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nuckolls.bob(at)aeroelect
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 Posted: Mon Oct 23, 2023 4:22 am Post subject: Pilot accessible B lead CB |
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At 06:34 PM 10/22/2023, you wrote:
| Quote: | Until now I have posted to Aeroelectric List on the website but I got locked out and have not been able to fix that so this comes by email and I suppose that will work OK.
Advanced Flight Systems, a subsidiary of Dynon, builds instrument panels for experimental aircraft and recommends a pilot-accessible resettable circuit breaker for the alternator B lead, which is contrary to Aeroelectric Connection's recommendation of a robust fuse, current limiter, or fuselink close to the master contactor.
I emailed AFS tech support to ask why.
==========
Their response:
(We had a customer) cook his instrument panel (due to) a runaway alternator. |
Which suggests his system was not fitted
with a well crafted ov management system.
| Quote: | We believe that the alternator field and B+ lead wires chafed and
shorted together inside the regulator (Dual EarthX batteries with
a B&C alternator), causing the alternator to become self powering. |
"inside the regulator"?????? There are no wires
inside a B&C regulator. Chaffing of insulation
to the extent that a hard connection is made between
bus and field? I'd really like to see the
carcase.
"we believe" . . . was no failure analysis
performed to turn belief into fact?
| Quote: | (The) panel was equipped with both an alt field switch and a
pilot accessible alternator CB (but) due to human factors only
the field was shut off, and this was insufficient to stop the
alternator. |
So if human factors prevented use of the b-lead
breaker as a last ditch effort to control a runaway,
how is it 'better' to add such a breaker to a design
that doesn't have one?
| Quote: | (Exacerbating) the problem was that the aircraft used an EarthX
(LiFePO4) battery, which is designed to internally disconnect itself
in an overvoltage event so that it doesn't explode. |
<snip>
| Quote: | An AGM battery, in contrast, has no provision to disconnect
itself and does not have the same risk of fire that an (LiFePO4)
battery does. In the same scenario with an AGM battery, it would
weather the runaway alternator by heating up some. Because
the battery would remain in the loop, the overvoltage the
avionics would have seen would not have been nearly as dramatic
or damaging. |
"heating up some"????? AGM batteries are not
reliable prophylactics for a runaway alternator
condition. They too will swell up, catch fire,
eject really smelly stuff. A well maintained,
flightworthy battery can be counted upon to
provide a temporary firewall during an ov
event. It will stand off the expected surge
that runaway alternators are capable off for
the TENS OF MILLISECONDS of ov protection delay
times.
We've had this discussion on the List about
20 years ago when some readers were adamantly
promoting the alternator b-lead breaker as
a last ditch mitigation for the runaway event.
In the best of circumstances a pilot will
need SECONDS to sense, recognize and react
by which time the bus voltage will have
exceeded survival limits per legacy rules.
There is another factor to consider. The
self excited, runaway alternator will easily
produce over 100V in under a second. When
you pull that breaker, an ARC is going to
form in the spreading contacts and may not
go out. The alternator is capable of dumping
thousands of watts of heat into that arc.
Needless to say, ensuing damage to the breaker
followed by chaos in the cockpit will
pose a whole new kind of risk.
| Quote: |
I would say in the event of an AGM battery being used...,
Nuckolls' favoring of a firewall mounted ANL... is
understandable. Given what we have seen, use of an
(LiFePO4)... battery means a pilot accessible breaker
should be strongly considered. Ultimately, this is a
matter of pilot choice, and there is no right or wrong answer. |
This wasn't MY idea. For decades, there have
been thousands of airplanes built with NO panel mounted b-lead
breakers. Bonanzas and Barons are noteworthy
of this feature. The b-lead protection is intended
to mitigate fault currents due to shorted alternator
diodes. If that breaker ever opens, (1) the alternator
is trashed or (2) the breaker is undersized or bad.
| Quote: | ==================
Seems doubtful the regulator was other than B&C as "... this
was a spare NO expense (spared) aircraft. The panel... had
dual AF-5000 EFIS displays, IFD-440, IFD-550. Dual battery
(EarthX) with a B&C alternator.
I have never heard of a B&C regulator failing to stop an OV event.
Obviously the B+ feeder does not pass through the regulator so
that part of the AFS response above is incorrect.
Curious to me the voltage only went to 100 and is described as a "spike".
There's a lesson there that due to Human factors the B lead CB was not pulled.
Without the opportunity to inspect the incident aircraft and
the EFIS logs the exact cause becomes speculative but I
would be interested if Bob or others can comment. Maybe someone
is even familiar with the incident aircraft. |
EXACTLY. This event begs for a detailed
failure analysis. From what we know so far,
it seems that there could have been better
choices for alternator management hardware.
Putting OV protection in a lithium battery's
BMS is a questionable practice. An OV
condition can come from only one fault . . .
a failed regulator . . . which by legacy design
rules should already have ov protection.
This dark-n-stormy-night narrative seems
to demonstrate the "Swiss Cheese"
analogy for failure. Several 'holes' in
design and selection of materials stacked
up to make the event possible. Adding
a b-lead breaker only adds one more 'hole'.
Better to plug the other holes instead.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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mike_tailwind
Joined: 06 Feb 2017
Posts: 12
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| Posted: Mon Oct 23, 2023 7:49 am Post subject: Pilot accessible B lead CB |
|
|
Without knowing the details, this is purely speculation, but this sounds like a scenario I was concerned with and posted about a month ago:
The potential exists that in a user modified automotive alternator that the B-lead can short to the field inside the alternator. This would cause an overvoltage event that cannot be contained by overvoltage protection at the regulator and no way to shut it down. The recommended solution was to secure the connection so that a short cannot occur (i.e. the probability is exceedingly small).
There are two ways for an overvoltage event to occur: failed regulator (covered) and shorted alternator (not covered, or covered by proper fabrication).
- Mike
On Monday, October 23, 2023 at 07:32:16 AM CDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
At 06:34 PM 10/22/2023, you wrote:
| Quote: | Until now I have posted to Aeroelectric List on the website but I got locked out and have not been able to fix that so this comes by email and I suppose that will work OK.
Advanced Flight Systems, a subsidiary of Dynon, builds instrument panels for experimental aircraft and recommends a pilot-accessible resettable circuit breaker for the alternator B lead, which is contrary to Aeroelectric Connection's recommendation of a robust fuse, current limiter, or fuselink close to the master contactor.
I emailed AFS tech support to ask why.
==========
Their response:
(We had a customer) cook his instrument panel (due to) a runaway alternator. |
Which suggests his system was not fitted
with a well crafted ov management system.
| Quote: | We believe that the alternator field and B+ lead wires chafed and
shorted together inside the regulator (Dual EarthX batteries with
a B&C alternator), causing the alternator to become self powering. |
"inside the regulator"?????? There are no wires
inside a B&C regulator. Chaffing of insulation
to the extent that a hard connection is made between
bus and field? I'd really like to see the
carcase.
"we believe" . . . was no failure analysis
performed to turn belief into fact?
| Quote: | (The) panel was equipped with both an alt field switch and a
pilot accessible alternator CB (but) due to human factors only
the field was shut off, and this was insufficient to stop the
alternator. |
So if human factors prevented use of the b-lead
breaker as a last ditch effort to control a runaway,
how is it 'better' to add such a breaker to a design
that doesn't have one?
| Quote: | (Exacerbating) the problem was that the aircraft used an EarthX
(LiFePO4) battery, which is designed to internally disconnect itself
in an overvoltage event so that it doesn't explode. |
<snip>
| Quote: | An AGM battery, in contrast, has no provision to disconnect
itself and does not have the same risk of fire that an (LiFePO4)
battery does. In the same scenario with an AGM battery, it would
weather the runaway alternator by heating up some. Because
the battery would remain in the loop, the overvoltage the
avionics would have seen would not have been nearly as dramatic
or damaging. |
"heating up some"????? AGM batteries are not
reliable prophylactics for a runaway alternator
condition. They too will swell up, catch fire,
eject really smelly stuff. A well maintained,
flightworthy battery can be counted upon to
provide a temporary firewall during an ov
event. It will stand off the expected surge
that runaway alternators are capable off for
the TENS OF MILLISECONDS of ov protection delay
times.
We've had this discussion on the List about
20 years ago when some readers were adamantly
promoting the alternator b-lead breaker as
a last ditch mitigation for the runaway event.
In the best of circumstances a pilot will
need SECONDS to sense, recognize and react
by which time the bus voltage will have
exceeded survival limits per legacy rules.
There is another factor to consider. The
self excited, runaway alternator will easily
produce over 100V in under a second. When
you pull that breaker, an ARC is going to
form in the spreading contacts and may not
go out. The alternator is capable of dumping
thousands of watts of heat into that arc.
Needless to say, ensuing damage to the breaker
followed by chaos in the cockpit will
pose a whole new kind of risk.
| Quote: |
I would say in the event of an AGM battery being used...,
Nuckolls' favoring of a firewall mounted ANL... is
understandable. Given what we have seen, use of an
(LiFePO4)... battery means a pilot accessible breaker
should be strongly considered. Ultimately, this is a
matter of pilot choice, and there is no right or wrong answer. |
This wasn't MY idea. For decades, there have
been thousands of airplanes built with NO panel mounted b-lead
breakers. Bonanzas and Barons are noteworthy
of this feature. The b-lead protection is intended
to mitigate fault currents due to shorted alternator
diodes. If that breaker ever opens, (1) the alternator
is trashed or (2) the breaker is undersized or bad.
| Quote: | ==================
Seems doubtful the regulator was other than B&C as "... this
was a spare NO expense (spared) aircraft. The panel... had
dual AF-5000 EFIS displays, IFD-440, IFD-550. Dual battery
(EarthX) with a B&C alternator.
I have never heard of a B&C regulator failing to stop an OV event.
Obviously the B+ feeder does not pass through the regulator so
that part of the AFS response above is incorrect.
Curious to me the voltage only went to 100 and is described as a "spike".
There's a lesson there that due to Human factors the B lead CB was not pulled.
Without the opportunity to inspect the incident aircraft and
the EFIS logs the exact cause becomes speculative but I
would be interested if Bob or others can comment. Maybe someone
is even familiar with the incident aircraft. |
EXACTLY. This event begs for a detailed
failure analysis. From what we know so far,
it seems that there could have been better
choices for alternator management hardware.
Putting OV protection in a lithium battery's
BMS is a questionable practice. An OV
condition can come from only one fault . . .
a failed regulator . . . which by legacy design
rules should already have ov protection.
This dark-n-stormy-night narrative seems
to demonstrate the "Swiss Cheese"
analogy for failure. Several 'holes' in
design and selection of materials stacked
up to make the event possible. Adding
a b-lead breaker only adds one more 'hole'.
Better to plug the other holes instead.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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nuckolls.bob(at)aeroelect
Guest
|
| Posted: Mon Oct 23, 2023 10:01 am Post subject: Pilot accessible B lead CB |
|
|
At 10:48 AM 10/23/2023, you wrote:
| Quote: | Without knowing the details, this is purely speculation, but this sounds like a scenario I was concerned with and posted about a month ago:
The potential exists that in a user modified automotive alternator that the B-lead can short to the field inside the alternator. This would cause an overvoltage event that cannot be contained by overvoltage protection at the regulator and no way to shut it down. The recommended solution was to secure the connection so that a short cannot occur (i.e. the probability is exceedingly small).
There are two ways for an overvoltage event to occur: failed regulator (covered) and shorted alternator (not covered, or covered by proper fabrication).
- Mike |
Absolutely . . . no argument here. The salient
point here is how best to craft the failure-tolerant
design. I.e. no single failure creates a hazardous
condition. Critical failures are easily pre-flight
detectable or annunciated in flight. There are
plan-b protocols established, very early in the
project lifetime, that prevent any such event from
becoming an emergency.
That's what we've studied here for many years.
Failure Mode Effects Analysis, artful
exploitation of lessons learned and
cultivation of personal skills.
Such a failure internal to a modified alternator
has to be rooted in poor design/fabrication.
There are plenty of opportunities for
mistakes: Improper torque on prop bolts,
battery driven into the ground for lack
of preventative maintenance, errors of
judgement like this sad narrative:
http://aeroelectric.com/Reference_Docs/Accidents/N811HB_Feb2008_LA-IVp/Figure%203_Dual_Feed_Bus_as_Installed.pdf
http://aeroelectric.com/Reference_Docs/Accidents/N811HB_Feb2008_LA-IVp/Narration_Analysis_Redacted.pdf
An exceedingly simple but critical 'enhancement'
to a recommended architecture cost a whole
lot of dollars, labor and health to occupants.
These are EXPERIMENTAL aircraft but the thing
that make them competitive with TC aircraft
in performance and safety is to MINIMIZE the
numbers and kinds of critical 'experiments'.
There are thousands of RV's flying with failure
mode mitigation equal to or better than any TC aircraft
when constructed per lessons learned from
countless processes now far removed from
'experimental'.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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nuckolls.bob(at)aeroelect
Guest
|
| Posted: Tue Oct 24, 2023 7:42 am Post subject: Pilot accessible B lead CB |
|
|
At 12:50 PM 10/23/2023, you wrote:
| Quote: | Thanks Bob.
I can believe AFS policy of Quick Panels having a B lead CB by default is as much legal CYA as technical. In their defense they cannot control electrical power system implementation or changes on OBAM aircraft. |
To be sure, throughout history of
electrical systems in aviation, there
are probably more airplanes with a
panel mounted breaker to the generator/
alternator feed than airplanes without.
There were a couple hundred thousand
airplanes built with breakers like those
pictured in the attachment. Non-pullable.
The 'policy' was to provide mandated
branch circuit protection from severe
overload . . . being able to pull a breaker
to mitigate a runaway alternator condition
was never a design goal.
The voltage ratings on breakers, relays
and switches are based on the ability of
the device to OPEN a circuit when experiencing
a specified fault current. A device rated
(and qualified) at 30 volts DC would
probably be in deep doo-doo attempting to
break a runaway alternator's b-lead.
In many instances policy has more to do
with tradition than with carefully considered
failure analysis or design rules for
accessories. In spite of the fact that
avionics master switches haven't been
a real thing for over 50 years, they're
still a feature on a lot of modern
airplanes.
The voltage ratings on breakers, relays
and switches are based on the ability of
the device to OPEN a circuit when experiencing
a specified fault current. A device rated
(and qualified) at 30 volts DC would
probably be in deep doo-doo attempting to
break a runaway alternator's b-lead.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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