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lrsecaldwell(at)earthlink
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 Posted: Tue Dec 05, 2006 6:05 am Post subject: Aux Altenator switching. |
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I am using Z13 with the 8 amp aux alternator.
I would like to insure that when I turn on the Aux Alt that the Main Alt
is off. I plan to use a dpdt (on-none-on) switch for the Aux
Alternator. The aux alternator would be wired normally. The main
alternator field would be wired in series with the Aux alternator such
that when the Aux Alt is off, the field power is enabled to the Main Alt
switch (Bat & main alt switch.). When the auxs alt switxh is on the
main alt field would be disconnected.
Does anyone see any problem with this plan?
Roger
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nuckollsr(at)cox.net
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| Posted: Tue Dec 05, 2006 8:36 am Post subject: Aux Altenator switching. |
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At 09:04 AM 12/5/2006 -0500, you wrote:
| Quote: |
<lrsecaldwell(at)earthlink.net>
I am using Z13 with the 8 amp aux alternator.
I would like to insure that when I turn on the Aux Alt that the Main Alt
is off.
|
Why?
| Quote: | I plan to use a dpdt (on-none-on) switch for the Aux Alternator. The
aux alternator would be wired normally. The main alternator field would
be wired in series with the Aux alternator such that when the Aux Alt is
off, the field power is enabled to the Main Alt switch (Bat & main alt
switch.). When the auxs alt switxh is on the main alt field would be
disconnected.
Does anyone see any problem with this plan?
|
Don't see a need for it. Further, any part that is
NOT on your airplane is not going to be a part that
fails. Having one switch exert command and control over
systems that are supposed to back each other up
does not produce nice failure modes effects analysis.
There is no danger to any equipment on the airplane by
having both alternators on at the same time. I'll
recommend you install Z-13 as published.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
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pwmac(at)sisna.com
Guest
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| Posted: Tue Dec 05, 2006 10:04 am Post subject: Aux Altenator switching. |
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Bob,
Does your comment "There is no danger to any equipment on the airplane by
having both alternators on at the same time. "
Does this mean if I add a John Deere 20a and run at the same time
as my Rotax 18 Amp unit that I can get 38 amps max case? Any down
side to doing this?
Thanks, Paul
================
At 08:35 AM 12/5/2006, you wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 09:04 AM 12/5/2006 -0500, you wrote:
>
>Caldwell <lrsecaldwell(at)earthlink.net>
>
>I am using Z13 with the 8 amp aux alternator.
>
>I would like to insure that when I turn on the Aux Alt that the
>Main Alt is off.
Why?
> I plan to use a dpdt (on-none-on) switch for the Aux
> Alternator. The aux alternator would be wired normally. The main
> alternator field would be wired in series with the Aux alternator
> such that when the Aux Alt is off, the field power is enabled to
> the Main Alt switch (Bat & main alt switch.). When the auxs alt
> switxh is on the main alt field would be disconnected.
>
>Does anyone see any problem with this plan?
Don't see a need for it. Further, any part that is
NOT on your airplane is not going to be a part that
fails. Having one switch exert command and control over
systems that are supposed to back each other up
does not produce nice failure modes effects analysis.
There is no danger to any equipment on the airplane by
having both alternators on at the same time. I'll
recommend you install Z-13 as published.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
|
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nuckollsr(at)cox.net
Guest
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| Posted: Tue Dec 05, 2006 10:40 am Post subject: Aux Altenator switching. |
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At 10:01 AM 12/5/2006 -0800, you wrote:
| Quote: |
Bob,
Does your comment "There is no danger to any equipment on the airplane by
having both alternators on at the same time. "
Does this mean if I add a John Deere 20a and run at the same time as my
Rotax 18 Amp unit that I can get 38 amps max case? Any down side to doing this?
|
There's a difference between risks for damage and performance as
shared suppliers of loads to the system. The problem is getting
respective voltage regulators of two engine driven power sources
to appropriately share total loads based on their respective
capabilities.
I've designed such regulators but the technology I've used
is not compatible with PM alternators. It would take a start
from scratch effort to get the proportionate paralleling
performance that's desired when running two power sources.
Yes, you can run two alternators and count on their added
capacities for total engine driven power . . . but without
hardware specific to making them share loads, you'll find
yourself fiddling with the regulation setpoints a lot.
If you can bolt a 20A PM alternator to your engine, why
not a 40A ND alternator with some REAL capacity to run
the whole airplane and save the smaller alternator for backup
a-la Z-13/8?
Bob . . .
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pwmac(at)sisna.com
Guest
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| Posted: Tue Dec 05, 2006 1:09 pm Post subject: Aux Altenator switching. |
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Yes, the small ND sure has merits and probably had the same issues as
any add on alternator for the Rotax. I wont need 40a but 25 or 30
would be nice to simplify my electrical system. Then the Rotax
marginal unit would just be a backup.
Thanks for your input, Paul
====================
At 10:39 AM 12/5/2006, you wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 10:01 AM 12/5/2006 -0800, you wrote:
>
>
>Bob,
>Does your comment "There is no danger to any equipment on the airplane by
>having both alternators on at the same time. "
> Does this mean if I add a John Deere 20a and run at the same time
> as my Rotax 18 Amp unit that I can get 38 amps max case? Any down
> side to doing this?
There's a difference between risks for damage and performance as
shared suppliers of loads to the system. The problem is getting
respective voltage regulators of two engine driven power sources
to appropriately share total loads based on their respective
capabilities.
I've designed such regulators but the technology I've used
is not compatible with PM alternators. It would take a start
from scratch effort to get the proportionate paralleling
performance that's desired when running two power sources.
Yes, you can run two alternators and count on their added
capacities for total engine driven power . . . but without
hardware specific to making them share loads, you'll find
yourself fiddling with the regulation setpoints a lot.
If you can bolt a 20A PM alternator to your engine, why
not a 40A ND alternator with some REAL capacity to run
the whole airplane and save the smaller alternator for backup
a-la Z-13/8?
Bob . . .
|
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nuckollsr(at)cox.net
Guest
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| Posted: Tue Dec 05, 2006 5:31 pm Post subject: Aux Altenator switching. |
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At 01:03 PM 12/5/2006 -0800, you wrote:
| Quote: |
Yes, the small ND sure has merits and probably had the same issues as any
add on alternator for the Rotax. I wont need 40a but 25 or 30 would be
nice to simplify my electrical system. Then the Rotax marginal unit would
just be a backup.
|
Keep in mind that your alternator has two functions: (1) carry the
max running load for equipment on board and (2) recharge the battery.
(Battery charging energy) = (alternator energy) - (running loads).
Just because your alternator is 'oversized' is not necessarily a
bad or even undesirable thing. If you had a hard time getting the
engine started or want to go flying after extended ground maintenance
ops from the battery, then being able to reload the battery quickly
with just your alternator output is a pretty nifty thing.
What's the weight difference? A 40A ND alternator compared to
the JD PM alternator + rectifier/regulator? I'll bet it's about
a wash and for my money, I'd take the 40A ND over a 20A JD
machine any day.
The SD-8 at 3.5 pounds and its compatibility with the AND20000
pad on the back of the engine is the recipe for success . . . but
I've never understood the perceived allure for the larger PM
alternators as compared to the smaller wound-field devices.
Bob . . .
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klehman(at)albedo.net
Guest
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| Posted: Wed Dec 06, 2006 5:53 am Post subject: Aux Altenator switching. |
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Weight difference? The JD 20 amp PM is about 2 lb lighter than the 40
amp ND. That could rise to about 2.5 lb if one adds a OV contactor to
the ND. The new ND was cheaper than the JD + regulator though for me.
Theoretically the ND should have a cleaner (less noise) output although
that made no noticeable difference for my system.
I actually agree with Bob's post but I did not have an accessory pad for
a SD-8 and chose a JD rather than a 40 amp ND as a second alternator for
OV considerations as well as the 2.5 lb saving. Perhaps I'm wrong, but I
had more confidence that a small relay would interupt the 20 amp ac
output than I have that a cheap contactor will interupt the 40 amp dc
output. The expensive OV contactor would have cost me more than an ND
alternator and replacing/servicing it would have been more difficult.
Also I prefer not to have excessively large alternators since a small
alternator that is running full on with a failed regulator will cause
the voltage to rise slower than a large unit and it will take longer to
"cook" a battery since less amps are available. With OVM protection most
of that wouldn't matter. However I have an electrically dependant
engine. Many years ago I was in a position of having to cycle a
generator on and off to get out of clouds largely based on how bad the
battery smelled between cycles. As it boiled and melted, the liquid
electrolyte battery absorbed a lot more excess energy than my RG
batteries will. Since there was no low or high voltage warning, the
smell from the battery was the first indication of a problem back then.
Anyway with the JD I know that even worst case I can fairly easilly load
the thing to capacity and manually keep the voltage nominal and that was
attractive to me.
Ken
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 01:03 PM 12/5/2006 -0800, you wrote:
>
>
> Yes, the small ND sure has merits and probably had the same issues as
> any add on alternator for the Rotax. I wont need 40a but 25 or 30
> would be nice to simplify my electrical system. Then the Rotax
> marginal unit would just be a backup.
Keep in mind that your alternator has two functions: (1) carry the
max running load for equipment on board and (2) recharge the battery.
(Battery charging energy) = (alternator energy) - (running loads).
Just because your alternator is 'oversized' is not necessarily a
bad or even undesirable thing. If you had a hard time getting the
engine started or want to go flying after extended ground maintenance
ops from the battery, then being able to reload the battery quickly
with just your alternator output is a pretty nifty thing.
What's the weight difference? A 40A ND alternator compared to
the JD PM alternator + rectifier/regulator? I'll bet it's about
a wash and for my money, I'd take the 40A ND over a 20A JD
machine any day.
The SD-8 at 3.5 pounds and its compatibility with the AND20000
pad on the back of the engine is the recipe for success . . . but
I've never understood the perceived allure for the larger PM
alternators as compared to the smaller wound-field devices.
Bob . . .
|
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rparigor(at)SUFFOLK.LIB.N
Guest
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| Posted: Wed Dec 06, 2006 10:50 am Post subject: Aux Altenator switching. |
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With regard to installing an additional charging devise on a Rotax 91X
four stroke, the vacuum pad spins slower than a Lyc. or Cont.
I know of no alternator larger than the SD20S that will fit on the vacuum
pad, with the SD20S being of the very best quality. I forget the exact
output of the SD20S using a LR3C (that eats a bit of power compared to a
switcher) but at cruise ~ 18 amps sounds correct on a 12 volt system.
You need the short nose SD20S (not SD20) to fit the Rotax. If you look on
B+Cs website under Cessna 210 for the SD20S. The output is identical to
the SD20, just the shorter nose. Actual it is a beautiful custom casting
drive side half of the alternator, the drive coupling is awful nice as
well.
If anyone knows of a 40 amp alternator that will put out above 30 amps on
a Rotax vacuum, I am all ears.
Some have taken a 40 amp alternator and drive it direct off the crankshaft
with a flex coupling and bracket it off the engine mount.
A bit off topic but semi pertinent:
Keep your Ducati Rotax regulator as cool as you can
If you ask more than 12 amps continuous from the Rotax generator the
regulator will fail in short order. If you keep changing regulators the
windings supposedly fail on the generator
SD20S with a LR3C is probably more robust at 18 amps than the supposedly
18 or 20 amp internal generator is at 12 amps.
I plan to limit continuous of the SD20S to ~15 amps
I forget exact set point of Ducati, think 13.6 or 13.7 volts, the LR3C
comes with ~14.4 but is adjustable. If you have both chargers on line, the
SD20S will do for the most part most of the work if setpoint is above the
Rotax generator. At less than cruise RPM the SD20S will not put out 18
amps, at taxi RPM not even close, I am not flying yet, but I believe that
the Rotax generator will help out a little at this time if the SD20S is
slumping voltage down to Ducati setpoint.
If you do use a SD20S, make sure you use one vacuum pad gasket, but be
sure to measure that the male driven spline on the SD20S is not bottomed
inside the female drive spline. (No big deal if it is, a few strokes on
the plastic male spline with a file rectifies (the fit) on the alternator!
Perhaps there is .750" of engagement, I needed to remove on my 914 .070",
not even up to the edge of the chamfer)
Ron Parigoris
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