Matronics Email Lists :: View topic - old B and C SD-8 Dynamo failure

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

old B and C SD-8 Dynamo failure

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

motodd(at)frontier.com
Guest

Posted: Mon Apr 03, 2017 9:35 pm Post subject: old B and C SD-8 Dynamo failure

Well, after 27 years and 2300+ hours, my good old SD-8 dynamo finally

gave me a problem.  It was installed in my day/VFR  RV4 in 1989 as the

only charging source.  It could produce up to 8.6 amps at high RPM and

met my modest electrical load requirements (<4 amps in cruise) for all

these years.  Of course, I could expect my low voltage light to come on

(at 12.5V) at low rpms depending on the loads.  I didn't mind.  It made

for a nice reminder to turn off my boost pump as I exited the runway on

landing.



On a recent flight, I noticed that the low voltage light came on a

little earlier than I expected on landing.   At high RPM, the voltage

was only going to 13.9 instead of the usual 14.1V.   A quick run through

my switchable loads showed they were pulling their expected currents.  

I have a switchable volt/amp gauge on my panel so I can look at one or

the other but not both simultaneously.  The amp readings are taken off

my B lead and it takes several seconds for the amp reading to stabilize

on my gauge after it's selected.  I never saw an unexpectedly high amp

reading on the gauge.  Back at the hangar, a brief look at my B lead

connections didn't reveal any problems.  On the next flight, the low

voltage light came on even sooner and the voltage only got to 13.7V.



A more detailed inspection was made of the wiring, including

micro-ohming some connections (using Bob's 100mA current clamp

micro-ohmmeter design I've enjoyed using for several years).  I thought

I detected a little bit of a burnt electrical smell near the dynamo

housing where the armature leads pass through a clip screwed into the

rim of the housing.   Using a cheap digital multimeter, I checked the

resistance  across the disconnected dynamo leads and got 5.6 ohms.  Not

sure what it's suppose to be.



I flew the plane again and this time, I got a low voltage light in

cruise and zero B lead amps when checked.  I checked the resistance

across the dynamo leads again with the same meter.. and got a reading of

zero.  My micro-ohm meter said it was about 700 milliohms.   I bought a

new SD-8 and am back in the air trouble free.  Since removing the

problem unit, I removed the clip that held the leads at the rim of the

dynamo housing and slid the protective sheathing back.  The lead wires

look fine, including the half-inch of wire I can see inside the

housing.  The resistance across the leads remains 'zero' when checked

with another cheap digital mulitmeter.



I concluded that I had probably experienced a progressive short within

the dynamo, probably in the windings themselves.  This dynamo was from

the 1980's  and the exterior design has changed a lot since then.  This

includes a protected routing of the leads out of the dynamo housing with

a better clamping system.   The insides have probably changed as well. 

Lord knows the new unit is easier to install with much better access to

the mounting nuts.



I have no complaints about this SD-8 failure.   I certainly  got a

reasonable service life out of this unit.  I just thought I'd share my

story as just one more data point, although I appreciate it's kinda

ancient history.  I'm planning on taking the dynamo apart (curiosity)

and maybe salvaging the magnets.



Bob, if you wanted to look at this dynamo for some reason, I'll be happy

to mail it to you.  I suspect you've got much better things to do than

'paleo-forensics' on this dated item.



Mark

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Tue Apr 04, 2017 3:04 am Post subject: Re: old B and C SD-8 Dynamo failure

The saying, "Ring it out", when referring to electrical testing, got its beginnings when troubleshooters used a doorbell for testing electrical motors.  There is not much difference in resistance between a good motor and one with a shorted winding.  But there is a difference in the inductance.  An experienced electrician could tell the difference in doorbell sound when connected in series with a shorted motor winding compared to a good winding.  Modern doorbells are not suitable for this task.  The doorbell must be of the old fashioned clanger and bell type.

  This information might be of use to you 27 years from now when your new SD-8 dynamo malfunctions.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 04, 2017 3:50 am Post subject: old B and C SD-8 Dynamo failure

 	  Quote: 	
		  

 I have no complaints about this SD-8 failure.   I certainly  got a

 reasonable service life out of this unit.  I just thought I'd share my

 story as just one more data point, although I appreciate it's kinda

 ancient history.  I'm planning on taking the dynamo apart (curiosity)

 and maybe salvaging the magnets. 	


   Are the windings smoked? Do they smell bad?



   The DC resistance of this product is less than

   0.25 ohms. So if you had a shorted turn or two,

   you could not resolve it with jelly-bean test

   equipment. The magnets are ferrites . . . rather

   brittle. You probably couldn't get them loose

   without breaking them up. 



   



  	  Quote: 	
		  Bob, if you wanted to look at this dynamo for some reason, I'll be happy

 to mail it to you.  I suspect you've got much better things to do than

 'paleo-forensics' on this dated item.



 Mark 	


   Actually, I would like to see it. I have

   a drive stand running that fits the SD8

   and I'm equipped to test/inspect it in

   detail. Getting a close up look at a sample

   with this kind of service on it would be

   illuminating.



   Send the rectifier/regulator too. I'll

   get them checked out and repaired/replaced

   as needed.

   



 

 

   Bob . . .

ashleysc(at)broadstripe.n
Guest

Posted: Tue Apr 04, 2017 6:43 am Post subject: old B and C SD-8 Dynamo failure

Hi Mark;

Hi All;

I read this as an endorsement, not a complaint. Who gets 27 years of operation from a car, washing machine, or computer? It gives me great confidence in B & C products.

Cheers!   Stu.



---

motodd(at)frontier.com
Guest

Posted: Wed Apr 05, 2017 4:08 pm Post subject: old B and C SD-8 Dynamo failure

 	  Quote: 	
		      Are the windings smoked? Do they smell bad?


	


I thought there was a burnt smell from the dynamo before I pulled it off

the engine.  Here at my bench, is smells fine.  Now I wonder if that

burnt smell was from something else in that 2300+ hour engine compartment.



 	  Quote: 	
		   

    The DC resistance of this product is less than

    0.25 ohms. So if you had a shorted turn or two,

    you could not resolve it with jelly-bean test

    equipment. The magnets are ferrites . . . rather

    brittle. You probably couldn't get them loose

    without breaking them up.


	


OK.



 	  Quote: 	
		   

 

> Bob, if you wanted to look at this dynamo for some reason, I'll be happy

> to mail it to you.  I suspect you've got much better things to do than

> 'paleo-forensics' on this dated item.

>

> Mark

    Actually, I would like to see it. I have

    a drive stand running that fits the SD8

    and I'm equipped to test/inspect it in

    detail. Getting a close up look at a sample

    with this kind of service on it would be

    illuminating.

 

    Send the rectifier/regulator too. I'll

    get them checked out and repaired/replaced

    as needed.

 

 

    Bob . . . 


	


I'll get the dynamo and regulator off to you within the next couple of

days, using your PO Box 130 address unless you instruct otherwise.



Thanks for looking at this.  If it checks out OK, I guess it'll mean

that I missed a faulty connection somewhere that got cleared up with the

replacement.  After all these years of flawless service, I can't decide

whether I'm rooting for the dynamo or me!



Mark

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 06, 2017 6:02 am Post subject: old B and C SD-8 Dynamo failure

 	  Quote: 	
		  



 I'll get the dynamo and regulator off to you within the next couple of

 days, using your PO Box 130 address unless you instruct otherwise.



 Thanks for looking at this.  If it checks out OK, I guess it'll mean

 that I missed a faulty connection somewhere that got cleared up with the

 replacement.  After all these years of flawless service, I can't decide

 whether I'm rooting for the dynamo or me! 	


    Thank YOU for making it available. It's a rare

    treat to get field returns on mature designs

    for evaluation. Products I designed at Electro-Mech

    were routinely serviced in house as E-M was the only

    FAA qualified overhaul and repair shop for those

    products . . . I was able to visit my former

    colleagues at E-M and look through the R/R

    records.



    In the OBAM aviation world it's more difficult

    to access such data. 



 

 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 12, 2017 3:20 pm Post subject: old B and C SD-8 Dynamo failure

 	  Quote: 	
		    	  Quote: 	
		  Bob, if you wanted to look at this dynamo for some reason, I'll be happy

 to mail it to you.  I suspect you've got much better things to do than

 'paleo-forensics' on this dated item.



 Mark 	


   Actually, I would like to see it. I have

   a drive stand running that fits the SD8

   and I'm equipped to test/inspect it in

   detail. Getting a close up look at a sample

   with this kind of service on it would be

   illuminating.



   Send the rectifier/regulator too. I'll

   get them checked out and repaired/replaced

   as needed. 	




     Got Mark's SD8 and R/R from the post office

     today. Ran the SD8. As I would have predicted,

     it runs just fine.



     The construction of these machines doesn't have

     much of a wear-out mode. The bearings

     are VERY lightly loaded. There are no brushes

     or slip rings. The stationary windings might

     be a some risk for aging were they operated

     at temperatures that pushed the insulation

     limits on the magnet wire.



     The numbers on Mr. Todd's SD8 track very

     closely with those from a new, current protection

     unit.



     I've got some wiring details to fiddle with

     before I can add the R/R to the bench setup . . .

     perhaps tomorrow.



     Watch this space . . .



 

 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 17, 2017 10:31 am Post subject: old B and C SD-8 Dynamo failure

Got Mark's SD-8 and original stock R/R running

 on the bench. The R/R seems to be fine too. I

 initially used a LiFePO4 battery (ETX36) in the

 test setup and observed some unexpected behaviors.



 Got a small lead-acid from the store a few minutes

 ago and put it on a maintainer.  Will resume the

 experiment when the battery tops off . . .



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 17, 2017 2:37 pm Post subject: old B and C SD-8 Dynamo failure

 	  Quote: 	
		  Bob, if you wanted to look at this dynamo for some reason, I'll be happy

 to mail it to you.  I suspect you've got much better things to do than

 'paleo-forensics' on this dated item. 	


    I've finished some preliminary operations on the

    as received SD8 and companion R/R. They seem to

    function pretty much as designed.



    2800 RPM produces 3+ amps at 14.4v

    3300 RPM produces 4+ amps at 14.3v

    3800 RPM produces 8+ amps at 14.1v



    At the final load setting, current

    in the SD8 windings was 10.5 A(rms)



    I can return this hardware if you'd like to

    have it around for spares. At the same time,

    it would be interesting/useful to add it to

    the constellation of test tools I'm

    building around a 2HP drive-stand with

    and AND20000 spline pad on it.



 [img]cid:.0[/img]



 

    As an interesting aside, test data were taken

    without a battery on line . . . this prevented

    pollution of current values dialed into the dynamic

    load bank. I was able to 'tickle' the dynamo-r/r 

    into operation with a momentary application of battery

    power. On one fire-up/shut-down cycle, the capacitor

    was still charged to about 3 volts and the system came

    on-line with only a small fraction of start up

    excitation offered by the ship's battery.



 

 

   Bob . . .

4e1742f.jpg

Description:

Filesize:

353.51 KB

Viewed:

5365 Time(s)

motodd(at)frontier.com
Guest

Posted: Tue Apr 18, 2017 12:40 pm Post subject: old B and C SD-8 Dynamo failure

 	  Quote: 	
		   

     I can return this hardware if you'd like to

     have it around for spares. At the same time,

     it would be interesting/useful to add it to

     the constellation of test tools I'm

     building around a 2HP drive-stand with

     and AND20000 spline pad on it.


	


Bob, I'm happy to contribute them to the cause.  BTW, I never had a big

cap or OVP module until I installed the new dynamo and regulator.



After just a couple of flights with the replacement hardware, I've had

no indication of a return of the problem. To be at ease, I'll just have

to go fly some more!



Mark

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum