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Z-* Question
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Rocketman1988



Joined: 21 Jun 2012
Posts: 57

PostPosted: Sat Jul 07, 2018 5:45 am    Post subject: Z-* Question Reply with quote

I am using a Z-14 based system.

I have a question on the alternator B leads.

Is there a advantage/disadvantage to connecting them to the BAT side of the contactor rather than the switched side? It appears that you could still isolate the battery from the alternator using the alternator field switch and in the event of a failed open contractor, the alternator could still feed the battery...

Just wondering...


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Mauledriver(at)nc.rr.com
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PostPosted: Sat Jul 07, 2018 7:33 am    Post subject: Z-* Question Reply with quote

I'm thinking that why would one want the alt to feed the Batt in the
case of a failed contactor - the rest of the system is offline at that
point, no?

On 7/7/2018 9:45 AM, Rocketman1988 wrote:
Quote:


I am using a Z-14 based system.

I have a question on the alternator B leads.

Is there a advantage/disadvantage to connecting them to the BAT side of the contactor rather than the switched side? It appears that you could still isolate the battery from the alternator using the alternator field switch and in the event of a failed open contractor, the alternator could still feed the battery...

Just wondering...


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=481467#481467




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rnjcurtis(at)charter.net
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PostPosted: Sat Jul 07, 2018 8:04 am    Post subject: Z-* Question Reply with quote

If you have an electrically dependent engine it should run off the battery buss and not through the contactor. Therefore if you put power to the battery you will have that energy available to keep the engine running longer

Roger
-------- Original message --------
From: Bill Watson <Mauledriver(at)nc.rr.com>
Date: 07/07/2018 11:33 (GMT-05:00)
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Z-* Question

--> AeroElectric-List message posted by: Bill Watson <Mauledriver(at)nc.rr.com>

I'm thinking that why would one want the alt to feed the Batt in the
case of a failed contactor - the rest of the system is offline at that
point, no?

On 7/7/2018 9:45 AM, Rocketman1988 wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>

I am using a Z-14 based system.

I have a question on the alternator B leads.

Is there a advantage/disadvantage to connecting them to the BAT side of the contactor rather than the switched side? It appears that you could still isolate the battery from the alternator using the alternator field switch and in the event of a failed open contractor, the alternator could still feed the battery...

Just wondering...


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=481467#481467




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Rocketman1988



Joined: 21 Jun 2012
Posts: 57

PostPosted: Sat Jul 07, 2018 8:38 am    Post subject: Re: Z-* Question Reply with quote

That was my thought, too. If the contactor were to fail OPEN, the alternator would still be able to feed the battery. The battery buss would then be powered as long as the engine was running.

You also retain the ability to isolated the battery from the alternator using the field switch.

It seems like a viable change to the Z-* systems. I posted the question because the Z-* schematics were drawn with the alternator feeding the switched side of the contactor. There must have been a reason...

Maybe Bob can weigh in...am I missing something?


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user9253



Joined: 28 Mar 2008
Posts: 1276
Location: Riley TWP Michigan

PostPosted: Sat Jul 07, 2018 1:41 pm    Post subject: Re: Z-* Question Reply with quote

If the alternator B lead connects directly to the battery and the battery contactor fails, then how does the alternator field get powered? The alternator quits. Now the main power bus has lost both sources of power. It is better to wire the aircraft with a proven, time tested design.
If there is smoke in the cockpit or if a forced landing is imminent, the pilot may want to shut off all electrical power at the source. It is not desirable to have the "B" lead arcing and sparking when gasoline is leaking after accident impact.


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Rocketman1988



Joined: 21 Jun 2012
Posts: 57

PostPosted: Sat Jul 07, 2018 6:00 pm    Post subject: Re: Z-* Question Reply with quote

Well, the alternator could get power from the battery buss...

Anyway, I am using a modified Z-14 for use with EFII systems. The essential buss will be powered from both batteries through a schottky diode bridge...


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PostPosted: Tue Jul 10, 2018 7:02 am    Post subject: Z-* Question Reply with quote

At 11:38 AM 7/7/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>

That was my thought, too. If the contactor were to fail OPEN, the alternator would still be able to feed the battery. The battery buss would then be powered as long as the engine was running.

You also retain the ability to isolated the battery from the alternator using the field switch.

I advise caution about 'tweaking' the z-figures
based on some notions of dealing with failures,
especially rare ones, that require crew to
(1) notice that a failure has occurred, (2) diagnose
the failure and (3) take low risk remedial action.
Be especially wary of the possibility that a
tweak may create a new, unconsidered failure
mode.

The first duty of crew is fly the airplane,
navigate to a low risk termination of flight,
communicate in your 'spare' time and LEAVE THE
TOOLBOX on the ground.

The Z-figures evolved out of nearly a century
of lessons learned. In 20 years of sifting
and adapting here on the List, the architectures
have demonstrated low risk performance while
minimizing the need to diagnose in flight . . .

I recall how a perfectly good L1011 full of passengers
was flown into the Florida swamps by a crew distracted with
diagnosis on a burned out light bulb while
warning squawks and beeps were going on all
around them.

These discussions are GOOD exercises that go to
achieving understanding of how a system works
along with confidence in having minimized risk
while REDUCING pilot workload when things do
go TU.




Bob . . .


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BMC_Dave



Joined: 04 Jul 2018
Posts: 17

PostPosted: Tue Jul 10, 2018 8:09 am    Post subject: Re: Z-* Question Reply with quote

I get the cautions about making changes, but would this one not be prudent?

I understand contactor failures are rare, but it is also said they wear pretty rough in-service. So why not remove a possible failure mode where you don't realize something is wrong until your engine quits?


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PostPosted: Tue Jul 10, 2018 10:06 am    Post subject: Z-* Question Reply with quote

At 11:09 AM 7/10/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com>

Appears to be the same question I raised here: http://forum.matronics.com/viewtopic.php?t=16770059

I get the cautions about making changes, but would this one not be prudent?

I understand contactor failures are rare, but it is also said they wear pretty rough in-service. So why not remove a possible failure mode where you don't realize something is wrong until your engine quits?

Okay, recite the narrative for any particular failure.
I presume we're talking about Z-14. How would any
single failure put engine ops at risk?



Bob . . .


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BMC_Dave



Joined: 04 Jul 2018
Posts: 17

PostPosted: Tue Jul 10, 2018 2:24 pm    Post subject: Re: Z-* Question Reply with quote

nuckolls.bob(at)aeroelect wrote:
At 11:09 AM 7/10/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85>

Appears to be the same question I raised here: http://forum.matronics.com/viewtopic.php?t=16770059

I get the cautions about making changes, but would this one not be prudent?

I understand contactor failures are rare, but it is also said they wear pretty rough in-service. So why not remove a possible failure mode where you don't realize something is wrong until your engine quits?

Okay, recite the narrative for any particular failure.
I presume we're talking about Z-14. How would any
single failure put engine ops at risk?


Bob . . .


I amended that because while I may have been thinking about it in my post I didn't actually discuss it. In any case, referring to Z-14 say the battery contactor opens in flight. Now the main battery bus is disconnected from the alternator, and in this case you have no alternative means to connect it to either alternator, so hopefully flight-critical systems aren't dependent on it.

Additionally, you have no warnings that this has occured.


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PostPosted: Tue Jul 10, 2018 3:44 pm    Post subject: Z-* Question Reply with quote

On 10/07/2018 6:24 PM, BMC_Dave wrote:
Quote:

nuckolls.bob(at)aeroelect wrote:
> At 11:09 AM 7/10/2018, you wrote:
>
>>
>>
>> Appears to be the same question I raised here: http://forum.matronics.com/viewtopic.php?t=16770059 (http://forum.matronics.com/viewtopic.php?t=16770059)
>>
>> I get the cautions about making changes, but would this one not be prudent?
>>
>> I understand contactor failures are rare, but it is also said they wear pretty rough in-service. So why not remove a possible failure mode where you don't realize something is wrong until your engine quits?
> Okay, recite the narrative for any particular failure.
> I presume we're talking about Z-14. How would any
> single failure put engine ops at risk?
>
>
> Bob . . .

I amended that because while I may have been thinking about it in my post I didn't actually discuss it. In any case, referring to Z-14 say the battery contactor opens in flight. Now the main battery bus is disconnected from the alternator, and in this case you have no alternative means to connect it to either alternator, so hopefully flight-critical systems aren't dependent on it.

Additionally, you have no warnings that this has occured.
Actually the low battery bus warning should activate as soon as the

battery stopped charging.

However I want the alternator to keep charging even if the battery
contactor is opened by accident or intent. And I want the alternator
charging voltage and the overvoltage protection to apply to the battery
buss with minimal resistance in the sense circuit to the VR circuit. I
want the engine to keep running if the battery goes open circuit. So I
do consider it prudent (but not essential) to connect the alternator as
directly as possible to the battery for my electrically dependent engine.

Ken
Ken


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PostPosted: Tue Jul 10, 2018 4:09 pm    Post subject: Z-* Question Reply with quote

Quote:
Quote:
Quote:
.

I amended that because while I may have been thinking about it in my post I didn't actually discuss it. In any case, referring to Z-14 say the battery contactor opens in flight. Now the main battery bus is disconnected from the alternator, and in this case you have no alternative means to connect it to either alternator, so hopefully flight-critical systems aren't dependent on it.

Z-14's bus loads have quad redundant
power sources. Every feeder in the
system can get power from multiple
sources. Flight critical loads can be
shared between two systems such that
no single failure puts the flight
at risk.

Quote:
Quote:
Additionally, you have no warnings that this has occured.
Actually the low battery bus warning should activate as soon as the battery stopped charging.

However I want the alternator to keep charging even if the battery contactor is opened by accident or intent. And I want the alternator charging voltage and the overvoltage protection to apply to the battery buss with minimal resistance in the sense circuit to the VR circuit. I want the engine to keep running if the battery goes open circuit. So I do consider it prudent (but not essential) to connect the alternator as directly as possible to the battery for my electrically dependent engine.

What are your engine loads?


Bob . . .


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BMC_Dave



Joined: 04 Jul 2018
Posts: 17

PostPosted: Tue Jul 10, 2018 6:28 pm    Post subject: Re: Z-* Question Reply with quote

yellowduckduo(at)gmail.co wrote:
On 10/07/2018 6:24 PM, BMC_Dave wrote:
Quote:

nuckolls.bob(at)aeroelect wrote:
> At 11:09 AM 7/10/2018, you wrote:
>
>>
>>
>> Appears to be the same question I raised here: http://forum.matronics.com/viewtopic.php?t=16770059 (http://forum.matronics.com/viewtopic.php?t=16770059)
>>
>> I get the cautions about making changes, but would this one not be prudent?
>>
>> I understand contactor failures are rare, but it is also said they wear pretty rough in-service. So why not remove a possible failure mode where you don't realize something is wrong until your engine quits?
> Okay, recite the narrative for any particular failure.
> I presume we're talking about Z-14. How would any
> single failure put engine ops at risk?
>
>
> Bob . . .

I amended that because while I may have been thinking about it in my post I didn't actually discuss it. In any case, referring to Z-14 say the battery contactor opens in flight. Now the main battery bus is disconnected from the alternator, and in this case you have no alternative means to connect it to either alternator, so hopefully flight-critical systems aren't dependent on it.

Additionally, you have no warnings that this has occured.
Actually the low battery bus warning should activate as soon as the

battery stopped charging.

However I want the alternator to keep charging even if the battery
contactor is opened by accident or intent. And I want the alternator
charging voltage and the overvoltage protection to apply to the battery
buss with minimal resistance in the sense circuit to the VR circuit. I
want the engine to keep running if the battery goes open circuit. So I
do consider it prudent (but not essential) to connect the alternator as
directly as possible to the battery for my electrically dependent engine.

Ken
Ken


I don't see anything on the Z14P architecture drawing that would warn you that the main battery bus has been disconnected from the alternator(s)

nuckolls.bob(at)aeroelect wrote:

Z-14's bus loads have quad redundant
power sources. Every feeder in the
system can get power from multiple
sources. Flight critical loads can be
shared between two systems such that
no single failure puts the flight
at risk.


Bob . . .


On Z14P, if the battery contactor opens then anything on the main battery bus will run until the 17AH main battery dies, right? If you have things like say, an electronic ignition, or electric fuel pump, that are required for flight you'd chug along completely unaware of the disconnect until your engine died, correct?


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PostPosted: Wed Jul 11, 2018 4:08 am    Post subject: Z-* Question Reply with quote

>I don't see anything on the architecture drawing that would warn you
that the main battery bus has been disconnected from the alternator(s)

Dave
I think this thread is a worthwhile discussion but I'm not sure exactly
where our miscommunication is.
I had assumed that we all agreed that it was essential to add a means of
incorporating immediate notification if the battery is not charging for
an EFI engine.
To me that means monitoring of the battery buss if the battery buss is
powering the EFI.
There are several ways of doing that over and above anything shown on a
Z figure. But all the low voltage warning devices are expected to
activate when the voltage drops below about 13.5 volts which will happen
as soon as the alternator goes offline.

Don't know if it is a factor for this conversation but folks flying with
a carb, mags, and vacuum instruments will think of low voltage warning
as being important for the avionics buss especially if IFR. Folks with
an electrically dependent engine like me will contend that it is more
important to monitor the battery buss directly. Most of the electrically
dependent engines that I've seen so far are automotive conversions that
often are VFR only so again the battery buss tends to be the important
thing to monitor.

Ken


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user9253



Joined: 28 Mar 2008
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Location: Riley TWP Michigan

PostPosted: Wed Jul 11, 2018 4:36 am    Post subject: Re: Z-* Question Reply with quote

Chances are that a failed battery contactor will result in unstable alternator output voltage that will set off an alarm in the EFIS.
If a failed battery contactor is such a big concern, why not put a relay in parallel with it?
If low battery voltage is a concern, why not install a voltmeter or low voltage warning?
The chances of making a forced landing for some reason are much greater than a battery contactor failing in flight. Wouldn't it be better to have the ability to shut off all electrical power at the source to minimize the chances of a a spark igniting leaking fuel?
If there is smoke in the cockpit, it is desired to be able to shut off all electrical power at the source. Keep always-hot wires as short as possible.


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PostPosted: Wed Jul 11, 2018 6:26 am    Post subject: Z-* Question Reply with quote

Quote:



On Z14P, if the battery contactor opens then anything on the main battery bus will run until the 17AH main battery dies, right? If you have things like say, an electronic ignition, or electric fuel pump, that are required for flight you'd chug along completely unaware of the disconnect until your engine died, correct?

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 . . .


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Joined: 10 Jan 2006
Posts: 1541
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PostPosted: Wed Jul 11, 2018 6:38 am    Post subject: Z-* Question Reply with quote

I am also curious about the concern about the battery contactor. In 40+
years of aircraft owning and piloting I have experienced exactly one
battery contactor develop higher than desired resistance, causing
starter performance issues, but it never failed. For it to open implies
that the energy holding the contactor closed is somehow lost. You would
either need the wire providing the ground to close the contactor to
fail, or the coil in the contactor to suddenly develop an open.
I can see one failing to close when master switch is activated, but
having one fail after closing seems to be a very low risk event.
Kelly

On 7/11/2018 7:25 AM, Robert L. Nuckolls, III wrote:
Quote:
>
> On Z14P, if the battery contactor opens then anything on the main
> battery bus will run until the 17AH main battery dies, right? If you
> have things like say, an electronic ignition, or electric fuel pump,
> that are required for flight you'd chug along completely unaware of
> the disconnect until your engine died, correct?

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 . . .



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kenryan



Joined: 20 Oct 2009
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PostPosted: Wed Jul 11, 2018 7:01 am    Post subject: Z-* Question Reply with quote

With the battery contactor working properly, the voltage at the battery will be "charging voltage" approx. 14 volts. When the battery contactor fails open, the charge will be removed and the voltage at the battery will instantly drop to "battery voltage" approx 13 volts. Therefore, if you are monitoring your voltage at the battery, you will be instantly notified of the contactor failure

On Tue, Jul 10, 2018 at 6:33 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)>


yellowduckduo(at)gmail.co wrote:
> On 10/07/2018 6:24 PM, BMC_Dave wrote:
>
> > 
> >
> >
> >  nuckolls.bob(at)aeroelect wrote:
> > > At 11:09 AM 7/10/2018, you wrote:
> > >   
> > >>
> > >>
> > >>   Appears to be the same question I raised here:  http://forum.matronics.com/viewtopic.php?t=16770059 (http://forum.matronics.com/viewtopic.php?t=16770059)
> > >>
> > >>   I get the cautions about making changes, but would this one not be prudent?
> > >>
> > >>   I understand contactor failures are rare, but it is also said they wear pretty rough in-service. So why not remove a possible failure mode where you don't realize something is wrong until your engine quits?
> > >     Okay, recite the narrative for any particular failure.
> > >     I presume we're talking about Z-14. How would any
> > >     single failure put engine ops at risk?
> > >
> > >   
> > >     Bob . . .
> >
> >  I amended that because while I may have been thinking about it in my post I didn't actually discuss it. In any case, referring to Z-14 say the battery contactor opens in flight. Now the main battery bus is disconnected from the alternator, and in this case you have no alternative means to connect it to either alternator, so hopefully flight-critical systems aren't dependent on it.
> >
> >  Additionally, you have no warnings that this has occured.
> > Actually the low battery bus warning should activate as soon as the
> >
>
> battery stopped charging.
>
> However I want the alternator to keep charging even if the battery
> contactor is opened by accident or intent.  And I want the alternator
> charging voltage and the overvoltage protection to apply to the battery
> buss with minimal resistance in the sense circuit to the VR circuit.  I
> want the engine to keep running if the battery goes open circuit.  So I
> do consider it prudent (but not essential) to connect the alternator as
> directly as possible to the battery for my electrically dependent engine.
>
> Ken
> Ken


I don't see anything on the architecture drawing that would warn you that the main battery bus has been disconnected from the alternator(s)


nuckolls.bob(at)aeroelect wrote:
>
>    Z-14's bus loads have quad redundant
>    power sources. Every feeder in the
>    system can get power from multiple
>    sources. Flight critical loads can be
>    shared between two systems such that
>    no single failure puts the flight
>    at risk.
>

>    Bob . . .


On Z14P, if the battery contactor opens then anything on the main battery bus will run until the 17AH main battery dies, right? If you have things like say, an electronic ignition, or electric fuel pump, that are required for flight you'd chug along completely unaware of the disconnect until your engine died, correct?




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BMC_Dave



Joined: 04 Jul 2018
Posts: 17

PostPosted: Wed Jul 11, 2018 7:18 am    Post subject: Re: Z-* Question Reply with quote

nuckolls.bob(at)aeroelect wrote:
Quote:



On Z14P, if the battery contactor opens then anything on the main battery bus will run until the 17AH main battery dies, right? If you have things like say, an electronic ignition, or electric fuel pump, that are required for flight you'd chug along completely unaware of the disconnect until your engine died, correct?

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?


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Last edited by BMC_Dave on Wed Jul 11, 2018 7:41 am; edited 2 times in total
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BMC_Dave



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PostPosted: Wed Jul 11, 2018 7:34 am    Post subject: Re: Z-* Question Reply with quote

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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