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B and C SD-8 dynamo problem

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thomas.n.gautier(at)jpl.n
Guest

Posted: Mon May 16, 2016 11:12 am Post subject: B and C SD-8 dynamo problem

Bob,



   I am getting to the final stages of my RV-10 project for which I

selected Z-13/8 as the electrical system model. My system design is

essential identical to Z-13/8 rev Q from Appendix Z Rev.12A change 4,

except that I am using ordinary mags for ignition.



   It¹s time to install the SD-8 dynamo on the engine so I finally, some

years after wiring it, got around to testing the control circuit for the

dynamo. I mounted the dynamo in a drill press to operate at about 2400 rpm

and arranged to load the dynamo/control circuit up to a maximum of 8A

using some modified electric toaster heating elements. I started with no

load.



   My test set produces no output voltage. When I turn on the drill press

the voltage at the positive terminal of the capacitor rises to 3.1v over a

period of 10 or 15 seconds and stays there. The dynamo is producing over

20vac and the voltage at the negative terminal of the bridge rectifier is

about -13v.



   I am in the process of wringing out my circuit construction to find the

problem but I would like your advice on a couple of issues. 1) Can you

suggest a definitive test of the voltage regulator module isolated from

the rest of the circuit? And 2) Can I test the control circuit without the

dynamo, perhaps with a DC supply for input power? If I can test it with DC

what voltage should I use? I imagine 16 or 17 volts would be right for

full 8A load. Would higher voltage be useful for lighter loads? I would

like to stress test my heat sinking arrangement for an hour or two but I

don¹t really like the idea of running the dynamo with the drill press for

that long. Also I¹d like to get the dynamo mounted on the engine.



  Thanks for any advice you can give me.



Nick Gautier

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user9253

Joined: 28 Mar 2008
Posts: 1935
Location: Riley TWP Michigan

Posted: Mon May 16, 2016 3:45 pm Post subject: Re: B and C SD-8 dynamo problem

When the dynamo is rotating, both it and the regulator should be outputting voltage, regardless of whether the relay is energized or not.

  What regulator are you using?  It should be mounted using heat-conductive paste.  Is the regulator grounded to the airframe during these tests?

We need to know exactly where both voltmeter leads are connected for each measurement. 

 The dynamo does not have to be rotating to test the relay.  An easy test is to put a 12 volt battery in the aircraft wired according to Z-13/8.    Connect a high wattage automotive lamp across the capacitor, then turn the AUX/ALT switch on and off.  If the lamp turns on and off, then the relay circuit is working.  The relay should always be energized with 12 volts nominal (14 is OK), never with 16 or 17 volts.

  The problem might be the test setup and not a component problem.  The best test is to install everything and go fly the plane.  Stick-on temperature strips can be affixed to the regulator to see how hot it gets.

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 17, 2016 9:06 am Post subject: B and C SD-8 dynamo problem

 	  Quote: 	
		     I am in the process of wringing out my circuit construction to find the

 problem but I would like your advice on a couple of issues. 1) Can you

 suggest a definitive test of the voltage regulator module isolated from

 the rest of the circuit? And 2) Can I test the control circuit without the

 dynamo, perhaps with a DC supply for input power? If I can test it with DC

 what voltage should I use? I imagine 16 or 17 volts would be right for

 full 8A load. Would higher voltage be useful for lighter loads? I would

 like to stress test my heat sinking arrangement for an hour or two but I

 don¹t really like the idea of running the dynamo with the drill press for

 that long. Also I¹d like to get the dynamo mounted on the engine. 	


   Not all rectifier/regulators will come alive without

   having voltage at "both ends" . . . i.e. both

   input and output. They need a battery on line

   to wake up.



   The stock SD-8 R/R is thermally marginal. It will

   be replaced with a more robust device shortly.

   I'm assembling a drive stand to do detailed

   energy studies on a range of R/R options for

   all of the B&C PM alternators. Kind of swamped

   right now with EMT classes but the drive stand

   is about ready to run.



   

 [img]cid:.0[/img]



 

   Please don't take this as any discouragement

   for gathering your own data. I'd be pleased

   to know your findings. 2400 RPM is a bit slow,

   the SD-8 doesn't reach full rated output

   below 3900 or so. Getting a grip on those

   critters to spin them is a bit of a hassle.

   Neal George fixed me up with some OEM mating

   parts for the spline. I did find that a 12-point,

   socket (11/16?) fits the male spline pretty

   well. I have an adapter fabricated from a

   socket that I elected not to use for permanent

   tooling. You're welcome to it if it's useful

   to you.



   In any case, I suggest you mock up a complete

   alternator-battery-load system. It should

   come alive and work for you then.



 

   Bob . . .

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thomas.n.gautier(at)jpl.n
Guest

Posted: Wed May 18, 2016 10:27 am Post subject: B and C SD-8 dynamo problem

Bob and everyone,



   Thanks for the replies.



   I was aware that the dynamo regulator might not come alive without

power on its output, but I thought that was what the

bridge-rectifier/3K-resistor come-alive circuit in Z-13/8 Rev Q was for. I

can¹t say that I understand just how that circuit works with the regulator

module but it reminds me of an old vacuum tube grid leak bias circuit.

That¹s why I thought the voltage (about -13vdc) at the junction of the

resistor and rectifier would be useful.



  I will test a more complete version of my electrical system with the

main battery attached and see if things work better. The best I can do is

3100 rpm for the dynamo but we¹ll see how that works. I¹ll report my

results. I have attached a composite picture of the test set up for those

of you who are interested. The guys at BandC said driving the dynamo from

the outside end wouldn¹t hurt it. The big sheet of aluminum is my stand-in

heat sink for the instrument sub-panel in the plane.



   Bob, do you have any idea how soon an improved version of the regulator

might be available?



Regards,

Nick Gautier



 	  Quote: 	
		  

Time: 10:06:58 AM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

Subject: Re: B and C  SD-8 dynamo problem

>    I am in the process of wringing out my circuit construction to find

>the

>problem but I would like your advice on a couple of issues. 1) Can you

>suggest a definitive test of the voltage regulator module isolated from

>the rest of the circuit? And 2) Can I test the control circuit without

>the

>dynamo, perhaps with a DC supply for input power? If I can test it with

>DC

>what voltage should I use? I imagine 16 or 17 volts would be right for

>full 8A load. Would higher voltage be useful for lighter loads? I would

>like to stress test my heat sinking arrangement for an hour or two but I

>don=B9t really like the idea of running the dynamo with the drill press

>for

>that long. Also I¹d like to get the dynamo mounted on the engine.



   Not all rectifier/regulators will come alive without

   having voltage at "both ends" . . . i.e. both

   input and output. They need a battery on line

   to wake up.



   The stock SD-8 R/R is thermally marginal. It will

   be replaced with a more robust device shortly.

   I'm assembling a drive stand to do detailed

   energy studies on a range of R/R options for

   all of the B&C PM alternators. Kind of swamped

   right now with EMT classes but the drive stand

   is about ready to run.

Emacs!

   Please don't take this as any discouragement

   for gathering your own data. I'd be pleased

   to know your findings. 2400 RPM is a bit slow,

   the SD-8 doesn't reach full rated output

   below 3900 or so. Getting a grip on those

   critters to spin them is a bit of a hassle.

   Neal George fixed me up with some OEM mating

   parts for the spline. I did find that a 12-point,

   socket (11/16?) fits the male spline pretty

   well. I have an adapter fabricated from a

   socket that I elected not to use for permanent

   tooling. You're welcome to it if it's useful

   to you.



   In any case, I suggest you mock up a complete

   alternator-battery-load system. It should

   come alive and work for you then.

   Bob . . .

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