Abstract: A lockout circuit which limits the field voltage in an alternator while the vehicle starter is activated. The lockout circuit may be configured to limit the field voltage while the charging circuit voltage is below a threshold value. A timer circuit may advantageously be employed with the lockout circuit. A temperature compensating function may also be employed to change the threshold value in response to temperature changes. The disclosed circuit is particularly advantageous when employed in cold weather conditions. A method of starting the engine of a vehicle is also disclosed.