To reinforce Mark's comment about checking the battery, I found that my
Horizon tach would intermittently shut down and recycle when I had a bad
battery. This has happened on 2 occasions.
Jim Griffin
----- Original Message -----
From: Yak Pilot
To: yak-list@matronics.com
Sent: Monday, November 16, 2009 8:34 PM
Subject: Re: Re: generator question
Hi Keith, thanks for the compliment. My professional field is
indeed electronics, 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 shut, but never-the-less are highly regarded experts in
their field. Rob Rowe 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 pretty good at something, I get a lesson in
humility from someone who is REALLY good. .
Also you're right. Say a few good words about the USMC, and I
will always come out of the wood-work. I have been absent from this
list for awhile as I have been going to school on long and short
baseline interferometry. Another lesson in how much more math I need.
In answer to the original question that dealt with the
over-voltage condition shutting down the tach. Hmmm..... seems unlikely
to me. The YAK series of aircraft has a built in over-voltage device
ALREADY. If you exceed 32 volts, it trips a circuit breaker and removes
field excitation to the generator, effectively shutting it off.
Further, even if that was defective, 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 darn 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 with 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 have a hard time really
believing the problem with the tach is an over-voltage condition.
That said, there are a lot of other issues that are possible. I
would suggest 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 generator 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 might indeed be "not quite right". As in... the people
that make it already admit that it has an over-voltage shut-down mode.
That means two 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 measure 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 voltage 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 RPM. If it goes up steadily with engine
RPM as you pass 75%, then something is bad wrong.
Voltage spikes: Sure Keith, voltage spikes are indeed a bad
thing, and in fact if you are concerned about them, adding a metal oxide
varistor, or "trans-sorb" is indeed do-able. However, voltage spikes
are typically caused by large inductive loads. The collapsing magnetic
fields are the cause... and the biggest cause of those puppy dogs are
STARTER MOTORS. Something the Yak happens to be missing! Honestly I
can't think of too many inductive loads in a Yak (as in motors and stuff
like them... INVERTER motor excepted!), so it comes back to the
generator itself. Generators don't usually put out nasty spikes, unless
they are defective. As in... really 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?" Normally 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 and 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 interested to know that in a lot of CESSNA model
aircraft, they have two DC bus controls. MAIN and AVIONICS. When the
starter motor is engaged, the AVIONICS BUS is turned OFF, for exactly
the reason you were concerned about.
Best Regards,
Mark Bitterlich (writing from my hangar email account)
p.s. Computing phase matched cells with simultanious short and
long based 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: Monday, November 16, 2009, 9:34 AM
<keith.mckinley@townisp.com>
Good point Dennis considering when this happens. For the
record I still think 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 fancy 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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