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  #1  
Old 08-02-2019, 12:09 AM
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jcarne jcarne is offline
 
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Question battery bus protection question

Ok the wiring preparation continues. I'm working off of Bob K's Z-11 schematic and he shows that the battery bus wire does not need protected as long as it is less than 6 inches long. I do not want to put my battery bus FWF so my question is would you use a fusible link, inline fuse, or something else? Take a look at the red oval below. I changed the drawing to an inline fuse but would like to see what you all think.

P.S. I only really care about running some cabin lighting but I don't know what else I might want to add. Either way I need to protect this wire coming from the battery.

Capture by Jereme Carne, on Flickr
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  #2  
Old 08-02-2019, 07:11 AM
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Jereme,

Specific to your question, yes, an "always hot" wire to your courtesy light bus should have some sort of circuit protection. The exact choice of circuit protection isn't critical as long as it is guaranteed to open before the wire gets too hot.

We tend to add things later. For example, you may wish to add a cigar lighter socket to the always hot bus so you can blow up your air mattress at OSH. If so, a 20ga wire and associated circuit protection would be marginal. I'd consider upsizing the supply wire and using something like an ANL, or perhaps just an inline blade fuse.

Now to the drawing as presented. I see an E-bus Alt Feed with a 30 amp fuse feeding from the courtesy light bus. I'm assuming it is an unintended artifact from drawing work in progress. If you do intend such a feed, you'll need to rethink some details.
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  #3  
Old 08-02-2019, 09:08 AM
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Originally Posted by DanH View Post
Jereme,

Specific to your question, yes, an "always hot" wire to your courtesy light bus should have some sort of circuit protection. The exact choice of circuit protection isn't critical as long as it is guaranteed to open before the wire gets too hot.

We tend to add things later. For example, you may wish to add a cigar lighter socket to the always hot bus so you can blow up your air mattress at OSH. If so, a 20ga wire and associated circuit protection would be marginal. I'd consider upsizing the supply wire and using something like an ANL, or perhaps just an inline blade fuse.

Now to the drawing as presented. I see an E-bus Alt Feed with a 30 amp fuse feeding from the courtesy light bus. I'm assuming it is an unintended artifact from drawing work in progress. If you do intend such a feed, you'll need to rethink some details.
Dan stellar catch on a couple accounts. Yes the drawing is still a work in progress but I'm glad you pointed some things out. I had forgotten about the cigarette lighter socket, definitely need one of them.

As far as the e-bus feed, I was planning on using one so I will need to upside the wire going from the battery to the battery bus. Good catch. Unless of course you think an e-bus is antiquated in today's EFIS world?
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Old 08-02-2019, 09:11 AM
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Jereme,
What page is this on? I looked and can't find it? Saw the script but not the figure.
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  #5  
Old 08-02-2019, 09:22 AM
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Jereme,
What page is this on? I looked and can't find it? Saw the script but not the figure.
The diagram in question is in Aeroelectric Connection (back of book) by Bob Knuckolls found here. I am using the CAD version he has on his website which is slightly updated in a couple of areas. (you can also make changes if you know CAD)

It's a great book to read as far as learning electrical stuff.
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  #6  
Old 08-02-2019, 09:43 AM
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Quote:
Originally Posted by jcarne View Post
As far as the e-bus feed, I was planning on using one so I will need to upside the wire going from the battery to the battery bus. Good catch. Unless of course you think an e-bus is antiquated in today's EFIS world?
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.
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  #7  
Old 08-02-2019, 10:04 AM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by DanH View Post
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.
Exactly correct. Essential buss schemes may support vacuum pumps and spinning iron gyros but they fall short of the mark for modern, IFR dual glass installs - even less for aircraft power dependent EI and EFI.

Carl
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  #8  
Old 08-02-2019, 01:03 PM
Mich48041 Mich48041 is offline
 
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It is usually bad practice to wire fuses in series. Sometimes a short circuit will
blow both fuses, even if one is much larger than the other. An exception is a
current limiter, which is very slow to blow, such as Maxi or ANL. The builder
should compare the danger of arcs and sparks to that of a fuse blowing and
disabling important electrical devices. The chances of a short circuit can be
minimized by good workmanship and double insulation at the firewall penetration.
An alternative is a heavy duty relay to turn on and off power coming from the
battery bus. Post crash fires are often started by electrical sparks. A relay can
shut off power close to the source in case of smoke or fire or imminent forced landing.
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  #9  
Old 08-02-2019, 01:31 PM
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jcarne jcarne is offline
 
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Quote:
Originally Posted by DanH View Post
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.
Quote:
Originally Posted by Carl Froehlich View Post
Exactly correct. Essential buss schemes may support vacuum pumps and spinning iron gyros but they fall short of the mark for modern, IFR dual glass installs - even less for aircraft power dependent EI and EFI.

Carl
What would you suggest then Dan and Carl? The plan is VFR initially but I want to add everything needed to make this bird IFR by adding a GPS and a backup battery. I'm trying to plan for IFR capabilities for the future. Main bus and avionics bus? Just one bus? Something else? I would like to only do my drawing once if possible. haha Thanks for your input, it is put to good use!

Quote:
Originally Posted by Mich48041 View Post
It is usually bad practice to wire fuses in series. Sometimes a short circuit will
blow both fuses, even if one is much larger than the other. An exception is a
current limiter, which is very slow to blow, such as Maxi or ANL. The builder
should compare the danger of arcs and sparks to that of a fuse blowing and
disabling important electrical devices. The chances of a short circuit can be
minimized by good workmanship and double insulation at the firewall penetration.
An alternative is a heavy duty relay to turn on and off power coming from the
battery bus. Post crash fires are often started by electrical sparks. A relay can
shut off power close to the source in case of smoke or fire or imminent forced landing.
Mich this inline fuse would be very close to the battery contactor. I'm not a big fan of running unprotected wires. If I lose this fuse and only lose my cabin lights and plug I'm ok with that. (assuming I abandon this e-bus theory) Or did I miss your point entirely?
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Last edited by jcarne : 08-02-2019 at 01:46 PM.
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  #10  
Old 08-02-2019, 01:58 PM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by jcarne View Post
What would you suggest then Dan and Carl? The plan is VFR initially but I want to add everything needed to make this bird IFR by adding a GPS and a backup battery. I'm trying to plan for IFR capabilities for the future. Main bus and avionics bus? Just one bus? Something else? I would like to only do my drawing once if possible. haha Thanks for your input, it is put to good use!
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Jereme,

PM me your email address and Iíll provide my power distribution scheme, and design objectives it supports.

Carl
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