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aadamson(at)highrf.com
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 Posted: Sun Mar 26, 2006 1:55 pm Post subject: Alt/Batt switch question |
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Take Z14 for example. I know there has been lots of discussion about not
doing Avionics masters, but I have a somewhat related question.
I have an IO-550 with dual alt/batts. One alt will be a regular engine
driven one and it will be on the primary buss. The other, and SD-20, will
be on the essential buss.
So, in the scenario where I perform the initial startup, How does the VR and
the Backup alternator perform under this scenario.
A) I put the primary master in ALT+BATT.
B) I leave the CROSS TIE contactor OFF,
C) I put the Essential buss master to BATT only, not to ALT. I do this
because the engine instrumentation is on the essential buss and I want to
prime and watch for static fuel pressure, etc.
So, the primary battery provides all the power required for start and the
fuel pump (it's a Mag based engine). The backup battery is providing just
the power for the essential buss (in my case, the PFD EFIS, the AHRS, the
Magnetometer and the Engine instruments).
Once running, I switch the essential master to ALT and that should start the
backup alternator charging the system.
My real question is, is just having the ALT switch to the VR open, enough to
cause the alternator *not* to put out a charge until after I switch the
switch?
Perhaps I don't understand all the mechanics, but from the B&C datasheet on
the VR, (it's one of theirs), that is how you test it, so I figured, it
wouldn't hurt to start this way?
Would it be better to switch the cross tie on prior to switching on the
second alternator, or does *any* of this matter?
Thanks for reading and any replies.
Alan
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nuckollsr(at)cox.net
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| Posted: Wed Mar 29, 2006 3:14 pm Post subject: Alt/Batt switch question |
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At 04:47 PM 3/26/2006 -0500, you wrote:
| Quote: |
<aadamson(at)highrf.com>
Take Z14 for example. I know there has been lots of discussion about not
doing Avionics masters, but I have a somewhat related question.
I have an IO-550 with dual alt/batts. One alt will be a regular engine
driven one and it will be on the primary buss. The other, and SD-20, will
be on the essential buss.
So, in the scenario where I perform the initial startup, How does the VR and
the Backup alternator perform under this scenario.
A) I put the primary master in ALT+BATT.
B) I leave the CROSS TIE contactor OFF,
C) I put the Essential buss master to BATT only, not to ALT. I do this
because the engine instrumentation is on the essential buss and I want to
prime and watch for static fuel pressure, etc.
|
You can turn on battery only or turn on both alternators too . . .
doesn't matter in the grand scheme of things.
| Quote: | So, the primary battery provides all the power required for start and the
fuel pump (it's a Mag based engine). The backup battery is providing just
the power for the essential buss (in my case, the PFD EFIS, the AHRS, the
Magnetometer and the Engine instruments).
Once running, I switch the essential master to ALT and that should start the
backup alternator charging the system.
My real question is, is just having the ALT switch to the VR open, enough to
cause the alternator *not* to put out a charge until after I switch the
switch?
|
Assuming that you're using externally regulated alternators as illustrated
in Z-14 then if the alternator switch is not ON, then the alternator
controlled
by that switch is OFF. You can turn it on after starting or before
starting,
it doesn't matter.
| Quote: | Perhaps I don't understand all the mechanics, but from the B&C datasheet on
the VR, (it's one of theirs), that is how you test it, so I figured, it
wouldn't hurt to start this way?
|
It doesn't HURT anything to start any way you wish. What you do
want to do is craft a preflight test that sorts through all your
marbles to see that they're in place before takeoff. From a human
factors perspective, you want to do one thing and observe one result.
MAIN bat ON . . . . stuff lights up. MAIN LO VOLTS
flashes.
AUX bat ON . . . . more stuff lights up. AUX LOW
VOLTS light flashes.
Engine START . . . . oil pressure rises.
MAIN alt ON . . . . MAIN LOW VOLTS warning
goes dark.
AUX alt ON . . . . AUX LOW VOLTS warning
goes dark.
| Quote: | Would it be better to switch the cross tie on prior to switching on the
second alternator, or does *any* of this matter?
|
Why? The cross tie is there for one of two reasons: (1) allow sharing
of energy sources during a failure event on one side or the other and
(2) letting two batteries do the job of getting the engine started. If
stuff on the aux bus doesn't run well in the real world of starter-
in-rush-brown-out, then (2) is not an option for you. This leaves only
(1) which (given the inherent reliability of modern batteries and
alternators) should be a very rare event. You might want to include it
in the pre-flight checklist by closing the cross tie, turn aux battery
and alternator OFF to see that the aux bus stays lit then return the
system to the flight configuration.
Bob . . .
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aadamson(at)highrf.com
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westexflyboy
Joined: 02 May 2008
Posts: 9
Location: Presidio, TX
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| Posted: Sat Mar 21, 2009 11:14 pm Post subject: Re: Alt/Batt switch question |
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[quote="nuckollsr(at)cox.net"]At 04:47 PM 3/26/2006 -0500, you wrote:
| Quote: | You might want to include it in the pre-flight checklist by closing the cross tie, turn aux battery and alternator OFF to see that the aux bus stays lit then return the system to the flight configuration.
Bob . . . |
Bob, am I understanding correctly that it is acceptable to close the crossfeed switch with both alternators and batteries turned on and functioning normally? Perhaps I am imagining a myth - that the two alternators are somehow phased differently and cannot both apply power to the same bus at the same time.
I, for one, would really appreciate an in-flight failure checklist along with a pre-flight checklist for Z-14. Perhaps operation instructions would dispell all misunderstandings.
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_________________
Chase Snodgrass
Presidio, Texas
www.flybigbend.com
Simultaneous RV-10 twins under construction |
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dale.r(at)cox.net
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| Posted: Sun Mar 22, 2009 5:32 am Post subject: Alt/Batt switch question |
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westexflyboy wrote:
| Quote: | ... Perhaps I am imagining a myth - that the two alternators are somehow phased differently and cannot apply power to the same bus at the same time.
|
Yes - you are myth-informed. Phasing in the alternators
doesn't matter, because they each have their own rectifiers;
so only DC hits the system wiring. Nevertheless, only one
of the alternators will end up doing all the work - the other's
regulator, having detected that higher voltage level, will will
cut it's field current, providing minimal output.
Dale R.
COZY MkIV #0497
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BobsV35B(at)aol.com
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| Posted: Sun Mar 22, 2009 5:37 am Post subject: Alt/Batt switch question |
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Good Morning Chase,
Different Bob here, but it is my understanding that a properly operating alternator has diodes or other rectification devices in the circuit that allow us to have direct current, not alternating current, at our disposal.
If we hook two alternators together at the point where they are still producing alternating current, the current will need to be put in phase or "paralleled" as the big boys say.
Once the output has been rectified or smoothed out enough to be considered direct current, paralleling ceases to be a problem. The source that has the highest voltage will hog the load. The lower voltage source will just wait until the voltage gets down to its level before it adds anything to the mix. That is how we balance the load between two power output devices, we mess with the voltage and the resistance between the current producing entities.
Make any sense at all?
Happy Skies
Old Bob
AKA
Bob Siegfried
Ancient Aviator
628 West 86th Street
Downers Grove, IL 60516
630 985-8502
Stearman N3977A
Brookeridge Air Park LL22
In a message dated 3/22/2009 2:17:43 A.M. Central Daylight Time, airplanedriver(at)gmail.com writes:
| Quote: | --> AeroElectric-List message posted by: "westexflyboy" <airplanedriver(at)gmail.com>
[quote="nuckollsr(at)cox.net"]At 04:47 PM 3/26/2006 -0500, you wrote:
| Quote: | You might want to include it in the pre-flight checklist by closing the cross tie, turn aux battery and alternator OFF to see that the aux bus stays lit then return the system to the flight configuration.
Bob . . .
|
Bob, am I understanding correctly that it is acceptable close the crossfeed switch with both alternators and batteries turned on and functioning normally? Perhaps I am imagining a myth - that the two alternators are somehow phased differently and cannot apply power to the same bus at the same time.
I, for one, would really appreciate both pre-flight and in-flight failure checklists for Z-14 to dispell all misunderstandings.
--------
Chase Snodgrass
Presidio, Texas
www.flybigbend.com
Simultaneous RV-10 twins under construction
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=235595#235595
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[quote][b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Mar 23, 2009 3:43 pm Post subject: Alt/Batt switch question |
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At 02:14 AM 3/22/2009, you wrote:
| Quote: |
<airplanedriver(at)gmail.com>
[quote="nuckollsr(at)cox.net"]At 04:47 PM 3/26/2006 -0500, you wrote:
> You might want to include it in the pre-flight checklist by
closing the cross tie, turn aux battery and alternator OFF to see
that the aux bus stays lit then return the system to the flight configuration.
>
> Bob . . .
Bob, am I understanding correctly that it is acceptable close the
crossfeed switch with both alternators and batteries turned on and
functioning normally? Perhaps I am imagining a myth - that the two
alternators are somehow phased differently and cannot apply power to
the same bus at the same time.
I, for one, would really appreciate both pre-flight and in-flight
failure checklists for Z-14 to dispell all misunderstandings.
|
Z-14 is two INDEPENDENT electrical systems intended
to operate in complete isolation from each other
except for (1) perhaps closing the crossfeed contactor
to use both batteries for starting or (2) being able
to power SOME loads from the opposite system in case
of alternator failure of one side.
It does take some special regulators to get two
alternators or generators to peacefully co-exist
on the same bus. I've got a set of z-figures check
lists in progress somewhere. I'll see if I can
find them.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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westexflyboy
Joined: 02 May 2008
Posts: 9
Location: Presidio, TX
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| Posted: Mon Mar 23, 2009 8:37 pm Post subject: Re: Alt/Batt switch question |
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[quote="nuckolls.bob(at)aeroelect"]At 02:14 AM 3/22/2009, you wrote:
| Quote: | I've got a set of z-figures checklists in progress somewhere. I'll see if I can find them.
Bob . . . |
Thank you, Bob. You've pretty much provided the the engine start checklist above and in previous posts. Assuming the two alternators are 60A and 20A respectively, let me propose an in-flight failure checklist to get the ball rolling. The will assume the pilot has been trained regarding load analysis of the systems and devices installed in the aircraft, and two electronic ignition systems connected directly to the positive and negative terminals of the two batteries separately:
Scenario #1
AUX Low Volts Lamp Illuminates (20A)
Check AUX ammeter. Discharge indicates probable AUX alternator failure. Recycle AUX Master switch to BATT then back to ALT. If discharge and low volts continues, move AUX Master to BATT.
Close Crossfeed Switch.
Check MAIN ammeter. Discharge indicates system overload. Reduce electrical load. Turn off all devices not required for flight safety. If positive charge indicated, non-essential devices may be re-introduced one device at a time while monitoring ammeter.
Check AUX Low Volts Lamp - DARK
If Low Volts lamp remains illuminated and ammeter continues to show discharge after turning off all devices, AUX system SHORT is indicated. OPEN Crossfeed switch, and move AUX Master to OFF.
Continue flight to nearest safe landing area.
Scenario #2
MAIN Low Volts Lamp Illuminates (60A)
Check MAIN ammeter. Discharge indicates probable MAIN alternator failure. Recycle MAIN Master switch to BATT then back to ALT. If still no charge, move MAIN Master to BATT.
Close Crossfeed Switch.
Turn off ALL devices not required for safe continuation of the flight.
Check AUX ammeter. Discharge indicates system overload. Reduce electrical load by intermittent and temporary use of essential devices (i.e. communications and navigation). Disconnect handheld GPS from aircraft bus and use self-contained batteries. Reduce electrical load until positive charge indicated.
Check MAIN Low Volts Lamp - DARK
If Low Volts lamp remains illuminated and ammeter continues to show discharge after turning off ALL devices, MAIN system SHORT is indicated. OPEN Crossfeed switch, and move MAIN Master switch to OFF.
In case of MAIN alternator failure at night or in Instrument Meteorologic Conditions, continue to nearest safe landing destination.
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_________________
Chase Snodgrass
Presidio, Texas
www.flybigbend.com
Simultaneous RV-10 twins under construction |
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