[DeTomaso] Ballast Resistors and Choke Heaters

[SOBill at aol.com]

Here's how the ballast resistance works:
 
The ignition coil is designed to work on 8 volts. Yes, 8  volts.
 
This done so when the battery voltage is dragged down  by cranking the 
engine, the coil will still produce an adequate  spark.
 
But unless something is done after the engine starts,  the coil, designed for 
8 volts, will be getting 12 to 14 volts from the  alternator. 12 to 14 volts 
is 50% more than the 8 volts the coil is  designed to handle. This will 
quickly overheat the coil and turn the  ignition points blue.
 
This problem is solved by having a set of contacts on the starter  relay 
which apply the battery voltage directly to the coil when the engine is  cranking. 
When the engine starts these contacts open and a wire from the  ignition key 
feeds the coil thru a resistor which reduces the coil voltage from  12 to 14 
volts to around 8 volts.
 
The required resistor on early cars was a physical resistor. The  resistor is 
a ceramic cased part mounted near the coil on the firewall. On later  cars 
the resistor is a piece of specially made resistance wire which comes  from the 
ignition switch terminal block near the steering  column.
 
Do not run an OEM ignition system without one or the other type of  resistor.
 
Heres' how the electric heater for the choke  operates:
 
The OEM choke heater is designed to operate on 6 volts. Yes, 6  volts.
 
Heat should only be applied to the choke when the engine is  running. If this 
were not done, the choke could open while the engine was  still cold.
 
The only source of 6 volts in a Pantera is the center tap of the  stator 
windings in the alternator. The stator center tap is the "S" terminal on  the 
voltage regulator. When the engine is running, the "S" terminal is at 6  volts. 
When the engine is not running, the "S" terminal is at 0  volts.
 
If the choke heater is connected to the coil positive terminal, the  choke 
heater current, which must flow thru the ballast resistor, will  reduce the 
voltage applied to the coil. This reduced coil voltage has proven to  be effective 
4,000 rpm rev limiter.
 
Have fun,
 
 
SOBill  Taylor
sobill at aol.com



************************************** Get a sneak peek of the all-new AOL at 
http://discover.aol.com/memed/aolcom30tour