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mcculleyja(at)starpower.n
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 Posted: Sat May 06, 2006 7:59 pm Post subject: SD-8 PM Alternator |
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'Lectric Bob,
On 4/22/06, you responded to my earlier report of a way to assure
bringing the SD-8 PM alternator on line without benefit of a battery
source of excitation. My finding that as little as one volt charge on a
capacitor was adequate to awaken the SD-8 apparently suggested to you
that there might be an even simpler way to modify the SD-8 regulator to
accomplish independence of the PM alternator from a battery source of
start-up voltage. Your proposed design was as follows:
(SNIP)Your experiments have shown that the regulator will come alive
| Quote: | with a very low voltage available at the 'b-lead'. A study
of the schematic for the Kubota regulator leads one to
conclude that once you have just enough voltage to forward
bias some junctions (The b-e junction of Q3 through R3
and D6) there is a potential for triggering the SCRs and
having the system wake up. I suspect the B&C regulator
is similar.
I thought of another approach to suggest. Since you're set up for
|
and have the mind-set to conduct the necessary experiments,please
consider . . .
| Quote: |
http://www.aeroelectric.com/Pictures/Schematics/PM_Regulator/Self_Excitation_Experiment.jpg
What we'd like to do is not let the b-lead voltage out
of the regulator be 100% dependent upon triggered SCRs in
the regulator. Suppose you added a couple of diodes
from the alternator winding along with a resistor to
ground to build a very inefficient keep-alive rectifier.
The two diodes parallel the SCRs but with a conduction
impedance too high for the system to deliver significant
power. We then need some small, fixed 'load' across the
output filter capacitor to prevent the unloaded alternator
voltage (as high as 40v) from charging the capacitor
to a level dangerous to the cap and system equipment
in case the alternator control relay is closed while the
capacitor is charged up.
I've shown a pair of 1K resistors. Use mechanically
hefty resistors . . . the 2W isn't need for electrical
reasons, just mechanical. Adjust the size of the series
resistor at the diodes to achieve a couple of volts or
more (but not greater than 14) across the capacitor
at max engine rpm with the alternator system OFF.
I suspect this resistor might be as high as 3 to 10K
and still make the system sleep with one eye open.
Here, we have an opportunity to go a step further
and modify the regulator's performance such that
it never quite goes to sleep and eliminate the
need for pilot intervention to kick-start the
system. If you can assist in conduction of this
experiment, we can prove/disprove my hypothesis
and perhaps generate an article that will help
others slay this dragon too.
Bob . . . (SNIP)
|
I am happy to report that I implemented your concept and conducted
successful ground testing today of the SD-8 installation on my Lycoming
180 HP Tailwind.
In order to achieve the desired range of voltage across the capacitor
when BOTH the alternator is OFF LINE and the MASTER switch is OFF, I
found it necessary to increase the suggested 10k ohm resistor from
ground to the pair of diodes to a value of 15k, and to increase the 1k
ohm resistor across the capacitor to 3k ohm.
In this configuration, the voltage across the capacitor slowly rises to
0.6 volts within a 3 minute period after engine start while warming up
at 1100 Engine RPM (1430 alternator RPM). This is insufficient to bring
the alternator on line if the Alternator switch is then turned on.
However, as the engine RPM is advanced to the range of 1700-1800 for mag
check, the alternator is now at 2210-2340 RPM with capacitor voltage
slightly above 0.6 v and if the alternator switch is now turned on the
alternator comes alive to produce an unloaded buss voltage of slightly
over 12 V. This unloaded buss voltage continues to rise with RPM to a
maximum of 14.42 V at engine rated 2700 RPM (alternator at 3510 RPM). As
buss load is added, the regulator maintains 14.29 V until enough load is
added to begin dropping the voltage in keeping with the alternator
design current limits. With the Master switch still OFF, the buss
voltage responds to the electrical load versus RPM in a predictable
manner. Even if the RPM/load combination is carried to an extreme that
produces buss voltage down to as little as 5 V, the alternator stays
activated and comes back up in voltage to no higher than 14.42 if the
load/RPM combination is re-adjusted.
I suspect the system would respond differently with a smaller capacitor
than the 56K mf unit that I adapted from my previous set-up, but I did
not observe any undesirable features, and at this preliminary stage I
believe the overall concept produces a fully automatic solution to
eliminate the fear that a PM alternator could fail to come on line in
the absence of a voltage source such as the ship's battery.
Please recognize that the above data during operation of the SD-8 just
after engine start-up is not the condition of interest in normal
operation. The engine (and alternator) would more likely be at higher
RPM during cruise flight when the buss voltage might be lost while the
SD-8 is not on line. In this situation,the alternator RPM and available
voltage across the capacitor would already be high enough to immediately
bring the alternator on line by simply turning the alternator switch on.
I will soon verify this on an upcoming flight.
Jim McCulley
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rshannon(at)cruzcom.com
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| Posted: Sat May 06, 2006 8:23 pm Post subject: SD-8 PM Alternator |
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|
Jim,
Thanks for the report on your excellent work! Am looking forward to
further chapters in this story, as your time permits.
Ron
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nuckollsr(at)cox.net
Guest
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| Posted: Sun May 07, 2006 6:02 am Post subject: SD-8 PM Alternator |
|
|
At 11:52 PM 5/6/2006 -0400, you wrote:
| Quote: |
<mcculleyja(at)starpower.net>
'Lectric Bob,
On 4/22/06, you responded to my earlier report of a way to assure
bringing the SD-8 PM alternator on line without benefit of a battery
source of excitation. My finding that as little as one volt charge on a
capacitor was adequate to awaken the SD-8 apparently suggested to you
that there might be an even simpler way to modify the SD-8 regulator to
accomplish independence of the PM alternator from a battery source of
start-up voltage. Your proposed design was as follows:
<snip>
I am happy to report that I implemented your concept and conducted
successful ground testing today of the SD-8 installation on my Lycoming
180 HP Tailwind.
In order to achieve the desired range of voltage across the capacitor
when BOTH the alternator is OFF LINE and the MASTER switch is OFF, I
found it necessary to increase the suggested 10k ohm resistor from
ground to the pair of diodes to a value of 15k, and to increase the 1k
ohm resistor across the capacitor to 3k ohm.
|
What was the voltage with the pair of 1K resistors? I would expect
it to be on the order of 2-6 volts at 2000 rpm with the alternator
switch off.
| Quote: | In this configuration, the voltage across the capacitor slowly rises to
0.6 volts within a 3 minute period after engine start while warming up
at 1100 Engine RPM (1430 alternator RPM). This is insufficient to bring
the alternator on line if the Alternator switch is then turned on.
|
Hmmm . . . we would expect that. The target voltage would be much
higher and I would adjust the paralleling resistor upward from 1K
to adjust for desired value.
| Quote: | However, as the engine RPM is advanced to the range of 1700-1800 for mag
check, the alternator is now at 2210-2340 RPM with capacitor voltage
slightly above 0.6 v and if the alternator switch is now turned on the
alternator comes alive to produce an unloaded buss voltage of slightly
over 12 V.
|
Yeah, this would represent the minimum speed for regulation (actually
a tad low 'cause it's still not up to the regulator setpoint) but
insufficient rpm to deliver significant energy. The fact that it
'came alive' is the significant point.
| Quote: | This unloaded buss voltage continues to rise with RPM to a
maximum of 14.42 V at engine rated 2700 RPM (alternator at 3510 RPM). As
buss load is added, the regulator maintains 14.29 V until enough load is
added to begin dropping the voltage in keeping with the alternator
design current limits. With the Master switch still OFF, the buss
voltage responds to the electrical load versus RPM in a predictable
manner. Even if the RPM/load combination is carried to an extreme that
produces buss voltage down to as little as 5 V, the alternator stays
activated and comes back up in voltage to no higher than 14.42 if the
load/RPM combination is re-adjusted.
|
Yup, as long as the output is kept above the wake-up voltage,
I would not expect it to go back to sleep. We're getting close
to a solution here. Find a value for the resistor in parallel
with the capacitor that gives us a wake-up voltage of 2-3 volts
at 2200 rpm.
The only time you would NEED the system to come up is in flight
and at 2200 rpm or higher. What we're looking for is the right value
for parallel R that gives us the 2-3 volts at 2200.
| Quote: | I suspect the system would respond differently with a smaller capacitor
than the 56K mf unit that I adapted from my previous set-up, but I did
not observe any undesirable features, and at this preliminary stage I
believe the overall concept produces a fully automatic solution to
eliminate the fear that a PM alternator could fail to come on line in
the absence of a voltage source such as the ship's battery.
|
Yes. The fat electrolytic will take a few seconds to come up
to a static value but in this came, time is not critical.
| Quote: | Please recognize that the above data during operation of the SD-8 just
after engine start-up is not the condition of interest in normal
operation. The engine (and alternator) would more likely be at higher
RPM during cruise flight when the buss voltage might be lost while the
SD-8 is not on line. In this situation,the alternator RPM and available
voltage across the capacitor would already be high enough to immediately
bring the alternator on line by simply turning the alternator switch on.
I will soon verify this on an upcoming flight.
|
Okay. What you could do is bring a wire into the cockpit
off the filter capacitor. Put a fuse in series with it at
the capacitor end. You can fiddle with the load resistor
value and monitor voltage on the lead from the operator's
seat.
I appreciate your time and interest in helping us craft
and conduct the experiment.
Bob . . .
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mcculleyja(at)starpower.n
Guest
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| Posted: Sun May 07, 2006 7:19 pm Post subject: SD-8 PM Alternator |
|
|
Bob,
Hope the following responses to your questions will be helpful. My
apologies for not having more detailed test data. A well controlled
bench test would be far better than my preliminary ground run-up testing
on the engine installation! That is a difficult environment.
(SNIP)In order to achieve the desired range of voltage across the
capacitor when BOTH the alternator is OFF LINE and the MASTER
switch is OFF, I found it necessary to increase the suggested 10k
ohm resistor from ground to the pair of diodes to a value of 15k,
and to increase the 1k resistor across the capacitor to 3K. (SNIP)
| What was the voltage with the pair of 1K resistors? I would expect
| it to be on the order of 2-6 volts at 2000 rpm with the alternator
| switch off.
I don't have that answer. Your schematic showed a 1k resistor at both
the diodes to ground as well as across the capacitor, but you commented
that you suspected the series resistor might be as large as 3k to 10k
and still make the system sleep with one eye open. I thought it best to
start with the higher 10k value and work downward if necessary. For this
reason I never tried less than 10k, because the initial run with 10k
produced a rise toward 15 volts while still below 2200 alternator RPM.
So I shut down and arbitrarily chose to increase the series value to 15k
and the paralleling 1K to 3k, expecting this to probably be excessive
and I could then fine tune with values in between.
(SNIP)In this configuration, the voltage across the capacitor slowly
rises to 0.6 volts within a 3 minute period after engine start
while warming up at 1100 engine RPM (1430 alternator RPM). This
is insufficient to bring the alternator on line if the Alternator
switch is then turned on. (SNIP)
| Hmmm . . . we would expect that. The target voltage would be much
| higher and I would adjust the paralleling resistor upward from 1K
| to adjust for desired value.
Since my previous arrangement with the normally open push button switch
activated the alternator at 1V (I didn't try it lower) why wouldn't it
probably also respond at 1V in this current configuration, rather than
needing 2-3V ? Just curious.
(SNIP)However, as the engine RPM is advanced to the range of 1700-1800
for mag check, the alternator is now at 2210-2340 RPM with
capacitor voltage slightly above 0.6 v and if the alternator
switch is now turned on, the alternator comes alive to produce an
unloaded buss voltage of slightly over 12 V. (SNIP)
| Yeah, this would represent the minimum speed for regulation
| (actually a tad low 'cause it's still not up to the regulator
| setpoint) but insufficient rpm to deliver significant energy. The
| fact that it 'came alive' is the significant point.
Yes, I was initially concerned that the 0.6V meant I had badly
over-corrected the resistors, but when the voltage rose rapidly as
alternator speed rose beyond about 2200 RPM, I continued slowly to its
maximum 3510 RPM without exceeding 14.42 V, still with the alternator
off line. I then reduced RPM, waited for the capacitor voltage to
stabilize around 0.6V and then increased speed slowly while periodically
turning on the alternator switch, with no results until reaching close
to 2100 alternator RPM, at which point the buss became alive with about
12V. Further speed increase raised the buss to a maximum of 14.42, which
was the maximum all the way to 3510 limit RPM. I assumed the energy
level at 0.6V was just too low to trigger the regulator but since it
finally triggered at an RPM that is well below a reasonable in-flight
value, maybe this is desirable and possibly avoids any tendency to
exceed the upper 14V level while still providing the desired end result.
(SNIP)This unloaded buss voltage continues to rise with RPM to a maximum
of 14.42 V at engine rated 2700 RPM (alternator at 3510 RPM). As
buss load is added, the regulator maintains 14.29 V until enough
load is added to begin dropping the voltage in keeping with the
alternator design current limits. With the Master switch still
OFF, the buss voltage responds to the electrical load versus RPM
in a predictable manner. Even if the RPM/load combination is
carried to an extreme that produces buss voltage down to as little
as 5 V, the alternator stays activated and comes back up in
voltage to no higher than 14.42 if the load/RPM combination is
re-adjusted. (SNIP)
| Yup, as long as the output is kept above the wake-up voltage,
| I would not expect it to go back to sleep. We're getting close
| to a solution here. Find a value for the resistor in parallel
| with the capacitor that gives us a wake-up voltage of 2-3 volts
| at 2200 rpm.
The voltage does rise rather rapidly as alternator RPM increases from
the 1430 level toward the 2200 level where the alternator responded to
being switched on. I didn't record the exact correlation and it might
require a pretty slow engine power increase to allow for the
larger-than-necessary capacitor to rise in voltage. I will attempt to
get better data, but doing so in a ground run has some inherent
operational hazards. The ideal method would be on a bench set-up.
| The only time you would NEED the system to come up is in flight
| and at 2200 rpm or higher. What we're looking for is the right
| value for parallel R that gives us the 2-3 volts at 2200.
I'm reasonably sure the voltage at 2200 RPM was several volts above 2-3.
Is it desirable to not exceed 2-3 even though we're not now going above
14.42V maximum at 3510 RPM when off line?
(SNIP)I suspect the system would respond differently with a smaller
capacitor than the 56K mf unit that I adapted from my previous
set-up, but I did not observe any undesirable features, and at
this preliminary stage I believe the overall concept produces a
fully automatic solution to eliminate the fear that a PM
alternator could fail to come on line in the absence of a voltage
source such as the ship's battery. (SNIP)
| Yes. The fat electrolytic will take a few seconds to come up
| to a static value but in this came, time is not critical.
(SNIP)Please recognize that the above data during operation of the SD-8
just after engine start-up is not the condition of interest in
normal operation. The engine (and alternator) would more likely be
at higher RPM during cruise flight when the buss voltage might be
lost while the SD-8 is not on line. In this situation,the
alternator RPM and available voltage across the capacitor would
already be high enough to immediately bring the alternator on line
by simply turning the alternator switch on. I will soon verify
this on an upcoming flight. (SNIP)
| Okay. What you could do is bring a wire into the cockpit
| off the filter capacitor. Put a fuse in series with it at
| the capacitor end. You can fiddle with the load resistor
| value and monitor voltage on the lead from the operator's
| seat.
The capacitor, paralleling resistor and quality digital test meter are
all inside the cockpit, so this is not a problem. Do you recommend any
change to the resistor between the diodes and ground from the 15k I now
have in place?
| I appreciate your time and interest in helping us craft
| and conduct the experiment. Bob . . .
I'm pleased to have your excellent guidance. Thanks for your time.
Jim McCulley
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