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grant.corriveau(at)TELUS.
Guest

Posted: Wed Jun 11, 2008 11:24 am Post subject: Fwd: Alternator

I got this excellent information from a fellow 601 builder and I pass on the links for everyone's enlightenment (below):



For anyone using an auto-conversion engines, the technical information on this site will be of special interest.  It appears that the ideal alternator rpm to produce near-100% power is about 6,000rpm.  On typical aviation engines this occurs somewhere around the expected redline rpm of those engines.  But my engine revs much higher in cruise.  The data graphs also show alternator temperature as a function of rpm.  So just letting the alternator run significantly faster than it needs too will have a cost in more frequent failures due to heat.

Two other issues arise - the rotation direction of the pulley fan blades for alternator cooling; and the material of the brushes themselves and the rate they wear in the much drier air at altitude vs. ground level.  If I continue to use an automotive alternator, presumably the fan rotation is correct, but if I switch to an aviation model does it become an issue?  As for the brushes, if there is increased wear in the dry air at altitude, I'm sure it will be amplified by excessive rpm in the alternator.  So should I continue with an automotive alternator, maybe changing brushes needs to become a routine annual event?  And alternator replacement a more frequent event as well if the commutator is wearing...

I originally thought it strange that my automotive (rebuilt?) alternator should only last 50 hours.  But after reading this tech stuff, I see that automotive alternators may not hold up well in this application.

What is the experience of similar automotive engine conversions (i.e. Subarus or others that would run about 2500-3,000 rpm in cars, but are now cruising around 4,500-5,500 rpm most of the time).  Are you experiencing alternator failures at higher that expected rates?

Check out this link for good information if nothing else (I am not associated with this product in any way) :



 	  Quote: 	
		   Grant: these alternators are bulletproof in certificated aircraft and light. ...They are lighter, all new, not rebuilt and have taken the certificated world by storm.  Im sure their mounting foot is fairly standard. 

 

 http://www.plane-power.com/

 

 http://www.aircraftspruce.com/catalog/eppages/lightweight_alternator.php 	


 [quote][b]

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Wed Jun 11, 2008 12:33 pm Post subject: Re: Fwd: Alternator

If you need to slow down or speed up your alternator you can always put a different pulley on it. That said you do know who builds most of those "bullet-proof" certified alternators that Lycoming and Cont. install don't you? They are build by companies like Ford and GM.



[quote="grant.corriveau(at)TELUS."]I got this excellent information from a fellow 601 builder and I pass on the links for everyone's enlightenment (below):



For anyone using an auto-conversion engines, the technical information on this site will be of special interest. ï¿½It appears that the ideal alternator rpm to produce near-100% power is about 6,000rpm. ï¿½On typical aviation engines this occurs somewhere around the expected redline rpm of those engines. ï¿½But my engine revs much higher in cruise. ï¿½The data graphs also show alternator temperature as a function of rpm. ï¿½So just letting the alternator run significantly faster than it needs too will have a cost in more frequent failures due to heat.

Two other issues arise - the rotation direction of the pulley fan blades for alternator cooling; and the material of the brushes themselves and the rate they wear in the much drier air at altitude vs. ground level. ï¿½If I continue to use an automotive alternator, presumably the fan rotation is correct, but if I switch to an aviation model does it become an issue? ï¿½As for the brushes, if there is increased wear in the dry air at altitude, I'm sure it will be amplified by excessive rpm in the alternator. ï¿½So should I continue with an automotive alternator, maybe changing brushes needs to become a routine annual event? ï¿½And alternator replacement a more frequent event as well if the commutator is wearing...

I originally thought it strange that my automotive (rebuilt?) alternator should only last 50 hours. ï¿½But after reading this tech stuff, I see that automotive alternators may not hold up well in this application.

What is the experience of similar automotive engine conversions (i.e. Subarus or others that would run about 2500-3,000 rpm in cars, but are now cruising around 4,500-5,500 rpm most of the time). ï¿½Are you experiencing alternator failures at higher that expected rates?

Check out this link for good information if nothing else (I am not associated with this product in any way) :



 	  Quote: 	
		   Grant: these alternators are bulletproof in certificated aircraft and light. ...They are lighter, all new, not rebuilt and have taken the certificated world by storm.ï¿½ Im sure their mounting foot is fairly standard.ï¿½

 

 http://www.plane-power.com/

 

 http://www.aircraftspruce.com/catalog/eppages/lightweight_alternator.php 	


  	  Quote: 	
		  [b]

- The Matronics Zenith-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Wed Jun 11, 2008 12:56 pm Post subject: Fwd: Alternator

I have over 230 hours on my Subaru powered Zodiac with no trouble with  

the automotive type alternator. Most aircraft alternators are just  

automotive alternators with a more extensive paper trail.



As far as alternator RPM is concerned, the RPM of the alternator will  

be the same as engine RPM only if both pulleys are the same size.  

Typically, the pulley on the engine is larger than the one on the  

alternator so the alternator runs faster than the engine. The speed  

ratio is the same as the diameter ratio. I don't know if my alternator  

is the same as the original Subaru unit or if the drive ratio is the  

same. It came with the engine from Stratus. The pulleys may have been  

selected to give the proper RPM for the expected cruise RPM of the  

engine.



On Jun 11, 2008, at 3:21 PM, Grant Corriveau wrote:



 	  Quote: 	
		   For anyone using an auto-conversion engines, the technical  

 information on this site will be of special interest.  It appears  

 that the ideal alternator rpm to produce near-100% power is about  

 6,000rpm.  On typical aviation engines this occurs somewhere around  

 the expected redline rpm of those engines.  But my engine revs much  

 higher in cruise.  The data graphs also show alternator temperature  

 as a function of rpm.  So just letting the alternator run  

 significantly faster than it needs too will have a cost in more  

 frequent failures due to heat.



 Two other issues arise - the rotation direction of the pulley fan  

 blades for alternator cooling; and the material of the brushes  

 themselves and the rate they wear in the much drier air at altitude  

 vs. ground level.  If I continue to use an automotive alternator,  

 presumably the fan rotation is correct, but if I switch to an  

 aviation model does it become an issue?  As for the brushes, if  

 there is increased wear in the dry air at altitude, I'm sure it will  

 be amplified by excessive rpm in the alternator.  So should I  

 continue with an automotive alternator, maybe changing brushes needs  

 to become a routine annual event?  And alternator replacement a more  

 frequent event as well if the commutator is wearing...



 I originally thought it strange that my automotive (rebuilt?)  

 alternator should only last 50 hours.  But after reading this tech  

 stuff, I see that automotive alternators may not hold up well in  

 this application.



 What is the experience of similar automotive engine conversions  

 (i.e. Subarus or others that would run about 2500-3,000 rpm in cars,  

 but are now cruising around 4,500-5,500 rpm most of the time).  Are  

 you experiencing alternator failures at higher that expected rates?


	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

- The Matronics Zenith-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Zenith-List

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

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