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z13 battery bus protection

 
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mmcelrea



Joined: 05 Nov 2017
Posts: 10

PostPosted: Sun Apr 15, 2018 12:59 pm    Post subject: z13 battery bus protection Reply with quote

Hi.
On the Z13 design the wire from the contactor to the battery bus is recommended to be 6" or less. I don't want to put the battery bus on the fwf but on a panel with the other fuseblocks which will require a significantly longer wire. Is it acceptable or necessary to protect this wire with a fuse link and if so what size wire should I use? Max potential load will be about 15 amps.
Does the main bus wire require similar protection? I'm using a 4.5ft length of 6awg for it.


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PostPosted: Sun Apr 15, 2018 2:41 pm    Post subject: z13 battery bus protection Reply with quote

At 03:59 PM 4/15/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "mmcelrea" <mmcelrea(at)hotmail.com>

Hi.
On the Z13 design the wire from the contactor to the battery bus is recommended to be 6" or less. I don't want to put the battery bus on the fwf but on a panel with the other fuseblocks which will require a significantly longer wire. Is it acceptable or necessary to protect this wire with a fuse link and if so what size wire should I use? Max potential load will be about 15 amps.

A battery bus is located proximal to the battery, else
it's not a battery bus. Fuseblocks on the panel? Why?
When would you EVER find value in fiddling with fuses
or breakers in flight? Have you read . . .

https://goo.gl/ytEfZJ

https://goo.gl/utXVam

https://goo.gl/L6VpN4

Quote:
Does the main bus wire require similar protection? I'm using a 4.5ft length of 6awg for it.

Study the z-figures . . . no such protection is required
or recommended for crew controlled FAT wires . . . i.e. they
go cold when the master is OFF.



Bob . . .


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PostPosted: Sun Apr 15, 2018 3:00 pm    Post subject: z13 battery bus protection Reply with quote

On 4/15/2018 5:40 PM, Robert L. Nuckolls, III wrote:

Quote:
At 03:59 PM 4/15/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "mmcelrea" <mmcelrea(at)hotmail.com> (mmcelrea(at)hotmail.com)

Hi.
On the Z13 design the wire from the contactor to the battery bus is recommended to be 6" or less. I don't want to put the battery bus on the fwf but on a panel with the other fuseblocks which will require a significantly longer wire. Is it acceptable or necessary to protect this wire with a fuse link and if so what size wire should I use? Max potential load will be about 15 amps.

A battery bus is located proximal to the battery, else
it's not a battery bus. Fuseblocks on the panel? Why?
When would you EVER find value in fiddling with fuses
or breakers in flight? Have you read . . .

https://goo.gl/ytEfZJ

https://goo.gl/utXVam

https://goo.gl/L6VpN4

Quote:
Does the main bus wire require similar protection? I'm using a 4.5ft length of 6awg for it.

Study the z-figures . . . no such protection is required
or recommended for crew controlled FAT wires . . . i.e. they
go cold when the master is OFF.



Bob . . .
Hi Bob,

Not to speak for the OP, but....

Note that he says *a* panel; not *the* panel. I can see the wiring logic in a single firewall penetration wire and multiple feeds on the cold side of the firewall from that battery bus. Perhaps there's a disconnect (pardon the pun) in how each of you is defining a 'battery bus'. I can think of at least one bus I'd want to bypass my master contactor: the engine bus for an electrically dependent engine that's using automotive style fuel injection. I fed mine using a fusible link to feed an engine bus switch, which feeds the engine bus. (With a switched alternate feed from the main bus.) 15 amps is a safe number for fuel pump, controller, injectors, coils, etc.

Charlie
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mmcelrea



Joined: 05 Nov 2017
Posts: 10

PostPosted: Sun Apr 15, 2018 11:19 pm    Post subject: Re: z13 battery bus protection Reply with quote

Hi.
I have no intention of messing with cb’s or fuses in flight. The fuse blocks are mounted on a drop down panel between the main and sub panels. I don’t want to mount the battery bus on the firewall but as this will require a longer wire does it now need protecting?


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user9253



Joined: 28 Mar 2008
Posts: 1326
Location: Riley TWP Michigan

PostPosted: Sun Apr 15, 2018 11:47 pm    Post subject: Re: z13 battery bus protection Reply with quote

Usually the main bus feeder does not have protection other than the ability for the pilot to shut it off via the battery contactor.
As for the #14 AWG wire connecting the battery to the battery bus, an 18 AWG fuselink could be used. The 6 inch rule is a rule of thumb, not mandatory. The longer the wire, the greater the chance of it making sparks which will ignite gasoline after a forced landing. Protect it well.


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PostPosted: Mon Apr 16, 2018 6:57 am    Post subject: z13 battery bus protection Reply with quote

At 02:47 AM 4/16/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

Usually the main bus feeder does not have protection other than the ability for the pilot to shut it off via the battery contactor.
As for the #14 AWG wire connecting the battery to the battery bus, an 18 AWG fuselink could be used. The 6 inch rule is a rule of thumb, not mandatory. The longer the wire, the greater the chance of it making sparks which will ignite gasoline after a forced landing. Protect it well.

An extended bus feeder calls for
fault protection . . . protection
that needs to be very robust in
comparison with the loads on the
bus (and associated protections).

Since you're using fuses on the extended
bus (MUCH faster than breakers) and
given that this bus is always hot, I
suggest that the feeder be increased
to 10AWG and that it be protected
with a 30A Maxifuse; much faster than
a fusible link in a fault condition
and much more robust than any single
feeder off that bus . . . you don't
want a fault on a single distribution
to open the feeder fuse and take down
the whole bus.



Bob . . .


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PostPosted: Mon Apr 16, 2018 11:41 am    Post subject: z13 battery bus protection Reply with quote

In this scenario, is there any reason why an ATC fuse bus (20 slot bandc type) could not be fed from batt and alt straight into the buss through two of the faston tabs?  (As opposed to the main bolt terminal) Each slot could have a 30a maxifuse?
Will


On Mon, Apr 16, 2018, 12:05 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 02:47 AM 4/16/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

Usually the main bus feeder does not have protection other than the ability for the pilot to shut it off via the battery contactor.
As for the #14 AWG wire connecting the battery to the battery bus, an 18 AWG fuselink could be used.  The 6 inch rule is a rule of thumb, not mandatory.  The longer the wire, the greater the chance of it making sparks which will ignite gasoline after a forced landing.  Protect it well.

   An extended bus feeder calls for
   fault protection . . . protection
   that needs to be very robust in
   comparison with the loads on the
   bus (and associated protections).

   Since you're using fuses on the extended
   bus (MUCH faster than breakers) and
   given that this bus is always hot, I
   suggest that the feeder be increased
   to 10AWG and that it be protected
   with a 30A Maxifuse; much faster than
   a fusible link in a fault condition
   and much more robust than any single
   feeder off that bus . . . you don't
   want a fault on a single distribution
   to open the feeder fuse and take down
   the whole bus.



  Bob . . .


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PostPosted: Mon Apr 16, 2018 12:00 pm    Post subject: z13 battery bus protection Reply with quote

What's the goal? If you're trying to protect the bus, it's an unneeded failure point when inserted as a 'master protection device' (detailed in Bob's earlier linked articles). If protecting the wire, the fuse is on the wrong end of the wire.

On 4/16/2018 2:40 PM, William Daniell wrote:

Quote:
In this scenario, is there any reason why an ATC fuse bus (20 slot bandc type) could not be fed from batt and alt straight into the buss through two of the faston tabs?  (As opposed to the main bolt terminal) Each slot could have a 30a maxifuse?


Will




On Mon, Apr 16, 2018, 12:05 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 02:47 AM 4/16/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

Usually the main bus feeder does not have protection other than the ability for the pilot to shut it off via the battery contactor.
As for the #14 AWG wire connecting the battery to the battery bus, an 18 AWG fuselink could be used.  The 6 inch rule is a rule of thumb, not mandatory.  The longer the wire, the greater the chance of it making sparks which will ignite gasoline after a forced landing.  Protect it well.

   An extended bus feeder calls for
   fault protection . . . protection
   that needs to be very robust in
   comparison with the loads on the
   bus (and associated protections).

   Since you're using fuses on the extended
   bus (MUCH faster than breakers) and
   given that this bus is always hot, I
   suggest that the feeder be increased
   to 10AWG and that it be protected
   with a 30A Maxifuse; much faster than
   a fusible link in a fault condition
   and much more robust than any single
   feeder off that bus . . . you don't
   want a fault on a single distribution
   to open the feeder fuse and take down
   the whole bus.



  Bob . . .




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PostPosted: Mon Apr 16, 2018 5:28 pm    Post subject: z13 battery bus protection Reply with quote

At 02:40 PM 4/16/2018, you wrote:
Quote:
In this scenario, is there any reason why an ATC fuse bus (20 slot bandc type) could not be fed from batt and alt straight into the buss through two of the faston tabs? (As opposed to the main bolt terminal) Each slot could have a 30a maxifuse?

Recall that circuit protection is for WIRES . . . and
that the protective device is installed as close as
practical to the SOURCE of energy that puts the wire
at risk.

In this case, a MAXIfuse in an in-line holder
taps power off the hot side of the battery or
starter contactors. Energy is then conducted via the
10AWG feeder to the input stud on the fuseblock.

What loads are being assigned to this bus?



Bob . . .


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mmcelrea



Joined: 05 Nov 2017
Posts: 10

PostPosted: Mon Apr 16, 2018 8:58 pm    Post subject: Re: z13 battery bus protection Reply with quote

In that case could a fuse link be used on the source end of the wire to protect the wire and then feeding the bus via one of the fast on rather than the main bolt terminal to provide fast blow protection to prevent the bus being taken out? Would 12awg feed wire with 16awg fuselink suffice, or 10awg with 14awg fusel-ink
The bus is supplying the essential bus as backup max load approx 15 amps.


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user9253



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PostPosted: Tue Apr 17, 2018 4:29 am    Post subject: Re: z13 battery bus protection Reply with quote

A fast blow fuse will INSURE that the bus IS taken out. Do not use a fast blow fuse in series with the Bus no matter which end of the wire it is located.

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mmcelrea



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PostPosted: Tue Apr 17, 2018 6:55 am    Post subject: Re: z13 battery bus protection Reply with quote

Will a maxifuse not blow as fast as a normal blade fuse? Is a slow blow blade fuse available?

The endurance bus feed wire from the hot battery bus is protected by a fuse at
one end and a fuselink at the other. Is it not acceptable to do the same with the feed wire to the hot battery bus from the battery?

I would prefer to keep the simplest, most durable protection devices within the engine compartment, ie a fuselink.


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PostPosted: Tue Apr 17, 2018 9:32 am    Post subject: Re: z13 battery bus protection Reply with quote

On the Littlefuse website,
http://www.littelfuse.com/products/fuses/automotive-passenger-car/blade-fuses/299.aspx
it says, "MAXI 32V Series - MAXI® Slo-Blo® 32V Automotive Blade Fuse"
I assume that "Slo-Blo" means slow blow. The datasheet
http://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/blade-fuses/littelfuse_maxi_32v_datasheet.pdf
graph looks like the 30 amp fuse will hold 40 amps for several minutes without blowing.
The reason that the endurance bus wire is protected at both ends is because there are two current paths.
The wire needs to be protected from current coming from either end.
A maxifuse is a blade type fuse, but it is twice as big as ATX and ATO fuses.


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PostPosted: Tue Apr 17, 2018 10:20 am    Post subject: z13 battery bus protection Reply with quote

At 09:55 AM 4/17/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "mmcelrea" <mmcelrea(at)hotmail.com>

Will a maxifuse not blow as fast as a normal blade fuse? Is a slow blow blade fuse available?

No . . . haven't got time right now to answer this
question carefully . . . but I will soon.

In the mean time, research the fault reaction time
curves for the devices being cited . . .

"Fast" and "slow" are un-quantified, squishy terms.


Bob . . .


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user9253



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PostPosted: Tue Apr 17, 2018 10:27 am    Post subject: Re: z13 battery bus protection Reply with quote

According to this chart:
http://www.litz-wire.com/New%20PDFs/Fusing_Currents_Melting_Temperature_Copper_Aluminum_Magnet_Wire_R2.011609.pdf
A #18 AWG fuselink will conduct up to 82 amps before it melts.


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PostPosted: Tue Apr 17, 2018 2:22 pm    Post subject: z13 battery bus protection Reply with quote

At 09:55 AM 4/17/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "mmcelrea" <mmcelrea(at)hotmail.com>

Will a maxifuse not blow as fast as a normal blade fuse? Is a slow blow blade fuse available?

No . . . and here's why . . .

Let's go to the engineering data for a sample of fuses
common to our designs. First the ATC10 plastic fuse
that fits the popular fuseholders . . . and probably
the largest fuse to be included on the battery bus
under consideration:

I have calculated a 'fusing constant' for this
fuse based on numbers taken from the ATC fuse
performance chart below. At approx 2x the 'carry
forever' current of the ATC10 fuse, it opens in
approx 0.4 seconds which produces an I(squared)T
value of 270. If we cause the fuse to carry twice
that value of 52A, we know that it will open in
approx ONE FOURTH that time or 0.1 seconds.
Double the current again to ~100A and we'll
anticipate fuse operation in ~0.05 seconds.

The chart below says it will be shorter still,
so perhaps my fusing constant number needs
trimming. Suffice it to say that the fusing
constant calculation carries an AMPS(SQUARED)
term in it suggesting that increasing current
shortens the operating time by 1/4th each doubling.


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

Now let us look at the 30A MaxiFuse. Note that
it has a much larger fusing constant (again perhaps
needing a tweak) but consider the operating time
at 100A. From the chart we read something on
the order of 3 SECONDS.

Suppose a MAX30 were protecting the battery
bus with a ATC10 fuse in it and you fault
that fuse with a 100A load. The ATC10 will open
many times faster than the MAX30 thus the
integrity of the bus feed is not at risk.

[img]cid:.2[/img]

Now, if we were protecting a SWITCHED bus in a TC
aircraft with similar distribution characteristics,
we might choose to use the ANL35 current limiter.

Note that its fusing constant is actually LESS
than the MAXI30. At 2x the ANL's carry forever
current, the fusing time is only 0.4 seconds. But
when loaded with our hypothetical fault of 100A
on an ATC10 fuse, the ANL35 is pretty close to
a never-operates condition.

[img]cid:.3[/img]
A take-away from this narrative has several points.

(1) 'Fast' and 'slow' are non-quantified, un-scientific
terms for evaluating performance of any circuit
protective device. You can say device A is faster
than device B under some cited conditions . . . but
that's about it.

(2) The fusing constant is useful for making some
broad predictions about performance between
two styles of product. For example, in the
charts about we see that Kf of 13K for the
ANL (a mechanically robust fuse compared to
the MAXI) is about 20x faster at the 2x
overload point than the MAXI with a Kf of 44K.

(3) I've not illustrated fusing characteristics
for the 18AWG fusible link . . . we know it's
going to be a BIG number. Now, considering that
the design goal for upstream protection of the
non-legacy battery bus is to MINIMIZE the
potential for expenditure of energy in a hard
fault condition, very robust devices like
fusible links are not consistent with the
design goal.

(4) The design goal calls for selection of an upstream
fuse with thermal characteristics consistent with
maintaining bus integrity under a downstream
BRANCH fault while minimizing energy expenditure
during a FEEDER fault.

(5) There is a significant simplification of the physics
in this narrative that does NOT consider PRE-
HEATING of the feeder protection due to normal
operating loads. Pre-heating figured heavily
in the demise of N811HB . . .

https://goo.gl/hWQdE6

I think I read the number 15A as the max running load
for this design. Assuming no branch fuse is greater than
10A . . . with most probably being smaller . . .
I'll s stand by my recommendation for a MAXI30 or
even a MAXI40 protecting a 10AWG feeder.

Having said that, I'd much rather the battery
bus was located near the battery.

The 30 Series aircraft at Beech have had fuses on the
firewall for decades

[img]cid:.4[/img]

Further, they were/are glass cartridge fuses (ugh!)
with threaded fasteners (fooey) . . . but I'm aware
of no problems with this design philosophy.



Bob . . .


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mmcelrea



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PostPosted: Tue Apr 17, 2018 10:29 pm    Post subject: Re: z13 battery bus protection Reply with quote

Bob, thankyou for your reply, much appreciated.
Miller


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PostPosted: Thu Apr 19, 2018 12:52 pm    Post subject: z13 battery bus protection Reply with quote

Bob
thanks sorry for late reply.
So in this case we are talking about your Z16 circuit diagram without an endurance buss.  (I have eliminated the endurance buss.  Following your dictum of no electrical systems which determine the safe termination of the flight I have Levil with battery back up for AI/flight instruments and a handheld radio).
Since the battery and therefore the battery contactor is under the baggage bay of my Europa, the power to the buss comes from one of the through-firewall bolts which connects the 4AWG from the battery to the starter contactor.    
Following the Z16 therefore, in this case, there is no requirement for wire protection between the through firewall bolt and the buss.  The cable run which is 10AWG is not more than 12".  The buss powers a dynon system with dual axis AP, radio/intercom, Airmaster prop,  flap motor,  backup instruments, fuel pump, landing and anti collision lights (these latter are low consumption LED).  The dynon ammeter shows 12A recharging and 8.5A normally with everything on.
Will

William Daniell

LONGPORT
+57 310 295 0744


On Mon, Apr 16, 2018 at 8:28 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 02:40 PM 4/16/2018, you wrote:
Quote:
In this scenario, is there any reason why an ATC fuse bus (20 slot bandc type) could not be fed from batt and alt straight into the buss through two of the faston tabs?  (As opposed to the main bolt terminal) Each slot could have a 30a maxifuse?

  Recall that circuit protection is for WIRES . . . and
  that the protective device is installed as close as
  practical to the SOURCE of energy that puts the wire
  at risk.

  In this case, a MAXIfuse in an in-line holder
  taps power off the hot side of the battery or
  starter contactors. Energy is then conducted via the
  10AWG feeder to the input stud on the fuseblock.

  What loads are being assigned to this bus?



  Bob . . .


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