![]() I have tried numerous ways to create these coils the method I discuss here provides the most consistent results. They can be almost impossible to fabricate without a specific technique. The suggested coils for this project are a flat pancake style that is reminiscent of the old Tesla primary coil design. The coil construction can be the most difficult part of this project. The following is a description of a coil design technique that is the culmination and the distillation of many moons of effort in the application of a single method. If you are going to design your own coils, try experimenting with varying diameters of wire, coil geometries, and different coil sizes. Building The Circuitīefore you can fully test the operation of the transmitter and receiver circuits, you will need to construct a set of coils. Inductive charger schematic with test points. The schematic shown in Figure 1 is an example system with test points for troubleshooting possible problems, plus the meter placement that is necessary to calculate power efficiency.įIGURE 1. A circuit to manage the charging process for Li-Ion or NiMH battery chemistries.A voltage regulator to create a useable voltage for charging depleted batteries.A full wave rectifier to convert the incoming AC to a DC value.A set of coils that serve as a primary transmitter and secondary for the receiver.A power transistor to serve as an amplifier for driving the primary coil.Any type of oscillator capable of producing the resonant frequency.You may want to start with the coils used in this project before you try using coils of your own design.Ī wireless charging system needs to contain the following circuit elements: There are online sites that serve as calculators that can make the job a lot easier there is one such calculator located at that can solve for frequency, capacitance, or inductance as long as you have two of the three variables. If you want to use your own coil design, you will need to find the resonant frequency for it. Using the resonant frequency formula just given, I discovered that the coil would resonate at 12.9 kHz. The coil was wound with 44 turns and had an inductance of 152 uH with a parasitic capacitance of 1 ♟. The coil was a flat, single layer spiral coil created with 26 AWG enameled magnet wire that had a 1” inner diameter and an outer diameter of 2.5”. The size of the coil was based on a dimension that was indicative of most of my average size projects. The prototype coil for this project was wound using some surplus wire I had left over from a previous project. Where C = Self capacitance in picofarads R = Radius of coil in inches L = Length of coil in inches You can use the following formula to determine the self-capacitance or the interwinding capacitance: You can use a meter to determine inductance, but not for the distributed capacitance that accumulates between windings. The formula for calculating the resonant frequency is: Wikipedia defines Resonant Inductive Coupling as “the near field wireless transmission of energy between two coils that are tuned to resonate at the same frequency.” So if you like the idea of having a wireless replacement for your USB port, open up your surplus parts drawer and let's start the induction process. Borrowing from the concept of the wireless chargers on the market, I decided to build my own. This is because the magnetic fields generated by the coils in your charger and phone have the potential to alter iron particles in the magstripe on a card that are used to hold data.ĮMV chips used to make your card more secure, as well as RFID chips that enable contactless payments are not affected by magnets and so are at no risk of being damaged.As an avid hobbyist, I would like to have a convenient way to recharge my battery powered projects without having to tie up the USB ports on my computer. This is extremely convenient for our ‘get up and go’ lifestyles but does it hold any risks – specifically to your banking cards should you store them in a card carrying phone case?Ĭell phone and wireless charging manufacturers will warn against leaving credit cards with a readable magnetic strip in the wallet area of your phone case when wirelessly charging. Wireless phone chargers stations use magnetic induction – the ability of a magnetic field to create current inside a conductor - to power your phone’s battery without plugging directly into a cable.
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