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jgswartout(at)earthlink.n
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 Posted: Thu Oct 12, 2006 8:13 am Post subject: SD-8 Self-Excitation Option |
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I can’t find the message now, but I believe I recall Bob saying that with the SD-8 self-excitation circuitry (Z-25), the SD 8 would be on all the time. If this is true (my knowledge of electronics is not sufficient to determine this for myself) it seems that, while innovative, this is not really useful. If one wants the SD-8 to always be on, the same battery that starts your engine could excite the SD-8 at the start of each flight. The only way self-excitation would be useful would be if you were out in the bush with a dead battery and had to hand-prop to start the engine.
First, is it correct that with Z-25 the SD-8 would always be on?
Second, I realize that the SD-8 is always spinning whenever the engine is turning, but is there any disadvantage to having it always on-line?
Third, could Z-25 be altered to allow self-excitation only when needed?
[quote][b]
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jgswartout(at)earthlink.n
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| Posted: Thu Oct 12, 2006 8:13 am Post subject: SD-8 Self-Excitation Option |
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I can’t find the message now, but I believe I recall Bob saying that with the SD-8 self-excitation circuitry (Z-25), the SD 8 would be on all the time. If this is true (my knowledge of electronics is not sufficient to determine this for myself) it seems that, while innovative, this is not really useful. If one wants the SD-8 to always be on, the same battery that starts your engine could excite the SD-8 at the start of each flight. The only way self-excitation would be useful would be if you were out in the bush with a dead battery and had to hand-prop to start the engine.
First, is it correct that with Z-25 the SD-8 would always be on?
Second, I realize that the SD-8 is always spinning whenever the engine is turning, but is there any disadvantage to having it always on-line?
Third, could Z-25 be altered to allow self-excitation only when needed?
[quote][b]
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nuckollsr(at)cox.net
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| Posted: Thu Oct 12, 2006 12:00 pm Post subject: SD-8 Self-Excitation Option |
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At 12:12 PM 10/12/2006 -0400, you wrote:
| Quote: | I can t find the message now, but I believe I recall Bob saying that with
the SD-8 self-excitation circuitry (Z-25), the SD 8 would be on all the
time. If this is true (my knowledge of electronics is not sufficient to
determine this for myself) it seems that, while innovative, this is not
really useful. If one wants the SD-8 to always be on, the same battery
that starts your engine could excite the SD-8 at the start of each
flight. The only way self-excitation would be useful would be if you were
out in the bush with a dead battery and had to hand-prop to start the engine.
|
Yup, you got it. Generators of yore carried sufficient
residual field magnetism to come on line without benefit
of external power sources. Generators that have stood
idle for a long time may loose this residual and require
recharging of the field poles with a technique called
"flashing".
Alternators were seldom if ever designed to support
any residual in the field so the vast majority of alternators
in service require external startup energy to come alive.
This can be an exceedingly small voltage . . . say between
0.2 and 1.0 volts of field voltage. However, given the
very high speeds for rotating a typical alternator on
Lycoming engines, some folks have reported that their
modern alternators will come alive without benefit of
external voltage applied.
| Quote: | First, is it correct that with Z-25 the SD-8 would always be on?
|
The SD-8 is a PERMANENT MAGNET alternator . . . if
it's spinning, it's producing voltage. So in this sense,
it's always ON and there's nothing you can do to change that.
Many SD-8 users have noted, however, that the REGULATOR
supplied with the SD-8 will not come alive solely on
voltage supplied from the alternator side of the system.
Again, an exceedingly small voltage on the system side
of the regulator (about .6 volts) to forward bias one
of the critical solid state devices in the regulator
would kick-start the regulator.
The notion of being "always ON" or "ON-OFF under
panel control" does not have the same meaning for the
SD-8 system as for it's bigger generator/alternator
cousins. However, given the special duty assigned to
the SD-8 in a Z-13 installation, it's not an unreasonable
design goal to have the system become useful whether or
not there is a battery present.
Earlier discussions about the quality of SD-8 power
sans battery suggests that a "self-excitation" feature
is useful. I've suggested that B&C pursue this as a
product improvement but until that happens, Z-25 is
the way to make it happen.
| Quote: | Second, I realize that the SD-8 is always spinning whenever the engine is
turning, but is there any disadvantage to having it always on-line?
|
It's not "on line" until a connection exists between
the regulator output and the bus. There are many systems
in aircraft that operate similarly. A number of generator
installations on turbine aircraft can be taken "off line"
by opening the reverse current control contactor . . . the
generator is still up and running, producing whatever voltage
the regulator commands . . . but no utilization of that
energy can be made until the contactor is closed. This is
how the SD-8 operates under the Z-13 architecture.
Know that if you pre-flight the SD-8, the first time you
turn it on after the engine is started, it will come alive
and remain alive as long as it's being turned by the engine.
The only thing that the Z-25 mod gets you is a cold startup
sans battery.
| Quote: |
Third, could Z-25 be altered to allow self-excitation only when needed?
|
Sure. Put the relay in series with the AC output from
the alternator . . . but then a second set of contacts
on the same relay would be used to keep a small amount
of bias current from constantly loading the battery when
the airplane is parked. You double the probability of
relay failure while adding no operational value for
having done so. Hence the configuration of Z-13 as you
see it whether or not modified per Z-25.
Bob . . .
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jgswartout(at)earthlink.n
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| Posted: Thu Oct 12, 2006 4:33 pm Post subject: SD-8 Self-Excitation Option |
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Priceless. Thank you for that lucid and thorough explanation, Bob.
John
DO NOT ARCHIVE
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klehman(at)albedo.net
Guest
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| Posted: Fri Oct 13, 2006 7:50 am Post subject: SD-8 Self-Excitation Option |
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I'm not sure that I'd want self excitation for my system. Also FWIW I
now believe that the 20,000 uF capacitor on the output of the PM
alternator regulator may be a really good idea. I omitted it because I
hard wired the output to an 8AH battery (without a battery contactor)
and figured that would suffice. There was no apparent electrical noise
from the alternator. As mentioned recently though, I started the engine
once with a completely dead battery. I closed the crossfeed contactor
(Z-14 architecture) and observed the alternator charging. Upon opening
the crossfeed contactor, the OVM module immediately tripped and cut
power to the input of the regulator. I did that a couple of times.
Problem was that the John Deere regulator was now failed in the full on
mode. I surmise that the totally dead battery was ineffective at
absorbing any current and keeping the voltage down and that the
regulator fried itself during the few milliseconds that it took for the
OVM to trip. The crossfeed autocloses during cranking and I had
previously closed it with the engine running with no problems. Actually
the system also ran fine with the failed VR and the crossfeed closed as
long as system loads were kept above the 20 amp output of the PM alternator.
I replaced the regulator but being hard headed I have not added a
capacitor. I now know enough not to bring the alternator on line with a
dead battery. However I did add some transorbs which might limit the
voltage for the short period until the OVM trips if I should be silly
enough to accidentally do somethng similar again.
I didn't learn much from an autopsy on the VR other than it uses output
semiconductors that appear to be fabricated on a copper plate instead of
off the shelf devices. The circuit board used surface mount devices and
I gave up on drawing a circuit diagram. I would like to find a
reasonably simple circuit for a homemade replacement VR. I don't really
have the time to properly test a completely new design.
Ken L.
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 12:12 PM 10/12/2006 -0400, you wrote:
> I can t find the message now, but I believe I recall Bob saying that
> with the SD-8 self-excitation circuitry (Z-25), the SD 8 would be on
> all the time. If this is true (my knowledge of electronics is not
> sufficient to determine this for myself) it seems that, while
> innovative, this is not really useful. If one wants the SD-8 to
> always be on, the same battery that starts your engine could excite
> the SD-8 at the start of each flight. The only way self-excitation
> would be useful would be if you were out in the bush with a dead
> battery and had to hand-prop to start the engine.
Yup, you got it. Generators of yore carried sufficient
residual field magnetism to come on line without benefit
of external power sources. Generators that have stood
idle for a long time may loose this residual and require
recharging of the field poles with a technique called
"flashing".
Alternators were seldom if ever designed to support
any residual in the field so the vast majority of alternators
in service require external startup energy to come alive.
This can be an exceedingly small voltage . . . say between
0.2 and 1.0 volts of field voltage. However, given the
very high speeds for rotating a typical alternator on
Lycoming engines, some folks have reported that their
modern alternators will come alive without benefit of
external voltage applied.
> First, is it correct that with Z-25 the SD-8 would always be on?
The SD-8 is a PERMANENT MAGNET alternator . . . if
it's spinning, it's producing voltage. So in this sense,
it's always ON and there's nothing you can do to change that.
Many SD-8 users have noted, however, that the REGULATOR
supplied with the SD-8 will not come alive solely on
voltage supplied from the alternator side of the system.
Again, an exceedingly small voltage on the system side
of the regulator (about .6 volts) to forward bias one
of the critical solid state devices in the regulator
would kick-start the regulator.
The notion of being "always ON" or "ON-OFF under
panel control" does not have the same meaning for the
SD-8 system as for it's bigger generator/alternator
cousins. However, given the special duty assigned to
the SD-8 in a Z-13 installation, it's not an unreasonable
design goal to have the system become useful whether or
not there is a battery present.
Earlier discussions about the quality of SD-8 power
sans battery suggests that a "self-excitation" feature
is useful. I've suggested that B&C pursue this as a
product improvement but until that happens, Z-25 is
the way to make it happen.
> Second, I realize that the SD-8 is always spinning whenever the
> engine is turning, but is there any disadvantage to having it always
> on-line?
It's not "on line" until a connection exists between
the regulator output and the bus. There are many systems
in aircraft that operate similarly. A number of generator
installations on turbine aircraft can be taken "off line"
by opening the reverse current control contactor . . . the
generator is still up and running, producing whatever voltage
the regulator commands . . . but no utilization of that
energy can be made until the contactor is closed. This is
how the SD-8 operates under the Z-13 architecture.
Know that if you pre-flight the SD-8, the first time you
turn it on after the engine is started, it will come alive
and remain alive as long as it's being turned by the engine.
The only thing that the Z-25 mod gets you is a cold startup
sans battery.
> Third, could Z-25 be altered to allow self-excitation only when needed?
Sure. Put the relay in series with the AC output from
the alternator . . . but then a second set of contacts
on the same relay would be used to keep a small amount
of bias current from constantly loading the battery when
the airplane is parked. You double the probability of
relay failure while adding no operational value for
having done so. Hence the configuration of Z-13 as you
see it whether or not modified per Z-25.
Bob . . .
|
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nuckollsr(at)cox.net
Guest
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| Posted: Fri Oct 13, 2006 9:02 am Post subject: SD-8 Self-Excitation Option |
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|
At 11:50 AM 10/13/2006 -0400, you wrote:
| Quote: |
I'm not sure that I'd want self excitation for my system.
|
What's the down-side for having it?
| Quote: | Also FWIW I now believe that the 20,000 uF capacitor on the output of the
PM alternator regulator may be a really good idea.
|
The value of this capacitor is to enable operations of the
SD-8 sans battery . . . but if you don't have a battery -or-
the capacitor -or- self excitation feature, then the SD-8
is at risk to being "stalled" if inadvertently overloaded
during alternator-only ops.
| Quote: | I omitted it because I hard wired the output to an 8AH battery
(without a battery contactor) and figured that would suffice.
|
I think the SD-8 regulator has places a small load (milliamps)
on any power source that is not disconnected during power down.
| Quote: | There was no apparent electrical noise from the alternator. As mentioned
recently though, I started the engine once with a completely dead battery.
I closed the crossfeed contactor (Z-14 architecture) and observed the
alternator charging. Upon opening the crossfeed contactor, the OVM module
immediately tripped and cut power to the input of the regulator. I did
that a couple of times.
Problem was that the John Deere regulator was now failed in the full on
mode. I surmise that the totally dead battery was ineffective at absorbing
any current and keeping the voltage down and that the regulator fried
itself during the few milliseconds that it took for the OVM to trip. The
crossfeed autocloses during cranking and I had previously closed it with
the engine running with no problems. Actually the system also ran fine
with the failed VR and the crossfeed closed as long as system loads were
kept above the 20 amp output of the PM alternator.
I replaced the regulator but being hard headed I have not added a
capacitor. I now know enough not to bring the alternator on line with a
dead battery. However I did add some transorbs which might limit the
voltage for the short period until the OVM trips if I should be silly
enough to accidentally do somethng similar again.
|
Contrary to the fondest wishes of several past participants,
the lowly Transorb is not suited for soaking up the overflow
from a runaway alternator . . . and without carefully crafted
source impedance control, they're not suited for corralling
a load-dump event either. I've had great success using them
to stand off indirect effects of lightning . . . but energies
in normal and abnormal events from engine driven power sources
are just not something we can reasonably expect a Transorb
to handle.
| Quote: | I didn't learn much from an autopsy on the VR other than it uses output
semiconductors that appear to be fabricated on a copper plate instead of
off the shelf devices. The circuit board used surface mount devices and I
gave up on drawing a circuit diagram. I would like to find a reasonably
simple circuit for a homemade replacement VR. I don't really have the time
to properly test a completely new design.
|
Here's a schematic that is quite common to
all PM alternator regulators.
http://www.aeroelectric.com/Pictures/Schematics/PM_Regulator/Kubota_Schematic.jpg
This design looks like it's free of power-down leakage.
As long as the Q4eb, Z1, D6 pathway is out of conduction,
it doesn't appear that anything would be turned on. There
are no voltage dividers across the battery lead either.
Bob . . .
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klehman(at)albedo.net
Guest
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| Posted: Fri Oct 13, 2006 9:37 am Post subject: SD-8 Self-Excitation Option |
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|
| Quote: | > There was no apparent electrical noise from the alternator. As
> mentioned recently though, I started the engine once with a
> completely dead battery. I closed the crossfeed contactor (Z-14
> architecture) and observed the alternator charging. Upon opening the
> crossfeed contactor, the OVM module immediately tripped and cut power
> to the input of the regulator. I did that a couple of times.
>
> Problem was that the John Deere regulator was now failed in the full
> on mode. I surmise that the totally dead battery was ineffective at
> absorbing any current and keeping the voltage down and that the
> regulator fried itself during the few milliseconds that it took for
> the OVM to trip. The crossfeed autocloses during cranking and I had
> previously closed it with the engine running with no problems.
> Actually the system also ran fine with the failed VR and the
> crossfeed closed as long as system loads were kept above the 20 amp
> output of the PM alternator.
>
> I replaced the regulator but being hard headed I have not added a
> capacitor. I now know enough not to bring the alternator on line
> with a dead battery. However I did add some transorbs which might
> limit the voltage for the short period until the OVM trips if I
> should be silly enough to accidentally do somethng similar again.
Contrary to the fondest wishes of several past participants,
the lowly Transorb is not suited for soaking up the overflow
from a runaway alternator . . . and without carefully crafted
source impedance control, they're not suited for corralling
a load-dump event either. I've had great success using them
to stand off indirect effects of lightning . . . but energies
in normal and abnormal events from engine driven power sources
are just not something we can reasonably expect a Transorb
to handle.
Understood. But transorbs might have kept the voltage reasonble for the
|
few milliseconds that it took for the OVM to trip as mentioned in the
top paragraph. The dead battery did not limit the voltage or the OVM
would not have tripped. A large capacitor might have helped a bit. I
think transorbs might help in this situation. The J.D. regulator goes
for $100. in my neighborhood.
Gee if they had only put component values on that schematic 
Ken L.
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nuckollsr(at)cox.net
Guest
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| Posted: Sat Oct 14, 2006 4:41 am Post subject: SD-8 Self-Excitation Option |
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|
| Quote: | >
> Here's a schematic that is quite common to
> all PM alternator regulators.
>
>http://www.aeroelectric.com/Pictures/Schematics/PM_Regulator/Kubota_Schematic.jpg
> This design looks like it's free of power-down leakage.
> As long as the Q4eb, Z1, D6 pathway is out of conduction,
> it doesn't appear that anything would be turned on. There
> are no voltage dividers across the battery lead either.
>
> Bob . . .
Gee if they had only put component values on that schematic
Ken L.
|
This circuit is not one that would benefit much
from gain and bias optimization. I'll bet if
you used 2N3906 for all transistors, 1K for
all resistors, 1N5243 for zener, and 1N400x
for small diodes, it would come up and run
just fine.
There are a variety of options for SCR's and
power diodes in the rectifier. SCR's should be
selected to trigger on less than 10ma else
value of R3 needs reduction accordingly.
Bob . . .
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