Alternators vs generators

Ken Ibold

Ken Ibold

Final Approach
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Ken Ibold
In looking at early Barons, I see that some of them have generators, and some of the generators have been replaced with alternators. What's the deal here? Why are alternators superior to generators? Is it load capacity, reliability, efficiency?
 
Ken Ibold said:
In looking at early Barons, I see that some of them have generators, and some of the generators have been replaced with alternators. What's the deal here? Why are alternators superior to generators? Is it load capacity, reliability, efficiency?
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Although the author is talking about cars, the general jist of the concept is the same:

http://www.rowand.net/Shop/Tech/AlternatorGeneratorTheory.htm
 
Ken Ibold said:
In looking at early Barons, I see that some of them have generators, and some of the generators have been replaced with alternators. What's the deal here? Why are alternators superior to generators? Is it load capacity, reliability, efficiency?
Click to expand...
Having had a 1960 Chevy with a generator............... I would say reliability. I had that gen rebuilt 3 times in 2 years.

AC output is greater at the same RPM. AC current is more stable.An alternator's output is at a constant rate, regardless of rotational speed, the generator's output is variable, depending on RPM

The Caravans I fly have a Started/Generator. It is one unit that does both. It puts out much more then the standby Alt & I have had only one go bad in 1500 hrs. Maybe they work better now, but I an sure there is a reason that they don't use them in cars since 1960.
 
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Related trivia ... the first G.A. airplane built with an alternator was the Piper Cherokee B 180, which came out at the end of 1962. The alternator itself was a Chrysler product.

-- Pilawt
 
If I remember correctly, one of the benefits of an alternator over a generator (besides reliability) is that an alternator is able to put out a constant voltage at varying RPM. So it is able to keep up with demand, even if the engine is running at a low RPM.
 
Alternators are substantially lighter for the current produced, produce greater current output at lower RPM and are more reliable as the brushes do not carry high amounts of current. They generally produce "cleaner" electricity than a generator because the current produced does not have to pass through a commutator and brushes.

Generators have voltage regulators too, so they should be producing controlled voltage.

All being said, the alternator is a better way to go.
 
The primary operational difference that I see is that a generator requires a higher minimum engine RPM to even GENERATE electricity...unless you're willing to run 1200-1400 rpm, you're discharging your battery until the point where you power up to takeoff into low IMC conditions ;)

Fly safe!

David
 
The conversion to alternators is pretty expensive. You need not only the Alternators, but the two voltage controllers, new breaker for the fields. Try to find an early one in which the conversion has been done. You fly IFR and the power load is quite hefty....and you want it all up and running before you depart into the IMC.
 
All of the above .... but the big one I believe for aircraft operations is weight.

Ken Ibold said:
In looking at early Barons, I see that some of them have generators, and some of the generators have been replaced with alternators. What's the deal here? Why are alternators superior to generators? Is it load capacity, reliability, efficiency?
Click to expand...
 
Pilawt said:
Related trivia ... the first G.A. airplane built with an alternator was the Piper Cherokee B 180, which came out at the end of 1962. The alternator itself was a Chrysler product.

-- Pilawt
Click to expand...
I know of an accident involving electrical failure in which an automotive alternator had been installed.
 
jkaduk said:
I know of an accident involving electrical failure in which an automotive alternator had been installed.
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What airplane and what were the circumstances?

Hey, I just made 500 posts!
 
some generators can run backwards and act as starters though right? so is the weight savings still there when you pull it out and put an alternator and starter in?

oh cool and I am over 1000!
 
Pilawt said:
Related trivia ... the first G.A. airplane built with an alternator was the Piper Cherokee B 180, which came out at the end of 1962. The alternator itself was a Chrysler product.

-- Pilawt
Click to expand...

I am not sure where you got that , My first airplane was a 63 180 cherokee. it had a generator, which *was* a chrysler, when I would get it rebuilt after it would fry about once a year, I would go the local shop that worked on cars and tell thenm it was from a Boat motor, and they would rebuild it.

I looked at replacing it with an Alt but it was a couple of thousand dollars so I never did.

On my Mooney, same thing EXCEPT I did replace the GEN with an Alt, (to make room for the Powerflow exaust in it's future) But the other thing to remember is the Alt weighs less, by a cpl of pounds.
 
my uncles cherokee 140 has a generator which he claims is also a chrysler car generator.
 
Ken Ibold said:
In looking at early Barons, I see that some of them have generators, and some of the generators have been replaced with alternators. What's the deal here? Why are alternators superior to generators? Is it load capacity, reliability, efficiency?
Click to expand...

Ken, my Bonanza had a 50 amp generator when I bought it and I swapped that out for an alternator after the first year. Generators on most aircraft provide no output whatsoever at idle and barely enough to power the radios and beacon below 1200-1500 RPM. At cruise RPM they work fine although alternators are by design a bit more robust since the high (output) current doesn't have to feed though brushes. The bottom line is that if you do much flying at night, there's a good chance that your battery will run down while taxiing across a big airport with the taxi/landing lights on in addition to the radios and beacon. This is probably an even bigger issue on a twin since they usually have too much static thrust at idle let alone 1300-1500 RPM and you'd probably wear out the brakes pretty fast trying to keep the RPMs up while taxiing. OTOH if you do almost all of your flying in the daylight, generators would probably be OK. Conversions run around 1500 per engine including labor IIRC.
 
tonycondon said:
some generators can run backwards and act as starters though right? so is the weight savings still there when you pull it out and put an alternator and starter in?

oh cool and I am over 1000!
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Only on turbines and tractors AFaIK. I've never seen a Continental or Lycoming piston engine with a combination starter/generator.
 
FiftyFour said:
I am not sure where you got that , My first airplane was a 63 180 cherokee. it had a generator, which *was* a chrysler
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"Pilot Report: Cherokee 180" by Richard B. Weeghman, Flying magazine, December 1962, p.92:
"One of the improvements common to all the Model B Cherokees over their predecessors is installation of an alternator in place of a generator."
​
Piper - A Legend Aloft by Edward H. Phillips (1993), p. 84:
"Piper officials claimed the Cherokee B was the first production light plane to use an alternator. The unit was developed for Piper by the Chrysler Corporation, who pioneered the use of alternators in automobiles in the early 1960's."
​
-- Pilawt
 
Ken,

I think the advantages go to the alternator - weight, reliability and generation of power at typical taxi RPMs. One advantage - though an very minor one to the generator is that the battery doesn't have to have a significant amount of stored energy for a generator to recharge it. The other advantage of the generator as Tom points out is that they can be repaired in the field. Of course, with overnight package delivery an alternator can be shipped to a shop where you might be stranded.

bbchien said:
The conversion to alternators is pretty expensive. You need not only the Alternators, but the two voltage controllers, new breaker for the fields.
Click to expand...

If you are looking to go the conversion route you may have to change fly wheels if, as on the Lycoming, the alternator is belt driven. Two reasons, the diameter of the fly wheel is different and the depth of the groove for the drive belt is different.

Len
 
Len Lanetti said:
If you are looking to go the conversion route you may have to change fly wheels if, as on the Lycoming, the alternator is belt driven. Two reasons, the diameter of the fly wheel is different and the depth of the groove for the drive belt is different.
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The 55, A55, and B55 all came from the factory with Continental IO-470s with belt driven generators or alternators. The C-D-E55s have IO-520s and came with gear driven alternators (no generators). B58s originally came with IO-520s (and gear driven alternators) but switched to IO-550s which also have gear driven alternators AFaIK.

And BTW, brushes and diodes can be changed in the field on some if not all alternators but I suspect that bearing failure is at least as common a failure mode as the others and I think you need a rebuilder for that.
 
Pilawt said:
Related trivia ... the first G.A. airplane built with an alternator was the Piper Cherokee B 180, which came out at the end of 1962. The alternator itself was a Chrysler product.

-- Pilawt
Click to expand...

Are you sure that's true? I have a 1965 Cherokee C 180, and I have a generator.
 
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