Stage 0 | Background discussion and research

Battery Safety! (an exercise from Aron)

Objective: Demonstrate that shorting batteries can be dangerous


Six 1.5 V batteries or one 9 V battery
A small bunch of steel wool
Two short (10 cm) wires with stripped ends
Tape or adventurous fingers


1) Tape or hold the batteries in series and attach one wire to each end

2) Thrust the other ends of the wires into the steel wool

3) Wait until something dramatic happens

Expected Result:

The steel wool should smoke, glow, and ultimately ignite

Safety Guidelines (written up by Anna)

Potential safety lab: create a voltage arc between two wires, and think about how that could be dangerous…

Safety Guidelines

Follow this advice to prevent accidents—read this entire section before doing anything with a high-voltage circuit!!

Why is this important?

Electrical accidents kill more than 1000 people from the US every year! When an electrical current flows through your body, it can cause deadly burns, heart attacks, and breathing problems. If you get shocked, a high current can squeeze your muscles so you can’t let go of the power source. Your body is mostly water, so you are a good conductor of electricity.

“High-voltage” means anything greater than 50 V, although low voltage equipment with high currents can also be dangerous. Depending on your weight, any DC current greater than 40 mA can be painful and dangerous. For AC voltages, a 60Hz current greater than 6 mA or a 10,000Hz current greater than 35 mA is just as dangerous.

Be aware that circuit problems can cause much higher voltages than you expect. This is even true for low-voltage systems!

Electrical equipment can also cause fires.

Basic safety checks

You should always keep these in mind when dealing with electrical equipment:

Do you feel a slight shock when you use the equipment?

Are any cords frayed, cracked, or damaged? Can you see the internal wiring?

Are any plug's prongs bent, broken or missing?

Is the plug or outlet blackened by electrical fire?

Was liquid spilled on or around the equipment?

Are any protective covers broken, cracked or missing?

Does the equipment or the cord overheat when it is running?

Does the equipment spark when it is plugged in or when switches or controls are used?

Be aware that:

Protection such as fuses and circuit breakers might not always work properly

Long lengths of cable can store extra energy

Lose or damaged cables can touch in unexpected places, and cause sparks or electrical arcs (when considerable electrical energy travels between two points and catches the air on fire)

If any of your electrical equipment is unsafe, immediately stop using it. Carefully unplug everything and turn it off. Put a note explaining the problem somewhere near the equipment, and tell everyone to be careful. Get help from an experienced electrician.

High Voltage Safety

When you’re working directly with high voltages, follow these steps in order:

1. Before you begin

If you know people who work with high voltages, ask for their help and advice. You may not be aware of all the possible dangers. Never work alone. Make sure at least one other person can see and hear you whenever you are working with high voltages. Know what to do in an emergency. Who should you talk to? Is there an emergency number to call? Where can you go for help? Make sure you're alert and awake. Get a good night's sleep before doing anything risky– you'll think more clearly and react faster. You need to know all your equipment, and what everything does. Ask for help if you’re confused!

2. Preparation

Wear rubber bottom shoes or sneakers. This will prevent electricity from running through your body to reach ground. Remove all metal watches, chains, rings, and other jewelry. Don’t use metallic pencils, rulers, or other objects when working with exposed circuits. Metal conducts electricity! Make sure your hands and your tools are dry, and you’re not standing on a wet surface. Water also conducts electricity! Read all the warnings that come with purchased equipment, and the notes that have been posted by other students. Make sure everything is switched off and unplugged before opening any protective covers or touching your circuit. Turn off both the external power switches and those connected directly to your circuit board. If the circuit is plugged into a battery, unplug it. Unplug cords from electrical outlets by pulling on the plug instead of pulling on the cord. Don’t connect back to the power source until you’re done. Discharge your capacitors at least twice. Wait a minute until all your capacitors discharge and everything shuts down. If you’re working with large power supply capacitors, use a voltmeter to check for any leftover charge.

3. Working

All systems should be switched off or disconnected from the power source before you begin. Touch the circuit with the back of your hand first. If you get shocked, you will be able to let go even if your muscles get stuck. Always keep one hand in your pocket when you’re working, so you never complete the circuit with your body. If you accidentally touch power with one hand and ground with the other hand, the current will run from one hand to the other across your chest and could damage your heart. Set up your work far away from possible ground potentials, for the same reason. Work slowly and carefully. Think about what you're doing before you touch anything. Be careful where you run your wires. Don’t put them along the floor or block walkways, and watch out for moving equipment. Squishing or pinching a cord will break down the insulation, and could cause a fire hazard. [IS THIS NEEDED??] When breaking an inductive circuit [DEFINE??], open the switch with your left hand and turn your face away to avoid danger from any arc of electricity across the switches. Use the proper handle and/or the base to pick up and carry portable equipment. Carrying equipment by the cord damages the cord's insulation. Make sure your cords, electrical strips, and wall outlets are made for the right voltage. They should be appropriately rated for the job. Don’t overload them! If you need to measure live voltages, put electrical tape over all but the last 2mm of the test leads to avoid the possibility of an accidental short. Clip the voltmeter to the appropriate ground, so you can measure with one hand.

4. Turning on the power

Everything at ground potential should be connected together. Check your circuit power supply voltages for their proper value and for their type (DC or AC? AC frequency?) before energizing the circuit. Don’t turn on the power until you’ve completed all of the steps above!a Put notes and thoughts below! Feel free to edit this page for a longer or better organized discussion, but if you just want to drop off a good link or small note, you can use this form:


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Brianna Conrad, 2012/05/06 06:48

DC vs. AC: AC is more dangerous in terms of electrocution. HOWEVER, DC is more likely to cause fires from arcs. This is because the direct current will sustain an arc longer. There are many more fires from electrical wiring than injuries from electrocution. This is not to say that electrocution is not a danger, just that fire is AS REAL a danger, and more of a danger with direct current.

How to prevent arcs? Make sure all connections are secure. Make sure there is adequate separation between conductors that are not connected. Inspect connections regularly. Brown or black discoloration or scorching indicates that a small amount of arcing is taking place. The faulty connection should be fixed before it causes a fire.

Brianna Conrad, 2012/03/08 17:58

for building a bigger panel (or may belong in system?): bypass diodes (I will put more about this at a later point)

Brianna Conrad, 2012/02/26 23:56

demonstrate water being a conductor?

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