Hi Keith, thanks for the compliment.- My professional field is indeed ele
ctronics, with RF as the strong suite, but let me tell you, there are a few
guys hanging around this list that are smart enough to keep their mouth sh
ut, but never-the-less are highly regarded experts in their field.- Rob R
owe is one, and when he opens his mouth, I listen closely.- Another gent
owns his own company, has a PhD, and develops a whole plethora of products.
- That said, just about any time in my life I feel I am starting to get p
retty good at something, I get a lesson in humility from someone who is REA
LLY good.- .-
-
Also you're right.- Say a few good words about the USMC, and I will alway
s come out of the wood-work.- I have been absent from this list for awhil
e as I have been- going to school on long and short baseline interferomet
ry.- Another lesson in how much more math I need.-
-
In answer to the original question that dealt with the over-voltage conditi
on shutting down the tach.- Hmmm..... seems unlikely to me.- The YAK se
ries of aircraft has a built in over-voltage device ALREADY.- If you exce
ed 32 volts, it trips a circuit breaker and removes field excitation to the
generator, effectively shutting it off.- Further, even if that was defec
tive, running over 32 volts DC in your aircraft for any effective period of
time would pretty much boil the electrolyte out of your batteries pretty d
arn quick.- Then we have Dennis's comments, which were are as usual, dead
on.- Of course you can check your actual voltage right in the cockpit wi
th your volt/ammeter!- Only takes a second to do that.- So couple that
check, with the built in over-voltage protection our aircraft have, and I h
ave a hard time really believing the problem with the tach is an over-volta
ge condition.-
-
That said, there are a lot of other issues that are possible.- I would su
ggest first that the gent check his battery voltage BEFORE he goes flying.
- After the aircraft has sat for awhile, check it and make sure it is 24
volts and not less.- If it is, then he has bad batteries, and the generat
or is going to be trying to constantly charge them.- This will result in
a higher noise output from the generator.- The more current it produces,
the more noise it will create.- This is a real shotgun comment of course.
- But it is a valid test.-
-
If I were to make a wild ass guess, it would be that this particular tach m
ight indeed be "not quite right".-- As in... the people that make it al
ready admit- that it has an over-voltage shut-down mode.- That means tw
o things can make it shut off.-
-
1.- An aircraft over-voltage.
2.- Something wrong with the over-voltage circuit in the tach itself!-
-
It might be number 2.-
-
Hey, if you really want to know... just do exactly as Dennis suggested.-
Put a good voltmeter on the DC line (the battery is a good place), and meas
ure the voltage before you start, then after with the engine run up as far
as you want to stand there and get beat to death by the prop blast!- But.
.. get it up to about 75% or so at least.- Make sure that you watch the v
oltage come up to between 27-29 VDC and then STABILIZE.- In other words,
it should reach a top limit and then STOP going UP as you increase engine R
PM.- If it goes up steadily with engine RPM as you pass 75%, then somethi
ng is bad wrong.-
-
Voltage spikes:- Sure Keith, voltage spikes are indeed a bad thing, and i
n fact if you are concerned about them, adding a metal oxide varistor, or "
trans-sorb" is indeed do-able.- However, voltage spikes are typically cau
sed by large inductive loads.- The collapsing magnetic fields are the cau
se... and the biggest cause of those puppy dogs are STARTER MOTORS.- Some
thing the Yak happens to be missing!-- Honestly I can't think of too ma
ny inductive loads in a Yak (as in motors and stuff like them... INVERTER m
otor excepted!), so it comes back to the generator itself.- Generators do
n't usually put out nasty spikes, unless they are defective.- As in... re
ally bad brushes.--
-
Bad brushes could INDEED cause the problem noted with the TACH shutting off
, but it is really low on my personal list of "could this be it?"-- Nor
mally if you have brushes THAT bad, you are going to hear it in your radio.
-
-
I've installed the-P-1000 Tach on a few aircraft and have never seen this
problem before, and my off the record personal guess is ... it may be the
tach... but only if I personally ran all the other tests suggested first an
d they all came back negative.-
-
Bottom line Keith, your comment about voltage spikes is perfectly true, but
not really a concern (in my humble opinion) with the YAK model aircraft.
- On the other hand, to prove your point as being VALID, you might be int
erested to know that in a lot of CESSNA model aircraft, they have two DC bu
s controls.- MAIN and AVIONICS.-- When the starter motor is engaged,
the AVIONICS BUS is turned OFF, for exactly the reason you were concerned a
bout.-
-
Best Regards,
-
Mark Bitterlich (writing from my hangar email account)-
-
p.s.- Computing phase matched cells with simultanious short and long base
d interferometery is really stretching my remaining gray matter.-
-
--- On Mon, 11/16/09, keithmckinley <keith.mckinley@townisp.com> wrote:
From: keithmckinley <keith.mckinley@townisp.com>
Subject: Re: generator question
To: yak-list@matronics.com
Date: Mon, 16 Nov 2009 06:35:36 PM PST
>
Good point Dennis considering when this happens. For the record I still thi
nk that anything that creates electricity can create a voltage spike. Might
not trash your stuff outright but overtime will ruin it. If I had some fan
cy EFIS on my plane I'd sure have a surge protector on it.
Of course I could be wrong!-
K
- :)
--------
Keith McKinley
700HS
KFIT
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