Witricity- Wireless Power Transmission

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Information about Witricity- Wireless Power Transmission

Published on February 28, 2014

Author: namanmahendroo

Source: slideshare.net


Wireless Power Transmission



ELECTROMAGNETIC INDUCTION Electromagnetic induction is the production of potential difference across a conductor when it is exposed to a varying magnetic field. ELECTRODYNAMIC INDUCTION  ELECTROSTATIC 

ELECTRODYNAMIC INDUCTION This action of an electrical transformer is the simplest form of wireless power transmission. Energy transfer takes place through a process known as mutual induction. ELECTROSTATIC INDUCTION It is a redistribution of electrical charge in an object , caused by the influence of nearby charges. -+-+-+-+-+--++ +-+-+-+-+++-+-+-+-+-++-+-+-+-+-+- -------------------- --++ --++


launched two smartphones (the Lumia 820 and Lumia 920) on 5 September 2012, which feature Qi inductive charging.

Google and LG launched the Nexus4 which supports inductive charging using the Qi standard.

STANDBY POWER CONSUMPTION The standby power consumption (also called “no-load power consumption”) is significant. A simple calculation shows that power consumed in standby mode is about the same as the energy consumed when loading the battery. We assume that many people will also keep their wireless battery chargers continuously plugged into the mains. One of our main design goals was, therefore, minimizing standby power. Go low! We did go low. In the mean time we have demonstrated a system with only 0.0001 Watt (100 µW) standby power consumption. And that is probably not the bottom.

CHARGING EFFICIENCY The other contributor is charging efficiency. Our wireless chargers have the same ingredients as a wired charger and one additional ingredient: The copper wire between adaptor and the mobile phone is replaced with a wireless link. That link is not as efficient as a copper wire (what can beat a copper wire?), but careful design made it possible to achieve at least 70% transfer efficiency. And that percentage can go up a bit if a manufacturer is willing to spend more on high-quality components.

TOTAL ENERGY CONSUMPTION A wireless power transmitter can be more efficient, or less efficient than the wired chargers it replaces. It depends on the number of wired chargers that are replaced. It also depends on the type of chargers, and on the habits of the owner. We estimate that in typical situations, the total energy consumption of a wireless power charger breaks even with wired chargers if you replace two wired chargers.

POWER CONSUMPTION OF WIRED CHARGERS Efficiency @ max load: 72% on average for 5 Watt adaptors Charging: 1 hour * 2 W / 72% = 2.8 Wh (this assumes that 5 W charger will supply, on average, 2 W during a complete charging cycle) Power consumption @ no load: 0.12W on average for 5 Watt adapters with a few exceptionally good adapters going down to 0.01 W. Standby (no load): 23 hours * 0.12 W = 2.8 Wh

WHAT ABOUT WIRELESS CHARGERS ? Our wireless chargers also contain an AC-DC power adapter. Let’s assume that is has the same efficiency (72%). [Let’s also assume (0.12 w). footnote: Wireless chargers can have a much lower standby power, but this keeps the that it has the same standby power comparison easier].The transfer efficiency of the wireless power link is typically 70%. Also assume that the wireless charger replaces wired chargers. The total energy consumption is: Charging: 1 hours * 4 W / 72% / 70% = 7.9 Wh (we are now 2 devices simultaneously) standby (no load): 23 hours * 0.12 W = 2.8 Wh charging 2

HOW DOES THAT COMPARE WITH THE WIRED CHARGERS ? Total power consumption of Two Wired chargers: 2 * ( 2.8 + 2.8 ) = 11.2 Wh Total power consumption of One wireless charger with two receivers: 7.9 + 2.8 = 10.7 Wh You see that the total energy consumption is comparable. Although wireless transfer is not as efficient as a direct contact charger, wireless power transmitters save standby power energy when the wireless transmitter replaces multiple external power adapters.

ADVANTAGES Electrical Shock Lower risk of electrical shock or shorting out when wet because there are no exposed conductors as used with conductive wireless charging, for example toothbrushes and shavers, or outdoors. Protected connections No corrosion when the electronics are all enclosed, away from water or oxygen in the atmosphere.

Convenience Rather than having to connect a power cable, the device can be placed on or close to a charge plate or stand. Easier than plugging into a power cable (important for disabled people).

DISADVANTAGES Lower efficiency, waste heat The main disadvantages of inductive charging are its lower efficiency and increased resistive heating in comparison to direct contact. More costly Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing. Inconvenience In current implementations of inductive charging (such as the Qi standard), the mobile device must be left on a pad, and thus can't be moved around or easily operated while charging. Incompatibility Unlike a standardized MicroUSB charging connector, there are no de facto standards, potentially leaving a consumer, organization or manufacturer with redundant equipment when a standard emerges.

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