Matronics Email Lists :: View topic - Z-17 battery/ alternator switch

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

Z-17 battery/ alternator switch

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

jpoint(at)wi.rr.com
Guest

Posted: Tue Mar 07, 2017 4:53 am Post subject: Z-17 battery/ alternator switch

All,



I'm building a simple day/ VFR airplane with Z-17 as the basis for my 

electric system.  I noticed that the battery/ alternator switch is a 

two-throw switch wired as "Off-battery-alternator", presumably to be 

able to start on battery power and bring the alternator online once the 

engine is running.  Other drawings (Z-13/8 for example) use a simple 

single-throw switch to bring battery and alternator on together.  I've 

flown with a Z-13-type system in my RV-6 for 13 years so I have faith in it.



Why the different switch design in Z-17?  Is there something about the 

PM dynamo alternator that requires it to be off during engine start?  Is 

it because Z-17 doesn't use a master contactor? Would there be any harm 

in starting with the PM alternator online?



Thanks



Jeff Point



Milwaukee WI

rene(at)felker.com
Guest

Posted: Tue Mar 07, 2017 5:11 am Post subject: Z-17 battery/ alternator switch

I always thought that the reason for split switches, etc, was so you could turn off the alternator without turning off the battery.  I always start with the alternator on.......just my 2 cents.



--

user9253

Joined: 28 Mar 2008
Posts: 1920
Location: Riley TWP Michigan

Posted: Tue Mar 07, 2017 5:46 am Post subject: Re: Z-17 battery/ alternator switch

 	  Quote: 	
		  Would there be any harm in starting with the PM alternator online? 	
No, in fact that is common practice and is recommended.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Mar 07, 2017 8:48 am Post subject: Z-17 battery/ alternator switch

At 07:46 AM 3/7/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 

 > Would there be any harm in starting with the PM alternator online? No, in fact that is common practice and is recommended. 	


    Actually, it's six-of-on, half-dozen-of-the-other.

    A bit of history:



 The first electrical systems to be installed on aircraft

 used generators . . . just like the ones on cars, tractors

 and trucks. These were simply shunt wound, DC MOTORS being

 PUSHED with mechanical energy into the shaft such that they

 became GENERATORS.



 They required rather sophisticated regulators that not

 only maintained the target bus voltage but limited

 output current (to prevent commutator and armature

 over-heat) and provided reverse current disconnect

 so that a NON rotating generator did not revert to

 it's roots as a motor and run the battery down after

 the engine stopped. These electro-mechanical analogs

 to modern electronics are exceedingly clever creations

 of the era.



 [img]cid:.0[/img]



 Generators were self-exciting (meaning that they would come

 on line with a simple input of mechanical energy (engine running)

 and flipping the field supply switch to ON. Further, they

 would run well without a battery on line.



 Modern starter-generators on turbine aircraft retain traits

 of their ancestors and they too run well without having a

 battery on line.



 Hence, aircraft with any form of generator will generally

 have BOTH battery master and generator control switches.

 Interestingly enough, the Beech Bonanza STILL has independent

 BATTERY and ALTERNATOR switches . . . which is another

 story.



 When we started putting alternators on TC aircraft (mid 60s)

 it was discovered that (1) the alternators did not self

 excite at ramp idle rpm and (2) voltage regulation dynamics

 were not as comfortable as the generators being replaced.

 Cessna (and others) were 'upgrading' the panel styles to incorporate

 rocker switches.



 Cessna approached Carling to supply a split-rocker switch that

 would (1) provide battery and alternator control in one device,

 (2) allow battery only operations and (3) prevent alternator

 only operations.



  http://tinyurl.com/zbo3yg6



 Nowadays, many if not most alternators will self excite at

 less than cruise rpms . . . voltage regulation dynamics

 are improved too . . . so it is less problematic to consider

 alternator-only ops. Given the inherent reliability of

 the artfully maintained battery, there is really no demontrable

 value in planning to accommodate alternator only ops . . . but

 it is not outside the realm of possibility . . . indeed, the

 POH for Bonanzas (and I think Barons) speak to this option.



 Now, how about the differences between the single-throw and

 three-throw options depicted in the Z-figures?



 EITHER approach is perfectly satisfactory. The single throw

 switch prevents alternator-only ops while a PULLABLE circuit

 breaker offers a means for breaking alternator field supply

 for battery-only ops on the ground. The three throw switch

 emulates the split-rocker switch functionality and design

 goals adopted by the TC aircraft guys . . . a philosophy

 that persists to this day.



 MYTHBUSTING: In some circles it has been believed and taught

 that turning an alternator ON/OFF while the engine is running

 is a bad thing . . . puts lots of stresses on shafts, shear

 couplings, gear trains, etc. etc. It has also been reputed

 to induce radio zapping transients into the electrical system.



 In a word . . . HOGWASH.



 I've spent hundreds of hours evaluating alternator/battery/

 airplane symbiosis in both in the lab and on airplanes. I've

 conducted, witnessed and instrumented hundreds of switching

 combinations of battery, alternators and system loads under

 the full constellation of conditions.



 There is no foundation in physics or practice for the admonition

 to start the engine with the alternator switch ON. Leaving

 it OFF does relive the battery of about 3A of parasitic load

 during cranking . . . a trivial concern.



 The short answer: Use which ever MASTER DC PWR switch

 philosophy floats ur boat. Either will perform as advertised.



 

 

   Bob . . .

3aa67d9.jpg

Description:

Filesize:

142.7 KB

Viewed:

9060 Time(s)

stuart(at)stuarthutchison
Guest

Posted: Tue Mar 07, 2017 3:03 pm Post subject: Z-17 battery/ alternator switch

Why is it recommended Joe?



Kind Regards, Stu



Sent from my iPhone



 	  Quote: 	
		   On 8 Mar 2017, at 00:46, user9253 <fransew(at)gmail.com> wrote:

 

 

 

 

> Would there be any harm in starting with the PM alternator online? 

 No, in fact that is common practice and is recommended.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=466963#466963

user9253

Joined: 28 Mar 2008
Posts: 1920
Location: Riley TWP Michigan

Posted: Tue Mar 07, 2017 6:11 pm Post subject: Re: Z-17 battery/ alternator switch

Recommended so that the pilot does not forget to turn it on.

_________________
Joe Gores

stuart(at)stuarthutchison
Guest

Posted: Wed Mar 08, 2017 3:28 am Post subject: Z-17 battery/ alternator switch

Thanks Joe.



I’d be interested to know yours and Bob's thoughts on the legitimacy of an article I read in the club house a few years back.



The author explained that aeroplane alternators seem have a higher rate of failure compared to motor vehicle alternators that are also more commonly subjected to mud, water and dust ingress.  His reasoning was that in a car the alternator field is isolated during the start sequence (as are the lights and most other power hungry devices that add to the battery load) until the key is released to its normal position.  By contrast, when cranking an aeroplane engine with the alternator field excited, the voltage regulator senses a substantial sag in bus voltage and attempts to draw max output from the alternator to fix the problem before the alternator has sufficient RPM to provide the required output.  I reasoned that this was why some manufacturers have split or separate alternator switches.  Any truth to this concept then?



Cheers, Stu

 	  Quote: 	
		   On 8 Mar 2017, at 13:11, user9253 <fransew(at)gmail.com> wrote:

 

 

 

 Recommended so that the pilot does not forget to turn it on.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=466988#466988

jpoint(at)wi.rr.com
Guest

Posted: Wed Mar 08, 2017 4:55 am Post subject: Z-17 battery/ alternator switch

Thanks for the detailed answer Bob, that makes a lot of sense.  One of 

my design goals is to keep the switch position and function as similar 

as I can to my other airplane, especially the power and ignition 

switches.  A single throw it will be.



Jeff Point

user9253

Joined: 28 Mar 2008
Posts: 1920
Location: Riley TWP Michigan

Posted: Wed Mar 08, 2017 7:33 am Post subject: Re: Z-17 battery/ alternator switch

 	  Quote: 	
		  Thanks Joe. I’d be interested to know yours and Bob's thoughts on the legitimacy of an article I read in the club house a few years back. 	
I am no expert on alternators.  But it would seem to me that maximum field current for several seconds should not cause premature failure.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Mar 08, 2017 9:15 am Post subject: Z-17 battery/ alternator switch

 	  Quote: 	
		  The author explained that aeroplane alternators seem have a higher rate of failure compared to motor vehicle alternators that are also more commonly subjected to mud, water and dust ingress.  His reasoning was that in a car the alternator field is isolated during the start sequence (as are the lights and most other power hungry devices that add to the battery load) until the key is released to its normal position.  By contrast, when cranking an aeroplane engine with the alternator field excited, the voltage regulator senses a substantial sag in bus voltage and attempts to draw max output from the alternator to fix the problem before the alternator has sufficient RPM to provide the required output.  I reasoned that this was why some manufacturers have split or separate alternator switches.  Any truth to this concept then? 	


   "higher rates of failure" is not very descriptive

   of cause and effect. While it's true that some

   alternators in aircraft have been problematic,

   most of my encounters have been grounded in

   design or manufacturing defect. We used to break

   a lot of brackets on some installations. Piper's

   love affair with the Chrysler 'pancake' alternators

   led to short service life on attach brackets. An

   alternator I conducted failure analysis on a

   few months back had press fit diodes pushed into

   oversized holes at odd angles using a hand-tool

   as opposed to the recommended hydraulic press.



 

 [img]cid:.0[/img] 



   The diodes were deprived of good heat sinking and in

   some cases, good electrical conductivity.



   The last task I mounted in TC aviation concerned alternators

   that wouldn't stay on line . . . a problem I'd worked at

   least two previous times over 30 years. Focus

   of the investigation was on alternators that had

   demonstrated problems over the years, but in this case

   it was the regulator's o.v. sense system that was

   overly sensitive to normal brush noise from this

   alternator . . . they struggled for weeks to "filter"

   the field leads (with limited success) while in fact,

   it was the regulator that needed to be changed out.



   At the same time, alternators supplied by B&C (and

   no doubt others) have an exceedingly low return

   rate.



   The hypothesis offered in the article is without

   foundation in physics or practice. If the author

   went to the lab, he would not be able to reproduce

   a failure by duplication of conditions cited in the

   hypothesis.



   It's all physics. For every failure there IS a

   combination of conditions leading up to that failure.

   Proper operations of switches by crew are exceedingly

   unlikely to be in the chorus of conditions. Joe is

   correct, a few seconds of full-field operation is

   of no particular hardship on an alternator.



 

 

   Bob . . .

8e94c69.jpg

Description:

Filesize:

153 KB

Viewed:

9017 Time(s)

stuart(at)stuarthutchison
Guest

Posted: Thu Mar 09, 2017 4:29 am Post subject: Z-17 battery/ alternator switch

Thanks Joe & Bob.

I’ve bought lots of parts from B&C, but in this case my PlanePower 70A (internally regulated) also seems very well made, with cooling air intake through the windings, hot air extracted by fans at both front and back ends, plus a ram-air cooling duct directly targeting the potted regulator.



The mounting brackets are very solid too, so hopefully the drive belt is the only part I’ll ever have to replace.



V/R, Stu



 	  Quote: 	
		  On 9 Mar 2017, at 04:12, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

     	  Quote: 	
		  The author explained that aeroplane alternators seem have a higher rate of failure compared to motor vehicle alternators that are also more commonly subjected to mud, water and dust ingress.  His reasoning was that in a car the alternator field is isolated during the start sequence (as are the lights and most other power hungry devices that add to the battery load) until the key is released to its normal position.  By contrast, when cranking an aeroplane engine with the alternator field excited, the voltage regulator senses a substantial sag in bus voltage and attempts to draw max output from the alternator to fix the problem before the alternator has sufficient RPM to provide the required output.  I reasoned that this was why some manufacturers have split or separate alternator switches.  Any truth to this concept then? 	
   "higher rates of failure" is not very descriptive   of cause and effect. While it's true that some   alternators in aircraft have been problematic,   most of my encounters have been grounded in   design or manufacturing defect. We used to break   a lot of brackets on some installations. Piper's   love affair with the Chrysler 'pancake' alternators   led to short service life on attach brackets. An   alternator I conducted failure analysis on a   few months back had press fit diodes pushed into   oversized holes at odd angles using a hand-tool   as opposed to the recommended hydraulic press.  <8e94c69.jpg>    The diodes were deprived of good heat sinking and in   some cases, good electrical conductivity.   The last task I mounted in TC aviation concerned alternators   that wouldn't stay on line . . . a problem I'd worked at   least two previous times over 30 years. Focus   of the investigation was on alternators that had   demonstrated problems over the years, but in this case   it was the regulator's o.v. sense system that was   overly sensitive to normal brush noise from this   alternator . . . they struggled for weeks to "filter"   the field leads (with limited success) while in fact,   it was the regulator that needed to be changed out.   At the same time, alternators supplied by B&C (and   no doubt others) have an exceedingly low return   rate.   The hypothesis offered in the article is without   foundation in physics or practice. If the author   went to the lab, he would not be able to reproduce   a failure by duplication of conditions cited in the   hypothesis.   It's all physics. For every failure there IS a   combination of conditions leading up to that failure.   Proper operations of switches by crew are exceedingly   unlikely to be in the chorus of conditions. Joe is   correct, a few seconds of full-field operation is   of no particular hardship on an alternator.  

   Bob . . .

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