I find this crap interesting. I readily admit that someone can be very good at building electric bikes, and still not know anything about the obscure details in the history of electrical devices, but…I felt like writing some of this down, so…here it is…
MAGNETS (and electromagnets)
The most popular legend describing the discovery of magnets is about an elderly Cretan shepherd about 4,000 years ago (Crete is a large island near Italy), when iron was just beginning to be used more often as a useful material (they were likely just iron meteorites the size of pebbles). Legend has it that this shepherd was herding his sheep in an area of Northern Greece called Magnesia. Suddenly, the iron tip at the bottom of his staff became firmly stuck when he set it down on a large black rock that he was standing on. To find the source of the attraction, he dug it up to find a material that they decided to call lodestones.
It was believed that the invisible force was leading any iron bits towards this magical stone. Lodestones contain magnetite, which is the naturally magnetic material Fe3O4. This type of rock was named magnetite after being found in Magnesia. If you put a sliver of lodestone onto a small float that is suspended in a bowl of water, it forms a crude compass, so they instantly became very popular for ships. The word “load” in that region meant to “lead”, in the way that a compass leads the ship.
Of course they didn’t understand that the Earth has a huge donut-shaped magnetic field, and the lodestone was aligning with it by always pointing north. However, it was so useful to have a compass, it didn’t really matter that they didn’t understand the physics behind it.
Right now, the flux of the Earths magnetic field flows through the center from the north pole to the south pole, but…it has reversed directions several times many centuries ago. In permanent magnets (plus electromagnets) the flux flows up the center from south “pole” towards the north.
One of the interesting quirks of physics is the repeating patterns that are found in nature. Electrons orbit the nucleus of an atom in the same way that planets orbit the sun. The fields in permanent magnets (and also electro-magnets which can be turned on and off) both have a similar shape to the magnetic field of the Earth itself.
The most common permanent magnets (PM’s) are ferrite or neodymium. First, the materials that make up the magnet are mixed together and formed, and then they are heated up to their “Curie temperature”, which is a physical state where every atom is free to move around. Then, a strong electromagnet that is near it is turned on, and all the atoms in the magnet will align with the strong magnetic field. Then, the magnet is cooled down while the electromagnetic field is maintained. Doing this literally locks all of the atoms in alignment, so that all of their individual magnetic fields (similar to the earths), are aligned with each other, instead of pointing in random directions. Unless the magnet is heated up to its Curie temperature again, it will remain a permanent magnet.
Neodymium magnets are very strong and can survive a reasonably high temperature, which is why they are popular for the PM electric motors in EV’s. Ferrite magnets use a ceramic base that is high in Iron oxides (rust), so they are very affordable, but they are not as strong as Neodymiums, and yet they also retain their magnetism at a much higher temp than the neo’s. Ferrite magnets are the dark gray style that is found in cheap refrigerator magnets, and 4-inch diameter ferrites are used inside a microwave oven, in a large ring-shape (in case you see a microwave being thrown away, and want a large free ferrite magnet).
There are several things that are important to notice about the bar magnet picture (posted above). Notice that the magnetic field is in the shape of two symmetrical loops. Also notice that in most of the field, there are few iron filings, indicating that the field is somewhat weak in those places. The most important part to see is that there is a thick cluster of iron filings right next the north and south tips of the bar magnet, and the size of the cluster is small and tightly packed.
This means that there is a tiny space in a specific location where the field is very strong, and the rest of the field (just a short distance away) is relatively weak. Electrical motors uses this phenomenon to create some movement between a stationary “stator”, and a rotating “rotor” in a motor. The distance between the stator and rotor should be very close, and it’s called the “air gap”.
Franklin, Volta, Maxwell, Oersted, and William Sturgeon
In the late 1700’s Benjamin Franklin performed many electrical experiments with a Leyden jar, which is a crude capacitor that was charged by spinning an electrostatic “friction-generator” (a disc made from wax, sulfur, and carbon soot, rubbed by stationary brush made with the fur from a cat or a rabbit). He also recorded that he sometimes filled his Leyden Jars to a very high voltage from the static electricity in the air during an electrical storm.
In 1799, an Italian named Alessandro Volta invented the Voltaic pile, which is a true chemical battery (copper and zinc discs, separated by paper soaked in salt-water as an electrolyte). Later, when transformers were invented, one turn of an electrical coil produced a certain amount of electrical pressure, and this unit was named a “Volt” in his honor.
In 1821, a Danish scientist named Hans Oersted showed that a current that is passed through a wire created a mild magnetic field around it.
In 1825, the British inventor William Sturgeon created a true electromagnet. The soft iron bar was only seven ounces in weight, but it was able to lift nine pounds of weight when it was energized (a ratio of roughly 18:1). This is a key milestone that has not been given the amount of recognition it deserves.
The two bowls shown above on the right hold mercury (an electrically conductive metal, which is liquid at room temperatures), and dipping an energized wire (d) into the mercury (Z) forms a simple switch. The copper wire is wrapped around a soft iron bar in the shape of a “U”. When it is energized, an iron object is attached to the two tips, which completes a circular iron path, and forms a magnetic field in the shape of a donut (a toroid).
In 1827 the Frenchman Andre Ampere was conducting experiments with electromagnets, and he needed a way to measure current, since varying the Intensity (“I”) of the current changed the power of the magnetic field in the coil, the “Amp” was named for him. (This is also why in engineering formulas, the current is abbreviated as an “I”)
Also in 1827, a German physicist Georg Ohm published a book describing the relationship between circuit resistance, current, and voltage. As a result, a unit of measuring resistance was named for him, called the Ohm. it is abbreviated by the letter “R” for Resistance, or sometimes by the Greek symbol Omega (Ω)
in 1831, a British genius with no formal university training named Michael Faraday made dozens of discoveries in a wide range of fields. His work on electromagnetism made him very famous, and he is credited with inventing the electric motor, although…his “homopolar” motor was only an interesting desktop demonstrator, since it could not perform any useful work, even if scaled up in size. His other experimental work was so important, that he never pursued the creation of a working electric motor. Of course, in those days there were no generators, electrical grids, or practical batteries to use (voltaic piles were weak and expensive at the time).
In 1871, a Scottish engineer named James Watt invented a workable steam engine that transformed all industry forever. He didn’t do any work with electrical devices, but his comprehensive calculations about power creation and transmission ended up with the “Watt” being chosen as a widely used measurement of power and work being accomplished.
In 1876, a Scottish scientist named James Maxwell had explored and defined the ways in which electricity and magnetism were deeply related, and published a book called “Matter and Motion“. His thorough set of formulas were so comprehensive and profound, they are still used today by electrical design engineers. This is another figure in the electrical world that deserves more recognition.
1885. William Stanley had read about the discovered principle of electro-magnetic “inductance” (how electrical current “induces” a magnetic field), and devised a simple transformer which could raise or lower voltage. It would “transform” electrical current into a magnetic field, and then transform it back into a current that had a different voltage. This is a vital development in the electrification of industry, because high volts are needed to efficiently transmit electricity long distances from a central generating station, but lower voltages were more practical for a machine to use at the end of the line.
In 1888, a Croatian-born Serbian genius named Nikola Tesla patented several types of electric motors while living in the United States. One of the motors he described is a three-phase brushless induction motor that used alternating current. Such a design is still widely used by industry today (130 years later). George Westinghouse hired Tesla, and also licensed the Induction motor patent.
That 1888 patent also includes a motor that appears to be the switched reluctance style, and you can read everything I found out about Switched Reluctance motors by clicking here (insert link here when article is finished).
“BATTERY” means “hit”?
EVERYONE who has an electric bike has frequently used the term “battery”, but…this is the one term that had the most WEIRD path into our common language.
It comes from the French term “battre”, which means to beat/hit. Have you ever heard the term “assault and battery” concerning a criminal proceeding? The legal term “assault” means to only threaten to hit, and the legal term “battery” means to actually beat someone. This was part of the French Napoleanic legal code from when New Orleans and Louisiana were a colony before the United States even existed.
A group of cannons that were “beating” a fort were called a Battre (for instance, in Manhattan/New York, the “Battery” is where the state stored their cannons, click here) . Also, when you are mixing the ingredients to make a cake or pancakes, you “batter” the components into a consistent mixture.
So…what does this have to do with electrical storage? Give me a minute, it gets even more complex.
As soon as gunpowder and cannon were invented, they were incredibly effective and valuable. If you wanted to move a cast-iron cannon from an old and broken carriage onto a new mount, you would likely tie ropes around its muzzle and breech (the front and rear), to lift it, using some type of wooden crane. To prevent the ropes from slipping, the muzzle (front) would be flared, and also have a cast ridge a short distance away (see pic above).
That takes care of the ropes lifting the front of a cannon, but how do you secure a rope-loop to the rear of the cannon in a way that is very secure and also is as cheap and inexpensive as possible? The shape of the common antique cast-iron cannon added a knob to the rear, called a “cascable” (stay with me for just one more minute).
I now have to take a side-road, but trust that I will come right back to tying this all together. You may have heard of a “capacitor” when discussing ebike controllers, or maybe the chargers, but…they were the first electrical storage devices. The first capacitors were called a “Leyden Jar”, named after the Leiden University in the Netherlands (please forgive the change in spelling over the years, the Dutch are known for drinking a LOT of beer).
Benjamin Franklin was an early enthusiast concerning the new world of scientific discovery in the late 1700’s (wait, what?…another tangent side-road?). There is a book named “Draw the Lightning down” (click here) which I highly recommend if you like this article (there must be at least a dozen of us). Old Ben proactively pursued an open line of communication between the handful of experimental universities of the day, so he was well aware of Leyden Jars, and how to make them.
Early experimenters in the 1700’s did not completely understand what they were dealing with but…they recorded their observations and experiments (an impressionable gentleman who was fascinated by Franklins experiments tried to replicate his flying of a kite during a lightning storm, and he was electrocuted). A Leyden jar had a very low amount of storage for electrical charge, based on the surface area of the dielectric (the non-conductive insulator between the positive and negative charge plates), which in this case is a glass jar (the thicker the glass, the higher the voltage it would store).
Old Ben had experimented with various voltages and had found that you could kill a chicken with a certain amount of charge (an electrocution), and then revive them with a smaller amount of charge. As morbid as these experiments may seem now, it reveals that the principle of reviving someone who had just died from a stopped heartbeat, and it was something that could have been used as early as the 1780’s (defibrillation).
In fact, published scientific papers on this phenomenon were the basis for Mary Shelleys 1823 book “Frankenstein”, where a man who was made from various “sewn together” dead body parts, was re-animated by lightning. Of course for me, the definitive Doctor Frankenstein will always be Gene Wilder from 1974 (click here).
That being said, how do you construct a Leyden Jar (capacitor)? You connect two conductive plates to either side of a thin insulator-plate, and connect the two conductive plates to the positive and negative of a static electrical charge. Franklin used the static electrical charge that was floating around in the air near the edge of an electrical storm as it was passing by (he lived in Philadelphia, USA).
He had a basement full of Leyden Jars, and they were all connected in parallel. One electrode was connected to a lightning rod, and the other was connected to a rod that was pounded into the ground. He was trying to make all of his Leyden Jars a “middle man” between the electricity in the air and the Earth, based on his observations of lightning.
And this brings me the the “spike and ball” we find on lightning rods and flagpoles. Lightning can cause a tremendous amount of damage, and in the 1700’s it was common for forts to have their gunpowder stores blown up from a lightning strike. Church towers were also a common victim of lightning strikes. Benjamin Franklin wrote that his greatest achievement in life was the invention of the lightning rod.
Until I read this book, I assumed that a lightning rod provided an easily replaceable sacrificial electrode that would draw a lightning strike, allowing an accumulated mass of loose electrons in the air a “low resistance” path to flow to the ground (instead of striking a building). However, I learned that a lightning rod provides a “low resistance” path for loose electrons in the air to flow into the ground as a drain, so there would not be enough loose electrons around to form a lightning strike in the first place!
Experimentation soon showed that due to a phenomenon that was eventually called “electrical corona”, a conductor termination that came to a sharp point would more easily conduct current through the air, and a termination that ended with a ball shape would be resistant to conducting loose electrons that were floating around in the air.
The practical result is that…if you want to design a lightning rod to drain electrons in the air to the ground, you put sharp spikes on top. And…if you don’t want loose electrons in the air to form a lightning bolt to strike a metal flagpole, you put a ball on top.
So…what the hell does this have to do with batteries? Hold on just a couple more seconds, cowboy (*sips beer). If you live in the 1700’s and have a few dozen Leyden Jars/capacitors in your basement (that you charged up during the last electrical storm, because a proper high-voltage generator had not been invented yet), how do you keep them from self-discharging to the air over time? Here’s how, you make the positive cathode tip a ball-shape (stay with me, bro).
Cast-iron cannons were very valuable to the military, and when they were put into storage, the barrels might rust from condensed humidity in the air. So, in order to keep the inside of the barrels as dry as possible (to reduce rust erosion), they were stored with the muzzle pointing down. Remember the “cascable knob” I showed on the breech-end of a cannon at the beginning of this section?
Back in the 1780’s, Benjamin Franklin noticed that a group of Leyden Jars in his basement looked very similar to a “Battery” of cannons that were in storage, since both of them were vertical cylinders with a ball on top. His Leyden Jars may have actually been what we call capacitors, but because of Benjamin Franklin, electrical storage devices are now called batteries.
Written by Ron/spinningmagnets, October 2019