Today's Message Index:
----------------------
1. 12:23 AM - AOPA Never Again electrical problem (Mickey Coggins)
2. 01:34 AM - Re: AOPA Never Again electrical problem (Werner Schneider)
3. 02:26 AM - Re: AOPA Never Again electrical problem (Brian Lloyd)
4. 02:41 AM - Re: AOPA Never Again electrical problem (Brian Lloyd)
5. 08:23 AM - Re: Labeling of wires (ALWAYSPDG@aol.com)
6. 02:07 PM - Getting oxidization off wires (John Slade)
7. 02:46 PM - Re: Buttal on OVP and Circuit Breakers. (Eric M. Jones)
8. 04:46 PM - Reformated--Re: Buttal on OVP and Circuit Breakers. (Eric M. Jones)
9. 08:09 PM - Re: RF breakthro on Vans gauges (Jim Bean)
Message 1
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| Subject: | AOPA Never Again electrical problem |
--> AeroElectric-List message posted by: Mickey Coggins <mick-matronics@rv8.ch>
Hi,
http://www.aopa.org/pilot/never_again/2004/na0405.html
This article discusses an electrical problem. Here
is the conclusion:
"That night, a quick check of the aircraft's manual found
the problem. Apparently the alternators would not kick in
if battery power was depleted below a threshold amperage.
This condition was created during static ground checks of
the camera equipment, which resulted in alternator
shutdown. The ammeter reading was correct but so borderline
that its warning was misinterpreted. The battery was charged
overnight and the mission continued the next day without
further incident."
Is this caused by a particular type of alternator?
Of course, I'll never have this problem with my Z11+Z30
equipped RV8, but I do still fly our club's aircraft.
Thanks,
Mickey
--
Mickey Coggins
http://www.rv8.ch/
#82007 QB Wings/Fuselage
Message 2
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| Subject: | Re: AOPA Never Again electrical problem |
--> AeroElectric-List message posted by: "Werner Schneider" <wernerschneider@compuserve.com>
A voltage readout would have shown the problem before they departed
Werner
----- Original Message -----
From: "Mickey Coggins" <mick-matronics@rv8.ch>
Subject: AeroElectric-List: AOPA Never Again electrical problem
> --> AeroElectric-List message posted by: Mickey Coggins
<mick-matronics@rv8.ch>
>
> Hi,
>
> http://www.aopa.org/pilot/never_again/2004/na0405.html
>
> This article discusses an electrical problem. Here
> is the conclusion:
>
> "That night, a quick check of the aircraft's manual found
> the problem. Apparently the alternators would not kick in
> if battery power was depleted below a threshold amperage.
> This condition was created during static ground checks of
> the camera equipment, which resulted in alternator
> shutdown. The ammeter reading was correct but so borderline
> that its warning was misinterpreted. The battery was charged
> overnight and the mission continued the next day without
> further incident."
>
> Is this caused by a particular type of alternator?
>
> Of course, I'll never have this problem with my Z11+Z30
> equipped RV8, but I do still fly our club's aircraft.
>
> Thanks,
> Mickey
>
>
> --
> Mickey Coggins
> http://www.rv8.ch/
> #82007 QB Wings/Fuselage
>
>
Message 3
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| Subject: | Re: AOPA Never Again electrical problem |
--> AeroElectric-List message posted by: Brian Lloyd <brianl@lloyd.com>
Mickey Coggins wrote:
> --> AeroElectric-List message posted by: Mickey Coggins <mick-matronics@rv8.ch>
>
> Hi,
>
> http://www.aopa.org/pilot/never_again/2004/na0405.html
>
> This article discusses an electrical problem. Here
> is the conclusion:
>
> "That night, a quick check of the aircraft's manual found
> the problem. Apparently the alternators would not kick in
> if battery power was depleted below a threshold amperage.
> This condition was created during static ground checks of
> the camera equipment, which resulted in alternator
> shutdown. The ammeter reading was correct but so borderline
> that its warning was misinterpreted. The battery was charged
> overnight and the mission continued the next day without
> further incident."
>
> Is this caused by a particular type of alternator?
I have an Aztec and I have studied its electrical system in detail. My immediate
reaction is to quote some of our British bretheren and state, "what rubbish."
(Actually I said something else but Matt says I am not to use those words
here.)
If there is enough power in the battery to start the engines and run the lights
and radios, there is more than enough to excite the alternators.
The Aztec has two alternators being driven by a single voltage regulator. The
alternators are run with both fields and B-leads in parallel. I can find nothing
in the system to ensure that they share the load equally but it seems to work
just fine anyway. There is a second VR that may be switched into the circuit
should the main VR fail. A toggle switch with a red flip-up cover on the
lower center console, conveniently out of sight, selects the VR. (The Aztec isn't
big on ergonomics and there are several controls that one must locate and
operate by feel.)
So what could the problem have been? Well, my guess is that they had an overvoltage
transient which tripped the overvoltage protection relay. This type of
OVP latches and won't release until all power is removed from the buss. I bet
dollars to donuts that if they had turned off the alternators (field switch)
and then cycled the battery master, the alternators would have come back on-line.
It also points out how Bob's crowbar OVP system communicates the problem much more
clearly to the pilot. When the field breaker pops you know what is wrong
(or have a pretty good idea) and resetting the breaker puts everything to right
unless there is really something wrong with the alternator system, at which
time you resort to your essential buss and get on the ground.
Getting back to the Aztec, it is possible that a weak battery would provide insufficient
stabilization on the buss that the bus voltage could have risen too
high when the alternators kicked on that the OVP relay was activated. Still,
the battery would have to have been so dead as to not be able to power anything
for that to be the case. Regardless, cycling the alternator field switch and
the battery master should have cleared the problem.
--
Brian Lloyd 6501 Red Hook Plaza
brian@greenflashnetworks.com Suite 201
http://www.greenflashnetworks.com St. Thomas, VI 00802
+1.340.998.9447 (voice) +1.360.838.9669 (fax)
--
Brian Lloyd 6501 Red Hook Plaza
brianl@lloyd.com Suite 201
http://www.lloyd.com St. Thomas, VI 00802
+1.340.998.9447 (voice) +1.360.838.9669 (fax)
There is a time to laud one's country and a time to protest.
A good citizen is prepared to do either as the need arises.
Message 4
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| Subject: | Re: AOPA Never Again electrical problem |
--> AeroElectric-List message posted by: Brian Lloyd <brianl@lloyd.com>
Werner Schneider wrote:
> --> AeroElectric-List message posted by: "Werner Schneider" <wernerschneider@compuserve.com>
>
> A voltage readout would have shown the problem before they departed
The Aztec has a combined volt/amp meter that has a three-position switch to display
bus voltage or load on either alternator. Part of the run up check list
is to cycle the switch through all three positions and abort if buss voltage is
not correct or if either alternator shows no load (no output). So you can't
miss this one. The meter readings are not subtle.
As I said in my previous message about this article, "what rubbish."
--
Brian Lloyd 6501 Red Hook Plaza
brianl@lloyd.com Suite 201
http://www.lloyd.com St. Thomas, VI 00802
+1.340.998.9447 (voice) +1.360.838.9669 (fax)
There is a time to laud one's country and a time to protest.
A good citizen is prepared to do either as the need arises.
Message 5
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| Subject: | Re: Labeling of wires |
--> AeroElectric-List message posted by: ALWAYSPDG@aol.com
Mark, thanks for the information.
Mike
Message 6
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| Subject: | Getting oxidization off wires |
--> AeroElectric-List message posted by: "John Slade" <sladerj@bellsouth.net>
Electric people.
The Florida humidity has got through my nicely crimped BNC connectors and
attacked all my antenna connections.
I'm planning to make one permanent join at the winglet (where I have a 6
inch stub of cable coming out of the fiberglass from the antenna) then run
new cable all the way to the panel. I thought I'd solder the inner cores,
shrink wrap with RTV, bring the shields together and solder them too. I need
to clean off the shielding to get a good solder connection. Currently the
shielding has black copper oxidization all the way up under the outside
cover as far as I can see. What can I dip the shielding in to get a good
join?
Other suggestions for how to do this would be welcome.
John Slade
Flying Turbo Rotary Cozy IV
http://canardaviation.com/cozy
Message 7
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| Subject: | Re: Buttal on OVP and Circuit Breakers. |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
The Aeroelectric OVP uses a Teccor S6025L silicon controlled rectifier. When
an overvoltage is sensed, the SCR (thyristor) quickly turns on and shorts
the 5A circuit breaker to ground. We want the breaker to open--but how
quickly must this happen?
Assuming the bus will supply it, the short circuit current will be
approximately 15V (16.2V-diode Vf)/(0.07CB ohm+0.01 ohm wiring
resistance)=188 Amps. (For these estimates).
Teccor's data is mainly for 50-60 Hz applications, not one-shot crowbars,
but the following limits single cycle non-repetitive surge capability---350A
peak for 8.3 milliSeconds. (Their recommended I
2*T for fusing is 510 Amp
2*
Sec, which is 50% of this.).
So we can estimate that something less than an I
2*T of 1000 Amp
2* Sec is
required. For the thyristor to survive, it must then suffer less than 188
Amps X 28 milliseconds to get an I
2*T under 1000 Amp
2* Sec (or so).
Otherwise the crowbar OVP will work maybe only ONCE.
Thus, you can clearly see that getting a circuit breaker that will trip in
less than 28 milliseconds under the specified short circuit conditions is
essential, else the OVP will fry.
I wish I could wrap all this up in a mathematically neat package, but the
trip time/overload specifications of most aircraft circuit breakers is
simply not available for currents over 10X rated load or 50A. But the
circuit breakers will trip far larger currents with ease....they just won't
specify the time lag.
----This is my experience from trying to discover why my crowbar OVP
disappeared in a flash and left a perfectly good thermal circuit breaker
untouched.
So I stand by what I said, use a fast breaker for the OVP/Alternator Field
line.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"When the Okies moved to California it raised the average IQ of both
states."
---Will Rogers
Message 8
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| Subject: | Re: Reformated--Re: Buttal on OVP and Circuit Breakers. |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
Sorry, This is hard enough without some of the math symbols trashing the
formatting...
The Aeroelectric OVP uses a Teccor S6025L silicon controlled rectifier. When
an overvoltage is sensed, the SCR (thyristor) quickly turns on and shorts
the 5A circuit breaker to ground. We want the breaker to open--but how
quickly must this happen?
Assuming the bus will supply it, the short circuit current will be
approximately 15V (16.2V-diode Vf)/(0.07CB ohm+0.01 ohm wiring
resistance)=188 Amps. (For these estimates).
Teccor's data is mainly for 50-60 Hz applications, not one-shot crowbars,
but the following limits single cycle non-repetitive surge capability---350A
peak for 8.3 milliSeconds. (Their recommended I sq * T for fusing is 510 Amp
sq *
Sec, which is 50% of this.).
So we can estimate that something less than an I sq * T of 1000 Amp sq * Sec
is
required. For the thyristor to survive, it must then suffer less than 188
Amps X 28 milliseconds to get an I sq * T under 1000 Amp sq * Sec (or so).
Otherwise the crowbar OVP will work maybe only ONCE.
Thus, you can clearly see that getting a circuit breaker that will trip in
less than 28 milliseconds under the specified short circuit conditions is
essential, else the OVP will fry.
I wish I could wrap all this up in a mathematically neat package, but the
trip time/overload specifications of most aircraft circuit breakers is
simply not available for currents over 10X rated load or 50A. But the
circuit breakers will trip far larger currents with ease....they just won't
specify the time lag.
----This is my experience from trying to discover why my crowbar OVP
disappeared in a flash and left a perfectly good thermal circuit breaker
untouched.
So I stand by what I said, use a fast breaker for the OVP/Alternator Field
line.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"When the Okies moved to California it raised the average IQ of both
states."
---Will Rogers
Message 9
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| Subject: | Re: RF breakthro on Vans gauges |
--> AeroElectric-List message posted by: Jim Bean <jim-bean@att.net>
hi,
My best result was from changing the radio antenna coax to double
shielded (RG-400 is good) with crimped connectors.
Jim Bean
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