Today's Message Index:
----------------------
1. 01:41 AM - Re: Did you install a "battery bus"? (JOHN TIPTON)
2. 01:54 AM - Re: Did you install a "battery bus"? (Werner Schneider)
3. 09:08 AM - Re: Re: Rotax Charging System (Richard Girard)
4. 12:08 PM - Re: Did you install a "battery bus"? (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Did you install a "battery bus"? |
No battery bus ---
Sent from my iPad
----x--O--x----
> On 18 Sep 2018, at 1:35 pm, Mickey Coggins <mick-matronics@rv8.ch> wrote:
>
> Hi,
>
> I'm struggling to find anything that really needs to be connected to an always-hot
battery bus.
>
> I have an io360 with pmags which will power themselves in case of issue with
the normal power bus, my mission is vfr day, GRT EFIS, Trig Radio and transponder,
some lights (that I don't really need), and that's about it.
>
> I could see some value in an always hot cigar lighter-type connection to charge
a phone while on the ground, or to send some electrons to the battery, but
not much else.
>
> Am I missing something or are there others that don't have a battery bus?
>
> Mickey Coggins
Message 2
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| Subject: | Re: Did you install a "battery bus"? |
Hi Mickey,
getting close :), I have some items on the Battery Bus but my design is
already 15 years flying (based on Z11) :)
I have on the battery bus:
-the connection to the Essential bus (alternate feed) (could be
direct on the battery)
-a connection to my handheld com
- a connection to my handheld GPS
- a connection to the Hoobs
Cheers Werner
On 18.09.2018 14:35, Mickey Coggins wrote:
> Hi,
>
> I'm struggling to find anything that really needs to be connected to
> an always-hot battery bus.
>
>
Message 3
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| Subject: | Re: Rotax Charging System |
Bob et al, I've had three instances where I've added a capacitor to a
charging system.
The first time was when a friend asked me to rewire the Harley Sportster he
was resurrecting. It had a magneto for ignition, a generator for power and
was kick start only. He didn't want a battery added. At that time CCI
(Custom Chrome Inc, or as I called it ChiCom Importers) had a kit with a
capacitor, a spring mount and a couple of connectors. It simply provided a
load for the generator. I remember the lights had a pronounced flikker at
idle rpm.
The second was with the Rotax two stroke installation manual, page 18-3
where there is a wiring diagram for installing the 866 080 rectifier
without a battery . Above the diagram is the note; "Attention, To avoid
excessive voltage in conjunction with the rectifier regulator 866080 a
constant minimum ballast load of 1 amp is required" On the next page there
is a diagram for installing that same rectifier with a battery and there is
no capacitor.
Third, was installing a Rotax 912. The Installation manual, section
24-00-00 page 7 says a capacitor of 22,000 uF at 25V is required to protect
the regulator and flatten voltage, along with the warning that if the
battery or the bus is disconnected from the system with the engine running
the capacitor will safely dissipate the charge from the generator (Rotax
term) and "otherwise the regulator will be damaged".
Whether it's an old pilot's tale or not I don't know, but the consistent
theme is that the capacitor is there to dissipate a charge and protect the
rectifier.
Rick Girard
On Tue, Sep 18, 2018 at 8:43 AM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 10:24 PM 9/17/2018, you wrote:
>
> I wonder if that capacitor is an artifact from back when PM alternators
> were operated in vehicles that were designed with no battery. Not unlike
> the avionics master as a holdover from the prehistoric germanium
> semiconductor days.
>
> Charlie
>
>
> An excellent hypothesis . . . but it seems
> it equally likely that somebody looked at that
> full wave rectifier downstream of an AC
> source and thought, "Gee, every circuit like
> that in the past has had a capacitor across
> the output . . . shucks . . . why not?"
>
>
> Let's noodle some of the math that helps
> us figure out just how effective a capacitor
> might be for 'filtering' a PM alternator system:
>
> A fundamental quality of capacitors is described
> by this formula:
>
> Volts/Second = Amps/Farad
>
> meaning that if you apply 1 amp of constant
> current to a 1 Farad capacitor, you'll see
> voltage across the capacitor rise at a rate
> of 1 Volt per Second.
>
> How rapidly will the voltage change
> across at 22,000uF capacitor in a
> PM alternator system with 10A load
> assuming the positive excursion has just
> charged the capacitor to the expected peak
> voltage?
>
> V/S = 10/0.022 = 454 Volts/Second or let's
> say about 500 mVolts/mSecond.
>
> Adding a 500 mV/mS plot to the no-capacitor
> plot of SD8 performance we see
>
> [image: Emacs!]
>
> By inspection we can deduce that the addition of
> 22KuF to the output would have no appreciable effect
> on the voltage plot shown. If we put a 47KuF cap
> on it (less than 1/2 the slope) we might see a reduction
> in pk-pk excursion to something on the order of 200mV
> . . . but why bother? We know that appliances qualified to run
> in aircraft EXPECT to see noises equal to or perhaps
> greater than what's depicted above with no capacitor.
>
> I might also add that automotive electrical systems
> are completely devoid of electrical system noise
> filters that address the spectrum of alternator
> ripple and switching.
>
> So if there is a reason based on physics for adding
> capacitors to the PM alternators, it's not intuitively
> clear.
>
> Bob . . .
>
--
=9CBlessed are the cracked, for they shall let in the light.=9D
Groucho Marx
<http://www.goodreads.com/author/show/43244.Groucho_Marx>
Message 4
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| Subject: | Re: Did you install a "battery bus"? |
>
>On 18.09.2018 14:35, Mickey Coggins wrote:
>>Hi,
>>
>>I'm struggling to find anything that really needs to be connected
>>to an always-hot battery bus.
Any airplane fitted with a battery bus has one or more
devices that need to be functional with the DC PWR master
switches OFF. When I worked at Cessna in '64, single engine
airplanes had two fuses mounted right at the battery box
to power the electric clock and the oil-pressure actuated
Hobbs hour meter. During the time I worked there, I can
recall only one other system that was tied to a 'battery
bus'. The T41 trainer (172 on steroids) had a third fuse
that powered a solid state 121.5 transceiver mounted
back behind the baggage compartment.
The suggested loads for the battery bus in OBAM
aircraft added features like dome lights, under-wing
utility lighting, baggage compartment lights, utility
jacks in cockpit for supporting a hand-held (backup
comm and/or ATIS/Clearance Delivery), and/or a handy port for
attaching battery maintainer to the ship's battery.
When electrically dependent engines came along, it
seemed prudent to run all engine support systems from
the battery bus so that DC PWR masters could be
shut off without compromising the engine.
Every builder's needs will be different and new
reasons to tap the battery directly may yet arise
as the art and science of our craft evolves.
But it's not difficult to imagine a project with
no such features.
Bob . . .
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