Today's Message Index:
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1. 07:05 AM - Re: SDS CPI-2 Circuit Protection Question (wsimpso1)
2. 01:57 PM - Re: SDS CPI-2 Circuit Protection Question (Robert L. Nuckolls, III)
3. 05:21 PM - Re: SDS CPI-2 Circuit Protection Question (Charlie England)
Message 1
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
First off, if Ross says run separate fusing and wiring to power things in his system,
it is a darned good thing to heed.
I do not even pretend to know what Ross did inside the box, but I suspect that
purple wires are sensor and computer power, while the red wires are stated as
coil power. Big amp difference, big noise difference and tolerance for noise,
different power needs, and suitable for separate fusing.
Had a conversation with a homebuilder of some note (who shall remain anonymous)
who has chatted with Ross about doing diode isolated independent power feeds
so that both engine buses are queued to power the ECU, spark coils, and injector
coils. Ross approved with his standard caution to make sure the pieces are
very secure or a wiring failure could be bad.
For electric fuel pumps, I would take the same perspective.
Power them from an always hot bus (or two) and know that none of this stuff can
go down for anything short of massive airframe damage.
This way you can have everything required to keep running the engine backed up
automatically, and in an emergency you can kill all other power to the airframe
while keeping the engine running, and see if you really need to go deadstick...
Billski
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=503261#503261
Message 2
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
>I think that there is, for multiple reasons.
>1st, the coil circuits are *really* noisy. With
>a common wire feeding both, the noise has a
>direct path into the supply for the ECU. (The
>'filter' method, the battery, would be a long
>ways away.)=C2 2nd, if he's using the system fuse
>to protect the cpu (not good practice, but many
>avionics makers have been known to do it), 10A
>won't do it. 3rd (for me, anyway), I'd fuse each
>coil block separately; not all coils on one
>fuse. All that separate fusing means a single
>failure can't take out something else, like the
>coil pack taking the ECU with it when the fuse
>blows. ATC/ATO fuse blocks are relatively cheap
>and very compact for many circuits, so it's easy
>to isolate each coil. If a coil goes shorted,
>separate fuses could at least keep one pair of
>cylinders firing. Might make the difference
>between the runway and the fence. (Failure modes effects analysis.)
Agreed. Do you KNOW what the current demands are on
each of those leads? I've communicated with perhaps
a half dozen electronic engine systems providers over
the years and I've yet to find one that could tell me
what the ENERGY requirements were on each supply line
nor could they define peak currents, duty cycles or
repetition rates. If they were being offered onto
a type certificated airplane, inquiring minds would
insist on knowing . . .
>One other thing that might be 'just me', but I
>would not put the engine circuits on the main
>bus, or any airframe bus. My reasoning is,
>training. Assuming that you have years of flying
>traditional a/c engines under your belt, if you
>ever have the very rare but heavily trained-for
>'smoke in the cockpit' situation, what's the
>first thing you're trained do? Will you be able
>to override decades of trained-in muscle memory?
>I doubt I could, so my engine stuff is on a separate, dedicated engine bus.
Why not the battery bus? Fuseblock next to battery
contactor. Conservative fuses to individual feeds.
Switches have absolute control over 'what's hot'.
Stone simple, minimal parts count distribution
system. Yes, ignitions are hot with switches ON
with the rest of the airplane shut down. Isn't
that how magnetos have operated since day-one?
I'd run electric fuel pumps and any other engine
support loads from the battery bus too. You do
have the option of crafting a Z101 style, dual
path engine bus . . . but for a simple airplane,
I would favor the battery bus support of the engine.
During conditions under which you're forced
to fly dark-panel, engine-support switching-options
might be more distraction than you need just
then.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 3
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
snipped
>
>> One other thing that might be 'just me', but I would not put the
>> engine circuits on the main bus, or any airframe bus. My reasoning
>> is, training. Assuming that you have years of flying traditional a/c
>> engines under your belt, if you ever have the very rare but heavily
>> trained-for 'smoke in the cockpit' situation, what's the first thing
>> you're trained do? Will you be able to override decades of trained-in
>> muscle memory? I doubt I could, so my engine stuff is on a separate,
>> dedicated engine bus.
>
> Why not the battery bus? Fuseblock next to battery
> contactor. Conservative fuses to individual feeds.
> Switches have absolute control over 'what's hot'.
> Stone simple, minimal parts count distribution
> system. Yes, ignitions are hot with switches ON
> with the rest of the airplane shut down. Isn't
> that how magnetos have operated since day-one?
>
> I'd run electric fuel pumps and any other engine
> support loads from the battery bus too. You do
> have the option of crafting a Z101 style, dual
> path engine bus . . . but for a simple airplane,
> I would favor the battery bus support of the engine.
>
> During conditions under which you're forced
> to fly dark-panel, engine-support switching-options
> might be more distraction than you need just
> then.
>
>
> Bob . . .
>
As we're both thinking, the goal was to keep operational 'switchology'
as close to mags/carb as was practical, given the forced reality
differences. There are extra switches within the engine system that
allow switching between ECUs, etc, but the basic 'mag switch(s) at one
switch location; airframe master at another location' was a prime goal.
I've got one fusible link protected heavy duty switch that controls the
engine bus (with a backup bus-tie switch to feed the bus from the main
bus in the unlikely event of a switch failure). All engine related
stuff including both fuel pumps are on the engine bus.
I probably would have considered the battery bus if it was ignition only
(very low current demand), but all the various full-bore electronic
injection type systems are going to draw around 12-15 amps continuous
when a fuel pump is included. Using a separate engine bus also allowed
mounting the bus (fuse block) in a much more convenient location. Mine
is not a 'cookie cutter' system even compared to the SDS, etc
aftermarket controller systems, and convenient access for testing, mods,
etc was one of the design goals.
Charlie
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