trying to locate electrical noise source

I have a perplexing problem that has been driving me crazy - Bad alternator whine (it goes up and down in frequency with engine RPM) present on my fixed-mount VHF, expecially when the batteries are discharged and the alternator is working hard cranking out amps. The whine nearly goes away when the batteries are fully charged. I'm hoping someone can help me track down the source.

My electrical system is complex, which does not help. Charging is via a Ample Power 150A hot wound smalll frame alternator with smart alternator regulator and ample power battery combiner/isolator. I have a house bank of AGM batteries, and a start bank with a single lead-acid battery. I have checked the alternator diodes with a multi-meter, and they tested good. I have not taken the alternator off to a shop yet for formal testing. I do have multi-bank solar on the boat as well, with 750 watts total run through three Victron Smart MPPT units.

The VHF runs through a Vesper antenna combiner to share the antenna with my AIS (XB-8000). I am pretty sure the AIS, Combiner, and VHF are likely not grounded at exactly the same location, but pretty close together on my negative bus (less than 2" apart). If it makes a difference, the VHF is a ICOM IC-M502 with the remote mount microphone. The whine occurs regardless of whether or not the remount mount mic is plugged in.

For grins, I have installed ferrite chokes on all wires in & out of the VHF to no effect.

Any ideas here?
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Old 19-01-2019, 13:16   #2
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Trying to locate electrical noise source

What model VHF radio is it?

Sorry, I seen it is an ICOM.

This problem is usually because the radio power comes not directly from the battery bank but from a bus where the alternator is also connected. Sometimes the alternator is connected to the disconnect switch. Thatís where the whine gets into the DC system.

As an experiment try running a pair of wires directly from the battery bank terminals to the VHF power leads. Put the proper type fuse in the + lead close to the battery. Keep the wires close together the entire run.

If that works then making it permanent will be the best long term solution. Come back and discuss the result of the test first.
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Old 19-01-2019, 13:19   #3
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Re: Trying to locate electrical noise source

Icom IC-M502 with remote CommandMic
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Old 19-01-2019, 15:04   #4
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Re: Trying to locate electrical noise source

Quote:
Originally Posted by Excalibur5 View Post
Icom IC-M502 with remote CommandMic


Sorry, I started typing before reading to the end. These are good radios. I guess the issue is how the DC power gets from batteries to the radio.
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Old 19-01-2019, 15:18   #5
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Re: Trying to locate electrical noise source

You could try putting a bypass capacitor on the output lug of the alternator. Cheap and easy, might help!

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Old 20-01-2019, 10:16   #6
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Re: Trying to locate electrical noise source

Alternator noise is AC ripple running down the alternator cables. The frequency is alternator rpm dependent and the strength of the noise is usually dependant upon how much work the alternator is doing.

Typically the ripple runs down the cables until it is dissipated. However, some ripple will be radiated in the atmosphere and can have an adverse effect upon AM radio and some of the HF bands. Rarely will the atmospheric ripple affect VHF as the frequency is too high and harmonics are much too weak at VHF.

So let's assume you're dealing with ripple running down the power cables. It is probably going into the audio stages of radio and yes it is really irritating. Frequently it will open the squelch adding to the problem

Lots of ham radio guys will mention 'smoothing' using either capacitors or inductors to soak up this ripple. Both work well and many auto stores have the bits needed.

The best smoother of AC ripple is, in fact, your battery bank that acts as a big capacitor. This is one of the reasons why many radio manufacturers suggest a direct connection to your battery. Dan mentioned this in one of the earlier posts but I have fleshed out the logic for you.

Personally, I feel it is also good engineering practice to have the VHF direct to the battery (with fuses) so that in case of emergency failures of other parts of the electrical system won't stop your dsc messages getting out.

If you are still getting noise some recommend putting a big capacitor used to help power the bass systems on car audio systems across the VHF radio power leads. It works put has other issues.
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Old 20-01-2019, 11:51   #7
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Re: Trying to locate electrical noise source

Sounds like it may be mechanical. If you don't have a stethoscope try using a long screwdriver to hear the bearings. Please be careful with entanglement.
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Old 20-01-2019, 13:17   #8
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Re: Trying to locate electrical noise source

Solid grounding is important - a buss bar main DC negative, not everything connected to the engine block and/or stacked up on a battery neg terminal. A high power alternator should preferably have an isolated neg stud and be wired directly to the neg buss. The pos output should have a direct, solid connection to the house bank, connection at the battery side of the main switch is good (observe circuit protection). Persistent noise can usually be filtered out of the power supply at the radio with a choke and capacitor, but these have to be fairly large, ferrites which snap over the wire are ineffective. One place to find a good choke coil would be a car stereo shop - the coils used for a high power subwoofer will do the trick. A proper filter capacitor will also be large, look for a value of 10,000 to 25,000 microfarad, 25 volts or higher. Stereo installers also deal with this issue and one may have filter capacitors as well. Ready made filters are sold but don't have the umph that you can put together yourself. Here's a cheap surplus source:

https://www.surplussales.com/Capacit...-300000uF.html

Choose a 'C' package which has screw terminals. I see a 10K mfd 25V for about 10 bucks. These are much more expensive if sourced from a regular electronics supply. There's a good choke coil on this page, the 680 uH 11 amp for $22, it does require soldering the connections:

https://www.surplussales.com/Inducto...FerMisc-4.html

The 45, 50 or 100 uH chokes on this page are a little small but probably will work, the 680 is overkill.

https://www.surplussales.com/Inducto...FerMisc-3.html

Connect the capacitor in parallel with the power lead (observe marked polarity), and the coil inline with the positive on the side away from the radio. These can be put anywhere in the power line between the main distribution panel and radio. This brute-force filter will block any noise that's getting to equipment via the power supply.
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Old 20-01-2019, 13:31   #9
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Re: Trying to locate electrical noise source

Before tearing things apart:
Check that the VHF antenna coax braid is connected to the VHF.
Do this by running the VHF coax directly to the VHF connector,bypassing the AIS splitter.
Even a loose PL259 connecter can allow elec. interference pickup.
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Old 20-01-2019, 13:47   #10
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Re: Trying to locate electrical noise source

All suggestions to fix this alternator whining in all previous posts are excellent. The cause of alternator whining noise is many times the capacitor inside the alternator that has gone bad. The noise can enter through the positive wire or through the antenna, if not grounded properly, especially on vehicles.
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Old 20-01-2019, 14:18   #11
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Re: Trying to locate electrical noise source

I have dealt with alternator whine hundreds of times over the decades. It is often caused (almost always?) from leaky output diodes in the alternator. The alternator shop will test them and say they are OK but you should insist they are replaced. They are on the way out.

If I had a dollar for every time this worked I would have a very large boat .

While interference can be masked with filters etc as mentioned in above posts, it is always better to remove it at the source rather than patch over it.
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Old 20-01-2019, 14:27   #12
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Re: Trying to locate electrical noise source

Wow these responses were exactly what I hoped for. I'll begin the troubleshooting process on my next trip down to the boat.

I do wonder if I have the bad capacitor or leaky diodes in the alternator. I think I'll take it into the shop to get really well checked out.

I do t think I have any connection issues with my antenna or feed line. VSWR according to my AIS is less than 2:1.
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Old 20-01-2019, 15:10   #13
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Re: Trying to locate electrical noise source

Quote:
Originally Posted by Excalibur5 View Post
Wow these responses were exactly what I hoped for. I'll begin the troubleshooting process on my next trip down to the boat.

I do wonder if I have the bad capacitor or leaky diodes in the alternator. I think I'll take it into the shop to get really well checked out.

......
Be aware that many alternator shops only do a simple DC go/no-go test on the diodes. This method doesn't really check for RF reverse bias leakage. To do that, it needs to be run up under load and the output checked for RF AC ripple, best done with an oscilloscope - or simply replace the diode pack anyway.

Good luck with getting it sorted whatever the fault is.
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Old 20-01-2019, 16:19   #14
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Re: Trying to locate electrical noise source

As a rule it is best to control electrical noise at the source before it is conducted and radiated all over the boat. A good approach is to make sure there is a good ground on the alternator case and also install a good power line interference filter sized for the rated DC current as close to the alternator as possible

A problem with DC applications is that the current saturates the ferrite cores of the filters and they are no longer effective.

A long shot: Take the alternator to a good shop (you will need recommendations for this) and ask them if it is particularly noisy.
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Old 20-01-2019, 16:48   #15
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Re: Trying to locate electrical noise source

Make sure your radio earth is a completely remote earth plate from other equipment on the vessel and is connected only to the radios.

Having checked that no one has linked the radio earth to any other earths or lightning sink grid, for any reason, your next check is to see if the antenna is properly isolated from contact with anything likely to contact, or in contact, with the engine or any of its wiring, either electrically (poor insultors) electrostatically (unscreened alternator or unsuppressed alternator) or electromagnetically--(antenna feed lying in close proximity to alternater input or any outlet battery lead.)

You may also find they you are using a battery to run your radio which is connected to the battery bank being charged.

That should not cause any problem as a rule, but I used a seperate radio and radar, AIS etc battery charged by a separate solar array. This was a safety thing, so that I would always be able to call for help in the event of a battery bank catastrophe when at sea. It may also have explained to some extent why I never noticed any alternatior noise, however faint..

So, because alternators provide DC current, and you are getting noise, perhaps the problem might be a smoothing capacitor has become faulty? I LIKE smoothing capacitors. They take that ripple out of the DC supply to the batteries without harming anything.


That noise you are hearing I suspect comes from the slip ring contacts on the alternator. There should be a spark suppression circuit of some kind across these--so check that also.

Here is a filter system just in case.

https://www.instructables.com/id/Car...se-Eliminator/
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