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Interesting thread on overvoltage event

 
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nuckolls.bob(at)aeroelect
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PostPosted: Mon Apr 10, 2017 4:56 pm    Post subject: Interesting thread on overvoltage event Reply with quote

At 06:47 PM 4/10/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

Here is a link to the VAF thread that Charlie mentioned.
http://www.vansairforce.com/community/showthread.php?p=1164359#post1164359
It seems that the pilot was unable to shut down the alternator with either the field switch or master switch.
Anyone who installs a Lithium battery should read the Dynon Support post #7 in that thread. Without aircraft electrical system over-voltage protection, a Lithium battery could disconnect itself from the electrical system to protect itself against an over-voltage event. Without a lead-acid battery to mitigate over-voltage, very expensive avionics are at the mercy of a runaway alternator.
Post number 17 by Dynon Support is also interesting.

The assertions made in this posting are largely
correct. The stock internally regulated alternator
has failure modes for ov conditions that cannot
be controlled from the outside.

With no battery on line to grunt the excess energy,
bus voltages of 100-200 volts are easily realized.
I had conversation with folks about this
very topic last week . . . the event chronicled
on the RV forum may have triggered the queries.

The battery has always been a CRITICAL component
of the overvoltage mitigation dynamic. The
auto-disconnect feature in EarthX batteries is
understandable from the battery safety
perspective . . . but it may upset the apple cart
when it fails to perform legacy duties expected
of lead-acid batteries.



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 11, 2017 8:53 am    Post subject: Interesting thread on overvoltage event Reply with quote

At 10:18 AM 4/11/2017, you wrote:
Quote:
Regarding the overvoltage event with an earthX battery. Apparently the fried system did not have an overvoltage module installed. Would the B&C overvoltage module have made this a non event?

Yes . . . sorta . . .

The B&C Crowbar OV module deliberately opens
the alternator's field supply breaker when
an ov event is detected.

The problem with STOCK automotive alternators
is difficulty of accessing the field supply
power path. The alternator must be disassembled
and modified for such service. This is what
B&C has routinely accomplished on all their
IR alternators since day-one.

Over the years, there have been numerous
articles in the OBAM aviation journals describing
techniques for modifying various brands of
IR alternator to external regulator service.

Early Plane Power products were modified to
to ADD the crowbar OV module right on the back
of the stock alternator housing . . . current
offerings have the module built in . . .

http://tinyurl.com/lnypyeq

Running an internally regulated
alternator with no ov protection is
a relatively low risk decision . . . but the
risk is NOT ZERO. Further, the stock alternators
do not permit the system integrator to offer
absolute on/off control of alternator output
by crew under all circumstances.



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Sat Apr 22, 2017 5:33 pm    Post subject: Interesting thread on overvoltage event Reply with quote

At 12:27 PM 4/20/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "nuckollsr" <bob.nuckolls(at)aeroelectric.com>

After the server upgrade at matronics, I'm still wrestling with some email issues . . . but these too will pass . . .

Got 2 out of 3 email channels 'unclogged' . . . we're back
in the saddle on the AeroElectric-List.

I'm working on a couple of new regulator designs.
There's a need for data describing performance
studies and system integration questions that bubbled
up with the advent of LiFePo4 batteries. The plan is
to fit the drive stand with a 12-bit, 8 channel data
acquisition system that will let us go measure things
. . . things that that both suppliers and users of products
offered to OBAM aviation should know.

Need to get the regulators into production first but
we'll add everything but the kitchen sink to the test
stand after that. Got all the hardware in boxes
waiting for software to be installed on the hosting
computers.



Bob . . .


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rv8ch



Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

PostPosted: Tue Apr 25, 2017 1:45 am    Post subject: Re: Interesting thread on overvoltage event Reply with quote

One point that is not clear for me about the internal/external VR discussion. I apologize in advance if this has been clarified somewhere else and I just missed it.

I don't understand why or how an external voltage regulator can safely cut the field using the crowbar method and an internal regulator cannot. If I look at the wiring diagrams there does not seem to be a difference. Is it just that the external VR is more robust?

Thanks for any clarity you can provide.


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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Tue Apr 25, 2017 4:04 am    Post subject: Re: Interesting thread on overvoltage event Reply with quote

The internally regulated alternator gets its field power from within the alternator. There is no easy way for the pilot or for an over-voltage protection module to interrupt that power.
The externally regulated alternator gets its field power from a panel mounted fuse or circuit breaker or switch. It is much easier to interrupt the external field power source.


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rv8ch



Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

PostPosted: Tue Apr 25, 2017 4:19 am    Post subject: Re: Interesting thread on overvoltage event Reply with quote

user9253 wrote:
The internally regulated alternator gets its field power from within the alternator. There is no easy way for the pilot or for an over-voltage protection module to interrupt that power.
The externally regulated alternator gets its field power from a panel mounted fuse or circuit breaker or switch. It is much easier to interrupt the external field power source.
Yes, this is what I thought as well, but looking at the Z diagrams for how to wire an external VR, it looks like control of the F is only done by the VR, so I'm struggling to see a difference between and Internal and and External VR.


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 25, 2017 5:19 am    Post subject: Interesting thread on overvoltage event Reply with quote

At 04:45 AM 4/25/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch>

One point that is not clear for me about the internal/external VR discussion. I apologize in advance if this has been clarified somewhere else and I just missed it.

I don't understand why or how an external voltage regulator can safely cut the field using the crowbar method and an internal regulator cannot. If I look at the wiring diagrams there does not seem to be a difference. Is it just that the external VR is more robust?

Thanks for any clarity you can provide.

The externally regulated alternator has NO electronics
inside . . . just a rudimentary alternator.

[img]cid:7.1.0.9.0.20170425080902.0207e8c0(at)aeroelectric.com.0[/img]

Interrupting the 'field input' line offers total
control over alternator output.

The internally regulated alternator has solid
state devices that control alternator output.
There is no field power input connection, only
a 'control' connection that talks to the
electronics.

[img]cid:7.1.0.9.0.20170425080902.0207e8c0(at)aeroelectric.com.1[/img]

There are failure modes INTERNAL to the alternator
that can cause an over voltage condition . . . a
condition not controllable from outside.

Hence, the legacy preference for externally regulated
alternators that allow a system integrator to include
over voltage protection in some form. It doesn't
have to be the 'crowbar' style . . . there are several
satisfactory approaches.

The crowbar ov module offers the simplest and most
robust configuration but it's not intended to displace
any other demonstrably functioning ov management system.


Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Apr 25, 2017 5:28 am    Post subject: Interesting thread on overvoltage event Reply with quote

Quote:
Yes, this is what I thought as well, but looking at the Z diagrams for how to wire an external VR, it looks like control of the F is only done by the VR, so I'm struggling to see a difference between and Internal and and External VR.

But the crowbar ov module in turn controls power
to the external regulator. Opening the field power
source to the regulator will also shut down the
alternator. That 'control' lead into an IR
alternator cannot be guaranteed to offer
absolute control under all failure modes.


Bob . . .


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PostPosted: Tue Apr 25, 2017 3:08 pm    Post subject: Interesting thread on overvoltage event Reply with quote

At 10:04 AM 4/25/2017, you wrote:
Quote:
Because I am installing the optional 40 amp Rotax alternator (internally regulated Denso) this discussion is very interesting to me. >From what I am reading, it sounds like the only way to shut it down would be to interrupt the output (B wire) with a switch or pull breaker.Â

If that is the case, what is the purpose of the IG wire, which runs from the bus, through the master switch, to the alternator?

This wire WILL control the alternator as long
as there are no failures of the electronics
that respond to that command.

To incorporate IR alternators in this manner
on airplanes argues with legacy design rules
driven by failure mode effects analysis that
assumes every part will fail . . . and then
designing a system that will mitigate that
failure. I.E. ov protection with absolute
control over field excitation.

Using the automotive convention for IR alternators
is acceptable in the TC world only if the
IR electronics can be declared to have a 1
in ten to the minus 9 failures per flight
hour (Part 25 or higher qualifications).
The stock automotive alternator is indeed
VERY reliable but the process controls and
sprinkling of holy water needed to declare
a 1 x 10^-9 failure rate would far exceed
the value of proposed market (see my earlier
posting about regulatory/bureaucratic mill-stones).

Hence, it's more 'practical' to convert the
stock automotive alternator to an externally
regulated machine (B&C approach) -OR- modify
the IR circuitry to bring out the (+) field
supply lead for implementation of absolute
control (PlanePower approach).



Bob . . .


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PostPosted: Wed Apr 26, 2017 6:33 am    Post subject: Interesting thread on overvoltage event Reply with quote

At 08:56 AM 4/26/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch>


ceengland7(at)gmail.com wrote:
> In the Z diagrams, follow all the wires leaving the regulator. One of them (the A terminal on the generic Ford model) goes through the alternator half of the master switch, to a 5A breaker, which is tied to the main buss. The 5A breaker supplies the regulator with its power. So with external regulators, you're removing the only source of electrons to the field by completely removing power from the regulator. This also prevents letting additional smoke out if the regulator 'guts' are shorted to ground internally.
Duh - now I get it - the light has turned on! [Idea] Thanks!

What you have 'discovered' is the process
by which an FMEA is accomplished. You study
power, control, and potential fault paths
for EVERY component in a system . . . to deduce:

a. How can this part fail?

b. If it fails, how will I know it?

c. Can it fail in a 'hidden' condition . . .
with a potential for misery in the cockpit?

-or-

d. is the failure pre-flight detectable?

e. if it does fail, what are the consequences
and what's the most elegant path to
resolution?

Unlike the reliability studies that
endeavor to build confidence in numbers
that may or may not have practical
validity (who tests batches of components
for a million hours?), the FMEA assumes
that EVERY part WILL fail.

Then the system integrator figures out how
to mitigate that failure . . . i.e. PLAN-B.

I've seen massive spread sheets that go into
minute detail on every little component or
feature in a system wherein the author proudly
announces "Eureka! We have achieved MTBF
Nirvana!"

I find it takes a tiny fraction of the time
and effort to conduct and resolve a simple
FMEA that offers a demonstrable degree of
probability for comfortable termination
of flight.

Congrats my friend with the hopes that
this new insight will serve you well . . .



Bob . . .


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