Message-ID: <00d301c33610$b32f3d20$0b3cfea9@new>
From: "Peter Cowan/Lexy Cameron" <cowcam@pipcom.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2434991@logan.com>
Subject: Re: [FlyRotary] Re: Starter Problem
Date: Wed, 18 Jun 2003 23:13:03 -0400
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> > The referenced article states that current through the starter switch
> >  >will
> >  >be somewhere between 25-35 amps.  Most switches I've seen are rated at
> >  >10-15 amps.  Pegasus Auto Racing, Inc. has a 40 amp push-button
starter
> >  >switch (p/n 4546) for $8.99, if that's what you
> >  >prefer.   http://www.pegasusautoracing.com/pdfs/047.pdf
>
> The rather long and small diameter wire that makes up the solenoid
windings
> limit current flow in two ways. Plain resistance and inductive reactance.
The
> closing of the starter button applies power to this coil. The current flow
> generates a flux field (that makes the armature move) and the expanding
flux field
> cuts through those same windings and in doing so, generates a current flow
> that opposes the battery generated current flow. So, that the current flow
> increases very slowly
> (in electrical terms) .
>
> There would seldom be any damage from latching up the solenoid. However,
> since the solenoid is a coil of many turns with a fully developed flux
field
> expanded through it, when you release the starter button, that flux field
collapses
> and this solenoid coil acts exactly like the ignition coil. Now the
> collapsing flux field re-cuts all of the coil windings in a very short
period, and
> starts an arc across the slowly (in electrical terms) opening contacts of
the
> starter button. Eventually the contacts will become so damaged and dirty
that
> current flow cannot be established.
>
> You can protect this set of contacts (points)? Just as the points in an
old
> car are protected. Just place a capacitor across the contacts. You can add
a
> high value resister to bleed down the capacitor if you like. You don't
need a
> high current switch at all. In my GTP Lola we used a micro switch. The
wires to
> the switch weighed as much as the switch. Or, if you worry about this kind
of
> thing, put in a 30 amp rated starter button.
>
> Any time you power up an inductive loop you should be aware of the very
high
> voltages and arcing that my occur when the circuit is opened.
>
Hi Lynn
What value capacitor do you suggest?
Peter