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There are a bunch of great instructables and other projects on the interwebs that involve high voltage power supplies. Most include a disclaimer that says some variant of "if you have any sense, don't do this project." But rarely is there a reasonable and rational discussion of the risks of working with high voltage, and best practices for managing those risks. This instuctable aims to change all of that.
High voltage electrical systems can be challenging and fun projects to experiment with. In addition, they are very important in the history of the scientific endeavor. As you work with high voltage systems, you are treading the footsteps of Ernest Lawrence, John Cockroft and Ernest Walton, Nicola Tesla, and Irving Langmuir. Many modern systems require or are informed by the technologies and practices of high voltage engineering, from CRT displays to plasma displays, microwave ovens to high power radar, neon lamps to the Sandia Z-machine to pulsed high power lasers.
I know I said no Disclaimers, but...
DISCLAIMER
While high voltage systems are interesting experimentally, they can be dangerous, and if not treated with care, respect and intelligence, they can result in fatal injuring. Low energy versions of these systems are no more dangerous than what William Gurstelle calls "The Golden Third," however, and with proper vigilance, they can yield to amateur experimentation and study. That said, DO NOT BEGIN WITH HIGH VOLTAGE EXPERIMENTS IF:
1. You are not comfortable with basic circuit concepts like current, voltage, resistance, capacitance, inductance, ground, current return, Kirchoff's voltage law, short and open circuit, etc. A good rule is that if you can't calculate the energy stored in a capacitor or inductor, or the power dissipated in a resistance for a given voltage or current, or identify a circuit ground, or calculate what will happen if a circuit component fails short or open, you should acquire that knowledge working on low voltage circuits first. There are many, MANY 3.3V or 5V circuit projects on the internet and in texts that will give you that knowledge. Then, come back to high voltage experimentation.
2. You or your family and friends cannot accept that YOU AND YOU ALONE ARE RESPONSIBLE for your safety and safety of others in any endeavor in which you engage. While this material is provided in hopes that it will keep some amateur scientists and inventors experimenting and inventing, YOU ARE RESPONSIBLE for verifying its accuracy and applicability to your project. YOU ARE RESPONSIBLE for knowing your limitations of knowledge and experience. You agree not to hold me responsible for your actions, nor for errors or omissions in this brief overview.
High voltage electrical systems can be challenging and fun projects to experiment with. In addition, they are very important in the history of the scientific endeavor. As you work with high voltage systems, you are treading the footsteps of Ernest Lawrence, John Cockroft and Ernest Walton, Nicola Tesla, and Irving Langmuir. Many modern systems require or are informed by the technologies and practices of high voltage engineering, from CRT displays to plasma displays, microwave ovens to high power radar, neon lamps to the Sandia Z-machine to pulsed high power lasers.
I know I said no Disclaimers, but...
DISCLAIMER
While high voltage systems are interesting experimentally, they can be dangerous, and if not treated with care, respect and intelligence, they can result in fatal injuring. Low energy versions of these systems are no more dangerous than what William Gurstelle calls "The Golden Third," however, and with proper vigilance, they can yield to amateur experimentation and study. That said, DO NOT BEGIN WITH HIGH VOLTAGE EXPERIMENTS IF:
1. You are not comfortable with basic circuit concepts like current, voltage, resistance, capacitance, inductance, ground, current return, Kirchoff's voltage law, short and open circuit, etc. A good rule is that if you can't calculate the energy stored in a capacitor or inductor, or the power dissipated in a resistance for a given voltage or current, or identify a circuit ground, or calculate what will happen if a circuit component fails short or open, you should acquire that knowledge working on low voltage circuits first. There are many, MANY 3.3V or 5V circuit projects on the internet and in texts that will give you that knowledge. Then, come back to high voltage experimentation.
2. You or your family and friends cannot accept that YOU AND YOU ALONE ARE RESPONSIBLE for your safety and safety of others in any endeavor in which you engage. While this material is provided in hopes that it will keep some amateur scientists and inventors experimenting and inventing, YOU ARE RESPONSIBLE for verifying its accuracy and applicability to your project. YOU ARE RESPONSIBLE for knowing your limitations of knowledge and experience. You agree not to hold me responsible for your actions, nor for errors or omissions in this brief overview.
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Signing UpStep 1Know the risks
Some excellent experiments on the effects of electricity on the human body were performed in the 1960s by Charles Dalziel at UC-Berkeley [1]. Dalziel performed tests on men (150 lbs) and women (115 lbs) at differing levels of electrical current, for direct current and alternating current at 60 and 10,000 Hz.
Damaging effects which can be induced in the body by electric shock or contact with live electrical systems include:
1. Ventricular fibrillation - defined by the New Oxford American Dictionary as "(of a muscle, esp. in the heart) make a quivering movement due to uncoordinated contraction of the individual fibrils." This is a potentially fatal condition where the heart muscle quivers rather than beats, eliminating blood flow and causing death.
2. Cardiac asystole - where the heart stops beating. Combined with ventricular fibrillation this constitutes cardiac arrest.
3. Respiratory arrest.
4. Burns from arc flash and resistive heating of body tissues.
5. Radio frequency burns if radio or microwave frequencies are used.
The onset of these effects is dependent on the electric current magnitude, its character (whether DC, AC 60 Hz or higher AC frequency), and the amount of time the electric current is applied. At 60 Hz, studies have shown that ventricular fibrillation occurs at I=100 mA*s / T[s], where T is the time applied in seconds over a range of 0.2-2 seconds [2]. So, at 0.5 seconds of 60 Hz applied, 200 mA of current produces VF, but for a 2 second application, only 50 mA of current is required. The amount of voltage needed to produce these effects depends on the contact resistance between the human and the circuit, which is often in the range of 1000-2000 ohms, but can be higher with protective equipment, or lower if the skin is broken, or wet, etc.
Back to Dalziel, his work showed that the amount of current required to produce pain and muscle contraction depends strongly on weight and frequency, with 60 Hz producing effects at the lowest currents [1]. So, at 60 Hz, only 10 mA are required to produce strong muscle contraction in a 115 lb person, but about 50 mA are required for DC or 10 kHz current.
There are some risks that are particular to high voltage and pulsed shocks [2]. They may cause cardiac asystole rather than ventricular fibrillation, at currents above 1 A. Pulsed shocks with energies above 50 Joules are potentially hazardous. Even at 0.25 Joules, the shocks are painful. Pulsed shocks (as used with pulsed electrical incapacitation devices) can have lasting effects that incapacitate a victim. An additional hazard with high voltage shocks is that the victim need not always contact an energized circuit. Air will breakdown about about 30 kV/cm or 75 kV/inch, potentially connecting a victim to a circuit at high voltage without direct contact.
Bottom line and Risk Mitigation
-----------------------------------------
1. Work on un-energized circuits if at all possible.
2. Be very careful around live 60 Hz electricity, since it requires very little current to injure. Your power supply can kill you!
3. Limit the current and energy to the lowest values possible. Lots of interesting experimentation can be done with low stored electrical energy and low currents of a few mA or even microamperes. Make it a habit to ask yourself if you really need this current or energy.
4. Keep your distance from live high voltage circuits. Since high voltages can breakdown air to connect you to a circuit, keep high voltage circuits in enclosures and behind barricades when in operation.
5. Be sure to properly ground your experiment and your enclosure. Take special care to safely de-energize and ground a circuit before working on it. Know when and how you can end up in the ground path in a circuit and put safeguards in place to eliminate this eventuality. This will be discussed more in step 4.
6. Never work alone, always have a partner who knows your equipment and the risks and hazards involved. That way, you have a second set of eyes to insure safety, and someone who can shut off the power and get help if you are injured.
[1] C. F. Dalziel, "Deleterious effects of electric shock," in Handbook of Laboratory Saftety, 2nd Ed., N.V. Steere, Ed. Cleveland, OH: Chemical Rubber Co. 1971, pp. 521-27.
[2] T. Bernstein, "Electrical Shock Hazards and Safety Standards," IEEE T. Educ. vol. 34, no. 3 (1991): 216-22.
Damaging effects which can be induced in the body by electric shock or contact with live electrical systems include:
1. Ventricular fibrillation - defined by the New Oxford American Dictionary as "(of a muscle, esp. in the heart) make a quivering movement due to uncoordinated contraction of the individual fibrils." This is a potentially fatal condition where the heart muscle quivers rather than beats, eliminating blood flow and causing death.
2. Cardiac asystole - where the heart stops beating. Combined with ventricular fibrillation this constitutes cardiac arrest.
3. Respiratory arrest.
4. Burns from arc flash and resistive heating of body tissues.
5. Radio frequency burns if radio or microwave frequencies are used.
The onset of these effects is dependent on the electric current magnitude, its character (whether DC, AC 60 Hz or higher AC frequency), and the amount of time the electric current is applied. At 60 Hz, studies have shown that ventricular fibrillation occurs at I=100 mA*s / T[s], where T is the time applied in seconds over a range of 0.2-2 seconds [2]. So, at 0.5 seconds of 60 Hz applied, 200 mA of current produces VF, but for a 2 second application, only 50 mA of current is required. The amount of voltage needed to produce these effects depends on the contact resistance between the human and the circuit, which is often in the range of 1000-2000 ohms, but can be higher with protective equipment, or lower if the skin is broken, or wet, etc.
Back to Dalziel, his work showed that the amount of current required to produce pain and muscle contraction depends strongly on weight and frequency, with 60 Hz producing effects at the lowest currents [1]. So, at 60 Hz, only 10 mA are required to produce strong muscle contraction in a 115 lb person, but about 50 mA are required for DC or 10 kHz current.
There are some risks that are particular to high voltage and pulsed shocks [2]. They may cause cardiac asystole rather than ventricular fibrillation, at currents above 1 A. Pulsed shocks with energies above 50 Joules are potentially hazardous. Even at 0.25 Joules, the shocks are painful. Pulsed shocks (as used with pulsed electrical incapacitation devices) can have lasting effects that incapacitate a victim. An additional hazard with high voltage shocks is that the victim need not always contact an energized circuit. Air will breakdown about about 30 kV/cm or 75 kV/inch, potentially connecting a victim to a circuit at high voltage without direct contact.
Bottom line and Risk Mitigation
-----------------------------------------
1. Work on un-energized circuits if at all possible.
2. Be very careful around live 60 Hz electricity, since it requires very little current to injure. Your power supply can kill you!
3. Limit the current and energy to the lowest values possible. Lots of interesting experimentation can be done with low stored electrical energy and low currents of a few mA or even microamperes. Make it a habit to ask yourself if you really need this current or energy.
4. Keep your distance from live high voltage circuits. Since high voltages can breakdown air to connect you to a circuit, keep high voltage circuits in enclosures and behind barricades when in operation.
5. Be sure to properly ground your experiment and your enclosure. Take special care to safely de-energize and ground a circuit before working on it. Know when and how you can end up in the ground path in a circuit and put safeguards in place to eliminate this eventuality. This will be discussed more in step 4.
6. Never work alone, always have a partner who knows your equipment and the risks and hazards involved. That way, you have a second set of eyes to insure safety, and someone who can shut off the power and get help if you are injured.
[1] C. F. Dalziel, "Deleterious effects of electric shock," in Handbook of Laboratory Saftety, 2nd Ed., N.V. Steere, Ed. Cleveland, OH: Chemical Rubber Co. 1971, pp. 521-27.
[2] T. Bernstein, "Electrical Shock Hazards and Safety Standards," IEEE T. Educ. vol. 34, no. 3 (1991): 216-22.
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