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SD-8 Self Exciting via Z25L

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andymeyer

Joined: 31 Mar 2015
Posts: 54
Location: SW MI

Posted: Sun Feb 26, 2023 4:28 pm Post subject: SD-8 Self Exciting via Z25L

I am setting up the regulator and components from Z25L for a self exciting SD-8 to support backup power for my second ignition and backup power for the aircraft E-Bus. 



One option is to screw this stuff to an Aluminum plate and let it hang out in the air - another is to 3D print an enclosure for everything. Question is how much heat do I have to deal with and what's the fire risk of these components if I have it running full tilt (not likely in my configuration, but...)



I'm not seeing more than a watt from the resistors if my math is right. How much heat from the regulator and diode bridge?

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chaskuss(at)yahoo.com
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Posted: Mon Feb 27, 2023 4:51 am Post subject: SD-8 Self Exciting via Z25L

The SD-8 produces power whenever it is moving. The faster it rotates, the more power it creates. The issue is shedding that power [which is converted to heat] when it isn't needed. So max heat is created at normal cruise power to max [2700] RPMs, when the unit's power is not required [normal operations]. That means you need max ability to shed heat 98% of the time. Better to keep the voltage control device out in the open on a large heat sink [aluminum plate]

Classic British motorcycles use this same sort of alternator and voltage control. Check out the large aluminum plates used to mount the drivers footpegs in the photo linked below [1975 Norton 850 Commando Mk III] The voltage control devices [Zener diodes] are mounted to the back side of these plates

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user9253

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

Posted: Mon Feb 27, 2023 8:32 am Post subject: Re: SD-8 Self Exciting via Z25L

It seems that you are saying that the voltage regulator for the SD-8 is

a shunt type.  Is there any documentation to support that?

Most modern voltage regulators for permanent magnet alternators are

the switching type.  They open the output for part of the AC cycle.  The 

power produced is determined by the connected load, provided that the 

permanent magnet alternator is spinning fast enough to maintain the voltage.

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 28, 2023 6:21 am Post subject: SD-8 Self Exciting via Z25L

At 06:28 PM 2/26/2023, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "andymeyer" <meyerkc135(at)gmail.com>



 I am setting up the regulator and components from Z25L for a self exciting SD-8 to support backup power for my second ignition and backup power for the aircraft E-Bus. 



 One option is to screw this stuff to an Aluminum plate and let it hang out in the air - another is to 3D print an enclosure for everything. Question is how much heat do I have to deal with and what's the fire risk of these components if I have it running full tilt (not likely in my configuration, but...)



 I'm not seeing more than a watt from the resistors if my math is right. How much heat from the regulator and diode bridge? 	


    This isn't a 'fire risk' . . . it's a risk of

    regulator failure. The SD-8 stock regulator is

    a 4-component, bridge rectifier, SERIES switch

    configuration that rejects something on the order

    of 30 watts at full load.



    The power-path components depend on thermal

    conductivity of the potting compound for heat

    rejection. The rectifier/regulator's service

    life is tied to optimizing thermal management.



    I've been considering an instrumented

    thermal study on this device but that's

    pretty far down on the to-do list right

    now.



    B&C installation instructions should be

    followed . . . when in doubt, calling

    B&C directly with such questions is a far

    more reliable than consulting folks

    who have no personal knowledge of the

    product construction and performance.



    They're really nice and helpful folks

    who enjoy hearing from their customers. 



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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user9253

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

Posted: Fri Mar 03, 2023 12:24 pm Post subject: Re: SD-8 Self Exciting via Z25L

I asked B&C about their voltage regulators for permanent magnet alternators.  Below is their reply:



The PMR1C is indeed a switching series regulator.



(The) AVC1 regulator, designed as a replacement for the PM Ducati regulator

 used on Rotax 912/914 engines, is (in contrast) a shunting device.

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Joe Gores

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