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 Posted: Fri Feb 05, 2010 11:57 am Post subject: Starter engaged light, was Starter and contactor wiring |
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Is this clutch protection found on SkyTec starters with a solenoid rather than a bendix for drive gear engagement? My LED starter warning light has stayed on many seconds after a successful start and made me wonder sometimes - I guess that's a separate issue of back-EMF energizing the solenoid somehow? I don't even have my wiring diagram in front of me at the moment...I should keep quiet and learn something 
Bill B
On Fri, Feb 5, 2010 at 2:15 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 10:04 AM 2/5/2010, you wrote:
| Quote: | --> AeroElectric-List message posted by: "glen matejcek" <aerobubba(at)earthlink.net (aerobubba(at)earthlink.net)>
Hi All-
It's been a while since I went down my decision tree on this topic, and I
might not recall all the details perfectly, but it seems to me that there
are a couple details of 'starter engaged' annunciation that might have been
overlooked. First, it seems to me that the objective is to know whether
there is power on the starter or not, so tapping the fat wire between the
solenoid and the motor would be in order.
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This is how it's done on TC aircraft when the
feature is installed.
| Quote: | This would then annunciate that
there was power to the starter motor itself. It also has the advantage of
monitoring the spin down of the motor. Should the pinion hang and the
motor remain engaged after the solenoid opens, the back emf can keep the
engaged light illuminated.
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Not true. Every starter has an over-run clutch that
prevents back-driving of the motor armature via a
stuck pinion gear. This is especially important for
modern, highly-geared starters where the armature
is already running 4-6000 rpm while cranking the
engine a couple hundred RPM.
Without an over-run clutch, an engine idling at
say 1000 rpm would either over-speed the armature
perhaps to destruction from thrown windings or
commutator bars or stripped gear teeth in the
gearbox.
| Quote: | It might be especially zippy if one were to use
a bi-directional led for the indicator, such that one could perhaps have
amber indicate normal engagement and red to indicate run-on.
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If a starter WERE in a back-drive mode, the polarity
of voltage would not reverse . . . hence the starter-stuck
light would not change colors . . . only get much brighter.
| Quote: | Including a zener diode could clip the spin-down indication during
normal operation while still allowing the run-on indication to
function, should that become desirable.
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An interesting hypothesis but not consistent with
either the physics of motor operations or with the
configuration of starter drive-trains.
Bob . . .
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