# When I measure the output of The Zapper with my DC Volt Meter it reads around 4 to 4.5 Volts. I thought the output is supposed to be 9 Volts?

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When I measure the output of The Zapper with my DC Volt Meter it reads around 4 to 4.5 Volts. I thought the output is supposed to be 9 Volts?

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This is a common (and good) question. First, the output of our Zapper is an AC Square-wave. Trying to measure AC with a DC Meter gives strange results. First, the frequency causes the output voltage to change from zero to 9 Volts 30,000 times a second (30 kHz)! This is not a DC output, it’s an AC output. Second, and most important is the 50% Duty Cycle of the output. The average output voltage would be 50% of the peak. Thus 50% of 9 Volts peak is…4.5 Volts! When you put a DC Volt Meter on the output expect to read around 4.5 Volts DC. If you were to use an AC Volt Meter, expect to see about 7-8 Volts DC due to the limited bandwidth of the voltmeter (it probably doesn’t respond to 30 kHz). The only definitive method of measuring the output is on an oscilloscope. On the ‘scope you can clearly see the peak-peak voltage, the 50% duty cycle, and the 30 kHz square-wave.