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mark.bitterlich(at)navy.m Guest
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Posted: Fri Feb 27, 2009 3:43 pm Post subject: Voltage Regulation LONG REPLY! |
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Well, as anyone who knows me has learned long ago, I never run away from
a good debate. So... That said, Gill, I do not know what you do for a
living, but I am a Avionics Field Engineer, and I am darn sure of what I
am talking about regarding this problem. Unfortunately what you are
passing to this gentleman is still incorrect and it is in fact ill
advised.
You said: "The problem originally described was that the generator light
went off at the normal point and then came on with increasing RPM, this
suggests that brushes may not be making solid contact and should be
easily checked as previously suggested."
You then also said: "I am not there so the mic (mechanic in command)
will have to decide."
First, you do not need to be an A&P to troubleshoot this. Most
mechanics are not familiar with very old design generator systems, and
it is a mistake to think that their word is gospel in a situation where
they are dealing with a foreign built aircraft that typically they have
no experience with. They also have to deal with minimum documentation
on the electrical system that usually is written in Cyrillic. Anyone
have a local A&P that speaks and reads Russian?
Second, your statement of what happened is out of context and
incomplete.
I have taken this electrical system apart piece by piece and I know
every single part and how it works and why it does what it does in ANY
situation. I wrote a complete white paper on this system that explains
it. So here's the COMPLETE breakdown of the whole problem.
READ IT VERY CAREFULLY BEFORE YOU REPLY PLEASE.
1. The generator light is on. He starts the engine. The light
remains on at idle. This is normal.
2. The engine RPM is increased. THE LIGHT GOES OUT. This is normal.
3. Now as the engine RPM is increased FURTHER, the generator light
COMES ON. In other words, we now have a fault. The only debate here is
what caused it to happen... You say it could be brushes or springs.
Well.. Read on.
3. As it went higher the OVER-VOLTAGE CIRCUIT BREAKER POPS and the Gen
light comes on again. It is SUPPOSED to come on when you have an
over-voltage condition. I'll tell you why later. But....Brushes and
springs can not cause a generator to put out too much voltage. That is
simply IMPOSSIBLE.
Let's review using the exact wording taken from the original message.
A. He said: "I connected a voltmeter to the DMR-200 as I ran it even if
I adjusted the regulation screw...I got no change in voltage."
STOP RIGHT THERE! Without going ANY further, just by that one statement
alone, he has a voltage regulation problem.
BUT, let's go on.
B. "as I increased power (at) 40% the light went out(started charging"
OK, the GENERATOR IS NOW WORKING AND SUPPLYING POWER TO THE AIRCRAFT
BUS.
C. He says: "Volts increase with throttle until 45%RPM and kicks Gen
offline at (at)30.5 volts."
Please pay particular attention to the MEASURED VOLTAGE OF 30.5 VOLTS
DC!!!! That is EXACTLY what the system was designed to do. Take the
generator output off line if it puts out too much voltage. From the
Russian manuals, that is the exact voltage which causes it.
But if you are still not convinced, he also says:
D. "Around 45% the Gen Fail light would come back on and POP THE
OVERVOLTAGE CIRCUIT BREAKER" (emphasis mine)
Ah, yeah... That would be what the over-voltage control circuit is
designed to do. Pop the breaker, which opens the main contactor,
removing generator voltage from the aircraft and protecting aircraft
components and avionics from too much voltage.
When the generator has uncontrolled regulation, the voltage will
increase with RPM. This is why it is highly likely that the problem he
has is directly tied to the voltage control rheostat.
Any design engineer always puts in over-voltage protection. In the YAK
and Sukhoi series of aircraft, this is a big silver box that is
constructed so that when the voltage gets up to about 30-31 volts
(exactly as he said), an internal circuit breaker that is covered with a
little red piece of rubber, POPS and when it does, it opens the circuit
to the main contactor relay and removes all generator output from the
aircraft. When the main contactor opens, a sense wire goes LOW and this
opens another relay behind the instrument panel that TURNS ON THE
GENERATOR LIGHT. Again, this has ZERO to do with brushes and springs.
By the way, it is very easy to KEEP this circuit operational when
installing a B&C PMG or Alternator, or anything else for that matter.
This circuit is very reliable and worth keeping.
To continue: The generator light is coming on because the main contactor
opened after an over-voltage circuit breaker popped, and not because the
generator is not putting out voltage, as would be the case if the
brushes and springs were bad. No, the generator is working perfectly
just putting out TOO MUCH VOLTAGE, which is why it got disconnected from
the aircraft power mains.
Want to see it happen for yourself? Just like this guy is seeing? Take
the middle wire off of your generator in your aircraft. Connect a new
piece of wire directly from that middle generator contact directly to
the contact marked with the big PLUS (+) sign. Now start your engine.
It will do exactly what this mans airplane does. By the way, doing that
is not an advised method of testing your generator, but it is done all
the time in the field. If you try this, make sure you have all possible
switches in your aircraft turned off, because if your over-voltage
system happens not to work, you will end up frying all your avionics.
Watch your internal voltmeter very closely if you do this. It will go
up and down with RPM very rapidly. Like I said, I do not advise this as
a normal step by anyone with less than a complete knowledge of how this
system works. This test also has no bearing on the present problem. By
the way, it is also very doubtful that your mechanic will know anything
about a test like this. A&P's are usually very up to date on
ALTERNATORS, but not so hot on old generator designs.
ANYWAY.
Something most people do not know and I will explain here. What does
the generator light really tell you? What makes it come on and what
makes it turn off?
The generator light is simply an indication that tells you the position
of the main contactor relay that connects the generator to the aircraft.
If that relay is closed, the generator light goes out. If the main
contactor relay is open, the generator light comes on. It is that
simple.
The main contactor relay itself is controlled by a whole SLEW of OTHER
factors. Generator voltage, forward and reverse current, and lastly, by
over-voltage conditions. However, what it is NOT is any kind of direct
indication that the generator is, or is not, putting out voltage.
Merely whether a big relay is either OPEN or CLOSED. It can not be used
in any way to determine the condition or operation of the generators
brushes and springs EXCEPT IF IT IS FLICKERING. In that case, you very
well might want to check your brushes and springs.
Of course if there is any doubt, I would advise consulting with a Master
Russian Mechanic like Vladimir Yatremski. But keep in mind that he often
comes to me for help with this system.
Mark Bitterlich
EA-6B Prowler Field Engineering
MCAS Cherry Point NC
Yeah, President Obama was here today....
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gill.g(at)gpimail.com Guest
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Posted: Mon Mar 02, 2009 9:17 am Post subject: Voltage Regulation LONG REPLY! |
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Mark,
You have way too much time on your hands. I too am an engineer and don't
that much time on my hands. I learned a long time ago that there is always
more than one approach in arriving at a solution. My approach is simply
check the generator first to make sure the brushes aren't floating just in
case it's something simple. I didn't mean to defame you by suggesting that
a simple mechanic could fix the problem.
By the way nice write up.
Gill
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lesknox
Joined: 31 Mar 2009 Posts: 4 Location: Australia
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Posted: Tue Feb 01, 2011 11:53 pm Post subject: Re: Voltage Regulation LONG REPLY! |
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Mark,
I have this exact problem and concluded it was the Regulator. Can you tell me how to proceed from here.
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CJ6XXK
Joined: 27 Jan 2011 Posts: 21 Location: Australia
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Posted: Wed Feb 02, 2011 12:57 am Post subject: Re: Voltage Regulation LONG REPLY! |
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Is that on a yak 18T?
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GeorgeCoy
Joined: 02 Dec 2010 Posts: 310
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Posted: Wed Feb 02, 2011 6:43 am Post subject: Voltage Regulation LONG REPLY! |
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We have some voltage regulators (used) here if you need one. We also have an
alternator conversion kit that will replace the voltage regulator, the
overvoltage controller, the DMR-200 relay and the Generator with a FAA
approved alternator and solid state regulator. We even have a service
bulletin for the kit for the Yak-52.
George Coy
CAS Ltd.
714 Airport Rd.
Swanton VT 05488
802-868-5633 off
802-363-5782 cell
802-868-4465 Fax
george.coy(at)gmail.com
http://coyafct.com/
SKYPE george.coy
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george(at)gesoco.com Guest
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Posted: Wed Feb 02, 2011 6:43 am Post subject: Voltage Regulation LONG REPLY! |
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We have some voltage regulators (used) here if you need one. We also have an
alternator conversion kit that will replace the voltage regulator, the
overvoltage controller, the DMR-200 relay and the Generator with a FAA
approved alternator and solid state regulator. We even have a service
bulletin for the kit for the Yak-52.
George Coy
CAS Ltd.
714 Airport Rd.
Swanton VT 05488
802-868-5633 off
802-363-5782 cell
802-868-4465 Fax
george.coy(at)gmail.com
http://coyafct.com/
SKYPE george.coy
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mark.bitterlich(at)navy.m Guest
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Posted: Wed Feb 02, 2011 9:51 am Post subject: Voltage Regulation LONG REPLY! |
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I am not sure what "exact problem" you are referring to. Sorry. Could
you please send me the details?
Mark
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lesknox
Joined: 31 Mar 2009 Posts: 4 Location: Australia
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Posted: Sun Feb 06, 2011 8:39 pm Post subject: Re: Voltage Regulation LONG REPLY! |
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The aircraft is a Yak-52, standard electrics.
Observation/ symptoms were:
Over voltage button IN
After start, GEN light on at idle, 24V
As the rpm is increased, GEN light extinguishes, >24V
Further rpm increase gives a fairly linear increase in volts
When volts just above 30, GEN light on, amps drop
The over-voltage button has now "popped".
Varying the cockpit regulator adjustment has no effect.
After getting as much info as I could, it was time to
try and find the problem
The Voltage Regulator is quite obvious when
you know roughly where and what to look for. In
the 52, it is in a recess in the front cockpit
floor, forward left side, near the firewall. It is
not easy to reach (seat needs to come out) and
clips holding it to the shock mount are difficult both
to remove and reattach. A thin person and long pliers
seem to help. Maybe there is better technique.
After a quick look at the reg itself, I
decided to check the wiring leading to the mounting plate.
They seemed to be intact and secure.
Next I removed the cockpit voltage adjustment
rheostat. This is, again, difficult because you
need to remove all the screws on the console on
the left side. They don't make gadgets like that
anymore. The connectors seemed to have
deteriorated a little (subsequently renewed). The
pot itself seemed fine, with linear change in
resistance. Only 0-6 Ohm.
At this stage I checked the integrity of
the circuit to the regulator mount and discovered that
there was a break between the cockpit adjuster and the
TC-9M-2 (which is I understand the Stabilizing Transformer
and is the large coil like device top outboard quadrant in
in the electrical system "grey box"). The applicable
connection to the TC-9M-2 is the bottom inboard post and
was the fault. It was not obvious because it was inside
the insulating material of the ring connector.
So the basic problem was a break in the voltage adjustment
line.
Replacing this connection might be the simplest first
step in troubleshooting this problem because it is relatively
accessible.
Little bit of rewiring, then everything back
where it belongs. Engine run carried out, with
system performing as it should.
Only took 8 hours in 40 degC heat! Still you
learn things this way.
Thanks to all who helped.
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mark.bitterlich(at)navy.m Guest
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Posted: Mon Feb 07, 2011 7:51 am Post subject: Voltage Regulation LONG REPLY! |
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Thanks for posting the results Les.
Mark
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