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Figure Z-13/8 with Dual EI (non-P/Emag)

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dilandl

Joined: 28 Dec 2007
Posts: 7
Location: Madison Alabama

Posted: Tue Jan 08, 2008 7:14 pm Post subject: Figure Z-13/8 with Dual EI (non-P/Emag)

Let me start off with stating that I absolutely agree with Bob's

statement about Z-13 - "I can deduce no other configuration that

delivers more value".  Use of the self powered Pmag for one of the

ignitions should ensure that the big fan keeps turning regardless of

what the rest of the electrical system is up to.  But what if you want

to use something other than a Pmag?  Lets say dual Lightspeeds or

something else?



Now I know that these would both be attached to the battery buss so they

are independent of the battery contactor, and the backup SD-8 and

battery could carry them after failure of the primary alternator.  I

would agree that this is probably enough.  But there is still one

failure mode, however remote, that could give a problem - battery

failing open, battery failing short, battery cable falling off, etc.

Now I know that this is exceeding unlikely but the probability is not

zero.  If I understand things correctly, the main alternator

could/would?  fail due to the "missing" battery and since the SD-8

backup was off line, both ignition systems would quit.  Depending on if

the SD-8 was wired according to Z-25 (self exciting) and the prop was

still turning, you perhaps could get things going again but it might get

tense for awhile.



Here's an idea:



Incorporate the self exciting feature of Z-25 into Z-13/8 to guarantee

that the SD-8 was up and running even without a preflight check.  Then,

provide the power feed to one of the ignitions from the junction of the

two steering diodes used  to provide power to the Z-25 OV relay (the

diodes might have to be up-sized for higher current).  Under normal

operation, this ignition would get its feed through the battery buss

connected diode.  If/when the SD-8 output voltage exceeded the normal

buss voltage, the SD-8 would carry the load.  Most importantly, the

ignition would be instantly "on" the SD-8 after any other failure of the

electrical system causing low (or no) voltage, including the unlikely

departure of the battery.



The only problem I see with this arrangement is that this ignition

system would not be protected from an SD-8 system over voltage event.

This might not be an issue with the Lightspeed which supposedly is good

from 4-35V but could be with other systems.



So,  am I totally out to lunch here?  Am I attempting to solve a

non-problem?  What do you think?

Dan Langhout

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_________________
Dan Langhout
Madison, AL
RV-7 in progress

dilandl

Joined: 28 Dec 2007
Posts: 7
Location: Madison Alabama

Posted: Wed Jan 09, 2008 1:59 am Post subject: Figure Z-13/8 with Dual EI (non-P/Emag)

Let me start off with stating that I absolutely agree with Bob's 

statement about Z-13 - "I can deduce no other configuration that 

delivers more value".  Use of the self powered Pmag for one of the 

ignitions should ensure that the big fan keeps turning regardless of 

what the rest of the electrical system is up to.  But what if you want 

to use something other than a Pmag?  Lets say dual Lightspeeds or 

something else?



Now I know that these would both be attached to the battery buss so they 

are independent of the battery contactor, and the backup SD-8 and 

battery could carry them after failure of the primary alternator.  I 

would agree that this is probably enough.  But there is still one 

failure mode, however remote, that could give a problem - battery 

failing open, battery failing short, battery cable falling off, etc.  

Now I know that this is exceeding unlikely but the probability is not 

zero.  If I understand things correctly, the main alternator 

could/would?  fail due to the "missing" battery and since the SD-8 

backup was off line, both ignition systems would quit.  Depending on if 

the SD-8 was wired according to Z-25 (self exciting) and the prop was 

still turning, you perhaps could get things going again but it might get 

tense for awhile.



Here's an idea:



Incorporate the self exciting feature of Z-25 into Z-13/8 to guarantee 

that the SD-8 was up and running even without a preflight check.  Then, 

provide the power feed to one of the ignitions from the junction of the 

two steering diodes used  to provide power to the Z-25 OV relay (the 

diodes might have to be up-sized for higher current).  Under normal 

operation, this ignition would get its feed through the battery buss 

connected diode.  If/when the SD-8 output voltage exceeded the normal 

buss voltage, the SD-8 would carry the load.  Most importantly, the 

ignition would be instantly "on" the SD-8 after any other failure of the 

electrical system causing low (or no) voltage, including the unlikely 

departure of the battery.



The only problem I see with this arrangement is that this ignition 

system would not be protected from an SD-8 system over voltage event.  

This might not be an issue with the Lightspeed which supposedly is good 

from 4-35V but could be with other systems.



So,  am I totally out to lunch here?  Am I attempting to solve a 

non-problem?  What do you think?

Dan Langhout

- 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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_________________
Dan Langhout
Madison, AL
RV-7 in progress

nuckolls.bob(at)cox.net
Guest

Posted: Wed Jan 09, 2008 2:20 am Post subject: Figure Z-13/8 with Dual EI (non-P/Emag)

At 08:34 PM 1/8/2008 -0600, you wrote:



 	  Quote: 	
		  



Let me start off with stating that I absolutely agree with Bob's

statement about Z-13 - "I can deduce no other configuration that

delivers more value".  Use of the self powered Pmag for one of the

ignitions should ensure that the big fan keeps turning regardless of

what the rest of the electrical system is up to.  But what if you want

to use something other than a Pmag?  Lets say dual Lightspeeds or

something else?



Now I know that these would both be attached to the battery buss so they

are independent of the battery contactor, and the backup SD-8 and

battery could carry them after failure of the primary alternator.  I

would agree that this is probably enough.  But there is still one

failure mode, however remote, that could give a problem - battery

failing open, battery failing short, battery cable falling off, etc.

Now I know that this is exceeding unlikely but the probability is not

zero.  If I understand things correctly, the main alternator

could/would?  fail due to the "missing" battery and since the SD-8

backup was off line, both ignition systems would quit.


	


   no, an alternator once running will continue to run

   unless hit with a transient load (big landing lights,

   landing gear pump motor, etc) that exceeds nameplate

   rating. Then it MIGHT stall . . . but I'm hearing that

   many alternators will self excite at the speeds we

   turn them on the front of a Lycoming. So no, loss of

   battery is not automatically a dark-panel situation.



 	  Quote: 	
		     Depending on if

the SD-8 was wired according to Z-25 (self exciting) and the prop was

still turning, you perhaps could get things going again but it might get

tense for awhile.



Here's an idea:



Incorporate the self exciting feature of Z-25 into Z-13/8 to guarantee

that the SD-8 was up and running even without a preflight check.


	


   If you incorporate the OV relay that opens the AC windings

   (preferred method) then the SD-8 comes up only after being

   turned ON at the panel.



 	  Quote: 	
		     Then,

provide the power feed to one of the ignitions from the junction of the

two steering diodes used  to provide power to the Z-25 OV relay (the

diodes might have to be up-sized for higher current).  Under normal

operation, this ignition would get its feed through the battery buss

connected diode.  If/when the SD-8 output voltage exceeded the normal

buss voltage, the SD-8 would carry the load.  Most importantly, the

ignition would be instantly "on" the SD-8 after any other failure of the

electrical system causing low (or no) voltage, including the unlikely

departure of the battery.



The only problem I see with this arrangement is that this ignition

system would not be protected from an SD-8 system over voltage event.

This might not be an issue with the Lightspeed which supposedly is good

from 4-35V but could be with other systems.



So,  am I totally out to lunch here?  Am I attempting to solve a

non-problem?  What do you think?


	


    Lost of a well maintained RG battery (or even a flooded battery)

    is so remote that I've never seen this scenario considered

    in a failure mode effects analysis. It's sorta like worrying

    about prop bolts failing. You're probably 100x

    more likely to suffer an open battery contactor due to wiring

    or contactor failure . . . this is why Z-13/8 was crafted in the

    two-layer philosophy wherein the battery contactor is not needed

    for operation of the backup alternator.



    The "cleaner" approach to addressing this concern is to

    avoid electrical system dependent ignition systems;

    install one or two p-mags . . .



    The most likely loss of battery scenario will hinge on failed

    fasteners (over or under torqued) and this can happen ANYWHERE

    in the system, including the feed to the battery bus. Craftsmanship

    is the best prophylactic against such losses . . . just like

    putting proper torque on the prop bolts.



    Bob . . .

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