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brian-1927(at)lloyd.com
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 Posted: Tue Dec 25, 2007 10:04 am Post subject: Alternator vs. Generator |
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Mark and I usually end up on the same side of an argument. I was a
bit surprised at his comment but I think that we are probably still
pretty much on the same side of this discussion too.
First, let me say that there is nothing wrong with a generator. They
have real advantages in some situations. Turbine engines often use a
generator because you can also use it as a starter to spin up the gas-
generator section.
A generator can be made much more reliable by replacing the
electromechanical (carbon pile or vibrator plus several relays)
regulator with a solid-state regulator. Zefftronics used to make them
for aircraft (PMA'd for spam cans) but I am having trouble finding
them now. Jimco makes them for older automobiles and tractors. See:
http://www.jimcotest.com/ji-gvr01.htm. These would be satisfactory in
an experimental aircraft.
But generators are more complex than alternators and require an
additional circuitry to prevent them from becoming electrical motors
and to prevent them from burning themselves up under heavy load.
Since the generator uses a rotating mechanical switch (the
commutator) to convert the AC into DC, you have additional
maintenance on brushes. The arcing at the commutator emits radio
frequency (RF) noise thus requiring some sort of filter on the output
of the generator to allow the radios to work properly. Also, the
field of a generator must be "flashed" (a high-current passed through
it) to ensure it has some residual magnetism to "kick-start" the
generator when the engine begins to turn. This is not an issue with
an alternator. The control circuitry for an alternator is just much
simpler. (Note: the wiring for a generator and an alternator is
pretty much the same.)
So an alternator is just flat-out a simpler device. Simple means
fewer things to go wrong and therefore better reliability.
Now to the $64 questions: should you replace your generator with an
alternator? Well, if the generator is working properly I would say
no. But when the generator fails I would seriously consider replacing
it with an alternator and pulling about 30 lbs out of the airplane in
the form of generator, filter, regulator, and associated wiring.
Your milage (and opinion) may vary. 
--
Brian Lloyd 3191 Western Drive
brian HYPHEN 1927 AT lloyd DOT com Cameron Park, CA 95682
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
— Antoine de Saint-Exupéry
PGP key ID: 12095C52A32A1B6C
PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
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yakplt(at)yahoo.com
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| Posted: Tue Dec 25, 2007 4:19 pm Post subject: Alternator vs. Generator |
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Everything Brian says is absolutely correct in my experience as well. As I said, we concur on most everything.... which means either we came from the same backgrounds with the same experiences, or... we might actually know what we're talking about ..... for me, that is true every once in awhile. With Brian, ... let's just say I would be very wary to engage in any argument with him over technical matters!
The reason my comments surprised him was simply because I was not clear and to the point. An alternator system is clearly the way to go. Otherwise you'd still be seeing generators on modern automobiles. Alternators are more simple and have much higher reliability. Period. They are lighter and easier to troubleshoot. If your generator goes bad in your YAK it makes perfect sense to replace it with an alternator system.
There is just one very minor point. Right now ... with very few exceptions,..... parts abound for the Yak generator systems. The carbon pile regulators fail once every blue moon. I have 4 spares. The generator quits every once in awhile too. I have two spares. The over-voltage unit has never failed to my knowledge. I have two spares. The Combined Device Relay is indeed a problem. It uses one device (the reverse current relay) that is rather unique. The rest of the relays inside of it are replaceable with American made parts. I have one spare. I've spent about $250 for all the above spares. With those parts I believe I can keep my 50 going for quite a long time with the original system. A B&C 45 amp Alternator with regulator goes for about a grand. If you ever make a mistake and manage to fry the alternator, it sells for a cool $750 or so all by itself.
The alternator is better in every way except for one thing. Price. In this one instance anyway. Could you gen up (pun intended) your own system for a much cheaper price? If you are very good... yes indeedy. On the other hand, I went with what I consided the easy way. I bought a bunch of spare parts. Right now, so can most anybody, and that alone was my intended point on keeping the original system intact.
By tfhe way, I called Tom and talked to him about his 50. From what he described, my GUESS (and that is all that it is right now) is that his whole system is actually intact and he may just have a bad battery. Or.... a resistive connection somewhere. Further tests will tell. The reason he was having such a hard time finding what was wrong with his generator system is likely because there was nothing wrong with his generator system.
Mark Bitterlich
Mark Bitterlich
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