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Z-* Question
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kenryan



Joined: 20 Oct 2009
Posts: 298

PostPosted: Wed Jul 11, 2018 9:04 am    Post subject: Z-* Question Reply with quote

If you "solve" the "problem" by moving the alternator feed wire to the battery side of the contactor, then you create a separate problem (one many would consider more serious) in that you will have nullified the ability to cut off all current by simply moving the master switch.

On Wed, Jul 11, 2018 at 7:40 AM BMC_Dave <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)>

It almost feels like I'm being intentionally gaslit, I'll try again. We're addressing the OPs use of Z14 and his concern about why the alternator isn't on the battery bus side of the contactor. Additionally, the current architecture doesn't include any LV warning on the battery bus side.

So as it is drawn currently drawn in Z14, running an electrically dependent engine is dangerous because you have a single point of failure (the contactor) and zero indication anything is wrong until your engine dies and you have no means to turn it back on...

Yes, we discussed adding a LV warning to the battery bus.... in other threads about other architecture drawings. It's a good idea, you should probably do that, or similar like putting the LR-3 LV sense on the battery bus instead.

I've heard many times about how contactor failures are rare, once followed immediately by a description of how hard they wear and steps that can be taken to mitigate that... Point is this single point of failure is easy to side-step with out adding anything to the system. The reluctance to do so is confusing and no one seems to want to explain why.




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user9253



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PostPosted: Wed Jul 11, 2018 9:34 am    Post subject: Re: Z-* Question Reply with quote

Quote:
The reluctance to do so is confusing and no one seems to want to explain why.

I explained why. If the alternator "B" lead is connected directly to the battery, then that "B" lead is always hot no matter if the field switch is on or off. That always hot wire is more likely to cause an incident than a failed contactor.
The Z figures just show the basic power layout. They are not meant to show every electrical circuit in an airplane. Notice that there is no radio or EFIS on the Z figure. It is up to the builder to wire his plane to make it safe. If you want a low voltage warning, then install it. If there is only one ignition system, then provide it with two sources of power via diodes or switches. Just do not make changes that create a new danger.


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BMC_Dave



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PostPosted: Wed Jul 11, 2018 9:54 am    Post subject: Re: Z-* Question Reply with quote

kenryan wrote:
If you "solve" the "problem" by moving the alternator feed wire to the battery side of the contactor, then you create a separate problem (one many would consider more serious) in that you will have nullified the ability to cut off all current by simply moving the master switch.

On Wed, Jul 11, 2018 at 7:40 AM BMC_Dave <bmcdave85> wrote:

Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85>

It almost feels like I'm being intentionally gaslit, I'll try again. We're addressing the OPs use of Z14 and his concern about why the alternator isn't on the battery bus side of the contactor. Additionally, the current architecture doesn't include any LV warning on the battery bus side.

So as it is drawn currently drawn in Z14, running an electrically dependent engine is dangerous because you have a single point of failure (the contactor) and zero indication anything is wrong until your engine dies and you have no means to turn it back on...

Yes, we discussed adding a LV warning to the battery bus.... in other threads about other architecture drawings. It's a good idea, you should probably do that, or similar like putting the LR-3 LV sense on the battery bus instead.

I've heard many times about how contactor failures are rare, once followed immediately by a description of how hard they wear and steps that can be taken to mitigate that... Point is this single point of failure is easy to side-step with out adding anything to the system. The reluctance to do so is confusing and no one seems to want to explain why.




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No it doesn't. Moving the alternator feed line to the battery side of the contactor doesn't change how the Main DC Pwr Master Switch turns off the alternator (by opening the ALT FLD circuit).

user9253 wrote:

I explained why. If the alternator "B" lead is connected directly to the battery, then that "B" lead is always hot no matter if the field switch is on or off.


Electrically, how is having the B lead after the contactor different than having it before the contactor if the contactor is closed?

What new danger is made by moving the alternator feed, and maybe the LO V warning from the LR-3, to the battery side of the contactor?

ETA: I thought alternators were turned on and off by closing and opening the field circuit, is this not correct?


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PostPosted: Wed Jul 11, 2018 10:21 am    Post subject: Z-* Question Reply with quote

Dave, you are correct that if the alternator is off, that wire will not be powered by the alternator. It WILL be powered by the battery because you have connected it directly to the battery right?

On Wed, Jul 11, 2018, 1:59 PM BMC_Dave <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)>


kenryan wrote:
> If you "solve" the "problem" by moving the alternator feed wire to the battery side of the contactor, then you create a separate problem (one many would consider more serious) in that you will have nullified the ability to cut off all current by simply moving the master switch.
>
> On Wed, Jul 11, 2018 at 7:40 AM BMC_Dave  wrote:
>
>
> > --> AeroElectric-List message posted by: "BMC_Dave"
> > 
> >  It almost feels like I'm being intentionally gaslit, I'll try again. We're addressing the OPs use of Z14 and his concern about why the alternator isn't on the battery bus side of the contactor. Additionally, the current architecture doesn't include any LV warning on the battery bus side.
> > 
> >  So as it is drawn currently drawn in Z14, running an electrically dependent engine is dangerous because you have a single point of failure (the contactor) and zero indication anything is wrong until your engine dies and you have no means to turn it back on...
> > 
> >  Yes, we discussed adding a LV warning to the battery bus.... in other threads about other architecture drawings. It's a good idea, you should probably do that, or similar like putting the LR-3 LV sense on the battery bus instead.
> > 
> >  I've heard many times about how contactor failures are rare, once followed immediately by a description of how hard they wear and steps that can be taken to mitigate that... Point is this single point of failure is easy to side-step with out adding anything to the system. The reluctance to do so is confusing and no one seems to want to explain why.
> > 
> > 
> > 
> > 
> >  Read this topic online here:
> > 
> >  http://forums.matronics.com/viewtopic.php?p=481560#481560 (http://forums.matronics.com/viewtopic.php?p=481560#481560)
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No it doesn't. Moving the alternator feed line to the battery side of the contactor doesn't change how the Main DC Pwr Master Switch turns off the alternator (by opening the ALT FLD circuit).


user9253 wrote:
>
> I explained why.  If the alternator "B" lead is connected directly to the battery, then that "B" lead is always hot no matter if the field switch is on or off. 


Electrically, how is having the B lead after the contactor different than having it before the contactor if the contactor is closed? Should the contactor open, and your B lead is on the battery side, this would have the same effect as opening the ALT field circuit, thereby shutting off the alternator. Unless I'm radically misunderstanding how alternators work...




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Rocketman1988



Joined: 21 Jun 2012
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PostPosted: Wed Jul 11, 2018 10:32 am    Post subject: Re: Z-* Question Reply with quote

I do not see the Z-14 as dangerous as drawn for my EFII aircraft. The ECUs can be split between the busses, the fuel pumps can be split and the injector supply will be come from a buss powered by both batteries through a diode bridge.

There is no possible way to make any system 100% reliable; if you drill down far enough, you can't always find a serious failure that will compromise the system. The point is risk mitigation...


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PostPosted: Wed Jul 11, 2018 10:40 am    Post subject: Z-* Question Reply with quote

At 10:34 AM 7/11/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com>

It almost feels like I'm being intentionally gaslit, I'll try again. We're addressing the OPs use of Z14 and his concern about why the alternator isn't on the battery bus side of the contactor.

So the b-lead is 'cold' when the master switch is OFF

Quote:
Additionally, the current architecture doesn't include any LV warning on the battery bus side.

Because in-flight contactor failure rates are very
low. But if one wishes to 'cover' that possibility,
lv warning on a battery-bus fed appliance would
provide the hedge.



Bob . . .


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PostPosted: Wed Jul 11, 2018 10:41 am    Post subject: Re: Z-* Question Reply with quote

cluros(at)gmail.com wrote:
Dave, you are correct that if the alternator is off, that wire will not be powered by the alternator. It WILL be powered by the battery because you have connected it directly to the battery right?



Ahhh, I see it now thanks. Yeah that's true, though I'm not positive on the placement of these things in relation to each other. If going to the starter contactor is a whole lot different than going to the bat side of the battery contactor.


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PostPosted: Wed Jul 11, 2018 10:45 am    Post subject: Z-* Question Reply with quote

Quote:
>
> Yes . . . unless you put low voltage monitoring
> on the battery . . . easy to do. But if engine
> dependency on fuel pressure and ignition is
> addressed by redundant systems, why are they
> all running from one battery?
>
>
> Bob . . .


That's the point, in Z14 they don't appear to be, correct?

Correct. I have shown primary systems on main battery,
secondary on the aux battery . . . hence even loss
of one battery contactor does not present an
intractable hazzard to comfortable termination
of flight. I have been assuming (possibly incorrectly)
that there was some feature of this discussion that
absolutely depended on energy from a single
battery bus for continued flight.


Bob . . .


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PostPosted: Wed Jul 11, 2018 10:47 am    Post subject: Re: Z-* Question Reply with quote

Rocketman1988 wrote:
I do not see the Z-14 as dangerous as drawn for my EFII aircraft. The ECUs can be split between the busses, the fuel pumps can be split and the injector supply will be come from a buss powered by both batteries through a diode bridge.

There is no possible way to make any system 100% reliable; if you drill down far enough, you can't always find a serious failure that will compromise the system. The point is risk mitigation...


Fair enough, I just see the architecture as-drawn to have a pretty serious single point of failure for electronically dependent engines. As it can occur with no notice to the pilot that something has happened, and no way to provide power to the bits that need it once your engine shuts off. The reluctance to acknowledge this is perplexing.


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PostPosted: Wed Jul 11, 2018 11:09 am    Post subject: Z-* Question Reply with quote

The starter contactor is on the other side of the battery contactor. With the battery contactor off, no battery power to the starter contactor, no battery power to the b lead.

On Wed, Jul 11, 2018, 2:46 PM BMC_Dave <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)>


cluros(at)gmail.com wrote:
> Dave, you are correct that if the alternator is off, that wire will not be powered by the alternator. It WILL be powered by the battery because you have connected it directly to the battery right?
>
>


Ahhh, I see it now thanks. Yeah that's true, though I'm not positive on the placement of these things in relation to each other. If going to the starter contactor is a whole lot different than going to the bat side of the battery contactor.




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PostPosted: Wed Jul 11, 2018 11:25 am    Post subject: Z-* Question Reply with quote

If one incorporates the Z-24 OVP protection for internal VR
alternators, that OVP contactor or relay disconnects the battery from
the B lead if the alternator is turned off.
Ken

On 11/07/2018 2:15 PM, Sebastien wrote:
Quote:
Dave, you are correct that if the alternator is off, that wire will
not be powered by the alternator. It WILL be powered by the battery
because you have connected it directly to the battery right?

On Wed, Jul 11, 2018, 1:59 PM BMC_Dave <bmcdave85(at)gmail.com
<mailto:bmcdave85(at)gmail.com>> wrote:


<bmcdave85(at)gmail.com <mailto:bmcdave85(at)gmail.com>>
kenryan wrote:
> If you "solve" the "problem" by moving the alternator feed wire
to the battery side of the contactor, then you create a separate
problem (one many would consider more serious) in that you will
have nullified the ability to cut off all current by simply moving
the master switch.
>
> On Wed, Jul 11, 2018 at 7:40 AM BMC_Dave wrote:
>
>
> >
> >
> > It almost feels like I'm being intentionally gaslit, I'll try
again. We're addressing the OPs use of Z14 and his concern about
why the alternator isn't on the battery bus side of the contactor.
Additionally, the current architecture doesn't include any LV
warning on the battery bus side.
> >
> > So as it is drawn currently drawn in Z14, running an
electrically dependent engine is dangerous because you have a
single point of failure (the contactor) and zero indication
anything is wrong until your engine dies and you have no means to
turn it back on...
> >
> > Yes, we discussed adding a LV warning to the battery bus....
in other threads about other architecture drawings. It's a good
idea, you should probably do that, or similar like putting the
LR-3 LV sense on the battery bus instead.
> >
> > I've heard many times about how contactor failures are rare,
once followed immediately by a description of how hard they wear
and steps that can be taken to mitigate that... Point is this
single point of failure is easy to side-step with out adding
anything to the system. The reluctance to do so is confusing and
no one seems to want to explain why.
> >
> >
> >
> >
> > Read this topic online here:
> >
> > http://forums.matronics.com/viewtopic.php?p=481560#481560
(http://forums.matronics.com/viewtopic.php?p=481560#481560)
> >
> >
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No it doesn't. Moving the alternator feed line to the battery side
of the contactor doesn't change how the Main DC Pwr Master Switch
turns off the alternator (by opening the ALT FLD circuit).
user9253 wrote:
>
> I explained why. If the alternator "B" lead is connected
directly to the battery, then that "B" lead is always hot no
matter if the field switch is on or off.
Electrically, how is having the B lead after the contactor
different than having it before the contactor if the contactor is
closed? Should the contactor open, and your B lead is on the
battery side, this would have the same effect as opening the ALT
field circuit, thereby shutting off the alternator. Unless I'm
radically misunderstanding how alternators work...


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PostPosted: Wed Jul 11, 2018 11:27 am    Post subject: Re: Z-* Question Reply with quote

So the reasoning is that having an always-hot B lead is more dangerous than the single point failure of the battery contactor? If I'm finally getting that point?

Is sparking of a severed B lead the only concern, or is there something else about having the alternator always hot that is no bueno? How long is that 10 AWG run from the AUX ALT? Or the 4 AWG run from the main battery to the contactor, it doesn't have an *?


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PostPosted: Wed Jul 11, 2018 11:28 am    Post subject: Z-* Question Reply with quote

At 01:47 PM 7/11/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com>


Rocketman1988 wrote:
> I do not see the Z-14 as dangerous as drawn for my EFII aircraft. The ECUs can be split between the busses, the fuel pumps can be split and the injector supply will be come from a buss powered by both batteries through a diode bridge.
>
> There is no possible way to make any system 100% reliable; if you drill down far enough, you can't always find a serious failure that will compromise the system. The point is risk mitigation...


Fair enough, I just see the architecture as-drawn to have a pretty serious single point of failure for electronically dependent engines. As it can occur with no notice to the pilot that something has happened, and no way to provide power to the bits that need it once your engine shuts off. The reluctance to acknowledge this is perplexing.

I don't think anyone is failing to acknowledge
anything. You have hypothesized a suite
of hardware that is not illustrated in Z-14.

As published, Z-14 purports to show that
redundant systems can improve on system
reliability by feeding them from separate
power systems . . . where it has been
judged that no single failure puts the
aircraft at risk.

If some primary component is not backed
up with a secondary -and- assuming that it
has only one feed point for power,
Z-14 offers no advice and the system
may benefit from some adjustments.

If an alternator feed is moved to the
battery (like 100% of cars) then the
regulator supply and voltage sense
must also be moved to the battery side
of the contactor as well. From a
performance perspective, there's nothing
wrong with it . . . and it would mitigate
the failed contactor scenario.

The only down side is that the b-lead
is hot all the time. This has post
crash safety implications and maintenance
implications (be sure to unhook battery(-)
before turning wrenches under the cowl
just like you do on your car.


Bob . . .


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Location: Riley TWP Michigan

PostPosted: Wed Jul 11, 2018 11:39 am    Post subject: Re: Z-* Question Reply with quote

If you look in the very bottom left corner of Z-14 at the aux battery bus, there are secondary ignition and secondary fuel pump fuses. So there is no single point of failure. If the main battery completely shorts out and dies, the engine keeps running because it will get electricity from the aux battery and aux alternator.
It might be confusing because the aux bus is drawn with part of it horizontal and part of it vertical.


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PostPosted: Wed Jul 11, 2018 11:42 am    Post subject: Re: Z-* Question Reply with quote

BMC_Dave wrote:
Rocketman1988 wrote:
I do not see the Z-14 as dangerous as drawn for my EFII aircraft. The ECUs can be split between the busses, the fuel pumps can be split and the injector supply will be come from a buss powered by both batteries through a diode bridge.

There is no possible way to make any system 100% reliable; if you drill down far enough, you can't always find a serious failure that will compromise the system. The point is risk mitigation...


Fair enough, I just see the architecture as-drawn to have a pretty serious single point of failure for electronically dependent engines. As it can occur with no notice to the pilot that something has happened, and no way to provide power to the bits that need it once your engine shuts off. The reluctance to acknowledge this is perplexing.


Ok, where specifically is the issue? The essentials will be powered by a buss supplied by BOTH batteries through a diode bridge. So:

one contractor fails > engine keeps running
one alternator fails > engine keeps running
one battery fails > engine keeps running

If the essentials include a fuel pump and ECU then:

two alternators and 1 battery fail > engine keeps running.

I have intentionally left the EFIS and radios from this discussion, focusing on only the engine.

Short of a combined multiple failure > engine keeps running.

Please explain your how the Z-14 as drawn has a single point of failure...


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BMC_Dave



Joined: 04 Jul 2018
Posts: 17

PostPosted: Wed Jul 11, 2018 12:00 pm    Post subject: Re: Z-* Question Reply with quote

Rocketman1988 wrote:
BMC_Dave wrote:
Rocketman1988 wrote:
I do not see the Z-14 as dangerous as drawn for my EFII aircraft. The ECUs can be split between the busses, the fuel pumps can be split and the injector supply will be come from a buss powered by both batteries through a diode bridge.

There is no possible way to make any system 100% reliable; if you drill down far enough, you can't always find a serious failure that will compromise the system. The point is risk mitigation...


Fair enough, I just see the architecture as-drawn to have a pretty serious single point of failure for electronically dependent engines. As it can occur with no notice to the pilot that something has happened, and no way to provide power to the bits that need it once your engine shuts off. The reluctance to acknowledge this is perplexing.


Ok, where specifically is the issue? The essentials will be powered by a buss supplied by BOTH batteries through a diode bridge. So:

one contractor fails > engine keeps running
one alternator fails > engine keeps running
one battery fails > engine keeps running

If the essentials include a fuel pump and ECU then:

two alternators and 1 battery fail > engine keeps running.

I have intentionally left the EFIS and radios from this discussion, focusing on only the engine.

Short of a combined multiple failure > engine keeps running.

Please explain your how the Z-14 as drawn has a single point of failure...


Battery contactor fails, engine keeps running... until?


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BMC_Dave



Joined: 04 Jul 2018
Posts: 17

PostPosted: Wed Jul 11, 2018 12:04 pm    Post subject: Re: Z-* Question Reply with quote

user9253 wrote:
If you look in the very bottom left corner of Z-14 at the aux battery bus, there are secondary ignition and secondary fuel pump fuses. So there is no single point of failure. If the main battery completely shorts out and dies, the engine keeps running because it will get electricity from the aux battery and aux alternator.
It might be confusing because the aux bus is drawn with part of it horizontal and part of it vertical.


Aren't those two separate buses? But yes I did miss the aux FP and IGN. So now at least you have a means to restore engine power once it stops after nothing tells you your main bat has run down completely. Unless you added the aforementioned low voltage warning that isn't indicated on the drawing.


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ceengland7(at)gmail.com
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PostPosted: Wed Jul 11, 2018 2:37 pm    Post subject: Z-* Question Reply with quote

On 7/11/2018 3:04 PM, BMC_Dave wrote:
Quote:

user9253 wrote:
> If you look in the very bottom left corner of Z-14 at the aux battery bus, there are secondary ignition and secondary fuel pump fuses. So there is no single point of failure. If the main battery completely shorts out and dies, the engine keeps running because it will get electricity from the aux battery and aux alternator.
> It might be confusing because the aux bus is drawn with part of it horizontal and part of it vertical.

Aren't those two separate buses?

Yes; driving two separate engine controllers (ignitions). If the main

contactor fails, and you fly the plane to main battery depletion, the
2nd engine controller keeps the engine running. You'll surely know you
have a problem the next time you try to start the plane, even if you've
managed to miss all the signs up to that point.

As everyone keeps saying, the Z figures are templates; *not* finished
schematics that can't be adjusted to fit individual needs. If you're
running a single ignition controller, fed by the battery bus, and if,
overall, you like Z-14 for your purposes, then add low voltage
monitoring to the battery bus. Wouldn't that solve your issue of
undetected contactor failure? If you like moving the B lead to the
battery bus, then add a contactor to the B lead so it can be interrupted
when the a/c is powered down (crash & maintenance protection). Or, if
you're comfortable with the B lead being always hot, and you're aware of
the implications, then hook it up that way, and move your high/low
voltage protection/monitoring to the battery bus.

Charlie

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nuckolls.bob(at)aeroelect
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PostPosted: Wed Jul 11, 2018 3:10 pm    Post subject: Z-* Question Reply with quote

At 03:04 PM 7/11/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com>


user9253 wrote:
> If you look in the very bottom left corner of Z-14 at the aux battery bus, there are secondary ignition and secondary fuel pump fuses. So there is no single point of failure. If the main battery completely shorts out and dies, the engine keeps running because it will get electricity from the aux battery and aux alternator.
> It might be confusing because the aux bus is drawn with part of it horizontal and part of it vertical.


Figure 17-5 in the 'Connection is accompanied by
a narrative describing the philosophy behind
Z-14.

The idea was to craft two, independent systems
that could be used in tandem for some flight
conditions:


[img]cid:.0[/img]


A cross-feed contactor could be closed during engine
cranking to offer better starter performance. All
normal ops are conducted with the cross-feed open.

If an alternator is lost, the cross-feed contactor
can be closed to share power offered by the remaining
alternator. A feeder off any of the four busses has
access to four power sources. This means that no
endurance bus is needed.

When electrically dependent power plants are
fitted with redundant sub-systems, then those
pairs are distributed between the two battery
busses.

With the exception of battery contactor loss, it is
exceedingly unlikely that any battery bus becomes
un-powered . . . and only after that battery
is depleted.

The only time that condition elevates risk is when a
non-redundant power plant subsystem is powered from
that bus.

This discussion underscores the value of doing
the load analysis for various flight conditions
combined with the FMEA to ensure power
distribution to accessories needed for comfortable
termination of flight.


Bob . . .


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jonlaury



Joined: 06 Nov 2006
Posts: 324

PostPosted: Thu Jul 12, 2018 7:31 am    Post subject: Re: Z-* Question Reply with quote

BMC_Dave wrote:
It almost feels like I'm being intentionally gaslit, I'll try again. ... (snip)


For the etymologically curious:

"The original (meaning) stems from 1938 stage play Gas Light and the dimming of the gas lights in the house that happened when the husband was using the gas lights in the flat above while searching for the jewels belonging to a woman whom he had murdered. The wife correctly notices the dimming lights and discusses it with her husband, but he insists that she merely imagined a change in the level of illumination."


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