Electrical Projects Occasionally you will want to test European appliances for their performance. Since most equipment from abroad will not operate as intended from standard American 60 Hz 115V outlets, a special power supply is needed for this task. This involves considerable expense which can be avoided by building a variable-frequency ac power supply.

This device can produce the 50 Hz output at 115-120V for which most European appliances are designed, as well as provide the 400 Hz output necessary for many power tools. The key component in the circuit is an audio-frequency oscillator with a range of 0-400 Hz (Eico makes a kit suitable for this purpose) whose output is coupled by shielded cable to an audio amplifier. The amplified signal at 72W across 8 ohms places 24V ac across the secondary winding of the 120-24V stepdown transformer. When a load is connected to J (a standard European two-prong receptacle), 120V is induced into the primary. Adjustment of the audio-frequency oscillator to 50 Hz and of the volume control on the audio amplifier for 115-120V output (indicated on voltmeter V) creates the necessary power for foreign equipment.

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August 20, 2008