Charging system failure cuts short a long X-Country

[Ron Lee[_2_]]

I first flew to Memphis to enter the Memphis 100 race. I did it.

Then on to Atlanta to visit family. The next day I flew to Kitty
Hawk. That was uneventful other than flying over water and
turbulence on approach and departure from the 15 knots gusting 25. An
aerial view is here:

http://home.pcisys.net/~ronlee/RV6A/KittyHawk/KittyHawkAirSmall.jpg

This is my aircraft with the memorial in the background:

http://home.pcisys.net/~ronlee/RV6A/KittyHawk/KittyHawkGroundSmall.jpg

I thought they took off from the hill but no. It was flat terrain
north of the hill. The starting point is here:

http://home.pcisys.net/~ronlee/RV6A/KittyHawk/FirstStartSmall.jpg

And the end of the first flight here:

http://home.pcisys.net/~ronlee/RV6A/KittyHawk/FirstEndSmall.jpg

I refueled at an airport west of Kitty Hawk and planned on getting
back to Atlanta right around sunset. Unfortunately, around Rayleigh
the voltage went to just over 12 and the amperage went negative. I
had been hearing a static like popping since leaving Kitty Hawk and
someone suggested that it was arcing from the failure.

I told approach that I was getting lower than the approaching cloud
deck and decided to make a precautionary landing at Sanford NC (KTTA).
No mechanics were around so I got a rental car and went into town for
the night.

The next morning I replaced the voltage regulator with no success so I
removed the lower cowl and found that the battery ring terminal wire
on the alternator B point was fatigued and broken. It was previously
bent to make proper contact.

I had a mechanic install a new ring terminal but that did not make the
alternator work. Using advice from a primo mechanic at home (and not
being able to find a replacement alternator), I bought a battery for
my Blazer, wire, ring terminals and added the new battery in parallel
with my aircraft battery.

Nothing blew up so I prepared to leave. The engine started normally
and to my surprise the alternator worked. It worked all the way home
with four restarts.

On this trip I flew below an overcast with less than 6000' between me
and the ground (perhaps 1500'). I flew over a broken cloud layer.
I flew in less than 100 nm visibility. As I approached Springfield MO
towards sunset, I descended thinking that I was about to overfly a
cloud layer. Nope. It was haze. Silly me. It made more sense to
stay where I could see ground to the sides anyway.

I had planned on going to Key West and the Bahamas but elected to get
home to fix the alternator problem. TS Noel would have kept me from
doing that anyway.

In retrospect, the alternator to bus wire/ring terminal should have
been made better long ago. That will be corrected. I am now in the
process of trying to decide which readily available alternator I will
install. The current one will not fly again.

I also did not know what my safe flying time was when the ring
terminal broke. Perhaps I could have flown another two hours (4-5 amp
current draw and one EI) on a PC925 battery. But since I did not know
for sure, I played it safe and landed at the nearest airport.

With the truck battery, it may well be 20 hours. Regardless, I did
buy a battery charger just in case.

I did find out that the RV community is awesome. Three guys stopped
by to offer assistance (I did the repairs on the ramp). The FBO at
Sanford was great as was the mechanic shop.

Stopping at new airports is fun. I expanded my flight experience
beyond CAVU but nowhere near scud running. The haze illusions were
baffling but I just reacted with safe flight adjustments.

[TheSmokingGnu]

Ron Lee wrote:
> In retrospect, the alternator to bus wire/ring terminal should have
> been made better long ago. That will be corrected. I am now in the
> process of trying to decide which readily available alternator I will
> install. The current one will not fly again.

Not that I wish to impose upon your own maintenance decisions or state
that safe is, in fact, not better than sorry, but the alternator may
well be just fine (excepting the ring terminal, of course).

Alternators have to be supplied with a sufficient current from the
battery in order to generate the larger currents required by the
aircraft systems. This is fine as long as the alternator is functioning,
because it is generating enough current to recharge the battery (and
then some). Without that initial current, though, the alternator will
never work, no matter how hard you spin it (a generator, on the other
hand, would).

It sounds as though the ring terminal broke, disconnecting the
alternator, and the battery discharged sufficiently in the intervening
time such that the alternator couldn't achieve a proper magnetic field.
Your mechanic's suggestion to add an additional battery in parallel
provided the system with the amperage it needed, and the alternator
began to work again.

My advice is to have the alternator tested before chucking onto yonder
scrapheap. Regardless, glad to hear you and the aircraft escaped unharmed.

TheSmokingGnu

[Dennis Johnson]

"Ron Lee" > wrote

>The engine started normally
> and to my surprise the alternator worked. It worked all the way home
> with four restarts.

Hi Ron,

Thanks for the report of your electrical problem. I always learn valuable
insights from reports like this. Thanks for sharing. By the way, beautiful
RV6!

I'm not arguing, just curious; why replace the alternator if it performed
normally on the way home? I'm no expert, but I wonder if the problem is in
the control circuitry or the old, partially discharged battery. How old was
the battery?

The real expert on stuff like this is Bob Nuckolls at
http://www.matronics.com/Navigator/?AeroElectric-List

Glad it worked out,
Dennis

[Ron Lee[_2_]]

TheSmokingGnu > wrote:

>Alternators have to be supplied with a sufficient current from the
>battery in order to generate the larger currents required by the
>aircraft systems. This is fine as long as the alternator is functioning,
>because it is generating enough current to recharge the battery (and
>then some). Without that initial current, though, the alternator will
>never work, no matter how hard you spin it (a generator, on the other
>hand, would).

This may be exactly what happened. The workings of an alternator are
"magic." Since I did have a similar alternator experience where it
would not start once before...and the solution was for an alternator
shop to energize it by touching the "N" terminal I believe with
positive voltage, I did that as well. Either it should have been the
"F" or "E" terminal or I did it incorrectly.

I am changing out to an internally regulated alternator that is easily
obtainable. My current alternator is not either.

Ron Lee

[Newps]

SockPuppet wrote:
> In article <cc1Xi.198$Cb.81@trnddc08>, anonymityisavirtue@
> 1111011010011.com says...
>
>>Alternators have to be supplied with a sufficient current from the
>>battery in order to generate the larger currents required by the
>>aircraft systems.
>>
>
> This is a new concept to me, can you elaborate?
>
> My understanding of alternators is that mechanical energy from the
> engine causes the alternator to spin, which then powers aircraft
> components and (when regulated correctly) can recharge the battery.
>
> Is there something about aircraft alternators that requires the battery
> to power them (rather than the other way around)?


Yes, they need a little charge in the battery to start charging
themselves. Absolutely dead battery? Alternator is useless.

[Morgans[_2_]]

"SockPuppet" > wrote

> Is there something about aircraft alternators that requires the battery
> to power them (rather than the other way around)?

Your car alternator works the same way. The only difference is that if your
car engine is running (and it's not a diesel) then it has electricity in the
first place, (to run the ignition, and probably a fuel pump) then there will
be electricity to create the magnetic field around the alternator for it to
produce more electricity.

The same can not be said for an airplane. It is perfectly happy to run
without any electricity, so with no electricity in the first place, there is
nothing to make the magnetic field in the alternator for it to produce more
electricity.

That, plus the fact that most alternators in airplanes have external voltage
regulators, and a switch in place as a standard device that is there to turn
off the magnetic field for the alternator windings. I can't think of any
cars that have that feature in place.
--
Jim in NC

[Ron Lee[_2_]]

Newps > wrote:

>>>Alternators have to be supplied with a sufficient current from the
>>>battery in order to generate the larger currents required by the
>>>aircraft systems.
>>
>> Is there something about aircraft alternators that requires the battery
>> to power them (rather than the other way around)?
>
>
>Yes, they need a little charge in the battery to start charging
>themselves. Absolutely dead battery? Alternator is useless.

I was able to start my engine several times easily so I doubt that
battery charge was an issue. My best recollection is that the voltage
was around 12.2 V.

Yet adding another battery in parallel did seem to make a difference.

It really is magic or I just am not well educated on the intricacies
of how they work...or don't work.

Ron Lee

[TheSmokingGnu]

SockPuppet wrote:
> In article <cc1Xi.198$Cb.81@trnddc08>, anonymityisavirtue@
> 1111011010011.com says...
>> Alternators have to be supplied with a sufficient current from the
>> battery in order to generate the larger currents required by the
>> aircraft systems.
>>
> This is a new concept to me, can you elaborate?
>
> My understanding of alternators is that mechanical energy from the
> engine causes the alternator to spin, which then powers aircraft
> components and (when regulated correctly) can recharge the battery.

First, recall that electricity induces magnetic fields and magnetic
fields induce electricity and vice versa, and vis a vis and so forth.

A simple generator is a wire coil rotating in opposite poles of two
permanent magnets. The magnetic field is provided by the magnet, and the
faster the coil spins, the more often the magnetic field cuts through
the coil (or more properly, the coil cuts through the magnet's field),
the more current is generated.

Alternators use a different method to generate current. There is a
wire-wound stator, within which spins a drum coil (with soft iron
cores). The drum coil (or rotor) has to be energized from an outside
source in order to generate the magnetic fields, necessary to induce
current in the stator windings. While the process is self-sustaining
once begun, alternators cannot "bootstrap" themselves into current
generation (since you can't generate the current to generate the fields
to generate the current, so to speak). Much like the magnetos need the
impulse coupling to push the engine over with a hot spark, the
alternator needs the external "kick in the pants" to begin outputting
current, which is the battery.

Now, as I recall, we use alternators instead because they're lighter,
more efficient, and higher output than can be achieved with a
bog-standard generator.

TheSmokingGnu

[[email protected]]

On Nov 5, 7:30 am, TheSmokingGnu
> wrote:
> SockPuppet wrote:
> > In article <cc1Xi.198$Cb.81@trnddc08>, anonymityisavirtue@
> > 1111011010011.com says...
> >> Alternators have to be supplied with a sufficient current from the
> >> battery in order to generate the larger currents required by the
> >> aircraft systems.
>
> > This is a new concept to me, can you elaborate?
>
> > My understanding of alternators is that mechanical energy from the
> > engine causes the alternator to spin, which then powers aircraft
> > components and (when regulated correctly) can recharge the battery.
>
> First, recall that electricity induces magnetic fields and magnetic
> fields induce electricity and vice versa, and vis a vis and so forth.
>
> A simple generator is a wire coil rotating in opposite poles of two
> permanent magnets. The magnetic field is provided by the magnet, and the
> faster the coil spins, the more often the magnetic field cuts through
> the coil (or more properly, the coil cuts through the magnet's field),
> the more current is generated.
>
> Alternators use a different method to generate current. There is a
> wire-wound stator, within which spins a drum coil (with soft iron
> cores). The drum coil (or rotor) has to be energized from an outside
> source in order to generate the magnetic fields, necessary to induce
> current in the stator windings. While the process is self-sustaining
> once begun, alternators cannot "bootstrap" themselves into current
> generation (since you can't generate the current to generate the fields
> to generate the current, so to speak). Much like the magnetos need the
> impulse coupling to push the engine over with a hot spark, the
> alternator needs the external "kick in the pants" to begin outputting
> current, which is the battery.
>
> Now, as I recall, we use alternators instead because they're lighter,
> more efficient, and higher output than can be achieved with a
> bog-standard generator.
>
> TheSmokingGnu

The alternator has diodes in it, and those cause a slight voltage
drop in the output process. If the battery is too weak to produce a
sufficiently strong magnetic field in the rotor to generate sufficient
voltage in the stator to overcome diode resistance, bootstrapping
cannot occur. The old generators had no diodes, and residual magnetism
in the field pole shoes would start the thing generating. There's a
bit of residual magnetism in the alternator's stator but not enough to
do any good with those diodes in the way.
Alternators in aircraft should be taken off, opened up and
inspected every 500 hours. The brushes wear and if they get short
they'll fall out of the holder and their springs will gouge up the
slip rings. Gets a lot more expensive than the 500 hour check.
Airplanes that don't fly much have alternator bearings in which the
grease dries out, and bearing failures happen.
Regulators, especially the newer electronic replacements for the
electromechanical-switch types, give us plenty of grief. Regulators
fail more often than alternators. And as the OP found, those dumb
crimp terminals breal through vibration fatigue. Alternator output
breakers age, their contacts corrode and cause resistance heating and
they start popping off,causing the naive mechanic to spend lots of
time looking for a short.

Dan

[Morgans[_2_]]

"Ron Lee" > wrote

> I was able to start my engine several times easily so I doubt that
> battery charge was an issue. My best recollection is that the voltage
> was around 12.2 V.
>
> Yet adding another battery in parallel did seem to make a difference.
>
> It really is magic or I just am not well educated on the intricacies
> of how they work...or don't work.


Could be that after starting it several times, there was voltage available,
but that it could not push enough amps to excite the alternator field.

Could also be that the voltage regulator has the ability to see very low
voltage, and not use any of the remaining electricity to excite the
alternator field.
--
Jim in NC

[Dana M. Hague]

On Sun, 11 Nov 2007 20:36:36 -0600, SockPuppet >
wrote:

>I have to say I'm pretty surprised to hear that aircraft alternators
>don't have permanent magnets. Wow. Of all places not to have permanent
>magnets: an aircraft, where so much is usually done for redundancy. I
>find it kind of amazing.
>
>All the alternators I've ever seen had permanent magnets...

Huh? I can't think of an alternator that DOES have permanent magnets,
unless you count the "lighting coils" on 2-strokes.

I missed the start of this discussion, but the reason NOT to use
permanent magnets in an alternator is that the output voltage will
vary with the rpm. This means that the alternator has to have
permanent magnets strong enough to produce sufficient 12V current even
at idle, and regulator has to be able to regulate the full rpm voltage
down to 12V while handling the full load current... which, just after
the engine starts and the battery's charging, can be a lot. This
means a big heavy regulator that needs to dissapate a lot of heat.
The field current is a lot less than the alternator's output current,
OTOH, so a fairly small, light regulator can handle the job, and no
regulation is needed on the alternator's output.

And, of course, an aircraft engine DOES have redundancy: Even if the
alternator or regulator fails, the magnetos keep the fan turning.

-Dana
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