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Okanogan Lew

Joined: 22 Jul 2010
Posts: 45

Posted: Sat Sep 15, 2012 2:18 pm Post subject: alternator failure CJ6

Guys, I had an in flight alternator failure today & found a broken wire that goes from a plastic plug in on the side of the alt. up to the main charging post.  In that line is a small round electronic looking piece that has solid wires coming out of both ends.  The wire broke at that round piece.  I am assuming that it is some kind of filter, but there are no numbers on it.  Any suggestions as to what I should replace it with?  Thanks.



Paul Lewis



p s this is not a B&C alternator

brian(at)lloyd.com
Guest

Posted: Sat Sep 15, 2012 9:24 pm Post subject: alternator failure CJ6

On Sat, Sep 15, 2012 at 3:18 PM, Okanogan Lew <vplewis(at)community.org (vplewis(at)community.org)> wrote:

 	  Quote: 	
		   --> Yak-List message posted by: "Okanogan Lew" <vplewis(at)community.org (vplewis(at)community.org)>

 

 Guys, I had an in flight alternator failure today & found a broken wire that goes from a plastic plug in on the side of the alt. up to the main charging post.  In that line is a small round electronic looking piece that has solid wires coming out of both ends.  The wire broke at that round piece.  I am assuming that it is some kind of filter, but there are no numbers on it.  Any suggestions as to what I should replace it with?  Thanks.

 	




Need more info. What kind of alternator? Can you provide pictures?



-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

 +1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)



  [quote][b]

okanoganlew(at)gmail.com
Guest

Posted: Sun Sep 16, 2012 2:22 pm Post subject: alternator failure CJ6

Brian, there is no identifing marks on it.  I sent photo's to B&C & they said that they had no idea who made it.  I did get some numbers off of the round electronic piece.  NTE 4934 with an arrow that has a bar on the point.  I looked it up on the inter-net & it is listed as a trans, supp 23.1V.  What ever that is?  Thanks for your help.

  

Paul

On Sat, Sep 15, 2012 at 10:22 PM, Brian Lloyd <brian(at)lloyd.com (brian(at)lloyd.com)> wrote:

[quote] 



On Sat, Sep 15, 2012 at 3:18 PM, Okanogan Lew <vplewis(at)community.org (vplewis(at)community.org)> wrote:

 	  Quote: 	
		    --> Yak-List message posted by: "Okanogan Lew" <vplewis(at)community.org (vplewis(at)community.org)>

 

 Guys, I had an in flight alternator failure today & found a broken wire that goes from a plastic plug in on the side of the alt. up to the main charging post.  In that line is a small round electronic looking piece that has solid wires coming out of both ends.  The wire broke at that round piece.  I am assuming that it is some kind of filter, but there are no numbers on it.  Any suggestions as to what I should replace it with?  Thanks.

  	


Need more info. What kind of alternator? Can you provide pictures?



-- 

 Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

 [url=tel:%2B1.767.617.1365]+1.767.617.1365[/url] (Dominica)

[url=tel:%2B1.916.877.5067]+1.916.877.5067[/url] (USA) 



   	  Quote: 	
		  



et="_blank">http://www.matronics.com/Navigator?Yak-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	




[b]

brian(at)lloyd.com
Guest

Posted: Sun Sep 16, 2012 2:59 pm Post subject: alternator failure CJ6

On Sun, Sep 16, 2012 at 3:19 PM, Paul Lewis <okanoganlew(at)gmail.com (okanoganlew(at)gmail.com)> wrote:

 	  Quote: 	
		   Brian, there is no identifing marks on it.  I sent photo's to B&C & they said that they had no idea who made it.  I did get some numbers off of the round electronic piece.  NTE 4934 with an arrow that has a bar on the point.  I looked it up on the inter-net & it is listed as a trans, supp 23.1V.  What ever that is?  Thanks for your help.

 	




All alternators work the same way. They are all pretty much wired the same way. The only thing you really need to know is whether it has an internal or an external voltage regulator. Frankly, a lot of people use internally-regulated GM truck alternators which are typically rated at 60A to 100A at 28V, more than enough to power a CJ6A (and the next 5 CJ's in the line up at the same time .  

 



(I have yet to see a CJ6A that needs more than about 20A once you remove the old Chinese radios.)



So, being able to see a picture of the alternator and any markings near the various terminals (oh, the markings on the data plate would be nice too) will help me identify the terminals and tell you how it should be wired. 

 



If you can get me pictures I will try to help.



-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

 +1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)



  [quote][b]

mark.bitterlich(at)navy.m
Guest

Posted: Mon Sep 17, 2012 6:27 am Post subject: alternator failure CJ6

Was this device hooked in series with the broken wire, or was it connected between two wires?   It is a Trans-sorb.  Normally this kind of device is connected between a voltage supply wire and ground.  It's purpose is to help prevent voltage spikes.  When the voltage exceeds a certain voltage it shorts out (conducts) and typically shunts the spike to ground.  I have never seen one connected in series with a main supply wire.  

 

Mark

 

 

 

________________________________



From: owner-yak-list-server(at)matronics.com on behalf of Paul Lewis

Sent: Sun 9/16/2012 6:19 PM

To: yak-list(at)matronics.com

Subject: Re: alternator failure CJ6

Brian, there is no identifing marks on it.  I sent photo's to B&C & they said that they had no idea who made it.  I did get some numbers off of the round electronic piece.  NTE 4934 with an arrow that has a bar on the point.  I looked it up on the inter-net & it is listed as a trans, supp 23.1V.  What ever that is?  Thanks for your help.

 

Paul

On Sat, Sep 15, 2012 at 10:22 PM, Brian Lloyd <brian(at)lloyd.com> wrote:





	On Sat, Sep 15, 2012 at 3:18 PM, Okanogan Lew <vplewis(at)community.org> wrote:

	



		

		

		Guys, I had an in flight alternator failure today & found a broken wire that goes from a plastic plug in on the side of the alt. up to the main charging post.  In that line is a small round electronic looking piece that has solid wires coming out of both ends.  The wire broke at that round piece.  I am assuming that it is some kind of filter, but there are no numbers on it.  Any suggestions as to what I should replace it with?  Thanks.

		

	Need more info. What kind of alternator? Can you provide pictures?

	



	-- 

	Brian Lloyd, WB6RQN/J79BPL

	3191 Western Dr.

	Cameron Park, CA 95682

	brian(at)lloyd.com

	+1.767.617.1365 (Dominica)

	+1.916.877.5067 (USA) 

	

	

	et="_blank">http://www.matronics.com/Navigator?Yak-List

	tp://forums.matronics.com

	_blank">http://www.matronics.com/contribution

okanoganlew(at)gmail.com
Guest

Posted: Mon Sep 17, 2012 11:01 am Post subject: alternator failure CJ6

Brian & Mark, photo's enclosed.  The broken wire was attached from the batt. post on the alt. to the bayonet fitting on the side of the alt.



On Sun, Sep 16, 2012 at 3:57 PM, Brian Lloyd <brian(at)lloyd.com (brian(at)lloyd.com)> wrote:

  	  Quote: 	
		  



On Sun, Sep 16, 2012 at 3:19 PM, Paul Lewis <okanoganlew(at)gmail.com (okanoganlew(at)gmail.com)> wrote:

  	  Quote: 	
		   Brian, there is no identifing marks on it.  I sent photo's to B&C & they said that they had no idea who made it.  I did get some numbers off of the round electronic piece.  NTE 4934 with an arrow that has a bar on the point.  I looked it up on the inter-net & it is listed as a trans, supp 23.1V.  What ever that is?  Thanks for your help.

  	


All alternators work the same way. They are all pretty much wired the same way. The only thing you really need to know is whether it has an internal or an external voltage regulator. Frankly, a lot of people use internally-regulated GM truck alternators which are typically rated at 60A to 100A at 28V, more than enough to power a CJ6A (and the next 5 CJ's in the line up at the same time .  

  



(I have yet to see a CJ6A that needs more than about 20A once you remove the old Chinese radios.)



So, being able to see a picture of the alternator and any markings near the various terminals (oh, the markings on the data plate would be nice too) will help me identify the terminals and tell you how it should be wired. 

  



If you can get me pictures I will try to help.



-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

  [url=tel:%2B1.767.617.1365]+1.767.617.1365[/url] (Dominica)

[url=tel:%2B1.916.877.5067]+1.916.877.5067[/url] (USA)



   	  Quote: 	
		  



et="_blank">http://www.matronics.com/Navigator?Yak-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution

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brian(at)lloyd.com
Guest

Posted: Mon Sep 17, 2012 1:33 pm Post subject: alternator failure CJ6

On Mon, Sep 17, 2012 at 11:58 AM, Paul Lewis <okanoganlew(at)gmail.com (okanoganlew(at)gmail.com)> wrote:

 	  Quote: 	
		   Brian & Mark, photo's enclosed.  The broken wire was attached from the batt. post on the alt. to the bayonet fitting on the side of the alt.

	




OK, that is an internally-regulated GM truck alternator. The wire jumper between the #2 terminal and the 'B' (battery) terminal is for sensing voltage. You definitely want that wired up. (If you want better voltage regulation you can run that wire back to your main bus but that will probably be more work than it is worth.) If that wire breaks it is possible for the alternator to turn on hard and cause a serious overvoltage event that can damage your battery and electronics. The other (unused) terminal (#1) is to provide connection to the idiot light but that also powers the internal regulator from battery voltage to start up the alternator. You might want to add an idiot light. It will come on if the alternator is not producing output. If you don't want to install a light you should probably install the 10 ohm, 10W resistor in place of the light. That ensures that the alternator will start right away.

 



There are actually two flavors of this alternator. One requires the idiot light or resistor and the other, the so-called "one-wire" alternator, doesn't. If you have the "one-wire" version you may have to run the engine up to 2000 RPM or so before the alternator will come on.

 



Here is a wiring diagram and a good explanation:

http://www.autorewire.com/tech/article/Delco10SInandd.html

 



http://bob_skelly.home.comcast.net/~bob_skelly/alternator_conversion/wiring_alternator1.html

 

-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

+1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)

 

  [quote][b]

mark.bitterlich(at)navy.m
Guest

Posted: Mon Sep 17, 2012 2:53 pm Post subject: alternator failure CJ6

I'll leave this one to Brian.  



--

mark.bitterlich(at)navy.m
Guest

Posted: Mon Sep 17, 2012 3:03 pm Post subject: alternator failure CJ6

Paul, it would help if you would also include a picture of the small

part that broke off that you copied the number off of so that Brian can

see that too. 



Mark



--

brian(at)lloyd.com
Guest

Posted: Mon Sep 17, 2012 3:11 pm Post subject: alternator failure CJ6

On Mon, Sep 17, 2012 at 2:30 PM, Brian Lloyd <brian(at)lloyd.com (brian(at)lloyd.com)> wrote:

 	  Quote: 	
		   



On Mon, Sep 17, 2012 at 11:58 AM, Paul Lewis <okanoganlew(at)gmail.com (okanoganlew(at)gmail.com)> wrote:

 	  Quote: 	
		    Brian & Mark, photo's enclosed.  The broken wire was attached from the batt. post on the alt. to the bayonet fitting on the side of the alt.

	




	




It looks like someone might have put a diode in series with the lead from the 'B' terminal to the #2 (sense) terminal. The diode is probably a 1N4007 and the banded end would be toward the #2 terminal and away from the 'B' terminal. That is a way to get the alternator to produce about 0.7VDC more output to raise the voltage to correct for voltage drop across the 'B' lead going to the battery and/or main aircraft bus. If someone used a smaller gauge wire from the 'B' terminal you could have a volt or so of drop and this would correct for that.

 



Of course, the right answer is to run the lead from the #2 (sense) terminal back to the bus rather than connecting it to the 'B' terminal, and then not use the diode.

As for the marking on the alternator, it just says that it is a 24V at 40A alternator. When you put the alternator back together be sure to push the brushes fully into their holders and put a stiff wire (paper clip will do) in the small hole in the brush holder to hold them in place until you have the alternator case back together.

 

-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

+1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)

 

  [quote][b]

okanoganlew(at)gmail.com
Guest

Posted: Mon Sep 17, 2012 3:28 pm Post subject: alternator failure CJ6

Brian & Mark, thanks so much for your help.  The alternator was on there when I bought the CJ.  I wonder how they rigged up the drive system?  Doug Sapp was up at the hanger looking at it & was curious.  I tried to pull it off, but it is gooped on with some kind of sealant & I didn't want to break that.  I have ordered new brushes from NAPA, & they confirmed that it is a 91 GMC unit. How do they get 24v out of a 12v system?  Paul  On , Brian Lloyd <brian(at)lloyd.com> wrote: >  >  > On Mon, Sep 17, 2012 at 2:30 PM, Brian Lloyd brian(at)lloyd.com> wrote: >  >  >  >  > On Mon, Sep 17, 2012 at 11:58 AM, Paul Lewis okanoganlew(at)gmail.com> wrote: >  >  >  >  > Brian & Mark, photo's enclosed.  The broken wire was attached from the batt. post on the alt. to the bayonet fitting on the side of the alt. >  >  >  >  > It looks like someone might have put a diode in series with the lead from the 'B' terminal to the #2 (sense) terminal. The diode is probably a 1N4007 and the banded end would be toward the #2 terminal and away from the 'B' terminal. That is a way to get the alternator to produce about 0.7VDC more output to raise the voltage to correct for voltage drop across the 'B' lead going to the battery and/or main aircraft bus. If someone used a smaller gauge wire from the 'B' terminal you could have a volt or so of drop and this would correct for that. >  >  >  >  > Of course, the right answer is to run the lead from the #2 (sense) terminal back to the bus rather than connecting it to the 'B' terminal, and then not use the diode. >  >  > As for the marking on the alternator, it just says that it is a 24V at 40A alternator. When you put the alternator back together be sure to push the brushes fully into their holders and put a stiff wire (paper clip will do) in the small hole in the brush holder to hold them in place until you have the alternator case back together. >  >  >  >  >  > --  > Brian Lloyd, WB6RQN/J79BPL > 3191 Western Dr. > Cameron Park, CA 95682 > brian(at)lloyd.com > +1.767.617.1365 (Dominica) > +1.916.877.5067 (USA) >  >  >  >  >  >  >  >  >  >  >  =============== >  >  >  >  >  >  >  >  >  =============== >  >  >  >  >  >  =============== >  >  >  >  >  =============== >  >  >  > [quote][b]

okanoganlew(at)gmail.com
Guest

Posted: Mon Sep 17, 2012 3:31 pm Post subject: alternator failure CJ6

Brian, should I use the 1N4007 diode or the NTE 4934?  Both are available.  On , okanoganlew(at)gmail.com wrote: > Brian & Mark, thanks so much for your help.  The alternator was on there when I bought the CJ.  I wonder how they rigged up the drive system?  Doug Sapp was up at the hanger looking at it & was curious.  I tried to pull it off, but it is gooped on with some kind of sealant & I didn't want to break that.  I have ordered new brushes from NAPA, & they confirmed that it is a 91 GMC unit. How do they get 24v out of a 12v system? >  >  >  >  >  > Paul >  >  >  >  >  > On , Brian Lloyd brian(at)lloyd.com> wrote: >  >  > >  >  >  > >  >  >  > > On Mon, Sep 17, 2012 at 2:30 PM, Brian Lloyd brian(at)lloyd.com> wrote: >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > > On Mon, Sep 17, 2012 at 11:58 AM, Paul Lewis okanoganlew(at)gmail.com> wrote: >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > > Brian & Mark, photo's enclosed.  The broken wire was attached from the batt. post on the alt. to the bayonet fitting on the side of the alt. >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > > It looks like someone might have put a diode in series with the lead from the 'B' terminal to the #2 (sense) terminal. The diode is probably a 1N4007 and the banded end would be toward the #2 terminal and away from the 'B' terminal. That is a way to get the alternator to produce about 0.7VDC more output to raise the voltage to correct for voltage drop across the 'B' lead going to the battery and/or main aircraft bus. If someone used a smaller gauge wire from the 'B' terminal you could have a volt or so of drop and this would correct for that. >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > > Of course, the right answer is to run the lead from the #2 (sense) terminal back to the bus rather than connecting it to the 'B' terminal, and then not use the diode. >  >  > >  >  >  > >  >  >  > > As for the marking on the alternator, it just says that it is a 24V at 40A alternator. When you put the alternator back together be sure to push the brushes fully into their holders and put a stiff wire (paper clip will do) in the small hole in the brush holder to hold them in place until you have the alternator case back together. >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > > --  >  >  > > Brian Lloyd, WB6RQN/J79BPL >  >  > > 3191 Western Dr. >  >  > > Cameron Park, CA 95682 >  >  > > brian(at)lloyd.com >  >  > > +1.767.617.1365 (Dominica) >  >  > > +1.916.877.5067 (USA) >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  > >  >  >  ================ >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  ================ >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >  ================ >  >  > >  >  >  >  >  > >  >  >  >  >  > >  >  >

mark.bitterlich(at)navy.m
Guest

Posted: Mon Sep 17, 2012 3:33 pm Post subject: alternator failure CJ6

Paul, 



If you read the part number incorrectly off the small device that broke

off, then Brian Lloyd's explanation is perfectly plausible and could

easily be correct.  



If you read the part number correctly and there is no chance that you

made an error, then the device is not a diode but instead a trans-sorb

and Brian's explanation of why it is there is possibly not correct.

Either way, it is no big deal.  



Personally, I am not sure why someone might wire up a trans-sorb in the

fashion that it is wired, but I am willing to admit that I don't know

everything in the world there is to know about electronics and someone

might have put it there that knows more about it than me. 



Given the fact that it was working perfectly for quite some time before

it happened to break, then I would make an assumption that it will work

just perfectly again after you replace the part.  If this is not the

case, then ignore what I am suggesting.  



Be absolutely sure what the number is on the side of the thing.  Order

one, try Digikey Electronics.  It will only cost a few dollars IF THAT.

Get it in, and if it looks exactly like the one that broke, wire it up

the same way it was, and be done with it. 



Mark Bitterlich



p.s.  Brian and I will agree to disagree on this one.  

--

mark.bitterlich(at)navy.m
Guest

Posted: Mon Sep 17, 2012 3:35 pm Post subject: alternator failure CJ6

"How do they get 24v out of a 12v system?"



Well that might actually have something to do with the little piece that

broke off.  



Mark



--

brian(at)lloyd.com
Guest

Posted: Mon Sep 17, 2012 3:40 pm Post subject: alternator failure CJ6

On Mon, Sep 17, 2012 at 4:31 PM, Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)> wrote:

  	  Quote: 	
		  --> Yak-List message posted by: "Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E" <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)>

  

p.s.  Brian and I will agree to disagree on this one.

	




 Which I don't understand because I don't disagree with what Mark is saying at all. But I am working on a posting that I hope will explain the whole system and why the parts are there, or not there, and why you might, or might not, want to use them, including the answer to your question about how a 12V alternator can produce 24V.

 

-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

+1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)

 

  [quote][b]

mark.bitterlich(at)navy.m
Guest

Posted: Mon Sep 17, 2012 3:49 pm Post subject: alternator failure CJ6

I believe it is possible that the NTE 4934 is part of a voltage

regulation scheme and I would not recommend replacing it with a 1N4007,

but instead would replace it with the exact part number that was already

in there.  I would not change any part of the design until the total

design is fully understood.  



At the present time a full understanding of system operation is not

present.  So either we dissect this thing down to Parade Rest, and then

redesign it from the ground up, or we replace the broken part and fire

it up. 



Your choice. 

Mark

--

brian(at)lloyd.com
Guest

Posted: Mon Sep 17, 2012 3:53 pm Post subject: alternator failure CJ6

On Mon, Sep 17, 2012 at 4:29 PM,  <okanoganlew(at)gmail.com (okanoganlew(at)gmail.com)> wrote:

 	  Quote: 	
		   Brian, should I use the 1N4007 diode or the NTE 4934?  Both are available. 

	




Frankly, neither. More below.

 

 	  Quote: 	
		   

On , okanoganlew(at)gmail.com (okanoganlew(at)gmail.com) wrote: 

 	  Quote: 	
		   Brian & Mark, thanks so much for your help.  The alternator was on there when I bought the CJ.  I wonder how they rigged up the drive system?  Doug Sapp was up at the hanger looking at it & was curious.  I tried to pull it off, but it is gooped on with some kind of sealant & I didn't want to break that.  I have ordered new brushes from NAPA, & they confirmed that it is a 91 GMC unit. How do they get 24v out of a 12v system? 


	


	




I am getting ready to launch into one of my infamous educational postings here. It will answer your questions and probably a lot more that you didn't have and maybe didn't want answered.

 



To my way of thinking it is really useful to understand how an alternator works so you can understand what all those wires are doing. When responding to your original posting I was making some assumptions based on best standard practices, such as, anybody in their right mind would install a 28V alternator in a 28V system, not try to make a 14V alternator produce 28V. BTW, a 14V alternator can produce 28V just by putting a 14V zener diode in series with the sense lead, looking a whole lot like what you have there. Frankly, that is a hack and not something I would do in an aircraft (or car, or anything else I cared about) but it certainly would work. (And some places sell zener diodes and call them "trans-sorbs".)

 



But here is the $64 question, do you want the long answer and my opinion of what you should do with your alternator?

And no I don't disagree with Mark at all on this. I am sure he can write what I was going to write just as well as I could.

 

-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

+1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)

 

  [quote][b]

czech6(at)mesanetworks.ne
Guest

Posted: Mon Sep 17, 2012 3:59 pm Post subject: alternator failure CJ6

My hair hurts just reading this!



On Sep 17, 2012, at 5:31 PM, "Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E" <mark.bitterlich(at)navy.mil> wrote:



[quote] 

 

 Paul, 

 

 If you read the part number incorrectly off the small device that broke

 off, then Brian Lloyd's explanation is perfectly plausible and could

 easily be correct.  

 

 If you read the part number correctly and there is no chance that you

 made an error, then the device is not a diode but instead a trans-sorb

 and Brian's explanation of why it is there is possibly not correct.

 Either way, it is no big deal.  

 

 Personally, I am not sure why someone might wire up a trans-sorb in the

 fashion that it is wired, but I am willing to admit that I don't know

 everything in the world there is to know about electronics and someone

 might have put it there that knows more about it than me. 

 

 Given the fact that it was working perfectly for quite some time before

 it happened to break, then I would make an assumption that it will work

 just perfectly again after you replace the part.  If this is not the

 case, then ignore what I am suggesting.  

 

 Be absolutely sure what the number is on the side of the thing.  Order

 one, try Digikey Electronics.  It will only cost a few dollars IF THAT.

 

 

 Get it in, and if it looks exactly like the one that broke, wire it up

 the same way it was, and be done with it. 

 

 Mark Bitterlich

 

 p.s.  Brian and I will agree to disagree on this one.  

 

 

 --

f4ffm2(at)roadrunner.com
Guest

Posted: Mon Sep 17, 2012 4:04 pm Post subject: alternator failure CJ6

As my neighbor/landlord back in Mineral Wells, Texas said to me many years ago, "ain't 'lectricty funny stuff?".   He knew.



Roger

On Sep 17, 2012, at 4:47 PM, Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E wrote:



[quote] 

 

 I believe it is possible that the NTE 4934 is part of a voltage

 regulation scheme and I would not recommend replacing it with a 1N4007,

 but instead would replace it with the exact part number that was already

 in there.  I would not change any part of the design until the total

 design is fully understood.  

 

 At the present time a full understanding of system operation is not

 present.  So either we dissect this thing down to Parade Rest, and then

 redesign it from the ground up, or we replace the broken part and fire

 it up. 

 

 Your choice. 

 

 

 Mark

 

 

 --

brian(at)lloyd.com
Guest

Posted: Mon Sep 17, 2012 4:08 pm Post subject: alternator failure CJ6

On Mon, Sep 17, 2012 at 4:47 PM, Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)> wrote:

  	  Quote: 	
		  --> Yak-List message posted by: "Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E" <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)>

  

 

I believe it is possible that the NTE 4934 is part of a voltage

 regulation scheme and I would not recommend replacing it with a 1N4007,

 but instead would replace it with the exact part number that was already

 in there.  I would not change any part of the design until the total

 design is fully understood.

 

 At the present time a full understanding of system operation is not

 present.  So either we dissect this thing down to Parade Rest, and then

 redesign it from the ground up, or we replace the broken part and fire

 it up.

 

 Your choice.

	




I agree with Mark. But my feeling is that the right answer is to indeed make sure that this has been done right rather than just replace the part and move off, fat, dumb, and happy. 

 



These internally-regulated GM alternators are dirt-cheap sources of power. They are also super simple. The built-in regulator controls the output of the alternator to keep its voltage at the desired level, i.e. around 14V (usually 13.7V) for a system with a 12V battery, or around 28V (usually 27.4V) for a system with a 24V battery. You can even make a 14v alternator into a 28V alternator by putting a 14V zener diode in series with the sense lead to the regulator, make the regulator see a voltage that is 14V below the bus voltage. 

 



Now here is the real kicker and the thing you really need to think about. When the voltage regulator in these alternators fail, it can fail one of two ways:

The output of the alternator can drop to zero and you are running on battery power only. 
The output of the alternator can jump up to about 100V quickly destroying the battery and shortly thereafter, everything else in the electrical system.Frankly, failure #2 bothers the heck out of me. No, it doesn't happen very often so maybe you don't have to worry about it ... much. 

 

FWIW, this is the reason that you almost never find internally-regulated alternators in aircraft unless the alternator has a fail-safe way to interrupt the current to the field (rotor) winding in the alternator. The stock GM alternator does not offer that. On my boat where I had a pair of these alternators to handle the battery charging chores, I opted to modify the alternators to remove the internal regulator and control them from an external regulator that had overvoltage protection, just like the standard charging systems in production aircraft.

 



Anyway, I am willing to expound further if you are interested.



-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

 +1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)



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