From: noel shelley (noel@shelley1722.freeserve.co.uk)
Date: Sun Jan 02 2005 - 07:23:58 PST
BOY how I love this list !
There are those who know very little ,ask simple questions and are willing
to learn about the complexities of motor vehicles !
Thought the question may be simple , sometimes the answer is far from simple
and those with knowledge , sometimes very detailed , share it with the rest
of us !
There are those who know some , are willing to share what they know and also
want to learn more ! Where a misconception or erroneous fact is posted it
will I hope be constructively be corrected !
And then --- There`s those who know it all ! And treat those who don`t as
low life !
How does one answer a question ? In simple terms to suit the first group ,
in more detail including theory for the second , or not at all as the third
group all ready know !
I consider myself to fall in the second group . I will endeavour to answer
the question below , without boring the first or third groups !
also require a replacement starter or re-wiring it?
NO ,in the starter motor fitted to most of the vehicles dealt with on this
list they are of the series or series parallel winding system ! To reverse
the rotation of these motors IN THE MAIN , needs the reversal of one or the
other of the two magnetic fields involved ie The stator field or armature
field .If you simply reverse the polarity of the supply you have changed
BOTH fields and it will rotate as before !
Though possible it`s not normally easy to change the polarity of one field ,
usually the stator field and having done so there is the problem of
achieving sparkless commutation to` avoid excessive burning of the
commutator and brushes !
Mid way between any two pole shoes is a point known as the geometrical
neutral plane where a conductor passes from one magnetic field to the next ;
for sparkless commutation the brushes must be positioned in this area . In
practice due to the interaction of the armature and stator magnetic fields
this point is moved backwards against the direction of rotation and is known
as the magnetic neutral plane , This dictates where the brushes are
positioned !
For those starter motors designed for reversal of rotation there will
NORMALLY be alternative positions for the brush plate for clock and anti
clock rotation !
For newer starters that use permanent magnet motors reversal is simply a
case of reversing the polarity although the issue of sparkless commutation
still applies !
It is possible to convert a starter motor to make an ideal electric winch if
one ignores the brush position issue or uses the compromise geometrical
neutral position !
Best wishes as always Noel
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