Re: Current draw through ignition switch

["Paul Irvine" <pi@domain.elided>]

Wayne Derossett wrote:
----------
Motor winding DC resistance is only part of the current draw.  Obviously, a
loaded motor draws more current than an unloaded motor.  This is because
most
electro-mechanical devices exhibit reverse EMF
----------

and John Fielding wrote:
----------
the current drawn by the starter is not simply the volts applied and the
armarture DC resistance!
The rotating armarture in the magnetic field induces a "back-EMF" in the
armarture windings which negates part of the applied voltage, so reducing
the effective applied voltage from the battery.
----------

This is true but for the purpose of rating a pushbutton starter switch that
you want to have long and reliable service from you need to figure the
maximum instantaneous current draw that occurs at the moment you first push
the switch. That is before the rotor starts turning and the back EMF comes
into play to reduce the current.

Paul Irvine - Antioch CA
Project Alfa - http://home.pcmagic.net/pi

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