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scc_ron(at)yahoo.com
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 Posted: Fri Sep 22, 2006 7:26 pm Post subject: strange electrical failure in flight |
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Hope someone has some ideas on how to troubleshoot an eletrical failure that I don't understand. I have Bob's Essential Bus and Main Bus setup, one battery, new plane (50 hours). In flight today I had an indication that I had a problem when my main bus connected items shut down. I turned on the Essential bus, turned off the Cessna type Master/Battery switch and continued on, landing uneventfully as planned with Bob's system.
Then I pulled the cowl to troubleshoot the problem. the master powered up the Main bus as if nothing happened. I started the engine and got 13.5 volts from the ND Alternator regardless of RPM. When I switched on the E Bus, the charge rate / output from the alternator jumped to 14.3. If I switched it off, the number again drops back to 13.5 volts. No blown fuses.
Anybody have an idea of what happened and what I might want to do? Thanks in advance.
Ron
RV-4 N8ZD
[quote][b]
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FLYaDIVE(at)aol.com
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| Posted: Sat Sep 23, 2006 3:27 am Post subject: strange electrical failure in flight |
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In a message dated 9/22/06 11:28:16 PM Eastern Daylight Time,
scc_ron(at)yahoo.com writes:
| Quote: |
Then I pulled the cowl to troubleshoot the problem. the master powered
up
|
| Quote: | the Main bus as if nothing happened. I started the engine and got 13.5
volts
|
| Quote: | from the ND Alternator regardless of RPM. When I switched on the E Bus, the
charge rate / output from the alternator jumped to 14.3. If I switched it
off,
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| Quote: | the number again drops back to 13.5 volts. No blown fuses.
Anybody have an idea of what happened and what I might want to do?
Thanks
|
| Quote: | in advance.
Ron
RV-4 N8ZD
===========================
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Ron:
It sure sounds like a bad GROUND. Second guess would be a bad B+ connection.
But, start with the GROUND, that is easy to check just by hooking a ground
wire to the battery and bypassing to the other ground connection points.
Been there, Done that. And POOF the problem was gone.
Barry
"Chop'd Liver"
"Show them the first time, correct them the second time, kick them the third
time."
Yamashiada
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khorton01(at)rogers.com
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| Posted: Sat Sep 23, 2006 3:35 am Post subject: strange electrical failure in flight |
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On 22 Sep 2006, at 23:25, Ron Patterson wrote:
| Quote: | Hope someone has some ideas on how to troubleshoot an eletrical
failure that I don't understand. I have Bob's Essential Bus and
Main Bus setup, one battery, new plane (50 hours). In flight today
I had an indication that I had a problem when my main bus connected
items shut down. I turned on the Essential bus, turned off the
Cessna type Master/Battery switch and continued on, landing
uneventfully as planned with Bob's system.
Then I pulled the cowl to troubleshoot the problem. the master
powered up the Main bus as if nothing happened. I started the
engine and got 13.5 volts from the ND Alternator regardless of RPM.
When I switched on the E Bus, the charge rate / output from the
alternator jumped to 14.3. If I switched it off, the number again
drops back to 13.5 volts. No blown fuses.
Anybody have an idea of what happened and what I might want to do?
Thanks in advance.
|
Don't worry about the difference in indicated voltage when you switch
the E Bus on and off. Your voltmeter is connected to the E Bus,
which is normally supplied from the Main Bus, through a diode. The
difference in voltages you see when the E Bus is switched on and off
is due to the voltage drop through the diode. This is normal.
In flight, did all the electrically powered items die at the same
time? If so, it looks like something happened that killed the power
supply to the Main Bus. Is your system wired so the normal feed to
the Main Bus comes from the starter contactor, with the battery
contactor and alternator feed also connected to that same bolt on the
starter contactor? If so, check the connection there, and at the
other end of that cable where it connects to the Main Bus.
If the electrically powered items failed one by one, then it sounds
like a low voltage condition, due to an alternator problem. Let us
know if this was the way things happened and we can work this avenue.
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8
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rvreynolds(at)macs.net
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| Posted: Sat Sep 23, 2006 3:41 am Post subject: strange electrical failure in flight |
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Because of the diode between the main and essential buses, there will be a lower voltage on the essential bus with the essential bus switch off if voltage is measured on the essential bus..
The best place to measure the charing voltage is at the alternaor side of the starter contactor or the battery contactor or the battery.
Where are you measuring the voltage?
Richard Reynolds
Norfolk VA
On Sep 22, 2006, at 11:25 PM, Ron Patterson wrote:
[quote]Hope someone has some ideas on how to troubleshoot an eletrical failure that I don't understand. I have Bob's Essential Bus and Main Bus setup, one battery, new plane (50 hours). In flight today I had an indication that I had a problem when my main bus connected items shut down. I turned on the Essential bus, turned off the Cessna type Master/Battery switch and continued on, landing uneventfully as planned with Bob's system.
Then I pulled the cowl to troubleshoot the problem. the master powered up the Main bus as if nothing happened. I started the engine and got 13.5 volts from the ND Alternator regardless of RPM. When I switched on the E Bus, the charge rate / output from the alternator jumped to 14.3. If I switched it off, the number again drops back to 13.5 volts. No blown fuses.
Anybody have an idea of what happened and what I might want to do? Thanks in advance.
Ron
RV-4 N8ZD
| Quote: |
atronics.com/Navigator?AeroElectric-List
ntribution
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[b]
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rv-9a-online(at)telus.net
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| Posted: Sat Sep 23, 2006 10:34 am Post subject: strange electrical failure in flight |
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Ron, did you measure the alternator output voltage directly at the
battery, or is your voltmeter connected to the main bus?
If you have any isolation diodes involved between the voltmeter and the
battery (such as automatic e-bus/main bus switching), this could be the
cause of your 13.5 volt reading.
Vern Little
Ron Patterson wrote:
| Quote: | Hope someone has some ideas on how to troubleshoot an eletrical failure
that I don't understand. I have Bob's Essential Bus and Main Bus setup,
one battery, new plane (50 hours). In flight today I had an indication
that I had a problem when my main bus connected items shut down. I
turned on the Essential bus, turned off the Cessna type Master/Battery
switch and continued on, landing uneventfully as planned with Bob's system.
Then I pulled the cowl to troubleshoot the problem. the master powered
up the Main bus as if nothing happened. I started the engine and got
13.5 volts from the ND Alternator regardless of RPM. When I switched on
the E Bus, the charge rate / output from the alternator jumped to 14.3.
If I switched it off, the number again drops back to 13.5 volts. No
blown fuses.
Anybody have an idea of what happened and what I might want to do?
Thanks in advance.
Ron
RV-4 N8ZD
*
*
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dreel(at)cox.net
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| Posted: Sat Sep 23, 2006 10:36 am Post subject: strange electrical failure in flight |
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The big increase in voltage with load could be due to high resistance in the
regulator sense circuit. The more load you add, the higher the current in
the alternator field coil. If the sense circuit is also the field coil
supply, any resistance in the circuit will cause a voltage drop and the
regulator will increase the voltage to make up for the sensed drop in
voltage. So, if you add lots of load, you could be getting voltage spikes
over 16v which would trip an overvoltage protector which you probably also
have. Check to see if your alternator field circuit breaker tripped.
I had to reduce the resistance in my field circuit to .02 ohms by removing
the fuse and wiring it directly to the buss through a fuse link before I
could get reliable operation from my system.
Dave Reel - RV8A
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nuckollsr(at)cox.net
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| Posted: Sat Sep 23, 2006 4:43 pm Post subject: strange electrical failure in flight |
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At 08:25 PM 9/22/2006 -0700, you wrote:
| Quote: | Hope someone has some ideas on how to troubleshoot an eletrical failure
that I don't understand. I have Bob's Essential Bus and Main Bus setup,
one battery, new plane (50 hours). In flight today I had an indication
that I had a problem when my main bus connected items shut down. I turned
on the Essential bus, turned off the Cessna type Master/Battery switch and
continued on, landing uneventfully as planned with Bob's system.
Then I pulled the cowl to troubleshoot the problem. the master powered up
the Main bus as if nothing happened. I started the engine and got 13.5
volts from the ND Alternator regardless of RPM. When I switched on the E
Bus, the charge rate / output from the alternator jumped to 14.3. If I
switched it off, the number again drops back to 13.5 volts. No blown fuses.
|
As others have noted, the approx 0.7 to 0.8 volt jump between e-bus
volts with alternate feed closed versus open is explained by the
0.7 volt drop in the normal feed diode. This is normal and is not
a big deal . . .
Consider that electro-whizzies for aircraft are generally expected
to operate hunky-dory from a battery which delivers it's energy
over a 12.5 to 11.0 volt domain. So, when the alternator is not working
and the e-bus switch is closed, what you see is what the battery is
able to deliver which starts out about 12.5 volts at 100% charged and
by the time it's down to 11.0 volts, it's 95% used up.
Turn on an alternator and the battery jumps up to 14.25 volts (recommended
regulator setting for 99.999% of all 14v regulators on the road and in
the air. Under this condition, with the e-bus alternate feed switch open,
one expects 14.2 - 0.7 or 13.5 volts at the e-bus. If 12.5 and down is
okay battery only, then I'll suggest that 13.5 with the alternator running
is okay too.
If you have only one voltmeter in the airplane, it's a good deal to
have it on the e-bus and just KNOW that the alternator is running 0.7
above e-bus reading. When the alternator is running, you don't much
care what the voltmeter reads . . . but when the alternator is not
running, knowing what the battery is a lot more useful. There is
when you find out if your battery maintenance and endurance bus
calculations were correct.
This explains the observed voltage variations you cited . . . which
I'll suggest were predicted, normal and no big deal. This doesn't
explain what was going on with your alternator. When you say the
main bus stuff "shut down" . . . does this mean the stuff went
completely dark? If the e-bus stuff stay up, I presume it was because
you were flying with the e-bus alternate feed switch closed. Not
a big deal . . . but it's a good idea to preflight the alternate
feed path. Use the e-bus alternate feed to get your ATIS/Clearance
before cranking up the engine. Then note that the e-bus DOES wiggle
by the predicted 0.7 volts as the switch is operated . . . this says
the diode is in place and good.
What kind of alternator? Regulator? Do you have a low votlage warning
light?
Bob . . .
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rv-9a-online(at)telus.net
Guest
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| Posted: Sun Sep 24, 2006 8:25 am Post subject: strange electrical failure in flight |
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This comment reminds me of a problem that I had with an externally
regulated alternator.
If the voltage drop between the battery and the regulator is too high
(or there is too much resistance in the circuit), the alternator output
will be too high, and it will be load dependent-- the more devices you
turn on, the higher the alternator voltage.
I had a faulty master switch that caused overvoltages due to this effect
(loose rivets on the terminals). Once the switch was replaced, the
alternator voltage stablized.
Exacerbating this problem can be a loose alternator belt, which will
cause oscillations in the output voltage. When the belt slips, the
regulator tries to force the alternator output higher... then the belt
grabs and it takes a moment for the regulator to turn the output back
down. The resulting spike can trip overvoltage circuits. This will be
more noticable at low engine RPMs.
As a note: I had an overvoltage 'event' due to the faulty master while
I was flying over the mountains. I switched the master switch OFF, and
continued to fly: My Dynon EFIS has an internal battery, my Garmin GPS
has an internal battery, my RMI engine monitor runs off an external
backup battery, and I have a hand-held nav/com. I do not have an
electronic ignition. This is a good example of a redundant design.
In none of my overvoltage cases did my B&C OVM-14 trip-- the overvoltage
was not enough to do so. Instead, my Monroy ATD-300 gave me a voice
warning 'Check Voltage'. Clever little device.
Vern Little
| Quote: |
The big increase in voltage with load could be due to high resistance in the
regulator sense circuit. The more load you add, the higher the current in
the alternator field coil. If the sense circuit is also the field coil
supply, any resistance in the circuit will cause a voltage drop and the
regulator will increase the voltage to make up for the sensed drop in
voltage. So, if you add lots of load, you could be getting voltage spikes
over 16v which would trip an overvoltage protector which you probably also
have. Check to see if your alternator field circuit breaker tripped.
I had to reduce the resistance in my field circuit to .02 ohms by removing
the fuse and wiring it directly to the buss through a fuse link before I
could get reliable operation from my system.
Dave Reel - RV8A
|
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scc_ron(at)yahoo.com
Guest
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| Posted: Mon Oct 02, 2006 6:47 am Post subject: Strange Electrical failure in flight |
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Just a note to let those of you who reponded to my question that I found the problem(s). I did, in fact, have a loose B lead and to some extent a loose main ground to the firewall. Once I tightened these connections up, no more problems. Thanks for all the help.
Ron
RV-4 N8ZD
[quote][b]
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