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1. 12:49 PM - Re: Re: AC current reading for Revmaster engine (Robert L. Nuckolls, III)
2. 04:25 PM - Re: Re: ULPower electrical system (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: AC current reading for Revmaster engine |
At 08:22 AM 9/25/2022, you wrote:
>I will be monitoring the temps of the stator coils
>and the voltage regulator. The voltage regulator I
>will use will be the "John Deere type which I've
>been told is the switching type.
SERIES switching might be a more descriptive
term to distinguish it from the overwhelming
predominance of SWITCHING regulators that manage
energy in high frequency inductors/transformers.
>I have been told by Revmaster that their regulator is the shunt type.
>Unfortunately there seems to be no way of knowing for sure beforehand
>what type of regulator a specific unit is. That information is
>not included in any descriptions.
I'm not sure that the voltage control philosophy
is terribly germane to your investigation. The
Revmaster community has predominately held that
alternator failures are closely associated with
loading of the alternator at or near maximum
output. This idea reinforced by suggestions
that batteries will particularly low internal
resistance are especially deleterious to
alternator service life.
When an alternator is heavily loaded
the shunting currents imposed by the regulator
are at a minimum. I.e. when heavily loaded,
stresses on the alternator are not
particularly driven by configuration of
regulator.
Another noteworthy feature of the failures I've
observed concerns the CONCENTRATION of overstress.
I've never personally encountered failed stator
on a rotating machine that did not present
uniform evidence of destruction over all
stator poles carrying that path of copper. We
see one such example in attached photo.
Some Revmaster alternators have tossed in the towel
after having toasted only one pole winding leaving
pristine poles on either side. But even the
illustration of total winding failure shows
one pole with much more damage than the rest.
I've seen assertions on the 'net describing
any combination of failures from single
pole to all poles.
It would be a real challenge to duplicate
a condition that replicates such a failure.
I'm reasonably certain that NO stress OUTSIDE
the alternator could produce such damage. Hence,
root cause is likely confined to INSIDE the
alternator.
Another curiosity arises with consideration
of the Revmaster PM alternator architecture.
The stator is wound with TWO separate windings
each of which drives a rectifier/regulator.
Either of the two windings is demonstrably
at risk for what seems to be an 'overload'
condition the magnitude of which is not numerically
defined but presumably considerably greater than
the factory's alternator power output ratings.
The Revmaster community has been thrashing about
looking for mitigation of failure while being
offered no methodology for quantifying and
guarding against such failures. Paul and Dan
are graciously volunteering to investigate the
cause/effect features and put numbers to them.
There have to be millions of exemplar alternator/
regulator/battery systems in everything from
mopeds to rather sophisticated heavier than
air machines. The physics for crafting such
systems having useful/satisfactory service life
is well understood.
Given my limited access to design decisions
and the totality of service history, I'm kinda
throwing darts here. But it seems that the
root cause for these failures is most likely
found in the MAGNETICS of the design as opposed
to any combination of electrics or environs. It
would be interesting to study the practicality
of fitting this engine with ONE alternator winding
of heavier wire spread over all stator poles
as opposed to TWO windings with demonstrably
fragile properties.
BTW . . . I've searched my library for a copy
of the R-2300 installation manual and came up
empty. Can anyone point me to a download link
or email me a copy?
>This charge system has (at least) 4 flaws. 1) low air flow/cooling.
>2) erroneous stator design with magnetically saturated laminates.
>3) no resin coating infusion on the windings
Not sure that impregnation/coating of windings would
be terribly significant. This is a labor intensive
rare process in this arena. The net benefit would
be to spread heating effects more uniformly through
the winding mass but would not contribute to improved
cooling. At E-M our varnish impregnated windings were
treated mostly for improved resistance to moisture
and vibration than for thermal management.
> 4) low air flow/cooling.
>I injected DC current from a lab supply through
>the stator winding on the bench and measured the
>rise in temperature of the surface of the stator
>wire and the center laminate steel. I've
>concluded that continuous DC at 15 amps with an
>ambient temperature of 100 F will not
>create a temperature rise that is damaging (steady state of below 140 F).
Not surprising. Temperatures required to 'toast' magnet
wire insulation are pretty severe. Back in my Electro-Mech
days, we slung a lot of magnet wire. We never used anything
less than 'class H' insulation . . . there was little to
be saved by going any lower. Most of our windings were
vacuum impregnated with a varnish and then baked. The
varnish was rated for temperatures equal to or greater than
the wire.
Another physical effect that may contribute to this
failure is tied to the temperature coefficient of resistance
for copper. This phenomenon has been studied in great
detail and accurately know for a very long time.
https://tinyurl.com/p2sjmhtn
As an practical/observable matter
Temperature rating for insulation does is not fall-off-
the-edge-of-the-earth limit. This paper speaks
to a temperature vs. service life for various insulations
https://tinyurl.com/2e7z7wwx
Class H insulation is qualified to function at rated temperature
limits for 20,000 hours with that number falling by 1/2 for
each 10 degree C increase.
Temperatures that toast the wires in one stator pole
while leaving adjacent poles relatively untouched
have to have a profound and probably very simple
explanation.
>Increasing air flow is job 1, wrt cooling this stator. Impregnating the
>wiring is an improvement that I advocate but do not have data on it.
>My direct conversation with the stator wire manufacturer, and
>their recommendation suggests to me it would be an improvement.
Did they quantify 'improvement'?
To quote a rather intelligent fellow of some years past:
Can you measure it? Can you express it in figures?
Can you make a model of it? If not, your theory
is apt to be based more upon imagination than upon
knowledge. === Lord Kelvin ==
>I can share the method of impregnating the stator wiring that I'm
>using with the web=9D, but I'm reluctant to advertise this until I
>can verify there is no damage to the ignition coils.
>I've tested impregnation on the stator coils but the locally
>mounted ignition coil wire is different (much smaller and from
>an unknown supplier).
It seems unlikely that the insulation will be any less
robust
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 2
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| Subject: | Re: ULPower electrical system |
At 03:51 PM 9/25/2022, you wrote:
>
>In the wiring diagram that Bob provided, can someone please explain
>why I need a fusible link and fuse in series for the alternator switch?
>
>Also, should I feed the alternator on/off switch from the battery,
>endurance, or main buss?
Most TC aircraft are fitted only with breakers
for protection in which case, the 5A alternator
field breaker would be mounted with its cousins
in the 'breaker patch' and driven directly from
the bus.
When using fuseblocks, the busses are centralized
in the blocks. Further, they're generally mounted
out of sight, out of reach given that there is
no practical reason to fiddle with fuses in flight.
The crowbar ov protection departs slightly from
from this philosophy because there might be electrical
events that cause the crowbar to operate when in
fact, no serious fault condition exists. In this
case, it's nice to have access to ONLY that
breaker allowing pilot reset to see if the problem
persists.
Hence, the BUS needs to be EXTENDED from the
fuseblock to the breaker. Faulting this piece
of wire offers potential for lots of smoke.
A fusible link limits this severity of such
an event.
This is a reminder that fusible links are not
replacements for fuses or breakers. They are
low resistance, high reliability, long fusing
constant protection of bus extensions . . . i.e.
conductors at risk for experiencing fault currents
supplied by a BATTERY.
They are used sparingly. Typically limited to
alternator b-leads, feeders to bus-tie contactors,
and . . . crowbar breakers located remote from
the bus buried in a fuse block.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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