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Update: Strange alternator behavior at Startup

 
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mstewart(at)iss.net
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PostPosted: Mon Feb 27, 2006 7:19 am    Post subject: Update: Strange alternator behavior at Startup Reply with quote

Update:
Was up north this weekend and was able to do a good test in the cold.
Temp was 10F and I cranked her up.
Set immediate idle at 800rpm. No charge. Sat ther for 10 seconds or so.
Went to 1100rpm for about 5 seconds. And Wallah, charging.
Back to 700rpm for 10 seconds. Still Charging.
Down to 350rpm for 10 seconds and still charging.

So it would seem that it needs that initial rpm to get the juices
flowing in the cold.
I can live with that.
Thanks to whom ever it was that suggested an initial burst of RPM to get
her going. Worked
Best,
Mike
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frank.hinde(at)hp.com
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PostPosted: Mon Feb 27, 2006 10:31 am    Post subject: Update: Strange alternator behavior at Startup Reply with quote

Your welcome...Exept I have to get to 2000RPM to get mine going...then
again my engine tops out at 5500RPM...Smile

Frank

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mprather(at)spro.net
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PostPosted: Mon Feb 27, 2006 1:09 pm    Post subject: Update: Strange alternator behavior at Startup Reply with quote

Hey everybody (especially Bob),

I've been sitting around thinking about how to make circuits more
complicated than they need to be (grin)... Here's an idea for turning off
an IR alternator with the end goal of not causing damage due to load dump.
It definitely adds parts count, and doesn't address over voltage nuisance
trips. The idea depends on the alternator using the sense lead as a
reference voltage input for the regulator. One of the schematics that I
looked at for an IR chip supported such behavior...

So, here's the idea. Actuating the 'off' position of the alternator
switch would actually connect a pumped ic regulator (LM1577 or similar)
output to the sense lead of the IR alternator at a voltage higher than
alternator output voltage. Say bump it up by 2Volts or so. This would
signal to the IR that the alternator output current needs to be reduced in
order to return to regulated voltage (in effect re-regulating, or fooling
the IR). After 1 sec or so, the alternator disconnect relay is then
opened, safely disconnecting the unit from the bus - no load-dump.
Turning the alternator switch back 'on' boots the circuit, closes the
alternator disconnect relay, and disconnects the pump regulator from the
sense lead circuit.

I can work up a schematic if this sounds interesting..
Matt-


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nuckollsr(at)cox.net
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PostPosted: Tue Feb 28, 2006 5:19 am    Post subject: Update: Strange alternator behavior at Startup Reply with quote

At 07:01 AM 2/28/2006 -0500, you wrote:

Quote:

<mstewart(at)iss.net>

Oh.
Well that is very interesting Brian. Could it be that my IGN wire is
dead?
I have the IGN with voltage applied before cranking (I think. I have not
checked it since initial install) and I have an idiot light installed
which does work as expected. I will check that IGN wire next time I have
the cowl off to verify it is supplying power before cranking. Based on
your note below, it is quite possible the IGN wire is doing nothing.
Wonder why temperature is at play though.

Ill check it and report back.

Brian, have you been holding out on us? I've not been aware of
any automotive products that would ultimately self-excite at
any time interval or speed conditions. An interesting phenomenon to
contemplate.

Just last year I shared the following from my experience with
the alternators on Bonanzas and Barons:

------------ May 2005 -----------------

Example: I was tasked with designing a regulator for Bonanzas
way back when. The spec from Beech required that I be able
to take advantage of the alternator's self-excitation
capabilities. Okay, went out to Beech and borrowed an alternator.
On the drive stand, the residual output from the b-lead with
the field disconnected was about 1.5 volts. Hmmmm, not enough
to get the regulator electronics to come alive . . . we were
working in a 28v system. I had to redesign the regulator
so that it would offer a bit of leakage through the powered-
down device.

Sure enough, the smallest amount of feedback from b-lead to
field would cause the system to wake up and run regulated.
Now, having accomplished the assigned task, I did NOT go
investigate the alternator's performance with respect to
bus voltage quality sans battery.

In later years . . . many later years, I heard of a fuss
about a batch of alternators that were rejected because
they would not self-excite. This caused a great thrashing
through the specs, purchase contracts, acceptance test
procedures, etc. The supplier was called on the carpet
and was feeling really beat up . . . "Look, there's
no requirement for this alternator to self excite."
Sho'nuf. Nobody could point to any controlling document
and cite a requirement for self-excitation. The vast
majority of alternators would do it . . . so many in
fact that Beech ASSUMED that it was a designed in feature
and decided to capitalize on it.

But when some process change or stack up of production
variables generated a batch of alternators that would
not self-excite, folks started shoveling garbage into
the fans. In fact, the supplier had never intended
that the alternator perform in this manner and Beech
simply assumed that the characteristic was designed in.

I've often wondered how much it would affect the
normal operation of an alternator to simply add
a little rare-earth magnet pellet to the field
assembly to cause some tiny but fixed amount of
field flux to always exist. We know that there are
alternator field assemblies with sufficient magnetic
retention to bring themselves on line but I wonder
if this is a controlled, design-in feature or
a happy fallout of production variables.

--------------------------------------------------------

Michael, the stagelight is on you sir. Do let us know
about that IGN wire!

Bob . . .

[quote]Thanks
Mike
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BobsV35B(at)aol.com
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PostPosted: Tue Feb 28, 2006 7:50 pm    Post subject: Update: Strange alternator behavior at Startup Reply with quote

In a message dated 2/28/2006 8:02:43 P.M. Central Standard Time,
mstewart(at)iss.net writes:

So it would seem that it needs that initial rpm to get the juices
flowing in the cold.
I can live with that.
Thanks to whom ever it was that suggested an initial burst of RPM to get
her going. Worked
Best,
Mike
Do not archive

Good Evening Mike,

Do you really want to give it that short burst of power?

Personally, I like to warm up the engine at as low an RPM as possible
consistent with adequate oil pressure and any need for the crankshaft to throw the
oil against the innards of the engine. I do not know what engine you have,
but I would not give it a burst above any RPM that I wanted to use for warm up
purposes.

Isn't that the whole idea behind doing a warm up?

Happy Skies,

Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503


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