Today's Message Index:
----------------------
1. 04:18 AM - Ground Power RV8 (Drum)
2. 05:06 AM - Main Power Routing RV8 (Drum)
3. 09:56 AM - Re: SDS CPI-2 Circuit Protection Question (Matthew Schumacher)
4. 11:44 AM - Re: SDS CPI-2 Circuit Protection Question (Charlie England)
5. 02:02 PM - Re: SDS CPI-2 Circuit Protection Question (Matthew Schumacher)
6. 04:03 PM - Re: SDS CPI-2 Circuit Protection Question (Charlie England)
Message 1
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| Subject: | Ground Power RV8 |
Hi Bob -
Thanks for your design and comments on ground power for my RV8. I finally finished
it. Trying to upload pix.
--------
Drum G
RV8 - Electrical/Avionics
Southport, CT
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=503267#503267
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| Subject: | Main Power Routing RV8 |
Hi - Im building RV8 with aft battery placement. From the battery contactor I
run 2AWG to a terminal block near panel where a buss bar connects main power
to main buss and some aux busses.
I am planning to run a 2AWG from same post where main power comes into terminal
block to the hot side of the starter contactor.
My would have preferred to run directly to starter contactor but I dont want to
lengthen the run with a backtrack from starter contactor to terminal block and
the busses off the terminal block - weight complexity and voltage drop reasons.
Are there compelling reasons not to break the main power wire at terminal block
with aft battery placement?
Thanks in advance.
Warm regards,
--------
Drum G
RV8 - Electrical/Avionics
Southport, CT
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=503268#503268
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
On 9/23/21 1:56 PM, Robert L. Nuckolls, III wrote:
>> 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.) 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 . . .
>
I'm the original poster of that VAF message. A few messages down I
posted this thread which explains what is going on:
https://vansairforce.net/community/showthread.php?p=1445172
It's as expected, they are worried about the coil being too noisy, but a
counter point to this is when it switches to backup power, it pulls both
ECU and coil power from a single 18g wire to the battery.
This begs a few questions:
1. How much impedance does a switch vs a fuse vs a breaker impose on
the system? Does having a single switch and breaker directly attached
to a battery with less than 2" of wire with both ECU and coil wires
connected south of that make a significant noise difference compared to
two switches and two breakers directly attached to the battery in the
same manor with the ECU and coil on each? From a wire perspective they
are nearly the same with only 2" of wire sharing both systems so I doubt
that would make a huge difference, but I'm less sure about the switches
and breakers.
2. With the talk of a dedicated engine bus, I'm assuming that it would
be attached to the battery directly. So, if you have 2ft 10g wire from
a battery to an engine bus and another 2ft 10g wire from a battery to a
main bus that has modern avionics on it, how much does that 4ft of 10G
wire insulate the avionics from the noisy coil?
Seems to me that this has more to do with contact points, wire gauge,
and length of runs over the simplistic "dedicated bus is good and shared
bus is bad."
schu
Message 4
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
On 9/24/2021 11:55 AM, Matthew Schumacher wrote:
> On 9/23/21 1:56 PM, Robert L. Nuckolls, III wrote:
>>> 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.) 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 . . .
>>
>
> I'm the original poster of that VAF message. A few messages down I
> posted this thread which explains what is going on:
>
> https://vansairforce.net/community/showthread.php?p=1445172
>
> It's as expected, they are worried about the coil being too noisy, but
> a counter point to this is when it switches to backup power, it pulls
> both ECU and coil power from a single 18g wire to the battery.
>
> This begs a few questions:
>
> 1. How much impedance does a switch vs a fuse vs a breaker impose on
> the system? Does having a single switch and breaker directly
> attached to a battery with less than 2" of wire with both ECU and coil
> wires connected south of that make a significant noise difference
> compared to two switches and two breakers directly attached to the
> battery in the same manor with the ECU and coil on each? From a wire
> perspective they are nearly the same with only 2" of wire sharing both
> systems so I doubt that would make a huge difference, but I'm less
> sure about the switches and breakers.
>
>
> 2. With the talk of a dedicated engine bus, I'm assuming that it
> would be attached to the battery directly. So, if you have 2ft 10g
> wire from a battery to an engine bus and another 2ft 10g wire from a
> battery to a main bus that has modern avionics on it, how much does
> that 4ft of 10G wire insulate the avionics from the noisy coil?
>
> Seems to me that this has more to do with contact points, wire gauge,
> and length of runs over the simplistic "dedicated bus is good and
> shared bus is bad."
>
> schu
>
>
If the entire backup power is supposed to be supplied on a single 18 ga
wire, then you might want to get a 2nd opinion on the quality of the
design. The system will need the same current and noise immunity from
the backup supply as the primary, unless some current consumer is
deleted in backup mode. What would that current consumer be? Why is it
not needed in backup mode, but it is needed in primary mode?
1. Don't understand the 2" of wire reference. No practical system will
have that. The battery is effectively a rather large 'filter'. If noise
from the high-power noise generator (the coils) has to flow all the way
back to the battery before traveling down the other power wire to the
ECU, the battery can at least partially attenuate some of that noise.
And noise isn't the only issue, as has been pointed out in other posts.
2. My requirement in my system for a separate engine bus, as stated in
other posts, has nothing to do with noise, or resistance, or impedance.
It's an *operational* requirement for me, to keep fundamental engine
control isolated from fundamental airframe electrical control. 'Mag
switches' independent of the airframe 'Master switch'. The goal is to
mimic as closely as possible the emergency procedures we were all
trained to follow when we suspect an electrical issue in flight. The
dedicated bus also eliminates multiple potential failure points in the
supply path to the engine which are not in the loop in traditional a/c
systems (master switch, master contactor, etc).
Charlie
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Message 5
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
On 9/24/21 11:47 AM, Charlie England wrote:
> If the entire backup power is supposed to be supplied on a single 18
> ga wire, then you might want to get a 2nd opinion on the quality of
> the design. The system will need the same current and noise immunity
> from the backup supply as the primary, unless some current consumer is
> deleted in backup mode. What would that current consumer be? Why is it
> not needed in backup mode, but it is needed in primary mode?
This is how it's designed:
http://www.sdsefi.com/cpi2switches.jpg
There are two wires for normal power, the red coil wire and the purple
ECU wire. For the backup battery both the coil and ECU are powered
through a single 18g wire through a fuse:
http://www.sdsefi.com/battbox1.jpg
My current plan is to tie the battery backup to my aux bus which has
it's own SD-8 alternator and a small battery. This conforms to their
recommendation of
"Please note, this battery will run a dual system for about 20 minutes
at 2500 rpm in the event that the main alternator and main battery go
down. If you need more power duration for your typical missions, we
suggest you install a larger battery than this one and/or a second
backup alternator."
Then, in the system, I would disable the charging circuit as my
alternator does that.
>
> 1. Don't understand the 2" of wire reference. No practical system will
> have that. The battery is effectively a rather large 'filter'. If
> noise from the high-power noise generator (the coils) has to flow all
> the way back to the battery before traveling down the other power wire
> to the ECU, the battery can at least partially attenuate some of that
> noise. And noise isn't the only issue, as has been pointed out in
> other posts.
The battery is not usually mounted near this stuff, typically you would
bring battery power to a bus bar with a large gauge wire, then from that
to your breakers and switches then to the device. In that case, what
exactly is the difference between powering each leg through a single
switch/breaker or dual switch/breakers assuming that the switches and
breakers are within inches of the bus bar. If there is a large
difference, how much of it is the short length of shared wire between
the bus bar and switch/breaker and how much of it is the fact that you
are sharing a switch/breaker?
Perhaps a picture is best. How much noise rejection difference would
one expect in the following:
> 2. My requirement in my system for a separate engine bus, as stated in
> other posts, has nothing to do with noise, or resistance, or
> impedance. It's an *operational* requirement for me, to keep
> fundamental engine control isolated from fundamental airframe
> electrical control. 'Mag switches' independent of the airframe 'Master
> switch'. The goal is to mimic as closely as possible the emergency
> procedures we were all trained to follow when we suspect an electrical
> issue in flight. The dedicated bus also eliminates multiple potential
> failure points in the supply path to the engine which are not in the
> loop in traditional a/c systems (master switch, master contactor, etc).
>
Noted. Thanks for that feedback.
schu
Message 6
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| Subject: | Re: SDS CPI-2 Circuit Protection Question |
On Fri, Sep 24, 2021 at 4:07 PM Matthew Schumacher <schu@schu.net> wrote:
> On 9/24/21 11:47 AM, Charlie England wrote:
>
> If the entire backup power is supposed to be supplied on a single 18 ga
> wire, then you might want to get a 2nd opinion on the quality of the
> design. The system will need the same current and noise immunity from the
> backup supply as the primary, unless some current consumer is deleted in
> backup mode. What would that current consumer be? Why is it not needed in
> backup mode, but it is needed in primary mode?
>
>
> This is how it's designed:
>
> http://www.sdsefi.com/cpi2switches.jpg
>
> There are two wires for normal power, the red coil wire and the purple ECU
> wire. For the backup battery both the coil and ECU are powered through a
> single 18g wire through a fuse:
>
> http://www.sdsefi.com/battbox1.jpg
>
> My current plan is to tie the battery backup to my aux bus which has it's
> own SD-8 alternator and a small battery. This conforms to their
> recommendation of
>
> "Please note, this battery will run a dual system for about 20 minutes at
> 2500 rpm in the event that the main alternator and main battery go down. If
> you need more power duration for your typical missions, we suggest you
> install a larger battery than this one and/or a second backup alternator."
>
> Then, in the system, I would disable the charging circuit as my alternator
> does that.
>
>
> 1. Don't understand the 2" of wire reference. No practical system will
> have that. The battery is effectively a rather large 'filter'. If noise
> from the high-power noise generator (the coils) has to flow all the way
> back to the battery before traveling down the other power wire to the ECU,
> the battery can at least partially attenuate some of that noise. And noise
> isn't the only issue, as has been pointed out in other posts.
>
>
> The battery is not usually mounted near this stuff, typically you would
> bring battery power to a bus bar with a large gauge wire, then from that to
> your breakers and switches then to the device. In that case, what exactly
> is the difference between powering each leg through a single switch/breaker
> or dual switch/breakers assuming that the switches and breakers are within
> inches of the bus bar. If there is a large difference, how much of it is
> the short length of shared wire between the bus bar and switch/breaker and
> how much of it is the fact that you are sharing a switch/breaker?
>
> Perhaps a picture is best. How much noise rejection difference would one
> expect in the following:
>
>
> 2. My requirement in my system for a separate engine bus, as stated in
> other posts, has nothing to do with noise, or resistance, or impedance.
> It's an *operational* requirement for me, to keep fundamental engine
> control isolated from fundamental airframe electrical control. 'Mag
> switches' independent of the airframe 'Master switch'. The goal is to mimic
> as closely as possible the emergency procedures we were all trained to
> follow when we suspect an electrical issue in flight. The dedicated bus
> also eliminates multiple potential failure points in the supply path to the
> engine which are not in the loop in traditional a/c systems (master switch,
> master contactor, etc).
>
> Noted. Thanks for that feedback.
>
> schu
>
Ah..the plot thins. ;-)
That 2" of #18 is telling you that no more than 2" of the small gauge wire
should be between 'unlimited' current and the fuses. That minimizes risk
from a shorted wire in the unprotected run to the fuse. The switches
*should* be able to be mounted where ever it's convenient, and if the wire
run is longer, the wire gets upsized to reduce voltage drop.
Your question about 1 wire for the backup vs 2 for normal operation is a
valid one, and should be addressed to SDS, and if you don't get a
satisfactory answer, get a 2nd opinion. If the system needs separate wires,
why is a single wire safe? If it doesn't need separate wires, then why
complicate the wiring? FWIW, the controller I'm personally familiar with
(not SDS or the other common Lyc controller) specifies a separate feed for
the ECU, and a separate feed for the coils, and a separate feed for the
injectors. I know the engineer that designed the system, and I trust his
opinion because he's who he is, and because it lines up with my decades of
experience in other fields dealing with electrical noise & interference.
BTW, there's been at least one a/c running an electronic controller system
that was lost when the master bus went down, taking the engine electrical
power with it. Food for thought....
Charlie
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