Today's Message Index:
----------------------
1. 06:06 AM - Re: Avionics Back-Up Power (Robert L. Nuckolls, III)
2. 06:29 AM - Re: Kitplanes article on an Elegant LED driver (David E. Nelson)
3. 06:33 AM - Re: Kitplanes article on an Elegant LED driver (David E. Nelson)
4. 07:48 AM - Re: Avionics Back-Up Power (Carlos Trigo)
5. 02:35 PM - Re: Avionics Back-Up Power (Robert L. Nuckolls, III)
Message 1
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| Subject: | Avionics Back-Up Power |
> How big a battery is it? How many batteries does the airplane
> carry already . . . in other words do you already have an
> AUX battery?
>
> Bob . . .
I don't know exactly, because I still don't know the exact weight I need
for W & B, but I am planning for a battery around 10Ah I do have 2 other
batteries, Main and AUX, since my engine is an electron-dependant Subaru.
Hmmmm . . . this is a bit problematic. Battery installation
philosophy in A/C calls for local disconnect (battery contactor
or relay). We also need to size the wiring so expected loads
and recharge currents do not experience too large voltage
drop. Finally, all wires need to be properly protected against
faults.
A 10 a.h. battery is good for about 10# of 'ballast'. If
you went further back on the airframe, could you get down
to say 5# of ballast? The reason for asking is that my present
image of this system suggests a plastic battery relay (one
of those 70A plastic things). A local fuse (use MAXI fuse
holder to make the battery(+) to battery relay jumper. Run
the battery feeder forward to the battery bus that runs
the panel during alternator out operations. We don't
want to leave that feeder hot while the airplane is
shut down . . . you need another relay at the forward
end of the feeder too and protect that end with another
MAXI fuse. The wire probably wants to be 10AWG and the
fuses at both ends are MAX30. Now you need a third battery
switch that closes both relays during flight operations.
This is electrically messy . . . not much better from
the pilot workload perspective either. As I mentioned
earlier, it might be better to minimize total added weight
by moving it as far back on the airframe as possible . . .
an letting it be dead-weight thus avoiding the bow-
of-spaghetti-wiring.
Bob . . .
Message 2
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| Subject: | Re: Kitplanes article on an Elegant LED driver |
Hi Ernest,
My apologies. My intention was not to loose site of the original question
should this be read years from now in one of the archives. ;)
Take care,
/\/elson
~~ Lately my memory seems to be like a steel trap .... without any spring. ~~
On Fri, 29 Aug 2008, Ernest Christley wrote:
> <echristley@nc.rr.com>
>
> David E. Nelson wrote:
>>
>> So now, why the MHz freq the LM3404?
>
> I think Bob answered that well. Switching power supplies have an easier time
> of it at higher frequencies. The power supply in the back of your computer
> converts the 60Hz line signal up to something like 10KHz (IIRC) for the same
> reason. It is much easier to transform and then rectify a higher frequency
> signal to a clean output. The components can be much smaller and there is
> less heat generated.
>
>
Message 3
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| Subject: | Re: Kitplanes article on an Elegant LED driver |
Hi Bob,
Thanks for the great explanation - as usual. ;)
Do not archive.
Take care,
/\/elson
~~ Lately my memory seems to be like a steel trap .... without any spring. ~~
On Fri, 29 Aug 2008, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@cox.net>
>
> At 08:31 AM 8/29/2008 -0500, you wrote:
>> <david.nelson@pobox.com>
>>
>>
>> Hi Bob,
>>
>> I'm curious, why is such a high freq (1-2MHz) needed for an application
>> such as this? Rather, why not in high 100's of Hz given that the eye can't
>> even discern above 30 Hz?
>>
>> Thank you,
>>
>> /\/elson
>
> Great question. The problem of selecting an operating
> frequency comes from a trade-off in reactances . . .
> in the form of inductors and capacitors. The higher
> you go in frequency, the more energy can be stored on
> a given size inductor (assuming the core is loss less).
> The higher you go in frequency, the easier it is to
> couple energy via capacitors . . . both for the purpose
> of bypassing and transfer.
>
> In this case, the power supply is an energy conversion
> system that stores a short pulse of current on and inductor
> and then retrieves that energy at a different voltage level.
> Given no other considerations for efficiency of the switching
> devices and losses in the magnetics, one would LIKE to operate
> at the highest possible frequency to drive down the physical
> size of components.
>
> Example. Step down transformers for 60 Hz AC delivered to
> the house can handle about 60 watts per pound of transformer
> core and copper. Airplanes use 400 Hz and the same transformer
> weight and volume can handle over 6 times the power . . .
> but the iron for the transformer must be tailored for low
> losses at the higher frequency.
>
> The high output LEDs need about 4v per lamp (whites) but
> they're CURRENT driven devices. The really cool thing about
> switchmode power supplies is that you can take energy in
> at voltages in a much below or above the desired output
> levels and bring the energy out as either a constant current
> or constant votlage. The LM3404 is designed to operate in
> the constant-current mode.
>
> Batteries are not constant voltage devices . . . so the
> most efficient flashlights will have a rather sophisticated
> voltage to constant current generator that accepts battery
> voltage over the full range useful output and delivers
> a constant current to the lamp until the batteries are
> truly drained. These converters need to be tiny and
> efficient . . . highest practical operating frequency
> is a strong consideration in meeting design goals.
>
> Bob . . .
>
>
Message 4
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| Subject: | Avionics Back-Up Power |
Bob
Thanks for your explanation and suggestions.
Anyway, which is the reason you say "we don't want to leave that feeder
hot
while the airplane is shut down=94 ?
If it=92s not so important, 2 relays and 1 switch could be avoided, and
pilot
workload as well=85
Carlos
> -----Original Message-----
> From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-
> server@matronics.com] On Behalf Of Robert L. Nuckolls, III
> Sent: s=E1bado, 30 de Agosto de 2008 14:05
> To: aeroelectric-list@matronics.com
> Subject: RE: AeroElectric-List: Avionics Back-Up Power
>
> <nuckolls.bob@cox.net>
>
> > How big a battery is it? How many batteries does the airplane
> > carry already . . . in other words do you already have an
> > AUX battery?
> >
> > Bob . . .
>
> I don't know exactly, because I still don't know the exact weight I
need
> for W & B, but I am planning for a battery around 10Ah I do have 2
other
> batteries, Main and AUX, since my engine is an electron-dependant
Subaru.
>
> Hmmmm . . . this is a bit problematic. Battery installation
> philosophy in A/C calls for local disconnect (battery contactor
> or relay). We also need to size the wiring so expected loads
> and recharge currents do not experience too large voltage
> drop. Finally, all wires need to be properly protected against
> faults.
>
> A 10 a.h. battery is good for about 10# of 'ballast'. If
> you went further back on the airframe, could you get down
> to say 5# of ballast? The reason for asking is that my present
> image of this system suggests a plastic battery relay (one
> of those 70A plastic things). A local fuse (use MAXI fuse
> holder to make the battery(+) to battery relay jumper. Run
> the battery feeder forward to the battery bus that runs
> the panel during alternator out operations. We don't
> want to leave that feeder hot while the airplane is
> shut down . . . you need another relay at the forward
> end of the feeder too and protect that end with another
> MAXI fuse. The wire probably wants to be 10AWG and the
> fuses at both ends are MAX30. Now you need a third battery
> switch that closes both relays during flight operations.
>
> This is electrically messy . . . not much better from
> the pilot workload perspective either. As I mentioned
> earlier, it might be better to minimize total added weight
> by moving it as far back on the airframe as possible . . .
> an letting it be dead-weight thus avoiding the bow-
> of-spaghetti-wiring.
>
> Bob . . .
>
Message 5
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| Subject: | Avionics Back-Up Power |
At 03:47 PM 8/30/2008 +0100, you wrote:
>Bob
>
>Thanks for your explanation and suggestions.
>
>
>Anyway, which is the reason you say "we don't want to leave that feeder
>hot while the airplane is shut down ?
>
>If it s not so important, 2 relays and 1 switch could be avoided, and
>pilot workload as well&
It's just not done (at least in the TC aircraft world) both for maintenance
and crash safety. How would you propose to wire it?
Bob . . .
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