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jonboede(at)hotmail.com
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 Posted: Sat Sep 18, 2010 12:26 pm Post subject: generator intermittent |
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I have a stock CJ-6A and the generator works about half the time... some flights it comes online at 1,000 rpm, some flights when the RPM gets higher, and some flights not at all.
Once it starts working it seems to stay working.
I've looked at the brushes and they seem fine.� All other electrical connections seem ok.
Any suggestions as to what to check next?
Thanks,
Jon
[quote][b]
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mark.bitterlich(at)navy.m
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| Posted: Sun Sep 19, 2010 2:37 pm Post subject: generator intermittent |
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Flash the field on the generator first. That is the easiest first thing to do and you just might get lucky.
Mark
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Jon Boede
Sent: Sat 9/18/2010 4:20 PM
To: yak-list(at)matronics.com
Subject: generator intermittent
I have a stock CJ-6A and the generator works about half the time... some flights it comes online at 1,000 rpm, some flights when the RPM gets higher, and some flights not at all.
Once it starts working it seems to stay working.
I've looked at the brushes and they seem fine. All other electrical connections seem ok.
Any suggestions as to what to check next?
Thanks,
Jon
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jonboede(at)hotmail.com
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| Posted: Sun Sep 19, 2010 3:39 pm Post subject: generator intermittent |
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Um... uh... ok.� How do I do that? 
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| Quote: | Subject: RE: generator intermittent
Date: Sun, 19 Sep 2010 18:27:15 -0400
From: mark.bitterlich(at)navy.mil
To: yak-list(at)matronics.com
Flash the field on the generator first. That is the easiest first thing to do and you just might get lucky.
Mark
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Jon Boede
Sent: Sat 9/18/2010 4:20 PM
To: yak-list(at)matronics.com
Subject: generator intermittent
I have a stock CJ-6A and the generator works about half the time... some flights it comes online at 1,000 rpm, some flights when the RPM gets higher, and some flights not at all.
Once it starts working it seems to stay working.
I've looked at the brushes and they seem fine. All other electrical connections seem ok.
Any suggestions as to what to check next?
Thanks,
Jon
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mark.bitterlich(at)navy.m
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| Posted: Mon Sep 20, 2010 2:28 pm Post subject: generator intermittent |
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Disconnect all three wires from the generator.
Make some wires up that have terminals on the ends, and connect one to the negative lead of the generator. Make sure it is at least 12 gage wire, and better yet 10 gage. Keep the wires short... no longer than 6 or 7 feet. Just enough to reach the ground. Get a KNOWN GOOD 28 volt battery that can flow at least 10 amps of current.
Hook the other wire to the middle terminal of the generator. Assuming this is an M-14 generator, but I think CJ's are the same. In any case you should have three terminals. PLUS and MINUS are big, and the third is the FIELD and it should be smaller.
Again, hook one wire to the MINUS side of the generator, and connect that to the minus wire on the battery.
Hook the other wire to the FIELD or middle, or smaller terminal. Now take the end of THAT WIRE and hold it against the PLUS side on the BATTERY for about 10 to 15 seconds MAXIMUM.
You do this WITH THE ENGINE NOT RUNNING BY THE WAY!
This puts a magnetic field back into the field winding.
You can do this more than once.... but usually if it does not work after the second time, it was either never the problem to begin with, or you have a totally bad generator.
But with your problem this is where I would start.
If after doing this, you still have a problem, you then need to do more troubleshooting.
There are several methods. One is to test the generator using a backyard test procedure that you have to be very careful with.
This time you take off the field wire, and the plus wire off the generator. Leave the negative wire connected.
Now connect a home made jumper wire between the field wire and the plus wire on the generator.
Now connect a volt meter to the generator connected to the plus and minus wire.
Start the engine. SLOWLY SLOWLY SLOWLY increase engine rpm. You should see a smooth increase in voltage out of the generator as you increase engine rpm. It will climb to 28 vdc quickly. Bring it up to 35 volts or so and make sure it reaches that and puts out steady output.
Now bring it to idle and shut if off like NOW.
Realize, that when doing this, you have TOTALLY BYPASSED ANY VOLTAGE REGULATION! If you run up the engine too high, the generator might easily fry itself. So be careful! But if it passes THIS test, then it is likely that there is nothing wrong with your generator.
Don't do this test right away.
Flash the field first.
Then hook it all back up and test the aircraft normally.
If it fails again, run the second test.
If that test passes, then we go to the next step and that is testing the voltage regulator and the 200 RELAY assy.
Lots of fun.
Mark
P.S. Did I mention that these tests are done at your own risk? And that if you screw them up things can get very ugly?
Best of luck.
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Jon Boede
Sent: Sun 9/19/2010 7:15 PM
To: yak-list(at)matronics.com
Subject: RE: generator intermittent
Um... uh... ok. How do I do that?
----------------------------------------
| Quote: | Subject: RE: generator intermittent
Date: Sun, 19 Sep 2010 18:27:15 -0400
From: mark.bitterlich(at)navy.mil
To: yak-list(at)matronics.com
Flash the field on the generator first. That is the easiest first thing to do and you just might get lucky.
Mark
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Jon Boede
Sent: Sat 9/18/2010 4:20 PM
To: yak-list(at)matronics.com
Subject: generator intermittent
I have a stock CJ-6A and the generator works about half the time... some flights it comes online at 1,000 rpm, some flights when the RPM gets higher, and some flights not at all.
Once it starts working it seems to stay working.
I've looked at the brushes and they seem fine. All other electrical connections seem ok.
Any suggestions as to what to check next?
Thanks,
Jon
|
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Vic
Joined: 12 Aug 2008
Posts: 115
Location: Southern Bavaria
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| Posted: Tue Sep 21, 2010 2:25 am Post subject: Re: generator intermittent |
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Hi Jon,
basically I don´t think that flashing the dynamo will do the trick because you say it works normally in times. So there is no reason to believe that polarity was wrong or has changed in the past. But certainly you could try Mark´s method at first before digging deeper. I suspect some fault in the wiring in the regulator etc. . If you decide to take the generator off the plane you could try to run it like an electric motor by connecting the field wire to the positive brush and hook the lot to a battery, maybe with a big bulb in series to keep the amps low. Then, in the same configuration the dynamo should produce more than 30 V and amps when you speed it up to 2000 - 3000 revs. Maybe Mark would check this advice because I am not completely familiar with the wiring around the dynamo and regulator.
Good luck in your failure hunting.
Electricity is a strange material, you don´t see it but it does all sorts of funny things.
Vic
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george.coy(at)gmail.com
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| Posted: Tue Sep 21, 2010 4:36 am Post subject: generator intermittent |
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I do not know if the CJ has a similar system to the Yaks. If so the problem
is with the reverse current relay. They are the failure point in the Yak
generating system. You can sometimes take them apart and rescue them. They
are made of "un-obtainiam" (the replacements are impossible to find) so the
usual fix it to replace the generating system with a western alternator. I
know many CJ's have installed B&C alternators. We often supply the parts for
the conversion.
George Coy
Motorstar NA
714 Airport Rd.
Swanton VT 05488
802-868-5633 off
802-363-5782 cell
george.coy(at)gmail.com
SKYPE george.coy
motorstarna.com
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mark.bitterlich(at)navy.m
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| Posted: Tue Sep 21, 2010 10:16 am Post subject: generator intermittent |
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To Vic (and Jon),
The generators on these aircraft are self-exciting. As such, they require a residual magnetic field in order to start outputting voltage. A generator that works sometimes and totally does not work at other times is a candidate for this type of failure. As generators of this type age, and especially if they are not run on a regular basis, the magnetic field can become weak. They do not "change polarity" per se.
This is not "my method" by the way, it is an established procedure for re-establishing a magnetic field in a generator, and is sometimes called "Flashing the Field". It is not well known in today's world due to the abundance of alternators. Just FYI, it just worked on another YAK aircraft just two weeks ago handled off-line.
So that said, yes there is a very "reasonable belief" that this gents generator has a weak magnetic field that could be causing his problem, and it is a very easy, cheap and foolproof first step, as long as it is done correctly.
The regulator itself is not likely the bad actor, because once the generator comes on line, it stays on line. Bad regulators of the carbon pile type used in this system will typically display incorrect regulating voltage at full output when they fail. However, there is a fault area NEAR the voltage regulator with the method used to mount it in the aircraft. The voltage regulator is attached to a MOUNT, and there are some wires that occasionally rub on that mount and short out. That can be inspected for when the voltage regulator is removed and inspected. However it is rare and is a last ditch kind of inspection, but something to be kept in mind.
I would not recommend trying to run the generator like a motor by removing it and connecting it to a battery. A generator can easily become a motor, but making it into one does not really solve the issue of what is wrong with the aircraft.
George Coy goes on in another message to discuss the possibility that this problem could be caused by a reverse current relay. And he is totally correct. It very well could be. There are some troubleshooting steps that can be used to help identify that as the problem as well. If the DMR-200 relay is indeed bad, they are (as he mentions) difficult to find and expensive to replace, although they can indeed be repaired SOMETIMES.
However, "we are not there yet" if you are willing to learn how this system works and take the time to troubleshoot it.
Any electrical or electronics system is approached in logical steps when it comes to repairing it. A lot of people like to dive-bomb what might be wrong in a hit and miss fashion. I do not do that.
In this case, the first thing to verify is that the generator itself is working properly. These generators can be purchased cheaply, typically around $100 or so, so we start there. Flashing the field is a 30 minute job with very little effort and could easily fix your problem. However, it might not... but we start there.
Then we move to check to see that the generator puts out when it is totally isolated from the rest of the aircraft. If it works there, then we move on.
If it is the reverse current relay, there is a trick to check that out too.
Keep in mind that the DMR-200 is indeed a reverse current relay, but it is also the main contactor relay, the source for how your cockpit generator light works, and a whole lot more. It is actually called the Combined Device. It is made up of a very special reverse current relay with a primary and counter magnetic field and two additional stand alone relays, plus the main power contactor relay as I said.
One last thing please.
How are the batteries in your aircraft? Go out to your aircraft and read the battery voltage with everything turned on. Is it below 20 volts? Please pass this on.
Mark Bitterlich
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Vic
Sent: Tue 9/21/2010 6:25 AM
To: yak-list(at)matronics.com
Subject: Re: generator intermittent
Hi Jon,
basically I don´t think that flashing the dynamo will do the trick because you say it works normally in times. So there is no reason to believe that polarity was wrong or has changed in the past. But certainly you could try Mark´s method at first before digging deeper. I suspect some fault in the wiring in the regulator etc. . If you decide to take the generator off the plane you could try to run it like an electric motor by connecting the field wire to the positive brush and hook the lot to a battery, maybe with a big bulb in series to keep the amps low. Then, in the same configuration the dynamo should produce more than 30 V and amps when you speed it up to 2000 - 3000 revs. Maybe Mark would check this advice because I am not completely familiar with the wiring around the dynamo and regulator.
Good luck in your failure hunting.
Electricity is a strange material, you don´t see it but it does all sorts of funny things.
Vic
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http://forums.matronics.com/viewtopic.php?p=313182#313182
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gill.g(at)gpimail.com
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| Posted: Tue Sep 21, 2010 1:18 pm Post subject: generator intermittent |
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Mark,
I was of the understanding that the CJ generator was not self exciting, i.e.
power to the fields is provided externally by the regulator, similar to how
alternators are regulated. It's been a while since I have looked into this,
so I could be wrong. I assume the YAK generator is the same.
Gill
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mark.bitterlich(at)navy.m
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| Posted: Tue Sep 21, 2010 7:12 pm Post subject: generator intermittent |
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I know zero about CJ's. The only electrical systems I have worked on extensively have been Yak's and Sukhoi's.
The YAK generator can power up completely without a battery.
The "field" input connection to the YAK generator is supplied from the output of the generator itself fed back from a carbon pile regulator.
This is not to say that it uses permanent magnets such as what are found in B&C's small 10 amp unit. Instead it relies on a residual magnetic field. If left to sit for a long period, this field can reduce in intensity to where initial operation can become intermittent and fail to come "on-line" predictably. This is where the "flashing the field" procedure comes into play. Following that procedure attempts to restore that residual field to regain reliable operation.
In the Sukhoi manual, there are actual specs on when the DMR-200 relay will close with the battery removed and with the battery operational. I am in Yuma right now and do not have access to that data, but will be glad to send it to you when I return.
Mark Bitterlich
________________________________
From: owner-yak-list-server(at)matronics.com on behalf of Gill Gutierrez
Sent: Tue 9/21/2010 5:14 PM
To: yak-list(at)matronics.com
Subject: RE: Re: generator intermittent
Mark,
I was of the understanding that the CJ generator was not self exciting, i.e.
power to the fields is provided externally by the regulator, similar to how
alternators are regulated. It's been a while since I have looked into this,
so I could be wrong. I assume the YAK generator is the same.
Gill
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