In cold weather the generator voltage is considerably higher than normal. This is sometimes noticeable by the bluish white color of the light from the bulbs. The increased voltage is caused by the low temperature of the electrolyte which increases the internal resistance in the battery, and in order to maintain a constant charging rate, the generator voltage correspondingly increases.
When bulbs burn out prematurely, it is because they are operating at too high a voltage as a result of poor or loose connections in the battery-generator circuit or due to the charging rate being set too high. The bulbs are designed to burn 100 hours at 6 1/2 volts. If the voltage goes up to, say, 7 1/2 volts, the bulbs will last less than 25 hours.
The remedy in such cases is to first make certain that all connections in the battery generator circuit are clean and tight, especially at the battery terminals, ground connections, and cut-out. Any loose connections build up resistance and cause high generator voltage. If the connections are all 0. K. but the bulbs continue to burn out, it will be necessary to cut down the generator charging rate approximately 2 to 4 amperes. Care should be taken, however, not to cut the generator charging rate too much or the battery will become undercharged. If it is necessary to reduce the charging rate to prevent lamps burning out, the gravity of the battery should be recorded at that time and an inspection made after the car has been driven 500 to 800 miles to note whether or not the gravity is falling off. If the gravity is rapidly falling off, it will be necessary either to slightly increase the rate or give the battery a bench charge. Otherwise, the battery may fail to turn the engine over if the weather is extremely cold.