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Voltage Regulation LONG REPLY!

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mark.bitterlich(at)navy.m
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Posted: Fri Feb 27, 2009 3:43 pm Post subject: Voltage Regulation LONG REPLY!

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

Posted: Mon Mar 02, 2009 9:17 am Post subject: Voltage Regulation LONG REPLY!

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

Posted: Tue Feb 01, 2011 11:53 pm Post subject: Re: Voltage Regulation LONG REPLY!

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

Posted: Wed Feb 02, 2011 12:57 am Post subject: Re: Voltage Regulation LONG REPLY!

Is that on a yak 18T?

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GeorgeCoy

Joined: 02 Dec 2010
Posts: 310

Posted: Wed Feb 02, 2011 6:43 am Post subject: Voltage Regulation LONG REPLY!

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

Posted: Wed Feb 02, 2011 6:43 am Post subject: Voltage Regulation LONG REPLY!

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

Posted: Wed Feb 02, 2011 9:51 am Post subject: Voltage Regulation LONG REPLY!

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

Posted: Sun Feb 06, 2011 8:39 pm Post subject: Re: Voltage Regulation LONG REPLY!

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

Posted: Mon Feb 07, 2011 7:51 am Post subject: Voltage Regulation LONG REPLY!

Thanks for posting the results Les.  



Mark

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