Static Electricity

This is the training topic by AC4HH for the YL Net

PROTECTING YOUR EQUIPMENT FROM STATIC ELECTRICITY

Since Harriet gave some training on static electricity a few weeks back, I thought I’d continue with additional training. Some of this material is from Wikipedia, some from an article written by Dino Papas, KL0S, on the ARRL website and some from an article by Bryan P. Bergeron, NU1N, also from the ARRL website.

Static electricity is a normal part of our environment. Anyone who has walked across a carpet and been shocked when reaching for a metal doorknob, especially on a dry winter day, has experienced a discharge of static electricity.

What we will cover tonight is (1) a review of what static electricity is; (2) how electrostatic discharges are generated; (3) how they affect electronic equipment; and (4) what steps you can take to prevent damage from such discharges.

First, static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electrical discharge. Static electricity is in contrast with current electricity, which flows through wires or other conductors and transmits energy.

A static electric charge can be created whenever two surfaces contact and separate, and at least one of the surfaces has a high resistance to electric current, acting as an electrical insulator. The effects of static electricity are familiar to most of us because we can feel, hear, and even see the spark. Perhaps you have attended a demonstration of the dangers of electricity in the past. I attended one at the hamfest in Dayton, OH, one year, and found it very impressive.

(2) Now, let’s talk about electrostatic discharge. This is caused when an excess charge is neutralized when brought close to a large electrical conductor creating a path to ground, or a region with an excess charge of the opposite polarity either positive or negative. This then is known as a static shock – more specifically, an electrostatic discharge.

Materials are made of atoms that are normally electrically neutral because they contain equal numbers of positive charges (protons in their nuclei) and negative charges (electrons in "shells" surrounding the nucleus). The creation of static electricity requires a separation of positive and negative charges. When two materials are in contact, electrons may move from one material to the other, which leaves an excess of positive charge on one material, and an equal negative charge on the other. When the materials are separated they retain this charge imbalance called the triboelectric effect. Triboelectic effect is the main cause of static electricity as observed in everyday life. Some high school science demonstrations involved rubbing different materials together to see what happened. For example, a balloon rubbed against the hair becomes negatively charged and when separated, caused a person’s hair to stand out. And when the balloon is placed near a wall, the charged balloon is attracted to the positively charged particles in the wall and can “cling” to it, appearing to be suspended against gravity.

Wikipedia shows a picture of Styrofoam peanuts clinging to a cat's fur due to the triboelectric effect which causes an electrostatic charge to build up on the fur due to the cat's motions. The electric field of the charge causes polarization of the molecules of the styrofoam resulting in a slight attraction of the styrofoam pieces to the cat’s charged fur. This effect is also the cause of static cling in clothes. Some of us can remember wearing a wool skirt and a nylon slip and being embarrassed by static cling.

(3) Next, let’s look at how these electrostatic discharges can affect electronics in your house.

A couple of decades ago, discussions of safety precautions centered around how to prevent serious personal injury from high-power supplies. But today we work more with low-voltage, high-density, solid-state components—i.e. circuit boards, such as the ones we worked in our soldering kits. And these solid-state components are found in numerous electronics in our houses—and they can be damaged by a discharge as low as 5 volts. In addition, the heat associated with an electrostatic discharge can be a major threat to semiconductor devices by vaporizing semiconductor material and the metal or polycrystalline silicon traces connecting them. But that is getting a little deep, so just remember that a stray spark can damage many of your possessions.

(4) OK. I’ll wrap this up with some ways to prevent or remove electrostatic discharges.

(a) On milder winter days open a window to let moisture in.

(b) Use a humidifier to increase the inside air moisture ideally to between 30% and 40%.

(c) Spray an antistatic agent on particularly sensitive equipment--that adds a conducting surface layer to ensure any excess charge is evenly distributed.

(d) I’m sure you remember to one about using fabric softeners and dryer sheets to the laundry—which is actually an antistatic agent.

(e) Conductive antistatic bags are sold to protect particularly sensitive electronic components such as network cards.

(f) Antistatic wrist straps are available, where a person places the strap on her wrist and clips an alligator clip to a circuit board to ground it.

(g) Antistatic key chains can eliminate static build-up between the car and the its driver.

There are other measures that are taken when working around the house or in the industrial settings, but we won’t go into those here.

FUTURE TRAINING TOPICS:

Band-pass filters

Why are amateur radio operators called “hams”?

History of ham radio as found in QSL cards

EMI filters between the radio and the controller

OTHER IDEAS ARE WELCOME