#597 Simple Wireless Power LED
Researching wireless power transmission and building a simpel wirelessly-powered LED demonstration.
The Qi standard for mobile wireless charging was released in 2011 by the Wireless Power Consortium, and since then wireless power has become pretty mainstream.
In al that time I’ve not paid much attention except increasingly as a user. But now I ahve the itch to try and incorporate wireless power in more projects.
So, this project is starting with the most basic demonstration - powering an LED wirelessly.
The power transmitter consists of a self-governing flyback oscillator, similar to circuits used in the Joule Thief. The two halves of the coil are wound in a continuous concentric circle - meaning that current flow is opposed in each half. Basic operation:
- on startup, current flows to the base of the transistor, turning it on
- as the transistor turns on, the current in the collector coild induces a field with opposes the flow of current in the coil to the base
- as the the base current reduces, the transistor turns off producing a large flyback voltage spike and the cycle repeats
The receiver is a simple coild that electromagnetically couples with the transmission coil. A LED rectifies the current flow and lights up accordingly.
The first coil tested, works fine to a range of about 3cm. Key dimensions:
- coil wire: 0.4mm insulated winding wire
- coil diameter: 45mm
- base coil: 15 turns
- collector coil: 15 turns
- receiver coil: 30 turns
The transmitter is oscillating at around 392kHz, peaking at 27V.
The second coil was a test to downsize a little: smaller coil and wire, compensated for with more windings. Also works fine to a range of 2-3cm:
- coil wire: 0.2mm insulated winding wire
- coil diameter: 10mm
- base coil: 30 turns
- collector coil: 30 turns
- receiver coil: 60 turns
This was very much a “suck it and see” experiment. It works, but the power transfered is very low.
Next I’d like to investigate increasing the power, range and efficiency:
- controlled oscillator
- optimal frequency and coil dimensions
- full-wave rectification on the receiver
Some references for inspiration: