The Truth About Wireless Charging

The Truth About Wireless Charging


This episode of Real Engineering is brought to you by Brilliant.org: a problem solving website
that helps you think like an engineer. There is over four billion
mobile phone users in the world, a figure that is expected to grow to five billion
by the end of the decade. We’ve all become hugely dependent
on this amazing tool and the feeling of it running out of battery
is all too familiar: that desperate scramble
before it goes gently into the night. These devices last, at best,
about one full day on a charge and must spend the better part
of the evening tethered to a wall. Unless you are constantly
carrying your charger with you, it is difficult to keep your phone from dying
over the course of a busy day. But what if we could charge our phones conveniently without having to find a plug
and carrying a charger with us at all times? With the proliferation of electric cars and electronic biomedical devices like Pacemakers, one vital piece of technology,
first developed about a century ago, is said to significantly improve
the way we keep our devices powered. Its called wireless charging, and it’s popping up in cafes,
fast food restaurants, and IKEA furniture. Although there are competing standards, wireless charging is power delivery
from a power source to an electronic device without the need for a tethered wired connection. Inductive charging is the most popular form
of wireless charging for mobile devices, and leading the way is the Wireless Power Consortium, with their Qi Open Interface standard. Using fundamentally the same technology, other groups are incorporating inductive charging tech
for use in electric vehicles. Getting to the bottom of inductive charging, you need to go all the way back to the mid-1800s, when Michael Farraday discovered
the underlying principles of electromagnetic induction. He discovered that,
in the presence of an alternating magnetic field, an electromotive force would be produced
across an electric conductor. By the late 1800s, Nikola Tesla utilized this idea, and demonstrated the phenomenon
of resonant inductive coupling by lighting an incandescent lamp wirelessly. By tuning the current to match
the resonant frequency of the coils, the two coils would couple,
providing higher efficiency power transfer. The discoveries that stemmed from Farraday’s led to the modern electrical motor
and other unmeasurably important inventions. However, for inductive charging,
the science proved easier than implementation. for starters, there weren’t many electronics
that would greatly benefit from such technology in the days of Nikola Tesla, and due to the limitations
in circuit board design and size constraints, it wasn’t until the 1990s and 2000s that the technology became viable at the consumer electronic level, where we started seeing wireless charging toothbrushes and, in 2008, wireless charging mobile phones. An inductive charger consists of only a few parts: AC current from the wall, an oscillator electrical circuit, and the transmission coil. The transmission coil is a tightly wound copper element that, as the alternating current passes through,
would produce a magnetic flux. The magnetic flux desnsity is based on things like the number of turns in the wire, the diameter of the transmission coil, the distance from the coil and other properties, such as current. On the receiver’s end the process is basically the same, except opposite. In the receiver device, a coil of the same type is embedded into the charging circuit. The alternating magnetic field is picked up by the receiving coil, and a current is induced. The AC power is passed through a power rectifier
and stabilizer to convert it into DC power the phone can use to charge the battery. Both the transmitter and the receiver
have electrical resonant frequencies, designed to be the same. For low displacement distances,
such as a mobile phone on a charging pad, it is actually LESS efficient to operate
at the circuit resonant frequency, due to heat generation. However, for a larger displacement distance, such as a car parked over a charging pad, operating at the resonant frequency causes inductive coupling to counteract
some of the displacement-related transmission losses. But there are many other factors that affect performance of transmission. And with no standardized design on the phones’ end yet, charging pads need ways
of detecting the type of device it is charging, have multiple coil arrangements and control modules to alternate between modes. The two big questions with inductive charging
are ones we keep coming back to: Do people really care about the technology? And what are the implications
of inductive charging becoming popular? Having a fully charged phone wirelessly, but nonetheless stuck to a charging pad, is barely a convenience. Teams are working within the Qi wireless standard
to create devices such as the Pi Charger, which can charge up to four devices
at a range of up to a third of a meter with a max power output of 10W per device. it’s completely conceivable
that the office furniture of the future will have inductive charging capability built in followed by most laptops,
cell phones and wireless mice. But consumers need to care about it, and hardware manufacturers need to see the value. But there is one industry
that inductive charging will make a meaningful impact, and it happens to indirectly involve Tesla, once again. Going to the petrol station is a legitimate inconvenience, and visiting a Tesla charging station
is an even bigger inconvenience. That’s why start-ups and corporations alike
are beginning to shift their attention to this lucrative opportunity. Similar to charging a cell phone on a charging pad, a transmitter would be installed in parking spaces, and a receiver on the bottom of the car. Imagine your autonomous electric vehicle
dropping you off for dinner, and seeking out a parking space
with inductive charging. No attendant needed: the car simply aligns itself with the transmission pad, and the charging process is initiated. If these industries can make this tech convenient, there is a huge chance people will want to use it. But is that a good thing? According to a study in 2015
conducted by the Wireless Consortium, the creators of the Qi standard, they found in real-world conditions,
the Qi wireless charger had an efficiency of about 59.4%,
with their competitor coming in at just 39.6%. With 30 million iPhone X sold in its first quarter, they have an impact of 415MWh per day, if charged fully once per day. With an efficiency of only 60%, that would result in an increase
of 278 MWh load on the grid, which is about 25 years’
worth of power for an average home. This is only accounting for one mobile phone, and not accounting for the other 2.5 billion smartphones projected to be in use by 2019. If all had inductive charging, the impact could be over
23,000 MWh consumed per day. To produce this power cleanly, the added load
would require an additional 1,400 wind turbines. Just for the added load. With electric vehicles,
things can get even more interesting. The Tesla Model 3 is getting between
4.5 and 5.5 km/KWh, depending on driving habits. With a daily commute of 35km, the Tesla uses 7 KWh: or almost the same power usage
as a small family home. So for every EV on the road,
it’s similar to adding another house on the grid. And when you introduce inductive charging it can equate to adding nearly two additional homes. National power grids
can likely accommodate this growth, but local infrastructure may not be capable,
or even willing, to expand their capacity
for the sake of convenience to EV drivers. A lot of the added stress on the grid is based on the fact
that inductive charging is an inefficient technology. But that may not necessarily be true forever. Oak Ridge National Lab recently demonstrated
a 20 KWh inductive charging system that operates at 90% efficiency, with power delivery
up to 3 times faster than traditional wired charging. Although it’s too early to know what the
real-world wall-to-battery efficiency will look like, it’s still promising
to see some of the sharpest engineers in the energy field digging deeper into the technology and beyond. Theoretically, it is possible to transfer energy
over greater distances with electromagnetic waves. NASA awarded one company
$900,000 for its laser-powered climbing robot. The robot had no power source on board, and managed to climb 900m
up a cable suspended from a helicopter in just under four minutes, using a high powered laser to provide enough energy
to solar cells on its undercarriage. This is a fascinating technology
that could have huge potential. We could have huge solar cells in space
beaming to Earth or other satellites, but right now the power loss in transmission
is far too great to be useful. and this is a problem
that is facing current technology on earth, whether we want to acknowledge it or not. Learning about simple core concepts like this
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