Abstract: The operating condition and/or characteristics of a battery is tested by obtaining the dynamic voltage-current characteristic of the battery as a function of the charge condition thereof. A controllably varying charging current is supplied to the battery, and the voltage produced across the battery while that current is supplied is measured. The dynamic voltage-current characteristic is obtained as a function of the measured voltage and supplied current. This voltage-current characteristic is compared to predetermined voltage-current characteristics representing batteries of the type being tested in order to determine the operating condition and/or characteristics of the battery under test.

Abstract: A power circuit for use in billet heating, surface heat treating and melting and protective circuitry associated therewith. The power circuit generally comprises a source of potential in series with a pair of inductances and an inverter module. The inverter module has two sections each comprised of a thyristor in parallel with a diode. A pair of series connected charging capacitors are connected across the source of potential and a load is connected from between the capacitors to between the two sections of the inverter module. Current flows through one thyristor, through the load and charges the capacitors. The capacitors discharge and a reverse current flows through the load and through the corresponding diode. This cycle is repeated then with the opposite section of the inverter module. A commutation failure protection circuit is provided which detects the voltage collapse condition accompanying a short circuit through the inverter module and when this occurs, it acts to shut off the thyristors.