How many volts does a defib machine put out?

Answer 1

Some modern external defibrillators are capable of putting out 2,000 V.

However, the first shock of a modern external defibrillator typically puts out much less: the first pulse is generally at the "120 joules at 10 ms" setting, which gives an average power during those 10 ms of 12000 watt.

An average patient has an impedance of around 75 Ohms, so those 12000 watts are applied at roughly 1000 V and 12 amps.

Individual patients may easily have half as much impedance or twice as much impedance.

Some modern defibrillators automatically compensate for the patient resistance so they consistently apply the same amount of current to the heart for a given setting:

When a patient has less resistance (smaller patients with less fat between the skin and the heart, internal defibrillators, etc.) the same amount of current can be applied to the heart at much lower voltage.

When a patient has more resistance (larger patients with more fat between the skin and the heart; extremely dry skin, etc.) the same amount of current requires a much higher voltage.

If the first pulse is not successful, an automatic external defibrillator will automatically use a higher setting on the next pulse (higher voltage and higher current, and therefore higher power; typically the same pulse time, and higher energy).