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Voyager
Joined: 30 Jun 2020
Posts: 77
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 Posted: Thu Sep 02, 2021 7:00 am Post subject: Possible Z-14 error?? |
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Hi Bob,
I am looking at wiring my RANS S-21 based to a large degree on your Z-14 architecture. As I am reviewing it and creating my schematics in SolidWorks, I noticed something odd. I am looking at what I believe is the latest revision (dated 24-Jun-2013).
On P1, the wire from the cross-feed contactor to the main battery contactor is 2 AWG as compared to 4 AWG from the aux battery contactor to the cross feed. Since both batteries are the same size, it seems these should be the same size conductor unless the lengths are dramatically different.
The bigger question I have is why is the conductor on P2 from the main battery contactor to the starter contactor 4 AWG when 2 AWG is used to the starter itself from its contactor? Did the wire sizes from the main battery contactor to starter contactor get transposed with the size from the cross-feed contactor to the main battery contactor? Or is the assumption that the length from the cross-feed contactor to the main battery contactor is long and the length from the main battery contactor to the starter contactor is short?
I plan to mount my two batteries side by side with short runs from the batteries to their contactors (hopefully less than 12") and short runs from the battery contactors to the cross-feed contactor, again 12" or less if practical. My batteries will likely be under the baggage compartment floor according to the RANS plans which is not my favorite location, but the firewall is too crowded and I really don't want to run clear back to the tail cone. This means that my cable from the battery contactor to the starter contactor will likely be 6' or more in length and then another 3-4 feet to the starter.
Given the above, I am leaning towards 4 AWG for the short runs between batteries and main and cross-feed contactors and then 2 AWG from battery or cross-feed contactor to the starter contactor and 2 AWG from starter contactor to starter. However, this isn't what I see on your architecture diagram hence my question. Although, RANS shows 4 AWG for everything from the battery to the starter so maybe I am being overly conservative.
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user9253
Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan
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| Posted: Fri Sep 03, 2021 9:27 am Post subject: Re: Possible Z-14 error?? |
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Your plan to use 2AWG for long runs and 4AWG for short runs sounds good.
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Joe Gores |
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nuckolls.bob(at)aeroelect
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| Posted: Mon Sep 06, 2021 8:33 am Post subject: Possible Z-14 error?? |
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At 10:00 AM 9/2/2021, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Voyager" <m.whiting(at)frontier.com>
Hi Bob,
I am looking at wiring my RANS S-21 based to a large degree on your Z-14 architecture. As I am reviewing it and creating my schematics in SolidWorks, I noticed something odd. I am looking at what I believe is the latest revision (dated 24-Jun-2013).
On P1, the wire from the cross-feed contactor to the main battery contactor is 2 AWG as compared to 4 AWG from the aux battery contactor to the cross feed. Since both batteries are the same size, it seems these should be the same size conductor unless the lengths are dramatically different.
The bigger question I have is why is the conductor on P2 from the main battery contactor to the starter contactor 4 AWG when 2 AWG is used to the starter itself from its contactor? Did the wire sizes from the main battery contactor to starter contactor get transposed with the size from the cross-feed contactor to the main battery contactor? Or is the assumption that the length from the cross-feed contactor to the main battery contactor is long and the length from the main battery contactor to the starter contactor is short?
I plan to mount my two batteries side by side with short runs from the batteries to their contactors (hopefully less than 12") and short runs from the battery contactors to the cross-feed contactor, again 12" or less if practical. My batteries will likely be under the baggage compartment floor according to the RANS plans which is not my favorite location, but the firewall is too crowded and I really don't want to run clear back to the tail cone. This means that my cable from the battery contactor to the starter contactor will likely be 6' or more in length and then another 3-4 feet to the starter.
Given the above, I am leaning towards 4 AWG for the short runs between batteries and main and cross-feed contactors and then 2 AWG from battery or cross-feed contactor to the starter contactor and 2 AWG from starter contactor to starter. However, this isn't what I see on your architecture diagram hence my question. Although, RANS shows 4 AWG for everything from the battery to the starter so maybe I am being overly conservative. |
Sorry for the delay on addressing this thread . . .
numerous pressing issues elsewhere . . .
The z-figures are ARCHITECTURE drawings
suggesting approaches to FAILURE TOLERANT electrical
systems for a constellation of aircraft and proposed
missions.
So yes, there are some 'anomalies' in wire and
fuse sizing . . . these drawings are assembled from
snippets of other drawings that described systems
in a constellation of aircraft. AFTER a configuration
is selected then do a LOAD ANALYSIS to confirm or
modify the suggested wire size and associated
protection.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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nuckolls.bob(at)aeroelect
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| Posted: Mon Sep 06, 2021 9:13 am Post subject: Possible Z-14 error?? |
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| Quote: | | Your plan to use 2AWG for long runs and 4AWG for short runs sounds good. |
10AWG wire is 0.001 ohms per foot. For every 3AWG steps in
wire size, resistance varies by a factor of 2. Hence
7AWG wire would be 0.0005 ohms/ft; 4AWG would be
0.00025 ohms/ft; 2AWG would be approx 2/3rds of the
way between 4AWG and 1AWG of 0.00012 ohms/ft. Let's
call it about 0.00016 ohms/ft. If you'd like a hard-copy
look-up, here's but one example https://tinyurl.com/4jw4heeh
For broad brush estimating, let's assume 200A for
a average starting current. So, 10 feet total 4AWG
wire in your cranking loop would drop 200A x 10ft x
0.00025 ohms/ft = 0.5 volts. An acceptably small
value. Replacing it with 10' of 2AWG would yield
a voltage drop of 200A x 10ft x 0.00016 = 0.32 volts
or 180 millivolts! If your loop is less than 10'
then the improvement is still smaller.
The attached figure is purloined from Chapter 2
of the 'Connection. In this figure I hypothesis
cranking performance of a 4AWG cranking loop in
a canard pusher . . . i.e. LONG cranking wires.
As you can see, even with these wire lengths,
cranking voltages are rather nominal. Starter
motors EXPECT to see voltages on the order of 9
volts.
In any case, up-sizing wire from 4 to 2AWG produces
about 30% improvement only in WIRE drop while doing
nothing for internal resistance of battery and
voltage drops across other hardware in the loop.
I suggest that with few exceptions (IO-540
engines in a composite seaplane - that airplane
hand a cranking loop of 48ft! We ran doubled
up strands of 2AWG), 4AWG will suffice
nicely for the cranking loop especially
in a metal airplane. A more detailed analysis
is called for in LONG runs on composite aircraft.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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