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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-381776@logan.com>
Subject: Re: [FlyRotary] alternator connections
Date: Fri, 27 Aug 2004 23:07:06 -0400
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Paul, with the stock Mazda alternator (can't speak for all), the idiot light
circuit provides the "bootstrap" voltage to the alternator to provide
sufficient magnetic field that the alternator can start generating its own
voltage.  Once this happens the idiot light circuit is no longer needed for
the alternator to produce power (until you shut it down and need to start it
again).

Here is where folks have gone wrong.  The Mazda circuit actually has a relay
and a diode between the voltage source and the alternator.  The light itself
is activated by the relay and is not directly in the link.  Where folks have
gone wrong, it they eliminated the relay and just inserted a light bulb (or
LED).  The LED generally drops too much voltage for it to work in the
circuit.  A filament bulb will work - UNTIL it burns out then you have no
alternator (you're probably OK if you engine is running when it goes out as
the alternator will keep producing voltage/current).  However, the
alternator will not start up again until the bulb is replaced.

So, my suggestion is to find any 12V relay meant for an automobile (I got
mine from Radio Shack - but, that was years ago).  I think they may have
them in the car Audio parts section.  I then got a 16-18volt diode capable
of handling 1 amp ( probably don't need that high a rating - but I've never
measure the current draw).

Hook up the relay and the diode in series such that the base of the diode
(generally marked with a colored band on the base end of the diode) is
hooked up toward the alternator.  With the alternator not turning, current
will flow through the relay and diode to the alternator.  This will cause
the relay to close (and if you have hooked up a light OR LED in this case -
since they are not directly in the idiot light circuit) cause the bulb to
light.  When the alternator starts producing its own voltage (engine
spinning it), it produces a positive voltage at the base of the diode which
causes it to stop conducting current, the relay opens and the idiot light
goes out.

Hope this helps

ED

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message ----- 
From: "paul" <sqpilot@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, August 27, 2004 10:07 PM
Subject: [FlyRotary] alternator connections


> Hi, fellow rotary enthusiasts.....I know this has been discussed before,
but
> I wasn't smart enough to save the critical information.  I have the stock
> alternator installed, and I have one wire (2/0 gage) going from the
> alternator to the battery (for charging), and the field is excited via a
> toggle switch on my EXP buss that turns the alternator on by supplying 12
> volts to it on one of the small wires on the alternator.  The third wire
is
> for the idiot light.  If I recall correctly, this needs to be hooked up to
> an idiot light for the alternator to work properly?
>       I was hoping not to have to go to through the efforts of running a
> wire all the way up to my instrument panel. (I have an engine monitor that
> will tell me if the voltage falls below any preset value), so I was
thinking
> maybe I could just install a very short wire and put a light or ? just
> inside of the firewall. (a pusher configuration).  I'm assuming I can just
> run this wire to a small light bulb socket, and connect the other wire
that
> comes out of the light bulb socket directly to ground?  Of course, if
anyone
> else has found any substitutions for the light, for instance an LED or ?
I
> would sure appreciate that info.   Thanks in advance for your replies.
Paul
> Conner, 13b powered SQ2000 canard.
>
>
>
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>