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Date: Sun, 20 Dec 2009 13:05:51 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Real Life No Alternator test
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Worn brushes would likely cause a lowered voltage, since the brushes 
carry 'excitation' current to the field. Lower field voltage = lower 
output voltage.

Try adding a 2nd voltmeter that directly measures the voltage on the 
'sense' terminal on the regulator. If voltage there is the same as your 
buss voltage (and too high), that is a strong indicator that the 
regulator is bad or out of adjustment.

Charlie

On 12/20/2009 11:49 AM, David Leonard wrote:
> HI Al, yes, I have been considering that.  My field is external like 
> yours.  In that supply I have a 10amp fuse and the switch itself, 
> along with the necessary crimps on the spade connectors.  I suppose I 
> could tryed a temporary short across those connections to see if that 
> that fixed the problem, but it did not.  Also voltage measured at the 
> field is the same as on my engine monitor.
> I wonder if we are wearing out the brushes more quickly because of our 
> high continuous RPM.
> -- 
> David Leonard
>
> Turbo Rotary RV-6 N4VY
> http://N4VY.RotaryRoster.net
> http://RotaryRoster.net
>
>
> On Sun, Dec 20, 2009 at 7:55 AM, Al Gietzen <ALVentures@cox.net 
> <mailto:ALVentures@cox.net>> wrote:
>
>     Dave;
>
>     Regarding the varying, or higher charging voltage, I’ve had
>     similar behavior.  I’ve determined that a possible cause is the
>     difference where you are measuring the voltage, and what the
>     regulator is seeing.  I provide the field current from a separate
>     source, having undone the internal connection from the alternator
>     output. You may have a similar setup. That means that any
>     resistance – voltage drops – from the battery to the alternator
>     field, will result in the regulator seeing a lower voltage, and
>     increasing the output.
>
>     I have two potential contact resistance points in that circuit;
>     the battery contactor, and a pullable breaker that I use to
>     turnoff the field current if I want.  A couple of weeks ago when I
>     started up the voltage (at the EM2) was reading over 15V, and
>     triggering the over limit light.  After a couple of resets of the
>     breaker, and a couple of shutdowns (turning off battery
>     contactor), the voltage settled down at 14-14.5.
>
>     I’m not fully convinced the contacts were the problem, but I think
>     it likely.  May be relevant to your situation.
>
>     Early this year I had replaced the voltage regulator after seeing
>     high voltage.  Next time I’ll replace the pullable breaker or the
>     battery contactor.
>
>     (I bet the skiing at mammoth was great, and the weather beautiful.)
>
>     Al
>
>     -----Original Message-----
>     *From:* Rotary motors in aircraft
>     [mailto:flyrotary@lancaironline.net
>     <mailto:flyrotary@lancaironline.net>] *On Behalf Of *David Leonard
>     *Sent:* Saturday, December 19, 2009 5:52 PM
>     *To:* Rotary motors in aircraft
>     *Subject:* [FlyRotary] Real Life No Alternator test
>
>     I have been having an intermittent and slowly worsening problem
>     with high voltage.  Over most of the last 30 hrs or so it settled
>     in around 14.6 or 14.7 volts.  But on yesterday's flight home from
>     Mammoth I noticed it hovering around 15V and some of my avionics
>     were acting up, so I decided to do a little alternator out experiment.
>
>     I turned off the alternator and all unnecessary draw - radio,
>     strobes, Blue Mountain EFIS, electric AI.  I kept on the engine
>     instrumentation, transponder, music (a most critical item given
>     the beauty of the sunset), audio panel, rocky mountain
>     microencoder, and trio auto pilot (also allowing me to more fully
>     enjoy the flight). I was showing 8 amps to run the engine bus
>     (coils and injectors).
>
>     With my 33 amp hour Panasonic SLA battery I flew for 45 minutes
>     and 200 miles over the Sierras, passing dozens of airports, and
>     into the LA basin before it got dark enough that I decided to turn
>     the lights on.  The plan was to turn the alternator back on when
>     the voltage dropped below 11.5 volts but it never dropped below
>     11.9V.  It did charge at a brisk 60amps when I turned the
>     alternator back on so there couldn't have been too much time
>     left.  Still, that did quite a bit of confidence building
>     regarding the ability to carry on in the event of an alternator
>     failure.
>
>     I also set a personal record for the most beautiful and clear
>     sunset I have seen while flying.  I could see San Nicholas Island
>     from over 150 miles away.
>
>     Time to install a spare alternator.
>
>
>     -- 
>     David Leonard
>
>     Turbo Rotary RV-6 N4VY
>     http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/>
>     http://RotaryRoster.net <http://rotaryroster.net/>
>
>
>
>