Large Capacitor off Alternator

[newhaul]

Originally Posted by a64pilot

You don’t motor in the ICW? Maybe where you are there isn’t much need for motoring, but that’s not true everywhere, in fact I’d say many motor, never been there, but hear it’s often called the motorterranian for example.
Average cruising boat it’s my understanding puts 300 to 500 hours on their motors a year and I doubt that’s all at anchor charging batteries

this is true and a choice of many they could go outside and sail. Remember I am on the left coast ( pacific side ) I think I put about 25 hours on the mains in the average year.
But I do get what you are talking about .

[a64pilot]

The alternator whine was so annoying on my little Cessna that I didn’t need a tach, the frequency of the whine told you RPM. It was so bad that I would turn off the intercom for any distance flying only turning it back on if I needed to talk to tower etc.

I probably ought to put a choke or filter on the power supply of my amplified speaker on the boat, just haven’t bothered.
But it’s got me thinking, anyone have any suggestions?

And on the Cap in the picture, that has me confused. Noise filter caps I’ve seen on alternators didn’t go inline with the field current, they had a single wire that went I believe on the output and the case was grounded?

[a64pilot]

I looked at the picture again, and I’m awfully sure that there is a noise cap on the backside of the alternator as well as the big blue one.

[Wotname]

Originally Posted by a64pilot

The alternator whine was so annoying on my little Cessna that I didn’t need a tach, the frequency of the whine told you RPM. It was so bad that I would turn off the intercom for any distance flying only turning it back on if I needed to talk to tower etc.

I probably ought to put a choke or filter on the power supply of my amplified speaker on the boat, just haven’t bothered.
But it’s got me thinking, anyone have any suggestions?

And on the Cap in the picture, that has me confused. Noise filter caps I’ve seen on alternators didn’t go inline with the field current, they had a single wire that went ai believe on the output and the case was grounded?

Re your Cessna, have the diode pack on the alternator checked, not just a simple DC go/no go check but for the AC ripple on the output. Or better still, just have them replaced.

Most (as in almost all) times alternator whine in your AM radio is an indication the diode pack is "leaky" and not so many alternator shops ever check for the leakage (IME).

Yes, filter caps do go on the output terminal (as does the OP's one) ad yes the case is usually grounded however the DIY cap the OP is using presumably has the other wire grounded. A cap is never in-line with the field current, if so, the alternator would cease working.

[model 10]

Back in the day of voltage regulators with coils and points, they would put a filter on the field terminal at the regulator (sparks etc inside) and another filter at the generator on the + terminal which in a generator is the brush set. Now you see a filter on the field term at the alternator which is the brush set. Brushes are noisy because they arc and spark all the time under load.

[Wotname]

Originally Posted by a64pilot

I looked at the picture again, and I’m awfully sure that there is a noise cap on the backside of the alternator as well as the big blue one.

I agree and I'm guessing the big blue cap was added as an extra or because the original noise cap was no longer working and never removed but maybe someone didn't know what they were doing... - it happens

[a64pilot]

Originally Posted by Wotname

Re your Cessna, have the diode pack on the alternator checked, not just a simple DC go/no go check but for the AC ripple on the output. Or better still, just have them replaced.



Most (as in almost all) times alternator whine in your AM radio is an indication the diode pack is "leaky" and not so many alternator shops ever check for the leakage (IME).



Yes, filter caps do go on the output terminal (as does the OP's one) ad yes the case is usually grounded however the DIY cap the OP is using presumably has the other wire grounded. A cap is never in-line with the field current, if so, the alternator would cease working.

Sure seems like a lot of excess wire if it’s grounded, who knows?

Actually I had a friend replace the radio and transponder etc and the new one is silent, the old one was horribly wired, it was a portable intercom that was wired in permanently. I gave him a new KX-155 with glide slope for doing the work.
Unfortunately I buried that friend last weekend, he was a good guy who became one of my Son’s few friends

[model 10]

[QUOTE=Wotname;2944755]Re your Cessna, have the diode pack on the alternator checked, not just a simple DC go/no go check but for the AC ripple on the output. Or better still, just have them replaced.

Pretty sure he has a generator.

[Wotname]

Originally Posted by Ecos

Back in the day of voltage regulators with coils and points, they would put a filter on the field terminal at the regulator (sparks etc inside) and another filter at the generator on the + terminal which in a generator is the brush set.

Agree

Now you see a filter on the field term at the alternator which is the brush set.

I wouldn't disagree but I have to say I have never seen it done - that clearly doesn't mean it isn't done somewhere sometimes but I suggest it isn't common.
Brushes are noisy because they arc and spark all the time under load.

Alternator brushes have very little sparking many due because they are transferring the current via slip rings and not a via a commutator. Also field current of a alternator is way less than the rotor current of a generator (for similar output).

[Wotname]

[QUOTE=Ecos;2944764]

Originally Posted by Wotname

Re your Cessna, have the diode pack on the alternator checked, not just a simple DC go/no go check but for the AC ripple on the output. Or better still, just have them replaced.

Pretty sure he has a generator.

Maybe he does although he did state it was an alternator so...

[model 10]

Originally Posted by Wotname

Alternator brushes have very little sparking many due because they are transferring the current via slip rings and not a via a commutator. Also field current of a alternator is way less than the rotor current of a generator (for similar output).

Yeah, aircraft are different sometimes but there are filters on the field term. They need all the help they can get with radio noise.

[Wotname]

Originally Posted by a64pilot

Sure seems like a lot of excess wire if it’s grounded, who knows?

Actually I had a friend replace the radio and transponder etc and the new one is silent, the old one was horribly wired, it was a portable intercom that was wired in permanently. I gave him a new KX-155 with glide slope for doing the work.
Unfortunately I buried that friend last weekend, he was a good guy who became one of my Son’s few friends

Sorry to hear of the loss of your friend and it's especially sad for your son - aviation (especially general aviation) is a tough game when it comes to the sudden loss of friends, colleagues and acquaintances

[Wotname]

Originally Posted by Ecos

Yeah, aircraft are different sometimes but there are filters on the field term. They need all the help they can get with radio noise.

Very true - now if they could only transition from AM to FM in the click of a finger , there would no longer be a problem.

Apologies to the OP for the somewhat off-topic discussion - we can return to regular programming shortly

[model 10]

[QUOTE=Wotname;2944769]

Originally Posted by Ecos

Maybe he does although he did state it was an alternator so...

It's just a term you use. You don't say generator whine, that makes no sense. Very few little old Cessna's have an alternator STC, if there even is one.

[maine50]

Back in early 90's with loran I had trouble occasionally pulling in both chains needed for a location. An electronic shop sold me a capacitor connected to the alternator that cured the problem. This was esp true near New London, Ct ( a sub base is there)