From: Lehanover@aol.com
Message-ID: <168.20409ffc.2c226f30@aol.com>
Date: Wed, 18 Jun 2003 21:43:12 EDT
Subject: Re: [FlyRotary] Re: Starter Problem
To: flyrotary@lancaironline.net
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In a message dated 6/18/2003 8:58:38 AM Eastern Daylight Time, 
msteitle@mail.utexas.edu writes:

> 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.  

Lynn E. Hanover