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12-18-2010, 09:02 PM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Is the Alternator Switch an Antique?
We are currently working on the switch list for the new RV-3, and I am beginning to think that I am ready to get rid of the alternator field switch. I figure that, at the very least, the idea should be able to generate some ?interesting? discussion?
Here?s the deal. I am quite happy with the ND internally regulated alternators that were, for years, supplied in the FWF kits, and are easily obtained at most auto parts stores. I like the fact that they can be picked up easily in an emergency away from home, and quite frankly, I have never had an airplane alternator (certified or not) last as long ? as long as you operate them the way they were designed. This means that you don?t want to switch them on or off while they are spinning. (I didn?t come up with this little gem of wisdom ? search the archives for alternator posts by GMCJETPILOT). This argument makes sense when you consider the sudden load that can hit the diode/regulator pack if you switch it while the rotor is going full tilt. In automotive use, they don?t have ?pilot? controlled switches, after all.
When I built my -8, I put in a Cessna split master, like many folks did. I brought the alternator on line after engine start. That alternator lasted a few hundred hours before the VR started to ?wander? a bit. I replaced it with a rebuilt unit, decided never to switch it while turning and that was about 800 operational hours ago. We have had similar experience with Louise?s RV-6. The bottom line is that the way the field power is wired is with a circuit breaker and switch in series. If the ONLY time you?re going to switch the alternator off is in a failure condition, then you could easily do that by pulling the breaker. The added benefit is that you are less likely to accidently turn it off without a switch there in a row with the other normally operated switches.
So in summary, I see two good reasons to delete the switch - less chance of accidental activation and the saving of critical panel space (the -3 is a small cockpit). I can?t see any real downside to it.
Relevant thoughts? And no, I am not planning on going with a B&C or PP alternator this time around?.
Paul
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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12-18-2010, 09:20 PM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,768
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I agree.
I used to have an "alternator" switch and like you, I switched it on after start. Alternators lasted a few hundred hours. I removed the switch and replaced it with an "Idiot light", and my alternator failure problem went away.
__________________
Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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12-18-2010, 09:25 PM
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Join Date: Aug 2007
Location: Wichita Falls, TX
Posts: 2,182
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Personally, I think the most value in an alternator field switch (or pullable breaker or toggle breaker) with today's modern internally regulated alternators (e.g. the ubiquitous Plane Power lightweight units used in so many RVs) is that if something does wrong with the alternator, you can easily disconnect the juice from the field coil to kill the circuit in an emergency. A simple pullable breaker is probably the cheapest and lightest weight way of accomplishing this.
EDIT: I put a toggle breaker in the RV-8 when it was built and after reading numerous stories of short alternator life, and after my friend lost his new alternator in his new RV-10 after less than 50 hours (regulator shorted and it was overcharging), I've just simply started leaving the alternator field toggle breaker turned on all the time now. My friend with the RV-10 does the same now and has had no more alternator problems either.
Edit #2: And speaking of antiques, my old Cherokee has no separate alternator switch from the factory. When the old fashioned DPDT master switch is turned on, one side of it switches on the field circuit to the alternator before the engine ever turns, and the ancient Chrysler alternator in the plane was been working just fine for more than 2000 hours (it was upgraded from generator to alternator long before the current engine overhaul was ever done and the current engine is now at mid-time). So yep, I agree that having a separate switch plus a pullable breaker for the field circuit is a waste.
__________________
Neal Howard
Airplaneless once again...
Last edited by Neal@F14 : 12-18-2010 at 09:41 PM.
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12-18-2010, 09:37 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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Externally regulated = Switch is good (my preference)
Internally regulated = No need for a switch, on all the time.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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12-18-2010, 09:44 PM
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Join Date: Apr 2005
Location: KSLC
Posts: 4,021
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The alternator field draws current. If I have the master switch on, to program the GPS, or whatever............I'd prefer to have the alternator field off. I'm not sure how much current it draws, but it's enough to make a noticeable swing on the ammeter.
L.Adamson --- RV6A
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12-18-2010, 09:50 PM
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Join Date: Feb 2007
Location: League City, TX
Posts: 595
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If you have a Cessna split master... Frame it!
Paul-
Over 10 years on my -8 using a DPDT master switch (master relay/alt field) with a circuit breaker in series on the alt field side. Never a problem and I will be using the same architecture on my -3. I agree with your thinking and my experience suggests that it provides trouble free operation. While I've got you on the line, the photos of you and Louise celebrating the arrival of your Mattituck Red/Gold are PRICELESS!
Edit: -8 =B&C externally regulated / -3 =Plane Power
__________________
R. E. "Ernie" Butcher
Friends of the RV-1/Eagle's Nest Projects
"Mentors build the student...
Students build the airplane." -Glen Salmon
Dedicated to the historical preservation of the RV-1 Aircraft
and organized for the purposes of promoting, supporting,
fostering, and engaging in aviation and aerospace education.
www.RV-1.org
www.EaglesNestProjects.org
Last edited by Special Delivery : 12-18-2010 at 10:05 PM.
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12-18-2010, 10:00 PM
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Join Date: Aug 2007
Location: Wichita Falls, TX
Posts: 2,182
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Pullable breakers...
Another thought... if I was wiring up the RV-8 all over again, I think this time I'd probably choose the cheaper, lighter, more compact Klixon pull breakers instead of the expensive, heavy Tyco units we bought. Probably could've saved a couple pounds of weight... but at the time those heavy duty Tyco breakers looked rugged and cool, like they belonged in a military aircraft.
__________________
Neal Howard
Airplaneless once again...
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12-19-2010, 05:31 AM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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I see no reason to have a separate alternator switch. I've got a three position Battery Master/Alternator switch on my RV-8. The mid position is Battery Master ON and Alternator OFF. But, there is no practical need for that mid position, as I can kill the alternator if needed by pulling the field CB. My GPS is on an Essential Bus that can be powered by a toggle switch, so I don't need to throw the Battery Master to program the GPS.
Go with the simple, light and cheap solution. Ditch the alternator switch.
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12-19-2010, 06:59 AM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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It's always nice to get a consensus that confirms my own opinion!
I always use pullable breakers (Yes, the Klixon's are light and compact, and I love 'em) because it gives me more control, especially in a Technically Advanced Airplane where I frequently power cycle components when doing maintenance and software updates. Since they rarely (if ever) get cycled in flight, I can save the weight and failure modes of a switch, and use the breaker for this occasional function.
I am going to do the same thing with the alternator switch - the breaker will serve the function just fine.
Paul
(And yes Ernie, I still walk out to just look at the engine every day....  )
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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12-19-2010, 07:23 AM
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Join Date: Apr 2008
Location: Indianapolis, IN
Posts: 1,069
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I am quite happy with the ND internally regulated alternators that were, for years, supplied in the FWF kits, and are easily obtained at most auto parts stores.
I am interested in these alternators, which brand and auto parts store can they be found?
__________________
Ryan Allen, CFII
RV7 N612RA, flying since july 2012
E-170/175
RV10 Tail Kit complete, Wings 90%, fuse on order
Acro Sport 2, building
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