[DeTomaso] Hot Start Issue

SOBill at aol.com SOBill at aol.com
Wed Dec 17 19:07:35 EST 2014


FWIW,
 
The Pantera OEM Ford starter motor has two windings: a field winding which  
creates a fixed location magnetic field and an armature which causes the 
direct  drive starter pinion to rotate in that magnetic field. Both windings 
are  composed of many turns of copper wire.
 
The coefficient of electrical resistance for copper wire is +0.004/degree  
C. The resistance of copper increases with increasing temperature. The  
electrical resistance of the field winding and the armature winding will  
increase with increasing temperature. For a 50 degree C temperature rise  from 
ambient, the resistance of each winding will increase by approximately  20%. 
Since each winding is fed by a direct current from the battery the current  in 
each winding will decrease by approximately 20%.
 
The torque of the starter motor is proportional to the product of  the 
field current and the armature current. A 20% reduction in the  field current 
concurrent with a 20% reduction in the  armature current will result in a 
starter motor with 64% of it's room  temperature torque. This problem will be 
compounded by BTDC ignition  firing (which try to spin a slowly cranked engine 
backward), cable losses due to  a remotely mounted battery (which reduce 
the voltage at the starter), an  increased engine compression ratio (which it 
hard to spin the engine), and  increased "drag" in a hot engine (which makes 
it hard to spin the engine).
 
Modern starter motors use very strong, rare earth material, permanent  
magnets for the fixed magnetic field and gear reduction mechanisms to allow the  
armature to spin faster than the starter pinion. Both of these design 
features  makes life much easier for the starter motor. The magnetic field is 
stable with  temperature, the battery supplies current only to the armature, 
and the armature  has more "leverage" via the gear reduction.
 
Ford recognized that the starter motors were becoming marginal. When  the 
Duraspark system was introduced, the White wire in the Duraspark harness was  
activated whenever the starter was engaged. The White wire retards the  
Duraspark ignition timing to make the engines easier to crank.
 
The main  thing is to keep the main thing the main thing.
Do the best you can with what  your have where you are.
Have fun today!
SOBill
 
 
-------------- next part --------------
   FWIW,



   The Pantera OEM Ford starter motor has two windings: a field winding
   which creates a fixed location magnetic field and an armature which
   causes the direct drive starter pinion to rotate in that magnetic
   field. Both windings are composed of many turns of copper wire.



   The coefficient of electrical resistance for copper wire is
   +0.004/degree C. The resistance of copper increases with increasing
   temperature. The electrical resistance of the field winding and the
   armature winding will increase with increasing temperature. For a 50
   degree C temperature rise from ambient, the resistance of each winding
   will increase by approximately 20%. Since each winding is fed by a
   direct current from the battery the current in each winding will
   decrease by approximately 20%.



   The torque of the starter motor is proportional to the product of the
   field current and the armature current. A 20% reduction in the
   field current concurrent with a 20% reduction in the armature current
   will result in a starter motor with 64% of it's room temperature
   torque. This problem will be compounded by BTDC ignition firing (which
   try to spin a slowly cranked engine backward), cable losses due to a
   remotely mounted battery (which reduce the voltage at the starter), an
   increased engine compression ratio (which it hard to spin the engine),
   and increased "drag" in a hot engine (which makes it hard to spin the
   engine).



   Modern starter motors use very strong, rare earth material, permanent
   magnets for the fixed magnetic field and gear reduction mechanisms to
   allow the armature to spin faster than the starter pinion. Both of
   these design features makes life much easier for the starter motor. The
   magnetic field is stable with temperature, the battery supplies current
   only to the armature, and the armature has more "leverage" via the gear
   reduction.



   Ford recognized that the starter motors were becoming marginal. When
   the Duraspark system was introduced, the White wire in the Duraspark
   harness was activated whenever the starter was engaged. The White wire
   retards the Duraspark ignition timing to make the engines easier to
   crank.



   The main thing is to keep the main thing the main thing.
   Do the best you can with what your have where you are.
   Have fun today!
   SOBill


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