Alternator whine.

[a64pilot]

I’m getting an annoying alternator whine in my amplified VHF speaker at the helm, the whine increases with the volume knob. I just got some ferrite chokes, I assume as the whine increases and decreases with the volume knob that the signal wire is carrying the noise? If it were the power wire then the whine would be constant?
No other system in the boat picks up the whine, so I don’t think suppressing the alternator is the way to go.
The power for the amplified speaker is connected to the same CB that the radio is powered from.
Asking what I should put the bead on, the power or the signal wire, I could just shotgun them both, but would rather understand the source of the problem.

[Sparx]

So the remote speaker whines, but not the radio speaker, correct? And when the engine is off the whine is eliminated?

What happens when the signal wire is disconnected at the radio? I might go looking for a knick or loose connection in the signal wire.

[smac999]

I had this problem on one boat with a vhf with external speaker. Only happened on external speaker. . Ended up just getting an isolated 12v to 12v to power radio

[Brian.D]

You mentioned that the whine increases with volume, but did not indicate if the whine changed in pitch with the engine throttle. That would probably tell you where the source is.

Might very well be between the engine and alternator, in which case you would need an alternator filter. Otherwise, it is being induced through the power line to the amplifier in the speaker.

If we suspect the power line then it is acting like an antenna. You can try the beads (if you have the right mix) to suppress this siginal, or you can try different lengths of power line.

If you are going to use beads, you have to have the correct mix (meaning the correct combination of material in the bead) for the offending frequency. I would also think the bead need to be big enough to wrap the power line around a few turns so as to create an opposing magnetic field.

So source could be engine to alternator and/or power line to amplified speaker.

PS - the reason I mentioned correct mix material for the beads is not all beads are designed to suppress interference. You will have to do some research for which bead for which emi suppression.

[a64pilot]

It’s external speaker only, whine frequency changes with engine RPM, and no whine with engine off, and whine is louder when the alternator is really putting out a lot of power, so later in the day when the batteries are pretty much charged and Solar is making most all of the power the whine isn’t objectionable.
Let the Wife turn on the inverter and use the toaster and the whine gets loud, so it definitely the alternator, plus I’ve heard this noise pretty often in aircraft, so it’s a familiar sound.
Aircraft you often out a capacitor or noise filter on the alternator itself.

I have a box of generic chokes from Amazon, 20 for $10 and different sizes, no idea of frequency they are made for.

[Bycrick]

If one really has alternator whine, it’s almost always the fault of the equipment, not the fault of the alternator. The alternator itself outputs 3-phase AC at a frequency determined by how many coils and poles it was built with and it’s rotation rate. The diodes in the alternator will turn this AC into DC, but you’ll find that this DC has a superimposed AC ripple of several volts. You can measure this ripple by putting an AC voltmeter on the output of the alternator. The battery that is being charged will tend, depending on its charging state, to suppress some of the ripple, but maybe not all of it.

If the offending device, ie speaker or radio, expects the input to be pure DC, and has inadequate filtering on its DC input, you’ll often get ripple coupled through to the speaker. The audio amplifier ICs used in speakers and radios often will pass ripple on the DC supply voltage right through to the output.

Ferrite beads usually have no effect on alternator whine because it’s too low a frequency, ie a few hundred hertz. A good inductance/capacitor filter can solve the problem but they’re often more expensive than the equipment you’re trying to quiet down. Or a good regulated DC-DC supply will solve the problem, but with the same relatively high cost factor.

[a64pilot]

I’ve put these on aircraft to reduce the whine
https://www.aircraftspruce.com/catal...atorfilter.php
If the ferrite beads don’t work, I’ll try the DC to DC convertor, some smaller ones to keep voltage stable are available at a decent price

[Wotname]

a64pilot, you have received a very good analysis of the source of the whine from Bycrick (below). I don't completely agree with his first sentence but that is probably due to our different backgrounds.

Certainly low grade (i.e. poor design) consumer electronics are sensitive to small levels of AC ripple from the alternator.

The audio whine you get on GA aircraft is mostly due to leaky diodes in the alternator causing high levels of AC ripple. In these cases, the proper fix is to repair the alternator (i.e. replace the diode pack) but some opt for a filter. A filter however is always a temporary fix as the alternator will be on it's way out! By the time you hear the whine in the aircraft audio system, you can be sure the AC ripple will be large - aircraft audio system design goes to a lot of trouble to ensure low levels of alternator ripple do not cause problems.

Low cost consumer electronics - not so much!

As Bycrick states, you know the frequency of the ripple as you can hear it. It will be somewhere between say 300Hz to 4,000Hz.

The best place to remove any interference is at the source so any filtering should be done near the alternator.

AC filters should consist of parallel capacitance and series inductance. Best is both! However series inductance on an alternator is hard to achieve cheaply so many opt first for a parallel capacitor mounted on the alternator connected to the B+ post with the case of the cap grounded on the alternator frame.

Originally Posted by Bycrick

If one really has alternator whine, it’s almost always the fault of the equipment, not the fault of the alternator. The alternator itself outputs 3-phase AC at a frequency determined by how many coils and poles it was built with and it’s rotation rate. The diodes in the alternator will turn this AC into DC, but you’ll find that this DC has a superimposed AC ripple of several volts. You can measure this ripple by putting an AC voltmeter on the output of the alternator. The battery that is being charged will tend, depending on its charging state, to suppress some of the ripple, but maybe not all of it.

If the offending device, ie speaker or radio, expects the input to be pure DC, and has inadequate filtering on its DC input, you’ll often get ripple coupled through to the speaker. The audio amplifier ICs used in speakers and radios often will pass ripple on the DC supply voltage right through to the output.

Ferrite beads usually have no effect on alternator whine because it’s too low a frequency, ie a few hundred hertz. A good inductance/capacitor filter can solve the problem but they’re often more expensive than the equipment you’re trying to quiet down. Or a good regulated DC-DC supply will solve the problem, but with the same relatively high cost factor.

[Wotname]

Further to the AC ripple of GA aircraft.

Pilots would report annoying audio whine and the A&P guys would say see the Avionics guys. Owner would take the alternator to the lowest cost shop who would do a quick check (DC only) and say it was OK and sell them a filter. Fast forward a couple of hundred hours and the problem returns.

Finally they would come to us (we were the highest cost avionics shop on the field).

We really did't need to check anything, simply replace the diode pack, re-certify, remove the filter and all was sweet. The reason we would remove the filter was it was no longer needed and was just another potential failure point.

Back to your external speaker problem. Probably best (and cheapest) to insert a series inductor in the positive wire and put a 1uF cap across the +ve and -ve power wires. Note the ferrite beads simply add series inductance into the wire they are on but they may not be suitable value. If you have them already, try them - it can't hurt!

[smac999]

the AC ripple of the alt is filtered by the battery.

I had a vhf whine problem on one boat years ago. load tested the battery and it was bad. new battery whine went away.

[Wotname]

Originally Posted by smac999

the AC ripple of the alt is filtered by the battery.

I had a vhf whine problem on one boat years ago. load tested the battery and it was bad. new battery whine went away.

Yes this is true - until it isn't .

The battery does act as a parallel capacitance but it can only do so much and ageing battery will exacerbate any medium to high levels of imposed AC volts.

[Compass790]

Thanks Wottie, you have given me an easy way to check alternator diodes without removing & stripping alternator.

[Bycrick]

Wotname was correct to question my first sentence, written in haste. It was way to simple.

All alternators produce some ripple. I found a number of articles saying that the acceptable ripple was anywhere between 50mv to several volts.

My point was that properly designed equipment for use on an alternator-charged battery system should be designed to filter out AC ripple on the DC power input. So when you have a piece of equipment on a properly functioning alternator system that has whine, it’s almost always the equipment.

Using an oscilloscope on the alternator output is a great way to check diodes.

[Compass790]

Originally Posted by Bycrick

Wotname was correct to question my first sentence, written in haste. It was way to simple.

All alternators produce some ripple. I found a number of articles saying that the acceptable ripple was anywhere between 50mv to several volts.

My point was that properly designed equipment for use on an alternator-charged battery system should be designed to filter out AC ripple on the DC power input. So when you have a piece of equipment on a properly functioning alternator system that has whine, it’s almost always the equipment.

Using an oscilloscope on the alternator output is a great way to check diodes.

Sadly I don't have an oscilloscope to check the diodes & don't know how to drive one. I could listen for the alternator whine on the vhf or am radio but our single banger Yammer is rather noisy. I can't have a conversation on the vhf whilst its running.
Can you or anyone else in the hive suggest any other tests for diode health I can do with a DMM without getting the diode bridge out?

[wsmurdoch]

"12V Doctor's Alternator Book" -- get the .pdf online. Page 79 then 84 and following for checking diodes with a VOM. But, you'll have to do some disassembly, maybe not removing the diode assemblies if you can get to them through the ventilation holes.