| The ballast works as impedance in series with the lamp, to control the current supplied to the lamp. The current supplied by the ballast depends on the voltage drop across the lamp, or more generally, on the condition of the lamp. We want some desired current value in 2 conditions :
- The correct arc current to get 40W power, thats about 430mA, when the lamp is working (100V)
- The correct current to preheat the electrodes, thats about 800mA, when the lamp is preheating (about 10..20V)
The ballast you got is a Lead Lag type. That means, that the impedance types ballasting the 2 lamps are different : Inductive for one lamp, and Capacitive for the other lamp. Actually, for the Capacitive side it is not just capacitor, but there still is a coil with Inductive impedance, and then capacitor with higher Capacitive impedance, that cancels out the Inductive and adds up more Capacitive, to get a total Capacitive
With one of the sides, the ballast design (its output voltage and the impedance) provides the correct current in both conditions - working and preheating
With the other side, (IIRC the Capacitive ?), the ballast design provides the correct current when the lamp is working, but could not be made to satisfy the preheating current demands at the same time. The preheating current must be corrected
The starter circuit going through the ballast is going through an additional winding, called the starting compensation winding, in order to tune the preheating current of this lamp to the correct value. As this winding is in series with the starter, it provides the needed correction only when preheating and does not affect the working of the lamp after it started
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