Late in the 19th century, two of the most famous inventors in America had a fight that still shapes your house today.
Historians call it the war of the currents, and it started in the late 1880s. Thomas Edison had developed and backed direct current, or DC. Nikola Tesla and the businessman George Westinghouse backed alternating current, or AC. The winner would settle the AC vs DC power grid question for the whole country.
They couldn't both win. So the battle got nasty, then expensive, and in the end it was decided by a waterfall.
AC vs DC: The Difference Between Alternating Current And Direct Current
Direct current (DC) flows in one direction only, like water down a hose. A battery gives you DC power.
Alternating current (AC) flips direction again and again. In the US it switches 60 times every second, and in Europe 50.
Here's the difference in playground terms. DC is a kid sliding down a slide, always the same way, while AC is a kid on a swing, back and forth.
That sounds like a strange way to move electricity. So why would anyone pick the swinging version?
What Was The Relationship Between Thomas Edison And Nikola Tesla?
Tesla worked for Edison for a few months in 1884, then quit and became his rival. A boss and his young helper became the two faces of the biggest feud in electricity.
Tesla had moved to New York that year. He believed his boss had promised him $50,000 for improving the company's generators, but Edison said he'd been joking. When he also refused him a raise, Tesla walked out.
Edison had already opened the first power station, Pearl Street in New York City, in 1882. Its generators made DC, providing power to 85 customers. He also earned money from his DC patents, so he had every reason to keep DC on top.
Tesla went the other way. In 1888 Westinghouse bought the rights to his AC motor and the system around it, including the generators, and the war was on.
The Ugliest Battle: Scaring People Away From AC
The DC side tried to scare the public. The plan was simple and cruel: show a crowd that AC kills.
In July 1888 an electrician named Harold Brown, a big fan of Edison, killed a dog with AC in front of an audience at Columbia College in New York. In December 1888 he did it again at Edison's lab, this time with calves.
By the end, the team had killed 44 dogs, six calves and two horses to make AC look deadly.
It didn't work, because the physics was on the AC side.
How AC Power Won: Transformers, A World's Fair And Niagara Falls
The answer is one word: distance.
Sending power down a long wire, which engineers call transmission, wastes some of it as heat. The trick is to push the electricity hard (scientists call that push "voltage") with only a small flow (the "current"). A small flow means less heat, so less power gets lost along the way.
AC can do this thanks to a box called a transformer. It's like a gearbox on a bike. It turns the voltage up for the long trip, and another one turns it back down to something safe for your house. DC in those days could not be changed that easily, and that made AC power the more efficient choice for long-distance transmission.
Then the invention got its two big chances in 1893. For the Chicago World's Fair, General Electric offered to light it with DC for $554,000. Westinghouse offered to do it with AC for $399,000, and he got the job.
That same year, Westinghouse won the contract to make power from Niagara Falls and transmit it to the nearest big city. On November 16, 1896, AC from the falls lit up Buffalo, 26 miles away.
Want to know the wildest part? Within a few years, 20 percent of all the electricity in the US came from Niagara Falls. Even General Electric, the company that had grown out of Edison's business, switched to AC.
Did Westinghouse Screw Over Tesla?
Not quite, but Tesla did give up his future royalties. Westinghouse had agreed to pay him $2.50 for every horsepower of power his AC system made, then asked him to give that up when the company ran short of money. Tesla agreed.
Westinghouse had bought the patents for $70,000. Tesla still died almost penniless in 1943, while his AC system powered the world.
Why DC Power Never Went Away
Here's the twist. AC won the wires. However, almost every gadget in your house still wants DC.
Computers, LED lights, solar cells and electric cars all run on DC. So every charger you own is a little converter. That brick on your phone charger turns wall AC into the DC your phone needs.
What The War Of The Currents Means For Off-Grid Systems
Off the grid, DC is everywhere on its own. Solar panels produce DC, a battery stores that energy as DC, and an LED lamp wants it.
But your fridge, washer and microwave expect normal AC sockets. So most off-grid systems use an inverter, a box that turns battery DC into AC for your appliances.
Every conversion loses a little energy as heat, and for off-grid living every bit of stored energy counts. That's why some off-gridders run DC lights, camper-style DC fridges and USB chargers straight from the battery.
For the practical side, our guide on AC and DC in an off-grid solar system follows the power from roof to plug. And if you're sizing the battery bank that holds all that DC, start with how home batteries work.
Most people still keep AC for the main house wiring, because almost every appliance in the store runs on the standard AC supply.
Edison Was Not Entirely Wrong: The Future Of DC
The old fight is mostly settled: AC for distribution through the grid, DC inside the device.
But DC is back on the big wires too. In 1954 Sweden opened the first commercial high-voltage DC line, to the island of Gotland. Today companies use this "HVDC" technology to transmit electricity over long distances with less loss, so DC has become part of the grid again.
So in a strange way, Edison wasn't wrong. He was just about 70 years early.
Sources
- US Department of Energy, The War of the Currents: AC vs. DC Power
- US EIA Energy Kids, Thomas Edison
- US EIA Energy Kids, Nikola Tesla
- HistoryNet, Nikola Tesla: The Wizard Who Electrified the World
- Discover Magazine, The Cruel Animal Testing Behind Thomas Edison's Quest to Show the Dangers of AC
- ENTSO-E, Continuing frequency deviation in the Continental European power system
- Hitachi Energy, The Gotland HVDC link
- MIT Environment, Health and Safety, Electrical safety
Hard Words
| Term | What it means |
|---|---|
| DC (direct current) | Electricity that flows in one direction, like water down a hose. Batteries and solar panels make DC. |
| AC (alternating current) | Electricity that flips direction many times a second: 60 times in the US, 50 in Europe. Wall sockets are AC. |
| War of the currents | The fight from the late 1880s over which current would power America. DC lost the grid, and AC became the standard. |
| Transformer | A device that turns voltage up or down, like a gearbox for electricity. The reason AC won long-distance power. |
| Voltage | How hard the electricity pushes. A big push with a small flow loses less power as heat in long wires. |
| Current | How much electricity is flowing. Measured in amps. |
| Inverter | A box that turns DC from a battery or solar panel into AC for your home appliances. |
| Rectifier | The opposite of an inverter. The brick on your phone charger turns wall AC into DC for the phone. |
| High-voltage DC (HVDC) | DC sent over long lines at a big push. The first commercial line opened in Sweden in 1954. |
Common Questions
Who won the war of the currents?
AC won. Westinghouse lit the 1893 Chicago World's Fair with AC, and by 1896 AC from Niagara Falls powered Buffalo.
Why is the socket in my wall AC and not DC?
Because a transformer can turn AC voltage up for long trips and back down for your house, which wastes less power in the wires. Back then DC could not be changed that easily, so the grid was built for AC.
Did Edison really kill animals with AC?
Yes. Starting in 1888, Edison's side killed dogs, calves and horses with AC to make it look deadly. It didn't stop AC from winning.
Is a battery AC or DC?
DC. A battery pushes its current one way only, from one end to the other, and so do solar panels and fuel cells. To run AC appliances from a battery you need an inverter.
Which kills, current or voltage?
The current, meaning how much electricity flows through your body. Voltage only decides how much current gets pushed through you. That's why both AC and DC can kill, and why you should never touch live wires of either kind.
How does an AC-DC power supply work?
It turns AC from the wall into the low-voltage DC your gadget needs. A phone charger brick is one.