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Over-voltage event w/ IR alternator (to Matt)

 
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gmcjetpilot(at)yahoo.com
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PostPosted: Wed Feb 15, 2006 12:32 pm    Post subject: Over-voltage event w/ IR alternator (to Matt) Reply with quote

Quote:
Subject: Re: Over-voltage event w/ IR alternator
From: "Matt Prather" <mprather(at)spro.net>



Hi Matt: Thanks for the great post let me see
if I can explain or at least share my
ignorance.


Quote:
Hello George, A couple of questions:
What causes the failed IR overvoltage event to max-
out at 17V (or 18V)? Is it loads and battery? Or
is the field current limited somehow. It seems
that we discussed that a short between Vb and the
field (through the main transistor, or otherwise)
would cause an OV event similar to what was
described - open loop output, controlled by RPM,
and load the battery being the primary load. Mr
Lee didn't mention whether he experimented with
eliminating loads, and revving the engine to a
higher RPM (I wouldn't have tried that on my daily
driver). But it seems that you are suggesting that
even had he done that, 17V would have been the peak
voltage seen on the bus. Am I reading you right?


To be honest I dont know what caused the OV.
If Mr. Lee would send the VR to me I will have
it evaluated and dissected. A large
manufacture of aftermarket VR of all brands
and types says they would check any VR of any
make or brand for me. They have a lab with x-
ray, test equipment and expertise to do
failure analysis.

Are you saying that this is indicative of a
dead short of the field driver transistor? Not
to be combative I would say prove it. Of the
few OV conditions I have seen with NDs, they
seem every time to peeks at 16 or 17 volts
(talking about ND alternators only). From a
Toyota repair manual it does seem when there
is a fault the alternator can go into a 16v
mode, albeit not a very stable or regulated,
it never allows the voltage to RUN-A-WAY. Also
if this is the worst that can happen I say so
what. It aint no biggie.

Mr. Lee did vary load and RPM. He did a great
job of testing RPM, Load and noticed the idiot
light went out and on with voltage. If there
was a dead short, the dreaded RUN-A-WAY, I
think it would pump out way more voltage than
18v even with load applied or not.

Yes I am suggesting 17 (1Cool volt is the peak
with THIS KIND of (typ) failure. I am sure it is
possible to have the single fault runaway with
a ND. I believe Bob N and from what little I
know, it is possible. However from the Mr.
Lees F150 OV I dont see this, nor did Mr. L.

I do see an alternator that went to an a-stable
condition where voltage varied from 13v to
18v. Noting more nothing less? If you tell me
that is a classic shorted transistor I say SO
WHAT? Ha ha ha ha. Who is worried about that.
If that is the worst that can happen, so what.

The urban legend does not match reality, busted!
I-VR's are cool, not the evil OV machine.


>How long can we predict that we can leave a typical
Quote:
17Ah AGM battery connected to 17V, and have it act
as a system filter? Is there any risk of fire
associated with long term (admittedly,
unquantified) operation in such a manner? Asked
another way, what's the charge rate on the battery
when pumped to 17V? I suppose your suggestion to
include a b-lead disconnect of some sort (breaker,
in your case) addresses this issue. As long as the
pilot registers that the bus voltage is
significantly out of limits.


Another great question. I would say that is
why we have an idiot light on the alternator
or a HI/Lo volt warning light. With the BIG
OLD FAT Circuit Breaker for the B-lead on the
panel, pulling it makes it a moot worry.

However to answer the question I think the
battery can take an over charge for a
reasonable about of time, a minute to 10?

Bob reported a case of a RV pilot who had an
OV and flew for quite a while with out any
action, despite smelling something burning.
When he noticed the volt meter was TOO high
(no value given) he turned the ALT off with
the ALT switch. The volts returned to normal.
When he landed the battery case had expanded
and was clearly bulging out. First no actual
time was given for the duration of the OV, but
it could be 10 minutes to 40 minutes. When he
noticed the volt meter (I think analog) he
stated it was HI but no value given. I am
guessing that it was 17 volts. No damage to
radios was reported, but it is assumed that it
was a basic VFR plane.

So I think there is a risk, but low. As far as
the battery it was being abused with high
volts from say 5-40 minutes(?) and it only
bulged. The alternator did not catch on fire
but Bob N. reported damage to internal parts,
no doubt from pumping out too much juice. As
long as the alternator is not near anything it
can catch on fire from heat and is not
dripping in oil it should not do anything but
get real hop. However if you turn the juice
off to the IGN lead of the alternator and pull
the b-lead CB it should shut down or just burn
out in short order.



Quote:
Without intending to put words into Bob (Nuckolls)'s
mouth, I believe He has said that he can't recommend
IR alternators in the context of designing an
electrical system with certificated-like behavior.
Not an all-out condemnation of these alternators as
a whole. I believe he has, on several occasions,
recognized the advantages of these low-cost devices.
>

Quote:
Regards, Matt-

Yes, you could be right. All I know is Bob was
OK with I-VR, or at least he allowed it in his
book with a Crow Bar and OV contactor as he
showed in his Z diagrams. Than Van said, he
will not warranty alternators they sold if an OV
device was used and did not recommend it. This
is after several (of Bobs) crow bars blew up
alternators. Bobs response was to call Van
ignorant and state he was taking out all
reference of I-VR in his book. Also on page 2:

http://www.aeroelectric.com/articles/Crowbar_OV_Protection/Crowbar_E.pdf

and, page one, right column, first Par, 2) for
years......

http://www.aeroelectric.com/articles/Alternator_Failures.pdf

I could be wrong. I got the idea he is anti I-
VRs. I agree with his claim that they cant be
certified for aircraft use, is true. However
automotive fuse blocks cant be certified. In
fact most experimental kit planes cant be
certified either. I dont hold the FAA good
house keeping stamp in such high absolute
terms. It seems like Bob N. will fall back on,
it cant be certified, when it suits him, and
push non standard or automotive technology
when it does suit him. I was in aircraft
certification new and modification of large
transport aircraft. I do know how it works.
However Bob N. has way more electrical
knowledge and experience than I do.


Take fuses you cant *fiddle with* as Bob
says or a fuse on B-leads under the cowl.
These are very alternative approaches and a
direct copy from automotive wiring
architecture. I doubt the FAA would approve
any airplane wired to Aeroelectric, E-VR or I-
VR. Does that make it Bad. No it makes it
better. So, can it be certified?, makes no impact
or impression on me. I know better. It is a
hollow claim, especially on experimental aircraft.
The SR71 and SpaceShip1 are not FAA approved.

Cheers George




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