Apple Re-Paves the Street

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I received an interesting question from a reader after my last article and I thought that I’d share it and explain in more detail here.

The question was about the recommendation that an inverter (or indeed, any power source) have a large amount of excess capacity if being used to run electric motors. For example, if you had an electric motor that required 100 watts, you might need a power source that could supply 300 watts, or more. This oversizing of power sources when it comes to electric motors is almost always true, and the reason why touches on many things I’ve discussed in articles before.

All electric motors (AC-induction or DC-brushed/brushless) share at least one thing: coils. These coils are what get energized by the electricity, thereby creating a magnetic field, thereby interacting with either a squirrel cage, or permanent magnets, and resulting in motion. If you really break it down and unwind the hundreds of feet of wire coil, the actual electric motor circuit becomes counterintuitively simple. It’s quite literally just a really long wire loop that we are passing power through. In the simplest form, there are no components in the circuit at all. No resistors, no capacitors, nothing. It’s just power applied to a wire loop. This is often called a short circuit. When power is applied to this uncoiled wire, there is no resistance (other than the wire itself), so the current can just flow at maximum unimpeded. Assuming an unlimited power source, the wire itself will eventually become a resistor (through resistive heating) once the current becomes sufficiently high, thereby preventing any kind of runaway situation. Nevertheless, the amount of current that initially flows through that wire loop (the first few milliseconds) can be immense. All inductors including the electromagnets in electric motors, are subject to this phenomenon.

But we know that electric motors 1) don’t consume infinite amounts of electricity and 2) don’t get super hot from resistive heating. This is because electric motors are also subject to something called **back-EMF** or **counter-EMF**. The EMF stands for ElectroMotive Force. Once an electric motor is spinning, a secondary electromotive force is created that is opposite in direction to the primary electromotive force (the one created by us applying power to the coils). This counter electromotive force interacts with the coils creating the primary electromotive force thereby putting downward pressure on the amount of current flowing through them. This is what ultimately prevents the runaway situation described earlier. However, this counter electromotive force is only present once the motor is up to speed, and its magnitude is directly proportional to motor speed. So when the motor is at a dead stop and power is applied, at that instant, there is NO counter electromotive force, and the motor/coils experience what is called “inrush current”. All inductive (and often capacitive) devices are subject to this inrush current and many are engineered with mechanisms to limit the amount of inrush current so that nothing is damaged. But they only limit it, they don’t typically eliminate it. Therefore, when you power up an electric motor, it may initially (for anywhere up to a few seconds) require more power (sometimes much more) than it would normally consume. A similar phenomenon occurs (in a more controlled fashion) if a load is placed on the motor causing it to slow down. Less rotor speed = less counter-EMF = more current flowing through the coils = more power being used.

An unloaded electric motor, of any size, only consumes just enough power to overcome the counter electromotive force and the friction of the bearings. You’ve actually probably observed effects of counter electromotive force. If you turn on a large electric motor, such as a drill press, circular saw, etc near an incandescent light, you may notice the light dim very briefly when you turn the device on. This is because the motor is not turning yet, and the amount of power it is consuming is very high, thereby causing a brief voltage drop for lights on the same circuit. Devices with large capacitors such as amplifiers can also experience large inrush current. My friends all used to laugh at my old Pioneer SA-8500 (a mere 60-watt per channel amplifier) because when you turned it on, the lights in the house dimmed briefly. Again, this is because the large capacitors in the amplifier need to fill up, and they do so rapidly.

This is why if you’re using a finite power source, such as an inverter on a battery, you need to oversize it relative to the motor you’ll be powering. You need to be able to supply that extra power initially to get the motor started. This isn’t to say that household power from the power company is infinite, but it’s a lot harder to drain all of the power from a regional nuclear plant or hydro station.

I am heartened by the overwhelming response to the executive order on immigration. Unless you are a native American, you are descended from immigrants. I know I am as my grand parents immigrated to the USA to escape persecution. And do not forget that son of a Syrian immigrant by the name of Steve Jobs! It is wonderful to see the peaceful non-violent demonstrations and the statements by Apple and other businesses including Budweiser who is airing an immigration-themed Super Bowl commercial.

Small Dog Electronics recognizes the intrinsic value of our immigrants and the diversity that makes our country strong and abhors the misguided executive order.

Thank you for reading this issue of Kibbles & Bytes!

Your Kibbles & Bytes Team,

_Don, Emily & Hadley_

We are celebrating Black History Month all of February and today we will honor the memory of Frederick Douglass, a former slave that devoted his life to the abolition of slavery.

Born into slavery, Frederick Douglass became one of the most respected orators and intellectuals of the time, advising Presidents on abolishing slavery, women’s rights and other topics.

Frederick Augustus Washington Bailey was born into slavery in Talbot County, Maryland, around 1818.

Frederick Douglass was given to Lucretia Auld, the wife of Thomas Auld, following the death of his master. Lucretia sent Frederick to serve her brother-in-law, Hugh Auld, at his Baltimore home. It was at the Auld home that Frederick Douglass first acquired the skills that would vault him to national celebrity. Defying a ban on teaching slaves to read and write, Hugh Auld’s wife Sophia taught Douglass the alphabet when he was around 12. When Hugh Auld forbade his wife’s lessons, Douglass continued to learn from white children and others in the neighborhood.

It is easier to build strong children than to repair broken men.

It was through reading that Douglass’ ideological opposition to slavery began to take shape. He read newspapers avidly, and sought out political writing and literature as much as possible. Hired out to William Freeland, he taught other slaves on the plantation to read the New Testament at a weekly church service. Interest was so great that in any week, more than 40 slaves would attend lessons. Although Freeland did not interfere with the lessons, other local slave owners were less understanding. Armed with clubs and stones, they dispersed the congregation permanently.

In 1833, Thomas Auld took Douglass back from his son Hugh following a dispute. Thomas Auld sent Douglass to work for Edward Covey, who had a reputation as a “slave-breaker.” Covey’s constant abuse did nearly break the 16-year-old Douglass psychologically. Eventually, however, Douglass fought back, in a scene rendered powerfully in his first autobiography. After losing a physical confrontation with Douglass, Covey never beat him again.

Frederick Douglass tried to escape from slavery twice before he succeeded. He was assisted in his final attempt by Anna Murray, a free black woman in Baltimore with whom Douglass had fallen in love. On September 3, 1838, Douglass boarded a train to Havre de Grace, Maryland.

Eventually Douglass was asked to tell his story at abolitionist meetings, after which he became a regular anti-slavery lecturer. William Lloyd Garrison was impressed with Douglass’ strength and rhetorical skill, and wrote of him in The Liberator. Several days after the story ran, Douglass delivered his first speech at the Massachusetts Anti-Slavery Society’s annual convention in Nantucket. Crowds were not always hospitable to Douglass. While participating in an 1843 lecture tour through the Midwest, Douglass was chased and beaten by an angry mob before being rescued by a local Quaker family.

In addition to abolition, Douglass became an outspoken supporter of women’s rights. In 1848, he was the only African American to attend the first women’s rights convention at Seneca Falls, New York.

No man can put a chain about the ankle of his fellow man without at last finding the other end fastened about his own neck.

Elizabeth Cady Stanton asked the assembly to pass a resolution stating the goal of women’s suffrage. Many attendees opposed the idea. Douglass stood and spoke eloquently in favor, arguing that he could not accept the right to vote as a black man if women could not also claim that right.

By the time of the Civil War, Douglass was one of the most famous black men in the country. He used his status to influence the role of African Americans in the war and their status in the country. In 1863, Douglass conferred with President Abraham Lincoln regarding the treatment of black soldiers, and with President Andrew Johnson on the subject of black suffrage.

Frederick Douglass was appointed to several political positions following the war. He served as president of the Freedman’s Savings Bank and as chargé d’affaires for the Dominican Republic. After two years, he resigned from his ambassadorship over objections to the particulars of U.S. government policy. He was later appointed minister-resident and consul-general to the Republic of Haiti, a post he held between 1889 and 1891.

Douglass became the first African American nominated for vice president of the United States, as Victoria Woodhull’s running mate on the Equal Rights Party ticket in 1872. Nominated without his knowledge or consent, Douglass never campaigned. Nonetheless, his nomination marked the first time that an African American appeared on a presidential ballot.