Piper Aztec - Alternator Conversion

: 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

As for bad diodes; I trust my ears....

What do you mean by this? That you hear something distinctive when a
diode goes out? Do you hear it directly, or is it through your headset
or audio system? What does it sound like?
--
Thanks!
John Clonts
Temple, Texas
N7NZ

"John Clonts" writes:

As for bad diodes; I trust my ears....

What do you mean by this? That you hear something distinctive when a
diode goes out? Do you hear it directly, or is it through your headset
or audio system? What does it sound like?

With all six diodes intact, the rectified DC from the 3-phase AC
waveform is reasonably low-ripple. Lose a diode and that takes a
chunk out. On a car, you can hear the whineeeeeee change pitch in
the radio, esp. AM, as you go through the gears.

See http://www.allaboutcircuits.com/vol_3/chpt_3/4.html and look at
the "3-phase full wave bridge rectifier" and the waveform below. Now,
take away the blue and see what it looks like....

But as a pilot, you are far smarter than Fred Freeway. You can
usually tell a bad diode without listening, just by the ammeter
readings. Not directly, but rather from knowing your aircraft.

Make some tests: run landing lights before approach, and at X rpm,
you see Y amps. Make a note. And so forth...If one day, it makes
about 30% less current than it normally does, in similar circumstances
[i.e. climb-out from your home field, at X rpm, for n minutes..];
be suspicious....

One confort: You'd think that losing one diode would increase the
strain on the other 2 and THEY'd soon fail as well. But I've seen
'whiners' that lasted for months. I guess the diodes are usually
NOT the weakest link; the ones that fail are not from overheating
but other causes [bad bonds, vibration, etc.]




--
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

Just a final comment to repeat my recommendation that every airplane
owner have a copy of Robert Nuckolls book THE AERO ELECTRIC CONNECTION
($33 and worth ten times that in what it will save you in mechanics
fees by identifying problems before they are problems)

http://www.aeroelectric.com/Catalog/AECcatalog.html

and scroll down...

It is aimed at the homebuilders, but tons of information any airplane
owner can use...

Denny

73 de k8do