Today's Message Index:
----------------------
1. 12:57 AM - Re: Re: Big H-bridge for Big Motors (Frank & Dorothy)
2. 06:00 AM - Re: Re: Big H-bridge for Big Motors (Robert L. Nuckolls, III)
3. 06:12 AM - Battery cables for aft batterys on RV-7 (Jerry Ballard)
4. 06:42 AM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Bob C.)
5. 09:02 AM - Re: Size of Fuse vs. Circuit Breaker - (Robert L. Nuckolls, III)
6. 09:13 AM - Size of Fuse vs. Circuit Breaker - Final Correction (Robert L. Nuckolls, III)
7. 10:21 AM - Re: Battery cables for aft batterys on RV-7 (Mickey Coggins)
8. 10:54 AM - Toggle switch - both master/battery and starter (Mitch Faatz)
9. 11:23 AM - Re: Big H-bridge for Big Motors (Eric M. Jones)
10. 11:32 AM - Re: Toggle switch - both master/battery and starter (Mark R Steitle)
11. 01:59 PM - Narco wiring harness- part needed (Jeff Point)
12. 03:13 PM - Re: Battery cables for aft batterys on RV-7 (Hans Teijgeler)
13. 04:31 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Bob C.)
14. 04:55 PM - Re: Size of Fuse vs. Circuit Breaker (Dennis Johnson)
15. 05:18 PM - Coax connector Garmin 196 (N27160@aol.com)
16. 05:46 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (John Schroeder)
17. 07:37 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (Fiveonepw@aol.com)
18. 08:00 PM - Re: Size of Fuse vs. Circuit Breaker - Corrected (John Schroeder)
19. 09:59 PM - Re: Measurements (j1j2h3@juno.com)
Message 1
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| Subject: | Re: Big H-bridge for Big Motors |
--> AeroElectric-List message posted by: Frank & Dorothy <frankv@infogen.net.nz>
Robert L. Nuckolls, III wrote:
>Guess it would help if I put the link in too . . .
>
>http://www.aeroelectric.com/Pictures/Big_H-Bridge.gif
>
>
Hi
I'm not sure what application this Big H-bridge is intended for, but
I've had a bit of experience with *little* H-bridges. After burning up a
few drive transistors (check out what happens if both drive transistors
are enabled at once), I moved to a so-called 'smokeless' H-bridge... a
simple 2-to-4 decoder IC (or circuit) prevents bad things from
happening. Smart guys even used the 4th state as a brake.
Frank
Message 2
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| Subject: | Re: Big H-bridge for Big Motors |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
There was a discussion on the list concerning solid state replacement
of relays with transistors for driving motors up to 7 amps or so.
Yes, virtually ALL h-bridge designs are vulnerable to the condition
you mentioned . . . One benefit of relays is that they can be
wired so that contrary commands translate into simple, smoke-free
stopping of the motor.
One should take care to design switching systems that drive
h-bridges to preclude simultaneous contrary commands via
gates or architecture of the control switches. Either may
be accomplished easily.
Bob . . .
At 09:38 PM 2/11/2005 +1300, you wrote:
>--> AeroElectric-List message posted by: Frank & Dorothy
><frankv@infogen.net.nz>
>
>Robert L. Nuckolls, III wrote:
>
> >Guess it would help if I put the link in too . . .
> >
> >http://www.aeroelectric.com/Pictures/Big_H-Bridge.gif
> >
> >
>Hi
>
>I'm not sure what application this Big H-bridge is intended for, but
>I've had a bit of experience with *little* H-bridges. After burning up a
>few drive transistors (check out what happens if both drive transistors
>are enabled at once), I moved to a so-called 'smokeless' H-bridge... a
>simple 2-to-4 decoder IC (or circuit) prevents bad things from
>happening. Smart guys even used the 4th state as a brake.
>
>Frank
Message 3
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| Subject: | Battery cables for aft batterys on RV-7 |
--> AeroElectric-List message posted by: "Jerry Ballard" <jbyrd@jbyrd-b52.com>
I've just ordered an H-6 Subaru for an RV-7A. For CG I'll probably
need to locate batteries in or aft of baggage compartment.
Question1: What size wire should I run from batteries to engine
compartment? Should this be a welding cable type wire? With the
H-6, reducing weight is more of a concern.
Question 2: I've already placed conduit to run power and/or signal
wiring for AOA, Whelen strobes, and Grand Rapids EFIS from front to aft
of baggage compartment. Can the battery cable be run in this conduit
or should it be relocated for separation from routine power and signal
wires. How much separation?
Jerry
Message 4
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| Subject: | Re: Size of Fuse vs. Circuit Breaker - Corrected |
--> AeroElectric-List message posted by: "Bob C. " <flyboy.bob@gmail.com>
Bob,
I don't understand you example:
"A good case in point deals with pitot tube heaters. Cold resistance
is very high and warmup speeds relatively slow. Some builders have
resorted to 30A fuses to protect a 14AWG wire driving a 100W heated
pitot that runs under 10 amps after it warms up."
If "cold resistance" is "hign" then current would be low. Why would
you need to "resort to 30A fuse"?
Thanks,
Bob
Message 5
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| Subject: | Re: Size of Fuse vs. Circuit Breaker - |
Corrected
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
Corrected
At 08:40 AM 2/11/2005 -0600, you wrote:
>--> AeroElectric-List message posted by: "Bob C. " <flyboy.bob@gmail.com>
>
>Bob,
>
>I don't understand you example:
>
>"A good case in point deals with pitot tube heaters. Cold resistance
>is very high and warmup speeds relatively slow. Some builders have
>resorted to 30A fuses to protect a 14AWG wire driving a 100W heated
>pitot that runs under 10 amps after it warms up."
>
>If "cold resistance" is "hign" then current would be low. Why would
>you need to "resort to 30A fuse"?
Good eye. Got my tongue tangled around my eyeteeth and couldn't
see what I was saying. Cold resistance is LOW and inrush currents
are HIGH. Further, due to slow response for temperature rise, this
"inrush" current is rather extended . . . it takes about a minute
for the temperature of the tube to reach final operating values
in flight.
The upshot is that builders have selected 14 AWG wire for
low voltage drop and 30A fuses so that the relatively fast
fuse is not nuisance tripped by the unique warm-up characteristics
of a pitot tube that only draws about 10A in operation.
Thanks for the heads-up.
Bob . . .
Message 6
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| Subject: | Size of Fuse vs. Circuit Breaker - Final Correction |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 07:23 AM 2/10/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Dennis Johnson"
><pinetownd@volcano.net>
>
>Greetings,
>
>I'm finally getting to the point of beginning the detailed electrical
>design stage of my Lancair Legacy. Although I'm planning to use fuses, I
>noticed in AC 43.13-1B, Table 11-3, that for certain wire sizes, it calls
>for a substantially larger circuit breaker rating than for a fuse. For
>example, a 14 AWG wire can be protected by a 20 amp breaker or a 15 amp fuse.
>
>Since I'm going to be using nearly all fuses, it doesn't particularly
>matter to my design, but just for educational purposes, I'm curious. I
>thought that fuses generally acted faster in response to mild overloads
>than breakers, but AC 43.13 seems to say the opposite. What gives?
In a nutshell . . . selection of a wire size is driven by two
considerations: (1) temperature rise as it affects the insulation
on the wire and (2) voltage drop to be tolerated over the length
of the wire run. The copper in a 22AWG wire will very happily
carry 15 amps at room temperature and free air. I just hooked a
16" piece of 22759/16 to a power supply and jacked it up to 15
amps. 20 minutes later, the wire was way too hot to touch. Voltage
drop was about 0.7 volts. No smells. No smoke. If this had been
PVC wire instead of Tefzel, perhaps the PVC would have melted off
the wire . . . no sweat, go with Teflon.
The REAL answers to your questions are:
(1) how will the wire to be protected be loaded?
Discussion: We routinely load 4AWG FAT wires in our airplanes
to 200 amps or more to crank an engine. Is this
a bad deal? AC43-13 sez protect this wire at
100A breakers or 70A with fuses. Section 5 of
Chapter 11 goes into lots of explanation for
rating wires and takes voltage drop and temperature
rise into consideration. Table 11-9 speaks to
continuous current ratings for wire but consider
notes at the bottom of the table where one reads
that the numbers apply for 70C ambients and free
air . . . higher ambient temps and burying a wire
inside a bundle gives one reasons to derate a wire
still further. One can tolerate what might be
considered severe overloading for short times as
long as voltage drop can be tolerated.
I recommend 4AWG fat wiring for aircraft where
battery is very close to engine. When battery
and engine are on opposite ends of airplane, 2AWG
is recommended. In some seaplanes, 0AWG is
called for. This decision is driven by voltage
drop issues during cranking.
(2) what is the temperature rating of the insulation on
the wire?
Discussion: As long as you're not dealing with voltage drop
issues, then insulation sets the current limits
105C, Tefzel limits at 150C, Teflon goes to 200C.
Got some asbestos sleeving laying around? Slip
that stuff over your wire and you can run it
up to cherry red temperatures. Is the wire hanging
out in the breeze for cooling or is it wrapped up
in a bundle with lots of other wires that
contribute their own heat dissipations to the
equation. Note that we STILL haven't talked about
fuses or circuit breakers.
(3) what kind of load does the wire feed?
Discussion: Are there large inrush or high momentary loads to
be considered? Fuses tend to be faster than thermal
breakers. Magnetic breakers are faster than most
fuses. Virtually ANY form of circuit protection can
be sized to adequately protect ANY wire. You won't
find a considered one-size-fits-all from the charts
and tables. A good case in point deals with pitot
tube heaters. Cold resistance is very LOW compared
to operating resistance. Further, warmup speed
is relatively slow. Some builders have resorted to
30A fuses to protect a 14AWG wire driving
a 100W heated pitot that runs under 10 amps after
it warms up.
The charts and tables will be conservative suggestions
that cover most situations but understand that some
systems will present special issues that drive
CONSIDERED departure from suggestions. There's no
substitute for knowing how the system works and
selecting both wire and circuit protection based
on that understanding.
Bob . . .
Message 7
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| Subject: | Re: Battery cables for aft batterys on RV-7 |
--> AeroElectric-List message posted by: Mickey Coggins <mick-matronics@rv8.ch>
Hi Jerry,
To size the cable, you need to know how much
current the starter will draw. No one seems
to be able to tell me, but hopefully when I
get my engine, I'll just test it. I've heard
some pretty small numbers thrown around, since
it is supposed to have a "geared starter".
Also, I really don't know what kind of voltage
drop the starter can handle, and still crank
the engine.
The engine supplier recommends AWG#6, and I
hope that will work, since that's what I
have installed now. If it doesn't work right,
I've got a bunch of Eric's Super-2-CCA Fat Wire
standing by.
Mickey
Jerry Ballard wrote:
> --> AeroElectric-List message posted by: "Jerry Ballard" <jbyrd@jbyrd-b52.com>
>
> I've just ordered an H-6 Subaru for an RV-7A. For CG I'll probably
> need to locate batteries in or aft of baggage compartment.
>
> Question1: What size wire should I run from batteries to engine
> compartment? Should this be a welding cable type wire? With the
> H-6, reducing weight is more of a concern.
>
> Question 2: I've already placed conduit to run power and/or signal
> wiring for AOA, Whelen strobes, and Grand Rapids EFIS from front to aft
> of baggage compartment. Can the battery cable be run in this conduit
> or should it be relocated for separation from routine power and signal
> wires. How much separation?
>
> Jerry
--
Mickey Coggins
http://www.rv8.ch/
#82007 Wiring
Message 8
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| Subject: | Toggle switch - both master/battery and starter |
--> AeroElectric-List message posted by: "Mitch Faatz" <mitchf@skybound.com>
With the goal of reducing my switch count, I'm wondering if it's possible to double
up the Master/Battery toggle and Starter switch but not sure it's possible
toggle-switch-wise. At first I thought if I could find a DPDT switch that is
Off-On-(On), I could do it. I've found a red toggle switchguard that returns
a toggle that is in the top position back to center (which would drop starter
back to master on) and leave a toggle that is in the bottom position alone (master
off stays master off).
Useability sounds good, switch guard up, switch to master on, momentary full up
for starter, returns to master on. With a DPDT switch I could have one pole
control starter, but I'm worried about the master/battery pole. If it goes from
middle position (on) to up position (momentary on for starter), will there
be a brief interruption and if so will that cause a problem?
Thanks in advance for any thoughts on this -
Mitch Faatz RV-6A Finish Kit Auburn, CA
Message 9
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| Subject: | Re: Big H-bridge for Big Motors |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<b.nuckolls@cox.net>
>One should take care to design switching systems that drive
>h-bridges to preclude simultaneous contrary commands via
>gates or architecture of the control switches. Either may
>be accomplished easily.
>Bob . . .
> AeroElectric-List message posted by: Frank & Dorothy
><frankv@infogen.net.nz>
>
>Robert L. Nuckolls, III wrote:
>
> >Guess it would help if I put the link in too . . .
> >
> >http://www.aeroelectric.com/Pictures/Big_H-Bridge.gif
>
>I'm not sure what application this Big H-bridge is intended for, but
>I've had a bit of experience with *little* H-bridges. After burning up a
>few drive transistors (check out what happens if both drive transistors
>are enabled at once), I moved to a so-called 'smokeless' H-bridge... a
>simple 2-to-4 decoder IC (or circuit) prevents bad things from
>happening. Smart guys even used the 4th state as a brake.
Having had a couple H-bridge designs shoot thru--one is advised to explore
the stunningly simple and reliable intergrated circuit solutions for this
design. They offer feature that you simply could not cobble together in the
conventional designs---even the very clever conventional designs.
For example IR3220S coupled to a pair of IRF7484Q's is 6A continuous WITHOUT
a heatsink--and offers shoot-thru protection, Sleep mode, braking, torque
control, self-adaptive dead time (don't ask!!!), over-temp, over-current,
soft start, inrush limits, etc etc.
This results in magnitudes better performance and reliability for less cost
and much less size and weight. The PCB is one square inch. AN-1032
application note has everything you ever wanted to know on the subject. Not
at all complicated but some SMD assembly skill is required.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"I only regret my economies."
Reynolds Price
Message 10
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| Subject: | Toggle switch - both master/battery and starter |
--> AeroElectric-List message posted by: "Mark R Steitle" <mark.steitle@austin.utexas.edu>
Mitch,
That sounds like what Bob recommends in his "book", and what I purchased
from B&C. It is an OFF-ON-(ON) switch. I believe it is p/n S700-2-50
(Bob can verify this). Wire it like Bob shows and it should work great.
I have been looking for a switch guard that returns the switch to the
center position. Can you post the source and p/n?
Thanks,
Mark S.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Mitch
Faatz
Subject: AeroElectric-List: Toggle switch - both master/battery and
starter
--> AeroElectric-List message posted by: "Mitch Faatz"
<mitchf@skybound.com>
With the goal of reducing my switch count, I'm wondering if it's
possible to double up the Master/Battery toggle and Starter switch but
not sure it's possible toggle-switch-wise. At first I thought if I
could find a DPDT switch that is Off-On-(On), I could do it. I've found
a red toggle switchguard that returns a toggle that is in the top
position back to center (which would drop starter back to master on) and
leave a toggle that is in the bottom position alone (master off stays
master off).
Useability sounds good, switch guard up, switch to master on, momentary
full up for starter, returns to master on. With a DPDT switch I could
have one pole control starter, but I'm worried about the master/battery
pole. If it goes from middle position (on) to up position (momentary on
for starter), will there be a brief interruption and if so will that
cause a problem?
Thanks in advance for any thoughts on this -
Mitch Faatz RV-6A Finish Kit Auburn, CA
Message 11
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| Subject: | Narco wiring harness- part needed |
--> AeroElectric-List message posted by: Jeff Point <jpoint@mindspring.com>
Hello all,
I'm in need of a radio part and I'm hoping someone has one laying
around. I need Narco p/n P810, which is the D-sub connector for the
wiring harness on a NAV122 VOR/ILS unit. What I really need is the
sliding locking piece which attaches to the D-sub hood. If anyone has
one laying around, please contact me.
Thanks
Jeff Point
RV-6
Milwaukee WI
do not archive
Message 12
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| Subject: | Re: Battery cables for aft batterys on RV-7 |
--> AeroElectric-List message posted by: "Hans Teijgeler" <hans@jodel.com>
Mickey,
For an apples-oranges comparison: I've got AWG 6 on my 17 Ah battery to run
my EJ-18 starter on my EJ-25 engine and the engine cranks like mad.
So far the apples.
As for the oranges: my battery is on my firewall rather than in the back,
which results in about 60 cm (2 ft) of cable.
Hope this is of some use
Cheers,
Hans
----- Original Message -----
From: "Mickey Coggins" <mick-matronics@rv8.ch>
Subject: Re: AeroElectric-List: Battery cables for aft batterys on RV-7
>
> The engine supplier recommends AWG#6, and I
> hope that will work, since that's what I
> have installed now.
Message 13
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| Subject: | Re: Size of Fuse vs. Circuit Breaker - Corrected |
--> AeroElectric-List message posted by: "Bob C. " <flyboy.bob@gmail.com>
Bob,
What's you conclusion on the pitot heater example . . . what would the
appropriate wire size be 14, 16 or 18?
Thanks,
Bob
On Fri, 11 Feb 2005 10:59:00 -0600, Robert L. Nuckolls, III
<b.nuckolls@cox.net> wrote:
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
Corrected
>
> At 08:40 AM 2/11/2005 -0600, you wrote:
>
> >--> AeroElectric-List message posted by: "Bob C. " <flyboy.bob@gmail.com>
> >
> >Bob,
> >
> >I don't understand you example:
> >
> >"A good case in point deals with pitot tube heaters. Cold resistance
> >is very high and warmup speeds relatively slow. Some builders have
> >resorted to 30A fuses to protect a 14AWG wire driving a 100W heated
> >pitot that runs under 10 amps after it warms up."
> >
> >If "cold resistance" is "hign" then current would be low. Why would
> >you need to "resort to 30A fuse"?
>
> Good eye. Got my tongue tangled around my eyeteeth and couldn't
> see what I was saying. Cold resistance is LOW and inrush currents
> are HIGH. Further, due to slow response for temperature rise, this
> "inrush" current is rather extended . . . it takes about a minute
> for the temperature of the tube to reach final operating values
> in flight.
>
> The upshot is that builders have selected 14 AWG wire for
> low voltage drop and 30A fuses so that the relatively fast
> fuse is not nuisance tripped by the unique warm-up characteristics
> of a pitot tube that only draws about 10A in operation.
>
> Thanks for the heads-up.
>
> Bob . . .
>
>
>
Message 14
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| Subject: | RE: Size of Fuse vs. Circuit Breaker |
--> AeroElectric-List message posted by: "Dennis Johnson" <pinetownd@volcano.net>
Thanks, Matt and Bob, for responding to my question about why AC 43.13 shows different
amperage ratings for fuses and circuit breakers. Matt, I'd guess you're
probably right that the table was made up based on specific specs for specific
fuses and breakers that were in use at that time.
Thanks again,
Dennis Johnson
Legacy #257
Do not archive
Message 15
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| Subject: | Coax connector Garmin 196 |
--> AeroElectric-List message posted by: N27160@aol.com
I have a Garmin 196 and to keep the mounting as tight as possible, I need a
coax connector for the antenna to be as compact as possible.
A regular straight connector is gonna require me to drill a hole behind the
196. Any ideas for an alternative?
Message 16
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| Subject: | Re: Size of Fuse vs. Circuit Breaker - Corrected |
--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
We have a run of about 25' from the fuse panel to the pitot tube for an
plastic airplane. That's 50' roundtrip. We used 11 amps start and ending
at 7.5 to 8 for steady state. Installed 12 AWG. The pitot heat is the
biggest current draw of anything in the aircraft - by a factor of about 2
to 3. Incidentally, the wire is in a conduit for about 75-80% of its
length.
John
>
> What's you conclusion on the pitot heater example . . . what would the
> appropriate wire size be 14, 16 or 18?
>
> Thanks,
> Bob
>
Message 17
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| Subject: | Re: Size of Fuse vs. Circuit Breaker - Corrected |
--> AeroElectric-List message posted by: Fiveonepw@aol.com
In a message dated 02/11/2005 7:47:16 PM Central Standard Time,
jschroeder@perigee.net writes:
The pitot heat is the
biggest current draw of anything in the aircraft - by a factor of about 2
>>
What, are ya hand-proppin' this baby?!
(apologies pre-flame!)
8-)
Mark do not archive
Message 18
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| Subject: | Re: Size of Fuse vs. Circuit Breaker - Corrected |
--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
Mark -
Of course, the starter draws more. But after that, can you think of any
item that can draw 11 amps. If so, let me know. I always have the felling
that we have forgotten something. :-))
BTW, Steve Davis said to tell you hello. We didn't get to go for barbecue
this time!!
Cheers,
John
> The pitot heat is the biggest current draw of anything in the aircraft -
> by a factor of about 2
>>>
> What, are ya hand-proppin' this baby?!
Message 19
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| Subject: | Re: Measurements |
--> AeroElectric-List message posted by: j1j2h3@juno.com
If you're really set on accurately measuring this, you can do it with
little expense, but some work in making calculations and experimenting
with the set up.
Analog ammeters are really millivoltmeters that are measuring the voltage
drop across a resistor. The value of the resistor, referred to as a
shunt, is very low and its current capacity is very high. Typically, it
is just a piece of metal or wire.
You can accomplish the same thing with your digital ammeter. You will
have to make the shunt out of wire that is small enough to have a voltage
drop that you can measure, but large enough to carry the expected maximum
current and also long enough to give you a measurable resistance. Then
measure its resistance and insert it in the circuit. With the circuit
energized, read the voltage drop across the shunt and use the known
resistance to calculated the amperage, using E = IR or I = E/R. When
analog meters were used, you also had to calculate the amperage through
the meter, but with digitals, this is negligible. The resistance of the
shunt will also affect the final result, but can be neglected if it is
very low. However, if you really wanted, you could calculate the total
resistance of the circuit, again using E = IR, where E is the output
voltage of your system, then recalculate the current with the shunt
resistance subtracted. This will get you very, very, close, but then the
resistance of the light bulb will change as the current increases with
the shunt removed, so you will still have a small unknown.
Jim Hasper - RV-7
Giving new meaning to the term "slow build"
Franklin, TN
Do not archive
> > --> AeroElectric-List message posted by: "Tinne maha"
> > <tinnemaha@hotmail.com>
> >
> > Bob/List,
> >
> > I would like to measure the current used by my landing/taxi light.
> The
> > multi-meters I have access to only measure up to 2 amps, but I'm
> sure my
> > light uses more than that (on the order of 5-10 amps, I believe).
> >
> > Can you tell me where I can get an ammeter that measures more than
> 2 amps?
> > Is it inadvisable to use the ammeter I will install in my plane?
> >
> > Any help is appreciated. Thanks,
> > Grant
> >
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