ACLUTCH-DRIVEN alternator, which will maintain its output frequency constant within one per cent although the driving speed varies more than 80 per cent, has been developed at the Naval Ordnance Laboratory. The 200-watt alternator is used in ordnance equipment wherein adequate mechanical power is available, but not at a constant speed. Two different types of slip clutches were developed to convert the variable-drive shaft speed to constant alternator rotor speed. Both are self-contained, require no external excitation or reference speed, and are capable of limited regulated speed adjustment.