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nuckolls.bob(at)aeroelect
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 Posted: Thu Jun 30, 2016 7:50 am Post subject: Hypothetical Battery Contactor Failure |
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At 08:13 AM 6/30/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Once an engine is running above idle, the battery no longer supplies electrical power to the aircraft. The alternator does. Many alternators will continue to operate if the battery is then disconnected. The electrical current needed to power the alternator field comes from the alternator output, whether the battery is connected or not. There may be some alternators that will not continue to run without a battery connected. Even for alternators that do continue to operate without a battery, the alternator could stop working if a very large electrical load is turned on which causes the system voltage to momentarily drop. |
WWWaaaayyyy back when, it was generally
assumed that running the aircraft sans battery
was not a good thing to do. Before alternators,
generator and battery switches were separate
and generators would self-excite. Given that
batteries are NOT good filters of power
generation noise, it didn't matter if the
battery was on-line or not.
The earliest alternators on Cessnas (and indeed
all other S.E. TC aircraft) were automotive
derivatives. I was not privy to any investigative
tests at Cessna but the corporate policy was
that their airplanes should not be operated
sans battery. Hence, the split rocker switch
was birthed.
Apparently, Beech experience was different. While
many if not most of the smaller S.E. aircraft
did the same battery-first-then-alternator
switching protocol. Re: B-23 Sundowner panel
excerpt below . . .
[img]cid:.0[/img]
The Bonanza and Barons were different. The first
regulator design I qualified for Beech was about 1978 and
their procurement specification stated that no feature
of the regulator's circuitry 'shall prevent the alternator
from coming up self-excited above xxxx rpm". This was
the first time I'd encountered an alternator EXPECTED to
come up all by itself. The Bonanza and Barons had totally
independent battery and alternator switches. Operation
sans battery was not prohibited and in fact the system
was designed to allow it.
I've got a new electro-mechanical test bench under
fabrication and will be doing some work on PM Dynamo
rectifier/regulators. The same facility will allow me
to explore and quantify the present state of the art
in production alternators. In the mean time, as long
as you don't hit the alternator with a really BIG load
(which few system are capable of doing anyhow), the
modern alternator runs self-excited and benefits immeasurably
from battery presence with respect to noise. More
details to follow.
So the answer to the opening question on this thread is:
"Loss of the battery contactor in flight will not
produce a behavior likely to be noticed in the air."
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan
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| Posted: Thu Jun 30, 2016 1:20 pm Post subject: Re: Hypothetical Battery Contactor Failure |
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Thanks for the knowledgeable answer. Once your new test bench is up and running, it would be interesting to verify or disprove this statement quoted from the Rotax 912 Installation Manual,
| Quote: | | Never sever connection between terminal C and B of regulator (e.g. by removal of a fuse) while the engine is running. Overvoltage and regulator damage can occur. |
I find that statement hard to believe. When voltage is removed from Rotax regulator terminal C, its DC output should shut off, not increase. Of course the AC voltage would increase due to lack of load, but not anymore than if all electrical loads were shut off.
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Joe Gores |
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jun 30, 2016 4:31 pm Post subject: Hypothetical Battery Contactor Failure |
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At 04:20 PM 6/30/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Thanks for the knowledgeable answer. Once your new test bench is up and running, it would be interesting to verify or disprove this statement quoted from the Rotax 912 Installation Manual,
> Never sever connection between terminal C and B of regulator (e.g. by removal of a fuse) while the engine is running. Overvoltage and regulator damage can occur. |
If we had a VERIFIED copy of the schematic
for the Ducatti R/R, the validity of that
statement could be confirmed or debunked.
I have seen THIS schematic offered from various
sources over the years
http://tinyurl.com/zfkte7c
A simply analysis of this drawing demonstrates
that "C" is both the voltage regulation sense
lead -AND- power source for the low-level
regulating circuity. Simple analysis of this
schematic shows that disconnection of the C
terminal causes the R/R to shut down . . . which
is consistent with a legacy design philosophy for
voltage regulators of all stripe.
| Quote: | | I find that statement hard to believe. When voltage is removed from Rotax regulator terminal C, its DC output should shut off, not increase. Of course the AC voltage would increase due to lack of load, but not anymore than if all electrical loads were shut off. |
This is an enduring problem with anecdotal
data gleaned from the catacombs of hangar-lore.
Open circuit voltage from the PM dynamo windings
may indeed be the voltage referred to by the
original assertions. Further, THAT voltage
generated by the engine running cruise rpm
just might be hazardous to the R/R . . . but
without the benefit of original designers
documentation, we might as well be discussing
Slobovian politics over a pitcher of beer.
In the TC world, we write specs, do test plans,
carry out experiments in the lab and airplanes on
the ground and airborne. Then we write test
reports which form the foundation for design
decisions or remedial actions to correct a deficiency.
Without that report (assuming one was ever produced)
the real meaning of the ideas floating around on
forums and hangars are at risk for (1) being mis-
interpreted and (2) being morphed with the telling
and re-telling into an entirely new significance.
If the FAA ever extends it's grip deeper into
OBAM aviation, a very strong excused is bound
to include our poor utilization of computing
and communications tools to keep (1) and (2)
in check.
So I'm with you my friend. I think the assertion
about the Rotax R/R is at best an idea that
suffered too many re-tellings by individuals
with little or no understanding.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jun 30, 2016 9:19 pm Post subject: Hypothetical Battery Contactor Failure |
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| Quote: | | If it's a PM style alternator, and the regulator is a shunt style regulator, and breaking that C-B connection removes the shunt load, then I can see how the regulator might be damaged. If the regulator sensing/control semiconductors are still connected to the alternator output but the shunt *isn't*, then the alternator could well be able to create a high enough voltage to exceed the max voltage ratings of the devices. |
Nobody has built a shunt style regulator in
a very long time. A few small systems on motor
bikes and snowmobiles popularized the simple
design but the B&C regulators have never been
shunt . . . the alleged schematic of the Ducatti
R/R is also a series regulator.
They are manufactured as a spares item but better
regulators are so easy to design, there's no reason
to stay with shunt style.
| Quote: | | Having the shunt *in* the circuit would ensure that the voltage never got that high. |
but it WOULD drive internal energy dissipation
to the max and, give the demonstrably poor
thermal management of many designs, could
toast the device. But I'm pretty sure
nobody builds/offers that control philosophy to
on the product we're using.
Bob . . .
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erich weaver
Joined: 16 Jun 2016
Posts: 11
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| Posted: Fri Jul 01, 2016 7:48 am Post subject: Re: Hypothetical Battery Contactor Failure |
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[quote="nuckolls.bob(at)aeroelect"]At 08:13 AM 6/30/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew>
In the mean time, as long
as you don't hit the alternator with a really BIG load
(which few system are capable of doing anyhow), the
modern alternator runs self-excited and benefits immeasurably
from battery presence with respect to noise. |
Just to clarify, did you really mean "benefits immeasurably"? I think maybe the opposite.
Immeasurable: Too large, extensive or extreme to measure.
regards,
Erich
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user9253
Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan
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| Posted: Fri Jul 01, 2016 9:34 am Post subject: Re: Hypothetical Battery Contactor Failure |
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"Benefits immeasurably" can be interpreted two ways:
Benefits are so small that they can not be measured.
Benefits are so greats that no scale exists to measure them.
Judging by his ending statement, I assume that he meant the benefits are very small.
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Joe Gores |
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erich weaver
Joined: 16 Jun 2016
Posts: 11
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| Posted: Fri Jul 01, 2016 1:53 pm Post subject: Re: Hypothetical Battery Contactor Failure |
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Right, and many believe that a battery DOES provide great benefit with respect to buffering electrical noise, so thought it would be important to clarify That Bob does not believe that to be the case.
Thanks
E
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jul 02, 2016 5:33 am Post subject: Hypothetical Battery Contactor Failure |
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At 10:48 AM 7/1/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "erich weaver" <erich.weaver(at)aecom.com>
[quote="nuckolls.bob(at)aeroelect"]At 08:13 AM 6/30/2016, you wrote:
> --> AeroElectric-List message posted by: "user9253"
>
> In the mean time, as long
> as you don't hit the alternator with a really BIG load
> (which few system are capable of doing anyhow), the
> modern alternator runs self-excited and benefits immeasurably
> from battery presence with respect to noise.
Just to clarify, did you really mean "benefits immeasurably"? I think maybe the opposite.
Immeasurable: Too large, extensive or extreme to measure. |
I've been thinking that word described an unquantifiable
entity; impossible to express in terms of quantity for any reason.
In fact, I've learned that it refers not to generally unknowable
numbers but only to nebulously large numbers.
I can go to bed tonight knowing something I did not
know this morning . . . it's a good day. Thanks for
the heads-up!
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jul 02, 2016 5:58 am Post subject: Hypothetical Battery Contactor Failure |
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At 04:53 PM 7/1/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "erich weaver" <erich.weaver(at)aecom.com>
Right, and many believe that a battery DOES provide great benefit with respect to buffering electrical noise, so thought it would be important to clarify That Bob does not believe that to be the case. |
It's easily demonstrated. I've made
numerous measurements on vehicles and
on the bench that show how the fully
charged battery becomes chemically
'disconnected' from its charging source.
I.e. its influence on minor wiggles (noise)
is diminished to insignificance.
Yes, during alternator runaway the battery
becomes the major 'load' that prevents
an predictable rise in bus voltage to 100
volts or more. An during high-inrush events,
the alternator's momentary overload or
slow dynamics in voltage regulation will also be
mitigated by the battery's ability to
dump energy back into the system during
the transient.
But for the itty-bitty wiggles we call
noise . . . excursions in hundreds of
millivolts over a broad range of frequencies,
the battery offers no significant 'filtering'
of these events.
The new test bench taking shape in my
shop is fitted with a large bonding surface
(copper clad top), lots of 120 vac outlets,
and a 2hp variable speed drive. The bench
is a shrine to Lord Kelvin. We will endeavor
to discover all the operating characteristics
of various components down to every measurable
detail with particular emphasis regulation
stability and efficiency.
I'll repeat the experiments that speak to
the battery's filtering qualities. The cool
thing is that we can document and publish
significant findings.
Bob . . .
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