Today's Message Index:
----------------------
1. 11:36 AM - wire sizing (John Tvedte)
2. 12:39 PM - Re: wire sizing (Matt Prather)
3. 03:31 PM - Re: wire sizing (Robert L. Nuckolls, III)
4. 05:38 PM - Re: Re: Low voltage indicator for LR3 (Robert L. Nuckolls, III)
Message 1
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Bob,
A couple questions concerning wire sizing.
Given: Aeroelectric FAQ, it was mentioned that typical field current draw for Alternators
(20, 40, 60A) is 1 to 1.5A, with 3A max...
What is the design Vd for Alternator field wiring?
What is the design I for the Alternator B lead? i.e. SD-20, L-40, L-60?
In Z14, 10 awg is suggested for the Aux alternator, and while fine Ampacity wise,
I am wondering about voltage drop meeting 2% -
Given a rated power output of 20A (SD-20), a 2% Vd - wire length allowed is approx.
5.5 ft (one way) if 10 awg was used throughout...however, as the return path
is a 2 awg suggested wire....??
FAA AC 43-13-1B on page 11-21 Par 11-66
"b. Voltage Drop in Wires. The voltage
drop in the main power wires from the generation
source or the battery to the bus should not
exceed 2 percent of the regulated voltage when
the generator is carrying rated current or the
battery is being discharged at the 5-minute
rate. The tabulation shown in table 11-6 defines
the maximum acceptable voltage drop in
the load circuits between the bus and the utilization
equipment ground."
Also - on Z14, 4awg is suggested for the Aux battery - can you provide some insight
into that suggestion?
Message 2
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Alternators are often grounded to the engine case. From there they are
grounded to the battery with a cable large enough to support starting
loads (hundreds of amps). So, I don't think you have to worry about
round-trip wiring length.
If the one-way wire run from the aux alternator to its buss is
significantly greater than 5.5ft, I'd up-rate the wire one size.
I believe the components listed on the Z-diagrams are suggestions for
architecture layout based on a large set of assumptions. If the circuit
appropriate for your particular airplane requires something different,
deviation from the Z-diagrams makes sense.
Regards,
Matt-
>
> Bob,
>
> A couple questions concerning wire sizing.
>
> Given: Aeroelectric FAQ, it was mentioned that typical field current draw
> for Alternators (20, 40, 60A) is 1 to 1.5A, with 3A max...
>
> What is the design Vd for Alternator field wiring?
>
> What is the design I for the Alternator B lead? i.e. SD-20, L-40, L-60?
>
> In Z14, 10 awg is suggested for the Aux alternator, and while fine
> Ampacity wise, I am wondering about voltage drop meeting 2% -
>
> Given a rated power output of 20A (SD-20), a 2% Vd - wire length allowed
> is approx. 5.5 ft (one way) if 10 awg was used throughout...however, as
> the return path is a 2 awg suggested wire....??
>
> FAA AC 43-13-1B on page 11-21 Par 11-66
>
> "b. Voltage Drop in Wires. The voltage
> drop in the main power wires from the generation
> source or the battery to the bus should not
> exceed 2 percent of the regulated voltage when
> the generator is carrying rated current or the
> battery is being discharged at the 5-minute
> rate. The tabulation shown in table 11-6 defines
> the maximum acceptable voltage drop in
> the load circuits between the bus and the utilization
> equipment ground."
>
> Also - on Z14, 4awg is suggested for the Aux battery - can you provide
> some insight into that suggestion?
>
>
Message 3
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At 01:30 PM 2/25/2008 -0600, you wrote:
>
>Bob,
>
>A couple questions concerning wire sizing.
>
>Given: Aeroelectric FAQ, it was mentioned that typical field current draw
>for Alternators (20, 40, 60A) is 1 to 1.5A, with 3A max...
>
>What is the design Vd for Alternator field wiring?
It depends. If your regulator has a separate bus
sense lead like the later LR series regulators
from B&C, then you can practically downsize the
field current feeder to 22AWG for most installations.
HOWEVER: if your regulator's field supply input
-AND- bus voltage sense share the same wire, then
VERY SMALL (order of 0.3 volts) of drop in this lead
combined with fluctuations of field current in response
to loads and rpms can cause alternator system instability.
This is common on many spam cans and produces the
"galloping ammeter" effect.
This is why the Z-figures show 20AWG in feeders
from bus to the alternator regulator. If you dropped
to 18AWG, it wouldn't give me any heartburn.
>What is the design I for the Alternator B lead? i.e. SD-20, L-40, L-60?
20, 40 and 60 Amps . . .
>In Z14, 10 awg is suggested for the Aux alternator, and while fine
>Ampacity wise, I am wondering about voltage drop meeting 2% -
>
>Given a rated power output of 20A (SD-20), a 2% Vd - wire length allowed
>is approx. 5.5 ft (one way) if 10 awg was used throughout...however, as
>the return path is a 2 awg suggested wire....??
>
>FAA AC 43-13-1B on page 11-21 Par 11-66
>
>"b. Voltage Drop in Wires. The voltage
>drop in the main power wires from the generation
>source or the battery to the bus should not
>exceed 2 percent of the regulated voltage when
>the generator is carrying rated current or the
>battery is being discharged at the 5-minute
>rate. The tabulation shown in table 11-6 defines
>the maximum acceptable voltage drop in
>the load circuits between the bus and the utilization
>equipment ground."
>
>Also - on Z14, 4awg is suggested for the Aux battery - can you provide
>some insight into that suggestion?
I would caution you and all OBAM aircraft builders
to approach AC43.13 with caution. It's more of an
engineering document than a cookbook. To make matters
worse, it was not crafted by individuals with a wide
range of practical experience that talked to each other
will writing their respective sections.
Unfortunately, folks charged showing us how much
more they know about airplanes that we do will snatch
things out of AC43.13 and flog the unwary designer
with it. Unless you plan to take up a career in
getting your handiwork certified, I'll suggest your
time is better spent doing a nice job on your
canopy installation or upholstery than slogging
your way through AC43.13.
Now to your question. If you size wires per the
suggestions in Figure 8.3 of the 'Connection
(See http://aeroelectric.com/articles/Wire_Chart.pdf )
. . . then you'll be fine. But know also that these
ratings are VERY conservative and sized for relatively
long runs where voltage drop MIGHT become an issue.
These ratings do not apply to FAT wires subject to
intermittent heavy loads. These would include battery,
starter and ground leads.
I show 4AWG for all these leads which are good values
if you're building a tractor a/c with battery
within 5 ft or so of engine. If you're building a
canard pusher with battery on other end of airplane,
a large composite a/c with aft mounted battery, or
a seaplane with 30 foot battery feeders, then the 4AWG
will serve you well.
Which, if any, wire sizes suggested in the z-figures
are of concern to you based on the special cases
cited above?
Bob . . .
Message 4
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Subject: | Re: Low voltage indicator for LR3 |
At 06:46 PM 2/24/2008 -0500, you wrote:
>
>Hmmm. I am planning a circuit that will light that same LED when the
>master or auxiliary contactor is engaged when the engine isn't running
>(eg. left on after flight). They neglected to mention this bias
>resistor when I called to ask about the circuitry inside. This will
>change my design somewhat.
>Do you know what the resistor value is ?
It's big . . . but keep in mind that the current
through the resistor is multiplied by the gain
of the transistor.
If the LR-3 is getting its power from the main bus
the light will flash any time any battery is feeding
the bus -AND- the alternator is off. What's the need
for alternative "design"?
Bob . . .
>Thanks !
>Jeff Page
>Dream Aircraft Tundra #10
>
>>At 07:20 PM 2/23/2008 -0500, you wrote:
>>>My notes from talking with someone at B&C is that pin 5 is a FET
>>>output protected by a 1N4752 zener (which is 33V). Where does the
>>>leakage come from ?
>>>Jeff Page
>>>Dream Aircraft Tundra #10
>>
>> If you study the schematic cited below, you'll see a resistor
>> connected from collector to base (or drain to gate if fet)
>> that generates an artificial leakage.
>>
>> This leakage is overcome by the hard pull-down on the
>> LV warn comparator but insufficient to illuminate an
>> incandescent lamp. The purpose of that leakage is to
>> cause a steady illumination of the LV warn lamp should
>> power to the LV warn circuitry within the LR-3 be lost.
>> The leakage will partially bias the lamp drive and cause
>> the lamp to glow steady.
>>
>> This design goal gets in the way of allowing an LED
>> to go completely dark. The tiny leakage current that
>> produced no light on an incandescent lamp produces
>> significant light in the LED. Hence, the load resistor
>> to make an LED look like an incandescent.
>
>
>--
>269.20.9/1295 - Release Date: 2/23/2008 9:35 PM
>
>
>incoming mail is certified Virus Free.
>Checked by AVG.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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