Discussion
Does anyone know if there is a resistor in the wiring loom? I have just installed a Mallory coil and Unilite Dizzy and have been told I need a ballast resistor if there is no resistance in the loom.
I have tried starting my car with a ballast resistor with no joy and yet it starts without it...!!! Not sure what I need or what I should do?
I have tried starting my car with a ballast resistor with no joy and yet it starts without it...!!! Not sure what I need or what I should do?
When you have a big old engine cranking over the load on the battery is quite high, this drops the available voltage down below what is needed for a decent spark - i.e. down to about 6V rather than 12.
So a lower voltage coil is fitted to give a decent spark at those volts - you may find that your new coil is marked 6V somewhere.
The trouble is that once started the voltage is back to 12v and the HT voltage is higher (more chance of distributor cap tracking to earth, HT lead breakdown) and higher current on the LT circuit wearing the points if you have them.
So where a 6V coil is fitted there is usually a resistor in the LT circuit for normal running and in addition a feed to the coil avoiding the resistor when cranking (i.e. feed from the solenoid - beware this feed doesn't energise the solenoid so it may need a diode or a relay). I don't know the value of the resistor but it is usually quite large (high wattage) and a low resistance.
Russ
So a lower voltage coil is fitted to give a decent spark at those volts - you may find that your new coil is marked 6V somewhere.
The trouble is that once started the voltage is back to 12v and the HT voltage is higher (more chance of distributor cap tracking to earth, HT lead breakdown) and higher current on the LT circuit wearing the points if you have them.
So where a 6V coil is fitted there is usually a resistor in the LT circuit for normal running and in addition a feed to the coil avoiding the resistor when cranking (i.e. feed from the solenoid - beware this feed doesn't energise the solenoid so it may need a diode or a relay). I don't know the value of the resistor but it is usually quite large (high wattage) and a low resistance.
Russ
That reminds me - some starter motors have an extra contact on the solenoid for exactly this purpose. When the solenoid engages the contact is taken to +12V and defeats the ballast resistor.
Trouble is, it probably only applies to quite old RV8 starters, and not the type used on wedges. You could take a diode-connected wire from the red-and-white stripe wire that goes to the starter motor, that runs fairly close to the coil and would be quite a handy pickup point.
I wouldn't run your coil for any length of time without the resistor or it'll either overheat or break down. Probably.
Trouble is, it probably only applies to quite old RV8 starters, and not the type used on wedges. You could take a diode-connected wire from the red-and-white stripe wire that goes to the starter motor, that runs fairly close to the coil and would be quite a handy pickup point.
I wouldn't run your coil for any length of time without the resistor or it'll either overheat or break down. Probably.
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