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Z-14 Question

 
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Rocketman1988



Joined: 21 Jun 2012
Posts: 57

PostPosted: Thu Jun 28, 2018 12:22 pm    Post subject: Z-14 Question Reply with quote

All,

I am going to use the Z-14 layout for my RV-10. The -10 has aft mounted batteries, so I will need to run the main buss wires from the back to the front, where all of the electronics are.

My question is: Do these wires need to have individual current limiters on them? The distance from the batteries to the battery buss location is about 8 1/2 feet. I am planning on using #8 AWG wire to feed each respective battery buss.

Thoughts?


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PostPosted: Thu Jun 28, 2018 3:09 pm    Post subject: Z-14 Question Reply with quote

At 03:22 PM 6/28/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>

All,

I am going to use the Z-14 layout for my RV-10. The -10 has aft mounted batteries, so I will need to run the main buss wires from the back to the front, where all of the electronics are.

My question is: Do these wires need to have individual current limiters on them? The distance from the batteries to the battery buss location is about 8 1/2 feet. I am planning on using #8 AWG wire to feed each respective battery buss.

Thoughts?

put the crossfeed contactor on the firewall and use it as
the grand-central-station for fat wires. Then all you
need running back to the batteries is a pair
of cranking feeders. 4AWG would be fine for these
as you'll have the the pair in parallel for
engine cranking.


Bob . . .


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user9253



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

PostPosted: Thu Jun 28, 2018 3:50 pm    Post subject: Re: Z-14 Question Reply with quote

Current limiters should not be used in the start circuit because they will drop the voltage to the starter motor.

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PostPosted: Thu Jun 28, 2018 4:10 pm    Post subject: Z-14 Question Reply with quote

On 6/28/2018 7:08 PM, Robert L. Nuckolls, III wrote:

Quote:
At 03:22 PM 6/28/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com> (Rocketman(at)etczone.com)

All,

I am going to use the Z-14 layout for my RV-10. The -10 has aft mounted batteries, so I will need to run the main buss wires from the back to the front, where all of the electronics are.

My question is: Do these wires need to have individual current limiters on them? The distance from the batteries to the battery buss location is about 8 1/2 feet. I am planning on using #8 AWG wire to feed each respective battery buss.

Thoughts?

put the crossfeed contactor on the firewall and use it as
the grand-central-station for fat wires. Then all you
need running back to the batteries is a pair
of cranking feeders. 4AWG would be fine for these
as you'll have the the pair in parallel for
engine cranking.


Bob . . .

I have a Z-14 in an RV10. Bob's approach sounds great. I like the symmetry. Not having asked the question 10 years ago when laying my Z-14 out, I took a different approach.
I have the Xfeed mounted with the other two contactors back on the battery tray. 2 AWG links them all up. Then I have a single 2AWG lead going to the starter Contactor. The other side has an 8AWG link going forward to one fuse panel (bus) and an 8AWG link going from the starter contactor to the other fuse panel (bus).
The current limiters on mounted on the firewall and protect the lines going from the 2 alternators to the 2 main bus feeds.
I've attached a schematic with the locations of devices implied.
Bill "I love my Z-14" Watson

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Rocketman1988



Joined: 21 Jun 2012
Posts: 57

PostPosted: Thu Jun 28, 2018 5:30 pm    Post subject: Re: Z-14 Question Reply with quote

Thanks! That is pretty much what I am going to do...all three contractors near battery, one #2 to starter solenoid, two #8 battery buss feeders going forward...

I like Bob's idea you, however, the #2 cable was run long ago and I do not think it would be an easy task to remove it...


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PostPosted: Thu Jun 28, 2018 5:57 pm    Post subject: Z-14 Question Reply with quote

On 6/28/2018 7:01 PM, Bill Watson wrote:

Quote:
On 6/28/2018 7:08 PM, Robert L. Nuckolls, III wrote:

Quote:
At 03:22 PM 6/28/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com> (Rocketman(at)etczone.com)

All,

I am going to use the Z-14 layout for my RV-10. The -10 has aft mounted batteries, so I will need to run the main buss wires from the back to the front, where all of the electronics are.

My question is: Do these wires need to have individual current limiters on them? The distance from the batteries to the battery buss location is about 8 1/2 feet. I am planning on using #8 AWG wire to feed each respective battery buss.

Thoughts?

put the crossfeed contactor on the firewall and use it as
the grand-central-station for fat wires. Then all you
need running back to the batteries is a pair
of cranking feeders. 4AWG would be fine for these
as you'll have the the pair in parallel for
engine cranking.


Bob . . .

I have a Z-14 in an RV10. Bob's approach sounds great. I like the symmetry. Not having asked the question 10 years ago when laying my Z-14 out, I took a different approach.
I have the Xfeed mounted with the other two contactors back on the battery tray. 2 AWG links them all up. Then I have a single 2AWG lead going to the starter Contactor. The other side has an 8AWG link going forward to one fuse panel (bus) and an 8AWG link going from the starter contactor to the other fuse panel (bus).
The current limiters on mounted on the firewall and protect the lines going from the 2 alternators to the 2 main bus feeds.
I've attached a schematic with the locations of devices implied.
Bill "I love my Z-14" Watson
Bill,

Your install is obviously working, but it should be noted that your alternator B lead protection should be on the other end. If there's a fault in that wire, it should be big enough to handle everything the alternator can throw at it, but it'll never be big enough to handle everything the battery(s) can throw at it.

FWIW,

Charlie
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Kellym



Joined: 10 Jan 2006
Posts: 1541
Location: Sun Lakes AZ

PostPosted: Thu Jun 28, 2018 6:20 pm    Post subject: Z-14 Question Reply with quote

Having a flying IFR RV-10 myself I question the benefits of dual
batteries along with dual alternators, etc. Almost all EFIS panels these
days offer a backup battery, good for 1 hour or more. I have one for
each of my EFIS screens. Most ship's batteries these days are good for
an hour or more of minimized current. An Ipad can provide hours of
moving map and GPS, and with some extras a nearly full EFIS screen.
I can see if you choose to have dual electronic ignition systems that
then you are vulnerable to lack of electrons for at least one. It seems
to me that the SD-20 alternator for a backup source of power, with a
small, Odessey 680 or less mounted on the firewall should handle any of
those needs. You only need one good sized battery, such as the Odessey
925 mounted in stock rear location, for starter operation.s Or just keep
one magneto for the backup, and eliminate need for dual electric power
sources. You get 85% of the electronic ignition by replacing one mag.
Just my opinion, but I would strive to keep the design as simple as
possible, and avoid having totally dual everything just because you can.
Just thinking your goals might be achieved with a simpler system.
Kelly

On 6/28/2018 6:56 PM, Charlie England wrote:

Quote:
>>
> I have a Z-14 in an RV10. Bob's approach sounds great. I like the
> symmetry. Not having asked the question 10 years ago when laying my
> Z-14 out, I took a different approach.
>
> I have the Xfeed mounted with the other two contactors back on the
> battery tray. 2 AWG links them all up. Then I have a single 2AWG
> lead going to the starter Contactor. The other side has an 8AWG link
> going forward to one fuse panel (bus) and an 8AWG link going from the
> starter contactor to the other fuse panel (bus).
>
> The current limiters on mounted on the firewall and protect the lines
> going from the 2 alternators to the 2 main bus feeds.
>
> I've attached a schematic with the locations of devices implied.
>
> Bill "I love my Z-14" Watson
>
Bill,

Your install is obviously working, but it should be noted that your
alternator B lead protection should be on the other end. If there's a
fault in that wire, it should be big enough to handle everything the
alternator can throw at it, but it'll never be big enough to handle
everything the battery(s) can throw at it.

FWIW,

Charlie



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Rocketman1988



Joined: 21 Jun 2012
Posts: 57

PostPosted: Fri Jun 29, 2018 5:46 am    Post subject: Re: Z-14 Question Reply with quote

Kelly,

Thanks for your opinion. I hesitate posting on these forums due to the “nay sayers” when anything other than the simplest tech from the 50’s is suggested. I have chosen to use a full EFII system and fully accept the additional complexities. I do appreciate your insight on things...

As for the previous post about the B lead current limiters, I would disagree with putting the fuse at the other end as that would place it between the battery and starter.


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Kellym



Joined: 10 Jan 2006
Posts: 1541
Location: Sun Lakes AZ

PostPosted: Fri Jun 29, 2018 6:06 am    Post subject: Z-14 Question Reply with quote

As I said, it is all about the builder's choices. I have too many years
working on type certified airplanes as well as homebuilts, fixing self
induced errors, etc. to be very enamored of new-fangled EFII. My
experience in automotive arena tells me that the incremental
improvements from continuous flow fuel injection that arrived in the
late '50s to single cylinder electronic fuel injection of all but the
latest cars is fairly small..while the current direct injection into the
cylinder has had a much bigger improvement than anything since the
switch from carburetors to fuel injection.
I applaud your willingness to take on the challenge of EFII. When it all
works as advertised, it certainly will make starting easier and may also
help reduce maintenance.
However, I don't believe it justifies having two separate systems of
equal capacity. Still, your choice.
Kelly

On 6/29/2018 6:46 AM, Rocketman1988 wrote:
Quote:


Kelly,

Thanks for your opinion. I hesitate posting on these forums due to the “nay sayers” when anything other than the simplest tech from the 50’s is suggested. I have chosen to use a full EFII system and fully accept the additional complexities. I do appreciate your insight on things...

As for the previous post about the B lead current limiters, I would disagree with putting the fuse at the other end as that would place it between the battery and starter.




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PostPosted: Fri Jun 29, 2018 6:59 am    Post subject: Z-14 Question Reply with quote

Help me here Charlie, I'm not quite following you. The B-lead protection (current limiters) are installed between the Alternator B-lead terminal and main bus line. The battery is not 'behind' the protection and the bus. Rather the battery has no protection between it and the bus fuse block(s).

What am I missing?

Bill

On 6/28/2018 9:56 PM, Charlie England wrote:

Quote:
Bill,

Your install is obviously working, but it should be noted that your alternator B lead protection should be on the other end. If there's a fault in that wire, it should be big enough to handle everything the alternator can throw at it, but it'll never be big enough to handle everything the battery(s) can throw at it.

FWIW,

Charlie

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PostPosted: Fri Jun 29, 2018 7:08 am    Post subject: Z-14 Question Reply with quote

On 6/29/2018 8:46 AM, Rocketman1988 wrote:
Quote:


Kelly,

Thanks for your opinion. I hesitate posting on these forums due to the “nay sayers” when anything other than the simplest tech from the 50’s is suggested. I have chosen to use a full EFII system and fully accept the additional complexities. I do appreciate your insight on things...

As for the previous post about the B lead current limiters, I would disagree with putting the fuse at the other end as that would place it between the battery and starter.
I guess I should have been more specific. The other end of the *wire*;

not the entire path. Look at the wire protection for the main alt, which
is at the hot side of the starter contactor end of the 8 ga wire
(correct). Now look at the protection on the aux alt B lead, at the
alternator end, instead of at the source end, which is the cross-tie
contactor.

When I took another look for this email, I also noticed that the 8 ga
wires feeding both fuse blocks don't have any protection. 'Conventional
wisdom' is that the battery contactor protects the 'fat wires', but
smaller wires need protection.  What I see is 2 ga wires stepping down
in size to 8 ga wires, with no switching (disconnect) and protection at
the start of the 8 ga wires.

That's not a problem, as long as there isn't a problem. Smile

Charlie

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PostPosted: Fri Jun 29, 2018 7:17 am    Post subject: Z-14 Question Reply with quote

Protection devices are to protect *wires*. In our aircraft environments the source of damage to wires is always the battery. Alternator B leads should be sized big enough to handle the max that the alternator can deliver, so they need no protection from the alternator. But the battery can deliver hundreds of amps (sometimes *many hundreds* of amps). The 4 ga and larger stuff can survive long enough to use the master contactor as protection, but smaller stuff runs a big risk of lighting up the insulation if there's no circuit protection.

No protection device on a wire is there to protect the battery.

Charlie

On 6/29/2018 9:58 AM, Bill Watson wrote:

Quote:
Help me here Charlie, I'm not quite following you. The B-lead protection (current limiters) are installed between the Alternator B-lead terminal and main bus line. The battery is not 'behind' the protection and the bus. Rather the battery has no protection between it and the bus fuse block(s).

What am I missing?

Bill

On 6/28/2018 9:56 PM, Charlie England wrote:

Quote:
Bill,

Your install is obviously working, but it should be noted that your alternator B lead protection should be on the other end. If there's a fault in that wire, it should be big enough to handle everything the alternator can throw at it, but it'll never be big enough to handle everything the battery(s) can throw at it.

FWIW,

Charlie

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PostPosted: Fri Jun 29, 2018 7:26 am    Post subject: Z-14 Question Reply with quote

I think Bob refers to my Z-14 in an RV-10 as 'everything including the
kitchen sink'. I other words, a bit too much.

Ten years ago when I started laying out my electrical system, I went
through the Z-schematics and frankly struggled to understand the various
backup scenarios. At one point I started sketching the Z-14 out and
everything became simple and symmetrical (I may have an excess of the
symmetry gene or something). More important, my desire coming into this
project was to have a state of the art panel which I could run for 10-15
even 30 minutes on the ground without worrying about a subsequent engine
start.

The need for this was driven home by 2 previous incidents; one being
flying in to New Orleans less than a year after the big hurricane and
finding myself sitting in my Maule staring at my Garmin 396 waiting for
a break in the usual gulf coast cu-nims. Why couldn't I sit in the FBO
and watch a Nexrad screen? Because it was still under reconstructions,
it lacked resources, and required a longish sprint to get to the
tiedowns. The other involved the Bahamas.

As my design came together, I ended up with (3) GRT HX EFIS screens and
assorted accessories. The GRTs did not have an integrated on/off switch
(or backup batts) and I wasn't interested in adding any. Main power on,
EFISs on; no accidental power-offs or reboots in the soup. Turned out
that those (3) screens are real power hogs, even dimmed down. Even now,
to run them for 30 mins on one Odyssey 680 suggests pulling a fuse on 1
or 2 might be a good idea (not really necessary). It made me question
the need for 3 screens but after encountering a couple of failures after
6 years of operation, it's cool to be able to swap out one of the 2
pilot oriented screens on the ramp at a remote location and fly with
100% of your normally used panel working.

The Z-14 has turned out to be a simple solution for me. I have 2 mags
and no electrically dependent ignition. I have 2 Odyssey 680s. Either
will start the engine, both guarantee it (I was happy to get rid of the
light weight starters in favor of the slow turning but stronger standard
starter). I can run my panel as long as I wish with the engine off.
Came in handy after the Breezy crash at Oshkosh a few years ago caused a
conga line of epic proportions. Etc etc.

I recently lost a voltage regulator. What did it require me to do?
Nothing except keep the x-feed switch on and turn off the non-working
side. No blip in the air, no shortened trip, no precautionary landing.
Flew 2 more legs like that with the same redundancy that most pilots fly
with most of the time.

Bill "I go what I wanted" Watson

On 6/28/2018 10:19 PM, Kelly McMullen wrote:
Quote:

<kellym(at)aviating.com>

Having a flying IFR RV-10 myself I question the benefits of dual
batteries along with dual alternators, etc. Almost all EFIS panels
these days offer a backup battery, good for 1 hour or more. I have one
for each of my EFIS screens. Most ship's batteries these days are good
for an hour or more of minimized current. An Ipad can provide hours of
moving map and GPS, and with some extras a nearly full EFIS screen.
I can see if you choose to have dual electronic ignition systems that
then you are vulnerable to lack of electrons for at least one. It
seems to me that the SD-20 alternator for a backup source of power,
with a small, Odessey 680 or less mounted on the firewall should
handle any of those needs. You only need one good sized battery, such
as the Odessey 925 mounted in stock rear location, for starter
operation.s Or just keep one magneto for the backup, and eliminate
need for dual electric power sources. You get 85% of the electronic
ignition by replacing one mag.
Just my opinion, but I would strive to keep the design as simple as
possible, and avoid having totally dual everything just because you can.
Just thinking your goals might be achieved with a simpler system.
Kelly

On 6/28/2018 6:56 PM, Charlie England wrote:

>>>
>> I have a Z-14 in an RV10. Bob's approach sounds great. I like the
>> symmetry. Not having asked the question 10 years ago when laying
>> my Z-14 out, I took a different approach.
>>
>> I have the Xfeed mounted with the other two contactors back on the
>> battery tray. 2 AWG links them all up. Then I have a single 2AWG
>> lead going to the starter Contactor. The other side has an 8AWG
>> link going forward to one fuse panel (bus) and an 8AWG link going
>> from the starter contactor to the other fuse panel (bus).
>>
>> The current limiters on mounted on the firewall and protect the
>> lines going from the 2 alternators to the 2 main bus feeds.
>>
>> I've attached a schematic with the locations of devices implied.
>>
>> Bill "I love my Z-14" Watson
>>
> Bill,
>
> Your install is obviously working, but it should be noted that your
> alternator B lead protection should be on the other end. If there's a
> fault in that wire, it should be big enough to handle everything the
> alternator can throw at it, but it'll never be big enough to handle
> everything the battery(s) can throw at it.
>
> FWIW,
>
> Charlie
>




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PostPosted: Fri Jun 29, 2018 8:43 am    Post subject: Z-14 Question Reply with quote

I guess I didn't understand the fat wire versus the less-than-fat wire exposure. My take on unprotected main power lines was that they can be run and terminated in robust and simple ways with minimal exposure to chafing, breaching of their insulation or shorting at the terminal ends. With that view in mind, I was thinking of my 8AWG wires as 'fat wires' just as my 2AWG wire is. So I view the 8AWG on the Aux side as a 'fat wire' with robust and simple terminations at the contactor and the fuse block.... with a firewall stud in the path which happens to be part of the current limiter unit. I'm quite confident that those 8AWG runs are simple and safe.

I should note that the 8AWG runs from the current limiter firewall studs to the fuse panels by the copilot's leg are quite short. Putting the current limiter on the Aux side near the x-feed contactor behind the luggage area would have required 2 long runs of 8AWG instead of 1.

I never considered the contactors as any kind of circuit protection. I thought of them as simply switches, switches for high current loads that can conveniently be thrown remotely by small switches. They enable you to manually disconnect a high current line but there's no automatic protection.

Bill

On 6/29/2018 11:18 AM, Charlie England wrote:

Quote:
Protection devices are to protect *wires*. In our aircraft environments the source of damage to wires is always the battery. Alternator B leads should be sized big enough to handle the max that the alternator can deliver, so they need no protection from the alternator. But the battery can deliver hundreds of amps (sometimes *many hundreds* of amps). The 4 ga and larger stuff can survive long enough to use the master contactor as protection, but smaller stuff runs a big risk of lighting up the insulation if there's no circuit protection.

No protection device on a wire is there to protect the battery.

Charlie

On 6/29/2018 9:58 AM, Bill Watson wrote:

Quote:
Help me here Charlie, I'm not quite following you. The B-lead protection (current limiters) are installed between the Alternator B-lead terminal and main bus line. The battery is not 'behind' the protection and the bus. Rather the battery has no protection between it and the bus fuse block(s).

What am I missing?

Bill

On 6/28/2018 9:56 PM, Charlie England wrote:

Quote:
Bill,

Your install is obviously working, but it should be noted that your alternator B lead protection should be on the other end. If there's a fault in that wire, it should be big enough to handle everything the alternator can throw at it, but it'll never be big enough to handle everything the battery(s) can throw at it.

FWIW,

Charlie

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PostPosted: Fri Jun 29, 2018 1:32 pm    Post subject: Z-14 Question Reply with quote

Ah, the joys of trying to communicate via the interwebs. Smile

I'd agree that really short runs (the Aeroelectric 'gold standard' seems to be 6", but I've probably fudged that in a place or two) are low risk. But if that #8 from the right side of the x-feed contactor to the current limiter runs the length of the plane, I'd want protection at the source end. Not sure why moving the protection would require two runs. If the protection is at the contactor, the #8 could run to either fuse block #2, or to the aux alternator B lead, as 'geographically convenient'. Then it would continue to the other component. Electrically identical to what you have now, except the long run (and the short run) of #8 would be protected from the battery. If the current limiter is now on the firewall, the only #8 in that run that's actually protected is between the limiter and the alternator B lead.

I'm not trying to tell you what to do; just wanted to mention a potential vulnerability. If you're comfortable with the design, then run with it. It's obviously been working ok so far. I know I've done a few things that others wouldn't be comfortable with, but I am, with my plane.

FWIW, I have a similar arrangement for my engine bus (electrically dependent alternative engine) to your fuse block #1, with the bus being fed off the hot terminal of the contactor. In my case, it's the master because everything's on the firewall in my plane, but same risk of unprotected #8 wire. I protected it, and both my #8 alternator B leads, by using #12 fuse link wire on the 'battery end' of each #8 wire. Just a 4"-6" long piece of the fuse link wire soldered on the end, with the joint insulated with heat shrink. Then the fuse link gets the terminal that connects to the contactor. The fuse link wire is an 'off the shelf' item available from automotive supply houses; it has built-in insulation to contain the heat if the protection is 'tripped'.

Charlie

On 6/29/2018 11:36 AM, Bill Watson wrote:

Quote:
I guess I didn't understand the fat wire versus the less-than-fat wire exposure. My take on unprotected main power lines was that they can be run and terminated in robust and simple ways with minimal exposure to chafing, breaching of their insulation or shorting at the terminal ends. With that view in mind, I was thinking of my 8AWG wires as 'fat wires' just as my 2AWG wire is. So I view the 8AWG on the Aux side as a 'fat wire' with robust and simple terminations at the contactor and the fuse block.... with a firewall stud in the path which happens to be part of the current limiter unit. I'm quite confident that those 8AWG runs are simple and safe.

I should note that the 8AWG runs from the current limiter firewall studs to the fuse panels by the copilot's leg are quite short. Putting the current limiter on the Aux side near the x-feed contactor behind the luggage area would have required 2 long runs of 8AWG instead of 1.

I never considered the contactors as any kind of circuit protection. I thought of them as simply switches, switches for high current loads that can conveniently be thrown remotely by small switches. They enable you to manually disconnect a high current line but there's no automatic protection.

Bill

On 6/29/2018 11:18 AM, Charlie England wrote:

Quote:
Protection devices are to protect *wires*. In our aircraft environments the source of damage to wires is always the battery. Alternator B leads should be sized big enough to handle the max that the alternator can deliver, so they need no protection from the alternator. But the battery can deliver hundreds of amps (sometimes *many hundreds* of amps). The 4 ga and larger stuff can survive long enough to use the master contactor as protection, but smaller stuff runs a big risk of lighting up the insulation if there's no circuit protection.

No protection device on a wire is there to protect the battery.

Charlie

On 6/29/2018 9:58 AM, Bill Watson wrote:

Quote:
Help me here Charlie, I'm not quite following you. The B-lead protection (current limiters) are installed between the Alternator B-lead terminal and main bus line. The battery is not 'behind' the protection and the bus. Rather the battery has no protection between it and the bus fuse block(s).

What am I missing?

Bill

On 6/28/2018 9:56 PM, Charlie England wrote:

Quote:
Bill,

Your install is obviously working, but it should be noted that your alternator B lead protection should be on the other end. If there's a fault in that wire, it should be big enough to handle everything the alternator can throw at it, but it'll never be big enough to handle everything the battery(s) can throw at it.

FWIW,

Charlie

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PostPosted: Fri Jun 29, 2018 2:43 pm    Post subject: Z-14 Question Reply with quote

At 11:36 AM 6/29/2018, you wrote:
Quote:
I guess I didn't understand the fat wire versus the less-than-fat wire exposure. My take on unprotected main power lines was that they can be run and terminated in robust and simple ways with minimal exposure to chafing, breaching of their insulation or shorting at the terminal ends. With that view in mind, I was thinking of my 8AWG wires as 'fat wires' just as my 2AWG wire is. So I view the 8AWG on the Aux side as a 'fat wire' with robust and simple terminations at the contactor and the fuse block.... with a firewall stud in the path which happens to be part of the current limiter unit. I'm quite confident that those 8AWG runs are simple and safe.

Agreed.

Quote:
I should note that the 8AWG runs from the current limiter firewall studs to the fuse panels by the copilot's leg are quite short. Putting the current limiter on the Aux side near the x-feed contactor behind the luggage area would have required 2 long runs of 8AWG instead of 1.

I never considered the contactors as any kind of circuit protection. I thought of them as simply switches, switches for high current loads that can conveniently be thrown remotely by small switches. They enable you to manually disconnect a high current line but there's no automatic protection.

Correct . . . powers-that-be consider them
'crew controlled protection', i.e. they're
used to disconnect sources of energy to smallest
practical footprint in times of stress . . .
like smoke or . . . short approach to the rocks.

B-lead protection is needed ONLY for the exceedingly
rare instance of shorted alternator diodes so
any such protection is located as close to the
bus/distribution node as practical.

Properly sized b-lead protection CANNOT be
opened by alternator energy.

Having recited the legacy philosophy I'll
note that all three of the vehicles in my
driveway ranging from 87GMC to 2006KIA
ALL connect the b-lead directly to the battery . . .
not even fusible links. In over 50 years
of driving alternators, never had diodes
short . . . I have had two instances of
diodes opening . . . one just two weeks
ago . . . but no shorts.

Of course, smoke from the b-lead in a
car is no big deal . . . as long as it
doesn't set the engine grease on fire.
Airplanes not so much.

Current limiters scattered around the bus
structures are very low return on investment . ..
probably zero.


Bob . . .


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PostPosted: Sun Jul 01, 2018 9:20 am    Post subject: Z-14 Question Reply with quote

At 08:22 AM 7/1/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>

Bob,

Along these same lines, I will have to run two battery buss leads from the aft batteries to the forward busses...about 8.5'.

Using the logic presented here, I need to install a current limiter in each battery lead, near the batteries...

Does this sound like a good plan, or am I missing something?

Yes, it's the NATURE of any probable fault that
determines the value of upstream protection.

Conduct a mental exercise considering all the
ways that your 8AWG bus feeders might experience
loads that put the 8AWG at risk for getting really
hot, smoking lots of insulation and perhaps burning
the wire in two.

This kind of fault (hard fault) simply cannot
arise in a properly installed/protected feeder
(a condition cited by another Lister a few days
ago). Fat wires in aircraft are at risk only
for soft faults . . . conditions that cause
arcing and heating levels too low to actually
damage the wire. This exercise is called an
FMEA (Failure Mode Effects Analysis).

Example: A C-90 on short final to Clovis NM about 1990 was
suddenly stricken with complete disconnect of control in pitch.
Elevator forces in wheel went to zero. The pilots did a go around
and managed to land safely with power and pitch trim.

A teardown revealed a mis-positioned wire bundle under the
cockpit floorboards where a 40A protected wire for co-pilot's
windshield heat had had been rubbing against the elevator
cable for a considerable period of time.

No smoke, no fire, no flickers in the electrical system, no
trips of the 40A breaker. Over the pre-failure interval,
MegaJoules of energy were released in the erosion of steel
wires (the copper wire was in pretty good shape . . . this
demonstrates why layers of copper are included in the design
of safes . . . nearly impossible to penetrate with a cutting
torch).

In other instances, it's easy to imagine a 10-cent resistor
burning up in a radio and making lots of nasty smells in the
cockpit while failing to open a 5A fuse that protects the
feed wire to the failed device.

Bottom line is that ALL thermally actuated protective devices
(fuses, heater actuated breakers, current limiters, fusible
links) and even magnetic breakers are incapable of reacting to
the low-rate, long-duration soft faults that are exemplified
by the two scenarios I offered above.

In the case for your intended bus feeders, it is sufficient
to route, support and otherwise eliminate probability
of a soft fault (like rubbing an elevator cable or vibrating
against the EDGE of a lightening hole in a bulkhead).

The FAA acknowledges the unique fault probabilities
of fat wires with words that speak to the design
of light aircraft:


[img]cid:.0[/img]
[img]cid:.1[/img]

Your proposed fat wires fall under
clause (2).


Bob . . .


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PostPosted: Sun Jul 01, 2018 11:34 am    Post subject: Re: Z-14 Question Reply with quote

Sooo...I do NOT need to use an ANL fuse on those 8AWG battery feeders...

Correct?


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PostPosted: Sun Jul 01, 2018 1:42 pm    Post subject: Z-14 Question Reply with quote

At 02:34 PM 7/1/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>

Sooo...I do NOT need to use an ANL fuse on those 8AWG battery feeders...

Correct?

yes



Bob . . .


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