Piper Aztec - Alternator Conversion

Is there a real need for the switch? The gennies have worked for 45
years... They are reliable... They don't go overvoltage and fry your
radios like an alternator can... Yes, they make less volts/current at
idle and low rpm, but you don't have to have everything turned on until
you roll onto the runway for take off... I have gennies still on Fat
Albert the Apache (1957) and looked hard at the alternator issue and
decided I was well off as is...

cheers ... denny

Denny,

It's not that I particularly wanted to rid of the generators, just that
the existing maintenance company cant get them to work properly!! They
dont have a vested interest as i'm taking the a/c to another mtce
organisation.

The new mtce guy is like you and doesnt think I should be so quick to
dump them, but to troubleshoot the problems on the right generator
first.

Dean

Denny wrote:
Is there a real need for the switch? The gennies have worked for 45
years... They are reliable... They don't go overvoltage and fry your
radios like an alternator can... Yes, they make less volts/current at
idle and low rpm, but you don't have to have everything turned on until
you roll onto the runway for take off... I have gennies still on Fat
Albert the Apache (1957) and looked hard at the alternator issue and
decided I was well off as is...

cheers ... denny

OK Dean, well that's just my opinion... Nothing wrong with either
alternators or gennies, just different methods to convert AC to DC....
Changing the system over to alternators is going to be expensive, and I
personally would do it only if the generators and regulators were
totally shot and needed to be replaced, then I would consider spending
the money for switching... I have to say that all the chargingn
failures I have had in flight over the past 4 decades have been the
alternators... I recognize that is just happenstance... But,
generators tend to give you lots of warning that they are hurting and I
have been lucky enough to recognize the cry for help before failure...
Not so with the alternator failures... Having said that, the RV7 I am
building will have dual alternators...
My suggestion is for you to spend the money for Bob Nucholl's book...
You will be a bunch more aware of the pitfalls of charging systems
after reading it (emminently readable and not loaded down with calculus
equations, etc)... He likes alternators, BTW...

Now, someone made a comment that one generator puts out more than the
other... Let me comment that for the generators to have automatic
selection, one has to have the regulator voltage set higher than the
other, otherwise the selector relay will `hunt'.... As a result of the
higher voltage set point that one will usually show more charging
current than the other when tested separately... I have found that
during local flights, turning off the gennie that always takes the load
(port engine on mine) and allowing the other to work, keeps the
starboard commutator healthy and ready to go if the port gennie does
shut down for real... Also, forget the current meter - it's close to
worthless... What you want is a voltage meter... On my plane the port
engine regulator is adjusted to 14.1 volts and the starboard to 13.8
volts... I don't have problems with the selector relay hunting and the
system works fine...

cheers ... denny

: shut down for real... Also, forget the current meter - it's close to
: worthless... What you want is a voltage meter... On my plane the port
: engine regulator is adjusted to 14.1 volts and the starboard to 13.8
: volts...

Not sure if you're talking of an ammeter or a loadmeter. What one really
needs to know the health of the system is *both* a voltmeter and loadmeter. If I
could only have one or the other, however, I'd agree that a voltmeter is more useful.
Anything under 13 and the alternator is maxing out (for a given RPM). Anything
under 12.5 and the battery is discharging. Anything over 14.4-ish and the battery is
boiling.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

writes:

: shut down for real... Also, forget the current meter - it's close to
: worthless... What you want is a voltage meter... On my plane the port
: engine regulator is adjusted to 14.1 volts and the starboard to 13.8
: volts...

Not sure if you're talking of an ammeter or a loadmeter. What one really
needs to know the health of the system is *both* a voltmeter and loadmeter. If I
could only have one or the other, however, I'd agree that a voltmeter is more useful.
Anything under 13 and the alternator is maxing out (for a given RPM). Anything
under 12.5 and the battery is discharging. Anything over 14.4-ish and the battery is
boiling.


But with dual generators/alternators; voltmeters alone will do you
little good diagnosing problems. You will need an ammeter on each
source, and a bus voltmeter. Someone should make a panel display
with LED's for all three, and a small digital meter that will cycle
between them.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Someone should make a panel display
with LED's for all three, and a small digital meter that will cycle
between them.
************************************************** ***************
Well, that would be a nice gadget, but I do take exception with the
need for an amp meter in flight... All the amp meter tells me is which
is higher in voltage, and therefore pushing the current at that
instant, the battery or the charger - it does not tell me what the
state of the charge is... The battery can be at 11.8 volts and the
alternator on it's last living diode at 12.0 volts, and you will not
show a big discharge on the amp meter, but you are in for deep doo doo,
very soon... Give me a good volt meter any day...
Luckily, aircraft share the 12 volts with autos, and any auto store
will have an expanded scale DC voltmeter that you can plug into the
cigarette lighter... Have one of those in the plane and you can
quickly verify that the alternator is doing the job or not... None of
this waiting for the amp meter to go into discharge to tell you are in
trouble - which is way too late - the volt meter will warn you of
impending problems long before the battery goes toes up...

I have used the voltage reading in the GPS295 as my generator testor
for years now... Unfortunately, Garmin did not include that feature on
the 296 on my yoke, and now on run up I have to lean over and look at
the copilot yoke to check the gennies... There I am, leaning way over
to the right, one hand down on the floor flipping generator switches,
one eye on the tach, one eye on the GPS295, and if my passenger is
young and female, my head between her boobs... Life is tough I gotta
tell ya...

cheers ... denny

"Denny" writes:


Someone should make a panel display
with LED's for all three, and a small digital meter that will cycle
between them.
************************************************* ****************

Well, that would be a nice gadget, but I do take exception with the
need for an amp meter in flight

But it WILL tell you that both {*}ators are working; not just one.
Or than one is doing 90% of the work, and the other 10%, etc.

(You can force the issue, to be sure. On the ramp; load the system
-- all lamps, electric heat props, whatever. Run up #1 and see what
happens. Throttle back and repeat w/#2. You don't need matched
regulators to see that both sides charge -- but in flight, I'd rather
have..

alternator on it's last living diode at 12.0 volts, and you will not
show a big discharge on the amp meter, but you are in for deep doo doo,
very soon... Give me a good volt meter any day...

On a twin; I'd want two single-ended ammeters, one on each {*}ator.
Not the zero center kind that tells you NET gain/loss the battery.
Then a good voltmeter on the bus/battery.

As for bad diodes; I trust my ears. But ammeters will tell you.

Luckily, aircraft share the 12 volts with autos, and any auto store
will have an expanded scale DC voltmeter that you can plug into the
cigarette lighter... Have one of those in the plane and you can
quickly verify that the alternator is doing the job or not... None of

With this proviso... that kind of crap [engineering term of art] is
notoriously uncalibrated.
http://www.its.bldrdoc.gov/fs-1037/dir-001/_0125.htm But so what?
You just want REPEATABILITY. Borrow a DVM and calibrate it with your
car, if nothing else. Mark the face at oh say 14v, 12v and maybe 15.

Then gather experience as you fly.

Note, BTW, that even a cheapo DVM typically offers good accuracy;
all the magic is the chipset and oscillator. Buy one.

this waiting for the amp meter to go into discharge to tell you are in
trouble - which is way too late - the volt meter will warn you of
impending problems long before the battery goes toes up...

Maybe....BUT one side could be all but dead and the other
coping just fine...until...



--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

They are reliable...

They are less reliable than alternators. Alternators have solid
commutators; generators have segmented ones - that's how a generator
makes DC. No diodes. Those segmented commutators cause arcing, and
that tends to foul them, get crap between the segments, etc. No big
deal to polish, but not fun either. This goes double if a bit of oil
that leaked from somewhere gets in there.

They don't go overvoltage and fry your radios like an alternator can...

Not true. Your generator can indeed go overvoltage. All it takes is a
failure in the overvoltage cutout on the regulator, or a field short to
ground. If the latter, the field switch will not be able to take the
generator offline. In fact, NOTHING will take it offline short of
pulling the breaker.

On top of that, even pulling the breaker is not a solution when you're
dealing with paralelled generators (and you are). That paralelling
relay system was developed for tractors (so there would not be a need
to built a very few expensive custom oversize generators) not airplanes
(with redundancy in mind). The failure I described (field short to
ground) is one that will take down the entire systems (as the
paralelling relay attempts to balance loads) and really hurts the
redundancy aspects.

Yes, they make less volts/current at
idle and low rpm, but you don't have to have everything turned on until
you roll onto the runway for take off...

Personally, I like to have all my avionics tunred on and set up when
launching into IMC, but that's just me.

In any case - I used to have all sorts of problems with my generator
system, to the point where I kept a spare generator on the shelf. Then
I replaced the 1930's-design vibrating point voltage regulators with a
Zeftronics set ($500 or so for the pair) and all the problems went
away, just like that. On top of that, the system is truly redundant
now - the regulators talk to each other and balance the laod based on
current, not voltage. If one is offline, it can't take down the other.

I suggest that as the real fix - I've had experience with the InterAv
conversion as well (friend had it on his PA-30) and was NOT impressed.
It too is a non-redundant system (master contactor failure takes down
the whole thing). The ideal soluteion would have been a truly
redundant alternator system. I understand Zeftronics was working on
that a couple of years ago - maybe they have it available now. I've
certainly been way more impressed by their stuff than anything InterAv
ever did.

Michael

Then
I replaced the 1930's-design vibrating point voltage regulators with a
Zeftronics set ($500 or so for the pair) and all the problems went
away, just like that. On top of that, the system is truly redundant
now - the regulators talk to each other and balance the laod based on
current, not voltage. If one is offline, it can't take down the other.


Michael,
Could you elaborate more on the Zeftronics system and it's components? I
believe that the regulators on our Aztec need adjustment as our left
alternator has a larger draw on it than the right. I've been told that
adjusting them isn't particularly fun and would be interested in the
Zeftronics system should we find adjusting the regulators does not solve our
output imbalance.
Thanks as always,
Jim Burns

Jim Burns wrote:
Could you elaborate more on the Zeftronics system and it's components? I
believe that the regulators on our Aztec need adjustment as our left
alternator has a larger draw on it than the right.

Unfortunately, I know nothing about their alternator system - only the
generator system.

I've been told that
adjusting them isn't particularly fun and would be interested in the
Zeftronics system should we find adjusting the regulators does not solve our
output imbalance.

I'm familiar with the process. I've never seen anyone get it right
except by luck. The mechanical regulators don't act the same with the
caps on as they do with the caps off.

Michael