Return-Path: Received: from imf21aec.mail.bellsouth.net ([205.152.59.69] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 812973 for flyrotary@lancaironline.net; Sun, 20 Mar 2005 20:19:07 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.152.59.69; envelope-from=ceengland@bellsouth.net Received: from [209.215.63.120] by imf21aec.mail.bellsouth.net (InterMail vM.5.01.06.11 201-253-122-130-111-20040605) with ESMTP id <20050321011821.XKRD20331.imf21aec.mail.bellsouth.net@[209.215.63.120]> for ; Sun, 20 Mar 2005 20:18:21 -0500 Message-ID: <423E20DB.2020903@bellsouth.net> Date: Sun, 20 Mar 2005 19:18:19 -0600 From: Charlie England User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 To: flyrotary Subject: [Fwd: AeroElectric-List: Re: Alternators]] Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Bob's response: (For those who don't know, he's a long time employee of Raytheon, working on both small & big iron.) -------- Original Message -------- Subject: AeroElectric-List: Re: Alternators] Date: Sun, 20 Mar 2005 16:05:48 -0600 From: Robert L. Nuckolls, III Reply-To: aeroelectric-list@matronics.com To: aeroelectric-list@matronics.com --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" At 12:47 PM 3/20/2005 -0600, you wrote: >--> AeroElectric-List message posted by: Charlie England > > >Bob, > >This showed up on another list & some would like to see your comments, >since you are directly involved in certified hardware. I'm pretty sure I >could write more about the inconsistencies here than he's written about >the differences, but I'd also like to see your opinion. I'll post back >to the other list if that's acceptable. > >Thanks, > >Charlie > >Begin quote: > > From Pifer's Airmotive, Inc. Pontiac MI > > DIFFERENCES BETWEEN AIRCRAFT & AUTO ALTERNATORS USING A FORD BELT DRIVEN 12v >OR 24v ALTERNATOR FOR A COMPARISON > > 1. Although alternators are bi-rotational, aircraft engines turn opposite of >automotive. This means cooling fans must be canted in the opposite direction. >Also, pulley and belt size vary due to coming-in speed. An automotive fan looses only 10 percent or so of its cooling efficiency when spun the wrong direction. Van used to sell or recommend an alternator that featured an external cooling fan. He recommended removing it because it turned "the wrong direction". Bad idea. The alternator went from a slightly compromised fan to NO fan. Modern alternators have bi-directional fans and I now believe most have brushes mounted right over the slip-ring shaft center so these alternators can be spun either direction without concerns. > 2. The thru bolts are of a higher tensile strength utilizing an >anti-rotation device in the form of a lock tab. The rectifier assembly has >a heavy duty >diode with higher voltage and amp. capacity. Also, one excites at 90 PIV (Peak >Inverse Voltage) and the other at 150 PIV. Radio suppression is designed for >108 frequencies and up which is the VHF and 108 and down which is FM band. The gentleman may indeed be looking at the specifications for some "certified" alternator. Further, the datasheet may be some revision printed in 1975 . . . It's difficult to know. Radio noise from alternators is not a big issue at VHF comm and nav frequencies. ADF and LORAN are the vulnerable systems. Many (if not all) of the alternators I've seen torn down over the last 5 years have hi-quality filters built in. AM radio receivers are the vulnerable system in cars and it's not difficult to include such filtering in the alternator's basic design. I doubt anyone even makes a diode that won't run at 200 volts plus. This used to be a big deal but it's so easy to craft a diode that nobody worries much about tailoring one for a low voltage application. Thru bolts are NOT an issue. The automotive conversions have run quite well by the thousands of installations over a decade. Certified aircraft alternators crap with regularity. The vast majority of B&C alternators sold over the past 15 years are still running as original installation parts. > 3. The brushes have a higher graphite content and they utilize a tin plate >on the brush leads to prevent corrosion. Bull hocky. Corroded brush leads are the very LEAST of one's concerns for brush life . . . don't know about the "graphite content" and can't imagine why it's an issue on slip rings. > 4. The stator is of the Delta wind rather than the Y" wind and it does not >utilize the stator terminal. The aircraft unit also carries H" insulation >which is capable of 200 degrees centigrade temperatures. It also is rated at >60 amp. instead of 55. Also bull hockey . . . one can wind the stator any way they wish to take advantage of some feature that gives is preference over another. I've read the sand-sifting offered by several folks on this subject but there are alternators wound both ways that perform just fine. Some older airplanes use the center tap "stator" terminal to drive an alternator failure warning system but this is super-antiquated. With a low voltage warning lamp, you can deduce everything the pilot NEEDS to know about altenrator performance whether the thing is Y or Delta wound. > 5. The rotor has a shorter shaft and a smaller thread size. Because of the >opposite rotation it is wound in the opposite direction. Yes, the nuts retaining the pulley on an ND alternator running in an airplane are put on with an impact wrench. Sometimes the pulley is keyed to a flange on the shaft which makes thread direction irrelevant for pulley retention. Alternator shaft torques are so low that clamp up forces on a properly installed nut totally negate any sensitivity to direction of threads. >It also uses "H insulation and Havel varnish. Everybody used class "H" insulation. An automotive alternator is more likely to run at temperature limits than anything on an airplane. Cars don't get the benefits of lower ambient temps and 100+ MPH ram air if needed. > 6. The front and rear housings are the same as automotive. > > With this brief description, I hope I have enlightened you on the >differences between aircraft and automotive alternators. Using automotive >units in an >aircraft creates a potential safety hazard as well as a short alternator life >and unreliability. My sense is that the data being offered is outdated and features offered as uniquely "aircraft" because the product has been spec'd onto somebody's type certificate are overblown or irrelevant to the application. Given the DEMONSTRATED service life of modern automotive alternators on OBAM aircraft and exemplar performance in automobiles, I venture to say that one wouldn't want to put an "aircraft alternator" on a car. They're expensive, fewer folks stock them, even fewer folks have parts for them and they don't last as long. I'd opt for an ND alternator modified to run external regulator for ANY belt driven certified alternator any day. Bob . . . _-======================================================================= _-= - The AeroElectric-List Email Forum - _-= Use the Matronics List Features Navigator to browse the many List _-= utilities such as the Subscriptions page, Archive Search & Download, _-= 7-Day Browse, Chat, FAQ, Photoshare, and much much more: _-= _-= http://www.matronics.com/ListFeaturesNavigator?AeroElectric-List _-=======================================================================