Aaron Coolidge wrote:
: Cory, it sounds like this is the 2 starter contactor situation like I
: mentioned. The jumper wire he's referring to goes between the solenoid and
: the PM motor itself.

I found a link to the graphic on Skytec's web page. One that says, "This is
for certified aircraft, this is for experimental." The experimental version is more
like an automotive setup... starter switch runs solenoid. The certified version
switches the main power.

: I liked your idea about a freewheeling diode, but you'd need a series diode
: on the input to the PM motor too (to keep the voltage in the PM motor to
: freewheeling diode circuit). I wouldn't worry about the current handling
: capacity here, 600 A diodes are easy to get, but the Vf of the diode would
: probably be like 1.0V. When cranking the voltage at the PM motor is probably
: only about 6 or 7 V (piper uses a 6V contactor for the starter) so 1V
: lost in the diode is a large fraction of the available power!
: --
: Aaron Coolidge

I'm going to look into modifying the system. By running the jumper wire from
the firewall starter relay's *input* to run the starter solenoid as well, that would
accomplish the same thing. A big current diode could then free-wheel the motor by
itself (no need to be in series... use the starter solenoid contactor for that). I've
contacted Skytec to see if they've every field-approved such a modification. I
understand why they don't do that for all the installations. It would have to be
tested/certified on every airframe/engine combination. If they rig it just enough to
work adequately as the one they replace, they can PMA it and it automatically works on
everything. It may not be optimal, but it works.

We'll see how it goes.
-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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