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nuckolls.bob(at)aeroelect
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 Posted: Fri Dec 20, 2019 2:25 pm Post subject: One battery/two alternators IFR z-diagram |
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At 08:26 PM 12/18/2019, you wrote:
| Quote: | After doing some reading on the FAQ list, it looks like I should consider the Z-13/8 with the Z-25 excitation mod, or else the Z-14. I think I also now understand one of the drawbacks of Z-12 architecture is if the battery contactor fails, both alternators go offline.
Michael- |
That's generally not true with modern alternators . . .
and only a few of the legacy alternators.
It's true that many alternators will not come
online without a battery present . . .but once
running, they'll hum along oblivious to battery
being there or not.
With HEAVY inrush loads like klieg-lights in the
wings or hydraulic pump motors. It was theoretically
possible to stall an alternator . . .from which
recovery would be impossible unless a battery were
present.
Such loads are rare in our neighborhood of the
GA community. Contactor failure in flight
is exceedingly rare . . . never heard of one . . .
but ANY change to engine cranking performance
on the GROUND calls for investigation . . . you
might have a contactor getting tired.
But if the engine starts right smartly then
you've 'preflighted' the contactor . . . probability
of loosing it in the next 3 hours of operation
is nil.
Z-12 is flying in hundreds if not thousands of
TC aircraft and they don't even have an e-bus.
If you've got a ROBUST standby alternator like
the contemporary SD20 machines, then the need
for load-shedding with loss of main alternator
is minimal if non-existent . . . hence, the need
for a refined load-shedding protocol is negated.
Of course, this should all be CONFIRMED by
completing the very first design document needed
for artful crafting of your system . . . the LOAD
ANALYSIS.
If it were my airplane, I'd go for Z12 with no
ebus and a well maintained battery. The auto-switch
feature for Z-12 is not necessary for flight
safety. I'd run an LR3 on the main alternator
and a generic VR166 on the standby alternator.
Leave standby alternator OFF until needed as
annunciated by a low volts warning.
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Fri Dec 20, 2019 3:03 pm Post subject: One battery/two alternators IFR z-diagram |
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| Quote: |
What is there a recommended replacement architecture for the z-13/20? |
Z13/8 was crafted with the notion of offering
a robust (meaning unlimited electrical endurance
in the alt-out mode) plan-b for loss of main alternator
assuming running loads can be reduced to 10A
or less . . . which is the capability of
the SD8.
I fiddled with the idea of a Z13/20 waayyy
back when . . . at time when the operating
philosophy for the SD20 called for b-lead
current sensing and cockpit indications
for reducing load to values at or below
the 'rated' output of the alternator.
This made the FAA happy . . . but in retrospect
was totally unnecessary. The SD20 has
a pedigree based on a 40A, automotive,
belt driven alternator (B&C's L40).
In a Lycoming installation, it runs
at 10KRPM or better, may indeed be expected
to produce 40A under some conditions
and is belt-driven which produces significant
axial loading on the bearings.
As an SD20, it's DERATED not for any physical
design limits . . . but because on the
vacuum pump pad it isn't driven at much
more than 3900 rpm. So in fact, you cannot
physically 'overload' this alternator to the
extend that functionality is at risk.
Its output sags and it's physically incapable
of producing the same output as the mother-machine
just 'cause it's not turning fast enough.
In years since, materials and processes for
the raw-stock have improved such that the
SD20 is now rated at more than 20A on a
pad drive.
The Z13/8 philosophy for minimizing running
loads while under standby power is not
especially valid for EITHER a Z12 or Z13/20
application.
So as mentioned in my post of a few mintues
ago, I think I'm going to revise Z-12 to (1)
remove the Endurance Bus and (2) replace the
standby regulator with something simple and
cheap. The best indicator of loading the standby
alternator too hard is depression of bus
voltage below 13.0 volts. Given the number
of voltmeters in most airplanes today, the
value of a over-current, under-voltage sensing
regulator on the standby system seems something
of overkill.
Modern electronics and lighting have made it
possible to craft even an IFR capable machine
with running loads below the output capability
of a pad-driven SD20.
Have I overlooked anything here? Considered
critical review is most welcome . . .
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan
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| Posted: Fri Dec 20, 2019 4:15 pm Post subject: Re: One battery/two alternators IFR z-diagram |
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| Quote: | So as mentioned in my post of a few mintues
ago, I think I'm going to revise Z-12 to (1)
remove the Endurance Bus and (2) replace the
standby regulator with something simple and
cheap. The best indicator of loading the standby
alternator too hard is depression of bus
voltage below 13.0 volts. Given the number
of voltmeters in most airplanes today, the
value of a over-current, under-voltage sensing
regulator on the standby system seems something
of overkill.
Modern electronics and lighting have made it
possible to craft even an IFR capable machine
with running loads below the output capability
of a pad-driven SD20.
Have I overlooked anything here? Considered
critical review is most welcome . . .
Bob . . . |
Great idea Bob. Simpler is better.
Many VFR sport planes do not even need a standby alternator.
Now if we could just convince builders to NOT install an avionics switch.
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_________________
Joe Gores |
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mburbidg(at)gmail.com
Guest
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| Posted: Fri Dec 20, 2019 8:00 pm Post subject: One battery/two alternators IFR z-diagram |
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Thanks for the detailed response Bob. You’ve probably responded to this question before. I looked for the archive of this mail list. But couldn’t find it. Is there an archive. I could swear I’ve used it before.
Michael
From: "owner-aeroelectric-list-server(at)matronics.com" <owner-aeroelectric-list-server(at)matronics.com> on behalf of "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
Reply-To: "aeroelectric-list(at)matronics.com" <aeroelectric-list(at)matronics.com>
Date: Friday, December 20, 2019 at 3:09 PM
To: "aeroelectric-list(at)matronics.com" <aeroelectric-list(at)matronics.com>
Subject: Re: One battery/two alternators IFR z-diagram
| Quote: |
What is there a recommended replacement architecture for the z-13/20? |
Z13/8 was crafted with the notion of offering
a robust (meaning unlimited electrical endurance
in the alt-out mode) plan-b for loss of main alternator
assuming running loads can be reduced to 10A
or less . . . which is the capability of
the SD8.
I fiddled with the idea of a Z13/20 waayyy
back when . . . at time when the operating
philosophy for the SD20 called for b-lead
current sensing and cockpit indications
for reducing load to values at or below
the 'rated' output of the alternator.
This made the FAA happy . . . but in retrospect
was totally unnecessary. The SD20 has
a pedigree based on a 40A, automotive,
belt driven alternator (B&C's L40).
In a Lycoming installation, it runs
at 10KRPM or better, may indeed be expected
to produce 40A under some conditions
and is belt-driven which produces significant
axial loading on the bearings.
As an SD20, it's DERATED not for any physical
design limits . . . but because on the
vacuum pump pad it isn't driven at much
more than 3900 rpm. So in fact, you cannot
physically 'overload' this alternator to the
extend that functionality is at risk.
Its output sags and it's physically incapable
of producing the same output as the mother-machine
just 'cause it's not turning fast enough.
In years since, materials and processes for
the raw-stock have improved such that the
SD20 is now rated at more than 20A on a
pad drive.
The Z13/8 philosophy for minimizing running
loads while under standby power is not
especially valid for EITHER a Z12 or Z13/20
application.
So as mentioned in my post of a few mintues
ago, I think I'm going to revise Z-12 to (1)
remove the Endurance Bus and (2) replace the
standby regulator with something simple and
cheap. The best indicator of loading the standby
alternator too hard is depression of bus
voltage below 13.0 volts. Given the number
of voltmeters in most airplanes today, the
value of a over-current, under-voltage sensing
regulator on the standby system seems something
of overkill.
Modern electronics and lighting have made it
possible to craft even an IFR capable machine
with running loads below the output capability
of a pad-driven SD20.
Have I overlooked anything here? Considered
critical review is most welcome . . .
Bob . . .
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johnbright
Joined: 14 Dec 2011
Posts: 165
Location: Newport News, VA
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| Posted: Wed Jan 08, 2020 7:37 am Post subject: Re: One battery/two alternators IFR z-diagram |
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| nuckolls.bob(at)aeroelect wrote: | At 08:26 PM 12/18/2019, you wrote:
| Quote: | After doing some reading on the FAQ list, it looks like I should consider the Z-13/8 with the Z-25 excitation mod, or else the Z-14. I think I also now understand one of the drawbacks of Z-12 architecture is if the battery contactor fails, both alternators go offline.
Michael- |
That's generally not true with modern alternators . . .
and only a few of the legacy alternators.
It's true that many alternators will not come
online without a battery present . . .but once
running, they'll hum along oblivious to battery
being there or not.
With HEAVY inrush loads like klieg-lights in the
wings or hydraulic pump motors. It was theoretically
possible to stall an alternator . . .from which
recovery would be impossible unless a battery were
present.
.
.
.
Bob . . . |
Hi Bob... question... need there be a load on a wound field alternator for it to continue working in case of battery disconnect?
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links |
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Jan 08, 2020 1:07 pm Post subject: One battery/two alternators IFR z-diagram |
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| Quote: |
Hi Bob... question... need there be a load on a wound field alternator for it to continue working in case of battery disconnect? |
No . . . you can 'stall' a free-running
alternator by hitting it with a big load,
generally larger than it's nameplate rating.
If you have and electro-hydraulic gear, then
inrush on the PM pump motor may well cause
a self-excited alternator to go down . . .
but if you remove most if not all loads, they'll
generally self excite and come back on line
whereupon you can turn some things back on.
Folks used to be fond of dual, 150 watt landing
lights . . . turning both of these puppies on at
the same time might take down an alternator that's
not supported by a battery.
With the advent of led lighting and the relative
rarity of retractable gear airplanes, those
antagonists are mostly ghosts of yesteryear.
Depending on the regulator design, most
alternators will come on line in an orderly
fashion with small or no loads . . . they
will run in a civilized manner as long as
you don't hammer them with a 'start up
transient' that exceeds nameplate rating.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Fri Jan 10, 2020 8:16 am Post subject: One battery/two alternators IFR z-diagram |
|
|
| Quote: |
Hi Bob... question... need there be a load on a wound field alternator for it to continue working in case of battery disconnect? |
No . . . you can 'stall' a free-running
alternator by hitting it with a big load,
generally larger than it's nameplate rating.
If you have and electro-hydraulic gear, then
inrush on the PM pump motor may well cause
a self-excited alternator to go down . . .
but if you remove most if not all loads, they'll
generally self excite and come back on line
whereupon you can turn some things back on.
Folks used to be fond of dual, 150 watt landing
lights . . . turning both of these puppies on at
the same time might take down an alternator that's
not supported by a battery.
With the advent of led lighting and the relative
rarity of retractable gear airplanes, those
antagonists are mostly ghosts of yesteryear.
Depending on the regulator design, most
alternators will come on line in an orderly
fashion with small or no loads . . . they
will run in a civilized manner as long as
you don't hammer them with a 'start up
transient' that exceeds nameplate rating.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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