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Z diagrams and fuseable links

 
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Jekyll



Joined: 22 Feb 2006
Posts: 44

PostPosted: Mon Mar 20, 2006 3:11 pm    Post subject: Z diagrams and fuseable links Reply with quote

I'm planning my electrical system and am intending to use a cludge of the Z-13/8 and Z-12. Basically, I'm deleting the SD-20 circuits from the Z-12 and inserting the SD-8 circuitry from the Z-13/8. Said another way, my intent is to use the Z13/8 but substituting the B&C VR (LRC3-14) for the VR shown. I'm using an E-Mag/P-Mag combination. I thought the remainder would be identical but close examination shows some differences (other than the ignition) which I don't understand.

a. The E-Bus alternate feed in Z-13/8 has a fuseable link and a 7A fuse but the Z-12 has just the fuse. Why the difference between the drawings? Why have both a fuseable link and a fuse in the same wire? I thought thier purpose and function were the same.

b. The Z-13/8 has a fuseable link and a 5 amp pullable CB between the main bus and the DC master power switch. The Z-12 just has the CB. Why the difference and should I use the fuseable link or just the CB?

c. The Z-13/8 indicates the E-bus and the main bus should be no more than 6 inches apart. Am I to read that as no more than 12 inches because of the isolation diode (6 inch max on each side of the diode) or should it be a combined total of 6 inches? The Z-12 doesn't identify this requirment. Should the 2 Z figures be the same in this regard and if not, which should I use (6 inches each or in total)?

d. The avionics ground bus shows a connection to the instrument panel ground bus indicated as 5X20AWG. I'm thinking this indicates a ground connection based on 5 seperate 20 AWG wires to individual faston tabs between the busses. Please confirm or correct my read on this.

Thanks

Jekyll


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nuckollsr(at)cox.net
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PostPosted: Mon Mar 20, 2006 6:47 pm    Post subject: Z diagrams and fuseable links Reply with quote

At 03:11 PM 3/20/2006 -0800, you wrote:

Quote:


I'm planning my electrical system and am intending to use a cludge of the
Z-13/8 and Z-12. Basically, I'm deleting the SD-20 circuits from the Z-12
and inserting the SD-8 circuitry from the Z-13/8. Said another way, my
intent is to use the Z13/8 but substituting the B&C VR (LRC3-14) for the
VR shown. I'm using an E-Mag/P-Mag combination. I thought the remainder
would be identical but close examination shows some differences (other
than the ignition) which I don't understand.

How does figure Z-13/8 fall short of your design goals?
I presume you understand that if you close the master
contactor during main alternator inop operations that
you have the same functionality as replacing the SD-20
with an SD-8 in Z-12 . . .

However, when wired as Z-13, you can continue flight
to airport of intended destination with minimal loads
thus saving the battery for approach to landing by reclosing
the master contactor and powering up everything you need
knowing that the battery's full capacity + SD8 output
is available for completion of flight.

I don't understand what you want to achieve with the
architecture you've suggested.
Quote:
a. The E-Bus alternate feed in Z-13/8 has a fuseable link and a 7A fuse
but the Z-12 has just the fuse. Why the difference between the drawings?
Why have both a fuseable link and a fuse in the same wire? I thought thier
purpose and function were the same.

Sorta . . . the operating time constant between fuses and fusible links
could not be further apart. Circuit breakers reside in between.
Sizing of fuses, breakers, wire and choices for style of
protective devices are all up to you. When you see protection
at both ends of a wire, it suggests that their are sources
of energy that put the wire at risk from either end.

Quote:
b. The Z-13/8 has a fuseable link and a 5 amp pullable CB between the main
bus and the DC master power switch. The Z-12 just has the CB. Why the
difference and should I use the fuseable link or just the CB?

I'll suggest you review the fusible link discussion
at

http://aeroelectric.com/articles/fuselink/fuselink.html


Quote:
c. The Z-13/8 indicates the E-bus and the main bus should be no more than
6 inches apart. Am I to read that as no more than 12 inches because of the
isolation diode (6 inch max on each side of the diode) or should it be a
combined total of 6 inches? The Z-12 doesn't identify this requirment.
Should the 2 Z figures be the same in this regard and if not, which should
I use (6 inches each or in total)?


There are no requirements, only recommendations based on
carry-overs and rules-of-thumb from the certified world.
The rule-of-thumb for leaving a wire "unprotected" is 6"
of length. If your own thumb is longer, feel free.
If you're not comfortable/conversant with the tradeoffs
for selection of protection, go for breakers/fuses sized
for your particular load analysis. Fusible links are limited
use devices and not universal replacements for more
conventional device.
Quote:
d. The avionics ground bus shows a connection to the instrument panel
ground bus indicated as 5X20AWG. I'm thinking this indicates a ground
connection based on 5 seperate 20 AWG wires to individual faston tabs
between the busses. Please confirm or correct my read on this.

Yes, this is one option. See Figure 18-17 in:

http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf

You can use multiple pins within the bus connector or
take a couple of fatter from the bus to firewall ground
block.


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Jekyll



Joined: 22 Feb 2006
Posts: 44

PostPosted: Mon Mar 20, 2006 7:57 pm    Post subject: Re: Z diagrams and fuseable links Reply with quote

nuckollsr(at)cox.net wrote:
At 03:11 PM 3/20/2006 -0800, you wrote:

How does figure Z-13/8 fall short of your design goals?
I presume you understand that if you close the master
contactor during main alternator inop operations that
you have the same functionality as replacing the SD-20
with an SD-8 in Z-12 . . .


Well, I think I said that 13/8 is using a generic Ford VR and that I looking at using the B&C VR part number LRC3-14. In looking at 13/8 and 12, I at first thought the only difference in the main alternator wiring is that the crow bar and low voltage monitoring portions depicted in the 13/8 are internal to the B&C VR used on the Z-12. But then I noticed subtle differences in the form of the fuseable links I mentioned.

I'm no genius at this stuff so I bought your book and use your site for assistance. Though I'm a babe in the woods with wiring airplanes, the main alternator circuitry and the logic flow between the e-bus, main bus, bat bus and instrument bus appear to be the same. This causes me to wonder why the differences I mentioned exist namely the fuseable link between the e bus and switch, the fuseable link between the main bus and the alt CB. With the similarities between the 2 drawings, I would have expected the same callouts in these areas.

So- why fuseable links in one and not the other? I'm not critisizing your designs, just trying to understand so that I can wire my bird with the confidence that comes from understanding.

Jekyll


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Bill Schlatterer



Joined: 09 Jan 2006
Posts: 195

PostPosted: Mon Mar 20, 2006 9:15 pm    Post subject: Z diagrams and fuseable links Reply with quote

Bob, your original Z13 from a couple of years back used the LRC3-14
regulator but recently you pulled that one and substituted a diagram using
the Ford Regulator. I understood Jekyll to say that he was using the Z13
diagram but needed to pull the regulator circuit from Z12 which you still
show with the LRC3-14. Thus the blend of Z13 and Z12. I have an old copy
of the original Z13 with the B&C regulator if that would help!

If I were to ask you for my perfect Z13 it would be the Z13/8 with B&C
regulator and one P-Mag,... But then you always said "they are just
architecture examples, modify as needed". Smile

Thanks for all your help!

Bill S
7a wiring

--


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blackoaks(at)gmail.com
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PostPosted: Wed Mar 22, 2006 2:41 pm    Post subject: Z diagrams and fuseable links Reply with quote

<snip> When you see protection
at both ends of a wire, it suggests that their are sources
of energy that put the wire at risk from either end.
<snip>

Bob,
This brings up another question. I have a Lancair ES and the weight and
balance requires the batteries to be aft of the baggage compartment. I have
the battery contactor within 6 inches of the battery but then have about a
12 foot run up to the main bus. If I need to have the battery contactor in
the rear to keep from having a long 'hot' wire why don't I need something
at the front end to keep the alternator from making the long wire 'hot' from
the other end?

--
John McMahon
Lancair Super ES


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klehman(at)albedo.net
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PostPosted: Wed Mar 22, 2006 7:14 pm    Post subject: Z diagrams and fuseable links Reply with quote

I think because the long wire is thick enough to not overheat from max
alternator output.
A 40 amp alternator can't put much more than 40 amps into the wire and
it is sized to handle that. A battery can put out many hundreds of amps
and overheat that wire. Remember overcurrent protection is only to
prevent overheating of the wire. A fuse won't shutdown something like a
high resistance arcing short to ground that draws less current than the
fuse rating. Hopefully you'd also be able to shut down the alternator if
you were experiencing smoke or obvious electrical distress.
Ken

John McMahon wrote:

Quote:


<snip> When you see protection
at both ends of a wire, it suggests that their are sources
of energy that put the wire at risk from either end.
<snip>

Bob,
This brings up another question. I have a Lancair ES and the weight and
balance requires the batteries to be aft of the baggage compartment. I have
the battery contactor within 6 inches of the battery but then have about a
12 foot run up to the main bus. If I need to have the battery contactor in
the rear to keep from having a long 'hot' wire why don't I need something
at the front end to keep the alternator from making the long wire 'hot' from
the other end?

--
John McMahon
Lancair Super ES




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