Today's Message Index:
----------------------
1. 02:05 AM - Re: Re: Engine mount ground? (Werner Schneider)
2. 07:48 AM - Re: Re: Engine mount ground? (Robert L. Nuckolls, III)
3. 08:04 AM - Re: Carling S700 2-3 switch failure. (Robert L. Nuckolls, III)
4. 11:05 AM - On-the-ground power jack (Carlos Trigo)
5. 11:43 AM - Re: On-the-ground power jack (Robert L. Nuckolls, III)
6. 12:36 PM - Re: On-the-ground power jack (Carlos Trigo)
7. 01:11 PM - Re: On-the-ground power jack (Robert L. Nuckolls, III)
8. 01:12 PM - Re: Schematic for twin PM alternators (user9253)
9. 01:23 PM - Rotax 914 Generator, Alternator, Starting and Fuel Pump Control (Ken Ryan)
10. 01:49 PM - Re: Re: Schematic for twin PM alternators (Charlie England)
11. 05:23 PM - Re: Schematic for twin PM alternators (user9253)
Message 1
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Subject: | Re: Engine mount ground? |
taking a different path is valid thinking (ask me how I know!!)
But then I rather would prefer to have a 2nd strap as backup as
otherwise you would need a bridge strap at the rubbermounts.
Cheers Werner
On 20.01.2016 02:22, rvdave wrote:
>
> Sort of what I thought but I've been getting some feedback that there should
also be a ground cable to the engine mount in case the firewall ground disconnects?
Message 2
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Subject: | Re: Engine mount ground? |
At 04:03 AM 1/20/2016, you wrote:
>
>taking a different path is valid thinking (ask me how I know!!)
>But then I rather would prefer to have a 2nd strap as backup as
>otherwise you would need a bridge strap at the rubbermounts.
As Neal pointed out earlier . . . and I have asserted
many times over the years, engine mounts are for holding
engines onto airplanes. They should not be pressed into
service as any part of the electrical system . . . voltages
impressed across structural joints due to large circulating
currents exacerbates corrosion. Not that this is a
demonstrated hazard but diligent failure mode effects
analysis dictates that using the engine mount as part of
the electrical system is simply not necessary and elevates
an otherwise zero-risk to some non-zero number.
Another point of interest is the risk for 'burning ship's
wiring' with starter currents should a firewall-to-crankcase
bond strap become unhooked. Throughout the 'Connection and
here on the List, builders have been cautioned about having
ANY pathway grounded in two places on the airplane . . .
with p-lead shields being the most common violation of that
philosophy. Multiple grounds for engine instrumentation run
a close second. These are 'ground loops by design', easy
(and sometimes important) to avoid.
Lastly, the firewall-to-crankcase bond strap should be
as "reliable as prop bolts". The only incident for loss
of crankcase grounding I witnessed was a mechanic's slip-
up on one of our airplanes at K1K1 . . . and yeah, it
burned the p-lead shields wired per Cessna factory
drawings. I recommend an flat braid strap from some
structural bold on engine to the firewall ground stud.
Alternatively, a 2AWG piece of WELDING CABLE with lugs
installed per
http://tinyurl.com/gm8lqxo
. . . and attached with robust hardware will give
your prop bolts a serious challenge in the longevity/
reliability race.
Bob . . .
Message 3
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Subject: | Re: Carling S700 2-3 switch failure. |
At 07:38 PM 1/19/2016, you wrote:
>This manual switch is in a high (8 amps?) fast switching injector
>circuit. I use it to disable the primary or secondary injectors
>prior to flight to determine if the engine will run on only one set
>of injectors. It failed in flight and the engine went very lean
>running on only one set of injectors.
>The switch initially had no continuity but made a high resistance
>contact after flipping it back and forth a few times.
First, I would REALLY like to have that switch
for failure analysis. How much time did you
have on the switch?
How is this switch wired? does the switch carry
injector currents in BOTH positions?
>
>Should I replace this switch with a more robust one and if so, where
>would I find a suitable switch?
There are many more robust switches suited to
the task not the least of which is this device
http://tinyurl.com/jhkg6ep
. . . but it's not clear to me that the S700-2-3
was not suited to the task either. It would be useful
for us to study the circumstance of the failure and
the in-flight situatin you encounted when it did.
Bob . . .
Message 4
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Subject: | On-the-ground power jack |
Hello group
Figure Z-31A of the Connection, which refers to the wiring of a "Military style
Ground Power jack", indicates a 22AWG wire connecting the 2nd coil post of the
contactor (where the BLK wire of the OVM-14 is also connected), with the "Main
Ground Buss", through a 2A circuit breaker.
Now forgive my dumb question: what is this wire for?
And 2 practical questions:
- can I strike this wire from my system?
- if not, and since the Ground Buss is in the firewall and the Ground power receptacle
and contactor are both in the tail of the RV-10, can I simply connect
this wire to the negative terminal of the battery?
Regards
Carlos
Enviado do meu iPhone
Message 5
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Subject: | Re: On-the-ground power jack |
At 01:01 PM 1/20/2016, you wrote:
>
>Hello group
>
>Figure Z-31A of the Connection, which refers to the wiring of a
>"Military style Ground Power jack", indicates a 22AWG wire
>connecting the 2nd coil post of the contactor (where the BLK wire of
>the OVM-14 is also connected), with the "Main Ground Buss", through
>a 2A circuit breaker.
Emacs!
The small, third terminal on the "mil-spec"
ground power jack serves a several purposes.
First, the pin is small . . . no high current . . .
just a sample of the voltage available from
the ground power source. Second, the pin is
SHORTER which means that nothing happens on this
pin until the larger two pins are in good
electrical contact wthe sockets in the ground
power plug. Using this pin as a source of
voltage to energize the ground power contactor
prevents the larger pins from trying to CARRY
current during the make/break operations.
The diode in series with that sense lead
prevents the contactor from closing should
you be inadvertently connected to a battery
cart that has been miss-wired and reverse
polarity. the crowbar ov module across the
coil will trigger if your ground power jocky
has inadvertently place the GPU in the 28V
mode . . . it's happened to me twice.
The crowbar ov module is designed to work
against a circuit breaker. In this case, I
suggest a switch-breaker not unlike . . .
Emacs!
I'm generally not a big fan of breaker-switches.
But in this case, the device can serve two
purposes . . . (1) as breaker to work in concert
with the crowbar ovm and (2) a switch
you can have on the panel that gives YOU
control over the application/removal of
ground power to your airplane.
>And 2 practical questions:
> - can I strike this wire from my system?
Not recommended . . .
> - if not, and since the Ground Buss is in the firewall and the
> Ground power receptacle and contactor are both in the tail of the
> RV-10, can I simply connect this wire to the negative terminal of the battery?
That breaker switch should be on your
panel . . . or perhaps on a bracket under
it . . . hence the the LONG wire is from
ground power contactor and the switch-breaker.
The wire between ground bus and the switch-
breaker is short.
Bob . . .
Message 6
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Subject: | Re: On-the-ground power jack |
Thanks Bob
For the quick response, and the excellent "instructions manual" that came al
ong with the response.
A last question, derived from your explanations:
- When the ground-power jockey connects the female military jack of the ba
ttery cart to the airplane, the electrons will not flow unless that breaker-
switch you recommended is On, right?
Carlos
Enviado do meu iPhone
No dia 20/01/2016, =C3-s 19:34, Robert L. Nuckolls, III <nuckolls.bob@aero
electric.com> escreveu:
> At 01:01 PM 1/20/2016, you wrote:
.pt>
>>
>> Hello group
>>
>> Figure Z-31A of the Connection, which refers to the wiring of a "Military
style Ground Power jack", indicates a 22AWG wire connecting the 2nd coil po
st of the contactor (where the BLK wire of the OVM-14 is also connected), wi
th the "Main Ground Buss", through a 2A circuit breaker.
>
> <2547f72d.jpg>
> The small, third terminal on the "mil-spec"
> ground power jack serves a several purposes.
>
> First, the pin is small . . . no high current . . .
> just a sample of the voltage available from
> the ground power source. Second, the pin is
> SHORTER which means that nothing happens on this
> pin until the larger two pins are in good
> electrical contact wthe sockets in the ground
> power plug. Using this pin as a source of
> voltage to energize the ground power contactor
> prevents the larger pins from trying to CARRY
> current during the make/break operations.
>
> The diode in series with that sense lead
> prevents the contactor from closing should
> you be inadvertently connected to a battery
> cart that has been miss-wired and reverse
> polarity. the crowbar ov module across the
> coil will trigger if your ground power jocky
> has inadvertently place the GPU in the 28V
> mode . . . it's happened to me twice.
>
> The crowbar ov module is designed to work
> against a circuit breaker. In this case, I
> suggest a switch-breaker not unlike . . .
>
> <2547f78b.jpg>
>
> I'm generally not a big fan of breaker-switches.
> But in this case, the device can serve two
> purposes . . . (1) as breaker to work in concert
> with the crowbar ovm and (2) a switch
> you can have on the panel that gives YOU
> control over the application/removal of
> ground power to your airplane.
>
>
>> And 2 practical questions:
>> - can I strike this wire from my system?
>
> Not recommended . . .
>
>> - if not, and since the Ground Buss is in the firewall and the Ground p
ower receptacle and contactor are both in the tail of the RV-10, can I simpl
y connect this wire to the negative terminal of the battery?
>
> That breaker switch should be on your
> panel . . . or perhaps on a bracket under
> it . . . hence the the LONG wire is from
> ground power contactor and the switch-breaker.
> The wire between ground bus and the switch-
> breaker is short.
>
> Bob . . .
Message 7
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Subject: | Re: On-the-ground power jack |
At 02:30 PM 1/20/2016, you wrote:
>Thanks Bob
>
>For the quick response, and the excellent "instructions manual" that
>came along with the response.
>
>A last question, derived from your explanations:
> - When the ground-power jockey connects the female military jack
> of the battery cart to the airplane, the electrons will not flow
> unless that breaker-switch you recommended is On, right?
Absolutely. If you have the option, the ground
power switch can be included in the DC POWER
group of system switches on your panel. When
ground power is plugged in, you can have
control of it from the pilot's position. Doesn't
need to be ON until you're ready, you can turn
it OFF as you decide.
Some of my readers have added a lamp from the
high side of contactor coil to ground. This
light will indicate when and if ground power is
available.
Bob . . .
Message 8
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Subject: | Re: Schematic for twin PM alternators |
I revised my schematic and attached it.
The relays now switch the AC. All electrical power can be shut off on the engine
side of the firewall.
The DC output from each regulator is fused separately so that a fault in one will
not disable the other one.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=452147#452147
Attachments:
http://forums.matronics.com//files/revmaster5a_214.pdf
Message 9
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Subject: | Rotax 914 Generator, Alternator, Starting and Fuel |
Pump Control
I developed the attached wiring based on input from a Rotax dealer in
British Columbia. It assumes that the optional external alternator (40 amp)
is installed in addition to the integrated generator (20 amp). The
integrated generator is used only to power the main fuel pump. The 914
requires an operational fuel pump to run. The ignition is independent. I
would appreciate input on the attached diagram. Thanks.
Message 10
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Subject: | Re: Schematic for twin PM alternators |
On Wed, Jan 20, 2016 at 3:10 PM, user9253 <fransew@gmail.com> wrote:
>
> I revised my schematic and attached it.
> The relays now switch the AC. All electrical power can be shut off on the
> engine side of the firewall.
> The DC output from each regulator is fused separately so that a fault in
> one will not disable the other one.
>
> --------
> Joe Gores
>
>
I wish I had the time/aptitude to knock out nice drawings like that. I'm
still scribbling in notebooks.
Some thoughts.
The path from buss through the alt breaker, SPDT switch contains multiple
single points of failure that can take out both alternators.
The alternators, as drawn in the original 'cartoon' installation drawing
seems to show one leg of each alternator connected to ground. If that's the
case, interrupting the 'wrong' leg might not shut that alt down, if there's
an internal short to ground.
Behavior of the IGN terminal is not known, and even if it does control the
alt, there's no guarantee that a failure mode won't keep the alt active.
Assuming that the IGN terminal can control the alt, the ganged master is a
single point of failure for the alts (though if it goes, the alts may not
matter. :-) ).
With B leads tied to the buss, a failure to ground in either charging
system might try to draw power from the buss (battery & other alt).
Some of the above may not be important if it's a purely VFR plane with no
electrical dependence, & nav can be handled with eyeballs &/or portable
nav/gps units. But it shouldn't be too difficult to make the system truly
redundant. (Independent OV modules, separate switches, contactors
interrupting the B leads, etc)
What do you think?
Message 11
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Subject: | Re: Schematic for twin PM alternators |
> I wish I had the time/aptitude to knock out nice drawings like that.
It helps to be retired.
You are right about the multiple single points of failure in the relay coil circuit.
To eliminate the danger, the circuit would have to be duplicated; 2 breakers,
2 capacitors, and two switches. The builder would have to weigh the danger
of a single part failing against the disadvantage of adding more parts.
I did not see any documents that indicated the AC winding was grounded. That would
be easy to check with an ohmmeter.
I assume [I know that is dangerous :-) ] that the MIA881279 regulator terminals
have functions the same functions as the Rotax regulator. See this thread:
http://www.matronics.com/forums/viewtopic.php?p=305164&sid=53455a09f9026927ea6c15eb6d6e198f
> there's no guarantee that a failure mode won't keep the alt active.
A regulator can not have an output if there is no AC input. The relays only allow
one AC dynamo to be connected at a time.
> the ganged master is a single point of failure for the alts
Yes, but many airplanes have a master switch that is a single point of failure.
> With B leads tied to the buss, a failure to ground in either charging system
might try to draw power from the buss (battery & other alt).
True, but it would have to be a resistive fault. A direct short to ground would
blow the 25 amp fuse with battery current.
Yes, the circuit could be made more failure tolerant. But is added complexity
warranted for the aircraft mission? This is a hobby for me. I do not want to
make it into a full time job. :-)
You bring up some interesting points. If it were my plane intended for hard IFR,
then I would spend more time honing the schematic.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=452153#452153
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