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SD-8 vs. SD-20 choice

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tompkinsl(at)integra.net
Guest

Posted: Sun Jun 01, 2008 2:59 pm Post subject: SD-8 vs. SD-20 choice

Although I already should have known, I was  recently reminded that, as a permanent magnet device, the SD-8 standby  alternator is producing output whenever it is rotating.  

  

 Looking on the B&C website, I determined that  the PMR1C regulator is a heat sink for the 100-120 watts produced when the  alternator is not delivering current to the endurance bus.  

  

 So Question #1 is whether the SD-8 is  "wearing" to a greater extent than the SD-20 since it is producing rated load  all the time one is operating the engine at cruise rpm?

  

 If Question #1 is yes, then Question #2 is: Does  the fact that the SD-8 is producing output and wearing all the time make it more  likely to be an electrical noise source or more likely to become an electrical  noise source (at an earlier time in its life cycle) than the SD-20?

  

 Although I most likely don't need 20A backup  capability for my endurance bus, I would like to minimize any electrical noise  potential.

  

 Thanks in advance to those who are more  knowledgeable than this electrically challenged mech. engr.

  

 Larry

  

  

   [quote][b]

frank.hinde(at)hp.com
Guest

Posted: Mon Jun 02, 2008 6:56 am Post subject: SD-8 vs. SD-20 choice

I'm in the same boat Larry being an  ME..

  

 In practice I have never heard any radio noise form  the SD8. I would also put the output nearer 12A rather than the 8A it is rated  for.

  

 Frank



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Larry  L. Tompkins, P.E.

Sent: Sunday, June 01, 2008 3:52 PM

To:  aeroelectric-list(at)matronics.com

Subject: SD-8 vs.  SD-20 choice

 

 Although I already should have known, I was  recently reminded that, as a permanent magnet device, the SD-8 standby  alternator is producing output whenever it is rotating.  

  

 Looking on the B&C website, I determined that  the PMR1C regulator is a heat sink for the 100-120 watts produced when the  alternator is not delivering current to the endurance bus.  

  

 So Question #1 is whether the SD-8 is  "wearing" to a greater extent than the SD-20 since it is producing rated load  all the time one is operating the engine at cruise rpm?

  

 If Question #1 is yes, then Question #2 is: Does  the fact that the SD-8 is producing output and wearing all the time make it more  likely to be an electrical noise source or more likely to become an electrical  noise source (at an earlier time in its life cycle) than the SD-20?

  

 Although I most likely don't need 20A backup  capability for my endurance bus, I would like to minimize any electrical noise  potential.

  

 Thanks in advance to those who are more  knowledgeable than this electrically challenged mech. engr.

  

 Larry

  

  

[quote]



ist">http://www.matronics.com/Navigator?AeroElectric-List

ics.com

.matronics.com/contribution



[b]

echristley(at)nc.rr.com
Guest

Posted: Mon Jun 02, 2008 8:54 am Post subject: SD-8 vs. SD-20 choice

Hinde, Frank George (Corvallis) wrote:

 	  Quote: 	
		   I'm in the same boat Larry being an ME..



 In practice I have never heard any radio noise form the SD8. I would also put the output nearer 12A rather than the 8A it is rated for.



 Frank



 ________________________________

 From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Larry L. Tompkins, P.E.

 Sent: Sunday, June 01, 2008 3:52 PM

 To: aeroelectric-list(at)matronics.com

 Subject: SD-8 vs. SD-20 choice



 Although I already should have known, I was recently reminded that, as a permanent magnet device, the SD-8 standby alternator is producing output whenever it is rotating.

   

 Looking on the B&C website, I determined that the PMR1C regulator is a heat sink for the 100-120 watts produced when the alternator is not delivering current to the endurance bus.

   

There are switching regulators available which run cool, and don't waste 
	


power.  Whether the extra cost and complexity is worth saving 100W of 

electricity is debatable.

 	  Quote: 	
		   So Question #1 is whether the SD-8 is "wearing" to a greater extent than the SD-20 since it is producing rated load all the time one is operating the engine at cruise rpm?

   

Maybe.  Maybe not.  You have some magnets (that are basically rated to 
	


last forever) that are spinning around a coil of wire, pushing the 

electrons out one side.  You can get more electrons out by increasing 

the strength of the pusher, or increasing the number of pushees.  The 

SD-20 could have more coils of wires, or magnets, or larger magnets, or 

some combination of all three.  If there were just more coils of wire, 

then the magnets are being asked to push harder, and their expected life 

would drop from "infinity" to "infinity minus something".

 	  Quote: 	
		   If Question #1 is yes, then Question #2 is: Does the fact that the SD-8 is producing output and wearing all the time make it more likely to be an electrical noise source or more likely to become an electrical noise source (at an earlier time in its life cycle) than the SD-20?



   

It would actually make LESS noise.  The only way for it to "wear" would 
	


be for the permanent magnets to loose their magnetism.  At that point, 

the generator isn't able to push as many electrons and the noise comes 

from the electrons getting pushed around.

 	  Quote: 	
		   Although I most likely don't need 20A backup capability for my endurance bus, I would like to minimize any electrical noise potential.

   

Then the 8A version is your best bet.

sportav8r(at)gmail.com
Guest

Posted: Mon Jun 02, 2008 10:32 am Post subject: SD-8 vs. SD-20 choice

Are we sure the regulator sinks the "unused" wattage from the generator?  If so, it's putting a full-output load on the engine at all times, robbing perhaps 1/4 hp - minor but not good.  I would have thought the generator with no electrical load is not drawing mechanical power from the engine, but what do I know?! 

 

I have an SD-8 sitting on the shelf since SnF 2006 that I have never gotten around to installing.  Maybe I should let it go to the highest reasonable offer and buy another if/when I ever get to finishing my fully redundant all-glass IFR panel for the RV.  Ditto for the Garmin 340 audio panel - it's not seeing much use on the shelf either.

 

-Bill B



On Mon, Jun 2, 2008 at 12:51 PM, Ernest Christley <echristley(at)nc.rr.com (echristley(at)nc.rr.com)> wrote:

[quote] --> AeroElectric-List message posted by: Ernest Christley <echristley(at)nc.rr.com (echristley(at)nc.rr.com)>

 

 Hinde, Frank George (Corvallis) wrote:

  	  Quote: 	
		   I'm in the same boat Larry being an ME..

 

 In practice I have never heard any radio noise form the SD8. I would also put the output nearer 12A rather than the 8A it is rated for.

 

 Frank

 

 ________________________________

 From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Larry L. Tompkins, P.E.

  Sent: Sunday, June 01, 2008 3:52 PM

 To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)

 Subject: SD-8 vs. SD-20 choice

 

 Although I already should have known, I was recently reminded that, as a permanent magnet device, the SD-8 standby alternator is producing output whenever it is rotating.

   Looking on the B&C website, I determined that the PMR1C regulator is a heat sink for the 100-120 watts produced when the alternator is not delivering current to the endurance bus.

   

 	
 There are switching regulators available which run cool, and don't waste power.  Whether the extra cost and complexity is worth saving 100W of electricity is debatable.

  	  Quote: 	
		   So Question #1 is whether the SD-8 is "wearing" to a greater extent than the SD-20 since it is producing rated load all the time one is operating the engine at cruise rpm?

   

 	
 Maybe.  Maybe not.  You have some magnets (that are basically rated to last forever) that are spinning around a coil of wire, pushing the electrons out one side.  You can get more electrons out by increasing the strength of the pusher, or increasing the number of pushees.  The SD-20 could have more coils of wires, or magnets, or larger magnets, or some combination of all three.  If there were just more coils of wire, then the magnets are being asked to push harder, and their expected life would drop from "infinity" to "infinity minus something".

   	  Quote: 	
		   If Question #1 is yes, then Question #2 is: Does the fact that the SD-8 is producing output and wearing all the time make it more likely to be an electrical noise source or more likely to become an electrical noise source (at an earlier time in its life cycle) than the SD-20?

  

   

 	
 It would actually make LESS noise.  The only way for it to "wear" would be for the permanent magnets to loose their magnetism.  At that point, the generator isn't able to push as many electrons and the noise comes from the electrons getting pushed around.

   	  Quote: 	
		   Although I most likely don't need 20A backup capability for my endurance bus, I would like to minimize any electrical noise potential.

   

 	
 Then the 8A version is your best bet.

 

 

 

 

 [b]

tompkinsl(at)integra.net
Guest

Posted: Tue Jun 03, 2008 9:49 am Post subject: SD-8 vs. SD-20 choice

Ernest:

  

 It is my understanding that the SD-20 has both  a wound stator and a wound coil, i.e., no permanent magnets.  Therefore it  is "off" until power to the field windings is switched on.

  

 Let me try to do a better job asking my  question.  The SD-8 is continuously producing output.  Does that mean  it also has the continuous potential to produce electrical noise?  On the  other hand, the SD-20 is spinning continuously, but does not produce output  unless the field circuit is switched "on."  What is the potential for the  SD-20 to generate electrical noise when it is spinning and not producing  output?

  

 My question about "wear" was exceptionally poorly  phrased.  I am actually interested in knowing whether there is more  mechanical wear (bearings) because the SD-8 is "on" all the time vs. the SD-20,  which would only be "on" during a primary alternator failure (I suspect  this may have more to do with the relative mechanical robustness of the devices  than anything else).  Further, I was trying to understand if mechanical  wear on the SD-8 would increase its "noise signature" over time and if  mechanical wear on the SD-20 would eventually result in an electrical  "noise signature" even with the alternator off.  I hope I did a better job  of asking my questions this time.

  

 Larry

   [quote][b]

echristley(at)nc.rr.com
Guest

Posted: Tue Jun 03, 2008 6:49 pm Post subject: SD-8 vs. SD-20 choice

Larry L. Tompkins, P.E. wrote:

 	  Quote: 	
		   Ernest:



 It is my understanding that the SD-20 has both a wound stator and a wound coil, i.e., no permanent magnets.  Therefore it is "off" until power to the field windings is switched on.



 Let me try to do a better job asking my question.  The SD-8 is continuously producing output.  Does that mean it also has the continuous potential to produce electrical noise?  

The amount of noise radiated would need some good lab equipment to pick 
	


up.  You won't have a problem with your radios.

 	  Quote: 	
		   On the other hand, the SD-20 is spinning continuously, but does not produce output unless the field circuit is switched "on."  What is the potential for the SD-20 to generate electrical noise when it is spinning and not producing output?



   

Zero.
	


 	  Quote: 	
		   My question about "wear" was exceptionally poorly phrased.  I am actually interested in knowing whether there is more mechanical wear (bearings) because the SD-8 is "on" all the time vs. the SD-20, which would only be "on" during a primary alternator failure (I suspect this may have more to do with the relative mechanical robustness of the devices than anything else).  Further, I was trying to understand if mechanical wear on the SD-8 would increase its "noise signature" over time and if mechanical wear on the SD-20 would eventually result in an electrical "noise signature" even with the alternator off.  I hope I did a better job of asking my questions this time.



 Larry

   

The nice thing about these generators vs an alternator is that they 
	


don't have the side loads imposed by a belt and pully system.  The gear 

will eventually wear out, but because the weights and forces on the 

spinning parts are all balanced, there is very little wear on the 

bearings.  And the gear will most likely outlast your engine.



-- 



http://www.ronpaultimeline.com

nuckolls.bob(at)cox.net
Guest

Posted: Wed Jun 04, 2008 7:39 am Post subject: SD-8 vs. SD-20 choice

At 03:52 PM 6/1/2008 -0700, you wrote:

 	  Quote: 	
		  Although I already should have known, I was recently reminded that, as a 

permanent magnet device, the SD-8 standby alternator is producing output 

whenever it is rotating.



Looking on the B&C website, I determined that the PMR1C regulator is a 

heat sink for the 100-120 watts produced when the alternator is not 

delivering current to the endurance bus.


	


    Unlike the earliest SHUNT regulators for PM

    alternators (makes alternator work full bore

    all the time) the regulators commonly offered

    today are SERIES devices . . .

 	  Quote: 	
		  

So Question #1 is whether the SD-8 is "wearing" to a greater extent than 

the SD-20 since it is producing rated load all the time one is operating 

the engine at cruise rpm?

    . . . that load the alternator in response to
	


    demands from system loads and/or state of battery

    discharge.

 	  Quote: 	
		  

If Question #1 is yes, then Question #2 is: Does the fact that the SD-8 is 

producing output and wearing all the time make it more likely to be an 

electrical noise source or more likely to become an electrical noise 

source (at an earlier time in its life cycle) than the SD-20?



Although I most likely don't need 20A backup capability for my endurance 

bus, I would like to minimize any electrical noise potential.



Thanks in advance to those who are more knowledgeable than this 

electrically challenged mech. engr.


	


   Alternators are the strongest sources of noise

   in the system . . . but quite manageable. Your main

   alternator or even an SD-20 is MUCH noisier than an

   SD-8. Products designed to run in DC systems powered

   by alternators live quite happily in this environment.

   Your concerns for alternator noise are not well

   supported by the physics.



   Bob . . .

nuckolls.bob(at)cox.net
Guest

Posted: Wed Jun 04, 2008 8:27 am Post subject: SD-8 vs. SD-20 choice

At 02:50 PM 6/2/2008 +0000, you wrote:

 	  Quote: 	
		  I'm in the same boat Larry being an ME..



In practice I have never heard any radio noise form the SD8. I would also 

put the output nearer 12A rather than the 8A it is rated for.


	


  The SD-8 is capable of 12A output if you spin it fast enough.

  Years ago, the SD-8 had a belt driven cousin that was mounted

  under the prop shaft on the O-200. This version spun fast

  enough to call it a 12A machine. See:



http://aeroelectric.com/Pictures/Alternators/SD8-Performance.pdf



  The "rating" is also dependent upon whether you're asking the

  alternator to CHARGE a battery, or simply SUPPORT the system

  at a voltage sufficient to PREVENT DISCHARGE of the battery.

  As the two curves cited above illustrate, when driven at

  vacuum pump pad speeds, you can rate the SD-8 at more than

  8A if your willing to let the bus voltage sag down to

  battery sustain levels.



  SD-8 noise is quite nominal. See:



http://www.aeroelectric.com/Pictures/Curves/SD-8_Noise_Data.pdf



  At 14.6v, 10.6 amps load and 4000 rpm filtered by

  a ratty 10K uF capacitor, I measured about 250 mV

  pk-pk noise. This is about 1/6 the noise you might expect

  from a 60A main alternator.



  Bob . . .

frank.hinde(at)hp.com
Guest

Posted: Wed Jun 04, 2008 9:05 am Post subject: SD-8 vs. SD-20 choice

Oh that makes sense because when I did my IFR test running more equipment than I though was possible (i.e right around 12A's worth) the batt volts would sag to 12v but it would only give me an alarm (11.8V I think) if I hit the transmit on the radio.



I took this to mean I could safely run this level of equipment to my destination.



Frank



 The "rating" is also dependent upon whether you're asking the

  alternator to CHARGE a battery, or simply SUPPORT the system

  at a voltage sufficient to PREVENT DISCHARGE of the battery.

  As the two curves cited above illustrate, when driven at

  vacuum pump pad speeds, you can rate the SD-8 at more than

  8A if your willing to let the bus voltage sag down to

  battery sustain levels.

nuckolls.bob(at)cox.net
Guest

Posted: Wed Jun 04, 2008 11:06 am Post subject: SD-8 vs. SD-20 choice

At 05:00 PM 6/4/2008 +0000, you wrote:

 	  Quote: 	
		  

<frank.hinde(at)hp.com>



Oh that makes sense because when I did my IFR test running more equipment 

than I though was possible (i.e right around 12A's worth) the batt volts 

would sag to 12v but it would only give me an alarm (11.8V I think) if I 

hit the transmit on the radio.



I took this to mean I could safely run this level of equipment to my 

destination.


	


    The battery begins to deliver energy at about 12.6 volts

    or so. So if you loaded the system to 12.0 volts, then

    no doubt the battery was carrying part of the total load.

    This is why I set LV Warning devices at 13.0 volts. At this

    level, the alternator may be "overloaded" . . . i.e. unable

    to charge a battery but it's still holding the battery

    in reserve for approach to landing.



    Bob . . .

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