Today's Message Index:
----------------------
1. 06:03 AM - Re: Re: Latching Relay Redux (Robert L. Nuckolls, III)
2. 06:27 AM - Re: Re: Using LEDs in Series (Robert L. Nuckolls, III)
3. 06:34 AM - Re: What guage wire for alternator to bus bar (Robert L. Nuckolls, III)
4. 08:22 AM - Re: Re: Latching Relay Redux (Ken)
5. 10:32 AM - Re: Re: Latching Relay Redux (Robert L. Nuckolls, III)
6. 12:30 PM - Re: Using LEDs in Series (Robert L. Nuckolls, III)
7. 02:59 PM - PM Alternator filter Capacitor - best practices (John Loram)
8. 03:19 PM - Re: PM Alternator filter Capacitor - best practices (Harley)
9. 03:23 PM - Re: PM Alternator filter Capacitor - best practices (Robert L. Nuckolls, III)
10. 04:47 PM - Re: PM Alternator filter Capacitor - best practices (John Loram)
11. 06:14 PM - Re: Re: Using LEDs in Series (mapratherid)
12. 07:17 PM - Re: PM Alternator filter Capacitor - best practices (Robert L. Nuckolls, III)
13. 07:44 PM - Re: Re: Using LEDs in Series (Robert L. Nuckolls, III)
14. 08:19 PM - Re: PM Alternator filter Capacitor - best practices (John Loram)
15. 08:33 PM - Re: Re: Latching Relay Redux (Robert L. Nuckolls, III)
16. 11:01 PM - Official AeroElectric-List FAQ (Frequently Asked Questions) (Matt Dralle)
17. 11:05 PM - Official AeroElectric-List Usage Guidelines (Matt Dralle)
Message 1
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Subject: | Re: Latching Relay Redux |
At 09:07 PM 7/30/2012, you wrote:
>
>I received this email today from Chuck (quoted below) in reference
>to my circuit "Contactor PWM.pdf " to reduce contactor holding current.
>http://forums.matronics.com/download.php?id=32370
>
> > Hello Joe
> > I built the circuit with one change. I replaced R1 with an
> adjustable 0-25k ohm pot. Works great, just dial in the PWM for the
> right duty cycle with R1 for the particular contactor being used.
> > Thanks Chuck
I recommend that the power saving duty cycle
be set for not less than 50%. This cuts average
voltage to contactor by 50% . . . hence average
current by 50% and total power dissipated by
75%.
While a 12v contactor will stay energized at
voltages of 2v or below, you want to make sure
that the contactor stays closed down to battery
end of life at 10.5 volts or so. 50% at 14 volts
with alternator running gives you 7 volts to hold
the contactor . . . 10.5 translates to 5.25 volts
or thereabouts . . . probably as low as you want
to go. 75% reduction in lost energy is pretty
substantial if you're in a battery-only operational
mode . . . or struggling to make the most of an
8A alternator.
Bob . . .
Bob . . .
Message 2
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Subject: | Re: Using LEDs in Series |
At 09:58 PM 7/30/2012, you wrote:
>Therein lies another problem, Eric. For a switching regulator
>(digital) that is "noise free with really good design," you say that
>it involves knowing what frequency spectrum you can use for
>switching ... something that won't interfere.
Switching regulators are ubiquitous and definitely
here to stay. ALL of the accessories that trumpet
10-30 volt supply inputs are fitted with such
power supplies.
Operating frequency for such supplies is never
'selected' to be compatible with the operating
environment. It's selected as a trade-off for
for the components selected to achieve maximum
efficiency at rated load.
After design goals for efficiency are achieved, then
careful board layout for controlling aperture
area (radiation concerns) and good management
of RF grounds (conduction concerns) and
dv/dt limiting (both concerns) will minimize
any necessary filtering and shielding to
meet DO-160 emissions limits.
Anyone who has done this exercise a couple
of times will never again be surprised in the lab
with failure of a new design to meet emissions
limits. It's like learning to bake cakes.
After my first few passes through the vibration
immunity testing, I never again shook a component
of a board . . . it's that 'learning curve' thingy.
The filter I crafted for the BuckPucks was
a brute force endeavor to fix a problem in
systems that were already under construction
and parts were on hand. The filter may be
more than was really necessary . . . but it
proved to be adequate to the task. A detailed
study in the RFI lab might show that a simpler
filter would do . . . but given the small
volume of sales for this particular LED drive
solution, it hardly justifies the expense of
a finely tuned development effort.
The BuckPuck was never intended for use in
an aircraft EMC environment else it would not
have been built that way. Some of the HID lamp
supplies I've played with are similarly burdened
with EMC issues for aircraft. That doesn't mean
that any of these devices were "poorly designed",
it only means that the customer base for thousands
of units don't care that the device going into their
boat, motorcycle or hot-rod is unsuited to airplanes.
In the OBAM aviation world, we are a primo filter
for searching out and identifying the best that
folks know how to do. But it's a fine demonstration
of the need for caveat emptor . . . give it a try
in low risk experiments and report findings to
the group. If a short-fall in performance is
noted, then try something else . . . or modify
the product (such as the filter board for the
BuckPucks). In any case, the ultimate goodness
of the device and the system in fits is up to
us and NOT the designer of the device who probably
never envisioned his work product going into
an airplane . . . and would probably rather that
it did not.
It used to be that a phone call to Gates about
v-belts had to be made in 'disguise' . . . if
you mentioned that you were working on an airplane,
the standard vociferous response was "our products
are not intended for use on aircraft" . . . i.e.
"you're on your own my friend".
Bob . . .
Message 3
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Subject: | Re: What guage wire for alternator to bus bar |
At 07:04 AM 7/31/2012, you wrote:
sorry ( i am a newbie to this forum ) if this is already answered
else where, but i would like to know the minimum gauge wire i should
use for a 60amp alternator (15V) to the Bus bar which is 5ft away.
In normal operation max current draw in flight would be 12 amps (
landing lights , nav lights, radio, transponder, solenoids)
6AWG would be good, 4AWG welding cable is
readily available, inexpensive and would
be better.
In addition, (and this may seem like a silly idea), but I actually
want to limit the maximum current that could go into my lithium Ion
Phosphate battery immediately after start up to say 10 amps, how
would I go about this ? Currently it is drawing max amps out of
the alternator for the rotation speed (1200 rpm) for a few minutes,
and I think this was the reason for my alternator drive coupling slipping.
We need more information here. Your alternator drive
system should be designed to function at the alternator's
rated output. In other words, if it slips under some
conditions of loading, then the answer is to fix the
drive system, not reduce the load.
Where does the 1200 rpm number come from . . . prop RPM?
What's the alternator RPM at this time?
Bob . . .
Message 4
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Subject: | Re: Latching Relay Redux |
Is that 75% power reduction correct??
I would have guessed that a 50% duty cycle gave full voltage and full
current for 50% of the time in a pulsed resistance circuit resulting in
a 50% power reduction. Not sure about an inductive coil contactor though.
Just asking but intuitively I would not have averaged the voltage and
applied the I squared power calculation to this.
Ken
On 01/08/2012 9:02 AM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 09:07 PM 7/30/2012, you wrote:
>> <fran4sew@banyanol.com>
>>
>> I received this email today from Chuck (quoted below) in reference to
>> my circuit "Contactor PWM.pdf " to reduce contactor holding current.
>> http://forums.matronics.com/download.php?id=32370
>>
>> > Hello Joe
>> > I built the circuit with one change. I replaced R1 with an
>> adjustable 0-25k ohm pot. Works great, just dial in the PWM for the
>> right duty cycle with R1 for the particular contactor being used.
>> > Thanks Chuck
>
> I recommend that the power saving duty cycle
> be set for not less than 50%. This cuts average
> voltage to contactor by 50% . . . hence average
> current by 50% and total power dissipated by
> 75%.
>
> While a 12v contactor will stay energized at
> voltages of 2v or below, you want to make sure
> that the contactor stays closed down to battery
> end of life at 10.5 volts or so. 50% at 14 volts
> with alternator running gives you 7 volts to hold
> the contactor . . . 10.5 translates to 5.25 volts
> or thereabouts . . . probably as low as you want
> to go. 75% reduction in lost energy is pretty
> substantial if you're in a battery-only operational
> mode . . . or struggling to make the most of an
> 8A alternator.
>
> Bob . . .
>
>
Message 5
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Subject: | Re: Latching Relay Redux |
At 10:20 AM 8/1/2012, you wrote:
Is that 75% power reduction correct??
I would have guessed that a 50% duty cycle gave full voltage and full
current for 50% of the time in a pulsed resistance circuit resulting
in a 50% power reduction. Not sure about an inductive coil contactor though.
Just asking but intuitively I would not have averaged the voltage and
applied the I squared power calculation to this.
-----------
Excellent question . . . and yes, consideration of
contactor inductance paralleled with a diode
is critical to the analysis.
When to the bench and set this up:
Emacs!
This test setup produced the following data:
Emacs!
If I go to 100% duty cycle, this El Cheeso,
Stancore/RBM contactor draws 0.9 amps 14.6 volts.
Dynamically, the coil current (Yellow trace) shows
some ripple at the switching frequency but averages
just under 0.5 Amp.
In the mean time, the power supply is showing a
load of just 0.21 amps or about 25% of the full-on
current draw.
If I put a 15 ohm resistor in place of the\
contactor, the 100% current goes to the expected
1 amp. At 50% duty cycle, the peak current is still
1 amp with average current falling to the predicted
0.5A . . . hence 50% duty cycle produces only 50%
reduction in power in the resistive circuit.
The L/R time constant of the inductive circuit
prevents achievement of full current during limited
on-time. The diode prevents current from falling
to zero during off-time.
After one hour, the outside temperature of the
contactor was not too hot to sustained touch . . .
Waayyy cooler than contactor operatied at 100%.
Bob . . .
Message 6
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Subject: | Re: Using LEDs in Series |
I have been experimenting with a product available
off eBay that offers 300, .05 x .05 LED's mounted
to a 3/8" wide x 16 foot flexible etched circuit
strip.
http://tinyurl.com/c33w25o
The leds are wired in paralleled series-clusters of
3 devices and a 150 ohm resistor. Here's a 2-cluster
segment of this product . . .
Emacs!
You can cut the strip every three devices and attach new
power leads at the solder pads visible in the photo.
I'm going to be using about 80 feet of this product in
my kitchen to put double rows of ceiling accent lighting high up,
double rows to replace recessed canister lights over the
counters and a third twin-row installation under the cabinets
for work lighting. The double-rows will be wired in series to run
off 24 volt supplies in the walls. My present lighting
is fraught with hot-spots from 11 different fixtures with
no accent lighting on a budget of about 700 watts. The working
end of my kitchen will be nicely lighted for both appearance
and working illumination on a power budget of about 175
watts total. This technique produces very wide-angle
illumination that is virtually shadow free.
The strips are fitted with peel and stick adhesive. I'm
going to use 3/4" wide strips of Formica to assemble one-
piece lighting assemblies that make it easy to get the
rows installed straight while laying on my back under
a cabinet.
The light output from these devices is very good. I suspect
that one could put a single strip of this product on the
under side of a glare shield and get more than enough
light . . . with devices easily dimmed. Due to the
series wiring of three, 3-volt devices, you would want
to control dimming with a series resistance or an
adjustable current supply like a Buck-Puck. Ten of
these clusters would give you about 30 leds and a max
bright current draw of 300 mA. A constant voltage
dimmer like B&C sells COULD be modified to have minimum
brightness occur at 9 volts instead of the present
4 volts. In any case, This product offers a host of
illumination opportunities not the least of which is
your airplane.
Bob . . .
Message 7
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Subject: | PM Alternator filter Capacitor - best practices |
What would be considered best practice for installation of the large
electrolytic capacitor used to filter the output of a PM alternator:
Mount it on the hot side of the firewall and protect the occupants
Mount it on the cool side of the firewall and protect the capacitor
Would appreciate any speculations, -john-
Message 8
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Subject: | Re: PM Alternator filter Capacitor - best practices |
Evenin', John,
Good timing for this question! Just finished installing mine
last week! And no speculation in my case...
I put mine inside, behind the passenger's head (Long EZ...pusher
engine not as bad as it sounds....a headrest pad and a couple of
canopy braces protect the passenger from the electronics on the
inside of the firewall) mainly because the installation
instructions with the B&C alternator specifically said NOT to
mount the cap on the engine side of the firewall because of the
heat there! Guess the passenger is less important than the
alternator!;-)
Harley Dixon
Long EZ N28EZ
-----------------------------------------------------------------
On 8/1/2012 5:57 PM, John Loram wrote:
> What would be considered best practice for installation of the
> large electrolytic capacitor used to filter the output of a PM
> alternator:
> Mount it on the hot side of the firewall and protect the occupants
> Mount it on the cool side of the firewall and protect the capacitor
> Would appreciate any speculations, -john-
> *
> *
Message 9
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Subject: | Re: PM Alternator filter Capacitor - best practices |
At 04:57 PM 8/1/2012, you wrote:
>What would be considered best practice for installation of the large
>electrolytic capacitor used to filter the output of a PM alternator:
>
>Mount it on the hot side of the firewall and protect the occupants
>
>Mount it on the cool side of the firewall and protect the capacitor
>
>Would appreciate any speculations, -john-
It's utility is limited. See in particular,
the second page of
http://tinyurl.com/cz7ekrf
even with no capacitor, the noises are
well under Mil-STD-704 limits for DC
power systems. So mounting it 'cool'
probably bodes best for service life
and has little effect on system
performance.
Bob . . .
Message 10
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Subject: | PM Alternator filter Capacitor - best practices |
Hmmmm... so why do we use this cap?
-john-
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Wednesday, August 01, 2012 3:23 PM
Subject: Re: AeroElectric-List: PM Alternator filter Capacitor - best
practices
At 04:57 PM 8/1/2012, you wrote:
What would be considered best practice for installation of the large
electrolytic capacitor used to filter the output of a PM alternator:
Mount it on the hot side of the firewall and protect the occupants
Mount it on the cool side of the firewall and protect the capacitor
Would appreciate any speculations, -john-
It's utility is limited. See in particular,
the second page of
http://tinyurl.com/cz7ekrf
even with no capacitor, the noises are
well under Mil-STD-704 limits for DC
power systems. So mounting it 'cool'
probably bodes best for service life
and has little effect on system
performance.
Bob . . .
Message 11
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Subject: | Re: Using LEDs in Series |
This looks pretty cool Bob. But I'm picky about color temp. Any idea what Ke
lvin color you'll end up with?
Regards,
Matt-
On Aug 1, 2012, at 1:29 PM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroelec
tric.com> wrote:
> I have been experimenting with a product available
> off eBay that offers 300, .05 x .05 LED's mounted
> to a 3/8" wide x 16 foot flexible etched circuit
> strip.
>
> http://tinyurl.com/c33w25o
>
> The leds are wired in paralleled series-clusters of
> 3 devices and a 150 ohm resistor. Here's a 2-cluster
> segment of this product . . .
>
> <1839fa0.jpg>
>
> You can cut the strip every three devices and attach new
> power leads at the solder pads visible in the photo.
>
> I'm going to be using about 80 feet of this product in
> my kitchen to put double rows of ceiling accent lighting high up,
> double rows to replace recessed canister lights over the
> counters and a third twin-row installation under the cabinets
> for work lighting. The double-rows will be wired in series to run
> off 24 volt supplies in the walls. My present lighting
> is fraught with hot-spots from 11 different fixtures with
> no accent lighting on a budget of about 700 watts. The working
> end of my kitchen will be nicely lighted for both appearance
> and working illumination on a power budget of about 175
> watts total. This technique produces very wide-angle
> illumination that is virtually shadow free.
>
> The strips are fitted with peel and stick adhesive. I'm
> going to use 3/4" wide strips of Formica to assemble one-
> piece lighting assemblies that make it easy to get the
> rows installed straight while laying on my back under
> a cabinet.
>
> The light output from these devices is very good. I suspect
> that one could put a single strip of this product on the
> under side of a glare shield and get more than enough
> light . . . with devices easily dimmed. Due to the
> series wiring of three, 3-volt devices, you would want
> to control dimming with a series resistance or an
> adjustable current supply like a Buck-Puck. Ten of
> these clusters would give you about 30 leds and a max
> bright current draw of 300 mA. A constant voltage
> dimmer like B&C sells COULD be modified to have minimum
> brightness occur at 9 volts instead of the present
> 4 volts. In any case, This product offers a host of
> illumination opportunities not the least of which is
> your airplane.
>
> Bob . . .
Message 12
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Subject: | PM Alternator filter Capacitor - best practices |
At 06:45 PM 8/1/2012, you wrote:
>Hmmmm... so why do we use this cap?
>
Now you done it . . . let's see if I recall.
I think I first saw it used on a power distribution
diagrams for some Rotax powered ultra-lights
back when I first started working in OBAM
aviation. Shucks . . . the rectifiers of AC
to DC power supplies had filter capacitors
on them . . . why not the rectified ac output
of a PM alternator?
The idea was attractive, only the numbers were
poorly understood. If you push 1 amp into a
1 Farad capacitor, you get a 1 volt per second
rate of rise in voltage. 10 amps is 10 volts
per second. Okay, how about a 1 microfarad
capacitor? The rise is 1 million times faster
or 10M volts per second. Now make the capacitor
20,000 times bigger and the voltage rise rate
drops by a factor of 20K or 500 volts per second.
Okay, the ripple period in the traces I published
for 4000 rpm was 7.5 milliseconds. .0075 x 500
= 3.75 volts is the best ripple reduction we might
expect from 20KF on a 10A machine. As you can see
from page 2 trace, the pk-pk excursions are already
below 400 mv. already 10X better than what we might expect
with but with no capacitor. To cut that to say, 40 mV
(nice anc quiet comparatively) we'd need a capacitor
100 times 20,000 or 2 Farads.
I was startled by the test results with the SD-8
on B&C's alternator stand. There was little or no
observable effect at ripple frequency for adding
the capacitor.
Yeah, we can buy such a critter but it's big,
heavy, expensive and goes toward an unnecessary
refinement of the system.
We know that a 3-phase alternator has about 5%
pk-pk ripple (0.75 volts on a 15v system)
plus transients. How many Farads would it take
to smooth say a 100A machine? The single phase
PM alternators like the SD-8 are obviously worse
but battery alone combined with loads at or
near max ratings have more smoothing effects than
the capacitor.
Given the physical impracticality of seeing
such pristine power, complimentary standards
and design goals were adopted to say (in Mil-
STD-704) that a 28v system can have 1 VRMS (3+
volts pk-pk) noise from 1 to 5K Hertz and
tapering off each side.
http://tinyurl.com/78kwfk8
1/2 that value for a 14v system.
The complimentary DO-160 design goals tell us
to EXPECT this kind of trash on the bus and
design to live with it.
The capacitor doesn't hurt anything and if
you have a particularly bad set of rectifier
switching transients (or similar fast rise
stuff elsewhere in the system, the 20-20K
computer grade capacitor will reduce the
effects of that stimulus.
Suffice it to say that MOST pilots now flying
such capacitors on their PM alternator installations
would notice nothing from the cockpit if that
capacitor were removed.
Radios and audio systems need really clean power
and the qualified designer provides smoothing
internally.
Emacs!
Our audio isolation amplifier design uses the LM317
to provide a smooth source of +8 volts to run the
circuitry.
As a general rule, the kinds of stimulus that benefits
from any sort of bus voltage filtering is fast-rise
transients at a ripple-current rate. Folks mistakenly
believe their inductor/capacitor or just a capacitor
is bypassing AUDIO frequency energy when in fact, it's
high frequency (fast transients) at the audio rate.
As the numbers above suggest, there's no practical way
to filter alternator ripple from the bus. The snow-mobile
engines with lighting coils converted to electrical
system alternators may well have benefited from the
use of such capacitors . . . depends on vulnerabilities
inherent in their electro-whizzies. Our electro-whizzies
are suited by design to live in the world of trashy
busses.
This is why switchmode power supplies can be so small
when delivering outputs in the tens of amps . . . their
operating frequencies (hence ripple frequency) is quite
high which allows smaller capacitors and inductors to
do the same degree of smoothing.
You can leave the cap out and see if you hear any
alternator whine in the audio . . . odds are that you
will not.
Bob . . .
Message 13
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Subject: | Re: Using LEDs in Series |
At 08:13 PM 8/1/2012, you wrote:
>This looks pretty cool Bob. But I'm picky about color temp. Any idea
>what Kelvin color you'll end up with?
You can select for cool, pure, or warm white colors
when you order. Given the cheapness of excess
brightness for you can probably do some shading with
theater lighting gels.
I had to match some lighting colors in incandescent
lamps about 25 years ago at Videmation. A local
theater supply store had every color hue and density
imaginable in gels for about $2 a sheet. We fiddled
with the filters until we got it right.
In my kitchen I'll be using the pure whites and
letting colors reflected from surfaces set the
mood. At Cessna, blue-white post lighting was a
high dollar option for panel illumination. You
could get the same thing by putting the appropriate
gel over the lamps.
Bob . . .
Message 14
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Subject: | PM Alternator filter Capacitor - best practices |
So we're not trying to control the bandwidth of the regulator loop with the
cap? Does the battery do that? Guess I don't really know what the frequency
response of a lead-acid battery is. Probably dependent on the state of
charge and the condition of the battery. And the load varies all over the
place, both real and imaginary components.... What would it look like with
and without the cap if the battery were out of the loop? ... Scary!
I'm running 3 phase (old Jab 3300).
Once I get this thing fired up I'll run some tests and let you know what
happens...
Just thinking out loud, -john-
p.s. ran into a message the other day that you wrote back in 2007. Said you
worked for H.L Yoh as a civilian instructor in the early 60's... Same here!
At the Naval ETA school on Treasure Island. Wasn't that fun. I learned more
electronics in six months instructing those kids than four years of collage!
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Wednesday, August 01, 2012 7:11 PM
Subject: RE: AeroElectric-List: PM Alternator filter Capacitor - best
practices
At 06:45 PM 8/1/2012, you wrote:
Hmmmm... so why do we use this cap?
Now you done it . . . let's see if I recall.
I think I first saw it used on a power distribution
diagrams for some Rotax powered ultra-lights
back when I first started working in OBAM
aviation. Shucks . . . the rectifiers of AC
to DC power supplies had filter capacitors
on them . . . why not the rectified ac output
of a PM alternator?
The idea was attractive, only the numbers were
poorly understood. If you push 1 amp into a
1 Farad capacitor, you get a 1 volt per second
rate of rise in voltage. 10 amps is 10 volts
per second. Okay, how about a 1 microfarad
capacitor? The rise is 1 million times faster
or 10M volts per second. Now make the capacitor
20,000 times bigger and the voltage rise rate
drops by a factor of 20K or 500 volts per second.
Okay, the ripple period in the traces I published
for 4000 rpm was 7.5 milliseconds. .0075 x 500
= 3.75 volts is the best ripple reduction we might
expect from 20KF on a 10A machine. As you can see
from page 2 trace, the pk-pk excursions are already
below 400 mv. already 10X better than what we might expect
with but with no capacitor. To cut that to say, 40 mV
(nice anc quiet comparatively) we'd need a capacitor
100 times 20,000 or 2 Farads.
I was startled by the test results with the SD-8
on B&C's alternator stand. There was little or no
observable effect at ripple frequency for adding
the capacitor.
Yeah, we can buy such a critter but it's big,
heavy, expensive and goes toward an unnecessary
refinement of the system.
We know that a 3-phase alternator has about 5%
pk-pk ripple (0.75 volts on a 15v system)
plus transients. How many Farads would it take
to smooth say a 100A machine? The single phase
PM alternators like the SD-8 are obviously worse
but battery alone combined with loads at or
near max ratings have more smoothing effects than
the capacitor.
Given the physical impracticality of seeing
such pristine power, complimentary standards
and design goals were adopted to say (in Mil-
STD-704) that a 28v system can have 1 VRMS (3+
volts pk-pk) noise from 1 to 5K Hertz and
tapering off each side.
http://tinyurl.com/78kwfk8
1/2 that value for a 14v system.
The complimentary DO-160 design goals tell us
to EXPECT this kind of trash on the bus and
design to live with it.
The capacitor doesn't hurt anything and if
you have a particularly bad set of rectifier
switching transients (or similar fast rise
stuff elsewhere in the system, the 20-20K
computer grade capacitor will reduce the
effects of that stimulus.
Suffice it to say that MOST pilots now flying
such capacitors on their PM alternator installations
would notice nothing from the cockpit if that
capacitor were removed.
Radios and audio systems need really clean power
and the qualified designer provides smoothing
internally.
Emacs!
Our audio isolation amplifier design uses the LM317
to provide a smooth source of +8 volts to run the
circuitry.
As a general rule, the kinds of stimulus that benefits
from any sort of bus voltage filtering is fast-rise
transients at a ripple-current rate. Folks mistakenly
believe their inductor/capacitor or just a capacitor
is bypassing AUDIO frequency energy when in fact, it's
high frequency (fast transients) at the audio rate.
As the numbers above suggest, there's no practical way
to filter alternator ripple from the bus. The snow-mobile
engines with lighting coils converted to electrical
system alternators may well have benefited from the
use of such capacitors . . . depends on vulnerabilities
inherent in their electro-whizzies. Our electro-whizzies
are suited by design to live in the world of trashy
busses.
This is why switchmode power supplies can be so small
when delivering outputs in the tens of amps . . . their
operating frequencies (hence ripple frequency) is quite
high which allows smaller capacitors and inductors to
do the same degree of smoothing.
You can leave the cap out and see if you hear any
alternator whine in the audio . . . odds are that you
will not.
Bob . . .
Message 15
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Subject: | Re: Latching Relay Redux |
At 12:30 PM 8/1/2012, you wrote:
>At 10:20 AM 8/1/2012, you wrote:
>
>Is that 75% power reduction correct??
>
>I would have guessed that a 50% duty cycle gave full voltage and
>full current for 50% of the time in a pulsed resistance circuit
>resulting in a 50% power reduction. Not sure about an inductive coil
>contactor though.
>
>Just asking but intuitively I would not have averaged the voltage
>and applied the I squared power calculation to this.
>-----------
P.S. just for grins, I thermocoupled the contactor
and let it stabilize for over an hour. Got a 120
F shell at 50% duty cycle for a 40F rise.
Let it run 100% duty cycle to stabilization and
got a 180F shell temperature for a 100F rise.
At that temperature, the 100% duty cycle current
draw was down to .6 amps from the cold start at
.9 amps. This copper temperature coefficient of
resistance rise in coil accounts for the less
than 4x temperature rise for 4x the dissipated power . . .
This means that a cooler contactor uses the power
you supply it more efficiently by running a
lower winding resistance. I.e. ampere turns
of magnetic flux that is more proportional to
applied voltage because the coil is cooler.
By the way, here's one approach to fabricating
a "contactor cooler" . . .
http://tinyurl.com/bolkoyc
On power up, both capacitors are discharged.
The 10uf holds down on the comparator pins
2,6 for about 100 milliseconds thus holding
the output pin 3 HI, turning the FED on hard
and energizing the contactor with full voltage.
The 10uF charges up in 100-200 milliseconds
thus allowing the 555 to 'hum' at about 200Hz
and 50% duty cycle. The diode and RC network
across the contactor coil should be mounted
right to the contactor terminals. All other
components can be remotely located but close
proximity to contactor is best.
Bob . . .
Message 16
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Subject: | Official AeroElectric-List FAQ (Frequently Asked Questions) |
Dear Listers,
Please read over the AeroElectric-List Frequently Asked Questions (FAQ) below.
The
complete AeroElectric-List FAQ including the Usage Guidelines can be found at the
following URL:
http://www.matronics.com/FAQs/AeroElectric-List.FAQ.html
Thank you,
Matt Dralle
Matronics Email List Administrator
[ Note: This FAQ was designed to be displayed with a fixed width font such as
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Download Via FTP
----------------
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AeroElectric-List Usage Guidelines
******************************************************************************
The following details the official Usage Guidelines for the AeroElectric-List.
You are encouraged to read it carefully, and to abide by the rules therein.
Failure to use the AeroElectric-List in the manner described below may result
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AeroElectric-List Policy Statement
The purpose of the AeroElectric-List is to provide a forum of discussion for
things related to this particular discussion group. The List's goals
are to serve as an information resource to its members; to deliver
high-quality content; to provide moral support; to foster camaraderie
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-------
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do not archive
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Subject: | Official AeroElectric-List Usage Guidelines |
Dear Listers,
Please read over the AeroElectric-List Usage Guidelines below. The complete
AeroElectric-List FAQ including these Usage Guidelines can be found at the
following URL:
http://www.matronics.com/FAQs/AeroElectric-List.FAQ.html
Thank you,
Matt Dralle
Matronics Email List Administrator
******************************************************************************
AeroElectric-List Usage Guidelines
******************************************************************************
The following details the official Usage Guidelines for the AeroElectric-List.
You are encouraged to read it carefully, and to abide by the rules therein.
Failure to use the AeroElectric-List in the manner described below may result
in the removal of the subscribers from the List.
AeroElectric-List Policy Statement
The purpose of the AeroElectric-List is to provide a forum of discussion for
things related to this particular discussion group. The List's goals
are to serve as an information resource to its members; to deliver
high-quality content; to provide moral support; to foster camaraderie
among its members; and to support safe operation. Reaching these goals
requires the participation and cooperation of each and every member of
the List. To this end, the following guidelines have been established:
- Please keep all posts related to the List at some level. Do not submit
posts concerning computer viruses, urban legends, random humor, long
lost buddies' phone numbers, etc. etc.
- THINK carefully before you write. Ask yourself if your post will be
relevant to everyone. If you have to wonder about that, DON'T send it.
- Remember that your post will be included for posterity in an archive
that is growing in size at an extraordinary rate. Try to be concise and
terse in your posts. Avoid overly wordy and lengthy posts and
responses.
- Keep your signature brief. Please include your name, email address,
aircraft type/tail number, and geographic location. A short line
about where you are in the building process is also nice. Avoid
bulky signatures with character graphics; they consume unnecessary
space in the archive.
- DON'T post requests to the List for information when that info is
easily obtainable from other widely available sources. Consult the
web page or FAQ first.
- If you want to respond to a post, DO keep the "Subject:" line of
your response the same as that of the original post. This makes it
easy to find threads in the archive.
- When responding, NEVER quote the *entire* original post in your
response. DO use lines from the original post to help "tune in" the
reader to the topic at hand, but be selective. The impact that
quoting the entire original post has on the size of the archive
can not be overstated!
- When the poster asks you to respond to him/her personally, DO NOT
then go ahead and reply to the List. Be aware that clicking the
"reply" button on your mail package does not necessarily send your
response to the original poster. You might have to actively address
your response with the original poster's email address.
- DO NOT use the List to respond to a post unless you have something
to add that is relevant and has a broad appeal. "Way to go!", "I
agree", and "Congratulations" are all responses that are better sent
to the original poster directly, rather than to the List at large.
- When responding to others' posts, avoid the feeling that you need to
comment on every last point in their posts, unless you can truly
contribute something valuable.
- Feel free to disagree with other viewpoints, BUT keep your tone
polite and respectful. Don't make snide comments, personally attack
other listers, or take the moral high ground on an obviously
controversial issue. This will only cause a pointless debate that
will hurt feelings, waste bandwidth and resolve nothing.
- Occasional posts by vendors or individuals who are regularly
subscribed to a given List are considered acceptable. Posts by
List members promoting their respective products or items for sale
should be of a friendly, informal nature, and should not resemble
a typical SPAM message. The List isn't about commercialism, but
is about sharing information and knowledge. This applies to
everyone, including those who provide products to the entire
community. Informal presentation and moderation should be the
operatives with respect to advertising on the Lists.
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